U.S. patent application number 11/789434 was filed with the patent office on 2008-01-24 for devices and methods for accelerometer-based characterization of cardiac synchrony and dyssynchrony.
Invention is credited to John Daniel III Dobak.
Application Number | 20080021336 11/789434 |
Document ID | / |
Family ID | 38972347 |
Filed Date | 2008-01-24 |
United States Patent
Application |
20080021336 |
Kind Code |
A1 |
Dobak; John Daniel III |
January 24, 2008 |
Devices and methods for accelerometer-based characterization of
cardiac synchrony and dyssynchrony
Abstract
Systems and methods according to the invention employ an
acceleration sensor to characterize the synchrony or dyssynchrony
of the left ventricle. Patterns of acceleration related to
myocardial contraction can be used to assess synchrony or
dyssynchrony. Time-frequency transforms and coherence are derived
from the acceleration. Information and numerical indices determined
from the acceleration time frequency transforms and coherence can
be used to find the optimal pacing location for cardiac
resynchronization therapy. Similarly, the information can be used
to optimize timing intervals including V to V and A to V
timing.
Inventors: |
Dobak; John Daniel III; (La
Jolla, CA) |
Correspondence
Address: |
MAYER & WILLIAMS PC
251 NORTH AVENUE WEST
2ND FLOOR
WESTFIELD
NJ
07090
US
|
Family ID: |
38972347 |
Appl. No.: |
11/789434 |
Filed: |
April 24, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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60794632 |
Apr 24, 2006 |
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60835171 |
Aug 1, 2006 |
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60839494 |
Aug 22, 2006 |
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Current U.S.
Class: |
600/508 |
Current CPC
Class: |
A61B 2562/028 20130101;
A61B 5/021 20130101; A61B 5/352 20210101; A61B 5/6852 20130101;
A61B 5/726 20130101; A61B 5/6851 20130101; A61B 5/11 20130101; A61B
5/6876 20130101; A61B 7/00 20130101; A61B 5/349 20210101; A61N
1/3627 20130101; A61B 5/6862 20130101; A61B 5/0031 20130101; A61B
5/287 20210101; A61B 5/6869 20130101; A61B 5/1102 20130101 |
Class at
Publication: |
600/508 |
International
Class: |
A61B 5/024 20060101
A61B005/024 |
Claims
1. A device for measuring cardiac dyssynchrony, comprising: a. a
catheter having a tubular polymeric outer lumen configured for
accessing the coronary sinus, the lumen having a proximal end and a
distal end, such that when installed in a patient the distal end
resides in the coronary sinus; b. a second tubular polymeric lumen
for receiving a guide wire; c. an acceleration sensor disposed at
the distal end of the outer lumen; and d. at least one decoupling
capacitor adjacent to said acceleration sensor.
2. A device of claim 1, further comprising a guide wire, wherein
said guide wire has an electrically conductive tip.
3. A device of claim 1 wherein said configuration includes a curve
of 90 degrees or greater.
4. A device of claim 1 wherein said sensor is surface mounted in
the distal catheter region to a circuit board.
5. A device of claim 1 wherein said decoupling capacitor is surface
mounted in the distal catheter region to a circuit board.
6. A device of claim 1 wherein said sensor measures 3 different
axes of acceleration.
7. A device of claim 1, wherein said sensor is a capacitive type
sensor.
8. A device of claim 1, further comprising a microprocessor.
9. A device of claim 1, wherein said microprocessor is programmed
to compute dyssynchrony indices from acceleration signals.
10. A device of claim 1 wherein said device measures global
dyssynchrony of the left ventricle.
11. A system for measuring dyssynchrony, comprising: a. a catheter
with an acceleration sensor mounted in the distal region of the
catheter; b. a pacing device; c. a microprocessor, said
microprocessor programmed to convert acceleration patterns into one
or more dyssynchrony indices; and d. a display for showing
acceleration patterns or dyssynchrony indices.
12. A system of claim 11, wherein said catheter is configured such
that the catheter can access the coronary sinus.
13. A system of claim 11, wherein said acceleration sensor measures
acceleration in 3 axes.
14. A system of claim 11, wherein said catheter further comprises a
lumen for receiving a guide wire.
15. A system as described in claim 11, wherein said pacing device
is a pacing guide wire.
16. A system as described in claim 11, wherein the microprocessor
is programmed to produce a phase average of acceleration and ECG
signals.
17. A system as described in claim 11, wherein the microprocessor
is programmed to identify the peak acceleration and a QRS component
of the ECG of the phased averaged signals.
18. A system as described in claim 11, wherein the microprocessor
is programmed to perform Fourier transformation of acceleration
signals.
19. A system of claim 11 wherein said dyssynchrony indices include
one or more of the following: Time delay from onset of ventricular
electrical activity to onset of LV motion during systole; Time
delay from onset of ventricular electrical activity to peak LV
motion during systole; Time delay from onset of ventricular
electrical activity to onset of LV motion during diastole; Time
delay from onset of ventricular electrical activity to peak LV
motion during diastole; The ratio of the peak motion during systole
and diastole; The time interval between the peak motion of systole
and diastole; Number of motion peaks during systole greater than a
threshold; Time delay between two highest peaks of motion during
systole; Variability of time delay from onset of ventricular
electrical activity to peak motion in each acceleration axis (X, Y,
or Z); Variability of peak motion in each independent axis (X, Y,
or Z); Reduction in the peak acceleration of delayed motion;
Frequency of peak amplitude of power spectrum; The acceleration
axis with the dominant frequency in power spectrum Cross
correlations of time-frequency transforms between ECG signal and
acceleration signals or between different acceleration signal
axes.
20. A method for measuring cardiac dyssynchrony, comprising: a.
placing one 3-axis acceleration sensor for disposition within a
patient's coronary sinus; b. wherein said sensor measures the
global acceleration of the left ventricle; c. and wherein said
measured acceleration forms a pattern indicative of global
dyssynchrony of the left ventricle.
21. A method of claim 20, further comprising: a. converting said
acceleration pattern into a numerical or dyssynchrony index; b.
wherein said numerical or dyssynchrony indices may include one or
more of the following: Time delay from onset of ventricular
electrical activity to onset of LV motion during systole; Time
delay from onset of ventricular electrical activity to peak LV
motion during systole; Time delay from onset of ventricular
electrical activity to onset of LV motion during diastole; Time
delay from onset of ventricular electrical activity to peak LV
motion during diastole; The ratio of the peak motion during systole
and diastole; The time interval between the peak motion of systole
and diastole; Number of motion peaks during systole greater than a
threshold; Time delay between two highest peaks of motion during
systole; Variability of time delay from onset of ventricular
electrical activity to peak motion in each acceleration axis (X, Y,
or Z); Variability of peak motion in each independent axis (X, Y,
or Z); Reduction in the peak acceleration of delayed motion;
Frequency of peak amplitude of power spectrum; The acceleration
axis with the dominant frequency in power spectrum Cross
correlations of time-frequency transforms between ECG signal and
acceleration signals or between different acceleration signal
axes.
22. A computer-readable medium, containing instructions for causing
a computer to carry out the method of claim 21.
23. A method for identifying an optimal pacing location,
comprising: a. introducing an acceleration-measuring catheter into
the coronary sinus of a patient; b. measuring a baseline pattern of
left ventricular myocardial acceleration; c. placing a right
ventricular pacing device in the right ventricle; d. placing a left
ventricular pacing device in or on the left ventricle; e. moving
the left ventricular pacing device to a plurality of locations in
or on the left ventricle; f. performing biventricular or left
ventricular pacing at the plurality of locations with the left
ventricular pacing device; g. measuring the acceleration pattern
with biventricular or left ventricular pacing; h. determining a
location of the left ventricle with a less dyssynchronous
acceleration pattern; and i. selecting the less dyssynchronous
location to implant a CRT pacing lead.
24. The method of claim 23 further comprising converting said
acceleration pattern into one or more dyssynchrony indices.
25. A computer-readable medium, containing instructions for causing
a computer to carry out the method of claim 24.
26. A method of claim 23 further comprising moving said right
ventricular pacing device to a plurality of locations in the right
ventricle and measuring dyssynchrony at the plurality of
locations.
27. A method of claim 26 further comprising implanting a right
ventricular pacing lead in a location with a less dyssynchronous
acceleration pattern or numerical index.
28. A method for optimizing the V to V and A to V timing intervals,
comprising: a. introducing an acceleration-measuring catheter into
the coronary sinus of a patient; b. measuring a baseline pattern of
left ventricular myocardial acceleration; c. placing a right
ventricular pacing device in the right ventricle; d. placing a left
ventricular pacing device in or on the left ventricle; e. moving
the left ventricular pacing to a plurality of locations in or on
the left ventricle; f. performing biventricular pacing at the
plurality of locations of the left ventricular pacing catheter; g.
measuring the acceleration pattern with biventricular pacing; h.
determining the location of pacing in or on the left ventricle with
a less dyssynchronous acceleration pattern; i. selecting the less
dyssynchronous location to implant a CRT pacing lead; j. varying
the V to V timing intervals between a range of millisecond delays
and selecting the timing that produces a less dyssynchronous
acceleration pattern.
29. A method of claim 28 further comprising using the acceleration
pattern to determine one or more dyssynchrony indices.
30. A method of claim 28, further comprising varying the A to V
timing interval within a range and selecting the timing that
produces a less dyssynchronous acceleration pattern.
31. A method for improving the outcome of CRT, comprising: a.
placing a catheter with an acceleration sensor in the coronary
sinus; b. diagnosing the presence of dyssynchrony by measuring an
acceleration pattern that characterizes dyssynchrony; c. inserting
a pacing guide wire; d. test pacing with said pacing guide wire a
plurality of locations in or on the left ventricle; e. identifying
locations with a less dyssynchronous acceleration pattern than that
found in step b; and f. implanting a left ventricular lead in said
identified location.
32. The method of claim 31, wherein the acceleration sensor
includes three acceleration axes.
33. The method of claim 30, further comprising using said
acceleration pattern to derive one or more dyssynchrony
indices.
34. A method of claim 32 further comprising deriving dyssynchrony
indices from said acceleration patterns.
35. A computer-readable medium, containing instructions for causing
a computer to carry out the method of claim 34.
36. A method for measuring cardiac dyssynchrony, comprising: g.
placing a 3-axis acceleration sensor for disposition within a
patient's coronary sinus; h. measuring the global acceleration of
the left ventricle with the sensor; i. creating a time-frequency
transform; and j. using frequency or frequency energy data from
said time-frequency transform to characterize dyssynchrony.
37. A method for measuring cardiac dyssynchrony, comprising: k.
placing a 3-axis acceleration sensor for disposition within a
patient's coronary sinus l. measuring the global acceleration of
the left ventricle with the sensor; m. using the acceleration data
to create a measure of coherence; and n. characterizing dyssynchony
using the coherence.
Description
REFERENCE TO CONTINUING APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Patent Application Ser. No. 60/794,632, filed Apr. 24, 2006,
entitled "Devices and Methods For Accelerometer-Based
Characterization of Cardiac Synchrony and Dyssychrony." This
application also claims the benefit of priority of U.S. Provisional
Patent Application Ser. No. 60/835,171, filed Aug. 1, 2006,
entitled "Devices and Methods For Accelerometer-Based
Characterization of Cardiac Synchrony and Dyssychrony," and of U.S.
Provisional Patent Application Ser. No. 60/839,494, filed Aug. 22,
2006, entitled "Devices and Methods For Accelerometer-Based
Characterization of Cardiac Synchrony and Dyssychrony." All of the
prior applications are incorporated herein by reference in their
entireties.
BACKGROUND
[0002] The human heart delivers oxygenated blood to the organs of
the body to sustain metabolism. The human heart has four chambers,
two atria and two ventricles. The atria assist with filling of the
ventricles, which pump blood to the body and through the lungs. The
right ventricle (RV) pumps blood through the lungs to be oxygenated
and the left ventricle (LV) pumps the oxygenated blood to the
body.
[0003] A graph of the cardiac filling and pumping cycle and
valvular events is shown in FIG. 1a and 1b. The cardiac LV pumping
cycle (LV cycle) is divided into two periods: diastole 52 and
systole 54. Diastole 52 is the filling period and systole 54 is the
ejection period. Five different phases of the LV cycle can be
identified within the systolic and diastolic periods: isovolumic
contraction 56, ejection 58, isovolumic relaxation 62, early
diastolic filling (rapid filling) 64, and late diastolic filling
(atrial contraction) 66. Mitral valve closure 68 ("MVC") occurs
during isovolumic contraction and aortic valve closure 72 ("AVC")
occurs during isovolumic relaxation. Also shown in the figures are
the left ventricular pressure LV Press 74, a regular
electrocardiogram ECG 76, the left ventricular end-diastolic volume
LVEDV 78, the left ventricular end-systolic volume LVESV 82, a
graph depicting heart sounds 84, the left atrial pressure LA Press
86, the aortic pressure 88, a-wave 92, c-wave 94, and v-wave
96.
[0004] Myocardial activation and systolic contraction is initiated
in the atria by a regular electrical depolarization wave that
spreads from the sinoatrial node to the ventricles at a normal
resting cycle of 60 to 80/minute. Cardiac electrical activity can
be sensed using a body surface electrocardiogram or ECG. The
depolarization of the atria is sensed as a P-wave 98 on the ECG. A
delay in depolarization between the atria and ventricles occurs and
is measured on the ECG as the PR interval 102. Ventricular
contraction and myocardial shortening starts at the
interventricular septum and rapidly spreads to the posterior and
lateral wall via the Purkinje system. Electrical depolarization
that leads to ventricular contraction is measured on the ECG by the
QRS complex 104. Following the QRS complex 104 is the T-wave 106,
which reflects ventricular repolarization.
[0005] In the normal heart, a short delay from interventricular
septal contraction to posterior-lateral contraction of
approximately 20-40 ms occurs such that the lateral free wall is
typically the first region of the heart to undergo shortening.
Aortic valve closure signifies the end of the ejection phase of
systole and the start of diastole. Diastole results in filling of
the ventricles with blood and lengthening of the myocardium. In the
normal heart diastole is typically longer than systole with the
ratio dependent on heart rate.
[0006] LV myocardial motion is complex and includes both vibration
and displacement (lengthening and shortening). Displacement occurs
primarily along the longitudinal axis (base to apex), but there is
also some radial displacement as well as clockwise and
counterclockwise rotation. Displacement of the entire heart can
also be caused by respiration. Superimposed on the large amplitude
displacement motion is low amplitude vibrational motion related to
isovolumic contraction/relaxation, valve closure, and valve
pathologies such as mitral regurgitation.
[0007] The origin of LV displacement motion can be traced to the
specific orientation and arrangement of muscle fibers in the
myocardium. Vibrational motion of the LV is thought to be caused by
acceleration and deceleration of the blood and turbulent blood
flow. Studies of myocardial architecture have shown that the fibers
are situated transverse and diagonal in a helical pattern.
Transverse circumferential fibers are present in the base and
midwall of the myocardium and produce radial narrowing of the
ventricle. Systole starts with the development of tension primarily
in the circumferential fibers, which stiffens and narrows the
ventricle, and causes primarily radial displacement. The start of
systole coincides with the isovolumic contraction phase of the LV
cycle and also causes a vibrational motion thought to be related to
directional changes of the blood and the accompanying
acceleration/deceleration. Mitral valve closure also occurs during
this isovolumic contraction period. Circumferential shortening is
followed by longitudinal-diagonal fiber shortening resulting in
primarily longitudinal displacement of the LV (base toward the
apex) and ejection of blood. The action of these fibers also
creates a rotation of the heart. This coincides with the ejection
phase of the LV cycle. Mitral regurgitation is prominent during
this ejection phase. Following ejection, lengthening and rotation
in the opposite direction begins, and the isovolumic relaxation
phase of the LV cycle occurs. Isovolumic relaxation is also thought
to be associated with vibrational motion related to the
acceleration/deceleration of the blood. Aortic valve closure also
occurs during this phase. Early rapid filling of the LV with blood,
as well as late filling, causes radial and longitudinal lengthening
of the LV.
[0008] This motion of the ventricular myocardium and the LV cycle
phases can be measured at the mitral annulus which is displaced
radially and longitudinally. In addition, some rotation and the
vibrational motion is transmitted at the annulus. Longitudinal
displacement is an integral part of the global contractile function
and has a good correlation with the overall ejection performance
and diastolic filling performance of the ventricle.
[0009] Heart failure or cardiomyopathy is a medical syndrome
characterized by deterioration of cardiac pumping performance. The
primary deterioration is a progressive loss of heart muscle
compliance and contractility. Loss of pump function leads to
cardiac dilation, blood volume overload, pulmonary congestion, and
ultimately organ failure. Symptoms of heart failure include
orthopnea, dyspnea on exertion, cough, fatigue, and fluid
retention. Many heart failure patients suffer from functional
mitral regurgitation that can worsen with exercise and contributes
to the progression of the disease. Lastly, patients with
cardiomyopathy are prone to rhythm disturbances such as
interventricular and intraventricular conduction delays leading to
mechanical dyssynchrony, and tachyarrhythmias.
[0010] In cardiac pathology, such as heart failure, electrical
conduction between atria and ventricles can be delayed excessively
such that pumping function of the heart deteriorates. In addition,
conduction delays in the spread of ventricular depolarization
thwart the uniform spread of ventricular contraction and result in
asynchronous ventricular shortening and a deterioration of
performance. Some of the ventricular depolarization delays are due
to abnormalities of the Purkinje system and are referred to as left
or right bundle branch blocks (LBBB or RBBB). Bundle branch blocks
are manifested by a wide QRS complex on the ECG.
[0011] A prolonged QRS, often manifested as an LBBB in patients
with cardiomyopathy, is associated with poor prognosis. In several
large clinical trials, lengthening of the QRS was independently
associated with poor survival. In addition, several deleterious
hemodynamic consequences arise in the presence of bundle branch
block including shortening of the diastolic filling period,
aggravation of mitral regurgitation, and abnormal systolic wall
motion. The overall result is a typical and sometimes dramatic
deterioration in cardiac performance.
[0012] Most therapies to improve cardiomyopathy are implemented and
tailored empirically, or indirectly, based on patient symptoms,
with little or no information on the mechanical optimization of
cardiac pumping. In practice, assessment of mechanical pumping
properties is difficult. Some information can be obtained by
inserting catheters into the chambers of the heart, but these
catheters cannot be left in chronically and it is impractical to
subject patients to repeated procedures.
[0013] Objectives of cardiomyopathy therapy are to increase
contractility, reduce afterload, i.e., the pressure against which
the LV must pump, control blood and body water volume, blunt
neurohumoral activation, improve cardiac compliance, increase
ejection fraction, and reduce mitral regurgitation. Drugs, medical
devices, and surgical treatments are employed to accomplish these
goals and include diuretic drugs, blood pressure drugs, beta
blocker drugs, cardiac pacing and resynchronization with or without
tachyarrhythmia therapy, coronary artery bypass grafting, and heart
transplantation.
[0014] Pacemaker therapy to treat heart failure is an established
medical therapy. This therapy is employed to correct the
dyssynchronous mechanical activity that occurs in heart failure by
controlling the electrical activity of the heart. This form of
pacing therapy is often referred to as cardiac resynchronization
therapy or CRT. Dual chamber pacing (right atrium and right
ventricle) to improve atrioventricular synchrony is a form of
pacemaker therapy. Biventricular pacing is a newer approach that
can improve cardiac function and mortality. Tachyarrhythmia and
defibrillation therapy are also incorporated into the pacing
therapy as heart failure patients often have problems with
tachyarrhythmia. An experimental implantable pacing therapy for
cardiomyopathy is cardiac contractility modulation ("CCM") in which
a voltage potential or current is applied to the myocardium during
the tissue's refractory period. This current improves myocardial
contractility.
[0015] CRT is achieved by pacing (inducing myocardial activation)
in the RV and LV, and has assumed prominence in patients with
advanced heart failure and refractory symptoms. Specific candidates
include patients with a prolonged QRS duration >120 milliseconds
and/or LBBB. In newer approaches the RV and LV pacing is controlled
and may occur at different intervals. LV free wall pacing only is
also being explored.
[0016] Most clinical trials have demonstrated that about two-thirds
of patients will have a clinical response to CRT as long as optimal
pharmacologic therapy is maintained. Clinical responses include
improvement in New York Heart Association functional class,
improved exercise capacity, a decreased need for diuretic, reduced
hospitalization for heart failure management, and the like.
Unfortunately, about one-third of patients do not respond, and
approximately 15% of patients can actually have a worsened clinical
outcome.
[0017] In biventricular pacing or CRT, cardiac leads are placed in
the right atrium (RA), the RV, and LV coronary veins via the
coronary sinus. The leads have electrodes that can sense cardiac
electrical activity and stimulate contraction in the myocardium.
The leads are connected to a hermetically sealed, battery powered,
programmable pulse generator and sensor/data storage device, termed
here an "IPG" that is implanted subcutaneously.
[0018] Crucial to successful CRT is deployment of the left
ventricular lead. This is typically accomplished by passing the LV
lead through the coronary sinus into one of its venous tributaries
overlying the epicardial left ventricular surface. Conventional
pacing target sites are the posterior and lateral myocardium. In
principle, the target site should be the segment of latest regional
myocardial contraction relative to the QRS or some other
measurement of the start of ventricular contraction. Although this
is predicted to be in the posterior-lateral region, the actual site
tends to be rather variable and difficult to predict in the
individual patient. One other criterion for employing CRT is the
identification of myocardial regions that contract in the
post-systolic period, or in the period after aortic valve closure.
Such regions are sometimes referred to as myocardial contractility
reserve, because these regions of myocardium can add or contribute
to systolic ejection if they can be forced to contract during
systole. Pacing of regions can induce contraction and shortening of
these late-contracting regions so that they contribute to systole.
Consequently, any patient with a region of myocardium that
contracts and deforms in the post-systolic period are candidates
for CRT, regardless of the QRS interval.
[0019] Tissue Doppler and its corresponding myocardial velocity
measurement have been used to measure various mechanical properties
of ventricles and atria. Characterization of systolic and diastolic
function can be performed. In addition, tissue Doppler has been
employed in the assessment of mitral regurgitation and
ischemia.
[0020] Tissue Doppler velocity measurements can detect tissue
velocity changes, but these changes do not necessarily correlate
with ventricular shortening which is required for cardiac pumping
during systole. In an asynchronous ventricle, contraction may not
be accompanied by shortening due to the effects of
earlier-contracting segments on late-contracting segments. Newer
techniques that employ measurements of cardiac strain and
shortening are able to assess cardiac motion.
