U.S. patent application number 12/603829 was filed with the patent office on 2010-02-18 for system and method for evaluating and optimizing the contribution of particular heart chambers to the overall efficacy of cardiac pacing therapy.
Invention is credited to Taraneh Ghaffari Farazi, Euljoon Park.
Application Number | 20100042173 12/603829 |
Document ID | / |
Family ID | 41681789 |
Filed Date | 2010-02-18 |
United States Patent
Application |
20100042173 |
Kind Code |
A1 |
Farazi; Taraneh Ghaffari ;
et al. |
February 18, 2010 |
SYSTEM AND METHOD FOR EVALUATING AND OPTIMIZING THE CONTRIBUTION OF
PARTICULAR HEART CHAMBERS TO THE OVERALL EFFICACY OF CARDIAC PACING
THERAPY
Abstract
Techniques are provided for evaluating and optimizing the
contribution of particular heart chambers to pacing efficacy.
Briefly, a pacemaker temporarily alters the mode with which pacing
therapy is delivered so as to selectively alter the heart chambers
that are paced. The pacemaker detects any transient changes in
pacing efficacy following the alteration in pacing mode. The
pacemaker then assesses the contribution of particular heart
chambers to pacing efficacy based on the alteration in the pacing
mode and on any transient changes in the pacing efficacy.
Additionally, techniques are provided herein for automatically
adjusting pacing parameters to optimize the contribution of
particular chambers to pacing efficacy.
Inventors: |
Farazi; Taraneh Ghaffari;
(San Jose, CA) ; Park; Euljoon; (Valencia,
CA) |
Correspondence
Address: |
STEVEN M MITCHELL;PACESETTER INC
701 EAST EVELYN AVENUE
SUNNYVALE
CA
94086
US
|
Family ID: |
41681789 |
Appl. No.: |
12/603829 |
Filed: |
October 22, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11330885 |
Jan 11, 2006 |
|
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12603829 |
|
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Current U.S.
Class: |
607/18 ; 607/17;
607/27 |
Current CPC
Class: |
A61N 1/368 20130101;
A61N 1/3684 20130101; A61N 1/3627 20130101; A61N 1/3688
20130101 |
Class at
Publication: |
607/18 ; 607/27;
607/17 |
International
Class: |
A61N 1/368 20060101
A61N001/368; A61N 1/08 20060101 A61N001/08; A61N 1/365 20060101
A61N001/365 |
Claims
1. A system for use with an implantable cardiac stimulation device
equipped to deliver pacing therapy to the heart of a patient in
which the device is implanted, the system comprising: a pacing
controller operative to control the delivery of pacing therapy; and
a heart chamber contribution evaluation unit operative to evaluate
the contribution of a particular heart chamber to the overall
efficacy of pacing therapy based on a temporary alteration in
pacing mode and based on any transient changes in the efficacy of
the pacing therapy following the alteration in pacing mode.
2. The system of claim 1 wherein the heart chamber contribution
evaluation unit includes: a pacing mode temporary adjustment unit
operative to temporarily alter the pacing mode with which pacing
therapy is delivered, the pacing mode specifying which chambers are
paced; a pacing efficacy detector operative to detect transient
changes in the efficacy of pacing therapy following the alteration
in pacing mode; and a heart chamber contribution determination unit
operative to determine the contribution of the particular heart
chamber to the overall efficacy of pacing therapy based on the
alteration in pacing mode and based on the transient changes in the
effectiveness of the pacing therapy.
3. The system of claim 1 wherein pacing therapy is controlled by
the pacing controller subject to one or more pacing parameters that
affect the efficacy of pacing therapy and wherein the system
further includes a heart chamber contribution optimization unit
operative to adjust the pacing parameters based on the contribution
of the particular heart chamber to pacing efficacy.
4. The system of claim 1 further comprising a diagnostic controller
operative to record diagnostic information indicative of the
contribution of the particular heart chamber to the overall
efficacy of pacing therapy.
5. The system of claim 1 further comprising a tracking unit
operative to track changes over time in the contribution of the
particular heart chamber to the overall efficacy of pacing
therapy.
6. The system of claim 1 further comprising an internal warning
device operative to generate warning signals if the contribution of
the particular heart chamber to the overall efficacy of pacing
therapy falls below a predetermined minimum acceptable amount.
7. The system of claim 2 wherein the pacing mode temporary
adjustment unit is operative to temporarily alter the pacing mode
by switching between a biventricular pacing mode and a
monoventricular pacing mode.
8. The system of claim 2 wherein the pacing mode temporary
adjustment unit is operative to temporarily alter the pacing mode
by switching between a dual-chambered pacing mode, wherein pacing
is performed in both the atria and ventricles, and a
non-dual-chambered pacing mode, wherein pacing is exclusively
performed in either the atria or the ventricles.
9. The system of claim 2 wherein the pacing mode temporary
adjustment unit is operative to temporarily alter the pacing mode
by switching among any of: AAI; VVI; DDD; DDI; VDD; and VOO pacing
modes.
10. The system of claim 2 wherein the pacing mode temporary
adjustment unit is operative to temporarily alter the pacing mode
for a duration in the range of two to sixty seconds.
11. The system of claim 2 wherein the pacing efficacy detector is
operative to detect signals representative of one or more of:
morphological features of an intracardiac electrogram (IEGM); blood
oxygen saturation; blood pressure; contractility; stroke volume;
cardiac output; and a heart output pulse waveform.
12. The system of claim 11 wherein the pacing efficacy detector is
operative to detect transient changes in the peak amplitude of the
signals.
13. The system of claim 3 wherein the pacing parameters include one
or more of: an atrioventricular (A-V) delay; an inter-ventricular
(V-V) delay; and an inter-atrial (A-A) delay.
14. The system of claim 3 wherein the heart chamber contribution
optimization system is operative to adjust the pacing parameters to
increase the contribution of the particular heart chamber to the
overall efficacy of pacing therapy.
15. The system of claim 14 wherein the heart chamber contribution
optimization unit is operative to adjust the pacing parameters to
maximize the contribution of the particular heart chamber.
16. The system of claim 3 wherein the heart chamber contribution
optimization unit is operative to adjust the pacing parameters to
decrease the contribution of the particular heart chamber to the
overall efficacy of pacing therapy.
17. A system for adjusting pacing parameters used in delivering
cardiac pacing therapy to the heart of a patient in which an
implantable cardiac stimulation device is implanted, the system
comprising: means for temporarily altering a pacing mode with which
pacing therapy is delivered, the pacing mode specifying which
chambers are paced; means for detecting any transient changes in
the efficacy of pacing therapy following the temporary alteration
in pacing mode; and means for evaluating the contribution of a
particular heart chamber to the overall efficacy of pacing therapy
based on any transient changes in the efficacy of the pacing
therapy following an alteration in pacing mode.
18. The system of claim 17 further comprising: means for
controlling pacing therapy by using one or more pacing parameters
that affect the efficacy of pacing therapy; and means for adjusting
the pacing parameters based on the contribution of the particular
heart chamber to pacing efficacy.
19. The system of claim 1 further comprising means for recording
diagnostic information indicative of the contribution of the
particular heart chamber to the overall efficacy of pacing
therapy.
20. The system of claim 1 further comprising means for generating
warning signals if the contribution of the particular heart chamber
to the overall efficacy of pacing therapy falls below a
predetermined minimum acceptable amount.
Description
RELATED APPLICATION
[0001] The following is a divisional application of and claims
priority and other benefits from U.S. patent application Ser. No.
