U.S. patent application number 10/566152 was filed with the patent office on 2006-08-24 for optimization method for cardiac resynchronization therapy.
Invention is credited to Ding Sheng He, Frank I. Marcus.
Application Number | 20060190045 10/566152 |
Document ID | / |
Family ID | 34115751 |
Filed Date | 2006-08-24 |
United States Patent
Application |
20060190045 |
Kind Code |
A1 |
Marcus; Frank I. ; et
al. |
August 24, 2006 |
Optimization method for cardiac resynchronization therapy
Abstract
The patterns of contraction and relaxation of the heart before
and during left ventricular or biventricular pacing are analyzed
and displayed in real time mode to assist physicians to screen
patients for cardiac resynchronization therapy, to set the optimal
AN or right ventricle to left ventricle interval delay, and to
select the site(s) of pacing that result in optimal cardiac
performance. The system includes an accelerometer sensor (40); a
programmable pace maker (35, 41), a computer data analysis module
(32), and may also include a 2D and 3D visual graphic display of
analytic results (43, 44), i.e. a Ventricular Contraction Map. A
feedback network (32) provides direction for optimal pacing leads
placement. The method includes selecting a location to place the
leads of a cardiac pacing device, collecting seismocardiographic
(SCG) data corresponding to heart motion during paced beats of a
patient's heart, determining hemodynamic and electrophysiological
parameters based on the SCG data, repeating the preceding steps for
another lead placement location, and selecting a lead placement
location that provides the best cardiac performance by comparing
the calculated hemodynamic and electrophysiological parameters for
each different lead placement location.
Inventors: |
Marcus; Frank I.; (Tucson,
AZ) ; He; Ding Sheng; (Tyngaboro, MA) |
Correspondence
Address: |
QUARLES & BRADY STREICH LANG, LLP
ONE SOUTH CHURCH AVENUE
SUITE 1700
TUCSON
AZ
85701-1621
US
|
Family ID: |
34115751 |
Appl. No.: |
10/566152 |
Filed: |
July 28, 2004 |
PCT Filed: |
July 28, 2004 |
PCT NO: |
PCT/US04/24469 |
371 Date: |
April 25, 2006 |
Current U.S.
Class: |
607/17 |
Current CPC
Class: |
A61B 5/6869 20130101;
A61N 1/36542 20130101; A61N 1/36843 20170801; A61B 5/7217 20130101;
A61N 1/3627 20130101; A61N 1/36842 20170801; A61N 1/3684 20130101;
A61B 5/1107 20130101; A61N 1/3682 20130101 |
Class at
Publication: |
607/017 |
International
Class: |
A61N 1/368 20060101
A61N001/368 |
Claims
1. A method for determining the effectiveness of cardiac
resynchronization therapy while stimulating a patient's heart at
different locations during an electrophysiology study, comprising
the steps of: (a) collecting seismocardiographic (SCG) data
corresponding to heart motion during paced beats of said patient's
heart; (b) collecting seismocardiographic (SCG) data corresponding
to heart motion during un-paced beats of said patient's heart; (c)
determining a hemodynamic parameter based on the SCG data of steps
(a) and (b); and (d) determining whether cardiac performance is
improved by comparing said hemodynamic parameter generated by step
(a) with that generated by step (b).
2. The method of claim 1, wherein the SCG data of steps (a) and (b)
are detected by an accelerometer.
3. The method of claim 1, wherein said hemodynamic parameter of
step (c) is selected from the group consisting of one or more of
the following: a pre-ejection period, a rate of contraction of left
ventricle, a duration of systole, a duration of an isovolumic
relaxation period, a rate of change of ventricular pressure, and an
ejection fraction.
4. The method of claim 1, wherein a ventricular contraction mapping
is generated from the SCG data collected in steps (a) and (b).
5. The method of claim 3, wherein the pre-ejection period is
determined from a ventricular contraction mapping.
6. The method of claim 3, wherein the rate of contraction of left
ventricle is determined from a ventricular contraction mapping.
7. The method of claim 3, wherein the duration of systole is
determined from a ventricular contraction mapping.
8. The method of claim 3, wherein the duration of isovolumic
relaxation period is determined from a ventricular contraction
mapping.
9. The method of claim 4, wherein the a rate of change of
ventricular pressure is determined from a ventricular contraction
mapping.
10. The method of claim 1, further including the step of (e)
determining whether left ventricular or biventricular pacing is
more beneficial to said patient by comparing said hemodynamic
parameter generated by step (a) with those generated by step
(b).
11. A method for selecting an optimal placement of leads of a
cardiac pacing device for cardiac resynchronization therapy during
implantation comprising the steps of: (a) selecting a lead
placement location to place a lead of said cardiac pacing device;
(b) collecting seismocardiographic (SCG) data corresponding to
heart motion during paced beats of a patient's heart; (c)
determining a hemodynamic parameter based on the SCG data of step
(b); (d) repeating steps (a)-(c) for other lead placement locations
for said cardiac pacing device; and (e) selecting a lead placement
location that provides a best cardiac performance by comparing said
hemodynamic parameter of step (c) for each different lead placement
location.
12. The method of claim 11, wherein the SCG data of step (b) are
detected by an accelerometer.
13. The method of claim 11, wherein said hemodynamic parameter of
step (c) is selected from the group consisting of one or more of
the following: a pre-ejection period, a rate of contraction of left
ventricle, a duration of systole, a duration of an isovolumic
relaxation period, a rate of change of ventricular pressure, and an
ejection fraction.
14. The method of claim 11, wherein a ventricular contraction
mapping is generated from the SCG data collected in step (b).
15. The method of claim 13, wherein the pre-ejection period is
determined from a ventricular contraction mapping.