[0021] General strategies for LV lead placement can be developed
with tissue Doppler imaging, a sophisticated echocardiographic
technique, which allows visualization of individual myocardial
segments and their contraction patterns, and allows visualization
and analysis of segmental wall motion and velocity. It has been
observed that up to 50% of patients may have the left ventricular
lead, when placed in a conventional fashion pacing in a zone that
does not correspond to the best myocardial contraction segment,
i.e. there is a mismatch between the desired target and the actual
target. Moreover, it is only those patients in whom a match
occurred between the paced segment and the target zone where a
clinical response was observed (only in about 30-50% of patients).
This may explain why there is a lower than desired clinical
response rate to CRT.
[0022] To improve CRT there is not only the need to identify target
zones for pacing, but also to identify suitable patients. Further,
a substantial percentage of patients with a normal or only
slightly-widened QRS interval may also be candidates for CRT.
Tissue Doppler scans can be suitable to measure ventricular
dyssynchrony and therefore may be able to identify appropriate
patients and optimize therapy. One measure of dyssynchrony
identified with tissue Doppler is the assessment of peak velocity
delays relative to the QRS onset of different myocardial segments
and the standard deviation of these delays. However, tissue Doppler
imaging requires specialists to perform the scan and can only be
performed during a clinical visit. Thus, continuous or daily
monitoring is not possible with this technique. Moreover, the
complexity of the technique makes it too cumbersome to use during
the LV lead placement.
[0023] Motion of the heart and LV, both displacement and vibration,
can be measured directly with an acceleration sensor. This motion
can be used to characterize the LV cycle phases. Integration of the
acceleration measurements during displacement provides myocardial
velocity data that may closely parallel tissue Doppler imaging
velocity measurements. Double mathematical integration of the
acceleration sensor signal would allow characterization of the
distance of displacement. Thus, an acceleration sensor-based system
could be used to identify target regions of myocardium for pacing,
optimize and characterize the regional and global LV response to
pacing of the target region, and identify candidates for CRT,
including those without a widened QRS. Since LV motion and cardiac
pathologies such as mitral regurgitation occur at different
frequencies, e.g., higher frequency vibration and lower frequency
displacement, acceleration signals at different frequencies are
ascertained. In this way, the complete LV cardiac cycle and cardiac
pathologies can be characterized and monitored for changes due to
pacing. An appropriately designed implantable myocardial
acceleration sensing device (IAD) could monitor global and regional
cardiac function long term, and would allow optimization of many
treatment aspects of heart failure, including pharmacologic
therapy. This monitoring may occur without the need for specialized
personnel and scanning. Moreover, the appropriately designed system
would allow characterization of the complete cardiac cycle (systole
and diastole) and global monitoring of cardiac mechanical
function.
[0024] Accelerometers have been used in pacemaker IPGs for rate
control purposes (U.S. Pat. No. 5,383,473 and U.S. Pat. No.
5,425,750). A sensor implanted in the heart mass for monitoring
heart function by monitoring the momentum or velocity of the heart
mass is generally disclosed in U.S. Pat. No. 5,454,838. A catheter
for insertion into the ventricle for monitoring cardiac
contractility having an acceleration transducer at or approximately
at the catheter tip is generally disclosed in U.S. Pat. No.
6,077,236. Implantable leads incorporating accelerometer-based
cardiac wall motion sensors and for arrhythmia discrimination are
generally disclosed in U.S. Pat. Nos. 5,628,777 and 6,002,963.
Accelerometers used for discrimination of various cardiac
arrhythmias are also generally disclosed in U.S. Pat. No.
5,268,777. Additionally, other disclosures have proposed the use of
an accelerometer to optimize pacing timing, such as AV
delay/interval and interventricular (V-V) timing (U.S. Pat. Nos.
5,549,650; 6,542,775; 5,549,650, 5,540,727 and U.S. Applications
2003/0105496 A1, 2004/0172079 A1, 2004/0172078 A1, and 2005/0027320
A1).
[0025] In addition to employing sensors for monitoring therapy for
cardiomyopathy, acceleration sensors have been previously disclosed
for measuring the amplitude of acceleration signals during
isovolumic contraction. Using a uniaxial accelerometer integrated
into a right ventricular (RV) pacing lead, work done by Plicchi
("An implantable intracardiac accelerometer for monitoring
myocardial contractility", PACE 1996, 19:2066-2071) and others
indicates that measurement of the peak amplitude of acceleration
signals during the ICP correlates ventricular contractility and the
rate of rise of ventricular pressure. Prior patent publications
also disclose the measurement of peak amplitude acceleration
signals to characterize contractility. For example, Chinchoy [US
2004/0172079A1 and US 2004/0172078 A1] discloses the measurement of
peak amplitude of the acceleration signal during the ICP from the
LV epicardium to optimize the atrioventricular ("AV") delay and
interventricular ("VV") timing interval of a CRT device and to
monitor long-term LV function. Yu and others disclose the
measurement of the phase shift in the peak amplitude of
acceleration signals derived from the LV and RV to optimize AV and
VV interval timing of a CRT device.
[0026] Accurate measurement of the peak amplitude of an
acceleration signal using an acceleration sensor as discussed in
prior disclosures, may be problematic due to variables that can
affect the signal. One variable is the influence of the
acceleration signal related to the gravitational field of the
earth. This acceleration signal will change with the angle of tilt
of the sensor relative to the gravitational acceleration vector.
Thus, depending on the orientation of the sensor in the heart, the
acceleration signal due to earth's gravity may increase or decrease
the peak amplitude. Another factor which may affect the peak
amplitude is the relative motion of the lead or catheter type
device to which the acceleration sensor is affixed. Relative motion
of the acceleration sensor device (e.g., a catheter LV lead) in the
direction of acceleration may increase the signal amplitude and, if
counter to the direction of myocardial acceleration, may reduce the
peak amplitude. Further, if the axis of the acceleration sensor is
not parallel to the axis of motion, the amplitude of the signal
will also be reduced. Lastly, the motion of the heart due to
respiration may affect the accuracy of the peak amplitude.
[0027] Further in the disclosures of Chinchoy and Yu [US
2003/0104596 A1], it is not clear if the sensor is measuring
vibrational or displacement motion of the heart. Measurement of
these different motion types requires signal acquisition in the
appropriate frequency band; however, these prior disclosures do not
indicate the acquired acceleration signal's frequency band.
Chinchoy indicates that the isovolumic contraction phase analyzed
from the acceleration signal correlates with the S1 peak of
myocardial Tissue Doppler velocity curve. However, this curve is a
measurement of the displacement motion of the LV and therefore does
not contain the vibrational component that may be more indicative
of LV function. These above disclosures do not provide for
measurement of pathologic vibrational motion, such as mitral
regurgitation or the third/fourth heart sounds, and monitoring
changes that may be indicative of improved LV function. Lastly, the
above disclosures do not disclose a system and method for
identifying target LV pacing sites for CRT through appropriate
analysis of the ICP.
SUMMARY OF THE INVENTION
[0028] None of the above disclosures discloses using acceleration
sensors to characterize all components of LV motion, displacement
and vibration, and to use this motion data to characterize the
different phases of the LV cycle for analyzing LV function. These
disclosures do not provide a means for separating out the
displacement and vibrational components of LV motion, which occur
at the same time, through different frequency sensing or filtering
and analysis. Prior disclosures do not provide devices or methods
for identifying the optimal myocardial pacing zone or region in the
left or right ventricle for CRT, such as measuring the onset of
motion relative to the onset of the QRS or isovolumic contraction
or mitral valve closure. Prior disclosures do not provide a method
for multiple catheter repositionings in the LV or coronary sinus or
great cardiac vein to map the motion of the LV for identifying the
optimal pacing region. Prior disclosures do not describe
characterizing the response to pacing of a target region by
measuring parameters indicative of r LV function (e.g., myocardial
performance index or QRS onset to aortic valve closure). Prior
disclosures also do not disclose measuring cardiac pathologies such
as mitral regurgitation, which may be sensed as vibration motion at
frequencies greater than about 150 Hz. Prior disclosures do not
disclose a means for optimizing complete cardiomyopathy therapy,
including drugs and devices, through the use of implantable
acceleration devices. Prior disclosures do not provide a means for
zeroing out gravity effects and tilt of the sensor. Prior
disclosures do not define the use of capacitive acceleration
sensors that integrate an inductive coil for wireless powering and
data transmission.
[0029] Rather, prior disclosures typically describe a single
acceleration sensor preferably disposed in the tip of an
implantable pacing lead. For example, a single accelerometer is
incorporated into the RV pacing lead to assess RV systolic activity
and correlate the readings with RV dP/dt ("An implantable
intracardiac accelerometer for monitoring myocardial
contractility", PACE 1996, 19:2066-2071). The sensor is designed to
detect only signals related to isovolumic contraction, and not the
motion related to displacement or valvular pathologies. In another
disclosure, an accelerometer is incorporated into an LV pacing lead
for optimization of CRT timing intervals (US Application
2004/0172079 A1). This prior disclosure proposes to sense LV
myocardial acceleration during isovolumic contraction and use this
information to optimize the atrioventricular delay and the
interventricular delay pacing signals. There is no disclosure on
the use of an acceleration sensor device to identify target pacing
regions and characterize the LV functional response to pacing.
There is no disclosure on a means for characterizing both the
displacement and vibration motion occurring at different
frequencies. Consequently, the disclosure does not provide a way to
monitor information on phases of the LV cycle that characterize LV
function such as, displacement related to ejection, filling,
afterload, volume status, and preload, nor can the same
characterize vibration related to mitral regurgitation.
Additionally, no disclosure is provided for integrating the
acceleration signal to yield LV displacement velocity and distance
measurements, which may provide additional information on LV
contractile function. Also, neither disclosure nor device design is
provided that would allow characterization of myocardial strain and
strain rate.
[0030] In U.S. Patent Application 2003/015496 A1 single
accelerometers are removably disposed at the tip of CRT leads in
the LV, RV and RA. A temporal phase shift between two different
sensors is proposed to optimize CRT interventricular timing.
Similar to the above, this disclosure generally describes
interventricular interval optimization and does not provide a means
for intraventricular target pacing region identification. Therefore
it lacks disclosure on any means for identifying LV pacing region,
means for identifying LV response to pacing, means for identifying
LV dyssynchrony irrespective of QRS width, and characterization of
LV motion and the phases of the LV cycle. Further, there is no
disclosure for multi sensor integration into the same lead
catheter, guidewire, or guide catheter/catheter system, and
analysis of acceleration at different frequencies.
[0031] In one embodiment, the invention employs an acceleration
sensor to characterize displacement and vibrational LV motion, and
uses this motion data to characterize the different phases of the
LV cycle for analyzing LV function. In another embodiment, the
invention measures acceleration in at least two different
frequencies with either two or more sensors or two or more
frequency filters to characterize LV motion. In yet another
embodiment, the invention senses high frequency (greater than about
150 Hz) low amplitude motion related to valvular pathology (e.g.,
mitral regurgitation), mid frequency (between about 20 Hz and 150
Hz) lower amplitude motion related to isovolumic
contraction/relaxation and valve closure, and low frequency (less
than about 20 Hz) high amplitude motion signals related to
displacement of the LV occurring during the ejection phase and
early and late diastole. In still a further embodiment, the
invention identifies a target pacing region or regions in the LV or
RV using an acceleration sensor by localizing regions of late onset
of motion relative to the QRS, or isovolumic contraction, or mitral
valve closure, or by pacing of target regions and measuring LV
function in response to pacing. In another embodiment, the
invention measures myocardial motion with an accelerometer relative
to the onset of isovolumic relaxation or aortic valve closure to
determine contractile reserve and/or the presence of post-systolic
shortening. In yet another embodiment, the invention identifies
target pacing regions in the LV using an acceleration sensor by
pacing different regions and measuring the regional and/or global
LV functional response to pacing. In still a further embodiment,
the invention uses an acceleration sensor to measure LV function by
sensing changes in the time interval length of the LV cardiac cycle
phases (isovolumic contraction/relaxation, ejection, and/or
filling); changes in mitral regurgitation signal amplitude and
duration; and changes in peak amplitude and slope of isovolumic
contraction, isovolumic relaxation, and ejection phases; and
frequency changes of the isovolumic contraction and relaxation
phases. In another embodiment, the invention may use an
acceleration sensor to identify patients with LV dyssynchrony or
asynchrony and a normal QRS width (90-120 ms), a modestly increased
QRS width (120 to 150 ms), and wide QRS or LBBB pattern (QRS>150
ms). In yet another embodiment, the invention facilitates
identification of the coronary ostium and LV vein branches into the
coronary sinus for cannulation with guidewires or catheters. In a
still further embodiment, the invention provides the physician with
data from acceleration sensing for management of optimal
pharmacologic treatment. In yet another embodiment, the invention
provides a wireless acceleration sensing medical device and system
for assessing LV motion and function.
[0032] Embodiments of the invention provide an implantable or
non-implantable acceleration sensor device for measuring LV motion
and characterizing LV function. An implantable myocardial
acceleration sensing system ("IAD") includes at least one
acceleration sensor, a data acquisition and processing device, and
an electromagnetic, e.g., RF, communication device. The system may
or may not have an internal battery. In one embodiment, an IAD is
integrated into the pacing lead of a CRT device and can operate
independently of the CRT IPG. In another embodiment, an IAD is used
without a CRT to monitor heart failure. In this embodiment, at
least one sensor is incorporated into an endovascular catheter that
can be placed in the epicardial venous system of the LV.
[0033] In one illustrative system, the accelerometer sensors are
micro-electromechanically ("MEM"s)-based to allow miniaturization,
low-power consumption, and multiple-axis sensing. The sensors are
conductively attached to the subcutaneously-implanted data
acquisition and processing device, which is capable of RF telemetry
communication and data transfer. The IAD monitors both vibrational
and displacement LV motion during systole and diastole in at least
the longitudinal axis. The IAD may also monitor LV acceleration in
at least one location near the mitral annulus.
[0034] In another illustrative system, the IAD is integrated with a
CRT device with a multi-electrode LV pacing lead. The IAD monitors
LV motion and can dynamically adjust the electrodes that are used
to pace. Similarly, the IAD can be integrated with or used with a
CCM device to help monitor mechanical function and optimize
therapy.
[0035] The IAD may perform data analysis algorithms that provide
useful output for optimizing cardiomyopathy therapy. The output can
be accessed by the multitude of physicians that are involved in
cardiomyopathy management. These physicians include primary care
physicians, internists, cardiologists, electrophysiologists, and
cardiac surgeons. Statistical analysis of long-term data can
identify periods in which cardiac function deviated significantly
from baseline values or how the function changed with therapy.
[0036] IADs may also be implanted in the context of other cardiac
procedures such as endovascular coronary procedures,
electrophysiology procedures, coronary artery bypass grafting, and
heart transplants. Thus, the patient is not subjected to an
additional procedure. Integration of an IAD with a CRT or CRT
pacing lead similarly offers the opportunity to optimize therapy
and response in the context of a known and regularly performed
procedure for cardiomyopathy.
[0037] In another embodiment, the sensor is a radiofrequency ("RF")
MEMs accelerometer that incorporates coils that can inductively
power or charge the sensor and transmit the data. Such an RF sensor
provides long term, batteryless, wireless monitoring. Data from the
wireless RF sensor may be acquired using an external antenna device
that wirelessly couples to the sensor by directing electromagnetic
energy of the appropriate frequency toward the sensor for inductive
powering and/or data transmission. The antenna device is connected
to a microprocessor-controlled display device that processes and
stores the myocardial acceleration data for LV motion and therapy
monitoring and optimization.
[0038] In another embodiment, one or more RF sensors can be
directly implanted into or on the heart for LV motion or therapy
monitoring or both. Alternatively, one or more RF sensors can be
integrated into various devices that are implanted into the heart.
In a further embodiment, one or more RF sensors are integrated into
an endovascular catheter that can be inserted into the chambers or
vessels of the heart. In another embodiment, one or more RF sensors
are incorporated into a coronary stent. In still another
embodiment, one or more RF sensors are incorporated into a cardiac
pacing lead.
[0039] In still another embodiment, an LV motion mapping system is
disclosed which can sense LV motion for optimizing CRT lead
placement. The system may include an LV venous catheter, LV lead,
guidewire, or guide catheter/catheter system with an acceleration
sensor, connected to a signal processing and powering module, and a
graphical display. The acceleration sensing catheter may be moved
to different locations in the LV and used to identify regions of
late systolic or post-systolic motion relative to a reference point
such as the QRS, valve closures, or isovolumic
contraction/relaxation. Alternatively, a pacing catheter or
guidewire may be moved to different LV locations and an
acceleration sensing catheter near the mitral annulus may measure
changes in LV function due to pacing. Both techniques may be used
to optimize CRT LV lead implantation. The mapping system may also
be used to determine optimal RV pacing sites which may mitigate the
need for placing an LV CRT lead.
[0040] Signals related to LV function include: earlier onset of
motion relative to the QRS; the interval time length of the LV
cycle including isovolumic contraction and relaxation, ejection,
and filling; degree of mitral regurgitation; peaks of isovolumic
contraction and relaxation; and the myocardial performance index.
One or more sensors or one or more filters or both may be used to
measure displacement or vibrational LV motion and the LV cycle
phases, as well as valvular pathology.
[0041] Monitoring changes in the frequency of the vibrational
component of the ICP may be more practical and accurate than
measuring amplitude changes for assessing cardiac function.
Similarly, monitoring the time interval of this phase may prove
more practical and accurate. Such an approach would reduce the
sensitivity of the acceleration signal measurement and the
interpretation of this measurement to the effects of gravity,
sensor axis orientation, relative motion of the sensing device to
which the sensor is affixed, and translational motion of the
heart.
[0042] In this disclosure, systems characterize cardiac function
using an acceleration sensor to acquire and analyze the frequency
dynamics associated with the isovolumic contraction phase ("ICP").
This information can be used to characterize heart function;
optimize therapy for cardiomyopathy, including CRT therapy
(including pacing intervals and required pharmacologic therapy);
and to optimize CCM therapy. In addition, this information can be
used to identify target pacing regions for CRT lead placement.
Lastly, but not exhaustively, analyzing the frequency dynamics can
be used to characterize pathologic heart vibrational motion, such
as mitral regurgitation and the third or fourth heart sound, and
the response of this motion to therapy for cardiomyopathy.
[0043] The system uses an acceleration sensor to characterize the
frequency dynamics of the isovolumic contraction phase as it
relates to contractility and ventricular function. In addition the
system measures pathologic heart vibrations such as mitral
regurgitation and the third/fourth heart sounds and the effect of
therapy on these signals. The sensor is placed into the ventricular
chambers, onto the ventricular epicardium (e.g. LV), into the
ventricular veins (e.g. the coronary sinus, great cardiac veins, or
tributaries of this vein), or into the esophagus along the
posterior side of the heart. The sensor can be integrated into an
LV lead for CRT or CCM therapy for monitoring LV function. The
sensor may also be incorporated into a catheter system for
identifying target CRT pacing regions. The sensor may also be
wireless and integrate into an implantable device (e.g. a stent)
for long term monitoring of cardiac function.
BRIEF DESCRIPTION OF THE DRAWINGS
[0044] FIGS. 1A and 1B show graphs depicting various parameters of
the cardiac pumping and ECG cycle.
[0045] FIG. 2 shows a drawing of an acceleration sensor mounted to
a coronary stent.
[0046] FIG. 3 shows placement during use of the sensor and stent of
FIG. 2.
[0047] FIG. 4 shows an alternative configuration of the sensor and
stent, in which the same are conductively coupled to an LAD.
[0048] FIG. 5 shows a schematic of a system including a batteryless
wireless acceleration sensor, an antenna wand, and a data
acquisition and processing system.
[0049] FIG. 6 shows a stent for the coronary sinus with an integral
inductive coil and an acceleration sensor.
[0050] FIG. 7 shows an alternate coiled LV lead design with
enhanced flexibility.
[0051] FIG. 8 shows an IAD device for long-term monitoring of LV
mechanical performance.
[0052] FIG. 9 shows an IAD integrated into an LV CRT pacing
lead.
[0053] FIG. 10 shows an implantable LV lead with a sensor wire
disposed such that it may be easily positioned at the mitral
annulus edge.
[0054] FIG. 11 shows a cross-sectional view of the lead of FIG.
10.
[0055] FIG. 12 shows the lead of FIG. 10 in a bent position,
showing in particular the extension of the sensor.
[0056] FIG. 13 shows an implantable LV lead with a sensor disposed
on the outside of the LV lead.
[0057] FIG. 14 shows the lead of FIG. 13 when positioned partially
in the coronary sinus.
[0058] FIG. 15 shows a CRT acceleration sensing and control
system.
[0059] FIG. 16 shows a flowchart of a data processing
algorithm.
[0060] FIG. 17 shows a graph of velocity measured at the
posterior-lateral edge of the mitral annulus.
[0061] FIG. 18 shows a representation of long-term monitoring and
therapy optimization.
[0062] FIG. 19 shows the orientation of systolic and diastolic
displacement as well as measurement of the displacement length.
[0063] FIG. 20(A)-(C) show an assessment of LV size for acute
response to CRT and long-term monitoring.
[0064] FIG. 21 shows positioning of a catheter employing multiple
sensor pairs in the LV vein.
[0065] FIG. 22 shows a graph indicating location of a mapping
catheter as well as sensors in the LV.
[0066] FIG. 23 shows differing shortening or displacement patterns
in various regions of the heart.
[0067] FIG. 24 shows a method for mapping the LV for CRT LV lead
placement.
[0068] FIG. 25 shows myocardial motion mapping, display output, and
target pacing identification.
[0069] FIG. 26 shows optimization of the pacing capture
threshold.
[0070] FIG. 27 shows a multi-sensor multi-electrode motion mapping
catheter system.
[0071] FIG. 28 shows a more detailed view of the system of FIG.
27.
[0072] FIG. 29 shows acceleration signals used to identify regions
of late deformation and for assessing various other variables
related to performance such as MPI, IVC time interval, peak IVC
height, etc.
[0073] FIG. 30 shows an alternative mapping strategy involving
multiple catheter repositionings.
[0074] FIG. 31 shows a roving pacing guide wire device and
acceleration sensing catheter for target pacing region
identification as well as for characterizing the changes in LV
function due to pacing.
[0075] FIG. 32 shows a guide catheter that may be used with the
system of FIG. 31.
[0076] FIG. 33 shows a system that may employ the guide wire of
FIG. 31 or the guide catheter of FIG. 32.
[0077] FIG. 34 shows a schematic diagram of a system according to
an embodiment of the present invention.
[0078] FIGS. 35-39 show a system for identification of a target
pacing region and for optimizing and characterizing the pacing
response.