11/330,885, filed Jan. 11, 2006, entitled "SYSTEM AND METHOD FOR
EVALUATING AND OPTIMIZING THE CONTRIBUTION OF PARTICULAR HEART
CHAMBERS TO THE OVERALL EFFICACY OF CARDIAC PACING
THERAPY,"incorporated herein by reference in its entirety.
FIELD OF THE INVENTION
[0002] The invention generally relates to implantable cardiac
stimulation devices for use in pacing the heart and in particular
to techniques for optimizing pacing parameters to improve pacing
efficacy.
BACKGROUND OF THE INVENTION
[0003] A pacemaker is an implantable cardiac stimulation device for
implant within a patient that analyzes an intracardiac electrogram
(IEGM) to detect various arrhythmias, such as an abnormally slow
heart rate (bradycardia) or an abnormally fast heart rate
(tachycardia), and then to selectively deliver electrical pacing
pulses to the heart in an effort to remedy the arrhythmias. An
implantable cardioverter-defibrillator (ICD) additionally or
alternatively detects atrial fibrillation (AF) or ventricular
fibrillation (VF) and delivers electrical shocks to terminate
fibrillation. For many patients, particularly those with congestive
heart failure (CHF), it is desirable to identify a set of control
parameters for controlling the operation of the pacemaker or ICD
that will optimize cardiac performance (also referred to as
hemodynamic performance). Cardiac performance is a measure of the
overall effectiveness of the cardiac system of a patient and is
typically represented in terms of stroke volume or cardiac output.
Stroke volume is the amount of blood ejected from the left
ventricle during systole in the forward direction. Cardiac output
is the volume of blood pumped by the left ventricle per minute
(i.e. stroke volume multiplied by the current heart rate of the
patient).
[0004] One particularly useful control parameter for optimizing
cardiac performance is the atrioventricular (A-V) pacing delay,
which for dual-chamber devices specifies the time delay between a
paced or sensed atrial event and a paced ventricular event. Another
useful control parameter is the inter-ventricular pacing delay
(V-V), which for biventricular pacing devices specifies the time
delay between a paced or sensed right ventricular (RV) event and a
paced left ventricular (LV) event. However, a wide variety of other
parameters also affect overall cardiac performance. Numerous
techniques have been developed for optimizing these and other
parameters so as to improve cardiac performance. See, for example,
U.S. patent application Ser. No. 11/366,930, of Muller et al.,
entitled "System and Method for Determining Atrioventricular Pacing
Delay Based on Atrial Repolarization," filed Mar. 1, 2006 (Atty.
Docket No. A06p1022); U.S. patent application Ser. No. 10/928,586,
of Bruhns et al., entitled "System and Method for Determining
Optimal Atrioventricular Delay based on Intrinsic Conduction
Delays", filed Aug. 27, 2004; U.S. patent application Ser. No.
11/231,081, of Turcott, entitled "System and Method for Rapid
Optimization of Control Parameters of an Implantable Cardiac
Stimulation Device", filed Sep. 19, 2005; and U.S. patent
application Ser. No. 11/199,619, of Gil et al., entitled "System
and Method for Determining Preferred Atrioventricular Pacing Delay
Values based on Intracardiac Electrogram Signals", filed Aug. 8,
2005.
[0005] Although an improvement in cardiac performance is often the
goal, pacing therapy may alternatively be delivered to achieve
other goals or to obtain other benefits. For example, for a patient
suffering from high blood pressure, pacing therapy may be delivered
so as to decrease blood pressure. If a patient is at risk of
certain arrhythmias, pacing therapy may be tailored so as to
decrease the risk of the arrhythmia. In one specific example,
wherein a patient is subject to atrial tachyarrhythmias, dynamic
atrial overdrive (DAO) pacing may be delivered so as to reduce the
risk of such arrhythmias. In still other examples, pacing therapy
is delivered so as to reduce the risk of VF. As can be appreciated,
a wide variety of pacing parameters may be selectively adjusted so
as to achieve a wide variety of goals. Hence, stated generally,
pacing parameters are preferably optimized to enhance overall
"pacing efficacy," where the efficacy of pacing is evaluated with
respect to the particular goal of the pacing regime. Numerous
techniques have been previously developed for use by implantable
medical devices to automatically adjust pacing parameters so as to
improve overall pacing efficacy within the context of specific
pacing regimes, such as the techniques of the patent applications
listed above.
[0006] Heretofore, however, it does not appear that many techniques
have been developed specifically for evaluating and optimizing the
contribution of particular chambers to pacing efficacy. That is,
predecessor techniques generally seek to determine pacing
parameters that will improve overall pacing efficacy without regard
to the specific contribution provided by particular heart chambers,
such as just the right atrial (RA) contribution or just the LV
contribution. By evaluating the contribution of particular chambers
to pacing efficacy, the device can provide diagnostic information
from which the physician can gain considerable insight into the
health of those chambers. Moreover, an evaluation of the
contribution of particular chambers to pacing efficacy can be
exploited by the device itself to enhance or optimize the
contribution of those chambers. In many cases, by optimizing the
contribution of particular chambers to pacing efficacy, the device
can thereby improve overall pacing efficacy so as to, for example,
improve overall cardiac performance. Accordingly, it would be
desirable to provide techniques for evaluating and optimizing the
contribution to pacing efficacy provided by particular heart
chambers. It is to this end that the invention is primarily
directed.
SUMMARY OF THE INVENTION
[0007] In accordance with the invention, techniques are provided
for evaluating and optimizing the contribution of particular
chambers to pacing efficacy. In one embodiment, the device
temporarily alters the pacing mode with which pacing therapy is
delivered, wherein the mode specifies which chambers of the heart
are paced. The device detects any transient changes in pacing
efficacy following the alteration in pacing mode. The device then
determines the contribution of particular heart chambers to the
pacing efficacy based on the alteration in pacing mode and on any
transient changes in pacing efficacy. For example, by temporarily
switching from biventricular pacing to RV-only pacing, the device
can evaluate the contribution of the LV to pacing efficacy. In this
regard, if there is little or no reduction in pacing efficacy
despite disabling LV pacing, then the LV contributes little to
pacing efficacy. In contrast, a significant reduction in pacing
efficacy following the switch to RV-only pacing is indicative of a
significant contribution of the LV to pacing efficacy. As another
example, by temporarily switching from dual-chamber pacing (i.e.
atrial and ventricular pacing) to ventricle-only pacing, the device
can evaluate the contribution of the atria to pacing efficacy.
Depending upon the particular goal of a pacing regime, the efficacy
of pacing therapy can be evaluated based on signals representative
of, e.g., blood oxygen saturation, blood pressure, contractility,
stroke volume, or cardiac output sensed via appropriate implanted
sensors or evaluated based on morphological features of the IEGM.
Diagnostic information indicative of the contribution of the
particular chambers to pacing efficacy is preferably stored within
the device for subsequent physician review. The degree of
contribution can also be compared against suitable thresholds
indicative of a minimum acceptable degree of chamber contribution,
with appropriate warning signals generated if the degree of
contribution falls below the threshold to thereby alert the patient
and/or physician.
[0008] In a preferred embodiment, the implantable device
additionally adjusts selected pacing parameters so as to optimize
the contribution of particular chambers. For example, during
dual-chamber pacing, the A-V delay can be adjusted so as to
optimize the contribution of the atria to pacing efficacy. As
another example, during biventricular pacing, the V-V delay can be
adjusted so as to optimize the LV contribution to pacing efficacy.
