U.S. patent application number 09/799710 was filed with the patent office on 2001-07-26 for four-chamber pacing system for optimizing cardiac output and determining heart condition.
This patent application is currently assigned to Medtronic, Inc.. Invention is credited to Bakels, Arnoldus, de Roos, Cobus, Leinders, Robert.
Application Number | 20010010009 09/799710 |
Document ID | / |
Family ID | 25536141 |
Filed Date | 2001-07-26 |
United States Patent
Application |
20010010009 |
Kind Code |
A1 |
Bakels, Arnoldus ; et
al. |
July 26, 2001 |
Four-chamber pacing system for optimizing cardiac output and
determining heart condition
Abstract
A pacing system and method for providing multiple chamber pacing
of a patient's heart, and in particular, pacing programmed for
treatment of various forms of heart failure. The system utilizes
impedance sensing for determining optimum pacing parameters, e.g.,
for pacing the left ventricle so that left heart output is
maximized. The impedance sensing also is used for determination of
arrhythmias or progression of heart failure. Impedance sensing is
provided for between selected pairs of the four chambers, to enable
optimizing of information for control and diagnosis. In a preferred
embodiment/of the invention, impedance measurements are obtained
for determining the timing of right heart valve closure or right
ventricular contractions, and the timing of delivery of left
ventricular pace pulses is adjusted so as to optimally synchronize
left ventricular pacing with the right ventricular contractions.
Impedance sensing in the left heart also provides timing of
mechanical contraction, and the pacemaker controls pacing to
maintain bi-ventricular mechanical synchronization adjusted for
maximum cardiac output.
Inventors: |
Bakels, Arnoldus;
(Simpelveld, NL) ; Leinders, Robert; (Limbricht,
NL) ; de Roos, Cobus; (Landgraaf, NL) |
Correspondence
Address: |
Thomas F. Woods
Medtronic, Inc., MS 301
710 Medtronic Parkway NE
Minneapolis
MN
55432
US
|
Assignee: |
Medtronic, Inc.
|
Family ID: |
25536141 |
Appl. No.: |
09/799710 |
Filed: |
March 7, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09799710 |
Mar 7, 2001 |
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08990427 |
Dec 15, 1997 |
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6070100 |
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Current U.S.
Class: |
607/9 |
Current CPC
Class: |
A61N 1/36521 20130101;
A61N 1/3622 20130101; A61N 1/368 20130101; A61N 1/3682 20130101;
A61N 1/3627 20130101 |
Class at
Publication: |
607/9 |
International
Class: |
A61N 001/362 |
Claims
1. A pacing system for providing pacing of a patient's left heart,
comprising: first means for obtaining indications of mechanical
contractions of the right ventricle; left ventricular pacing means
for pacing the left ventricle; and LV control means for controlling
the timing of said left ventricular pacing relative to indicated
right ventricular mechanical contractions:
2. The pacing system as described in claim 1, comprising second
means for obtaining indications of mechanical contractions of the
left ventricle, and wherein said LV control means has means for
controlling the timing of said left ventricular pacing so as to
provide substantially synchronous left and right ventricular
mechanical contractions.
3. The pacing system as described in claim 1, wherein said LV
control means has means for delivering a left ventricular pacing
pulse just before the expected time of the next right ventricular
mechanical contraction.
4. The pacing system as described in claim 2, comprising left
atrial pacing means for pacing the patient's left atrium; left AV
control means for controlling the left AV delay between pacing the
left atrium and the left ventricle, cardiac output means for
measuring left heart output as a function of said left AV delay,
and wherein said left AV control means further comprises maximizing
means for adjusting said left AV delay to maximize left cardiac
output.
5. The pacing system as described in claim 4, comprising means for
sensing sinus signals, and left atrial timing means for timing
delivery of left atrial pacing pulses relative to said sinus
signals.
6. The system as described in claim 1, wherein said first means
comprises an impedance measuring circuit for obtaining an impedance
signal representative of impedance between the patient's right
atrium and right ventricle, and processing means for processing
said impedance signal to determine the timing of right heart valve
closures.
7. The system as described in claim 1, comprising second impedance
means for obtaining a left impedance signal representative of
impedance change over the patient's left heart, and second
processing means for processing said left impedance signal to
obtain a measure of left heart output.
8. The system as described in claim 7, comprising third processing
means for processing said left impedance signal to obtain filling
signals indicative of the filling of the left ventricle, and
wherein said LV control means comprises means for controlling
timing of said left ventricular pacing signals as a function of
said filling signals.
9. The system as described in claim 1, further comprising means for
obtaining indications of left ventricular mechanical contractions,
and wherein said LV control means comprises mechanical sync means
for controlling said left ventricular pacing to achieve mechanical
synchrony of said left and right mechanical contractions.
10. The system as described in claim 9, wherein said mechanical
sync means comprises adjusting means for adjusting the timing of
aid left ventricular pacing so as to maximize left heart
output.