[0079] FIGS. 40(A) and (B) show guide catheter acceleration sensor
systems for determining valve closure with an LV lead acceleration
sensor for determining myocardial motion via differential frequency
processing.
[0080] FIGS. 41-44 show a mapping system for optimizing and
identifying target pacing regions.
[0081] FIGS. 45-46 shows a system for wire attachment to a sensor
chip which may be employed in the construction of a sensing
catheter.
[0082] FIG. 47 shows a circuit diagram that may be employed in
embodiments of the invention.
[0083] FIG. 48 shows a printed circuit board layout that may be
employed in embodiments of the invention.
[0084] FIG. 49 shows a graph depicting various parameters of the
cardiac pumping and ECG cycle.
[0085] FIG. 50 shows a graph depicting the correlation of peak
frequency during the isovolumic contraction phase and the change in
pressure rise in the left ventricle (dP/dt).
[0086] FIG. 51 shows vibrational acceleration signals from the
epicardial surface of the left ventricle during isovolumic
contraction, as measured with an accelerometer.
[0087] FIG. 52 (A)-(D) shows a roving pacing guide wire device and
acceleration-sensing catheter system for target pacing region
identification and for characterizing the changes in LV function
due to pacing.
[0088] FIG. 53 shows improved myocardial performance
post-stimulation as determined by an increase in the peak frequency
of the isovolumic contraction phase and a shortening of the time
interval of the isovolumic contraction phase.
[0089] FIG. 54 shows myocardial motion mapping, display output, and
target pacing identification.
[0090] FIGS. 55 (A)-(C) show a subpectoral or subcutaneous
implantable acceleration sensor with a wireless communications
capability for monitoring S1, S2, S3, and S4 and murmur-related
heart sounds.
[0091] FIG. 56 shows a graph indicating how the proper placement of
an LV lead can be predicted using methods and devices according to
embodiments of the invention.
[0092] FIG. 57 shows a graph demonstrating how information from the
acceleration sensor can be employed to develop a predictive
algorithm for determining CRT response.
[0093] FIG. 58 shows a representative dyssynchronous contraction
pattern measured from a 3-axis acceleration sensor placed in the
coronary sinus.
[0094] FIGS. 59 and 60 show the power spectrum of the composite
acceleration signal.
[0095] FIGS. 61 A, B, and C show each individual axis from the
acceleration sensor of FIG. 57.
[0096] FIGS. 62 A, B, and C show each individual axis from the
pattern of FIG. 58.
[0097] FIG. 63 shows each individual channel from the pattern of
FIG. 59.
[0098] FIG. 64 shows each individual channel from the pattern of
FIG. 60.
[0099] FIG. 65 illustrates synchronous contraction (normal sinus
rhythm).
[0100] FIG. 66 illustrates dyssynchronous contraction.
[0101] FIG. 67 illustrates inter heart beat coherence synchronous
contraction (normal sinus rhythm): Coherence is present at greater
than 100 Hz during the systole or isovolumic contraction phase.
Time to peak coherence is approximately 12 ms. The dashed line
indicates the onset of ventricular electrical activity.
[0102] FIG. 68 illustrates inter heart beat coherence
dyssynchronous contraction showing loss of inter heart beat
coherence above approximately 100 Hz for systole or immediately
after onset of ventricular electrical activity or the isovolumic
contraction phase.
DETAILED DESCRIPTION
[0103] Acceleration sensors are well-suited for measuring both
vibration and displacement motions. They can be oriented along an
appropriate axis to maximize the motion signal and to accurately
measure the displacement. An acceleration sensor placed in or on
the heart can measure vibrational or displacement components of
heart motion, or both thereby allowing the characterization of
pumping function and various pathologies.
[0104] The sensor may be based on MEMs principles, which allows for
miniaturization and low power consumption. The design and
fabrication of capacitance MEMs-based accelerometers are known to
those skilled in the art. MEMs-based accelerometers are typically
fabricated from silicon or semiconductor substrates. In one
illustrative system, the sensor is fabricated from a
radiation-resistant semiconductor as the sensor will be implanted
in many cases under fluoroscopic guidance. The general design of
the accelerometer measures capacitance changes due to the movement
of a proof mass beam with a side arm interdigitated between two
capacitor plates. As the proof mass beam and side arm move with
acceleration or vibration, the capacitance changes and this signal
can be output as a measure of motion. These accelerometers are
fabricated from silicon substrates which allows for single-chip
fabrication of the sensor with the necessary signal processing
circuitry. This single-chip design increases the device's
sensitivity as extremely small changes in capacitance can be
measured. MEMs-based acceleration sensors as described above can
measure milli- or even micro-Gs (1G equals 9.8 meters/sec.sup.2)
which is suitable for myocardial acceleration measurements which
may typically measure between 50 and 500 milli-Gs or higher.
[0105] Other acceleration sensor designs could also be utilized and
are known to those skilled in the art. For example, a thermal
acceleration sensor could also be employed in which the proof mass
is a gas. Also, while a multi-axis (2 or 3 axes) sensor may be most
useful, single axis sensors could also be used and oriented
appropriately to detect different axes of motion. It should also be
noted that a pressure sensor can sense motion and could be used in
place of an acceleration sensor in certain systems when determining
the onset of motion relative to reference points such as the QRS or
isovolumic contraction of mitral valve closure.
[0106] Both the vibrational and displacement LV motion can provide
useful information for diagnosis of CRT candidates and optimization
of CRT therapy, as is described below. The sensors may be tuned to
sense high-frequency, low-amplitude myocardial vibration, or
low-frequency, high-amplitude displacement motion. Alternatively,
the signal-processing filters could eliminate or reduce frequency
bands that are lower or higher. For the purposes of this
specification, high frequency signals are those greater than about
150 Hz and are related to vibrational motion and correspond to
valvular pathologies such as mitral regurgitation; intermediate
frequencies range between about 20 and 150 Hz can be used to sense
vibrational motion and low-amplitude displacement motion related to
isovolumic contraction or relaxation and valve closure (e.g.,
aortic and mitral); low-frequency signals are those with
frequencies less than about 10 Hz or 20 Hz and are used to detect
high-amplitude displacement, both lengthening and shortening,
related to ejection and filling.
[0107] The frequency associated with the peak amplitude of valve
closure is approximately 40-60 Hz. Thus, when sensing in the
mid-frequency range, and to sense valve closure events, a narrower
band may be used in this range than the typical mid-frequency
range. This signal is closely related to isovolumic contraction and
relaxation. Because many cardiac events such as isovolumic
contraction and mitral valve closure, or LV shortening and mitral
regurgitation, or LV lengthening and mitral valve opening, occur
simultaneously, two or more sensors or two or more filters may be
required to characterize these different cardiac signals. For the
purposes of this specification, references made to the LV motion,
LV cycle phases (e.g., isovolumic contraction or relaxation), and
valvular phenomenon (e.g., aortic, pulmonic, or mitral closure or
mitral regurgitation), should be assumed to be sensed with one or
more sensors, in the appropriate axis, at the appropriate
frequency. While this specification focuses on using valve closure
events to provide reference points for characterizing target pacing
regions and CRT optimization, valve opening could also be used.
[0108] Sensors can be oriented in the devices described below to
optimally detect the desired LV motion. In one embodiment, a
uniaxial sensor is oriented anatomically longitudinally (heart base
to apex) to sense displacement of the LV. In addition, this sensor
could detect vibrational motion through appropriate filtering.
Alternatively, two uniaxial sensors oriented longitudinally and
radially, i.e., toward the ventricular chamber, or three uniaxial
sensor oriented longitudinally, radially, and coronally may be
used. A single triaxial sensor could measure all these components.
In another embodiment, two dual-axis sensors are oriented
perpendicularly to each other in the catheter or LV-lead device.
Three axes may be used for LV motion sensing with filtering used to
detect motion at the appropriate frequency. The fourth axis may be
used as to detect valvular events such as closure or high frequency
pathologies such as mitral regurgitation. In still another
embodiment, three dual-axis sensors may be oriented perpendicularly
to each other with the three axes used to detect displacement
motion and three axes used to detect mid- and high-frequency
vibrations related to isovolumic contraction or relaxation and
valvular pathology such as mitral regurgitation.
Implantable RF-Based Acceleration Sensor Devices
[0109] In one implantable embodiment, the MEMs-based sensor as
described above also incorporates circuitry for electromagnetic
(e.g., RF) inductive coupling to create an RF sensor, as shown in
FIGS. 2-5.
[0110] FIG. 2 shows the placement of a RF MEMS sensor 108
positioned on a coronary stent 112. A second sensor 108' may be
employed at a fixed distance from sensor 108 for measurement of
strain rate. An inductive coil 114 can further be integrated into
the stent 112. A third or more sensors 108'' may also be employed.
This stent may be expanded in known fashion, employing a balloon.
Referring to FIG. 3, the stent and sensor may be disposed at a
lateral edge 156 of the mitral annulus 148 for wireless long-term
monitoring of LV 146 function.
[0111] In an alternative embodiment, shown in FIG. 4, the stent and
sensor may be conductively coupled to an IAD 154, having a battery,
signal processing capability, and data transmission circuitry and
capability.
[0112] In more detail, FIG. 5 shows a schematic diagram of a
batteryless wireless acceleration sensor mounted to, e.g., a
coronary stent, and a corresponding data acquisition and processing
system. Referring to FIG. 3, an RF MEMs acceleration sensor 108, in
an optional single chip design, is shown coupled via an RF
transmission scheme 120 to a receiver system 114 which is in turn
coupled to a data processing system 110. The RF transmission scheme
120 may be employed both for inductive powering and also for data
transmission.
[0113] The MEMs acceleration sensor 108 includes an RF inductive
coil 116 which may surround RF circuitry 118. RF circuitry 118 is
coupled to signal processing circuitry 122. In another part of the
chip, the capacitive MEMS accelerometer 124 is resident. As further
indicated in the figure, a microprocessor, as an ASIC or otherwise,
may be integrated onto the chip as well, along with optional data
storage 128. Additional details of the MEMs acceleration sensor 108
design are given below.
[0114] The receiver system 114 includes a wand 132 which encloses
an antenna 134 via which data and power are transmitted. An
amplifier 136, such as a MMIC amplifier, may be employed to
precondition the signal prior to transmission.
[0115] The data processing system 110 generally includes a
microprocessor 138, a data output and display subsystem 142, and a
data storage area 144.
[0116] A main component of the RF circuitry is the inductive coil
which is used for data transmission and/or inductive powering.
Alternatively, separate coils could be used for inductive coupling
and data transmission. A representative silicon-etched inductive
coil for powering capacitive MEMs sensors is disclosed in U.S. Pat.
No. 6,667,725. The RF circuitry, including the inductive coil, may
be incorporated into the same sensor chip. Alternatively this
circuitry and coil may be fabricated separately and conductively
linked to the sensor. For example, a planar RF antenna for
inductive powering and data transmission may be fabricated on a
flexible polymer substrate (e.g., polyimide) by winding or etching.
The antenna may be planar. The sensor can be soldered to the
flexible antenna circuit at bonding pad areas. The flexible polymer
may then be wrapped around a vascular stent or incorporated into
other cardiac devices and implanted into the body. In another
embodiment a flat planar coil on a polyimide substrate is created
with a long thin section. The planar coil can reside subcutaneously
and the long thin section can reside transvenously within the body
or within a device such as an LV pacing lead.
[0117] In addition, non-volatile memory may be used for storage of
captured acceleration data. Similarly, this memory may be
integrated into the same sensor chip, but may also reside as a
separate chip and or in a separate location with appropriate
connections. Lastly, a microcontroller or an application-specific
integrated circuit (ASIC) may be incorporated into a sensor chip
design or the same may reside on a separate chip and in a separate
location. It should be noted that all device descriptions below
that are based on RF coupling could be replaced with conductive
element coupling for data transmission and power supply from a
battery.
[0118] The RF accelerometer sensor can be hermetically sealed and
packaged in a biocompatible housing to form a rugged sensor device
for implantation into the body or cardiovascular system.
Appropriate packaging may also reduce damage due to exposure to
fluoroscopic radiation. Appropriate packaging would also not
interfere with RF coupling. The device would have appropriate
mechanisms for attachment to the body or cardiovascular system,
including: tines, helical screws, suture pads, retention struts,
and structures, such as porous titanium, to allow tissue ingrowth.
There are various form factors the packaged accelerometer sensor
device may have to facilitate implantation and various strategies
for affixing the sensor device to the body.
[0119] An exemplary use of an RF sensor device is in cardiac
surgery. Cardiac surgery and transplant patients can have severe
myocardial dysfunction. An RF sensor could be affixed to the
epicardial surface of the left or right ventricle. In this
embodiment, the packaged sensor device may be circular and 2 cm or
less in diameter and less than 5 mm thick. The device's epicardial
surface may be flat and may have a helical screw for fixation into
the myocardial tissue. Various polymeric materials maybe
incorporated into the sensor epicardial surface to promote
attachment to the myocardium. The upper device surface is
curvilinear to conform to the chest wall. One or more sensors could
be used to detect LV motion and related LV cycle phases, valve
closure, and valve pathologies such as mitral regurgitation. Again,
conductive elements and a battery supply could replace the RF
components.
[0120] In another embodiment, an RF MEMs accelerometer sensor is
incorporated into a coronary stent that is implanted in the LV
arteries. The stent may also be implanted in the lateral coronary
sinus or great cardiac vein or other LV veins near or proximate to
the lateral edge of the mitral valve annulus. This is akin to
implanting a sensor directly onto the epicardium and hence
acceleration sensing of LV motion and the LV cycle phases can be
measured. If two or more sensors are used separated by a known
distance, strain and strain rate can be measured. The sensor or
sensors could also be used to sense valve pathologies such as
mitral regurgitation. Design and implantation of stents are known
to those skilled in the art. The transceiver coil could be
integrated into the stent body, or the stent body of a coiled stent
design could serve as the transceiver, as shown in FIGS. 2 and 3.
In still another embodiment, RF acceleration sensors are
incorporated into a CRT or CCM pacing lead and preferably the LV
lead. In this way, the sensor monitoring may occur independently of
the CRT system via RF inductive powering and data transmission. RF
acceleration sensors incorporated into a CRT lead or CCM lead could
measure LV motion and characterize LV function, including valve
pathologies such as mitral regurgitation, as described below.
Additionally, RF MEMs sensors may be incorporated into guide
catheters or guide wires for the same purpose.
[0121] RF sensor monitoring and data transfer could occur via an
antenna device connected to a microprocessor which is worn by the
patient or held near the sensor (e.g., over the chest). An
appropriate antenna device would have a large enough antenna to
inductively couple with the sensor. In one illustrative system, the
antenna device may couple with the sensor at a distance of 5 to 15
cm and up to 15 feet. An exemplary antenna device is discussed in
"RF telemetry system for an implantable bio-MEMs sensor", Rainee
Simons, et al., NASA Glen Technical Reports, June 2004, NASA
TM-2004-212899. As discussed in this paper, an MMIC amplifier
connected to the antenna can allow for a reduction in the size of
the sensor coil and the reader antenna.
[0122] The antenna would transfer the sensor data to a
microprocessor or computing device that applies processing
algorithms to the data and display the data to the physician for
therapy monitoring. The microprocessor computing device and reader
may be integrated into one device. Various signal processing
functions may be carried out by the microprocessor such as
filtering different band widths for different sensors to
differentiate vibrational motion signals indicative of valve
closure or mitral regurgitation from lower-frequency displacement
motion related to LV ejection or filling. Because patients may have
various valve anomalies, such as mitral regurgitation or aortic
stenosis, the motion related to isovolumic contraction and
relaxation may be especially monitored and may be indicative of
valve closure events due to the short time period (about 10-30
milliseconds) between isovolumic contraction or relaxation and
valve closure. Signals may be timed for detection after onset of
the QRS, an endocardial electrogram, or other electrical signals.
For example, sensing isovolumic contraction may occur immediately
after sensing of the QRS for an interval of 50-150 ms, i.e., to
allow particular attention to be given to this period. In addition,
the microprocessor could carry out various statistical
manipulations to monitor long-term trends. It should be noted that
the microprocessor could also be located in an implantable device
conductively coupled to the sensors.
[0123] Data transfer could be conducted by the physician
periodically. Alternatively, the antenna device could be connected
to the patient's home computer and transferred data could be sent
to a physician or monitoring center over a network. An RF
sensor-reading antenna integrated into or connected to a cellular
phone would allow data to be wirelessly transmitted to a physician
or monitoring center. Similarly a hand-held computing device with
wireless communications could transfer sensor data wirelessly to a
physician or monitoring center.
[0124] In another embodiment, at least one RF sensor, and even two
or more, are incorporated into an endovascular catheter with or
without a guidewire through lumen that can be implanted into the
blood vessels of the body. In this illustrative system, at least
one sensor is capable of sensing valve closure, isovolumic
contraction or relaxation phases, or mitral regurgitation either by
sensor tuning or filtering. This sensor catheter is placed via
transvascular methods form the subclavian vein, internal jugular,
or cephalic vein into the coronary sinus, or its tributaries,
including the left ventricle drainage veins. The proximal portion
of the catheter has a means for implantation and anchoring in the
subcutaneous tissue.
[0125] Methods for inserting catheters into the coronary sinus and
LV veins are well-known to those skilled in the art. In general,
insertion occurs over a guidewire after accessing the coronary
sinus ostium with a guide catheter. This placement is done under
fluoroscopic visualization so the sensors are constructed to
withstand the radiation exposure or are otherwise protected in a
capsule that does not interfere with RF coupling. The catheter is
flexible, may or may not be braided, and is made of a biocompatible
polymer such as silicone or PBAX. The sensor catheter could have
various features to facilitate placement and anchoring including
fixed angles, a guidewire lumen, tines, and tip deflectability or
steerability. In addition, the catheter may have an occlusion
balloon and contrast injection lumen and port for acquiring an LV
venogram. Alternatively the venogram features are incorporated into
the guide catheter. Preferably, one sensor is located at the
posterio-lateral or lateral edge of the mitral annulus. Additional
sensors may be located on the catheter separated by known fixed
distances (e.g. 5-10 mm) to provide strain and strain rate data.
The above catheter allows long-term monitoring of myocardial
mechanical activity and the LV cycle phases via wireless sensor
powering and data transmission, thereby minimizing device
complexity.
[0126] Preferably the region of the catheter where the sensors are
located is suitably flexible to move with the displacement motion
of the heart. Referring to FIG. 4, if two sensors are employed to
measure strain or strain rate, the region between these two sensors
should be suitably flexible to ensure that the two sensors move
relative to each other during LV displacement. The sensors may,
e.g., move radially and longitudinally relative to each other. The
flexibility may be achieved by fabricating the region of the
catheter where the sensors are located with a metallic or polymeric
helical coil. Alternatively, a thin-walled polymeric catheter
tubing could be employed. It may also important that the sensors
lay adjacent to the myocardium as closely as possible or are
prevented from moving within the vessel in a direction counter to
the contracting or relaxing myocardium. This may be accomplished by
weighting the bottom portion of the catheter where the sensors are
located such that they lie flat on the myocardium.
[0127] For example, referring to FIG. 6, a system is shown
including a catheter having a coiled sensor segment or LV lead
design which enhances flexibility between the sensors for detecting
myocardial strain or displacement. A catheter body 158 has a distal
end 162 and adjacent to distal end 162 is sensor segment 164. A
guidewire lumen 166 may accommodate a guidewire 168 for effective
placement of the distal end 162 of the catheter. The sensor segment
164 includes a metallic or polymeric coil 178. A displacement
sensor 172 may be mounted to the coil 178, along with a sensor 174
to detect valve closure or isovolumic phases or mitral
regurgitation. One or more electrodes 176 may also be provided for
sensing cardiac electrograms and delivering ablative RF energy if
required.
[0128] Alternatively, a structure can be used to constrain the
sensors or sensor region of the catheter in the blood vessel, as
shown in FIG. 7. This may be accomplished with a flexible wire cage
that extends around the sensors or sensor region of the catheter at
a diameter approximating or greater than the vessel diameter. An
inflatable balloon or expanding deployable structure could also be
used to constrain the sensors or sensor region of the catheter in
the vessel. Lastly, angling or coiling may be employed of the
region of the catheter with the sensors such that the bend helps
constrain the sensor to the epicardium.
[0129] In particular, referring to FIG. 7, a system is shown in
which a coiled sensor or LV lead design is disposed at the distal
end of a catheter, the coiling allowing enhanced flexibility. A
catheter body 182 has a sensor segment 184 at the distal end 202
thereof. A displacement-sensing sensor 188 is provided along with a
sensor 186 which may measure valve closure, isovolumic phases, or
mitral regurgitation. Coils 192, 194, and 196 provide enhanced
flexibility for the sensor segment 184. It should be noted that the
actual number of coils and sensors may vary depending on the design
and requirements of the catheter. Coils 192, 194, and 196 may have
a polymeric or metallic construction. Sensor 186 may be surrounded
by a wire cage 206 which may be employed for constraining the
sensor at a predetermined location in a vessel. Wire cage 204 may
serve a similar purpose for sensor 188. The wire cages 206 and 204
further assist in preventing movement of the sensors during
contraction.
Implantable Non RF-Powered Acceleration Sensor Devices
[0130] In an alternative illustrative embodiment, and referring to
FIG. 8, an IAD (is fabricated by incorporation of one or more
non-RF MEMs acceleration sensors into an LV venous catheter, as
previously described. In this system, long-term monitoring of LV
mechanical performance can be performed. Acceleration related to
both LV vibration and displacement, and valve pathologies such as
mitral regurgitation, are measured by sensing at the appropriate
frequency with the one or more sensors and employing filtering and
signal processing.
[0131] In particular, FIG. 8 shows a heart 200 and subclavian vein
216. Also shown are the left atrium 218, the right atrium 222, the
right ventricle 224, and the left ventricle 226. The catheter 210
may enter the heart through the subclavian vein 216, and extend
through the coronary sinus ostium 38 into the coronary sinus 242
adjacent to which is the mitral annulus 244. After passing partway
through the coronary sinus, up to the cardiac vein 248, the
catheter may extend into the LV vein 246.
[0132] The catheter 210 includes, near a first end 228, one or more
sensors 208 and 212. For appropriate sensing, the sensors may be
separated by an approximate pre-determined distance, e.g., 10 mm.
One sensor may reside at the posterior-lateral edge 214 of the
mitral annulus. The sensors may be conductively connected via the
catheter 210, at a second end 232, to a subcutaneously-implantable
data acquisition and processing device 234, which contains a
battery supply, RF telemetry circuitry, a microprocessor, and data
storage. The implantable data acquisition and processing device may
be housed in a hermetically-sealed titanium shell. The processing
unit 234 may connect to the catheter 210 via a proximal catheter
connector 236. The sensors are encapsulated in a structure that
protects them from fluoroscopic radiation damage; however, because
the sensors in this embodiment are not directly RF-coupled,
concerns about interfering with this coupling are eliminated.
