U.S. patent application number 09/904056 was filed with the patent office on 2002-10-17 for system and method for programmably controlling electrode activation sequence in a multi-site cardiac stimulation device.
Invention is credited to Levine, Paul A..
Application Number | 20020151934 09/904056 |
Document ID | / |
Family ID | 25268332 |
Filed Date | 2002-10-17 |
United States Patent
Application |
20020151934 |
Kind Code |
A1 |
Levine, Paul A. |
October 17, 2002 |
System and method for programmably controlling electrode activation
sequence in a multi-site cardiac stimulation device
Abstract
An implantable multi-chamber cardiac stimulation device includes
flexibly programmable electrode sensing configurations, and is
capable of precisely controlling the stimulation sequence between
multiple sites. The stimulation device provides a plurality of
connection ports that allow independent connection of each
electrical lead associated with a particular stimulation site in
the heart. Each connection port further provides a unique terminal
for making electrical contact with only one electrode such that no
two electrodes are required to be electrically coupled.
Furthermore, each electrode, whether residing on a unipolar,
bipolar or multipolar lead, may be selectively connected or
disconnected through programmable switching circuitry that
determines the electrode configurations to be used for sensing and
for stimulating at each stimulation site. The stimulation device
possesses unique sensing and output configurations associated with
each stimulation site, such that depolarizations occurring at each
stimulation site can be detected independently of events occurring
at other sites within the heart, and such that each site can be
stimulated independently of other sites or on a precisely timed
basis triggered by events occurring at other sites. The stimulation
device is further capable of uniquely programming coupling
intervals for precisely controlling the activation sequence of
stimulated sites. Coupling intervals are selected so as to provide
optimal hemodynamic benefit to the patient.
Inventors: |
Levine, Paul A.; (Santa
Clarita, CA) |
Correspondence
Address: |
PACESETTER, INC.
15900 Valley View Court
Sylmar
CA
91392-9221
US
|
Family ID: |
25268332 |
Appl. No.: |
09/904056 |
Filed: |
July 11, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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09904056 |
Jul 11, 2001 |
|
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|
09835006 |
Apr 12, 2001 |
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Current U.S.
Class: |
607/9 |
Current CPC
Class: |
A61N 1/36843 20170801;
A61N 1/3627 20130101; A61N 1/3918 20130101; A61N 1/3684 20130101;
A61N 1/368 20130101 |
Class at
Publication: |
607/9 |
International
Class: |
A61N 001/18; A61N
001/36 |
Claims
What is claimed is:
1. A method of automatically controlling an activation sequence of
a plurality of electrodes that are positioned in multiple cardiac
chambers, for use with a multi-site cardiac stimulation device, the
method comprising the steps of: defining a plurality of electrode
configurations corresponding to available activation sequences of
the electrodes; selectively delivering a stimulus, on demand, to a
cardiac chamber; sensing a cardiac event in the cardiac chamber by
using a first electrode configuration; initiating a coupling
interval for the multiple cardiac chambers; controlling the
activation sequence of the electrodes by selecting an electrode
configuration based on the cardiac chamber in which the cardiac
event is sensed or a stimulus delivered; automatically acquiring a
measurement of the cardiac event using the electrode configuration;
and automatically adjusting the coupling interval in response to
the measurement of the cardiac event.
2. The method according to claim 1, wherein the sensing step
includes sensing intrinsic depolarizations in at least two cardiac
chambers.
3. The method according to claim 2, wherein the step of delivering
a stimulus includes stimulating at least two cardiac chambers.
4. The method according to claim 3, further including the step of
determining an inter-atrial conduction (A-A) delay by selecting a
coupling interval defined according to whether an intrinsic atrial
depolarization is first sensed in a right atrium or in a left
atrium.
5. The method according to claim 4, wherein the step of
automatically adjusting includes selecting a right-to-left atrial
coupling interval to control an interval between an intrinsic right
atrial depolarization (P-wave) and a delivery of a left atrial
stimulus.
6. The method according to claim 4, wherein the step of
automatically adjusting includes selecting a left-to-right atrial
coupling interval to control an interval between an intrinsic left
atrial depolarization (P-wave) and a delivery of a right atrial
stimulus.
7. The method according to claim 1, wherein the step of
automatically adjusting further includes adjusting the coupling
interval based on a stimulation event in any one of the multiple
cardiac chambers.
8. The method according to claim 1, wherein the step of initiating
a coupling interval includes initiating a unique coupling interval
for a stimulation site, between the stimulation site and remaining
stimulation sites, in terms of any one or more of: a stimulations
event or an intrinsic depolarization occurring at the stimulation
site.
9. The method according to claim 1, further including sensing an
occurrence of an intrinsic atrial depolarization in any one or more
of a left atrium or a right atrium.