11. A four-chamber pacing system for providing pacing of a
patient's left heart to improve cardiac output, comprising: RV
means for determining the timing of right ventricular mechanical
contractions; LV means for determining the timing of left
ventricular mechanical contractions; and pacing sync means for
pacing the patient's left ventricle; and control means for
controlling said pacing means so as to substantially synchronize
said left and right mechanical contractions;
12. The four-chamber pacing system as described in claim 13,
comprising: LA means for determining the timing of left atrial
depolarization; CO means for measuring cardiac output from the
patient's left heart; and wherein said control sync means comprises
LAVD means for controlling said pacing means to deliver pacing
pulses to said patient's left ventricle at a left atrio-ventricular
delay following left atrial depolarizations, and adjusting means
for adjusting said left atrio-ventricular delay to correspond to
maximum measured cardiac output.
13. A system for bi-ventricular pacing, comprising: RVP generating
means for generating and delivering pacing pulses to the patient's
right ventricle; LVP generating means for generating and delivering
pacing pulses to the patient's left ventricle; atrial sense means
for determining the cyclical time of excitation of the patient's
right and left atria; RAVD control means for controlling said RVP
generating means to deliver pace pulses at a predetermined RAVD
delay following right atrial activation; LAVD control means for
controlling said LVP generating means to generate pace pulses at an
LAVD delay following left atrial activation; output means for
determining a measure of cardiac output from the patient's left
ventricle; adjusting means for adjusting said LAVD and RAVD delays
and determining the optimum relationship of said LAVD and RAVD
delays which results in maximized cardiac output; and program means
for programming said RAVD control means and said LAVD control means
to control delivery of pacing pulses to the left and right
ventricles with said optimum relation.
14. The system as described in claim 13, comprising second
adjusting means for adjusting said LAVD and RAVD equally, and
wherein said output means obtains values of LAVD and RAVD
corresponding to maximum cardiac output and wherein said program
means controls said RAVD control means and said LAVD control means
to deliver pacing pulses with said values.
15. The system as described in claim 14, comprising means for
obtaining the difference between LMAVD and RMAVD corresponding to
optimized cardiac output, and means for maintaining said
difference.
16. A method of cardiac pacing, comprising: cyclically determining
mechanical events indicative of left ventricular contraction and
right ventricular contraction; cyclically determining cardiac
output from the patient's left ventricle; pacing said patient's
left ventricle with varying timing relative to said right
ventricular contractions and determining the relative mechanical
synchronization of left ventricular and right ventricular
contractions which results in maximum cardiac output; and
maintaining said relative mechanical synchronization.
17. A method as described in claim 16, comprising: determining
atrial excitations of the patient; controlling delivery of each
left ventricular pace pulse at an LAVD delay following each said
atrial excitation; and adjusting said LAVD to obtain said relative
mechanical synchronization for optimum cardiac output.
18. The method as described in claim 16, comprising pacing the
patient's right ventricle at an RAVD delay a following said atrial
excitation, and controlling said RAVD and LAVD delays to maintain
said relative mechanical synchronization.
19. The method as described in claim 17, comprising.
20. A method of bi-ventricular pacing, comprising sensing sinus
signals from the patient's right atrium; cyclically generating and
delivering left and right ventricular pace pulses for pacing the
patient's left and right ventricles respectively; cyclically
determining a measure of cardiac output from the patient's left
ventricle; and adjusting the relative timing of said left and right
ventricular pace pulses to correspond to maximum cardiac
output.
21. The method as described in claim 20, comprising sensing
patient-sinus signals, timing out an LAVD delay between a sensed
sinus signal and delivery of the left ventricular pace pulse and an
RAVD delay between a sensed sinus signal and delivery of a right
ventricular pace pulse, varying said LAVD delay relative to said
RAVD delay, and determining the relationship between said LAVD
delay and said RAVD delay which results in said maximum cardiac
output.
22. The method as described in claim 21, having electrodes
positioned in each of a patient's four heart chambers, comprising
further adjusting both said LAVD and RAVD delays by equal amounts
and determining the values of said delays corresponding to maximum
cardiac output.
23. A four chamber pacing system, having electrodes positioned in
each of a patient's four heart chambers, comprising: impedance
means for obtaining impedance measurements between a selected pair
of said four chambers; processing means for processing said
impedance measurements, and determining changes in said
measurements over a period of time; and determining means for
determining whether any said change occurs which indicates a
physically abnormal heart condition.
24. The system as described in claim 22, wherein said determining
means determines whether any such change occurs which is indicative
of an arrhythmia.
25. The system as described in claim 22, wherein said determining
means comprises means for determining whether said any such change
occurs which indicates a heart failure condition.
26. The system as described in claim 22, comprising programmable
selection means for selecting impedance measurements between any
two of said four heart chambers.
Description
FIELD OF THE INVENTION
[0001] This invention relates to cardiac pacing systems and, more
particularly, to four-chamber pacing systems with sensors for
measuring cardiac mechanical characteristics so as to improve
cardiac output for congestive heart failure and other patients.