Insulated, multifillar, coiled wires 252, only a portion of which
are shown in FIG. 8 for clarity, conductively connect the sensors
to the proximal catheter connector 236. The connector attaches to
the implantable data acquisition and microprocessor device 234,
which powers the sensors, captures the sensor data, processes the
data, and stores the data. The microprocessor controls the data
sampling period and data sampling intervals. Captured acceleration
data can be subjected to various data processing algorithms as are
described below. This processed data can be stored in memory for
later RF telemetry data transfer.
[0133] The battery in this embodiment may be rechargeable or
typical of implantable battery sources. A typical implantable
battery cell design is lithium silver vanadium oxide. Lithium
carbon monoflouride may be also be used and has certain advantages
due to its low weight.
[0134] Data storage may include readable and writable memory. A
constant power input from the battery can allow volatile random
access memory to be used for data storage and control functions.
However, non-volatile data storage such as EEPROM or flash may also
be used. A combination of volatile and non-volatile memory storage
may be used. Flash memory is non-volatile, compact and operates in
the voltage range of implantable device batteries. Access to the
data is rapid and megabyte storage capacity is available in a small
size. Data may be stored on a first-in-first-out basis if memory
becomes full prior to RF telemetry data transfer.
[0135] IAD acceleration data acquisition occurs over a sampling
period that may be continuous or may be only a short period such as
several seconds to up to 30 seconds or even several minutes. Data
acquisition may occur at various sampling intervals such as from 8
to 1,440 times each day. Sensor data is sampled at rates
sufficiently high to provide useful information for diagnosis and
monitoring of CRT patients, target pacing regions, and heart
failure (or cardiomyopathy) patients, and preferably at rates of
100 per second to 1000 per second. Sample rate, sample time, and
interval periods are in part dependent on data storage capacity.
Data captured and stored can be transferred by telemetry to a
computing device either daily by the patient or weekly to monthly
or longer by the physician. Data storage may be sufficient to allow
at least one day of data storage and up to six months of data
storage at the optimal data sampling rate, time, and interval to
provide the physician with useful information.
[0136] In another illustrative system the IAD described above is
integrated with the proximal portion of a cardiac pacing lead, and
preferably an LV CRT pacing lead, as shown in FIG. 9. At least one
and possibly two sensors or more, shown as sensors 254-262, are
incorporated into the LV pacing lead to measure LV motion and
characterize LV function. The catheter may have an endovascular
portion 270, and a subcutaneous portion 280, with a subcutaneous
anchoring device 272 to anchor the adjacent portion of the catheter
to the chest wall.
[0137] If strain or strain rate data is to be measured, two or more
sensors may be incorporated at a known distance from each other,
e.g., 5, 10, or 15 mm. One or more sensors are positioned on the
lead as in the above embodiments with least one sensor residing at
or near the posterior-lateral or lateral edge of the mitral valve
annulus. The region of the lead between and around the sensors is
made suitably flexible as previously described to ensure
measurement of LV displacement and strain or strain rate. Sensing
is carried out at different frequencies or with one or more
sensors, or both, to measure both displacement and vibration to
characterize the LV cycle phases and function, and pathologies such
as mitral regurgitation. This IAD-integrated cardiac lead design
allows cardiac mechanical monitoring independent of the CRT or CCM
IPG. In this pacing lead embodiment, an implantable data
acquisition and processor component 278 may be made as small as
possible. Thus the battery cell used may be ultra miniature and may
be rechargeable. Exemplary batteries are available from Quallion,
Inc., of Sylmar, Calif., some of which have a 2.9 mm outer diameter
cylindrical implantable battery (2.7-4.0 V, 3 mAmp-hours). A
compact, non-volatile memory such as flash memory may be used in
this system for processed data storage. Data processing algorithms
may be performed after RF telemetry data transfer. The IAD RF
telemetry may occur at a frequency that does not interfere with a
CRT device 284. In addition to the battery power, data storage, and
RF telemetry components, the implantable accelerometer data
processor 278 may include a microprocessor, and may connect to the
catheter via connector 282 at a distal end of Y-connector portion
290.
[0138] The catheter may be disposed using guide wire 274 having
distal tip 292 adjacent tine 298, the guide wire being enclosed
within a guidewire lumen (not shown).
[0139] Data and signals from the sensors and the data acquisition
and processing component 278 are sent to the CRT device 284 via
connector 276. The CRT device 284 may also receive signals from RA
lead 286 and RV lead 288.
[0140] The design of LV pacing leads is known to those skilled in
the art. In general, the LV CRT lead and fixation is similar to
currently deployed leads with the exception of the requirement of
accommodating the accelerometer-based sensors. The lead may be
unipolar or bipolar. The conductive wires for the electrode may be
coiled, mutifillar, and sheathed in a polymer such as silicone or
polyurethane. A connector 276 at the proximal end 277 allows
connection to the IPG and may be universal according to the IS-1
standard. A set of pacing electrodes 264-268 and 296 can be
variously fabricated as a blunt-nosed tip (296), ring (264-268), or
coiled. Non-corrosive alloys and metals can be used in the
electrodes/lead such as platinum iridium or titanium iridium oxide
or nickel cobalt or others such as are known in the art. The lead
may elute a steroid drug via a drug elution component 294 to
minimize inflammation at the electrode site location to keep
capture thresholds lower. The lead could also have an ePTFE coating
at the electrode to minimize fibrosis.
[0141] In another illustrative LV lead implantable system, a sensor
302 is incorporated into a sensor wire 304 that integrates with an
implantable LV lead 300 (See FIGS. 10-14). This design allows the
pacing lead to be positioned in the target pacing region and LV
vein and the sensor can be positioned along the lateral or
posterior edge of the mitral annulus. The sensor wire can also
serve as a guidewire for the LV lead 300. The sensor 302 is
attached to the sensor wire 304 via a stalk 306. The electrical
conductors 308 of the sensor 302 run through the stalk 306 and down
the length of the sensor wire 304. At the proximal end 310 of the
sensor wire 304 is a connector 312 for linking the sensor 302 to an
IAD 314. Even more proximal of end 310 may be a connector 342 to
connecting the LV lead to a CRT device 344.
[0142] The sensor wire is integrated into the LV lead via a side
wire lumen 316 along the length of the LV lead 300. The side wire
lumen 316 is split to allow the sensor to be shuttled along the
surface of the lead body 300. The sensor wire 304 may reside in the
side wire lumen 316 and the sensor stalk 306 may reside along the
split in the lumen 316. Thus the acceleration sensor 302 can be
shuttled to the desired location at the mitral annulus 322 (see
FIG. 14), such as near to the lateral border 326 of the mitral
annulus 322, while the pacing lead 324 can go to the target pacing
region, e.g., region 330. If the pacing lead 324 makes a bend to
cannulate and LV branch that feeds into the coronary sinus, the
sensor wire 304 can continue straight within the coronary sinus 326
or great cardiac vein to the desired location. In other words, the
sensor can be placed in a desirable location for measuring LV
function while the pacing lead is disposed in the proper location
for pacing of the ventricle.
[0143] Also shown in FIG. 10 is a central guide wire lumen 318
(which emerges from opening 336) that may be employed to position
the LV lead 300, as well as components of the pacing lead 324, such
as ring electrode 332, optional acceleration sensor 334, and
microporous tip electrode 338.
[0144] In use, as the LV lead 300 bends to enter the posterior to
lateral LV vein 342, the sensor wire 304 and sensor 302 bend out of
the side lumen 316 due to the stiffness of the sensor wire 304. In
this way, while the LV lead 300 goes into the LV vein 342, the
sensor 302 continues on to a position near the mitral annulus or
the lateral border thereof.
[0145] In another illustrative system, as shown in FIG. 15, the IAD
is integrated with the CRT or CCM IPG device, here shown as device
350 In this CRT acceleration sensing and control system, sensor
data is used to control the output of pacing signals to electrodes
in regions of late contraction and deformation.
[0146] As before, acceleration sensors 352-358 are integrated into
the LV pacing lead 360. Circuitry and control of sensor data
acquisition and processing may be integrated with the electronics
of the CRT. Algorithm-processed acceleration data, described below,
can be used to control and optimize the CRT such as via the
atrioventricular interval, the interventricular interval, and may
further be used to optimize the LV pacing site. Motion sensing may
be used to dynamically change the pacing at multiple LV electrodes
to continuously optimize the LV pacing over time. Cardiac events
such as valve closure or isovolumic phases could control the
timing, similar to a cardiac electrogram. At least one sensor may
be designed to detect valve closure or isovolumic contraction and
relaxation and may be positioned in the vessel to do so. Such a
device that senses mechanical cardiac activity, e.g., valvular
events, isovolumic contraction phases, and deformation, may be more
optimal than controlling pacing signals with a sensed cardiac
electrogram since cardiomyopathy causes mechanical dyssynchrony.
Because some CRTs have defibrillation capability, the sensors and
their attendant circuitry may have to withstand the energy
delivered during a defibrillation event. This device may be capable
of standard CRT functions, including multi-chamber EGM sensing,
pacing, and trigger or inhibition control. Event sensing and
storage would also be typical. Antitachyarrhythmia and
bradyarrhythmia control of the atria and ventricles as is currently
available may also be present and may include overdrive pacing,
cardioversion and defibrillation. The device also allows periodic
assessment of electrode capture threshold and adjustments to this
threshold. This preserves battery life and ensures optimal
myocardial activation and therapy. Hence myocardial deformation or
strain rate may be monitored and pacing signals directed to the
electrode where late deformation is occurring. Consequently, this
type of CRT system may have an LV lead with multiple electrodes and
acceleration sensors.
[0147] In more detail, device 350 may be connected to various leads
via connector 392. The leads may be RA lead 370, RV lead 380, and
LV lead 360. The RA lead 370 and the RV lead 380 may have optional
acceleration sensors 346 and 348, as well as electrodes 362 and
364, and helical fixation points 378 and 382. Besides the
acceleration sensors already noted on LV lead 360, a number of
electrodes 366-374 may also be disposed. A guide wire lumen 384 may
be disposed for use with a guide wire to aid is positioning the
lead. The distal tip of the lead may include a tine 376 to help
stabilize the lead in the vein. An optional balloon occluder 386
may be employed for venogram acquisition, with a contrast injection
port 388 adjacent, but distal, thereto. The remainder of the
catheter system is as has been already described.
Signal Processing, Data Analysis, and Monitoring
[0148] In one illustrative system, the LV motion signals and data
analysis are produced from a sensor along the mitral valve annulus.
Mitral annular velocities have been shown to provide an accurate
assessment of global left systolic and diastolic function. Mitral
annular motion may also be best to measure displacement of the LV.
Thus, this displacement motion may be subjected to a mathematical
integration algorithm, as shown in FIG. 16, to yield velocity and
distance.
[0149] In particular, the first step is to acquire acceleration
data (step 394). Following this initial step, the data may be
averaged over a predetermined sample period (step 396). The
acceleration data may then be integrated to obtain the velocity
(step 398).
[0150] A velocity curve may then be output to indicate systole and
diastolic velocities (step 402). From this an analysis of peaks
over time may be output (step 404). Finally, a measurement may be
taken of the onset of displacement velocity versus the QRS peak
(step 406).
[0151] If a second sensor acquires, or can be used to acquire,
velocity data as well (step 408), displacement and strain rate may
be obtained. From the first and second sensor velocity data, the
strain rate can be calculated (step 412), and a strain rate curve
may be output (step 416). From the strain rate and the velocity
data, the data can be integrated to obtain the ventricular
displacement (step 414), from which a displacement curve may be
output (step 418). In general, LV motion signals may be processed
in a manner best used for interpretation and therapy optimization.
This includes analyzing indices or variables of LV function such
as: peaks and slopes of acceleration, velocity, and distance
curves, interval times of LV cycle phases, and analysis of
pathological valve signals. Curves, such as a velocity curve of LV
displacement, may be plotted with velocity in millimeters or
centimeters/sec as the ordinate and cardiac cycle time in
milliseconds as the abscissa. The algorithm may also involve
calculating strain rate by processing acceleration data from at
least two sensors separated by a known distance, e.g., 5 to 15 mm
millimeters apart. Vibrational motion signals, e.g., that related
to mitral regurgitation, may be presented as an amplitude and
duration or a change in the frequency.
[0152] 3-axis sensing is utilized in some illustrative systems. A
more accurate measurement of peak amplitude can be measured by
calculating the composite acceleration vector of each axis (x, y,
and z). This can account for the gravitational acceleration and its
effects on sensor tilting. The composite vector can be calculated
by taking the square root of the sum of the x-axis measurement
squared plus the y-axis measurement squared plus the z-axis
measurement squared. This peak amplitude calculation can be applied
to both the vibrational motion and the displacement motion. This
may be particularly accurate during the implantation of an LV lead
for CRT therapy when the patient is lying still on a procedure
table. Here the sensor measures the peak in the LV veins or
coronary sinus.
[0153] Thus, LV acceleration signals are sampled at a designated
rate for a set time period, which is the sample period. Sensor data
from the sample period can be averaged over several or more cardiac
cycles to smooth out effects related to respiration and patient
motion. The averaged data can then be used to produce a cardiac
cycle acceleration curve which includes tissue acceleration, in,
e.g., mm or cm/sec.sup.2 versus cardiac cycle time, in
milliseconds. This curve can then be mathematically integrated to
produce a tissue velocity curve, e.g., in mm-cm/sec vs. cardiac
cycle time. A second integration can performed to produce a
distance curve, with units of mm or cm. Point-by-point acceleration
sensing and integration can also be performed with peak
identification, integration, and presentation as an individual data
point rather than a curve.
[0154] Strain and strain rate curves and data points may be
generated from velocity curves or data points. Generally at least
two sensors are needed to measure strain rate. Velocity curves or
data are generated from the two sensors in at least one axis.
Strain rate or strain rate curves are created by integrating the
difference in velocity data from the two sensors at the same point
in the cardiac cycle and dividing this difference by the distance
between the sensors .intg.(v.sub.1-v.sub.2)/1. Since the distance
of the sensors along the length of the implanted catheter or pacing
lead is fixed, the distance between sensors is known. The strain
curve is generated by integrating the strain rate curve.
[0155] Referring to FIG. 17, the velocity of LV displacement from
the mitral annulus, generally at the posterior-lateral edge
thereof, produces peaks representative of LV function during
systole and diastole. Analysis of the peaks including: magnitude of
the change, e.g., positive and negative, peak slopes, peak/peak
ratios, slope/slope ratios, peak/slope ratios, and peak
integration, provides specific information on LV function related
to contractility, afterload, volume status, preload, ventricular
compliance, ejection fraction, and ventricular synchrony. As above,
FIG. 17 and the like may represent a composite of all three axes,
x, y, and z, of the acceleration sensor.
[0156] This information is useful for the physician for long term
management of the cardiomyopathic patient. This curve 422 often has
two peaks during systole (S1 424 and S2 426) and three peaks during
diastole (isovolumic relaxation 428, E 432, and A 434), though at
times not all of the peaks are discernable. Trends in these peaks
can provide useful information to the physician. These trends may
prompt changes in pharmacologic therapy such as drug
addition/elimination or dosage changes.
[0157] For example, referring to FIG. 18, which shows a
representation of long-term monitoring and therapy optimization, a
patient is seen with a baseline level of maximum peak magnitude of
the average of daily sample intervals of S1 or S2 annular
velocities (line 436, with a standard error of mean (SEM) of daily
average peak data 437 and 437'). Decline 438 may be seen, which
corresponds to a decline in contractility, e.g., of the S1 peak.
The decline may be defined in various ways, such as by a one or two
SEM deviation from the baseline. A therapeutic intervention at 442
is shown, which is done to improve contractility. A new baseline is
then evident at 444, with SEM bars at 446 and 446'.
[0158] These trends may also indicate when additional interventions
are warranted such as cardiac surgery, endovascular
revascularization, or CRT. It may be noted that these peaks have
been characterized with tissue Doppler imaging at the
posterio-lateral edge of the mitral valve annulus in a single
plane. An epicardial acceleration sensor in the same region, that
is recording acceleration in 1, 2 or 3 axes, may produce a somewhat
different velocity curve. However, it is believed that the curve
can be analyzed in a manner analogous or similar to that discussed
below to provide useful information to the physician.
[0159] The S1 peak can be used to assess myocardial contractility
with a higher peak indicating improved contractility and a lower
peak indicating reduced contractility. A main goal of heart failure
therapy is to improve myocardial contractility. Contractility can
be improved with CRT therapy and pharmacologic therapy. The slope
of this peak may provide similar information.
[0160] The S2 peak can be used to assess afterload, which is a
measure of the resistance the heart must pump against as it
circulates blood to the body. It is the goal of heart failure
therapy to reduce afterload, primarily with the use of
pharmacologic agents. Increases in the S2 peak represents increases
in afterload, and decreases in the S2 peak represents reductions in
afterload. Alternatively, integrating the area under the S2 peak
may provide information on the afterload. The S2 peak also
correlates with ejection fraction and rate of pressure change
(dP/dt).
[0161] The E and A peaks can be used to assess cardiac compliance
and patient volume status. In heart failure therapy, optimizing the
patient's volume status and its effect on left heart pressure is
important. Cardiomyopathy patients have a tendency to retain water
and can become volume overloaded. When this occurs, the function of
the heart deteriorates and symptoms such as pulmonary congestion
occur. Diuretic drugs such as Lasix are commonly used to reduce
water retention. Monitoring of the E and A peaks and slopes, and
integrating the area under the curve, can provide information on
volume status. In addition, the relationship of the E and A peaks
(E/A) is indicative of ventricular compliance. Ventricular
compliance can change with ischemic events and can be reduced with
long-term elevated afterload. Beta-blocker therapy can affect
compliance in cardiomyopathy patients and therefore may be
monitored with the E and A peak data.
[0162] The A peak which represents atrial contraction can also be
used to optimize atrioventricular timing in a patient with CRT
therapy. AV synchrony optimizes preloading of the heart and
improves pumping performance in part via the Frank Starling
mechanism. Ideally, ventricular contraction occurs at the
completion of atrial contraction, which produces optimal preloading
of the ventricle. The end of atrial contraction and ventricular
filling can be determined at the point at which the ventricular
velocity crosses the abscissa after the peak of the A wave (FIG.
11). Subsequently, ventricular pacing signals can be triggered at
this point.
[0163] Other measures of LV function can also be obtained by
analyzing the time intervals of different phases of the cardiac
cycle. Several time interval measures include the isovolumic
contraction, ejection phase, isovolumic relaxation and LV filling
time. Time intervals can be estimated from the acceleration,
velocity, and distance data. The start of a time interval may be
identified as an acceleration amplitude above a certain threshold
(e.g., +/-milli Gs) and the end of an interval may be indicated by
the dipping of the acceleration amplitude below a threshold value.
Also, the number of zero crossings may also be used to estimate
time intervals. A reduction in the isovolumic contraction or
relaxation time interval would be indicative of a favorable
response. Increase in the ejection phase time interval, e.g., QRS
to aortic or pulmonic valve closure, and the filling time interval,
would also be indicative of a favorable response.
[0164] The myocardial performance index (MPI) is a measure of
systolic and diastolic function that is a good predictor and
monitoring indicator for heart failure. The index is calculated as
the isovolumic contraction time plus the isovolumic relaxation time
divided by the ejection phase time (FIGS. 18 and 21). A reduction
in the value of the MPI is indicative of better LV function. The
MPI may be assessed using an acceleration sensor by measuring the
intervals as described above. In addition it may be assessed by
monitoring mitral valve opening and closing from the coronary sinus
or great cardiac vein and measuring the ejection phase due to LV
shortening. Thus the time interval during systole between mitral
valve closure and mitral valve opening minus the time interval of
LV shortening divided by the time interval of LV shortening is
indicative of the MPI.
[0165] Longitudinal displacement of the mitral annulus inferiorly
during systole and superiorly during diastole is also a good
measure of LV function. Thus a sensor in the coronary sinus or
proximal the great cardiac vein with at least one axis oriented
longitudinally will measure the acceleration of the annular region
in the inferior and superior directions. From this, velocity and
distance can be calculated through integration. The peak
acceleration, peak velocity, and distance traveled by the annular
region during systole are indicative of performance with higher
values indicating better function. Similarly the velocity and peak
acceleration during diastole as well as the distance traveled is a
measure of LV performance with higher values indicating better
function. The clockwise or counterclockwise rotation of the basal
and annular region can be measured in the coronary sinus with an
acceleration sensor oriented horizontally. Again, higher values of
acceleration, velocity, and rotation are indicative of LV
performance. Narrowing and widening anteriorly/posteriorly and
medial/laterally of the mitral annulus is also indicative of LV
function. An acceleration sensor oriented radially to the heart in
the coronary sinus or proximal the great cardiac vein could assess
this motion with higher values indicative of better function. A
3-axis sensor could measure all axes of motion of the mitral
annulus: longitudinal, radial, and rotational, for complete
characterization of LV function from the coronary sinus. This would
be useful for long term monitoring, identifying, and optimizing LV
pacing regions during CRT lead placement as described below.
[0166] Referring to FIG. 19, in which displacement, in, e.g., cm or
mm, is shown as the ordinate, low frequency (1 to 10 Hz or less
than 20 Hz) acceleration sensing associated with LV displacement
and its respective integration of velocity and distance may appear
as a semi-sinusoidal wave (curve 448) of positive and negative
deflections with a frequency as a function of the heart rate. The
orientation of the sensor axes determines if longitudinal
displacement is a positive deflection or a negative deflection. By
convention, longitudinal shortening is usually displayed as a
negative or downward-moving deflection and lengthening as a
positive or upward-moving deflection. If the orientation of the
sensor is not known and cannot be determined easily, information
recorded by the sensor may not allow the physician to distinguish
systolic shortening from diastolic lengthening. Orientation can be
determined by synchronizing the low frequency sensor data with the
high frequency data or the QRS (see curve 458 and points 454, which
signify mid-frequency (20-150 Hz) valve closure signals. Isovolumic
contraction and relaxation signals occur with a similar
mid-frequency.). Thus, the start of systole and shortening can be
determined as the deflection that occurs after isovolumetric
contraction, mitral valve closure, or alternatively the QRS. The
double integration of the peak amplitude of the sensor data after
mitral valve closure or isovolumic contraction or QRS is
representative of peak longitudinal shortening. The same rationale
can be applied to orienting longitudinal lengthening using
isovolumic relaxation or the aortic valve closure sensor data or
the T-wave (see FIG. 1B) as the reference point. Isovolumic
contraction or relaxation or mitral or aortic valve closure can
have distinctive vibrational signals detected by higher frequency
sensing, allowing the same to be distinguished. However, mitral
valve closure can be determined by comparing the sensor signal to
the ECG, whereas the mitral valve signal will be the first signal
detected after the QRS. The microprocessor can be programmed to
display the shortening and lengthening according to convention.