16. The method of claim 13, wherein the rate of contraction of left
ventricle is determined from a ventricular contraction mapping.
17. The method of claim 13, wherein the duration of systole is
determined from a ventricular contraction mapping.
18. The method of claim 13, wherein the duration of isovolumic
relaxation period is determined from a ventricular contraction
mapping.
19. The method of claim 13, wherein the a rate of change of
ventricular pressure is determined from a ventricular contraction
mapping.
20. A system that selects an optimal placement of leads of a
cardiac pacing device for cardiac resynchronization therapy during
implantation, comprising: a cardiac pacing device with leads
implanted into a patient's heart; means for collecting
seismocardiographic (SCG) data corresponding to heart motion during
paced beats of said patient's heart; means for determining a
hemodynamic parameter based on said SCG data; and a processing
device that compares said hemodynamic parameter; wherein the
optimal placement of leads of said cardiac pacing device is
determined by comparing said hemodynamic parameter for different
lead placement locations.
21. The apparatus of claim 20, wherein said means for collecting
SCG data comprises an accelerometer.
22. The system of claim 20, wherein said hemodynamic parameter is
selected from the group consisting of one or more of the following:
a pre-ejection period, a rate of contraction of left ventricle, a
duration of systole, a duration of an isovolumic relaxation period,
a rate of change of ventricular pressure, and an ejection
fraction.
23. The system of claim 20, wherein a ventricular contraction
mapping is generated from the SCG data.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to U.S. Provisional Patent
Application Ser. No. 60/399,028, which was filed on Jul. 29, 2002
by the same inventors.
BACKGROUND OF INVENTION
[0002] 1. Field of Invention
[0003] The present invention relates generally to the implantation
of a cardiac pacing device used for cardiac resynchronization
therapy (CRT). More specifically, the present invention relates to
a real time method for CRT candidate screening, for optimizing the
placement of one or more leads, and for determining optimal
settings for cardiac pacing devices.
[0004] 2. Description of Related Art
[0005] Heart failure afflicts about twenty-five million people
worldwide, with about two million new cases diagnosed each year. In
the United States, hospitalization for heart failure amounts to
more than 6.8 million days a year, and the total cost of treatment
is more than $38 billion annually, which is increasing as the
population ages. The prevalence of congestive cardiac failure is
also increasing due to improved survival from both myocardial
infarction and hypertension that has resulted from the use of drug
therapies, such as angiotension-coverting enzyme inhibitors,
beta-blockers, and digoxin. Nevertheless, many patients remain
markedly symptomatic despite maximal medical therapy. Furthermore,
patients with left ventricular failure are at an increased risk of
progressive heart failure or sudden death.
[0006] In some heart patients, congestive cardiac failure affects
the synchronous beating of the ventricles. Accordingly, the left
ventricle is not able to pump blood efficiently to supply the body
with needed oxygen and nutrients. In approximately 30% of patients
with heart failure, an abnormality in the heart's electrical
conduction system, called an intraventricular conduction delay or
bundle branch block, causes the left ventricle to beat in an
asynchronous fashion. This greatly reduces the efficiency of the
left ventricle in patients whose hearts are already damaged. In
addition, the right and left ventricles begin to beat slightly out
of phase instead of beating simultaneously.
[0007] A significant minority of patients with congestive heart
failure have marked prolongation of the QRS complex of their
electrocardiographic (ECG) profile, which represents the time it
takes for the depolarization of the ventricles. The prolongation is
an indicator of intraventricular conduction abnormality and is
associated with decreased left ventricular systolic function. The
development of new QRS prolongation is associated with reduced left
ventricular function.
[0008] Normally, electrical activation is conducted by the His
bundle and Purkinje system, and an impulse spreads transmurally
from the septum to multiple paraseptal regions resulting in
synchronous contraction of the ventricles. Many patients with heart
failure have poor electrical conduction in the heart that results
in a pattern called left bundle branch block (LBBB) or
intraventricular conduction delay. In these patients, the duration
of the QRS complex may exceed 130 milliseconds (ms) compared with a
normal duration of less than 100 ms. In LBBB, the left ventricle is
activated belatedly throughout the septum from the right ventricle,
with anteroseptal crossing preceding inferioseptal crossing. The
latest activation is in the posterior inferior aspect of the left
ventricle, often remote from the base.
[0009] Additionally in patients with LBBB, the delay between the
onset of left and right ventricle systole may be prolonged to 85 ms
resulting in significantly later aortic opening, aortic valve
closure, and mitral valve opening. LBBB does not affect the timing
of right ventricle events, and the delay in the left ventricle
events leads to a reversal of the usual sequence of right and left
ventricle systole. In addition, the range of isovolumic contraction
times in patients with LBBB is wide (20-100 ms), suggesting
heterogeneity of left ventricle activation. The delay in aortic
valve closure leads to a relative decrease in the duration of left
ventricle diastole. In patients with LBBB, prolonged depolarization
or abnormal depolarization may result in regional myocardial
contraction into early diastole, causing a delay of mitral valve
opening with prolongation of left ventricle isovolumic relaxation
time of up to 300% and shortened left ventricle filling time. LBBB
is also associated with abnormal diastolic function on Doppler
echocardiography examination. Further, left ventricle
intraventricular conduction delay may add significantly to
dyssynchrony, particularly in ischemic heart disease.
[0010] In patients with an intraventricular conduction defect or
with LBBB, cardiac resynchronization therapy (CRT) shortens the
duration of the QRS complex and has been shown to improve the
patient's symptoms markedly. CRT is the use of a specialized
pacemaker to improve contraction coordination of the left
ventricle. The specialized pacemaker may also be programmed to
coordinate the beating of the two ventricles by pacing the left
ventricle individually to match the beating of the right ventricle
or both ventricles simultaneously. It has been shown that
resynchronization of abnormal intraventricular and interventricular
asynchrony with left ventricular or biventricular pacing may
symptomatically improve patients with severe ventricular failure.