In many cases, optimizing the contribution of particular chambers
serves to improve overall pacing efficacy so as to, for example,
improve overall cardiac performance. Preferably, a given pacing
parameter is incrementally adjusted throughout a predetermined
range of acceptable values. The implantable device evaluates the
degree of contribution of selected heart chambers at each value of
the parameter. The implantable device then chooses the value of the
parameter that achieved the greatest degree of contribution for use
in further pacing so as to optimize the contribution of the
selected heart chambers. In one particular example, V-V delay
values are incrementally adjusted throughout a range of V-V values.
At each particular V-V value, the device temporarily switches from
biventricular pacing to RV-only pacing and then evaluates the
contribution of the LV to pacing efficacy at that particular V-V
value. The V-V value that yields the greatest contribution of the
LV to pacing efficacy is then selected for use in further
biventricular pacing. As another example, A-V delay values are
incrementally adjusted throughout a predetermined range of A-V
values. At each particular A-V value, the device temporarily
switches from dual-chamber pacing to ventricular-only pacing and
then evaluates the contribution of the atria to pacing efficacy at
that particular A-V value. The A-V value that yields the greatest
contribution of the atria to pacing efficacy is then selected for
use in further dual-chamber pacing.
[0009] Thus, techniques are provided for evaluating and optimizing
the contribution of particular chambers to pacing efficacy. Since
only a temporary alteration in pacing mode is needed to assess the
contribution of particular chambers, the technique can be
frequently performed by the device to assess chamber-specific
contributions and to adjust and optimize the pacing parameters
accordingly. Although the invention is advantageously implemented
with the implantable device itself, principles of the invention are
also applicable for use by external devices, such as external
programmers used in conjunction with implantable devices.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The above and further features, advantages and benefits of
the invention will be apparent upon consideration of the present
description taken in conjunction with the accompanying drawings, in
which:
[0011] FIG. 1 illustrates pertinent components of an implantable
medical system having a pacemaker or ICD equipped to evaluate and
optimize the contribution of particular heart chambers to pacing
efficacy;
[0012] FIG. 2 is a flow chart providing an overview of an exemplary
evaluation technique for use by the implantable system of FIG. 1
wherein transient changes in pacing efficacy are detected following
temporary changes in pacing mode;
[0013] FIG. 3 is a graph illustrating an exemplary pacing efficacy
curve and particularly illustrating a transient reduction in pacing
efficacy following a temporary change in pacing mode performed in
accordance with the technique of FIG. 2;
[0014] FIG. 4 is a flow chart illustrating an iterative
optimization technique performed in accordance with the general
evaluation technique of FIG. 2, wherein pacing parameters are
iteratively adjusted to optimize chamber-specific contributions to
pacing efficacy;
[0015] FIG. 5 is a flow chart illustrating a first exemplary
implementation of the iterative technique of FIG. 4, wherein an A-V
delay is iteratively adjusted to optimize the atrial contribution
to stroke volume during dual-chamber pacing;
[0016] FIG. 6 is a graph illustrating a set of exemplary stroke
volume curves and particularly illustrating transient reductions in
stroke volume following temporary changes from DDI to VVI pacing
performed in accordance with the iterative technique of FIG. 5;
[0017] FIG. 7 is a flow chart illustrating a second exemplary
implementation of the iterative technique of FIG. 4, wherein a V-V
delay is iteratively adjusted to optimize the LV contribution to
cardiac output during biventricular pacing;
[0018] FIG. 8 is a graph illustrating a set of exemplary cardiac
output curves and particularly illustrating transient reductions in
cardiac output following temporary changes from biventricular to
RV-only pacing performed in accordance with the technique of FIG.
7;
[0019] FIG. 9 is a simplified, partly cutaway view, illustrating
the pacer/ICD of FIG. 1 along with a set of exemplary leads
implanted in the heart of the patient; and
[0020] FIG. 10 is a functional block diagram of the pacer/ICD of
FIG. 9, illustrating basic circuit elements that provide
cardioversion, defibrillation and/or pacing stimulation in four
chambers of the heart and particularly illustrating components for
evaluating and optimizing heart chamber contributions to pacing
efficacy.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] The following description includes the best mode presently
contemplated for practicing the invention. This description is not
to be taken in a limiting sense but is made merely to describe
general principles of the invention. The scope of the invention
should be ascertained with reference to the issued claims. In the
description of the invention that follows, like numerals or
reference designators will be used to refer to like parts or
elements throughout.
Overview of Implantable Medical System
[0022] FIG. 1 illustrates an implantable medical system 8 having a
pacer/ICD 10 equipped to evaluate the contribution of particular
heart chambers to pacing efficacy, such as only the atrial
contribution or only the contribution of the RV. Depending upon the
goal of a particular pacing regime, the contribution to pacing
efficacy may be evaluated based on an analysis of IEGM signals
sensed via a set of pacing leads 12 or based on physiological
signals received from various sensors (not separately shown in FIG.
1.) Only a pair of leads is shown. A more complete set of
pacing/sensing leads is illustrated in FIG. 9 and is described
below. Once the contribution of the particular chamber or chambers
has been evaluated, pacing parameters are automatically adjusted by
pacer/ICD 10 so as to optimize the contribution of the particular
chambers. In many cases, optimizing the contribution of particular
chambers serves to enhance overall pacing efficacy to, e.g.,
improve overall cardiac performance. If the contribution of
particular chambers is found to be deficient, suitable warning
signals may be generated using an internal warning device 14, if
one is provided. Warning device 14 may be a vibrating device or a
"tickle" voltage device that, in either case, provides perceptible
stimulation to the patient to alert the patient. Tickle warning
device are discussed in U.S. Pat. No. 5,328,460 to Lord, et al.,
entitled "Implantable Medication Infusion Pump Including
Self-Contained Acoustic Fault Detection Apparatus." Warning signals
may additionally or alternatively be transmitted to a bedside
monitor 16, which generates audible or visual warnings. The bedside
monitor may be networked with other external systems so as to
automatically forward the warnings to a physician or other medical
professional. A system incorporating bedside monitoring units
connected to a centralized external programmer system is described
in U.S. Pat. No. 6,622,045 to Snell et al., "System and Method for
Remote Programming of Implantable Cardiac Stimulation Devices." In
this manner, if the contribution of a particular chamber, such as
the LV, is found to be deficient due to cardiomyopathy or other
ailments, the physician can be notified to take corrective
action.
[0023] Thus, FIG. 1 provides an overview of an implantable medical
system for evaluating and optimizing the contribution of particular
heart chambers to pacing efficacy. It should be appreciated that
systems provided in accordance with invention need not include all
of the components shown in FIG. 1. In many cases, for example, the
implantable system will include only the pacer/ICD and its leads
with no implantable warning device. The bedside monitor is
optional. No attempt is made herein to describe all possible
combinations of components that may be provided in accordance with
the general principles of the invention. Note also that, although
an internal signal transmission line interconnecting the pacer/ICD
and the implantable warning device is shown, wireless signal
transmission may alternatively be employed. In addition, the
particular size, shapes and implant locations of the various
components are merely illustrative and do not necessarily
correspond to the actual sizes, shapes and locations.
Overview of Heart Chamber Contribution Evaluation
[0024] FIG. 1 provides an overview of the evaluation technique
performed by the pacer/ICD of FIG.1 or other suitable device.