[0167] To accurately measure the length or magnitude of ventricular
deformation, peak velocities, or peak accelerations, during systole
(or even diastole) along the radial or longitudinal axes, a zero
reference point is preferably ascertained. This can be seen in FIG.
19 as point 456, for the zero point systolic deformation for length
measurement, which also represents the peak diastolic length. A
different peak 458 represents the zero point diastolic
displacement, which is also the peak systolic shortening. As the
sensor devices are maneuvered in the patient or as a patient moves,
the tilt of the sensor with respect to gravity, i.e., the angle
versus the gravity vector, will change. This sensor output due to
the tilt signal must be accounted for or offset to accurately
measure peak amplitudes and distance of shortening. For mechanical
mapping (see below), the magnitude of shortening, or peak
velocities or peak acceleration, could be assessed and regions that
are activated earlier and have a greater magnitude of shortening
would be selected for long-term CRT pacing. Also, the optimal
pacing capture threshold could be determined by applying pacing
signals of increasing strength (millivolts). Monitoring the
magnitude of the deformation and correlating this with the pacing
signal strength optimizes the pacing threshold. Further, the
qualitative assessment of lengthening or shortening is facilitated
by having a zero point.
[0168] Referring again to FIG. 19, valve closure or isovolumic
contraction or relaxation can provide the zero-offset reference
point. Alternatively, the onset of the QRS can be used to determine
the zero point. Hence, length of systolic shortening 460 is
measured as the peak amplitude of the double integration of
acceleration data sensed after isovolumic contraction and/or mitral
valve closure or QRS onset. Similarly, the length of diastolic
lengthening 450 is measured as the peak amplitude of the double
integration of the acceleration data after isovolumic relaxation
and/or aortic valve closure, i.e., the diastolic zero point. The
tilt reading, or tilt offset, of the sensor can also be accounted
for by using the QRS onset, mitral valve closure, or aortic valve
closure from the signals measured. Thus, the capacitive signal
sensed by the sensor at the above reference points can be
subtracted out from subsequent signals being measured to detect LV
lengthening and shortening. Accurate assessment of diastolic
lengthening as noted above allows the physician to monitor the
filling and the dilated state of the left ventricle.
[0169] Trends of increasing diastolic lengthening are indicative of
volume overload, while reduction in diastolic lengthening
represents improvements due to volume unloading. This data may be
trended in an implantable device according to an embodiment of the
current invention and is useful in the mapping procedure to assess
the effect of pacing the target region which may then shows a
reduction in peak diastolic lengthening due to improved pumping and
volume unloading.
[0170] Referring to FIG. 20(A)-(C), assessment of LV size for acute
response to CRT and long-term management is shown. As heart
patients regain fluid the LV can become enlarged. Benefits are seen
as reduced LV volumes. By having a sensor on the lateral wall, the
relative movement as the LV is enlarged could be monitored. Sensors
also allow the establishment of a reference point.
[0171] FIG. 20(A)-(B) shows mitral annulus 462, LV wall 464, and
cardiac vein 466 in which is situated high frequency sensor 468 and
low frequency sensor 472. FIG. 20(B) shows the position of the
sensor on the heart at the end of the filling phase (post
isovolumic relaxation). If the heart improves, the sensor moves
inward to reflect the smaller size (FIG. 20(A)). If the heart
enlarges the sensor moves outward (FIG. 20(C)). Thus, used in this
was, embodiments of the invention give a measure of diastolic
filling or dilation.
[0172] Mitral regurgitation can be caused by LV dilation and
functional decline, which worsens the symptoms of heart failure and
is associated with faster deterioration of the heart. CRT can
improve mitral regurgitation. Mitral regurgitation can cause higher
frequency (>200 Hz) motion that can be sensed at the mitral
valve annulus from the LV vasculature with the acceleration sensor.
The amplitude of the acceleration signal and duration relative to
the ejection phase may be good indices to measure for improvement.
A reduction in amplitude and duration is indicative of improvement.
A change in the frequency may also be indicative of improvement.
The vibrational motion associated with isovolumic contraction may
be indicative of the contractility of the heart. Increases in the
peak of this signal may indicate better contractile function.
[0173] For trend monitoring (e.g., with an IAD), acceleration data
is sampled at regular intervals during the day, termed the
"interval period", and this data is averaged. Peak amplitudes can
be plotted as the ordinate with the monitored time interval (e.g.,
days, weeks, or months) as the abscissa (See FIG. 18). Data points
may indicate the average amplitude of the peaks from the interval
samples. Statistical analysis of these trends can identify changes
from baseline function that may warrant an intervention.
Disposable and Mapping Acceleration Sensor Devices
[0174] LV motion may be useful for identifying target pacing
regions for CRT. Target pacing regions may be identified by how
late the region of the LV starts shortening relative to a reference
point such as onset of systole or end of systole (See, e.g., FIGS.
21-24).
[0175] Referring to FIG. 21, a catheter 462, which may perform
mapping, is shown within the posterior LV or lateral LV 464, and in
particular within the LV vein 466. The catheter 462 includes a
sensor pair 468, a sensor pair 472, and a sensor pair 474. The
catheter 462 also includes electrodes 476. Area 470 indicates the
segment of late displacement. The mitral annulus is shown at
position 478.
[0176] FIG. 22 shows displacement curves which identify a late
shortening segment in the posterior region. Pacing of this region
causes earlier displacement and synchrony with other segments. The
abscissa represents time in milliseconds. The ordinate represents
ventricular displacement, but similar curves may be drawn
representing velocity or strain rate. The measurement from sensor
pair 468 is shown by curve 482; the measurement from sensor pair
472 is shown by curve 484; and the measurement from sensor pair 474
is shown by curve 486. An ECG is shown as curve 488, with
representative QRS waveforms.
[0177] Along curve 482, feature 492 represents late shortening.
Feature 494 represents a pacing signal from one of electrodes 476,
in particular an electrode adjacent sensor pair 468. Feature 496
depicts earlier shortening of the late segment and optimized
ventricular synchrony. Along curve 486, the baseline is chosen as
the sensor position at QRS onset, or the onset of isovolumic
contraction, or the end of the A-wave. The negative deflection
shown in feature 498 reflects the shortening of the LV.
[0178] Uncoordinated LV contraction due to delayed regional
shortening reduces the efficiency and effectiveness of blood
pumping and hence delayed regions are targets for pacing.
Myocardial shortening that occurs after aortic valve closure, i.e.,
post-systolic, does not contribute to the ejection of blood and may
exacerbate pathologic conditions such as mitral regurgitation and
hence these regions are also targets for pacing. Both longitudinal
and radial shortening may be delayed. Late onset shortening or
post-systolic shortening may be best measured at low frequency
acceleration signals related to displacement. The integration of
the acceleration signal to a velocity or distance may also smooth
out the signal and make it easier for the physician to interpret. A
reference point for delayed systolic shortening and post-systolic
shortening may be the QRS onset and T-wave, respectively.
[0179] FIG. 23, shows various shortenings or displacement patterns
in various regions that indicate dyssynchronous LV signals and
probable responders to CRT. Delayed onset shortenings and
post-systolic shortenings are target pacing regions.
[0180] Curve 502 represents an ECG with the Q, RS, and T waveforms
shown. Curve 516, which is straight, shows sound waveforms of the
MVC and AVC. Curve 504 represents a post-mid-segment measurement.
Curve 506 represents a post-basal measurement. Curve 508 represents
a post-basal-lateral measurement. Curve 512 represents a
basal-lateral measurement. Curve 514 represents a mid-lateral
measurement. Various features of these curves will now be
described. In all the curves, points 526 represent the zero point
position of the sensor at either QRS onset, MVC, or AVC. Also in
all curves, the target pacing region was the basal lateral, and the
example shows delayed onset shortening, early systolic lengthening,
and post-systolic shortening.
[0181] Referring to curve 504 in FIG. 23, features 516 represent a
shortening and lengthening dyssynchronous pattern. Features 518
show a dyssynchronous contraction pattern. Referring to curve 506,
which shows a delayed hypokinetic response, feature 522 reveals a
delayed onset motion relative to the QRS or MVC. Feature 524
reveals a reduced peak displacement or shortening hypokinesis.
Curve 508 shows an akinetic or dyskinetic response. Curve 526 shows
a dyskinetic response with post-systolic shortening. This curve
also shows early systolic lengthening at feature 528, post-systolic
shortening relative to AVC at feature 532, and normalized
displacement or shortening at feature 534 following pacing spike
530. Curve 514 shows a normal heart rhythm with peak shortening at
feature 536.
[0182] Alternatively, vibrational components of the LV cycle may be
used as reference points. Thus a reference point for delayed
systolic shortening within systole may be the vibrational motion
associated with isovolumic contraction or mitral valve closure.
Similarly, vibrational motion associated with isovolumic relaxation
or aortic valve closure may serve as reference points for
post-systolic shortening. These reference points occur in the
mid-frequency range (e.g., 20 Hz-150 Hz), while the displacement
motion occurs at the low frequency range (e.g., <10 Hz). These
signals can thus be separated out by appropriate filtering. Post
systolic shortening more than about 20-50 milliseconds or greater
than 20% of the total regional shortening after aortic valve
closure could be a target pacing region. Other targets are
dyskinetic regions that have periods of lengthening during early
systole followed by shortening deformation, or akinetic regions
that have lengthening throughout systole (FIG. 16).
[0183] LV motion, both regional and global, can be used to
characterize indices of LV function in response to pacing. Thus,
identification of a region of late or post-systolic shortening may
be performed, and/or a pacing electrode can be positioned in the
region and paced at a threshold that ensures tissue capture.
[0184] FIG. 17 shows a mapping method, for the LV, for CRT LV lead
placement. A first step is to place the guide catheter in the
coronary sinus (step 538). A next step is to insert the catheter
with the acceleration sensor into the guide catheter and into the
coronary sinus (step 542). A next step, which is optional, is to
measure the onset of displacement motion, e.g., velocity or
distance, relative to the onset of systole, as determined via QRS
or isovolumic contraction (step 544). Step 544 may be performed by
moving the catheter in the coronary sinus and great cardiac vein or
tributary veins, e.g., in a septal to lateral manner. A next step
is to insert the pacing guide wire through the guide wire lumen of
the acceleration sensing catheter and then into the tributary veins
of the coronary sinus and the great cardiac vein (step 546), e.g.,
the basal, mid, and apical regions. A next step is to pace the
region in the tributary vein (step 548). A next step is to measure
the acceleration signal characteristic of LV function, e.g., QRS to
AVC; the myocardia performance index (MPI); or mitral regurgitation
(step 552), for which the peak acceleration is at the isovolumic
contraction. The final step is to insert the LV lead over the
guidewire to the target region, i.e., the region with improved LV
function (step 554).
[0185] Referring to FIGS. 25 and 33, which shows myocardial motion
mapping, display output, and target pacing identification through a
roving pace guidewire, changes or variables indicative of a
favorable LV functional response may be sensed at the low, mid, and
high frequency ranges. In the figure, "MVR" refers to mitral valve
regurgitation, "IVC" refers to isovolumic contraction, and "IVR"
refers to isovolumic relaxation. The top curve is ECG 556, curve
558 shows the velocity or LV displacement, obtained by integrating
the acceleration signal, curve 562 shows LV function, and curve 562
shows the sounds of mitral valve regurgitation.
[0186] ECG 556 shows the QRS and T waves along with a pacing spike
566 which is delivered in the LV vein region. Examination of curve
558 shows a delayed onset motion 568 but a lessened delayed onset
motion 572 following the pacing spike. Curve 562 shows a value of
ejection phase 574, as measured by the time between the MVC or IVC
and the AVC or IVR, and then a longer ejection phase 576. Here the
MPI can be seen to be MPI=(a+b)/c. Finally, curve 564 shows a
reduced MVR signal 578 as compared to the pre-pacing MVR signal
582.
[0187] As shown above, low frequency changes or variables
indicative of a favorable response to pacing include but are not
limited to: either temporally earlier or more synchronous
shortening of the paced region; increases in longitudinal or radial
displacement of the mitral valve annular region; increases in peak
acceleration or velocity of longitudinal or radial displacement of
the mitral annular region (S1 or S2 peak). The change in radial and
longitudinal shortening may reflect the ejection fraction, a
variable correlated with outcome in heart failure. The position of
the LV wall as determined by the sensor may determine the effects
of pacing on LV volume (See FIG. 20). Mid frequency indices or
variables associated with improved LV function include but are not
limited to: steepening of the slope or an increase in the peak
amplitude of the isovolumic contraction phase; shortening of the
isovolumic contraction time interval; shortening in the isovolumic
relaxation time interval; increases in the LV filling time relative
to the cardiac cycle length; increases in the time of aortic valve
closure or mitral valve opening from QRS onset divided by the
cardiac cycle length; increases in the systolic ejection phase time
interval; increases in the time from QRS onset to aortic or
pulmonic valve closure; and increases in the time from QRS onset to
aortic or pulmonic valve closure divided by the cardiac cycle
length. Changes in LV function indicative of a favorable response
to pacing at the high frequency range would be a reduction in
mitral valve regurgitation amplitude and duration as well as a
frequency change. Lastly, the myocardial performance index may be
also utilized as a measure of LV functional response and the same
may be determined from mid-frequency signals or a combination of
mid- and low-frequency signals. Pacing of certain regions may not
produce improvements in LV function. Ischemic regions may not
respond to pacing or may contract poorly due to the presence of
non-contractile tissue and may therefore be avoided. It should also
be noted that the displacement and the related strain rate can be
used to diagnose areas of ischemia, which may also be useful in
optimizing CRT, such as by avoiding the pacing of these regions. As
an example, regions where shortening is delayed or disappears under
stress conditions, e.g., increased oxygen demand, such as
dobutamine infusion, are likely due to ischemic blood flow. Other
factors, such as the ability to electrically couple to the region,
may affect pacing. Pacing capture thresholds must be determined,
which could occur by increasing the pacing stimulus and measuring
the displacement, which is shown in FIG. 26. In particular, curves
584-592 represent pacing signals from 0.5 mV to 3.0 mV. Curve 584
shows a small shortening, curve 586 shows more, and curve 588 shows
still more. However, no difference in shortening is seen between
curve 588 and curve 592, thus the optimal capture threshold can be
determined to be 2.0 mV. Interval timing such as simultaneous
ventricular pacing, RV first pacing, or LV first pacing, may also
need to be optimized to produce the desired response.
[0188] LV motion sensing with an acceleration sensor primarily at
low frequency may allow the identification of candidates for CRT.
Many patients with a low ejection fraction and history of ischemic
heart disease undergo the implantation of a defibrillator. During
the defibrillator placement, a candidate for CRT could be
identified and an LV lead placed, thus preventing the exposure of
the patient to two separate procedures.
[0189] One way to assess candidates for CRT is by assessing
contractile reserve. The presence of shortening during diastole is
indicative of contractile reserve. The difference in peak ejection
velocity or shortening or the start of motion or shortening in any
two regions, e.g., the septal to posterior region or the posterior
to lateral region, is indicative of dyssynchrony that may respond
to therapy. These differences may be based on the time from onset
of systole for each region or may be the direct difference between
two regions. Thus, a difference in peak velocity from the septal to
posterior wall of greater than 50-100 ms may indicate a target
pacing region of the posterior wall. Septal motion could be
detected by a sensor located in the RA/RV or near the opening to
the coronary sinus or near the posterior interventricular vein
branch. Specific displacement patterns, such as both shortening and
lengthening, that occur between QRS onset and aortic valve closure
(FIG. 23), are indicative of dyssynchrony. These delays in regional
shortening, post-systolic shortening, and dyssynchronous
contraction patterns, may be present regardless of QRS duration and
hence can be used to identify candidates and responders even if the
QRS is normal or only modestly widened.
[0190] To accomplish target pacing region identification,
characterization, pacing optimization, and to identify candidates
for CRT as described above, a myocardial motion mapping system may
be employed (FIGS. 25, 27 and 28). This system shows a
multi-sensor, multi-electrode motion mapping catheter system 594.
An acceleration sensing device, such as a catheter, LV lead,
guidewire, guide catheter/catheter system, or a combination
thereof, is used as a mapping device by positioning the device in
various locations of the coronary sinus and LV vasculature (FIGS.
22 and 23). If desired, the acceleration sensing devices may be
placed in the ventricular chambers, preferably the LV. If a single
or two axis sensing is used, the catheter can be rotated until the
optimal signal is detected. This may occur when at least one sensor
is parallel to the axis of motion. Marker bands on the catheter
could indicate the appropriate sensor orientation during the
procedure or reference points as described previously could be
used. Alternatively, 4-axis sensing could be employed using two
dual axis sensors as described above. In this configuration, three
of the four axes are used to measure acceleration in the x-, y-,
and z-orientations for 3-axis sensing and the fourth channel may be
used for sensing vibrational motion and valvular events or
pathology. Alternatively, 6-axis sensing with three perpendicular
dual axis sensors could be employed with three axes used to detect
displacement motion and three axes used to detect vibrational
motion. The acceleration sensing device could be guidewire directed
or steerable, including tip deflection. Steerability is
accomplished by having one-to-one, or as substantially close to
this as possible, torqueability which can be accomplished with a
braided catheter design. Tip deflection can be accomplished with
wires 596 that run the length of the device and are affixed to the
tip 598 (FIG. 27). A lever 602 in the handle 604 of the catheter
pulls the deflection wires 596, producing deflection at the tip
598. Steerable deflection devices are familiar to those skilled in
the art. One or more sensors 606 and pacing electrodes (see FIG.
28) may be located immediately adjacent to each other or the pacing
electrode may be located between the sensors. The region of the
sensor in the mapping catheter may be highly flexible as described
above to ensure that the sensors move in concert with the
myocardium. The catheter 594 may further be equipped with a
connector 608 that includes a hub 626 and a plurality of connectors
628, which may include acceleration input connectors and electrode
pacing connectors, that may connect to an microprocessor-based
display system (see FIG. 28) including a manifold 632.
[0191] Referring to FIG. 28, the system 594 may further include a
guidewire insertion port 634 for guidewire 636, an optional port
for contrast injection 638 with an accompanying contrast port 646,
an optional port for balloon inflation and deflation 642 coupled to
an optional venogram balloon 644. Also included are, e.g., three
sets of sensor pairs 646, 648, and 652, and three sets of
electrodes 654, 656, and 658. The sensors may be, e.g., 5-10 mm
apart.
[0192] Referring to FIG. 28, the mapping acceleration sensing
device 594 may be directly connected to a microprocessor-controlled
display 612 that presents motion signals as acceleration 614,
velocity curves 616, strain rate curves 618, and displacement
curves 622, or some combination of the three, with ECG data 624.
The catheter and acceleration signal can also be input into a
cardiac electrogram data acquisition system as may be already used
by the physician. The acceleration signal may be displayed as a
voltage, similar to the cardiac electrogram. The onset of motion
signals may be easily displayed and compared to the surface ECG or
intracardiac electrogram. Other reference points, as disclosed
earlier, such as isovolumic contraction or valve closure, may also
be displayed. (FIG. 25). The mitral valve regurgitation signal may
further be displayed.
[0193] Also shown in FIG. 28 is close-up display 660, containing
curves 662-666. These curves display displacement data
corresponding to the three pairs of acceleration sensor data for
mechanical mapping. In these figures, shortening is exhibited by a
negative deflection.
[0194] Additionally, the mapping acceleration sensing device may be
used to facilitate coronary sinus access and cannulation of LV vein
branches that feed into the coronary sinus, necessary steps in the
mapping process and LV lead implantation. One method to achieve
access to the coronary sinus is conducted by dragging the mapping
device from the AV node superiorly along the base of the RA, the
interatrial septum, or the medial RA wall. When the device moves
over or is near the coronary sinus ostium, the flow of blood from
the ostium into the RA causes the device and/or tip to deflect or
vibrate. The deflection or vibration may be sensed by the
acceleration sensor. In addition, once the device is in the
coronary sinus, it can be dragged or pushed along the inferior or
lower border of the sinus. LV veins are detected by deflection or
vibration by the sensor as it passes over the ostia, or branches,
of the veins that drain into the coronary sinus. Alternatively,
Doppler flow crystals and MEMs pressure sensors, and anemometry
flow sensors may be used for coronary ostium identification and LV
vein branches. These sensors may also be combined with the
acceleration sensor.
[0195] In one embodiment, motion signals may be derived from
serial, or various, combinations of the sensors or sensor pairs, at
a known distance of separation, e.g., 5-15 mm, and may provide
multiple velocity, displacement, and strain rate curves synched
with a signal related to the start of systole such as single QRS or
a contraction stimulus, or isovolumic contraction or mitral valve
closure (FIGS. 23 and 28). Systole may also be induced by a
separate pacing catheter conductively coupled to the RA or RV
septum. Regions of late motion onset relative to the onset of
systole, determined by the R wave of the ECG, septal activation on
the EGM, or mitral valve closure, may be identified. Also, regions
of post-systolic shortening relative to isovolumic relaxation or
aortic valve closure or the t-wave may be identified. These late
and post-systolic shortening regions may subsequently be paced by
electrodes between the sensors that identified the late motion
onset to elicit earlier activation. A new set of deformation curves
may then be analyzed to confirm that the region of early activation
pacing produces a more synchronous deformation. Further, the
mid-frequency sensor measures the change in peak acceleration or
velocity during the pacing of the identified target region,
confirming a positive response to pacing (FIGS. 23 and 29). LV
functional responses such as the myocardial performance index could
also be measured during the test pacing (FIGS. 25 and 29).
[0196] Referring in more detail to FIG. 29, a chart is shown which
may be used to identify regions of late deformation and for
assessing various other variables related to performance. Curve 668
shows the ECG signal, curve 672 shows the acceleration signal,
where the left-most point is the zero point established by the QRS,
"EP" refers to the ejection phase, "E" refers to early diastolic
filling, "A" refers to atrial contraction filling, time interval
"A" measures the start of IVC to the end of IVR, and time interval
"B" measures the time interval of the EP. MPI=(A-B)/B. Curve 674
shows the acceleration signal from region #1, showing in particular
the IVC time interval 676 and the peak IVC signal 678, as well as
the delayed mechanical shortening 682 in the target pacing region.