10. The method according to claim 9, further including delivering a
right atrial stimulation pulse when no intrinsic atrial
depolarization is sensed.
11. The method according to claim 10, wherein the step of
initiating the coupling interval includes initiating one or more
coupling intervals from the right atrial stimulation pulse to any
one or more of: a left atrial stimulation pulse, a right
ventricular stimulation pulse, or a left ventricular stimulation
pulse.
12. The method according to claim 10, further including detecting
an occurrence of an intrinsic right atrial depolarization.
13. The method according to claim 12, wherein when the intrinsic
right atrial depolarization is not sensed, initiating one or more
coupling intervals from the intrinsic right atrial depolarization
to any one or more of: a left atrial stimulation pulse, a right
ventricular stimulation pulse, or a left ventricular stimulation
pulse.
14. The method according to claim 13, wherein when an intrinsic
left atrial depolarization is sensed, initiating one or more
coupling intervals from the intrinsic left atrial depolarization to
any one or more of: a right atrial stimulation pulse, a right
ventricular stimulation pulse, or a left ventricular stimulation
pulse.
15. The method according to claim 1, further including
automatically selecting a sensing polarity for each sensing site in
the multiple cardiac chambers.
16. The method according to claim 15, wherein the step of
automatically selecting the sensing polarity includes designating
any of an anode or a cathode assignment to at least one of the
plurality of sensing electrodes.
17. The method according to claim 16, wherein the step of
designating includes selecting a left ventricular tip electrode as
the cathode, and further selecting a right ventricular tip
electrode as the anode.
18. The method according to claim 16, wherein the step of
designating includes selecting a right ventricular tip electrode as
the cathode, and further selecting a left ventricular tip electrode
as the anode.
19. The method according to claim 16, wherein the step of
designating includes assigning any of an anodal sensing or a
cathodal sensing to at least one of the plurality of sensing
electrodes.
20. The method according to claim 16, wherein the step of
designating includes assigning any of an anodal sensing or a
cathodal sensing to at least one of the plurality of sensing
electrodes.
21. The method according to claim 16, further including
automatically selecting a stimulation polarity for each stimulation
site in the multiple cardiac chambers.
22. The method according to claim 21, wherein the step of
automatically selecting the stimulation polarity includes
designating any of an anode or a cathode assignment to at least one
of a plurality of stimulation electrodes.
23. The method according to claim 22, wherein the step of
designating includes selecting a left ventricular tip electrode as
the cathode, and further selecting a right ventricular tip
electrode as the anode.
24. The method according to claim 22, wherein the step of
designating includes selecting a right ventricular tip electrode as
the cathode, and further selecting a left ventricular tip electrode
as the anode.
25. The method according to claim 22, wherein the step of
designating includes assigning any of an anodal sensing or a
cathodal sensing to at least one of the plurality of sensing
electrodes.
26. The method according to claim 1, further including allowing
intrinsic depolarizations occurring at each stimulation site to be
sensed independently.
27. The method according to claim 1, wherein the step of
automatically adjusting the coupling interval includes determining
a current stimulation state of the stimulation device; when the
stimulation device is stimulating a ventricle, attempting to
inhibit ventricular stimulation by extending an atrial-ventricular
(AV) delay; when the stimulation device is stimulating an atrium,
attempting to inhibit atrial pacing by reducing a base pacing rate;
measuring one or more baseline physiological parameters; and
modulating one or more combinations of the coupling intervals for
altering the activation sequence so as to determine an activation
sequence that allows optimal improvement in the current stimulation
state.
28. A multi-site cardiac stimulation device capable of
automatically controlling an activation sequence of a plurality of
electrodes that are positioned in multiple cardiac chambers,
comprising: a discriminator, coupled to the plurality of
electrodes, that senses a cardiac signal in each of the cardiac
chambers, and that identifies a cardiac chamber of origin in which
the cardiac signal originates; a pulse generator, connected to the
electrodes, to selectively deliver stimulation pulses on demand to
the cardiac chambers; and timing control circuitry, connected to
the electrodes, the pulse generator, and the discriminator to
initiate coupling intervals for the multiple cardiac chambers based
on the cardiac chamber of origin in which an intrinsic
depolarization is sensed or a stimulus is delivered, for
controlling a timing of the activation sequence, and the timing
control circuitry further automatically adjusting the coupling
intervals based on measurements acquired by the discriminator.
29. The stimulation device according to claim 28, wherein the
discriminator senses an occurrence of an intrinsic atrial
depolarization in any one or more of a left atrium or a right
atrium.
30. The stimulation device according to claim 29, wherein the pulse
generator delivers a right atrial stimulation pulse in the absence
of an intrinsic atrial depolarization.