Initially, at step 100, the pacer/ICD temporarily alters the
current pacing mode. The pacing mode specifies, among other
attributes, which chambers of the heart are paced. Many such pacing
modes are specified by standard three letter codes such as: AAI;
VVI; DDD; DDI; VDD; and VOO. Briefly, the first letter of the code
designates which chamber is paced (A for atrium, V for ventricle, D
for both, and O for neither). The second letter designates which
chamber is sensed. The third letter designates what action is taken
in response to a sense (I for inhibiting delivery of a pacing
pulse, T for triggering a pacing pulse, D for both triggering and
inhibiting, depending upon the chamber, and O for no action). A
fourth letter R is sometimes appended to the code if a
rate-adaptive pacing mode is used.
[0025] Thus, by way of example, DDD indicates a pacing mode wherein
the pacer/ICD senses and paces in both the atria and the ventricles
and is also capable of both triggering and inhibiting functions
based upon events sensed in the atria and the ventricles. VDD
indicates a mode wherein the pacer/ICD senses in both the atria and
ventricles but only paces in the ventricles. A sensed event on the
atrial channel triggers ventricular outputs after a programmable
delay. VVI indicates that the pacer/ICD paces and senses only in
the ventricles and only inhibits the functions based upon events
sensed in the ventricles. DDI is identical to DDD except that the
pacer/ICD only inhibits functions based upon sensed events, rather
than triggering functions. As such, the DDI mode is a non-tracking
mode precluding triggering of ventricular outputs in response to
sensed atrial events. VOO identifies fixed-rate ventricular pacing,
which ignores any potentially sensed cardiac signals. This mode is
quite different from the aforementioned "demand" modes, which only
pace when the pacemaker determines that the heart is "demanding"
pacing. Other pacing modes are possible that are not necessarily
represented by three letter abbreviations of this type. For
example, if the pacer/ICD is equipped for biventricular pacing,
then the pacing mode may further specify whether pacing or sensing
is performed in the LV, the RV or both. Likewise, if the pacer/ICD
is equipped for biatrial pacing, then the pacing mode may further
specify whether pacing or sensing is performed in the RA, the left
atrium (LA) or both. As can be appreciated, numerous pacing modes
are possible and no attempt is made herein to list all such
modes.
[0026] The period of time during which the pacing mode is altered
may vary depending upon the particular pacing modes and the pacing
efficacy to be evaluated. Typically, however, the pacing mode is
temporarily altered for a period of between two and sixty seconds.
At step 102, the pacer/ICD detects transient changes in the
efficacy of pacing therapy following the alteration in pacing mode
at step 100. Pacing efficacy is defined with respect to the goal of
the pacing regime. For example, if pacing is performed so as to
increase cardiac performance, then an increase in cardiac
performance indicates an increase in pacing efficacy. The increase
in cardiac performance may be quantified using, e.g., stroke
volume, cardiac output, etc. In contrast, if pacing is performed so
as to affect a change in a particular morphological feature of the
IEGM, perhaps to reduce the risk of certain arrhythmias, then a
change in the amplitude of that morphological feature indicates an
increase in pacing efficacy. Hence, depending upon the
circumstances, any of a wide variety of parameters may be sensed to
provide an indication of pacing efficacy. Other examples include:
blood oxygen saturation, blood pressure, contractility, or the
shape of a heart output pulse waveform.
[0027] Techniques for evaluating morphological features of the IEGM
are described in: U.S. Pat. No. 5,779,645 to Olson, et al. entitled
"System and Method for Waveform Morphology Comparison" and U.S.
Pat. No. 6,516,219 to Street, entitled "Arrhythmia Forecasting
Based on Morphology Changes in Intracardiac Electrograms."
Techniques for detecting blood oxygen saturation using an
implantable medical device are described in: U.S. patent
application Ser. No. 11/378,604, of Kroll et al., filed Mar. 16,
2006, entitled, "System and Method for Detecting Arterial Blood
Pressure based on Aortic Electrical Resistance using an Implantable
Medical Device" (A05e1123). Techniques for detecting blood pressure
are described in: U.S. Pat. No. 5,615,684 to Hagel, et al.,
entitled "Medical Device for Detecting Hemodynamic Conditions of a
Heart" and U.S. Pat. No. 6,575,912 to Turcott, entitled "Assessing
Heart Failure Status Using Morphology of a Signal Representative of
Arterial Pulse Pressure." Techniques for detecting contractility
are described in: U.S. Pat. No. 5,800,467 to Park et al., entitled
"Cardio-Synchronous Impedance Measurement System for an Implantable
Stimulation Device." Techniques for detecting stroke volume and/or
cardiac output are described in U.S. patent application Ser. No.
11/267,665, filed Nov. 4, 2005, of Kil et al., entitled "System and
Method for Measuring Cardiac Output via Thermal Dilution using an
Implantable Medical Device with Thermistor Implanted in Right
Ventricle." The heart pulse output waveform may be sensed using an
implantable photoplethysmograph (PPG), which is an optical detector
that indicates the volume of blood in or passing through an area of
tissue. By placing the photoplethysmograph around an artery, the
pulse waveform can be detected and measured. Implantable PPG
devices are discussed, e.g., in U.S. Pat. No. 6,997,879 to Turcott,
entitled "Methods and Devices for Reduction of Motion-induced Noise
in Optical Vascular Plethysmography."
[0028] In many cases, multiple parameters may be combined to
provide a combined measure or "metric" of pacing efficacy.
Techniques for combining different parameters into a single metric
value for evaluation are set forth in U.S. Pat. No. 7,207,947 to
Koh et al., entitled "System and Method for Detecting Circadian
States Using an Implantable Medical Device", issued Apr. 24,
2007.
[0029] FIG. 3 illustrates exemplary pacing efficacy curves 104 and
106 subject to transient variations following a temporary change in
pacing mode. The pacing efficacy curves of FIG. 3 are intended to
represent any of a variety of exemplary pacing efficacy parameters
such as stroke volume, blood pressure, contractility, etc. or a
combination thereof. Initially, pacing is provided within two or
more chambers. At time 108, the pacing mode is altered to disable
pacing in at least one chamber. At time 110, pacing reverts to the
original mode. Pacing may be disabled in at least one chamber by,
for example, switching from DDI to VVI pacing or by switching from
biventricular pacing to RV-only pacing. As can be seen, there is a
transient reduction in pacing efficacy caused by the temporary
alteration in pacing mode. In the specific example of curve 104,
the reduction is significant, indicating that the chamber or
chambers where pacing had been disabled were providing a
significant contribution to pacing efficacy. In the specific
example of curve 106, the reduction is not significant, indicating
that the chamber or chambers where pacing had been disabled were
providing only a minimal contribution to pacing efficacy.
Preferably, diagnostic information representative of the transient
alteration in pacing efficacy is stored for automatic analysis and
physician review. Note that the curves illustrated in the graphs of
FIG. 3, and in the various other graphs described herein, should
not be construed as depicting actual clinically-obtained data. The
curves set forth hypothetical data provided to clearly illustrate
features of the invention. Hence, actual transient variations in
pacing efficacy may differ.
[0030] Returning to FIG. 2, at step 112, the pacer/ICD determines
the contribution of particular heart chambers to the overall
efficacy of pacing therapy based on the alteration in pacing mode
and on any transient changes in the observed pacing efficacy. That
is, the pacer/ICD analyzes curves such as those presented in FIG. 3
to evaluate the contribution of the chambers that had pacing
temporarily disabled. In one example, the pacer/ICD quantifies the
reduction in pacing efficacy as a contribution index value. For
example, if the pacing mode is altered from DDI to VVI so as to
temporarily disable pacing in the atria, the numerical decrease in
pacing efficacy may be represented as an atrial contribution index.