Referring to FIG. 30, an alternative mapping strategy may also be
employed in which a simplified catheter with only a 1, 1 pair
sensor, i.e., perpendicular to each other, or 3 sensors, each
perpendicular to each other, uniaxial, biaxial, or triaxial, is
positioned in various LV and LV locations, e.g., septal to lateral
in the coronary sinus and great cardiac vein). One sensor or sensor
pair detects both the onset of systole or diastole, e.g.,
isovolumic contraction or relaxation; or aortic or mitral valve
closure, and regional motion, or one of two sensors or one of two
sensor pairs may be utilized to detect the same onset of systole or
diastole and the other sensor or sensor pair detects the regional
motion. Alternatively, 3 axes of a dual axis pair may be used for
displacement sensing and the 4.sup.th axis may be used for
vibration sensing. Alternatively, 3 axes of a 3-sensor device may
be used for sensing displacement motion, and the other 3 axes may
be used for sensing vibrational motion. No electrodes, one
electrode, or two electrodes may be employed.
[0197] The regional motion from each location is recorded and
stored and displayed. The motion at each location is compared
against the QRS or endocardial pacing signal or the other systolic
and diastolic reference points. The region of latest motion
relative to the reference point is identified and the lead is
positioned to the same anatomical location. It should also be noted
that epicardial mapping may be performed during open chest or
minimally invasive procedures using the same principles and sensors
as above and appropriate device designs.
[0198] In another mapping strategy, a roving electrode (e.g., a
guidewire) can be positioned in various locations of the LV venous
system and RV chamber and a test pacing stimulus applied to the
myocardium. Referring to FIGS. 24 and 31, a guidewire 684 with an
uninsulated region or electrode region 686 may be connected to a
pulse generator via connector 688 and unipolar pacing may be
performed. The guidewire may also have two uninsulated regions or
two electrode regions for bipolar pacing. The LV functional effects
of the test pace can be measured by an acceleration sensor or a
dual axis sensor pair perpendicular to each other. The sensor or
sensors may reside on a coronary sinus guide catheter 692 (see FIG.
32) or on a catheter 700 within the lumen within the coronary sinus
guide catheter 692 (see FIG. 33). The catheter 700 may further have
a pacing guidewire port 702 to accommodate guidewire 684.
[0199] For example, the sensors 694 may reside on catheter 690, and
may be battery powered via battery 698. The sensors may number one,
two, or three, each perpendicular to the others, and may have
outputs corresponding to a low-frequency (<20 Hz) signal 704, a
mid-frequency (20-150 Hz) signal 706, and a high-frequency (>150
Hz) signal 708.
[0200] In this way, and referring to FIG. 34, the mapping system
710 is made of the acceleration sensing catheter 700 and the pacing
guidewire 684. The pacing guidewire may be powered by a pulse
generator 712.
[0201] The output of the sensors may be connected to a signal
conditioning module and battery power module 714 prior to input
into the electrogram recording 716 and display device 718. The
output of the signal conditioning module may be analog signals if
the electrocardiogram display is to be used. The signal
conditioning module may also be used to correct or zero out the
effects of gravity and the related tilt signal. Output from the
signal conditioning module may also be digital. A microprocessing
chip in the conditioning module may also perform functions such as
forming a composite signal from multiple orientation axes and
integration. The catheter within the guide catheter may have a
guidewire lumen through which a pacing guidewire may be used to
test pace target sites. This catheter may also have a port for
contrast injection and may additionally have a balloon to perform
an occlusive venogram.
[0202] The sensor catheter 700 may also have a curved tip (e.g.,
with a 90-degree bend) to facilitate access to tributary veins of
the coronary sinus and great cardiac vein. The sensor catheter
within the coronary guide catheter could also be moved from septal
to lateral within the coronary sinus and great cardiac vein to
identify general regions of dyssynchrony. The pacing wire could
then be directed to the tributary veins of the coronary sinus or
great cardiac veins or to the general region of delayed onset
displacement motion. Variables such as the time from QRS onset to
aortic valve closure (increase), peak acceleration during
isovolumic contraction (increase), the length of the isovolumic
contraction time interval (decrease), may be measured and are
indicative of a favorable or therapeutic response and a more
optimal LV or RV pacing region (FIG. 25). The changes in time
intervals of LV cycle (e.g., LV filling time) may be normalized by
dividing by the cardiac cycle length or the square root of the
cardiac cycle length or by some other method. Other measures of LV
function as sensed by the acceleration sensor may be utilized
including favorable changes in the mitral regurgitation signal. The
myocardial performance index (isovolumic contraction time plus the
isovolumic relaxation time divided by the ejection time) may also
be used as a performance indicator with decreases in indicator
viewed as more favorable. When a region of improved LV function is
identified, the pacing guidewire is left in place and the CRT LV
lead is inserted over the pacing guidewire to the target pacing
region.
[0203] Some patients may respond with favorable LV mechanics with
only RV pacing if it is performed in the correct location. The
optimal RV site to maximize LV function can be identified in the
mapping strategy above. The acceleration sensor may reside in the
coronary sinus while the RV pacing site is identified. This may
eliminate the need for an LV lead in some patients.
[0204] Alternative embodiments are apparent from the above
description such as separating the higher frequency sensing
accelerometer from the myocardial motion sensing accelerometer.
Thus, referring to FIGS. 35 and 36, a system is shown for
identification of the target pacing region and optimizing and
characterizing the pacing response. The higher frequency sensing
accelerometer may be incorporated into an LV lead or coronary guide
catheter 724 or guidewire (see guide catheter 724 of FIG. 36).
Guide catheters and guidewires are commonly used in CRT procedures.
The acceleration sensor 726 on the guide catheter 724 may reside in
the right atrium, at the coronary sinus ostium, or within the
coronary sinus. The guide catheter 724 may be curved to facilitate
access of the coronary sinus. Additionally, valve closure sensing
may be performed externally with an acoustic sensing device.
[0205] The remainder of the system may be the mechanical mapping
catheter 722, which includes a guidewire lumen 728 with ports 732
and 734, a pacing electrode 736, acceleration sensor 738, e.g., one
that is perpendicular to the catheter's longitudinal axis, an
optional acceleration sensor 742, an electrode connector 744, and a
sensor connector 746. The catheter 722 may be angled to facilitate
LV vein cannulation. FIG. 37 shows one potential arrangement of
sensor 738 and guidewire lumen 734. Alternatively, as shown in FIG.
38, an electrode 736' may be disposed at the distal tip of the
catheter 722 while a sensor 738' is disposed proximal thereof.
[0206] Thus, in still another embodiment, and referring in
particular to FIGS. 39 and 40(A)-(B), an acceleration sensor 752
for mid- to high-frequency sensing of the onset of systole and
diastole and mitral regurgitation may be incorporated into a
coronary sinus guide catheter 750. A set of conductive elements 748
for the sensor 752 may be coupled to a connector 754 that is used
to connect to the microprocessor display.
[0207] A myocardial motion sensing accelerometer 746 is
incorporated into a mapping catheter or LV lead 760. In the LV lead
design, the conductive elements 754 for the low-frequency
myocardial motion accelerometer 746 may be coupled to a proximal
lead connector 758. The connector of the lead may be compatible
with typical CRT IPGs (e.g., IS-1), although this is not necessary;
in fact, the sensor connector and sensor signal may be designed to
generally not interfere or even be read by the CRT IPG. Element 762
indicates the CRT pacing and sensing connector area. Connector 756
is also shown, which indicates a removable LV lead accelerometer
connector for signal display.
[0208] Placement of the catheter is shown in FIG. 39, relative to
the coronary sinus 770 and the coronary ostium 780. An optional
pacing electrode 764 is shown, as well as guidewire, which may
employ an integrated sensor for low-frequency myocardial motion
sensing in the manner of FIG. 24.
[0209] During placement, the lead connector may be coupled to the
acceleration sensor microprocessor display for visualizing
myocardial motion signals and optimizing the LV lead placement.
Alternatively, the LV lead sensor may be conductively coupled to a
removable connector in the proximal lead portion, thus allowing the
measurement of myocardial motion during lead placement. The LV lead
sensor connector may also be capped after mapping and for long-term
implantation. Alternatively, the sensors in this design may be RF
MEMs accelerometers that are inductively-powered and which
wirelessly transmit the data, thereby eliminating the need for
conducting wires or elements.
[0210] FIG. 40A shows an embodiment of a guidewire-mounted sensor
for use with the above guide catheter. In particular, guidewire 766
may have at a distal tip a soft tip 774, adjacent to which is a
flexible coil section 768, within which is a sensor 772.
[0211] FIG. 40B shows an embodiment of an alternative LV lead
design 790 or mapping catheter which may be used with the above
guide catheter. LV lead 790 has at a distal tip a flexible coil
768' which terminates at a distal tip in a soft tip 774'. Within
the flexible coil 768' is a sensor 772'. Electrode 776 may be
provided adjacent to but proximal of the flexible coil 768'.
[0212] Referring to FIGS. 41-44, another alternative mapping device
system and method for optimizing and identifying a target pacing
region may include a venous guide sheath, a double lumen pacing
catheter, and an acceleration sensing guidewire. The system also
identifies the coronary ostium and coronary sinus vein branches
using the accelerometer sensor.
[0213] A venous sheath 838 is used to gain access to the right
atrium ("RA") via the subclavian or femoral vein. This sheath may
include an optional mid- to high-frequency acceleration sensor 842.
The sheath may have appropriate bends to facilitate entry into the
coronary sinus.
[0214] A sensing guidewire with one or more sensors 792, 794, at
least one being a lower-frequency sensor disposed on a highly
flexible tip 796 (e.g., a coil tip 796), is placed into the RA via
the sheath. The lower-frequency sensor may be multi-axis. An
optional additional sensor may also be provided to sense low or
high frequencies. The distance between the sensors may be, e.g.,
5-10 mm. The sensor guidewire 800 is used to identify the coronary
ostium (as above) by detecting the flow of blood into the RA and is
then inserted into the coronary sinus. The guidewire 800 is
shapeable or may have a slight bend 798 in the distal region, e.g.,
a 135 degree bend. The sensor guidewire 800 can then be positioned
along the coronary sinus and into the LV veins for measuring
myocardial deformation and velocity and comparing it to the
reference point signal, i.e., vibrations related to isovolumic
contraction/relaxation and/or valve closure, provided by the guide
sheath sensor. Alternatively, a double lumen catheter 802 may be
positioned into the RA or coronary sinus over the sensor guidewire
800 and an optional higher frequency sensor 804 on this device is
used to provide reference signals.
[0215] The sensing guidewire 800 maps regions of late deformation,
and may further include an electrical connector 806 and an optional
proximal sensor 808 for sensing perivalvular events.
[0216] The double lumen pacing catheter 802 contains two guidewire
lumens 812 and 814, lumen 812 serving as a guidewire sensor lumen
and lumen 814 serving as a coronary wire sensor lumen, with
openings in the distal tip 816, a pacing electrode 818, an optional
coronary sinus occlusion balloon 822 with inflation port 824 for
obtaining a venogram, optional acceleration sensors 804, such as
for measuring high frequency signals, and the same may also be
steerable. The overall diameter may be, e.g., 2-3 mm. Referring in
addition to FIG. 43, a hub 826 may be provided with a sensor
guidewire port 828, a coronary wire port 832, a high-frequency
sensor connector 834 coupled to conductors within a lumen 834', and
an electrode connector 836 coupled to conductors within a lumen
836'.
[0217] The double lumen pacing catheter is placed in the coronary
sinus over the sensing guidewire. The venous guide sheath may be
advanced into the ostium prior to double lumen catheter placement
or LV lead placement. The balloon of the double lumen catheter may
be inflated and a venogram obtained by injecting contrast though
one of the catheter's lumens. After a target pacing region is
identified in an LV vein with the sensor guidewire, the double
lumen pacing catheter is advanced over the sensor guidewire to the
region. Pacing is conducted with the double lumen pacing catheter
and optimization of the target pacing site and intervals is carried
out. A second guidewire for the LV lead is then advanced down the
second lumen of the double lumen pacing catheter and into the
target region. The pacing catheter and sensor guidewire are then
removed, leaving the lead guidewire in place. The LV lead is then
positioned into the target region over the second guidewire. With
the double lumen configuration, the sensor guidewire can be made
larger and more maneuverable without limiting the ability to place
a small over-the-wire LV lead in the target region.
[0218] Myocardial motion mapping would be ideal for LV pacing that
involves multiple electrodes. CRT may be optimized by pacing and
early activation of all late deforming LV sites. Deformation
mapping may identify these regions and then guide the placement of
electrodes in the areas for CRT. Alternatively, if the mapping
catheter is also the LV CRT lead, then the mapping lead may be left
in the optimal location and connected to the IPG.
[0219] In the above catheter and implantable embodiments,
miniaturization of the sensor is critical and wafer or die scale
packaging of the sensor component is preferred. Consequently, where
the MEMs sensor is attached by conductive elements to a connector
and then to a microprocessor and/or display device, specific
designs for attachment of the conductive elements to the silicon
substrate of the wafer package chip must be utilized. It is
particularly important to minimize the number of conductive
elements that require attachment to the acceleration sensor.
Potentially, at least 5 connections are required for a 3-axis
sensor; however, using multiplexing circuitry or averaging the
signal from all three sensors can eliminate two wires thus reducing
the connections to three. In one embodiment, solder balls are
integrated into the sensor die. A flex circuit with bonding pads
that aligns with the solder balls is used for attachment to the
die. The bonding pads of the flex circuit are in electrical
communication with conductive elements that are used to attach to
connectors at the proximal end of the catheter. The die part is
flipped onto the bonding pad, which is heated to allow the flow of
the solder and bonding of the die to the flex circuit.
[0220] Alternative methods for conductive element attachment of
MEMs sensors are provided in, e.g., U.S. Pat. No. 5,715,827 for a
pressure sensor. FIGS. 45-46 show one potential embodiment to
accomplish attachment for an acceleration sensor. The sensor chip
840 has an elongated silicon substrate 842. V or U-shaped via wells
844 are etched using silicon etching techniques into the elongated
substrate 842. The wells 844 run the length of the elongated
substrate 842 and abut against semiconductor output connectors 846
from the acceleration sensor integrated circuitry 848. Usually a
sensor has three connectors: one for power, one for ground, and one
for output. Additional connectors may be used for each axis output.
A single output connector with a multi-axis sensor may have
circuitry for multiplexing each axis output. Alternatively, the
output may be an average or composite of the different axes. Hence
three wells are etched and made continuous with the sensor
circuitry for power 852, ground 854, and output 856. The silicon
substrate well bottom and walls are doped to provide conductivity.
The wells are then coated with metal 858 through a sputtering
process or via other such processes. For example, a sputtered
chromium and gold coating may be used. The uninsulated terminal
length of small gauge copper wires 862 (e.g., 48 AWG) or a doped
polymer flexible connector is then soldered to the wells. An epoxy
or glass lid 864 or other such material, such as a wafer or polymer
cap, may be bonded to the top of this chip/wire hybrid to protect
the structure from damage. These wires or conductive polymers are
now conductively coupled to the chip sensor and can be extended
down the length of a catheter component and attached to a connector
that will plug into a microprocessor data acquisition
component.
[0221] FIG. 47 shows a circuit diagram of a system that may be
employed in embodiments of the invention. In particular, FIG. 47
shows a pin layout for a sensor chip that may be employed, along
with the x-, y-, and z-outputs from the sensor chip.
[0222] FIG. 48 shows a portion of a flexible circuit board that may
employ the sensor chip. The sensor chip is mounted on the left side
of the board, which is the portion that enters the patient.
Capacitors C1-C5 are employed and are disposed directly adjacent
the sensor chip as may be seen.
[0223] As noted above, the general design of the accelerometer
sensors measures capacitance changes due to the movement of a proof
mass beam with a side arm interdigitated between two capacitor
plates. As the proof mass beam and side arm move with acceleration
or vibration, the capacitance changes and this signal can be output
as a measure of motion.
[0224] In this way, the sensor chip can measure extremely small
changes in capacitance and thus acceleration. One of the functions
of capacitors C1-C5 is to decouple certain voltages so that only
signals from the sensor chip are registered at the signal analysis
system (another is to provide the circuitry for the passband so
that only a certain bandwidth of signals are passed). To ensure
that a minimum of stray noise voltage is picked up by the
conductive leads, capacitors C1-C5 are disposed as close to the
chip as is practical, so that the signal travel distance is as
short as possible.
[0225] Using the accelerometer sensors above, the frequency
dynamics of the isovolumic contraction phase and pathologic cardiac
vibrations may also be monitored.
[0226] A graph of the cardiac filling and pumping cycle and
valvular events is shown in FIG. 50. The cardiac LV pumping cycle
(LV cycle) is divided into two periods: diastole and systole.
Diastole is the filling period and systole is the ejection period.
Five different phases of the LV cycle can be identified within the
systolic and diastolic periods: isovolumic contraction 56, ejection
58, isovolumic relaxation 62, early diastolic filling (rapid
filling) 64, and late diastolic filling (atrial contraction) 66.
Mitral valve closure 68 ("MVC") occurs during isovolumic
contraction and aortic valve closure 72 ("AVC") occurs during
isovolumic relaxation. Also shown in the figures are the left
ventricular pressure LV Press 74, a regular electrocardiogram ECG
76, the left ventricular end-diastolic volume LVEDV 78, the left
ventricular end-systolic volume LVESV 82, a graph depicting heart
sounds 84, the left atrial pressure LA Press 86, the aortic
pressure 88, a-wave 92, c-wave 94, and v-wave 96.
[0227] During the isovolumic contraction phase, the ventricles
begin to contract but there is no ejection of blood into the aorta.
As the myocardial cells contract, they generate a force that
results in the development of wall tension in the ventricles. This
contraction causes vibrational motion that is related to cardiac
and ventricular resonance. The resonance is related to ventricular
diameter, wall thickness, and mechanical properties of the muscle,
such as viscoelasticity. Thus monitoring this resonance or
vibration may be useful for determining the health or status of the
ventricle. For example, in cardiomyopathy the ventricle may dilate
and the LV diameter increases. This may be monitored as a reduction
in the resonance frequency and changes (increases or decreases)
would indicate improving or worsening heart failure. This
vibrational motion in its audible form is thought to be the cause
the first heart sound and is associated with mitral valve closure.
The vibrations may be related to abrupt changes in acceleration and
direction of flow of the blood in the ventricular chamber.
[0228] In the normal heart, the isovolumic contraction starts
within about 10-20 ms of ventricular depolarization (i.e., the R
wave on the ECG), and lasts from about 30 milliseconds to 75
milliseconds depending on the heart rate and contractility of the
ventricles. In the cardiomyopathic heart, the time interval of the
isovolumic contraction phase is prolonged.
[0229] The frequency of the vibration motion that occurs during
isovolumic contraction changes with the development of myocardial
tension. Time-frequency transform analyses of this motion indicates
that in the normal heart the frequency rises from about 20 Hz to
about 150 Hz in the first 20-50 ms of the isovolumic contraction
period. There are approximately 5-8 cycles that occur in this time
period. Referring to FIG. 52, vibrational acceleration signals from
the epicardial surface of the LV are shown during isovolumic
contraction as measured with an accelerometer. The amplitudes of
these cycles ranges from about 50 to 100 milli Gs (1 G=9.8
m/sec.sup.2) up to about 1 to 3 Gs.
[0230] Analysis of the frequency dynamics of the ICP can be used to
characterize cardiac function and myocardial health. Thus the
starting frequency of the ICP vibration motion signal, the peak
frequency, and the time interval of change in frequency, may be
affected by the mechanical and contractile properties of the
ventricles. Peak frequency of this vibrational motion during ICP is
probably related to the tension that develops in the ventricles and
hence may be related to the contractility of the myocardium.
Referring to FIG. 51, which shows the correlation of peak frequency
during the isovolumic contraction phase and the change in pressure
rise in the LV in dP/dt, a correlation between dP/dt (a surrogate
for myocardial contractility) and the peak frequency during the ICP
exists. The time interval over which this frequency rises may also
be a measure of contractile function. The starting frequency during
this phase may be related to the baseline ventricular wall
tension.
[0231] In diseased hearts, such as those with cardiomyopathy, the
contractile function of the myocardium is reduced, and changes in
the thickness and diameter of the LV can cause an increase in the
wall tension. These changes also lead to an increase in the time
interval of the isovolumic contraction phase. Therefore, monitoring
changes in the frequency dynamics of the isovolumic contraction
phase can give insights into the cardiac and LV function in
cardiomyopathy patients. This frequency information may also be
used to monitor the effects of therapy, such as CRT, and to
identify target pacing regions in CRT. Similarly, monitoring
changes in the time interval of the ICP can be indicative of
cardiac function and the response to therapy. Because the frequency
and time interval can be measured without having an accurate
measure of amplitude, this approach may be preferred.
[0232] Similarly, vibrations from pathologic heart conditions may
also be indicative of cardiac function and response to therapy. The
frequency of the mitral regurgitation signal in cardiomyopathy is
related to the degree of LV dilation and the back flow of blood
through the mitral valve. Therapies that reduce dilation and or
back flow, e.g., CRT or percutaneous annuloplasty, show a favorable
response in the frequency and frequency dynamics of this vibration
motion. The third or fourth heart sounds are also a vibrational
motion that may be present in cardiomyopathy. Changes in the
presence and frequency of these signals may be indicative of
cardiac function and response to cardiomyopathy therapy. For
example, the frequency dynamics of the S4 correlates with
ventricular mass which can be indicative of worsening (increased
mass) or improving (reduced mass) heart failure. The frequency of
the S1 may also correlate with LV stiffness.
[0233] Acceleration sensors are well suited for measuring ICP
vibration motion and pathologic cardiac vibrational motion. The
sensor is preferably based on micro electromechanical (MEMs)
principles, which allows for miniaturization and low power
consumption. The design and fabrication of capacitance MEMs-based
accelerometers are known to those of ordinary skill in the art and
may be used in this system. MEMs-based accelerometers are typically
fabricated from silicon or semiconductor substrates. The sensor may
be fabricated from a radiation-resistant semiconductor as the
sensor will be implanted in many cases under fluoroscopic guidance.
The general design of the accelerometer measures capacitance
changes due to the movement of a proof mass beam with a side arm
interdigitated between two capacitor plates. As the proof mass beam
and side arm move with acceleration or vibration, the capacitance
changes and can be output as a measure of motion. These
accelerometers are fabricated from silicon substrates which allows
for single-chip fabrication of the sensor with the necessary signal
processing circuitry. This single-chip design increases the
device's sensitivity as extremely small changes in capacitance can
be measured. MEMs-based acceleration sensors as described above can
measure milli Gs (1G equals 9.8 meters/sec.sup.2) which is suitable
for myocardial acceleration measurements which may occur between 50
and 2000 milli Gs or higher. While a capacitive sensor may be used
in this embodiment, other acceleration sensor designs could be
utilized and are known to those skilled in the art. For example, a
thermal acceleration sensor could also be utilized in which the
proof mass is a gas. Also, while a multi axis (2 or 3 axes) is
preferred, single axis sensors could also be used and oriented
appropriately to detect different axes of motion. It should also be
noted that a pressure sensor can sense vibrational motion and may
also be used to indirectly monitor the frequency dynamics of the
ICP.