BACKGROUND OF THE INVENTION
[0002] Congestive heart failure (CHF) is defined generally as the
inability of the heart to deliver enough blood to the peripheral
tissues to meet metabolic demands. Frequently CHF is manifested by
left heart dysfunction, but it can have a variety of sources. For
example, CHF patients may have any one of several different
conduction defects. The natural electrical activation system
through the heart involves sequential events starting with the
sino-atrial (SA) node, and continuing through the atrial conduction
pathways of Bachmann's bundle and internodal tracts at the atrial
level, followed by the atrio-ventricular (AV) node, Common Bundle
of His, right and left bundle branches, and final distribution to
the distal myocardial terminals via the Purkinje fiber network. A
common type of intra-atrial conduction defect is known as
intra-atrial block (IAB), a condition where the atrial activation
is delayed in getting from the right atrium to the left atrium. In
left bundle branch block (LBBB) and right bundle branch block
(RBBB), the activation signals are not conducted in a normal
fashion along the right or left bundle branches respectively. Thus,
in a patient with bundle branch block, the activation of the
ventricle is slowed, and the QRS is seen to widen due to the
increased time for the activation to traverse the conduction
path.
[0003] CHF manifested by such conduction defects and/or other
cardiomyopathies are the object of considerable research into
treatments for improving cardiac output. For example, drug
companies have recognized CHF as a market opportunity, and are
conducting extensive clinical studies organized to test the outcome
of newly developed drugs in terms of improving cardiac performance
in these patients. Likewise, it is known generally that
four-chamber cardiac pacing is feasible, and can provide
significant improvement for patients having left atrial-ventricular
dysfunction, or other forms of cardiac heart failure. While there
has been relatively little commercialization of four-chamber
pacing, the hypothesis remains that cardiac pump function can
clearly be improved by such pacing.
[0004] The benefits of four-chamber pacing generally have been
disclosed and published in the literature. Cazeau et al., PACE,
Vol. 17, November 1994, Part II, pp. 1974-1979, disclose
investigations leading to the conclusion that four-chamber pacing
is feasible, and that in patients with evidence of interventricular
dyssynchrony, a better mechanical activation process can be
obtained by resynchronizing depolarization of the right and left
ventricles, and optimizing the AV sequence on both sides of the
heart. In the patent literature, U.S. Pat. No. 4,928,688 is
representative of a system for simultaneous left ventricular (LV)
and right ventricular (RV) pacing; natural ventricular
depolarizations are sensed in both chambers, if one chamber
contracts but the other one does not within a window of up to 5-10
ms, then the non-contracting ventricular chamber is paced.
[0005] In addition to the above-mentioned disclosures concerning
the advantages of substantially simultaneous or synchronous pacing
of the two ventricles, it is known that there is an advantage to
synchronous pacing of the left atrium and the right atrium for
patients with IAB, inter-atrial block. In a normal heart, atrial
activation initiates with the SA node, located in the right atrial
wall. In a patient with IAB, the activation is slow being
transferred over to the left atrium, and as a result the left
atrium may be triggered to contract up to 90 ms later than the
right atrium. It can be seen that if contractions in the left
ventricle and the right ventricle are about the same time, then
left AV synchrony is way off, with the left ventricle not having
adequate time to fill up. The advantage of synchronous pacing of
the two atria for patients with IAB is disclosed at AHA 1991,
Abstract from 64th Scientific Sessions, "Simultaneous Dual Atrium
Pacing in High Degree Inter-Atrial Blocks: Hemodynamic Results,"
Daubert et al., No. 1804. Further, it is known that patients with
IAB are susceptible to retrograde activation of the left atrium,
with resulting atrial tachycardia. Atrial resynchronization through
pacing of the atria can be effective in treating the situation.
PACE, Vol. 14, April 1991, Part II, p. 648, "Prevention of Atrial
Tachyarrythmias Related to Inter-Atrial Block By Permanent Atrial
Resynchronization," Mabo et al., No. 122. For patients with this
condition, a criterion for pacing is to deliver a left atrial
stimulus before the natural depolarization arrives in the left
atrium.
[0006] In view of the published literature, it is observed that in
CHF patients improved pump function can be achieved by increasing
the filling time of the left ventricle, i.e., improving the left AV
delay, and specifically the left heart mechanical AV delay (MAVD);
decreasing mitral valve regurgitation, (back flow of blood through
the nearly closed valve) by triggering contraction of the left
ventricle when and as it becomes filled; and normalizing the left
ventricular activation pattern, i.e., the time sequence of left
atrial contraction relative to right atrial contraction. More
specifically, for a cardiac pacing system used for treating a CHF
patient, the aim is to capture the left atrium; optimize the left
AV delay so as to properly fill the left ventricle and provide a
more normal AV delay; and activate the left ventricle as much as
possible in accordance with the natural propagation path of a
healthy left heart. Particularly, left ventricular timing with
respect to the left atrial contraction is crucial for improving
cardiac output. The mechanical closure point of the left, or mitral
valve, is a crucial moment which needs to be adjusted by
programming of the left AV delay. Correct programming of this
variable is key for optimizing the filling of the left ventricle,
and optimizing ejection fraction, or cardiac output (CO).
[0007] An observation which is important to this invention is that
the exact timing of mechanical events are important for properly
controlling pacing so as to optimize left ventricular output.