As another example, if the pacing mode is altered from
biventricular to RV-only so as to temporarily disable pacing in the
LV, the numerical decrease in pacing efficacy may be represented as
an LV contribution index. Preferably, the index values and/or other
appropriate diagnostic information are recorded for subsequent
physician review. As already noted, warning signals may be
generated if the contribution of a particular chamber is deemed to
be deficient.
[0031] At step 114, the pacer/ICD automatically adjusts pacing
parameters so as to modify a particular heart chamber's
contribution to pacing efficacy. For example, if the initial
alteration in pacing mode was performed to evaluate the atrial
contribution to pacing efficacy, the pacing parameters may be
adjusted so as to optimize the atrial contribution. Techniques for
implementing step 114 will be described in greater detail below
with reference to FIGS. 4-8. Typically, the pacing parameters are
adjusted so as to maximize a selected chamber's contribution to
pacing efficacy. However, in some cases, it may be appropriate to
selectively reduce a given chamber's contribution. In other cases,
if particular chambers are found not to contribute significantly to
pacing efficacy, pacing within those chambers may simply be
disabled to prevent waste of power within the device. Typically,
these decisions are made by a physician based on the measured
contribution index and other factors. However, in some cases, the
device itself may be programmed to automatically deactivate pacing
within particular chambers. This may be achieved merely be changing
the pacing mode to a mode where the particular chambers are not
paced.
[0032] Thus, FIGS. 2 and 3 provide an overview of the heart chamber
contribution evaluation techniques of the invention. Turning now to
FIGS. 4-8, techniques for optimizing a given chamber's contribution
to pacing efficacy will now be described.
Heart Chamber Contribution Optimization Techniques
[0033] FIG. 4 illustrates an iterative technique for optimizing
pacing parameters to maximize the contributions of particular heart
chambers to pacing efficacy. Briefly, in this iterative technique,
the evaluation steps of FIG. 1 are repeated while iteratively
adjusting pacing parameters through a range of values to determine
the particular values yielding the greatest pacing efficacy.
Beginning at step 200, the pacer/ICD paces the heart subject to one
or more pacing parameters, such as A-V, V-V and/or A-A delay
values, set to current values. The current values may be, e.g.,
default values or values set as a result of a previous optimization
session. At step 202, the pacer/ICD evaluates overall pacing
efficacy by monitoring physiological parameters such as one or
more: blood oxygen saturation; blood pressure; contractility;
stroke volume; cardiac output; heart output pulse waveform and/or
morphological features of the IEGM. At step 204, the pacer/ICD
temporarily alters the pacing mode by switching, e.g., among: AAI;
VVI; DDD; DDI; VDD; and/or VOO modes or between biventricular and
monoventricular pacing modes, so as to selectively change the
chambers in which pacing therapy is delivered. At step 206, the
pacer/ICD detects transient changes in pacing efficacy following
the alteration in pacing mode based on observed changes in the
amplitude of the appropriate physiological parameter. At step 208,
the pacer/ICD determines and records the contribution of selected
heart chambers--such as just the atria or just the ventricles--to
the overall efficacy of pacing therapy based on the alteration in
pacing mode and on any transient changes in the efficacy of pacing
therapy. Steps 200-208 generally correspond to steps 100-102 and
112 of FIG. 1.
[0034] At step 210, the pacer/ICD incrementally adjusts selected
pacing parameters within a predetermined range of acceptable
values. Examples will be described below wherein A-V and V-V delay
parameters are incrementally adjusted. However, a wide variety of
other pacing parameters may alternatively be adjusted. The
predetermined range of values depends upon the parameter being
adjusted and is typically specified by the programming of the
device. In many cases, parameters can only be set to certain
discrete values within the range of values. Incremental adjustment
then simply involves setting the parameter to another of the
predetermined discrete values. Processing then returns to step 200
so that steps 200-208 can be repeated to evaluate the contribution
of the selected heart chambers using the new pacing parameters.
Typically, only one parameter is adjusted at a time. However, in
some implementations, it may be appropriate to adjust two or more
parameters simultaneously. In any case, once steps 200-208 have
been repeated with the new parameter values, the parameters are
incrementally adjusted yet again, and the process repeats until
iterative adjustment throughout the entire predetermined range of
values is complete. Finally, at step 212, the pacer/ICD then
selects the particular pacing parameter values that maximize the
contribution of the selected heart chambers to pacing efficacy and
then continues pacing using the newly selected values. In many
cases, optimizing the contribution of an individual chamber serves
to improve overall pacing efficacy to, for example, improve overall
cardiac performance. Preferably, the procedure of FIG. 4 is
repeated periodically, such as once per week, to update the pacing
parameters to account for any changes in the health of the patient,
any changes in prescribed medications, etc. Ideally, the
optimization procedure is performed at about the same time during
the day and under the same conditions so that variations in patient
activity and posture do not unduly influence the optimization
procedure. In one example, the procedure is performed only at night
while the patient is asleep.
[0035] Two specific examples will now be described with reference
to FIGS. 5-8. In the example of FIGS. 5-6, an A-V delay value is
adjusted so as to optimize the atrial contribution to cardiac
performance, as measured by stroke volume. At step 300, the
pacer/ICD paces the heart in DDI mode subject to a specific A-V
delay value, which may be, e.g., a default value or a value set via
a previous optimization session. At step 302, the pacer/ICD
evaluates pacing efficacy by monitoring stroke volume and/or other
relevant physiological parameters. At step 304, the pacer/ICD
temporarily alters the pacing mode to VVI so as to momentarily
disable atrial pacing. At step 306, the pacer/ICD detects transient
changes in pacing efficacy following the switch to VVI pacing, then
resumes DDI pacing. At step 308, the pacer/ICD determines and
records an "atrial contribution index" representative of the
contribution of the atria to the efficacy of pacing therapy based
on the transient changes in stroke volume. In this regard, a
minimal change in stroke volume is indicative of minimal
contribution of the atria to pacing efficacy. A significant change
in stroke volume is indicative of a more significant contribution
of the atria to pacing efficacy. At step 310, the pacer/ICD
incrementally adjusts the A-V delay within a predetermined range of
acceptable values. Typically, this is achieved by merely resetting
the A-V delay value to a different one of a set of permissible A-V
values already programmed into the device. Steps 300-308 are
repeated at the new A-V delay value to assess the atrial
contribution to pacing efficacy at that new A-V delay value, until
all or most of the permissible values for the A-V delay have been
tested. Finally, at step 312, the pacer/ICD selects the particular
A-V delay yielding the largest atrial contribution index and then
continues DDI pacing using the selected A-V delay value. In this
manner, the contribution of the atria to enhanced stroke volume is
maximized.
[0036] FIG. 6 illustrates a set of four exemplary stroke volume
curves 314 recorded during four iterations of the steps of FIG. 5.