While the results have been positive, most studies have shown that
approximately 30% of patients do not obtain any measurable benefit
from the therapy. It is now being tested to see if this therapy
will increase the duration of life.
[0011] In biventricular pacing, one wire or catheter is implanted
in the right ventricle and another is threaded into a vein, the
coronary sinus, which drains into the right atrium to pace the left
ventricle. The coronary sinus catheter is then guided to the
lateral or posterior part of the left ventricle. Alternatively, a
left ventricular lead can be implanted by thoracotomy (i.e.,
through a small incision between the ribs, the lead is implanted on
the surface of the left ventricle) or even by crossing the atrial
septum and inserting the lead inside the left ventricle. Yet, the
exact and best position for each catheter position is difficult to
determine at the time of insertion. In fact, there are no
physiological means to determine the best site at the time of lead
placement except possibly the use of echocardiography, which is
time consuming and poses a problem in keeping the operative field
sterile.
[0012] In addition, it is difficult to predict the effectiveness of
CRT before the insertion of the cardiac pacing device. Currently,
physicians often measure a decrease in QRS duration after
biventricular pacing to evaluate CRT. However, the decrease in the
QRS duration does not correlate well with the improvement of
cardiac function in some patients. Other parameters have been also
used to determine the effectiveness of CRT, such as improvement of
New York Heart Association (NYHA) classification score, six-minute
hall walk results, etc. However, these parameters cannot be
evaluated in real time and do not provide information that
physicians need to know at the time of lead and device implantation
to determine if the patient will benefit from CRT. Finally, it is
not clear if one lead implanted into the coronary sinus is as good
as two leads implanted into the right and left ventricles.
[0013] Another problem encountered, particularly with the use of
dual-chamber pacemakers, is the proper setting of the so-called
"A-V delay interval." Basically, the A-V delay interval refers to
the time interval between a ventricular stimulation pulse and a
preceding atrial depolarization. Because the sequence of atrial and
ventricular pacing is vital to the efficiency of the heart as a
pump, a non-optimal A-V delay interval can seriously impact heart
performance. Indeed, relatively small departures from the optimal
A-V delay interval value can greatly reduce the hemodynamic
contribution of the atria in patients with congestive heart
failure.
[0014] At present, physicians select and program the A-V delay
interval empirically. Since the hemodynamic contribution of the
atrial depolarization to cardiac output is well known, every effort
is made to select the optimal A-V delay interval for a given
patient. However, the optimal A-V delay value can vary over time as
the patient ages or the disease state changes.
[0015] Therefore, there is a need for a way to provide a reliable
prediction for whether a patient would be a good candidate for
cardiac resynchronization therapy, for a way to determine the
optimal placement of leads of a cardiac pacing device in real time
while the pacing device is implanted into the patient, and for a
way to optimize the selection of the A-V delay interval, both
during the initial placement of a dual-chamber pacemaker and during
follow-up evaluations.
SUMMARY OF INVENTION
[0016] The invention generally relates to a real time method for
CRT candidate screening, for optimizing the placement of pacemaker
leads, and for determining optimal settings for cardiac pacing
devices. The system of the invention includes an accelerometer
sensor, a programmable pace maker or other means for stimulating
heart pacing, a computer data analysis module, and a 2D and 3D
visual graphic display of analytic results, i.e., a ventricular
contraction map. The method includes placing the leads of a cardiac
pacing device, collecting seismocardiographic (SCG) data
corresponding to heart motion during both normal (i.e., unpaced)
conduction and during paced beats of a patient's heart, determining
hemodynamic parameters based on the SCG data, and using this data
to screen patients for CRT and to determine optimal lead
placement.
[0017] Accordingly, a main objective of the present invention is to
determine if a patient is an appropriate candidate for
resynchronization therapy in real time during an electrophysiology
study.
[0018] An additional objective of the present invention is to
determine the optimal site(s) of lead implantation for cardiac
resynchronization therapy, and, therefore, enhance the
effectiveness of the therapy.
[0019] Another objective of the present invention is to determine
if the patient needs only the left ventricular pacing instead of
biventricular pacing in real time during an electrophysiology
study.
[0020] According to the preferred embodiment, an accelerometer
placed over a patient's chest at the time of insertion of pacing
leads can help identify the optimal site. A computer algorithm
processes the seismocardiographic measurements and generates a
ventricular contraction mapping, which displays the rate of
pre-ejection and ejection, the duration of the pre-ejection period,
duration of systole, and duration of isovolumic relaxation period.
Examining changes in the relevant data at different lead locations
results in the determination of the best site of lead placement.
For example, indicative behavior includes a shortening of the
pre-ejection period, and an increase in the rate of contraction of
the left ventricle. Additionally, the degree of mitral valve
regurgitation, which alters the patterns of chest wall motion,
should markedly decrease with the optimal site.
[0021] It is possible that accelerometer patterns will help
identify patients who would be likely to benefit from CRT by
showing a recognizable pattern of minimal desynchronization (in
which case CRT would not be beneficial) or marked desynchronization
(in which case CRT would be most helpful).
[0022] Thus, the invention may be used during an electrophysiology
study (EPS) to help determine if CRT is an effective treatment for
a particular patient. During an EPS, catheters are placed in the
heart and electrically stimulate different areas to identify
abnormalities in the heart's conductive system. According to the
present invention, an accelerometer measures the
seismocardiographic behavior at different stimulation locations.