[0234] Preferably 3-axis sensing is utilized. A more accurate
measurement of peak amplitude can be measured by calculating the
composite acceleration vector of each axis (x, y, and z). This can
account for the gravitational acceleration and its effects on
sensor tilting. The composite vector can be calculated by taking
the square root of the x-axis measurement squared, plus the y-axis
measurement squared, plus the z-axis measurement squared. This peak
amplitude calculation can be applied to both the vibrational motion
and the displacement motion. This may be particularly accurate
during the implantation of an LV lead for CRT therapy when the
patient is lying still on a procedure table. Here the sensor
measures the peak in the LV veins or coronary sinus.
[0235] Vibrational motion related to ICP may be sensed in a
frequency range greater than 10 Hz and up to 200 Hz. The sensors
may be tuned to sense the desired range. Alternatively, band pass
filters or digital signal processing could eliminate or reduce
frequency bands that are lower or higher.
[0236] Sensors can be mounted on devices that access the heart or
are disposed near the heart (e.g., via an esophageal probe) to
optimally detect the desired ICP. In one embodiment, a uniaxial
sensor is oriented such that the axis of acceleration is parallel
to the radial plane of the heart, i.e., toward the center of the
ventricular chamber. Alternatively, two uniaxial sensors could be
oriented longitudinally, e.g., anatomically base to apex, and
radially, or three uniaxial sensors, oriented longitudinally,
radially, and laterally, may be used. A single triaxial sensor
could measure all these components. In another embodiment, two
dual-axis sensors are oriented perpendicularly to each other in the
catheter or LV lead device. This provides three axes in the
appropriate planes.
[0237] The acceleration sensor is coupled to a signal processing
and powering module. A battery may be used to power the sensor but
other sources may also be utilized. Acquisition of the signal may
be triggered by a ventricular depolarization signal from a cardiac
electrogram. For example, the R-wave from a surface cardiac
electrogram (ECG) may serve as a trigger. The vibrational
acceleration signal may then be acquired for about 100 ms. A
shorter time interval for sampling could also be used (e.g., 50 ms)
to focus in on the initial frequency associated with a rise in
ventricular wall tension. A longer sampling interval may be used to
acquire the mitral valve regurgitation and third/fourth heart sound
signals. The R-wave or another signal of ventricular depolarization
can also be used to provide a zero point for the acquisition of
acceleration signals, and will also factor in the effects of
gravity and tilt of the sensor. Thus, the accelerations signal
measured around the time of the R-wave signal can be used as an
off-set correction for subsequently acquired signals.
[0238] The signal may be first amplified by an isolation amplifier
that provides an isolation barrier to reduce the potential for
electric shock hazard. The signal may be then band-pass-filtered to
remove lower frequency (e.g. <10 Hz) and high frequency (e.g.
>300 Hz) signals. The signal may then be subject to processing,
both digital and analog, to characterize and identify the frequency
changes of the ICP. Representative analog processing may be used to
measure the spacing between signal crossing above a certain
threshold (e.g. +/-10-50 milli Gs). The time interval between the
first two crossings may be indicative of the base line frequency.
The shortest time interval between crossings may be indicative of
the highest frequency. Digital signal processing could include the
mathematical computations such as time-frequency transforms (See,
e.g. "Time-frequency transforms: a new approach to first heart
sound frequency dynamics", IEEE transactions in Biomedical
Engineering, vol. 39, no. 7, July 1992) with peak frequency
identification. Taking the mathematical derivative of the
acceleration signal, analog or digital, would identify jerk motion.
Measuring the jerk signals and the time difference between these
signals could similarly characterize the frequency signal.
[0239] The output of the signal processing could be digital or
analog and could be displayed on a workstation for graphical
display of the ICP vibration. For example, an analog output would
allow the signal to be input into a multi-channel electrogram
recorder. The workstation would typically have data storage and
analysis capabilities. Alternatively a single number, such as the
peak frequency or peak frequency divided by measured time interval,
could be displayed. An accurate peak amplitude could be multiplied
or divided by the time interval or frequency, or both multiplied
and divided by the time interval or frequency, to yield a value
related to LV function and improved response to therapies such as
cardiac resynchronization therapy. Changes in this number would be
used to guide the therapy and make changes such as the position of
the LV pacing lead.
[0240] Devices and systems for incorporating acceleration sensors
are described in the pending non-provisional patent application
incorporated by reference above. The disclosed devices could be
used to characterize the frequency dynamics of the ICP and
pathologic LV vibration motion. Descriptions of exemplary devices
are representative of acceleration sensing devices for the ICP and
pathologic heart sounds.
[0241] An acceleration sensor may be incorporated into a catheter
for insertion into the LV veins such as the coronary sinus, great
cardiac veins, or tributary vessels of these veins. The
acceleration sensor may also be incorporated into a probe inserted
into the esophagus, which lies immediately behind the posterior
surface of the heart. The acceleration sensor may be a single dual
axis sensor oriented perpendicularly to the long axis of the
catheter. This orientation of the sensor allows the measurement of
longitudinal and radial acceleration signals, which predominate in
the heart, from the coronary sinus and great cardiac vein. The
catheter probe may have a guidewire lumen; however this may not be
required for an esophageal probe. The catheter or esophageal probe
may monitor the frequency dynamics of the ICP and assess LV
function. The esophageal probe could be used to monitor the ICP and
third and fourth heart sounds to detect ischemia, for example
during surgical procedures. For example, a decrease in amplitude of
the ICP signal as measured by the esophageal probe could be
indicative of ischemia. Because the esophageal probe would not move
with heart contraction and the patient would be still during
surgery, more accurate amplitude measures could be obtained.
[0242] In addition the catheter and esophageal probe may be used to
identify target LV pacing regions for CRT using a pacing guide
wire. Referring to FIG. 53(A)-(E), a guide catheter 102 is shown
with a proximal end 104. An acceleration sensing catheter 100, that
may be inserted into the guide catheter 102, is shown with a pacing
guidewire port 114 and a guidewire lumen 108. The guidewire lumen
may have a diameter of, e.g., 0.014'' to 0.038''. The catheter 100
also has a sensor assembly 106 that may have one, two, or three
acceleration sensors disposed within, the sensors being disposed
perpendicularly to each other. The catheter 100 may have a bend
near the distal end thereof, as shown in FIG. 4(B). The bend may be
from 0 degrees to 90 degrees. At the proximal end of catheter 100
is also disposed a power source such as a battery 126, a connector
for lower frequency (<20 Hz) signals 124, a connector for
mid-frequency (20 Hz to 150 Hz) signals 122, and a connector for
high frequency (>150 Hz) signals 118.
[0243] A pacing guidewire 120 is shown in FIG. 53(C) having an
insulated region 128 and an uninsulated region 132 for pacing. A
flexible conductor 134 is disposed at the proximal portion of the
guidewire 120, as well as a connector 136 to a pulse generator.
[0244] FIG. 4(D) shows a more detailed view of the catheter 100,
showing the guide lumen 108 and an alternate sensor assembly 112.
The sensor assembly 112 is perpendicular to the long axis of the
catheter 100.
[0245] Referring to FIG. 53(E), the mapping system 710 is made of
an acceleration sensing catheter 700 and a pacing guidewire 684.
The pacing guidewire may be powered by a pulse generator 712.
[0246] The output of the sensors may be connected to a signal
conditioning module and battery power module 714 prior to input
into the electrogram recording 716 and display device 718. The
output of the signal conditioning module may be analog signals if
the electrocardiogram display is to be used. The signal
conditioning module may also be used to correct or zero out the
effects of gravity and the related tilt signal. Output from the
signal conditioning module may also be digital. A microprocessing
chip in the conditioning module may also perform functions such as
forming a composite signal from multiple orientation axes and
integration. The catheter within the guide catheter may have a
guidewire lumen through which a pacing guidewire may be used to
test pace target sites. This catheter may also have a port for
contrast injection and may additionally have a balloon to perform
an occlusive venogram.
[0247] A pacing guidewire would be positioned in various regions of
the LV veins to elicit contractions. The LV response to this pacing
may be measured by monitoring the frequency dynamics of the
vibrational motion during ICP with the catheter. FIG. 54 indicates
this technique. In particular, the figure shows improved myocardial
function post-stimulation as determined by an increase in the peak
frequency of the isovolumic contraction phase. The left side of
FIG. 54 shows the pre-stimulation signal, and the right side shows
the post-stimulation signal. As can be seen, the peak frequency
increases post-stimulation from about 80 Hz to about 170 Hz (note
that the peak frequency is related to the time interval of the
threshold crossing). Also seen is a shortening of the time interval
of the isovolumic contraction phase from about 100 ms to about 75
ms. The isovolumic contraction phase signal was acquired by
sampling over a 100 ms time period after the onset of the QRS ECG
signal.
[0248] Alternatively the frequency dynamics or amplitude could be
measured with the esophageal probe. LV regions associated with
changes in the ICP frequency indicative of improved LV function
would be target pacing regions. For example, an increase in the
peak frequency, the rate of change of the frequency over time, a
reduction in the baseline frequency, or some combination of the
three may be indicative of improved LV function. Similarly, the
location of implantation and pacing of the RV lead or right atrial
lead may also be optimized by test pacing and monitoring the
frequency dynamics of the ICP.
[0249] The change in the presence or frequency of the third or
fourth heart sounds may also be indicative of a favorable response
to pacing and hence help identify a target pacing region. Changes
in the frequency and duration of vibration motion related to mitral
valve regurgitation may also help guide therapy and target pacing
regions. Thus a reduction in the frequency or duration of the
signal may be indicative of a favorable response.
[0250] In more detail, referring to FIG. 55, which shows myocardial
motion mapping, display output, and target pacing identification
through a roving pace guidewire, changes or variables indicative of
a favorable LV functional response may be sensed at the low, mid,
and high frequency ranges. In the figure, "MVR" refers to mitral
valve regurgitation, "IVC" refers to isovolumic contraction, and
"IVR" refers to isovolumic relaxation. The top curve is ECG 556,
curve 558 shows the velocity or LV displacement, obtained by
integrating the acceleration signal, curve 562 shows LV function,
and curve 562 shows the sounds of mitral valve regurgitation.
[0251] ECG 556 shows the QRS and T waves along with a pacing spike
566 which is delivered in the LV vein region. Examination of curve
558 shows a delayed onset motion 568 but a lessened delayed onset
motion 572 following the pacing spike. Curve 562 shows a value of
ejection phase 574, as measured by the time between the MVC or IVC
and the AVC or IVR, and then a longer ejection phase 576. Here the
MPI can be seen to be MPI=(a+b)/c. Curve 564 shows a reduced MVR
signal 578 as compared to the pre-pacing MVR signal 582. Finally,
it is noted that paced signal shows no third heart sound.
[0252] The accelerometer for monitoring the frequency dynamics of
heart sounds may also be integrated into a pulse generator of a
CRT/defibrillator device, including leadless defibrillator devices
implanted subcutaneously over the chest. This device would be
implanted subcutaneously on the chest or abdomen and would sense
the vibrational motion of the heart sounds (S1, S2, S3, S4 and
valvular murmurs) to characterize the peak amplitude and frequency.
This pulse generator could perform software algorithms to
characterize the frequency dynamics of these sounds and assess LV
function and pathology including contractility, mitral
regurgitation, LV thickening etc. The start of systole as measured
by the cardiac electrogram (internally or externally measured by
the IPG) could be used to synchronize the accelerometer sensor with
the onset of systole. Thus the S1 vibrational motion as measured by
the accelerometer would occur within a few milliseconds of the
sensed electrogram. Thereafter, additional vibrational motion (S2,
S3, and S4 and murmurs) could be identified based on there
occurrence after the electrogram and S1. Additional a time window
of sensing with the acceleration sensor (e.g. 100 ms) could be
sensed to measure only the S1. This information could be uploaded
via a radiofrequency link to provide a read out to the physician
for monitoring purposes. The RF communication device that would
acquire the data from the pulse generator could reside at the
patients home and be transmitted to a physician or central
monitoring station via the internet or a phone line link. The
accelerometer could be used to sense that the patient in whom the
device is implanted is not moving and is in the proper orientation
(e.g., upright or lying flat) prior to the acquisition of the heart
function data.
[0253] A stand alone implantable accelerometer device (IAD) (i.e.,
not incorporated into the IPG/CRT device) could also be implanted
subcutaneously or subpectorally and not require a transvenous lead
or extension. For example, referring to FIG. 56(B), a
subpectorally-placed IAD 208 may be disposed adjacent the pectoral
muscle 210 of a patient. The device 208 may have an acceleration
sensor 220, an RF communications transceiver chip 214 and antenna
212, signal processing and control circuit 218 with digital memory
storage capacity 222, and a battery 216. Referring to FIG. 56(A),
the device 208 may be contained in a hermetically sealed titanium
shell 202. The device could have a curved form factor as shown in
FIG. 56(A) to lie flat along the chest. The antenna could be wire
wound or integrated onto the communications chip. The sensor may be
a low-power consumption 3-axis MEMs device. The device may sense at
a frequency greater than about 10 Hz to avoid acceleration signals
due to respiration or displacement motion of the heart. Optional
electrodes 204 and 206 with accompanying circuitry may be employed
to obtain a surface cardiac electrogram. As shown in FIG. 56(A),
the electrodes would reside on the side of the device that is
oriented toward the heart. 3-7 years of battery life may be
provided, although variations are within the scope of the
invention. Low power RF transceiver chips (e.g., applications
specific integrated circuits or "ASICs"), such as that produced by
Zarlink Semiconductor of San Diego, Calif. (e.g., model number ZL
70100) can improve battery life and data transmission of the
device. The device need not require leads that extend into the
heart and may reside in proximity to the left ventricle after
subcutaneous or subpectoral implantation. The device may sense and
measure vibrational data related to LV function and pathology such
as frequency dynamics, time intervals, and peak amplitude of the
ICP, S1, S2, S3, S4, and valvular murmurs. The surface of the
device oriented toward the heart may have electrodes for sensing
the surface electrocardiogram and the onset of the QRS. Similar to
the inventor's prior applications, incorporated by reference above,
this allows for the identification of the S1 as the vibrational
signal immediately following the QRS. The subsequent vibrational
signals could also be identified and time windows of sensing could
also be incorporated to focus on the desired heart
sound/vibrational motion. A narrow window of sensing that
ascertains only the S1 vibrational signal may be preferred to avoid
signal distortion or noise caused by movement of the heart against
the chest during displacement or ejection. The S1 may be sensed and
averaged over several to many beats. The vibrational motion could
be sensed continuously or periodically. Periodic sensing may be
used to extend battery life. The data may be collected at the same
time during each day (e.g., at bedtime during quiet resting). The
acceleration data could be stored or uploaded via an RF link in
real time. The accelerometer could be battery-powered or
inductively-powered with an RF coil. The data could be periodically
or in real time uploaded with an RF link to a signal processing
station for monitoring of the LV function such as contractility and
pathology such as LV mass/thickness and valvular murmurs. The
uploaded data could be sent via the internet to a physician or
central monitoring station or both. The device could also interface
with a cell phone type device for the same purpose of uploading
data from the IAD.
[0254] Analysis of the frequency dynamics of the ICP (catheter or
esophageal probe) could also be used to optimize the pacing timing
intervals for CRT (A-V and V-V). Thus the V-V timing could be set
to 0 ms (both ventricles paced simultaneously), and the AV delay
could be varied between about 100 and 140 ms. The AV delay that
provides the highest peak frequency (or some other measure of
improved cardiac function) during ICP could be chosen. Subsequently
the A-V delay would be fixed at the previously determined optimal
value and the V-V delay could be varied between -30 ms (LV to RV;
thus -30 means the RV was paced 30 ms before the LV) to +30 ms LV
to RV. Again the interval causing the highest peak frequency during
ICP may be chosen. An automated system could run through the
various pacing timing intervals and monitor the frequency dynamics
of the ICP and provide optimal timing intervals.
[0255] The acceleration sensor may also be incorporated into the
lead of a CRT or CCM device. The sensor may monitor the frequency
dynamics of the ICP to ascertain cardiac function in a manner
similar to the above. The sensor could also be used to test
different timing intervals for the atrioventricular and
interventricular timing. The sensor may also be integrated into
other implantable devices such as cardiac stents or epicardial
leads to monitor cardiac function through analysis of the frequency
dynamics of the ICP and pathologic heart sounds.
[0256] FIG. 57 shows how information from the acceleration sensor
can be employed to develop a predictive algorithm for determining
CRT response. The peak amplitude and peak frequency are seen at LV
site #3. A linear threshold relationship, or other such
relationship, may be employed to determine when LV lead placement
is acceptable for any given patient. If the amplitude is high
enough at a certain frequency, and thus is above the linear
threshold, then the response may be deemed to be good and the site
chosen as a location for an LV lead.
[0257] A 3-axis acceleration sensing coronary sinus catheter can be
used to directly measure dyssynchrony of the heart and LV globally
from the coronary sinus. Dyssynchrony may be a better assessment of
response to CRT therapy than indices related to LV function, as
tissue Doppler studies have correlated improvement in synchrony
with improvements in response to CRT, including: LV remodeling,
six-minute walk test, ejection fraction, and other clinical and
physiologic outcomes. Measuring synchrony with the acceleration
sensing catheter can also be used to guide LV lead placement and
optimize timing intervals.
[0258] Motion of the heart may be defined as acceleration,
velocity, or displacement. Much of the motion of the heart is
longitudinal acceleration from the base to the apex, with the
region of the mitral valve plane descending inferiorly. Radial
acceleration to stiffen the ventricle also occurs at the mitral
valve plane as well as rotational acceleration of the heart as it
contracts longitudinally. Thus global LV motion, or acceleration,
occurs in three different axes. Because the coronary sinus runs
along the AV groove at the mitral valve plane this global LV motion
or contraction at the mitral valve plane can be sensed with a
3-axis accelerometer device placed in the coronary sinus. A three
axis accelerometer is ideally suited to measure the three
components of cardiac motion. Some of the dyssynchronous motion can
be measured in the lower frequency displacement motion (less than
about 20 Hz). Each axis of acceleration can be measured
independently or a composite such the square root of axis X squared
plus axis Y squared plus axis Z squared (referred to as RMS in
figures). The acceleration signal from each axis can be integrated
to determine velocity and a composite of the velocity signal can be
formed. The frequency changes below 20 Hz between 20 Hz and 200 Hz,
related to myocardial motion, measured at the coronary sinus can
also be used to assess dyssynchrony using a multi-axis acceleration
sensing coronary sinus catheter.
[0259] Prior disclosures (e.g. Chinchoy 20040172079 and Yu
6,923,772) use accelerometers to measure ventricular wall motion at
more than one location and compare acceleration between the two
walls. The greater the difference in the time between the two wall
accelerations the less synchronous the contraction is. It is not
practical, particularly for the different left ventricular walls,
to place multiple accelerometers. This disclosure provides for a
simpler approach using a single triaxial accelerometer to be placed
in the coronary sinus, a readily accessible vessel, using a
catheter device.
[0260] Also, prior disclosures (Chinchoy U.S. Pat. No. 6,871,088;
Marcus U.S. Pat. No. 6,978,184) use the accelerometer signal as a
surrogate for hemodynamic parameters of the heart such as dP/dt or
ejection fraction. Hemodynamic changes, such as an increase in
dP/dt, do not necessarily predict the outcome or response to CRT
therapy. Dyssynchrony, which is a measure of how coordinated or
uniformly the ventricle contracts, does predict outcome and
response to CRT. Hence a direct measure of dyssynchrony and
identification of dyssynchrony indices would be preferred.
[0261] A coronary sinus catheter with an integrated acceleration
sensor can be constructed using a silicon-based 3-axis capacitive
based MEMS sensor (e.g. ST Microelectronics LIS302AL). The sensor
and electronics can be surface mount packaged into a 3 mm.times.5
mm housing. The sensor housing or external package can be shaved or
milled by 0.005 to 0.010 inches along the length on each side and a
chamfer can be cut into the top edge at up to and approximately
0.015 inches per side without affecting performance of the device.
This allows the construction of a smaller diameter catheter to
facilitate placement in the coronary sinus. The acceleration sensor
can be surface mounted with the appropriate capacitors, as
previously described, onto a circuit board approximately 0.100
inches wide and up to about 1.000 inches long. The circuit board
also has contacts for surface mounting of capacitors. Approximately
30 gauge wire can be soldered to the proximal portion of the board
to traverse the length of the catheter for making appropriate
electrical connections. The distance between the power source and
the sensor in a catheter design is inherently long and may be
greater than 50 cm and as long as 10 feet particularly if the power
source must be kept out of the sterile field. Because the sensor is
capacitive and ratiometric, wherein the sensor output acceleration
signal is proportional to the excitation supply voltage at the
sensor, the excitation supply voltage must be kept constant at the
sensor to avoid or minimize sensor output variations, erroneous
signals, or significant deviations in signal quality, due to input
supply voltage fluctuations from environmental electromagnetic
interference induced or coupled along the length of the catheter
wires. To accomplish this, decoupling capacitors must be mounted in
close proximity to the sensor on the sensor board. In this catheter
design the decoupling capacitors for power are mounted adjacent to
the sensor on the printed circuit board in the catheter tip. Hence
the capacitors must be of appropriate size and design for
integration into the tip. In addition, capacitors are mounted
adjacent to the sensor for each acceleration output to band limit
and filter the signal to the desired frequency range to prevent
sensor self resonance from corrupting the true acceleration
signals. An appropriately sized capacitor can be selected for each
acceleration channel to limit the high frequency response of the
sensor to ensure high frequency oscillations from self resonance
can be effectively filtered out and eliminated.
[0262] The sensor and board can then be bonded into a polymeric
tube with a guide wire lumen. A Y-connector at the proximal portion
of the catheter will allow guide wire lumen access and the wires
from the sensor board to be routed to a connector that interfaces
with a power and signal conditioning unit. The signal conditioning
unit receives the wires in electrical communication with each axis
of the sensor via the board. In addition, the unit provides power
and ground to the sensor from a 9 V battery. The signal
conditioning unit can filter the sensor signal to less than about
600 Hz, provide electrical isolation to meet endovascular catheter
medical standards (e.g. current leakage less than 10 microamperes),
and convert the signal output to be compatible with an ECG display.