The curves are shown superimposed over one another so as to
emphasize the differences therebetween. In actuality, the curves
are obtained sequentially over a period of time by iteratively
adjusting the A-V delay, then temporarily switching the pacing mode
from DDI to VVI, as just described. A first curve illustrates the
transient reduction in stroke volume observed while pacing is
performed with the A-V delay set to a first specific A-V delay
value (during DDI pacing); a second curve illustrates the transient
reduction in stroke volume observed while pacing is performed with
the A-V delay set to a second specific A-V delay value (during DDI
pacing); and so on, up to a 4th A-V delay value. In each case, the
reduction in stroke volume from DDI to VVI is quantified as the
atrial contribution index, which represents the difference in
stroke volume between the volume observed just prior to the switch
to VVI and the minimum stroke volume occurring as a result of the
switch the VVI. Hence, each curve has a different atrial
contribution index associate therewith.
[0037] In the particular example of FIG. 6, the largest atrial
contribution index is observed while the first A-V delay value is
used. This particular curve is highlighted with a bold line. The
smallest atrial contribution index is observed while the fourth A-V
delay value is used. Hence, at step 312 of FIG. 5, the pacer/ICD
sets the A-V delay to the first A-V delay value for use with
subsequent DDI pacing, thereby optimizing the atrial contribution
to pacing efficacy. Although not shown in FIG. 6, typically, a
greater number of stroke volume curves are preferably obtained by
iteratively adjusting the A-V delay through a greater number of
values, thus allowing the pacer/ICD to select the optimal A-V delay
from among a greater number of test A-V delay values. Note that, in
this particular example, the largest atrial contribution index
occurs at the A-V delay value that also provides the greatest
overall stroke volume. In other cases, however, the largest atrial
contribution index may occur at an A-V delay value that does not
yield the largest stroke volume. In such cases, it is often
preferred to set the A-V delay to the value that yields the largest
overall stroke volume.
[0038] In the example of FIGS. 7-8, a V-V delay value is adjusted
so as to optimize the LV contribution to cardiac performance, as
measured by cardiac output. At step 350, the pacer/ICD paces the
heart in a biventricular pacing mode wherein both the LV and RV are
paced subject to a specific V-V delay value, which may be, e.g., a
default value or a value set via a previous optimization session.
At step 352, the pacer/ICD evaluates pacing efficacy by monitoring
cardiac output and/or other relevant physiological parameters. At
step 354, the pacer/ICD temporarily alters the pacing mode to
RV-only (i.e. mono-ventricular) pacing so as to momentarily disable
LV pacing. At step 356, the pacer/ICD detects transient changes in
pacing efficacy following the switch to RV-only pacing, then
resumes biventricular pacing. At step 358, the pacer/ICD determines
and records an "LV contribution index" representative of the
contribution of the LV to the efficacy of pacing therapy based on
the transient changes in cardiac output. In this example, a minimal
change in observed cardiac output is indicative of minimal
contribution of the LV to pacing efficacy. A significant change in
observed cardiac output is indicative of a more significant
contribution of the LV to pacing efficacy. At step 360, the
pacer/ICD incrementally adjusts the V-V delay within a
predetermined range of acceptable V-V delay values, i.e. the
pacer/ICD sets the V-V delay value to a different value within a
predetermined range of acceptable V-V values already programmed
into the device. Steps 350-358 are repeated at the new V-V delay
value to assess the LV contribution to pacing efficacy at that new
V-V delay value. Finally, once the range of values has been tested
then, at step 362, the pacer/ICD selects the particular V-V delay
that maximizes the LV contribution index and continues
biventricular pacing using the newly selected V-V delay value so
that the contribution of the LV to enhanced cardiac output is
maximized.
[0039] FIG. 8 illustrates a set of five exemplary cardiac output
curves 364 recorded during five iterations of the steps of FIG. 7.
As with FIG. 6, the curves of FIG. 8 are shown superimposed over
one another so as to emphasize the differences therebetween,
although the curves are actually obtained sequentially over a
period of time. A first curve illustrates the transient reduction
in cardiac output observed while the V-V delay is set to a first
specific V-V delay value (during biventricular pacing); a second
curve illustrates the transient reduction in stroke volume observed
while the V-V delay is set to a second specific V-V delay value
(during biventricular pacing); and so on, up to a 5th V-V delay. In
each case, the reduction in cardiac output from biventricular
pacing to RV-only pacing is quantified as the LV contribution
index, which represents the difference in cardiac output between
the value observed just prior to the switch to RV-only pacing and
the minimum value observed as a result of the switch to RV-only
pacing. Hence, each curve has a different LV contribution index
associate therewith. In this particular example, the largest LV
contribution index is observed while the fourth V-V delay value is
used. This particular curve is highlighted with a bold line. The
smallest LV contribution index is observed while the first V-V
delay value is used. Hence, at step 362 of FIG. 7, the pacer/ICD
sets the V-V delay to the fourth V-V delay value for use with
subsequent biventricular pacing, thereby optimizing the LV
contribution to pacing efficacy. Although not shown in FIG. 8,
typically, a greater number of cardiac output curves are preferably
obtained by iteratively adjusting the V-V delay through a greater
number of values, thus allowing the pacer/ICD to select the optimal
V-V delay from among a greater number of tested V-V delay
values.
[0040] What have been described are various exemplary techniques
for evaluating and optimizing the contributions of particular heart
chambers to pacing efficacy. The techniques have been described
with respect to examples wherein the implantable system performs
the evaluation and the optimization. However, principles of the
invention are applicable to other systems. For example, the
iterative adjustment in pacing parameters may instead be performed
under the control of an external programmer. The transient changes
in pacing efficacy can instead be detected using an external
system. Exploitation of the invention within an implanted device is
preferred as it allows the device itself to periodically evaluate
the heart chamber contributions and adjust pacing parameters
accordingly. For the sake of completeness, an exemplary pacer/ICD
will now be described.
Exemplary Pacer/ICD
[0041] With reference to FIGS. 9 and 10, an exemplary pacer/ICD
will now be described. FIG. 9 provides a simplified block diagram
of the pacer/ICD, which is a dual-chamber stimulation device
capable of treating both fast and slow arrhythmias with stimulation
therapy, including cardioversion, defibrillation, and pacing
stimulation. To provide atrial chamber pacing stimulation and
sensing, pacer/ICD 10 is shown in electrical communication with a
heart 412 by way of a left atrial lead 420 having an atrial tip
electrode 422 and an atrial ring electrode 423 implanted in the
atrial appendage. Pacer/ICD 10 is also in electrical communication
with the heart by way of a right ventricular lead 430 having, in
this embodiment, a ventricular tip electrode 432, a right
ventricular ring electrode 434, a right ventricular (RV) coil
electrode 436, and a superior vena cava (SVC) coil electrode 438.
Typically, the right ventricular lead 430 is transvenously inserted
into the heart so as to place the RV coil electrode 436 in the
right ventricular apex, and the SVC coil electrode 438 in the
superior vena cava. Accordingly, the right ventricular lead is
capable of receiving cardiac signals, and delivering stimulation in
the form of pacing and shock therapy to the right ventricle.
[0042] To sense left atrial and ventricular cardiac signals and to
provide left chamber pacing therapy, pacer/ICD 10 is coupled to a
CS lead 424 designed for placement in the "CS region" via the CS os
for positioning a distal electrode adjacent to the left ventricle
and/or additional electrode(s) adjacent to the left atrium. As used
herein, the phrase "CS region" refers to the venous vasculature of
the left ventricle, including any portion of the CS, great cardiac
vein, left marginal vein, left posterior ventricular vein, middle
cardiac vein, and/or small cardiac vein or any other cardiac vein
accessible by the CS. Accordingly, an exemplary CS lead 424 is
designed to receive atrial and ventricular cardiac signals and to
deliver left ventricular pacing therapy using at least a left
ventricular tip electrode 426, left atrial pacing therapy using at
least a left atrial ring electrode 427, and shocking therapy using
at least a left atrial coil electrode 428. With this configuration,
biventricular pacing can be performed. Although only three leads
are shown in FIG. 9, it should also be understood that additional
stimulation leads (with one or more pacing, sensing and/or shocking
electrodes) might be used in order to efficiently and effectively
provide pacing stimulation to the left side of the heart or atrial
cardioversion and/or defibrillation.