The resulting data is analyzed to determine whether the patient
only needs left ventricular or biventricular pacing or if CRT would
be beneficial at all. If CRT is found to be an effective treatment,
the cardiac pacing device could be implanted during the same
procedure with the leads placed at an optimal location. Since one
third of patients who have left ventricular or biventricular pacing
do not improve with this procedure, the accelerometer-guided
ventricular pacing could diminish this high incidence of
ineffectiveness. Thus, the method and system of the invention can
provide reliable prediction whether the patients would be
candidates for CRT as well as provide optimal location for pacing
lead placement during the implantation. Also, optimal settings for
delay between onset of right and left ventricular contraction could
be determined.
[0023] Furthermore, the method of the invention may be used to
select an optimal A-V delay interval for a patient based on
comparing an index of cardiac performance for several delay
intervals. In a preferred embodiment, various candidate A-V delay
intervals and pacing rates are programmed into the pacemaker and
real time seismocardiographic (SCG) data and electrocardiographic
(ECG) data are collected. The collected data is processed to
develop a canonical SCG waveform. Next, certain features in the SCG
waveform are identified and used to determine time intervals
between the atrial depolarization and ventricular stimulation pulse
events. This time interval information is used to define an index
of cardiac performance that can be compared with other indices
representing several different pacemaker A-V delay intervals.
[0024] Various other purposes and advantages of the invention will
become clear from its description in the specification that
follows. Therefore, to the accomplishment of the objectives
described above, this invention includes the features hereinafter
fully described in the detailed description of the preferred
embodiments, and particularly pointed out in the claims. However,
such description discloses only some of the various ways in which
the invention may be practiced.
BRIEF DESCRIPTION OF DRAWINGS
[0025] FIG. 1 is a schematic diagram depicting the relationship
between pacemaker events, electrocardiogram (ECG) events,
seismocardiographic (SCG) events, and the physical motion of the
heart.
[0026] FIG. 2 is a schematic depiction of an SCG/ECG analysis
system and pacemaker lead placement test system connected to wires
or catheters inside a patient.
[0027] FIG. 3 is a flow chart illustrating the method used to
collect and analyze the ECG and SCG waveforms in FIG. 1.
Abbreviations are defined in the Detailed Description.
[0028] FIG. 4 is a partial screen display generated by the SCG/ECG
analysis system.
[0029] FIG. 5 is a block diagram showing in outline the optimal
lead placement method for cardiac resynchronization therapy.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0030] The invention relates in general to a method for providing a
reliable prediction for whether a patient would be a good candidate
for cardiac resynchronization therapy and for determining the
optimal placement of leads and settings of a cardiac pacing device
in real time while the pacing device is implanted into the patient.
In one embodiment, the method of the invention preferably includes
detecting hemodynamic parameters corresponding to the motion of a
patient's heart with an accelerometer, converting the detected
parameters into digital data that is fed into an analysis module
for calculation and display of ventricular contraction mapping, and
comparing the results generated by different pacemaker lead
placement to provide an optimal lead location. In another
embodiment, hemodynamic parameters are detected and compared to
those generated by an unpaced heart, thereby predicting whether CRT
is an appropriate option for a given patient.
[0031] The invention further relates to a method for selecting an
A-V delay interval for a pacemaker patient that includes the steps
of selecting and setting an initial A-V delay value, collecting SCG
data corresponding to heart motion during paced beats of the
patient's heart, locating the mitral valve closure point, the
atrial valve opening point, and the atrial valve closing point in
the SCG data, calculating the time interval between the
aforementioned points, computing an index of cardiac performance
based on the aforementioned points, and selecting the A-V delay
value that optimizes the index of cardiac performance.
[0032] FIG. 2 is a schematic diagram representing the various
connections between the pacemaker patient 31, the pacemaker
programmer 41, and the SCG/ECG analysis system 32. The drawing
shows a dual chamber pacemaker 35 implanted in the pacemaker
patient 31 and coupled to the patient's heart 33 through a suitable
lead 36. Although one lead is shown, it should be recognized that
pacemakers having more than one lead may be used with the invention
(for example, a pacemaker with an atrial lead and one or more a
ventricle leads). The pacemaker programmer 41 communicates with the
implanted pacemaker 35 through a programming head 42 shown in
position over the pacemaker 35 implant site. The pacemaker
programmer 41 can be used to alter the A-V delay interval, the
right ventricle to left ventricle delay, pacing rate, and pacing
mode of the implanted pacemaker 35 via telemetry.
[0033] The SCG/ECG system 32 is coupled to the pacemaker patient 31
and used to collect real time ECG data from an array of surface
electrodes 37, 38, and 39 which are placed upon the patient's chest
34. The surface ECG reflects both the electrical activity arising
from the patient's heart 33 and the pacing artifacts arising from
the pacemaker 35. The SCG/ECG system 32 can detect and distinguish
both sensed and paced cardiac events. Paced cardiac events
typically generate a narrow pulse artifact on the surface ECG of
the patient. Pacing may also cause inversion of the associated
physiologic wave form. Therefore, it is preferred to use ECG "QRS"
detection algorithms that recognize narrow pacing artifacts and
that recognize negative going and positive going physiologic wave
forms. While any of a variety of well known techniques can be used
to achieve this result, it is preferred to discriminate the atrial
and ventricular pacing artifacts based upon their high slew rate
and to recognize physiologic wave forms based upon the absolute
value of their amplitudes rather than the sign of their
amplitudes.
[0034] The SCG/ECG system 32 may be coupled to the pacemaker
programmer 41 through a data link 30, which permits the system 32
to receive marker channel diagnostic telemetry from the implanted
pacemaker 35. Diagnostic telemetry permits the pacemaker programmer
41 to access near real time sensing and pacing information from the
implanted pacemaker 35. Examples of such cardiac events include the
occurrence of atrial events, both sense (AS) and pace (AP), and
ventricular events, both sense (VS) and pace (VP).