The signal conditioning unit also contains an ECG input that allows
the acceleration signal to be synched with the ECG input for
simultaneous display of both the ECG and acceleration wave
forms.
[0263] The catheter can placed into the coronary sinus of an animal
from the right or left internal jugular or subclavian. A guide wire
and guide catheter may be used to facilitate cannulation of the
coronary sinus. Alternatively, the acceleration catheter is of
appropriate shape and design to cannulate the coronary sinus.
Appropriate shapes have a curve or arc ranging from approximately
90 to 270 degrees with a radius of approximately 3-10 cm. In
addition, the catheter preferably has a proximal brained section to
improve torqueability and pushability. The acceleration catheter
can be placed over a standard 0.035 guide wire into the coronary
sinus to a position in the mid to lateral region of the sinus. The
sensor may be maintained in about the same location. A right
ventricular pacing catheter or implantable pacing lead may be
positioned in to the RV and the location can be fixed. The pacing
catheter or implantable lead can be connected to one arm of a "Y"
electrical connector to the output of an external pacing device.
The other arm of the Y connector attaches to preferably an LV
pacing guide wire or pacing device. The LV pacing guide wire may
have an electrically uninsulated or conductive tip and proximal
uninsulated or conductive portion allowing electrical pacing pulses
to be delivered by the wire to the myocardium. The LV pacing guide
wire can be maneuvered in the coronary sinus and tributary veins of
the LV through the lumen of the acceleration sensing catheter guide
wire lumen or separately. Baseline acceleration signals are
captured. The acceleration pattern can be displayed on an ECG or
endocardial electrogram output or CRT device programmer.
Biventricular or left ventricular test paces are delivered to the
heart from different locations on the LV. The pattern of
acceleration can be observed to identify a location that provides
the most synchronous pattern. Alternatively numerical indices of
dyssynchrony can be determined and the location that gives the most
optimal change in the numerical index can be identified. Once the
desired pacing location in the LV is identified the pacing guide
wire is left in that location. The implantable CRT LV pacing lead
can then be maneuvered over the wire and positioned in the optimal
location. Subsequently, a series of timing intervals for the V-V
timing between about +40 ms to about -40 ms LV contraction to RV
contraction can be tried and the interval that gives the greatest
improvements in acceleration patterns and numerical indices can be
selected. Similarly, a series of A-V timing intervals from about
150 ms to about 300 ms can tried and the interval that gives the
greatest improvements in acceleration patterns and numerical
indices can be selected.
[0264] FIG. 57 shows a representative synchronous acceleration
pattern of the left ventricle from the coronary sinus from a 3-axis
acceleration sensor placed in the coronary sinus shown as composite
(denoted as RMS on the figure) of the three individual signals
(FIG. 61 A,B,C shows each individual axis). The data in FIG. 57
show a 400 millisecond window after the peak of the R-wave on the
ECG for the synchronous contraction. FIG. 58 shows a representative
dyssynchronous contraction pattern measured from a 3-axis
acceleration sensor placed in the coronary sinus shown as a
composite of the three individual signals (FIG. 62 A, B, C shows
each individual axis). The data in FIG. 58 show a 400 ms time
window from the onset of the V-like wave on ECG after RV pacing for
the dyssynchronous contraction. Finding the optimal pacing region
and timing intervals may involve identifying a pacing region that
produces a left ventricular contraction pattern more closely
resembling a synchronous LV contraction. The more optimal the
pacing location, the more synchronous the pattern of acceleration
may appear. The location may be optimized by pacing from the right
ventricle with a fixed electrode and pacing the left ventricle
simultaneously with a roving guide wire and observing changes in
the acceleration pattern (as outlined above). For example in FIG.
58 a large acceleration peak occurs at the end of the systolic
phase just prior to and coincident with relaxation as determined by
the T-wave. This delayed acceleration indicates dyssynchrony. A
pattern of acceleration peaks, measured from the coronary sinus,
that includes at least one substantial acceleration peak (e.g.
greater than approximately 1/3 the highest acceleration peak)
occurring greater than 50 ms after the onset of electrical activity
of the left ventricle/isovolumic contraction, or mitral valve
closure, may be indicative of global LV dyssynchrony. Elimination
or reduction in this late acceleration through biventricular pacing
or CRT has also correlated with a favorable response to CRT
therapy. The LV pacing roving guide wire can be maneuvered into
different tributary veins and within a single tributary vein
through the lumen of the acceleration sensing catheter or
independently of it. Ideally the acceleration sensing catheter is
maintained in a nearly fixed location of the coronary sinus. Once
an optimal location is found the timing intervals including the V-V
(interventricular) timing and A-V (atrioventricular) timing can be
optimized by running through a series of intervals and assessing
the changes to a more ideal contraction pattern. Similarly, the
changes in frequency patterns can be assessed to determine
improvements in synchrony. FIG. 59 and FIG. 60 show the power
spectrum of the composite acceleration signal (FIGS. 63 and 64 show
the individual axes 63A, 63B, 63C and 64A, 64B, and 64C). The
frequency at which peak amplitude on the power spectrum occurs
increases with a more synchronous contraction. It is useful to look
at the frequency spectrum above 1-2 Hz or even 10 Hz depending on
the rate, to avoid analyzing the dominant frequency related to
overall heart rate.
[0265] It may be more desirable to characterize an acceleration
pattern with numerical indices, which may be referred to as
dyssynchrony indices. Numerical indices can be determined from
acceleration patterns through microprocessor based signal
processing. In this way, improvements in dyssynchrony can be
monitored by assessing the changes in the numerical value (e.g.
increase or decrease). The indices may be used to determine
responders to CRT therapy. More than one index may be combined to
better assess numerical changes and identify improved dyssynchrony,
including thresholds that may indicate a response to the therapy.
The acceleration pattern can be processed by a microprocessor, with
appropriate algorithms or instructions, to compute the indices from
the acceleration pattern or waveform. Instructions may be stored on
computer readable medium. The microprocessor may be incorporated
into the signal conditioning module or may be in an external
microprocessor device that the signal conditioning module outputs
to. The processing instructions of the pattern to compute one or
more dyssynchrony indices may involve normalizing the acceleration
signals by subtracting out the average signal for each axes, phase
averaging of the measured acceleration signals, correction for
gravity, computing the composite acceleration signal from multiple
acceleration axes, detecting the peak (s) of the acceleration
signal (s), detecting the peak of the ECG signals, computing time
intervals, and calculating the variability of the time intervals.
The processing may also involve performing Fourier transforms and
generating frequency spectrums.
[0266] There are several numerical indices that can be measured to
assess dyssynchrony that can be ascertained from FIGS. 57-64. The
acceleration signal may be integrated once or twice to determine
velocity or displacement and the analogous indice for these
measurements may be utilized. Representative examples of
dyssynchrony indices include the following. First is the time delay
from onset of ventricular electrical activity (e.g. peaks of the
QRS complex or onset of QRS components such as R wave or S) to
onset of motion, acceleration, velocity, or displacement of the LV
during systole (e.g., systole may determined as the time between
QRS onset and the T-wave on ECG or by mitral valve
closure/isovolumic contraction as discussed above as measured by
the acceleration sensor).
[0267] Second is the time delay from onset of ventricular
electrical activity (e.g., peaks of the QRS complex or onset of QRS
components such as R wave or S) to peak motion, acceleration,
velocity, or displacement of the LV during systole (e.g., systole
may determined as the time between QRS onset and the T-wave on ECG
or by valve mitral valve closure/isovolumic contraction as
discussed above as measured by the acceleration sensor).
[0268] Third is the time delay from onset of ventricular electrical
activity (e.g., peaks of the QRS complex or onset of QRS components
such as R wave or S) to the onset of motion, acceleration,
velocity, or displacement of the LV during diastole (e.g. diastole
may be determined as the time after the T-wave on ECG or by aortic
valve closure/isovolumic relaxation as determined by the
sensor).
[0269] Fourth is the time delay from onset of ventricular
electrical activity (e.g., peaks of the QRS complex or onset of QRS
components such as R wave or S) to peak motion, acceleration,
velocity, or displacement of the LV during diastole (e.g., diastole
may be determined as the time after the T-wave on ECG or by aortic
valve closure/isovolumic relaxation as determined by the
sensor).
[0270] Fifth is the ratio of the peak motion, acceleration,
velocity, or displacement, during systole and diastole.
[0271] Sixth is the time interval between the peak motion
acceleration, displacement, or velocity of systole and diastole
(shorter the time interval the greater the dyssynchrony).
[0272] Seventh is the number of motion peaks during systole greater
than a threshold (e.g. 100 or 200 milli gs or some proportion, such
as approximately 30% to 50%, of the largest peak).
[0273] Eighth is the time delay between two highest peaks motion,
acceleration, velocity, or displacement during systole (larger
delay between peaks correlates with dyssynchrony).
[0274] Ninth is the variability (e.g. standard deviation) of time
delay from onset of ventricular electrical activity (e.g. peaks of
the QRS complex or onset of QRS components such as R wave or S) to
peak motions, acceleration, velocity, or displacement in each
acceleration axis (X, Y, or Z)
[0275] Tenth is the variability (e.g. standard deviation) of peak
motion, acceleration, velocity, or displacement in each independent
axis (X, Y, or Z).
[0276] Eleventh is the reduction in the peak acceleration (milli
gs) of delayed contraction/acceleration.
[0277] Twelfth is the frequency of peak amplitude of power spectrum
above threshold (e.g. greater than 4 or 8 Hz).
[0278] Thirteenth is the acceleration axis with the dominant
frequency (indicating a shift in the orientation of the
motion).
[0279] Fourteenth are the cross correlations of time-frequency
transforms between ECG signal and acceleration signals or between
different acceleration signal axes. Cross correlations would
indicate the required shift in frequency or time required to
synchronize two different frequency spectra.
[0280] Data from these indices is provided in the table below
demonstrate the differentiation of dyssynchrony and synchrony using
some of the above indices. TABLE-US-00001 Indices of Dyssynchrony
Synchronous Dyssynchronous 1. Time delay to peak acceleration 51 ms
155 ms 3. Number of peaks >200 m gs 3 peaks 6 peaks 4. Time
delay between 2 highest peaks 14 ms 135 ms 5. Standard deviation
peak acceleration 5 ms 79 ms each axis X, Y, & Z 6. Frequency
peak power spectrum 22 Hz 15 Hz >10 Hz 7. Channel with peak
power spectrum Channel 3 Channel 2 >10 Hz
[0281] Time frequency transforms (FIGS. 65 and 66) may also be used
to characterize synchrony and dyssynchrony and to develop indices
for these states. In particular, FIG. 65 illustrates synchronous
contraction (normal sinus rhythm), showing dominant vibrational
energies during isovolumic contraction (IVC) or systole or after
onset of ventricular electrical activity and isovolumic relaxation
(WR) or after T-wave of ECG. Peak IVC frequency is approximately 60
Hz and peak IVR frequency is greater than 120 Hz. Time to peak
vibrational energy is less than 20 ms (approximately 12 ms). Low
frequency vibrational energy just prior to IVC is consistent with
atrial contraction. The dashed line indicates onset of ventricular
electrical activity (R-wave).
[0282] FIG. 66 illustrates dyssynchronous contraction (RV pacing
induced). Loss of vibrational energy may be seen during isovolumic
relaxation, especially at frequencies above 100 Hz. Widely
dispersed (20 to 100 Hz) vibrational frequencies are seen during
isovolumic contraction or after onset of ventricular electrical
activity. Time to peak vibrational energy is greater than 20 ms
(approximately 32 ms). Loss of low frequency vibrational energy is
seen due to atrial contraction. The dashed line indicates onset of
ventricular electrical activity.
[0283] One method used to characterize synchrony and dyssynchrony
and to develop indices for these states may be ECG-locked spectral
perturbation. The accelerometer data are first aligned to event
(e.g., R-wave of ECG) onsets. The power spectrum is then computed
over a sliding latency window and average across the resultant
spectral information from multiple heart beats. In the ECG spectral
change image, the color at each time/frequency image pixel then
indicates power (in dB) at a given frequency and latency relative
to the time locking event. Typically, for n trials, if F.sub.k (f,
t) is the spectral estimate of trial k at frequency f and trial
latency t, then ECGSP .function. ( f , t ) = 1 n .times. k = 1 n
.times. .times. ( F k .function. ( f , t ) ) 2 . ##EQU1## To
compute F.sub.k (f, t), a short-time Fourier transform, a
sinusoidal wavelet transform (i.e., a short-time discrete Fourier
transform), wavelet, or a Slepian multitaper decomposition
(Thompson, 1982) may be used. Differences between these
decompositions as applied to accelerometer/ECG data may be small
(though the number of cycles in each data window may be
critical).
[0284] Patterns of time frequency transforms during synchronous
contraction indicate a peak frequency energy of about 50 to 60 Hz
occurring within 15 milliseconds of the onset of ventricular
electrical activity (R-wave or systole or at isovolumic
contraction) on the on the surface ECG. These higher energy
(>about 5-10 dB) frequencies are primarily seen in the
longitudinal and radial axes (Channels 1 & 3) of the
accelerometer, with very little higher energy frequencies in these
ranges seen in the Y-axis (Channel 2). During relaxation (after the
T-wave on the ECG and isovolumic relaxation), there are higher
energy frequencies that occur above 100 Hz and are present in all
three axes of the accelerometer (Channels 1, 2 & 3). Numerical
indices may be derived based on these time-frequency plots, which
characterize a synchronous contraction.
[0285] During a dyssynchronous contraction, there is a wide
dispersion of frequency energy ranging from 20 Hz to 100 Hz
occurring within about 30 to 35 milliseconds after the onset of
ventricular electrical activity (R-wave) on the surface. ECG. There
is loss of higher energy frequencies occurring during relaxation
(after the T-wave on ECG) and a complete loss of these frequencies
above 100 Hz. Improvements in dyssynchrony associated with pacing
(biventricular or left ventricular) may be assessed by monitoring
the return of higher frequencies during relaxation, a reduction in
the time to peak frequency energy, and a reduction in the
dispersion or variability of frequency energy during systole or
after onset of ventricular electrical activity. In addition,
numerical indices may be derived based on these time-frequency
plots, which would allow the assessment of an improvement in
dyssynchrony with pacing. Other features and characteristics that
distinguish dyssynchrony and synchrony may be ascertained by review
of FIGS. 65 and 66. Inter heart beat coherence may also be analyzed
to assess synchrony (see FIGS. 67 and 68). FIG. 67 illustrates
inter heart beat coherence synchronous contraction (normal sinus
rhythm). Coherence is present at greater than 100 Hz during the
systole or isovolumic contraction phase. Time to peak coherence is
approximately 12 ms. The dashed line indicates the onset of
ventricular electrical activity. FIG. 68 illustrates inter heart
beat coherence dyssynchronous contraction (RV pacing induced). Loss
of inter heart beat coherence is seen above approximately 100 Hz
for systole or immediately after onset of ventricular electrical
activity or the isovolumic contraction phase. Time to peak
coherence is approximately 32 ms. The dashed line indicates onset
of ventricular electrical activity.
[0286] Inter acceleration axes, or acceleration sensor channel,
coherence may also be analyzed. Coherence is the property of
wave-like states that enables them to exhibit interference. It is
also the parameter that quantifies the quality of the interference
(also known as the degree of coherence). It was originally
introduced in connection with Young's double-slit experiment in
optics but is now used in any field that involves waves, such as
acoustics, electrical engineering, and quantum physics. In
interference, at least two wave-like entities are combined and,
depending on the relative phase between them, they can add
constructively or subtract destructively. The degree of coherence
is equal to the interference visibility, a measure of how perfectly
the waves can cancel due to destructive interference.
[0287] Waves of different frequencies (in light these are different
colors) can interfere to form a pulse if they have a fixed relative
phase-relationship (see Fourier transform). Conversely, if the
waves of different frequencies are not coherent then when combined
they create a wave that is continuous in time (e.g., white light or
white noise). The temporal duration of the pulse .DELTA.t is
limited by the spectral bandwidth of the light .DELTA.f according
to: .DELTA.f.DELTA.t.gtoreq.1 which follows from the properties of
the Fourier transform (for quantum particles it also follows from
the Heisenberg uncertainty principle.
[0288] If the phase depends linearly on the frequency (i.e.,
.theta.(f) .varies.f) then the pulse will have the minimum time
duration for its bandwidth (a transform-limited pulse), otherwise
it is chirped (see dispersion).
[0289] Inter-heartbeat Coherence (IHC), or more precisely
inter-heartbeat phase coherence (IHPC), measures the partial or
complete reliability of spectral phase at a particular frequency
and latency across a set of trials. This measure was introduced in
EEG literature by Tallon-Baudry et al. (1996) as the `phase locking
factor.` The term `inter-trial coherence` refers to its
interpretation as the event-related phase coherence between
recorded EEG activity and an event indicator function (e.g., a
Dirac or cosine function centered on the time-locking events).
Using the same notation as above IHPC .function. ( f , t ) = 1 n
.times. k = 1 n .times. F k .function. ( f , t ) F k .function. ( f
, t ) ##EQU2## where .parallel. represents the complex norm.
[0290] Synchronous contraction is associated with the presence of
inter heart beat coherence during systole (isovolumic contraction
or immediately after onset of ventricular electrical activity) at
frequencies greater than about 80 to 100 Hz. The time to peak
coherence occurs within about 15 milliseconds. Dyssynchronous
contraction is associated with a loss of inter heart beat coherence
at frequencies greater than about 80 to 100 Hz and a delayed time
to peak coherence to greater than about 30 milliseconds.
Improvements in dyssynchrony associated with pacing (biventricular
or left ventricular) may be assessed by monitoring a return of
coherence in the higher frequencies and/or a reduction in the time
to peak coherence. Other features and characteristics that
distinguish dyssynchrony and synchrony may be ascertained by review
of FIGS. 67 and 68. Numerical indices may also be derived from the
coherence analysis, which would allow the assessment of an
improvement in dyssynchrony with pacing. Inter accelerometer axis
coherence may also distinguish synchrony from dyssynchrony and
allow assessments of improvement with pacing.
[0291] Indices related to dyssynchrony which may be derived from
time frequency transforms and coherence analysis include:
dispersion of or variability of frequency energy during systole,
isovolumic contraction, or following onset of ventricular
electrical; time to peak frequency and energy systole during
systole, isovolumic contraction, or following onset of ventricular
electrical; magnitude or presence of frequency energy during
relaxation or following the T-wave on ECG; shift in acceleration
sensor axis with peak frequency energy; loss of higher frequency
inter heart beat coherence (e.g. greater than about 80 Hz); and
reduced inter accelerometer axis coherence.
[0292] Monitoring changes in these indices may indicate a more
synchronous heart function during treatment such as pacing. For
example, a reduction in the dispersion of frequency energy may
indicate better dyssynchrony.
[0293] Gathered or acquired information of a subject is
mathematically processed so as to identify relationships among the
multiple variables that correlate with predefined classes. Once
such relationships (also referred to as patterns, classifiers, or
fingerprints) have been identified, they can be used to predict the
likelihood that a subject belongs to a particular class represented
in the population used to build the relationships. In practice, a
large set of information, termed the training or development
dataset, is collected and used to identify and define diagnostic
patterns that are then used to prospectively analyze the acquired
information of subjects that are members of the testing,
validation, or unknown dataset and that were not part of the
training dataset to suggest or provide specific information about
such subjects.
[0294] There are a number of data analysis methods that have been
implemented and documented with application to disease recognition.
Analysis methods fall under the headings of data mining,
information retrieval, pattern recognition, clustering,
classification, statistical analysis, machine learning and other
artificial intelligence techniques, and discriminator analysis to
name a few. Preferably, signal processing techniques are applicable
to correlate specific traits with a known or unknown disease
marker. Within those methods, particular algorithms that are known
to those of skill in the art and that have been employed include
k-means, k-nearest neighbors, artificial neural networks, t-test
hypothesis testing, genetic algorithms, self organizing maps, as
well as principal component regression. See, for example, Duda et
at, 2004, Pattern Classification, John Wiley & Sons, Inc.;
Hastie et al., 2001, The Elements of Statistical Learning: Data
Mining, Inference, and Prediction, Springer, New York; and Agresti,
1996, An Introduction to Categorical Data Analysis, John Wiley
& Sons, New York, Russell & Norvig, 2004, Artificial
Intelligence: A Modern Approach, Prentice Hall; 2.sup.nd edition;
each which are hereby incorporated by reference in their entirety.
The manner in which these building-block algorithms are implemented
and combined can vary significantly. Different methods can be more
effective for different types of multivariate data or for different
types of classification (e.g., diagnostic vs. prognostic).
[0295] Methods for disease recognition or correlation utilizing the
above methods have been documented in various references. See, for
example, Hitt, "Heuristic Method of Classification," United States
Patent Publication No. 2002/0046198, published Apr. 18, 2002; Hitt
et al., "Process for discriminating between biological states based
on hidden patterns from biological data," United States Patent
Publication No. 2003/0004402, published Jan. 2, 2003; Petricoin et
al., 2002, "Use of proteomic patterns in serum to identify ovarian
cancer," Lancet 359, pp. 572-7, Lilien et al., 2003, "Probabilistic
Disease Classification of Expression-Dependent Proteomic Data from
Mass Spectrometry of Human Serum," Journal of Computational
Biology, 10, pp. 925-946; Zhu et al., 2003, "Detection of
cancer-specific markers amid massive mass spectral data,"
Proceedings of the National Academy of Sciences 100, pp.
14666-14671; and Wang et al., 2003 "Spectral editing and pattern
recognition methods applied to high-resolution magic-angle spinning
1H nuclear magnetic resonance spectroscopy of liver tissues,"
Analytic Biochemistry 323, pp. 26-32; each of which is hereby
incorporated by reference in its entirety.
[0296] Specifically, Hitt et al. "Process for discriminating
between biological states based on hidden patterns from biological
data," United States Patent Publication No. 2003/0004402, published
Jan. 2, 2003 disclose a method whereby a genetic algorithm is
employed to select feature subsets as possible discriminatory
patterns. In this method, feature subsets are selected randomly at
first and their ability to correctly segregate the dataset into
known classes is determined. As further described in Petricoin et
al., 2002, "Use of proteomic patterns in serum to identify ovarian
cancer," Lancet 359, pp. 572-7, the ability or fitness of each
tested feature subset to segregate the data is based on an adaptive
k-means clustering algorithm. However, other known clustering means
could also be used. At each iteration of the genetic algorithm,
feature subsets with the best performance (fitness) are retained
while others are discarded. Retained feature subsets are used to
randomly generate additional, untested combinations and the process
repeats using these and additional, randomly generated feature
subsets.
* * * * *