Specifically, it is known that actual contraction of one
ventricular chamber before the other has the effect of moving the
septum so as to impair full contraction in the later activated
chamber. Thus, while concurrent or simultaneous pacing of the left
and right ventricle may achieve a significant improvement for CHF
patients, it is an aim of this invention to provide for pacing of
the two ventricles in such a manner that the actual mechanical
contraction of the left ventricle, with the consequent closing of
the valve, occurs in a desired time relationship with respect to
the mechanical contraction of the right ventricle and closing of
the right value. For example, if conduction paths in the left
ventricle are impaired, delivering a pacing stimulus to the left
ventricle at precisely the same time as to the right ventricle may
nonetheless result in left ventricular contraction being slightly
delayed with respect to the right ventricular contraction. As a
consequence, it is important for this invention to provide a
technique for measurement of mechanical events, such as a
mechanical closure point of each of the ventricles, so as to be
able to accurately program the sequence of pacing to achieve the
desired dual ventricular pacing which optimizes ejection fraction,
or cardiac output, for the individual patient.
[0008] In view of the above-noted importance of measuring
mechanical events, such as mitral or tricuspid valve closure, and
the importance of measuring cardiac output, it is necessary for the
pacing system of this invention to employ sensors which can provide
this information. It is known to use impedance sensors in pacing
systems, for obtaining information concerning cardiac function. For
example, reference is made to U.S. Pat. No. 5,501,702, incorporated
herein by reference, which discloses making impedance measurements
from different electrode combinations. In such system, a plurality
of pace/sense electrodes are disposed at respective locations, and
different impedance measurements are made on a time/multiplexing
basis. As set forth in the referenced patent, the measurement of
the impedance present between two or more sensing locations is
referred to "rheography." A rheographic, or impedance measurement
involves delivering a constant current pulse between two "source"
electrodes, such that the current is conducted through some region
of the patient's tissue, and then measuring the voltage
differential between two "recording" electrodes to determine the
impedance therebetween, the voltage differential arising from the
conduction of the current pulse through the tissue or fluid between
the two recording electrodes. The referenced patent discloses using
rheography for measuring changes in the patient's thoracic cavity;
respiration rate; pre-ejection interval; stroke volume; and heart
tissue contractility. It is also known to use this technique of
four point impedance measurements, applied thoracically, for
measuring small impedance changes during the cardiac cycle, and
extracting the first time derivative of the impedance change,
dZ/dt. It has been found that a substantially linear relation
exists between peak dZ/dt and peak cardiac ejection rate, providing
the basis for obtaining a measure of cardiac output. See also U.S.
Pat. No. 4,303,075, disclosing a system for measuring impedance
between a pair of electrodes connected to or in proximity with the
heart, and processing the variations of sensed impedance to develop
a measure of stroke volume. The AV delay is then adjusted in an
effort to maximize the stroke volume.
[0009] Given the demonstrated feasibility of four-chamber cardiac
pacing, and the availability of techniques for sensing natural
cardiac signals and mechanical events, there nonetheless remains a
need for developing a system which is adapted to the cardiac
condition of a patient with CHF, so as to provide pacing sequences
which are tuned for improving cardiac output, and in particular for
improving left heart function. It is a premise of this invention
that such a system is founded upon accurate measurements of
mechanical events, and use of the timing of such mechanical events
to control and program pacing sequences.
SUMMARY OF THE INVENTION
[0010] It is an overall object of this invention to provide a
pacing system for multiple chamber pacing, and in particular, for
pacing the patient's left heart in coordination with the electrical
activation and mechanical events of the patient's right heart, so
as to optimize left heart output. In accordance with this
invention, there is provided a four-chamber pacing system, having
leads carrying electrodes positioned for pacing and sensing in or
on each of the four cardiac chambers. Additionally, the leads are
connected to obtain impedance measurements from which accurate
timing signals are obtained reflecting mechanical actions, e.g.,
valve closures, so that accurate timing information is available
for controlling electrical activation and resultant mechanical
responses for the respective different chambers. The impedance or
mechanical sensing determinations are preferably made by
multi-plexing through fast switching networks to obtain the desired
impedance measurements in different chambers.
[0011] In a preferred embodiment, control of four-chamber pacing,
and in particular left heart pacing, is based primarily upon
initial detection of a spontaneous signal in the right atrium, and
upon sensing of mechanical contraction of the right and left
ventricles. In a heart with normal right heart function, the right
mechanical AV delay is monitored to provide the timing between the
initial sensing of right atrial activation (P-wave) and right
ventricular mechanical contraction. The left heart is controlled to
provide pacing which results in left ventricular mechanical
contraction in a desired time relation to the right mechanical
contraction; e.g., either simultaneous or just preceding the right
mechanical contraction; cardiac output is monitored through
impedance measurements, and left ventricular pacing is timed to
maximize cardiac output. In patients with intra-atrial block, the
left atrium is paced in advance of spontaneous depolarization, and
the left AV delay is adjusted so that the mechanical contractions
of the left ventricle are timed for optimized cardiac output from
the left ventricle.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a schematic representation of a system in
accordance with this invention, whereby four bipolar leads are
provided, the leads being shown carrying bipolar electrodes
positioned in each of the respective cardiac chambers.