[0035] The SCG/ECG system 32 also collects real time SCG data from
a suitable seismic sensor 40, which is placed upon the patient's
chest 34. The seismocardiogram reflects accelerations of the
patient's heart 33 walls during the cardiac cycle. The SCG/ECG
system 32 evaluates this input data and presents canonical wave
forms and other output data on a video display 43 and on a printer
44.
[0036] Suitable SCG/ECG systems 32 for carrying out the invention
are manufactured by Bard Electrophysiology of Lowell, Mass., GE
Medical Systems, or EPMED. The preferred instrument is a
multiple-channel electophysiological recording and analysis system
that can acquire physiological signals, i.e., surface and
intracardiac electrograms, hemodynamic data (e.g., arterial blood
pressure), as well as fluoroscopic, ultrasound, MIR and/or CT
images. These signals could be acquired in both analog and digital
format. The SCG signal would be acquired by the accelerometer (40)
and fed into the physiological system. The SCG signal would then be
processed by special computer algorithm and a series of hemodynamic
and electrophysiological parameters would be generated or
interpolated. For example, the patient's dp/dt (the rate of change
of the ventricular pressure) and ejection fraction (EF, an
indication of the ventricular function), etc. can be determined.
Essentially, one can calculate the dp/dt from a SCG signal of the
left ventricular pressure curve during the contraction using
previously developed algorithms. For the EF, a value could be
interpolated.
[0037] Thus, to evaluate the effectiveness of pacing and assess the
optimal leads placement, baseline SCG parameters would be collected
and analyzed. Then the SCG parameters collected during pacing at
the testing sites would be collected and analyzed. The change of
those key parameters will be served as a Stoke Index to determine
the optimal pacing site and/or settings (e.g., A-V or right
ventricle to left ventricle interval delay).
[0038] In addition, real time baseline SCG parameters, i.e. PEP,
LVET, PEP/LVET, also could be displayed and analyzed. The real time
data could be stored as a template for comparisons later. Then the
set of real time-time SCG parameters could be collected and
compared with the template and the changes of those parameters and
the correlation coefficient, r, could be generated. Based on the
magnitude of the changes of the SCG parameters and the correlation
coefficient, the optimal site of the leads placement could be
determined.
[0039] Any apparatus capable of carrying out the process of the
invention may be used. An example of how the method of the
invention can be practiced is shown in FIG. 3.
[0040] Process 50 involves initializing the pacemaker and requires
selection of an initial candidate A-V delay interval. It is
preferred to have this value and subsequent values set by a
physician through the use of a pacemaker programmer 41. However,
process 50 may be performed automatically by the pacemaker, or
invoked by the SCG/ECG system through the data link 30.
[0041] The preferred method for carrying out process 50 is
illustrated in the pacemaker marker channel telemetry wave form 10
(FIG. 1), which shows A-V sequential pacing (DVI) of the patient's
heart at a rate above the patient's intrinsic rate. The V-V lower
rate escape interval 19 selected for the patient and the A-V delay
interval 18 are shown in the telemetry wave form 10. Consecutive
lower rate escapes result in a sequence of paced beats depicted in
the telemetry wave form 10, while the response of the heart 33 to
this pacing regime is shown in the canonical ECG wave form 12. The
corresponding motion of the heart is depicted in the canonical SCG
wave form 14, while the corresponding state of the heart valves are
set forth in the heart pictograph panel 16.
[0042] More specifically, an initial atrial pace (AP) event is
shown as atrial pace event 13 in wave form 12 and as atrial pace
event 11 in wave form 10. The atrial sequential pacing regime also
gives rise to the ventricular pace event (VP) shown in wave form 12
as ventricular pace event 15 and shown in wave form 10 as
ventricular pace event 17. This ventricular pace event occurs after
the programmed A-V delay interval 18 shown in the telemetry wave
form 10. A second set of atrial pace events 20 and 22 are shown
with corresponding ventricular pace events 21 and 23 in FIG. 1.
[0043] Although the pacing modality and range of pacing rates may
be varied, the purpose of this process 50 is to generate a sequence
of ventricularly paced events. Preferred pacing rates range from
about 60 bpm to about 115 bpm (that latter rate would be
appropriate during exercise). For each given pacing rate, the A-V
delay interval 18 may be varied from a nominal minimum value of
less than about 100 ms to a nominal maximum value of approximately
250 ms. As would be recognized by one skilled in the art, the
pacing rate must be faster than the intrinsic heart rate of the
patient. Otherwise, one sees no paced beats if the pacemaker is set
in inhibited mode or some beats if it is not. Also, the pacemaker
may be set to pace the atrium, but with a shorter A-V delay than
normal for the patient so that the ventricles are paced and
captured.
[0044] Process 51 represents the collection of real time ECG data
from the electrode array 37,38, 39 and the collection of real time
SCG data from the seismic sensor 40. After appropriate isolation,
these real time signals are bandpass filtered in process 52 to
eliminate noise. The filtering and scaling functions of process 52
may be carried out in analog hardware as taught by the incorporated
references or in the digital domain by a dedicated processor or
other software forming a part of the SCG/ECG instrument 32. It has
been determined that the low frequency cutoff is the most important
bandpass characteristic for the real time signals and the lowest
possible low frequency corner is preferred for both ECG and SCG
signals.
[0045] Process 53 completes digitization of the ECG and SCG real
time signals and generates a pair of data sets, referred to as the
SCG data set and the ECG data set. The temporal relationship
between these two data sets is preserved during processing and the
SCG data and ECG data sets may be considered "companions."