[0043] A simplified block diagram of selected internal components
of pacer/ICD 10 is shown in FIG. 10. While a particular pacer/ICD
is shown, this is for illustration purposes only, and one of skill
in the art could readily duplicate, eliminate or disable the
appropriate circuitry in any desired combination to provide a
device capable of treating the appropriate chamber(s) with
cardioversion, defibrillation and pacing stimulation as well as
providing for the aforementioned apnea detection and therapy.
[0044] The housing 440 for pacer/ICD 10, shown schematically in
FIG. 10, is often referred to as the "can", "case" or "case
electrode" and may be programmably selected to act as the return
electrode for all "unipolar" modes. The housing 440 may further be
used as a return electrode alone or in combination with one or more
of the coil electrodes, 428, 436 and 438, for shocking purposes.
The housing 440 further includes a connector (not shown) having a
plurality of terminals, 442, 443, 444, 446, 448, 452, 454, 456 and
458 (shown schematically and, for convenience, the names of the
electrodes to which they are connected are shown next to the
terminals). As such, to achieve right atrial sensing and pacing,
the connector includes at least a right atrial tip terminal
(A.sub.R TIP) 442 adapted for connection to the atrial tip
electrode 422 and a right atrial ring (A.sub.R RING) electrode 443
adapted for connection to right atrial ring electrode 423. To
achieve left chamber sensing, pacing and shocking, the connector
includes at least a left ventricular tip terminal (V.sub.L TIP)
444, a left atrial ring terminal (A.sub.L RING) 446, and a left
atrial shocking terminal (A.sub.L COIL) 448, which are adapted for
connection to the left ventricular ring electrode 426, the left
atrial ring electrode 427, and the left atrial coil electrode 428,
respectively. To support right chamber sensing, pacing and
shocking, the connector further includes a right ventricular tip
terminal (V.sub.R TIP) 452, a right ventricular ring terminal
(V.sub.R RING) 454, a right ventricular shocking terminal (V.sub.R
COIL) 456, and an SVC shocking terminal (SVC COIL) 458, which are
adapted for connection to the right ventricular tip electrode 432,
right ventricular ring electrode 434, the V.sub.R coil electrode
436, and the SVC coil electrode 438, respectively. Although not
shown, an additional terminal may be provided for coupling to an
implantable warning device 14, if one is provided.
[0045] At the core of pacer/ICD 10 is a programmable
microcontroller 460, which controls the various modes of
stimulation therapy. As is well known in the art, the
microcontroller 460 (also referred to herein as a control unit)
typically includes a microprocessor, or equivalent control
circuitry, designed specifically for controlling the delivery of
stimulation therapy and may further include RAM or ROM memory,
logic and timing circuitry, state machine circuitry, and I/O
circuitry. Typically, the microcontroller 460 includes the ability
to process or monitor input signals (data) as controlled by a
program code stored in a designated block of memory. The details of
the design and operation of the microcontroller 460 are not
critical to the invention. Rather, any suitable microcontroller 460
may be used that carries out the functions described herein. The
use of microprocessor-based control circuits for performing timing
and data analysis functions are well known in the art.
[0046] As shown in FIG. 10, an atrial pulse generator 470 and a
ventricular pulse generator 472 generate pacing stimulation pulses
for delivery by the right atrial lead 420, the right ventricular
lead 430, and/or the CS lead 424 via an electrode configuration
switch 474. It is understood that in order to provide stimulation
therapy in each of the four chambers of the heart, the atrial and
ventricular pulse generators, 470 and 472, may include dedicated,
independent pulse generators, multiplexed pulse generators or
shared pulse generators. The pulse generators, 470 and 472, are
controlled by the microcontroller 460 via appropriate control
signals, 476 and 478, respectively, to trigger or inhibit the
stimulation pulses. The microcontroller 460 further includes timing
control circuitry (not separately shown) used to control the timing
of such stimulation pulses (e.g., pacing rate, atrioventricular
(A-V) delay, atrial interconduction (inter-atrial or A-A) delay, or
ventricular interconduction (V-V) delay, etc.) as well as to keep
track of the timing of refractory periods, blanking intervals,
noise detection windows, evoked response windows, alert intervals,
marker channel timing, etc., which is well known in the art. Switch
474 includes a plurality of switches for connecting the desired
electrodes to the appropriate I/O circuits, thereby providing
complete electrode programmability. Accordingly, the switch 474, in
response to a control signal 480 from the microcontroller 460,
determines the polarity of the stimulation pulses (e.g., unipolar,
bipolar, combipolar, etc.) by selectively closing the appropriate
combination of switches (not shown) as is known in the art.
[0047] Atrial sensing circuits 482 and ventricular sensing circuits
484 may also be selectively coupled to the right atrial lead 420,
CS lead 424, and the right ventricular lead 430, through the switch
474 for detecting the presence of cardiac activity in each of the
four chambers of the heart. Accordingly, the atrial (ATR. SENSE)
and ventricular (VTR. SENSE) sensing circuits, 482 and 484, may
include dedicated sense amplifiers, multiplexed amplifiers or
shared amplifiers. The switch 474 determines the "sensing polarity"
of the cardiac signal by selectively closing the appropriate
switches, as is also known in the art. In this way, the clinician
may program the sensing polarity independent of the stimulation
polarity. Each sensing circuit, 482 and 484, preferably employs one
or more low power, precision amplifiers with programmable gain
and/or automatic gain control and/or automatic sensitivity control,
bandpass filtering, and a threshold detection circuit, as known in
the art, to selectively sense the cardiac signal of interest. The
outputs of the atrial and ventricular sensing circuits, 482 and
484, are connected to the microcontroller 460 which, in turn, are
able to trigger or inhibit the atrial and ventricular pulse
generators, 470 and 472, respectively, in a demand fashion in
response to the absence or presence of cardiac activity in the
appropriate chambers of the heart.
[0048] For arrhythmia detection, pacer/ICD 10 utilizes the atrial
and ventricular sensing circuits, 482 and 484, to sense cardiac
signals to determine whether a rhythm is physiologic or pathologic.
As used herein "sensing" is reserved for the noting of an
electrical signal, and "detection" is the processing of these
sensed signals and noting the presence of an arrhythmia. The timing
intervals between sensed events (e.g., AS, VS, and depolarization
signals associated with fibrillation which are sometimes referred
to as "F-waves" or "Fib-waves") are then classified by the
microcontroller 460 by comparing them to a predefined rate zone
limit (i.e., bradycardia, normal, atrial tachycardia, atrial
fibrillation, low rate ventricular tachycardia, high rate
ventricular tachycardia, and fibrillation rate zones) and various
other characteristics (e.g., sudden onset, stability, physiologic
sensors, and morphology, etc.) in order to determine the type of
remedial therapy that is needed (e.g., bradycardia pacing,
antitachycardia pacing, cardioversion shocks or defibrillation
shocks).