[0013] FIG. 2A is a block diagram of a four channel pacing system
in accordance with this invention, for pacing and sensing in each
ventricle, and for obtaining impedance signals from the left heart
and the right heart;
[0014] FIG. 2B is a schematic representation of an arrangement in
accordance with this invention for detecting left ventricular
impedance for determination of cardiac output.
[0015] FIG. 3 is a block diagram of a four-chamber pacemaker with
the ability to time multiplex impedance measurements, in accordance
with this invention.
[0016] FIG. 4 is a block diagram of a system implementation in
accordance with an embodiment of this invention for controlling
left ventricular pacing in a patient with LBBB.
[0017] FIG. 5 is a flow diagram for a system implementation in
accordance with an embodiment of this invention, for controlling
left atrial and ventricular pacing in a patient with IAB.
[0018] FIG. 6 is a flow diagram of a routine in accordance with
this invention for optimizing bi-ventricular pacing to provide
maximum cardiac output.
[0019] FIG. 7 is a block schematic of a pacemaker in accordance
with this invention for providing selectable four-chamber pacing
and cardiac signal sensing, as well as impedance sensing between
selected combinations of the four heart chambers.
[0020] FIG. 8A is a flow diagram of a process using inter-atrial or
inter-ventricular impedance measurements for determination of
existence of arrhythmias;
[0021] FIG. 8B is a flow diagram illustrating a procedure for
obtaining atrio-ventricular cross-impedance measurements for
obtaining indications of heart failure.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] In the description of the preferred embodiments, and with
reference to the drawings, the following designations are used:
1 DRAWING DESIGNATION DEFINITION RA right atrium RV right ventricle
RH RA and RV LH LA and LV LA left atrium LV left ventricle LAS left
atrial sense RAS right atrial sense LAP left atrial pace pulse LVP
left ventricular pace pulse RMAVD time interval between RAS and
mechanical contraction of RV (as measured, e.g., by valve closure)
LMAVD time interval between LAS or LAP and mechanical contraction
of LV RAVD time interval between RAS and QRS in RV LAVD time
interval between LAS or LAP, and QRS in LV
[0023] Referring now to FIG. 1, there is shown a schematic
representation of a four-chamber pacing system, illustrating four
pacing leads providing bipolar electrodes positioned for pacing and
sensing in each of the respective heart chambers, and also for
impedance measurements. Pacing lead 38 is positioned conventionally
such that its distal end is in the right ventricular apex position.
It carries bipolar electrodes 38a and 38b adapted for pacing and
sensing; additionally, these electrodes can also be used for
impedance sensing as discussed below. Likewise, atrial lead 36 is
positioned so that its distal end is positioned within the right
atrium, with bipolar electrodes 36a, 36b. Lead 34 is passed through
the right atrium, so that its distal end is positioned in the
coronary sinus for pacing, sensing and impedance detection through
electrodes 34a, b, as shown. Likewise, lead 32 is positioned via
the coronary sinus a cardiac vein, e.g., the middle or great
cardiac vein, so that distal electrodes 32a and 32b are positioned
approximately as shown for pacing, sensing and impedance detection
with respect to the left ventricle. The pacing leads are connected
to pacemaker 30 in a conventional manner. It is to be understood
that each of the four leads can have one or more additional
electrodes; however, by using time multiplexing techniques as
discussed below and in the referenced U.S. Pat. No. 5,501,702,
pacing, sensing and impedance detection can be accomplished with
only two electrodes per lead. Referring now to FIGS. 2A and 2B,
there is shown a simplified block diagram of a four channel
pacemaker in accordance with this invention, having the additional
capability of impedance detection to sense valve movement of the
left and right ventricles. Although discussion of FIG. 2A is
presented with respect to valve movement, it is to be understood
that the impedance detection scheme may be altered to detect other
mechanical events, such as ventricular wall contraction, in a known
manner.
[0024] The system of FIG. 2A contains, in the pacemaker, a central
processing block 40, indicated as including timing circuitry and a
microprocessor, for carrying out logical steps in analyzing
received signals, determining when pace pulses should be initiated,
etc., in a well known fashion. Referring to the upper left-hand
corner of the block diagram, there is shown signal amplifier
circuitry 41, for receiving a signal from the right atrium.
Electrode 36a is illustrated as providing an input, it being
understood that the second input is received either from bipolar
electrode 36b, or via an indifferent electrode (the pacemaker can)
in the event of unipolar sensing. Likewise, a pulse generator 42,
acting under control of block 40, generates right atrial pace
pulses for delivery to electrode 36a and either electrode 36b or
system ground. In a similar manner, right ventricular pace pulses
(RVP) are generated at output stage 43 and connected to electrode
38a, and sensed right ventricular signals are inputted to sense
circuitry 44, the output of which is delivered to control block 40.