Typically, subsequent software processes will generate pointers
from the ECG data set to point into the companion SCG data set to
collect segments of the companion SCG data for further
analysis.
[0046] In process 54, the ECG data set is analyzed to find the
location of the QRS complexes. The algorithm must detect naturally
occurring depolarization as well as paced complexes from unipolar
and bipolar pacers. At present, the preferred detection rule looks
for the high amplitude rapid rise time pacemaker artifact to
identify ventricular and atrial paced events, although other
detection techniques may be freely substituted without departing
from the scope of the invention. The principle purpose of this
process is to find the QRS reference point to facilitate further
analysis of the SCG data.
[0047] In optional process 55, a rhythm analysis is performed on
the ECG data set based upon the locations of the QRS complexes in
the ECG data. The primary purpose of the rhythm analysis of the ECG
data is to exclude those segments of the companion SCG data from
further processing which arise from electrically abnormal heart
beats. This process is skewed toward over exclusion of beats to
prevent corruption of the canonical SCG wave form. Reference may be
had to the incorporated references for details on a suitable
exclusion rhythm analysis process. However, it should be understood
that there is great flexibility in carrying out this process. Also,
many patients do not exhibit premature ventricular beats (PVCs)
when paced above their intrinsic rate. This step may be used
optionally, and the exemplary data shown in FIG. 4 was not
submitted to rhythm analysis.
[0048] In optional process 56, the rhythm analysis of process 55 is
used to point into the companion SCG data set to select segments of
the companion SCG data for further processing. The selected SCG
data is referred to as the "reduced SCG data set." The primary
purpose of this optional process is to exclude non-sinus, non-paced
beats from further analysis, because such data would otherwise
frustrate the development of the canonical SCG.
[0049] In process 57, the location of the QRS complex is used to
define a set of fiducial points which are transferred into the SCG
data set. These fiducial points are used to break the SCG data into
"wavelets."
[0050] In process 58, the instantaneous heart rate is used to
define a set number of comparison points and to define a comparison
window. It is preferred to set the comparison window to eighty
percent of this measured heart rate interval, and to use
approximately one hundred comparison points.
[0051] In process 59, the SCG data set is broken into comparable
wavelets by applying the comparison points defined in process 58
about the fiducial points defined in process 57. In general, the
fiducial point defines the origin for the distribution of the set
of comparison points. It is preferred to distribute twenty percent
of the comparison points to the SCG data collected prior to the QRS
fiducial point and to apply eighty percent of the comparison points
to the SCG data set collected after the QRS fiducial point. The
application of comparison points in this process permits SCG
wavelets recorded at different heart rates to be compared to each
other without introducing rate induced distortions in the SCG
morphology. The purpose of this process is to segment the SCG data
set into comparable wavelets for subsequent cross-correlation.
[0052] In process 60, the individual wavelets are cross-correlated
to ascertain the degree of similarity. Each wavelet is sequentially
compared with all other wavelets. Those wavelets with a correlation
coefficient of 0.9 or greater are grouped into one family. At the
conclusion of the iterative cross-correlation, there is typically
one dominant family with usually ninety percent or more of all the
wavelets. If a dominant family of highly self-similar wavelets
emerges, it is presumed that preceding processes have eliminated
bad data from the analysis.
[0053] In process 62, the corresponding and complimentary or
companion ECG data are also added or averaged together to form a
canonical ECG wave form shown in FIG. 1 as wave form 12 and in FIG.
4 as wave form 77. Thus, FIG. 1 and FIG. 4 represent processed data
and is not a representation of any particular real time wave
forms.
[0054] In process 63, certain events are extracted from the
canonical ECG data set. Referring back to FIG. 1, the underlying
electrical events in the heart give rise to certain repetitive
features which can be identified in the surface ECG shown as the
canonical wave form 12. The atrial paced event 13 gives rise to the
atrial depolarization of the heart shown as "P-wave" 80 in wave
form 12. The subsequent ventricular paced event 15 generates the
QRS complex, which includes the Q-wave 81, the R-wave 82, and the
S-wave 83. The repolarization of the ventricular tissues give rise
to the T-wave 79 feature in the wave form 12. A morphology
detection algorithm is applied to the ECG data set to extract the
R-wave 82 and the pacing spike associated with ventricular paced
event 15. Peak/valley decision rules are applied to the digitized
ECG data set. This "reduced data set" is evaluated for both the
Q-wave and T-wave locations for individual heart beat cycles. The
location of the Q-wave 81, and the (VP) ventricular paced event 15
are used in the subsequent resynchronization process, but addition
events may be useful for further analysis of the canonical SCG
waveform.
[0055] In process 64, certain repetitive features from the SCG
recording are extracted. These events are identified on FIG. 1 by
two-letter codes as follows: AS (atrial systole) event 91, MC
(mitral closure) event 92, IM (isometric contraction) event 93, AO
(aortic opening) event 94, RE (rapid emptying) event 96, AC (aortic
closure) event 97, MO (mitral opening) event 98, and RF (rapid
filling) event 99. These features of the canonical SCG wave form 14
have been related to underlying mechanical motions of the heart.
The AS event corresponds to peak atrial systole as shown by heart
pictograph 90. The AO event 94 corresponds to the opening of the
aortic valve as seen in heart pictograph 87. The AC event 97
corresponds to the aortic valve closure as seen in heart pictograph
88. The MC event 92 correspond to the mitral valve closure as seen
in heart pictograph 86.
[0056] Therefore, the ventricular heart beat cycle begins with the
ventricular paced event 15, which causes a contraction of the
ventricles as indicated by the Q-wave 81. After a brief
electromechanical delay, 85, the SCG wave from 14 shows the MC
event 92. The time interval from mitral valve closure as indicated
by MC event 92 and the opening of the aortic valve as indicated by
AO event 94 is an isometric contraction phase contained in the
pre-ejection period shown as PEP 24 in FIG. 1. The systolic phase
of the heart extends from the MC event 92 to the AC event, which
indicates aortic valve closure.