[0049] Cardiac signals are also applied to the inputs of an
analog-to-digital (A/D) data acquisition system 490. The data
acquisition system 490 is configured to acquire intracardiac
electrogram signals, convert the raw analog data into a digital
signal, and store the digital signals for later processing and/or
telemetric transmission to an external device 502. The data
acquisition system 490 is coupled to the right atrial lead 420, the
CS lead 424, and the right ventricular lead 430 through the switch
474 to sample cardiac signals across any pair of desired
electrodes. The microcontroller 460 is further coupled to a memory
494 by a suitable data/address bus 496, wherein the programmable
operating parameters used by the microcontroller 460 are stored and
modified, as required, in order to customize the operation of
pacer/ICD 10 to suit the needs of a particular patient. Such
operating parameters define, for example, pacing pulse amplitude or
magnitude, pulse duration, electrode polarity, rate, sensitivity,
automatic features, arrhythmia detection criteria, and the
amplitude, waveshape and vector of each shocking pulse to be
delivered to the patient's heart within each respective tier of
therapy. Other pacing parameters include base rate, rest rate and
circadian base rate.
[0050] Advantageously, the operating parameters of the implantable
pacer/ICD 10 may be non-invasively programmed into the memory 494
through a telemetry circuit 500 in telemetric communication with
the external device 502, such as a programmer, transtelephonic
transceiver or a diagnostic system analyzer, or with a beside
monitor 16. The telemetry circuit 500 is activated by the
microcontroller by a control signal 506. The telemetry circuit 500
advantageously allows intracardiac electrograms and status
information relating to the operation of pacer/ICD 10 (as contained
in the microcontroller 460 or memory 494) to be sent to the
external device 502 through an established communication link 504.
Pacer/ICD 10 further includes an accelerometer or other physiologic
sensor 508, commonly referred to as a "rate-responsive" sensor
because it is typically used to adjust pacing stimulation rate
according to the exercise state of the patient. However, the
physiological sensor 508 may further be used to detect changes in
cardiac output, changes in the physiological condition of the
heart, or diurnal changes in activity (e.g., detecting sleep and
wake states) and to detect arousal from sleep. Accordingly, the
microcontroller 460 responds by adjusting the various pacing
parameters (such as rate, A-V delay, V-V delay, etc.) at which the
atrial and ventricular pulse generators, 470 and 472, generate
stimulation pulses. While shown as being included within pacer/ICD
10, it is to be understood that the physiologic sensor 508 may also
be external to pacer/ICD 10, yet still be implanted within or
carried by the patient. A common type of rate responsive sensor is
an activity sensor incorporating an accelerometer or a
piezoelectric crystal, which is mounted within the housing 440 of
pacer/ICD 10. Other types of physiologic sensors are also known,
for example, sensors that sense the oxygen content of blood,
respiration rate and/or minute ventilation, pH of blood,
ventricular gradient, PPG etc. Multiple sensors may be
provided.
[0051] The pacer/ICD additionally includes a battery 510, which
provides operating power to all of the circuits shown in FIG. 10.
The battery 510 may vary depending on the capabilities of pacer/ICD
10. If the system only provides low voltage therapy, a lithium
iodine or lithium copper fluoride cell may be utilized. For
pacer/ICD 10, which employs shocking therapy, the battery 510 must
be capable of operating at low current drains for long periods, and
then be capable of providing high-current pulses (for capacitor
charging) when the patient requires a shock pulse. The battery 510
must also have a predictable discharge characteristic so that
elective replacement time can be detected. Accordingly, pacer/ICD
10 is preferably capable of high voltage therapy and appropriate
batteries.
[0052] As further shown in FIG. 10, pacer/ICD 10 is shown as having
an impedance measuring circuit 512 which is enabled by the
microcontroller 460 via a control signal 514. Thoracic impedance
may be detected for use in tracking thoracic respiratory
oscillations; lead impedance surveillance during the acute and
chronic phases for proper lead positioning or dislodgement;
detecting operable electrodes and automatically switching to an
operable pair if dislodgement occurs; measuring respiration or
minute ventilation; measuring thoracic impedance for determining
shock thresholds; detecting when the device has been implanted;
measuring respiration; and detecting the opening of heart valves,
etc. The impedance measuring circuit 120 is advantageously coupled
to the switch 74 so that any desired electrode may be used.
[0053] In the case where pacer/ICD 10 is intended to operate as an
implantable cardioverter/defibrillator (ICD) device, it detects the
occurrence of an arrhythmia, and automatically applies an
appropriate electrical shock therapy to the heart aimed at
terminating the detected arrhythmia. To this end, the
microcontroller 460 further controls a shocking circuit 516 by way
of a control signal 518. The shocking circuit 516 generates
shocking pulses of low (up to 0.5 joules), moderate (0.5-10 joules)
or high energy (11 to 40 joules), as controlled by the
microcontroller 460. Such shocking pulses are applied to the heart
of the patient through at least two shocking electrodes, and as
shown in this embodiment, selected from the left atrial coil
electrode 428, the RV coil electrode 436, and/or the SVC coil
electrode 438. The housing 440 may act as an active electrode in
combination with the RV electrode 436, or as part of a split
electrical vector using the SVC coil electrode 438 or the left
atrial coil electrode 428 (i.e., using the RV electrode as a common
electrode). Cardioversion shocks are generally considered to be of
low to moderate energy level (so as to minimize pain felt by the
patient), and/or synchronized with a VS event and/or pertaining to
the treatment of tachycardia. Defibrillation shocks are generally
of moderate to high energy level (i.e., corresponding to thresholds
in the range of 5-40 joules), delivered asynchronously (since VS
events may be too disorganized), and pertaining exclusively to the
treatment of fibrillation. Accordingly, the microcontroller 460 is
capable of controlling the synchronous or asynchronous delivery of
the shocking pulses.
[0054] Insofar as heart chamber evaluation and optimization are
concerned, the microcontroller includes a heart chamber
contribution evaluation system 501 operative to evaluate the
contribution of particular heart chambers to the overall efficacy
of pacing therapy based on a temporary alteration in pacing mode
and based on any transient changes in the efficacy of the pacing
therapy following the alteration in pacing mode, in accordance with
the techniques described above in connection with FIGS. 1-8. System
501 includes various components such as: a pacing mode temporary
adjustment unit 503 operative to temporarily alter the pacing mode
with which pacing therapy is delivered; a pacing efficacy detector
505 operative to detect transient changes in the efficacy of pacing
therapy following the alteration in pacing mode; and a heart
chamber contribution determination unit 507 operative to determine
the contribution of the particular heart chambers to the overall
efficacy of pacing therapy based on the alteration in pacing mode
and based on the transient changes in the effectiveness of the
pacing therapy. Additionally, the microcontroller includes a heart
chamber optimization system 509 operative to adjust the pacing
parameters based on the contribution of the particular heart
chambers to the overall efficacy of pacing therapy. This may be
achieved using the various optimization techniques described above
with reference to FIGS. 4-8. A warning/diagnostics controller 511
controls the generation of warning signals and the storage of
diagnostics data pertaining to the heart chamber evaluation and
optimization procedures. Depending upon the implementation, the
various components of the microcontroller may be implemented as
separate software modules or the modules may be combined to permit
a single module to perform multiple functions. In addition,
although shown as being components of the microcontroller, some or
all of these components may be implemented separately from the
microcontroller.
[0055] In general, while the invention has been described with
reference to particular embodiments, modifications can be made
thereto without departing from the scope of the invention. Note
also that the term "including" as used herein is intended to be
inclusive, i.e. "including but not limited to."
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