Also illustrated is impedance detector 45, which receives inputs
from electrodes 36a, 38a, for delivering information corresponding
to right heart valve closure, which timing information is inputted
into control block 40. Thus, the system enables pacing and sensing
in each chamber, as well as impedance detection to provide an
indication of the timing of right heart valve closure, which
represents the time of mechanical contraction of the right
valve.
[0025] Still referring to FIG. 2A, there are shown complementary
circuit components for the left atrium and the left ventricle.
Output generator stage 47, under control of block 40, delivers left
atrial pace pulses (LAP) to stimulate the left atrium through
electrode 34a and either electrode 34b or system ground. Inputs
from the left atrial lead are connected through input circuitry 46,
the output of which is connected through to control block 40. In a
similar fashion, output stage 48, under control of block 40,
provides left ventricular stimulus pace pulses (LVP) which are
delivered across electrode 32a and either electrode 32b or system
ground; and left ventricular signals are sensed from lead 32 and
inputted to input circuit 49, which provides an output to block 40
indicative of left ventricular signals. Also, dual inputs from the
left atrial electrode 34a and left ventricular electrode 32a are
inputted into left heart impedance detector 50, which provides
timing pulses to block 40 indicative of the timing of left heart
(mitral) valve closure. With this arrangement, the pacemaker has
the basic timing and cardiac signal information required to program
delivery of pace pulses to respective heart chambers in accordance
with this invention. Block 40 contains current generators for use
in impedance detection; microprocessor or other logic and timing
circuitry; and suitable memory for storing data and control
routines.
[0026] Referring to FIG. 2B, there is shown a diagrammatic sketch
of an arrangement for detecting left ventricular impedance change,
which is processed in block 40 to obtain an indication of cardiac
output. As shown, a current source 52 provides a constant current
source across electrode 53 in the right atrium, which suitably can
be electrode 36a; and right ventricular electrode 54, which
suitably can be electrode 38a. The current source can be pulsed, or
it can be multiplexed in a manner as discussed below. Impedance
sensors 57 and 58 provide signals representative of impedance
changes therebetween, the impedance being a function of blood
volume and valve closure, as discussed above. The outputs from
electrodes 57, 58 is connected across impedance detector 56, which
represents the microprocessor and/or other processing circuitry in
block 40 for analyzing the impedance changes and making a
determination of cardiac output. As is known, a measure of cardiac
output can be obtained by extracting the first time derivative of
cyclical impedance changes, dz/dt; a linear relationship exists
between peak dz/dt and peak ejection rate.
[0027] Referring now to FIG. 3, there is shown a block diagram of a
pacemaker 30 in accordance with a preferred embodiment of this
invention, for multiplexing connections to electrodes so as to
provide for pacing and sensing in any one of the four cardiac
chambers, as well as for impedance determinations between
respective different lead electrodes. Reference is made U.S. Pat.
No. 5,501,702, incorporated herein by reference, for a full
discussion of this circuit, and in particular the multiplexing
arrangement carried out by switch matrices 68, 70. The pacemaker 30
operates under control of circuitry 62, which may include a
microprocessor or custom integrated circuitry, as well as
associated memory, in a manner well known in the pacemaker art.
Circuitry 62 provides for processing of data, and generation of
timing signals as required. Control circuitry 62 is coupled to
pace/sense circuitry 64, for processing of signals indicating the
detection of electrical cardiac events, e.g., P-waves, R-waves,
etc. sensed from conductors which connect electrically to
electrodes 32a-38b, as shown. The aforementioned leads are also
coupled to a first switch matrix 68 and a second switch matrix 70.
Matrix 68 establishes a selectable interconnection between specific
ones of the electrodes of leads 32, 34, 36 and 38, and the current
source 72, is controlled by circuit 62. In a similar manner, switch
matrix 70 establishes a selectable interconnection between lead
conductors corresponding to selected electrodes, and impedance
detection circuit 74, for the purpose of selecting impedance
measurements. Still referring to FIG. 3, current source 72 receives
control signals on line 73 from circuitry 62, and is responsive
thereto for delivering constant current rheography pulses onto lead
conductors selected by switching matrix 68, which in turn is
switched by signals on bus 83. Impedance detection circuit 74 is
adapted to monitor the voltage between a selected pair of
electrodes which pair is selectably coupled by operation of switch
matrix 70 which in turn is switched by signals on bus 80. In this
manner, circuit 74 determines the voltage, and hence the impedance,
existing between two selected electrodes. The output of circuitry
74 is connected through A/D converter 76 to control circuitry 62,
for processing of the impedance signals and determination of the
occurrence of mechanical events, such as left or right heart valve
closure. The control of switch matrix 68 through signals on bus 78,
and the control of switch matrix 70 through signals on bus 80,
provides for multiplexing of different impedance signals.
[0028] It is to be understood that in the system arrangement of
FIG. 3, pace/sense circuitry 64 may include separate stimulus pulse
output stages for each channel, i.e., each of the four-chambers,
each of which output stages is particularly adapted for generating
signals of the programmed signal strength. Likewise, the sense
circuitry of block 64 may contain a separate sense amplifier and
processor circuitry for sensed signals from each chamber, such that
sensing of respective wave portions, such as the P-wave, R-wave,
T-wave, etc. from the RH and the LH, can be optimized. The pulse
generator circuits and sense circuits as used herein are well known
in the pacemaker art. In addition, other functions may be carried
out by the control circuitry including standard pacemaker functions
such as compiling of diagnostic data, mode switching, etc.