[0057] The conclusion of the systole and the beginning of the
diastole is reflected by the aortic valve closure point indicated
by AC event 97, and this phase of the heart cycle extends to the
next mitral valve closure point indicated as MC event 84.
[0058] Identification of these wave form features is done based
upon slope and amplitude information. The preferred decision rules
applied to the representative wave forms are set forth as
follow:
[0059] The MC event is the first peak occurring in time after the
peak of the ECG R-wave;
[0060] The AO event is the first valley after the MC;
[0061] The RE event is the next peak after the AO;
[0062] The AC event is the first peak after the end of the ECG
T-wave;
[0063] The MO event point is taken as the second valley following
the AC event;
[0064] The RF event is the next peak after the MO; and
[0065] The AS event is taken as the last peak before the onset of
the Q-wave in the ECG.
[0066] It should be noted that T-waves are notoriously hard to
locate due to the slow slope and low amplitude. In the absence of
successful T-wave detection based upon slope information, the
approximate T-wave position is defined based on measured QRS to QRS
interval and the corresponding AC location is interpolated and
defined as a result.
[0067] In process 65, time intervals are computed based upon the
identified points. For example, the time interval 24 between the MC
event 92 and the AO event 94 is measured and defined as the
pre-ejection period. The time interval between the AO event 94 and
the AC event 97 is measured and taken as the left ventricular
ejection time. The specific interval measured relate to the
specific index of cardiac performance that is selected for
optimization.
[0068] In process 66, the preferred index of cardiac performance is
the ratio of the pre-ejection period (PEP) to the left ventricular
ejection time (LVET), which may be expressed as (PEP/LVET). For
example, the maximum cardiac output at any given heart rate is
maximized by the A-V delay interval which minimizes the ratio of
the pre-ejection period to the left ventricular ejection time and
optimization of this ratio is desirable. It appears that the
maximization of the LVET is more important than minimization of PEP
for most pacemaker patients. Similarly, other indexes of cardiac
performance can be defined including: ((Q to MC)/LVET) and ((VP to
MC)/LVET). These non-traditional measures may be better indicators
of cardiac performance for some pacemaker patients.
[0069] These ratios involve pacing events that are readily detected
and include electrical and electromechanical delay components. It
should be recognized that the normal sinus depolarization of the
heart has a different activation sequence than a paced beat, and
measured PEP may vary between paced and sinus beats. For this
reason, it may be preferable to optimize A-V delay based upon one
of these non-traditional indices of cardiac performance.
Consequently, although the preferred ratio of PEP to LVET is
described in detail, the methods of the present invention may be
extended to these and other non-traditional indices of cardiac
performance.
[0070] In process 67, the lead placement and pacemaker settings
that result in optimal resynchronization are determined. To provide
a method for screening CRT candidates, SCG data is acquired from
patients who have benefitted from CRT and compared to data from
those who have not. For placement of pacemaker leads, the physician
looks for an optimum location of leads, e.g., one that gives a
global minimum for the ratios of PEP/LVET. Other parameters may be
discovered during electrophysiological studies that are better
indicators of CRT success for certain patients.
[0071] FIG. 4 is broken into panels that represent hard copy output
45 from printer 44. The upper panel 70 represents the canonical SCG
and ECG waveforms annotated with SCG and ECG event locations. The
table 72 of FIG. 4 shows the A-V delay intervals set and the
corresponding time interval measurements along with computed
ratios.
[0072] Process 67 selects the minimum value for the ratio of
PEP/LVET and places the asterisk 74 in the table 72 to indicate the
global minimum. This value can be considered by the physician and
programmed into the pacemaker via the pacemaker programmer 41, or
the value can be automatically selected and transmitted to the
pacemaker programmer 41 via data link 30, to automatically program
the pacemaker 35 to this value.
[0073] FIG. 5 schematically illustrates the optimal lead placement
method for cardiac resynchronization. The system that accomplishes
the method of the invention consists of the following components:
an accelerometer sensor, pacing leads and a programmable electrical
simulator (pacemaker), a computer analysis module, which includes
unique algorithm that calculates numerous parameters during the
cardiac cycle (including but not limited to duration of presystolic
period, duration and pattern of ventricular ejection and diastolic
relaxation period), and a computerized 2D and 3D display which
includes ventricular contraction mapping that represents details of
ventricular contraction.
[0074] The pacing leads are generally first placed at the right
ventricular apex and left ventricular posterior or lateral wall
through the coronary sinus. Next, a seismographic signal is
obtained from an accelerometer that is placed on the chest of a
patient and is processed by a computer algorithm. The results of
this seismographic signal is analyzed and displayed as a
ventricular contraction map with multiple parameters including the
pre-ejection period, the duration of systole and the duration of
isometric diastolic period as well as other parameters. Comparing
these hemodynamic parameters during pacing with those during
non-pacing (as well as at different pacing sites) will enable the
physician to determine the best pacing site(s) and to screen
candidates for CRT.
[0075] The present invention should provide data at the time of the
pacing implant procedure to achieve the best resynchronization for
left or biventricular pacing therapy. Numerous studies have
reported that most patients with congestive heart failure, who have
left bundle brunch block and QRS duration of greater than 130 ms,
can be markedly improved by CRT accomplished by left ventricular or
biventricular pacing. In addition, the selection of patients who
would benefit and the results of the procedure should be greatly
improved if the best pacing site(s) could be determined at the time
of implantation. If it is found that synchronization therapy will
also provide therapeutic benefit for patients with right bundle
branch block, this invention could also be applied to these
patients.