[0029] Referring now to FIG. 4, there is shown a logic control flow
diagram for controlling the system of this invention to pace a
patient with LBBB. The assumption is that the RH is normal, and
that sinus signals from the SA node are being normally conducted to
the LA; but that the LBBB is manifested by slow conduction to the
LV, such that the LV does not contract when it should. As a
consequence, there is mitral regurgitation, or backflow of blood
through the valve because the LV does not contract when it is
filled from the LA; and the contraction of the LV, when it occurs,
is later than that of the RV, further contributing to decrease of
LH output.
[0030] As seen at 101, the pacemaker monitors the RH, and gets a
measure of RMAV. This is done by sensing right valve closure
through RH impedance measurement, and timing the delay from the
atrial depolarization (RAS) to valve closure. Then, at 102, the
pacemaker is controlled to pace LV with an LAVD such that LMAVD is
about equal to RMAVD. During this step, impedance measurements are
made in the LV, and a measure of LMAVD is obtained. Based on this
determination, the value of LAVD is adjusted to substantially match
LMAVD with RMAVD. Note that normal conduction through the LV takes
on the order of 50-60 ms, so it is expected that the LV should be
paced in advance of the occurrence of RV valve closure, so that LV
valve closure occurs at about the same time as, or even a bit
before RV valve closure. Causing the LV to contract just before the
RV might provide an increase of LH output which outweighs the small
resulting RV dysfunction due to the septum being pulled toward the
LV first. Thus, the timing of delivery of each LVP is adjusted to
set LMAVD approximately equal to RMAVD. Then, at 104, the value of
LAVD is further adjusted, while R and L valve closure is monitored,
and LMAVD is adjusted relative to RMAVD. This adjustment, or
variation of LMAVD, may be made by incrementally changing LAVD each
cycle, or each n cycles, to scan relative to the value of RMAVD.
Cardiac output is obtained through a left heart impedance
measurement, and appropriate signal processing, for each setting of
the differential between the right and left valve closures, and
respective values of CO and LMAVD are stored at 105. The highest,
or maximum value of cardiac output is determined, and LAVD is set
so that the resultant MLAVD is at the differential compared to
RMAVD to yield the highest cardiac output. In this manner, the
timing of left ventricular pace pulses is set to produce
substantial bi-ventricular mechanical synchronization for the
greatest cardiac output. The determined value of LAVD and the
corresponding LV-RV difference is stored.
[0031] Still referring to FIG. 4, at 106 the pacemaker proceeds to
pace the LV with this established value of LAVD, providing
mechanical synchronization. Of course, if the natural sinus rate
varies, the pacemaker wants to follow; if the spontaneous RAVD
varies, but the LAVD doesn't follow the change, the mechanical
synchronization will be lost. Accordingly, at 107 the pacer
monitors the natural sinus rate, or atrial pacing rate, and
determines if there has been a significant change in atrial rate.
If yes, at 109, the pacer adjusts LAVD accordingly to maintain
mechanical sync for optimum output. Although not shown, the
pacemaker can periodically go back to block 101 to re-determine the
desired value of LAVD.
[0032] Referring now to FIG. 5, there is shown a flow diagram for
pacing of a patient with IAB; such patient may have LBBB as well.
Here, it is necessary to take control of the LA by pacing before
atrial depolarization is conducted (late) to the LA. At 110, the
pacemaker monitors the pattern of LA depolarization relative to RA
depolarization, i.e., it determines the inter-atrial delay. At 111,
it is determined whether the LA should be paced, based on the
atrial depolarization pattern. If yes, the pacemaker sets an RA-LA
delay at 112, which corresponds to a healthy heart, and which
enables capture of the LA. At 114, the value of RMAVD is obtained,
as was described in connection with FIG. 4. Then, at 116, LAVD is
determined for a first setting of mechanical sync; this can be done
by setting LAVD to produce LV contraction at the same time as RV
contraction (valve closure), or earlier by a small time increment.
Then, LAVD is varied, as shown at 117, and LMAVD and CO are
determined corresponding to each value of LAVD. The value of LAVD
is set to that value which corresponds to maximum cardiac output,
and this value and the LV-RV mechanical relation, or mechanical
sync value is stored for the chosen LAVD. At 118, the pacemaker
paces LA and LV, in accord with the values that have been
determined. In the event of significant change in atrial rate, LAVD
is adjusted to compensate for the rate change, and to substantially
maintain the LV-RV mechanical relationship previously found to
correspond to maximum cardiac output, as shown at 120, 121.
Although not shown, in the event of large changes in the sinus
rate, or passage of a predetermined amount of time, determination
of inter-atrial delay and LAVD can be repeated automatically.