[0076] Three recently published reviews provide background
information about resynchronization therapy for the treatment of
congestive heart failure in a select group of patients. Dr. William
Abraham in "Reviews of Clinical trails and Criteria for Identifying
the Appropriate Patient," 2003 Vol. 4 (Supplement 2): S30-S37
reviewed the clinical trials that evaluated this treatment for
heart failure. A total of 12 clinical trials has been completed or
is still enrolling patients. The criteria for enrollment are
generally patients who are in New York Heart Association function
class 2-4 congestive heart failure, who have a QRS duration of
greater than or equal to 120 ms (normal less than 100 ms), and who
are in sinus rhythm. Most patients suffer from intraventricular
conduction delay or left bundle branch block. Relatively few
patients evaluated for this therapy are in atrial fibrillation or
have right bundle branch block. These studies have shown the
results of cardiac resynchronization therapy include an improvement
of quality of life score, an increase in functional class, an
increase in distance walked in six minutes, and an increase in peak
oxygen consumption during exercise. Furthermore, one trial, "the
Companion Trial," was powered and did show a decrease in all cause
mortality and hospitalization.
[0077] However, most studies have shown that approximately 30% of
patients identified by the above criteria do not obtain any
measurable benefit from this therapy. Therefore, this represents a
challenge. The lack of benefit may be due to lack of precision in
selection criteria and/or lack of identification of the optimal
pacing site or sites. A review by David A Cass "Ventricular
Resynchronization: Pathophysiology and Identification of
Responders" in "Reviews in Cardiovascular Medicine" 2003: Vol. 4
(Supplement 2: S3-S13) noted that QRS duration does not
consistently narrow after biventricular pacing with many subjects
displaying no change or even widening of the QRS duration.
[0078] Thus, QRS duration is at best an indirect correlation of
mechanical desynchronization which is the real substrate that
causes a decline in chamber function. Therefore, data have
confirmed the initial results showing a general correlation between
the basal QRS duration with efficacy of biventricular pacing but
with a poor predictive value for identifying responders versus
non-responders. The ability to predict responders is not yet clear.
However, among the factors that are being considered and evaluated
primarily by echocardiography include the interventricular
dyssynchrony, the intraventricular dyssynchrony, successful lead
placement, adequate pre-excitation, and physiological
atrial-ventricular delay. Cass reviewed the data in the literature
that show that a greater than 22% improvement in the maximum rise
in left ventricular pressure (dp/dt max) acutely has been
associated with consistent responders with few false negatives.
Intraventricular delay appears to be more important than
interventricular delay for defining responders. Intraventricular
conduction delay may cause mechanical dispersion of motion between
the septal and lateral walls. The most common means of detecting
this is by echocardiography. Various techniques using
echocardiography have been utilized including M-mode echo imaging
and various tissue Doppler imaging techniques to detect and
quantitate dyssynchrony. Although these techniques may be useful in
helping to identify patients who may benefit from cardiac
resynchronization therapy, these techniques have not been evaluated
on a large scale to assess the percentage of patients who will
benefit from cardiac resynchronization therapy.
[0079] In addition, echo evaluation is difficult if not impractical
to assess the site of optimal lead placement at the time of the
procedure for inserting the leads. As noted in the Review article
by Sululdie T. B., Henein N. Y. and Surton R. A Pacing and Heart
Failure: Patient and Pacing Mode Selection, European Heart Journal
2003, Vol. 24 pp. 977-986, the aim of the biventricular pacing or
ventricular resynchronization therapy is to optimize segmental
electrical excitation, timing of contraction, relaxation and
consequently cycle efficiency and that is the aim of the present
invention. Sulukhe et al. reviewed data from a retrospective study
that attempted to identify predictors of responders to
biventricular pacing. There was no significant difference between
the left ventricular lead position sites between the responders and
the non-responders, but there was a trend toward a greater number
of lateral and anterior left ventricular sites in patients whose
symptoms and exercise tolerance improved.
[0080] Nevertheless, there has not been a study in which the
optimal pacing sites have been compared at the time of implantation
since there has not been a practical way of identifying optimal
resynchronization at the time of the implant procedure. It is
recognized that there are technical difficulties in positioning the
pacing lead in the left ventricle by the coronary vein sine optimal
sites may not always be accessible and are limited by venous
anatomy by current lead placement technology. However, there are
recent advances in lead placement technology including
over-the-wire techniques and other methods that may permit greater
flexibility in positioning the coronary sinus lead.
[0081] Once again, an aim of the current invention is to obtain
patterns of chest wall motion that reflect cardiac
desynchronization to help select patients who may benefit from this
procedure and, at the time of lead placement, to identify the
optimal lead site that will accomplish this. Data that will also be
collected to help identify the effect of different AV delays on
identifying optimal patters of optimal cardiac efficiency and
output. These and other parameters can be assessed, including
changes in the interventricular conduction delay. Additional
parameters that can be assessed by the present invention are the
duration of the pre-ejection period, the possible presence of
mitral regurgitation as it affects the pre-ejection period, the
rate of rise of the left ventricular ejection as determined by the
accelerometer, the duration of systole, the rate of decrease of
deceleration after peak acceleration and peak systole, the duration
of systole, and the duration diastole.
[0082] Various changes in the details and components that have been
described may be made by those skilled in the art within the
principles and scope of the invention described in the
specification and defined in the appended claims. Therefore, while
the present invention has been shown and described herein in what
is believed to be the most practical and preferred embodiments, it
is recognized that departures can be made within the scope of the
invention, which is not to be limited to the details disclosed
herein but is to be accorded the full scope of the claims so as to
embrace all equivalent processes and products.
* * * * *