[0033] Referring now to FIG. 6, there is shown a simplified flow
diagram for a procedure in accordance with this invention for
carrying out bi-ventricular pacing so as to maximize cardiac output
(CO). This routine is adapted for patients who need right
ventricular pacing, and who can benefit from synchronous left
ventricular pacing as well. In this example, it is assumed that
atrial pacing is not required, but if the patient requires atrial
pacing, the routine can be adapted appropriately.
[0034] At block 130, a common value of AV delay (AVD) is first set.
At block 132, both the left ventricle and the right ventricle are
paced, initially with the previously set value of AVD, but then
with a varying AVD. As AVD is varied, or scanned relative to the
initial setting, the pacemaker makes determinations of cardiac
output by processing impedance signals from the left heart, or left
ventricle, in the manner discussed above. Values of CO are stored
together with the different values of AVD, and the optimum value of
a common AVD is determined corresponding to maximum CO. Then, at
block 134, the value of LAVD is varied relative to RAVD, such that
the left pacing pulse is delivered at differing times from the
right pacing pulse. It is to be remembered, as discussed above,
that for maximum cardiac output, it may be desirable to pace the
left ventricle shortly before the right ventricle, and this step is
a searching step to determine the time relationship between the two
ventricular pace pulses which results in the best cardiac output.
CO is determined as the ventricular sync relationship is varied,
and the corresponding optimum LAVD is determined. When this has
been obtained, the routine goes to block 136 and paces the patient
at the determined values of LAVD and RAVD. Periodically, as
indicated at 138, the pacemaker can determine whether a test is
desired. If yes, the routine branches back to 130, to loop through
the test and redetermine the optimum values of LAVD and RAVD. It is
to be noted that the steps of blocks 132 and 134 can be done in a
reverse sequence, i.e., step 134 first and then step 132.
[0035] Referring now to FIG. 7, there is shown an alternate block
diagram of component portions of a pacemaker in accordance with
this invention, for providing maximum flexibility in terms of
pacing, cardiac signal sensing and impedance sensing. At least two
electrodes are positioned in or proximate to each heart chamber, in
the manner as discussed above in connection with FIG. 1, and
connected in turn to block 150. As indicated in FIG. 7, block 150
is an output/input switch matrix, and interconnects with block 152
in the manner as described in FIG. 3. Thus, block 152 provides
pacing pulses which can be connected through matrix 150 to each of
the four chambers, and has sense amplifier circuitry for sensing
signals from each of the four chambers. Block 150 further provides
a multiplex switch array for switching a current source across
selected pairs of the eight electrodes for impedance measuring
purposes, again in accordance with the discussion of FIG. 3. The
sensed impedance signals are suitably transferred from array 150 to
digital signal processing circuitry 161, which is part of block
152. Block 152 is in two-way connection with the timing modules
shown in block 154, for timing generation of pace pulses, current
source pulses, and the generation of sensing windows. Blocks 150,
152 and 154 are further inter-connected by control bus 163. Data is
transferred between signal processing block 170 and block 154
across data bus 157. Block 154 in turn is inter-connected with
microprocessor 156, through household bus 151, data bus 153 and
control bus 154. By this arrangement, impedance sensing can be
carried out across any combination of the four heart chambers,
e.g., right atrium vs. left atrium; right ventricle vs. left
ventricle; right atrium vs. left ventricle; and left atrium vs.
right ventricle. Impedance measurements between these combinations
of chambers can be carried out in accordance with this invention,
for purposes of analyzing and confirming arrhythmias, including
fibrillation. Further, changes in conduction patterns, as seen in
the morphology of such impedance measurements, can be monitored and
processed for making determinations of progression of heart
failure. Thus, cross-measurements of RA-LV and LA-RV can be useful
in obtaining histories to determine changes indicating progression
of heart failure.
[0036] Referring now to FIG. 8A, at block 160, the pacemaker first
obtains impedance measurements either between LA and RA, or between
LV and RV. These impedance values are processed at 162, and at 164
a determination is made as to whether the atrial or ventricular
rhythms are regular or non-physiological. This determination can be
made, for example, simply by sensing differences over time and
comparing such differences to predetermined criteria. If a rhythm
is determined not to be regular, then a determination of arrhythmia
is made at 166. A suitable response is made at 168. Referring to
FIG. 8B, at block 170 the pacemaker obtains cross-measurements of
impedances, e.g., between RA and LV or between LA and RV. These
measurements are stored and processed as indicated at 172, and
evaluated at 174 to determined whether they indicate HF or
progression toward HF. If yes, an appropriate response can be made,
illustrated at 176, e.g., providing a warning which can be
retrieved by an external programmer.
[0037] The scope of the invention extends to other conditions of
CHF, in addition to the ones illustrated here. In each case, the
condition of the patient must be responded to on an individual
basis. However, in accordance with this invention, the system
response includes a determination of mechanical events, e.g., valve
closure, preferably in each side of the heart, and programming of
pacing escape intervals based on consideration of the mechanical
events and a determination of variations of cardiac output with
variations of LAVD and/or mechanical ventricular synchronization.
The system of this invention can be used in an implanted pacemaker
system; or, the system procedures can be carried out with an
external system, for determination of optimum programming of a
pacemaker which is to be implanted or re-programmed.
* * * * *