31. The stimulation device according to claim 29, wherein the
timing control circuitry initiates one or more coupling intervals
from a right atrial stimulation pulse to any one or more of: a left
atrial stimulation pulse, a right ventricular stimulation pulse, or
a left ventricular stimulation pulse.
32. The stimulation device according to claim 29, wherein the
sensing circuitry is adapted to further sense an occurrence of an
intrinsic right atrial depolarization; and wherein in the absence
of an intrinsic right atrial depolarization, the timing control
circuitry initiates one or more coupling intervals from the
intrinsic right atrial depolarization to any one or more of: a left
atrial stimulation pulse, a right ventricular stimulation pulse, or
a left ventricular stimulation pulse.
33. The stimulation device according to claim 29, wherein in the
presence of an intrinsic left atrial depolarization, the sensing
circuitry initiates one or more coupling intervals from the
intrinsic left atrial depolarization to any one or more of: a right
atrial stimulation pulse, a right ventricular stimulation pulse, or
a left ventricular stimulation pulse.
34. The stimulation device according to claim 28, wherein the
plurality of electrodes include sensing electrodes; and further
including a switch bank that automatically selects polarities for
the plurality of sensing electrodes.
35. The stimulation device according to claim 30, wherein the
plurality of electrodes include stimulation electrodes; and further
including a switch bank that automatically selects polarities for
the plurality of stimulation electrodes.
36. The stimulation device according to claim 30, further including
a multi-port connector for connection to any one or more of
uni-polar, bi-polar, or multi-polar leads.
37. The stimulation device according to claim 36, wherein the
multi-port connector includes four bipolar connection ports: a left
ventricular connection port that couples to a left ventricular lead
with terminals associated with a ventricular tip electrode, a left
ventricular ring electrode, and a left atrial coil electrode; a
left atrial connection port that couples to a left atrial lead with
terminals associated with a left atrial tip electrode and a left
atrial ring electrode; a right ventricular connection port that
couples to a right ventricular lead with terminals associated with
a right ventricular tip electrode, a right ventricular ring
electrode, a right ventricular shocking coil, and a right
ventricular coil electrode; and a right atrial connection port that
couples to a right atrial lead with terminals associated with a
right atrial tip electrode and a right atrial ring electrode.
38. A multi-site cardiac stimulation device capable of
automatically controlling an activation sequence of a plurality of
electrodes that are positioned in multiple cardiac chambers,
comprising: means for sensing a cardiac signal in each of the
multiple cardiac chambers; means for detecting a cardiac chamber of
origin in which the cardiac signal originates; means for
selectively generating stimulation energy, on demand, to the
multiple cardiac chambers; and means for initiating coupling
intervals for the multiple cardiac chambers based on the cardiac
chamber of origin in which an intrinsic depolarization is sensed or
a stimulus is delivered, for controlling a timing of the activation
sequence, and for automatically adjusting the coupling intervals
based on measurements acquired by the sensing means.
39. The stimulation device according to claim 38, wherein the
sensing means senses an occurrence of an intrinsic atrial
depolarization in any one or more of a left atrium or a right
atrium.
40. The stimulation device according to claim 39, wherein the means
for generating stimulation energy delivers a right atrial
stimulation pulse in the absence of an intrinsic atrial
depolarization; wherein the initiating means initiates one or more
coupling intervals from a right atrial stimulation pulse to any one
or more of: a left atrial stimulation pulse, a right ventricular
stimulation pulse, or a left ventricular stimulation pulse; wherein
in the absence of an intrinsic right atrial depolarization, the
initiating means initiates one or more coupling intervals from the
intrinsic right atrial depolarization to any one or more of: a left
atrial stimulation pulse, a right ventricular stimulation pulse, or
a left ventricular stimulation pulse; and wherein in the presence
of an intrinsic left atrial depolarization, the initiating means
initiates one or more coupling intervals from the intrinsic left
atrial depolarization to any one or more of: a right atrial
stimulation pulse, a right ventricular stimulation pulse, or a left
ventricular stimulation pulse.
41. The stimulation device according to claim 38, wherein the
plurality of electrodes include sensing electrodes; and further
including switching means for automatically selecting polarities
for the plurality of sensing electrodes.
42. The stimulation device according to claim 38, wherein the
plurality of electrodes include stimulation electrodes; and further
including switching means for automatically selecting polarities
for the plurality of stimulation electrodes.
43. The stimulation device according to claim 38, further including
a multi-port connecting means for connection to any one or more of
uni-polar, bi-polar, or multi-polar leads; and wherein the
multi-port connecting means includes four bipolar connection ports:
a left ventricular connection port that couples to a left
ventricular lead with terminals associated with a ventricular tip
electrode, a left ventricular ring electrode, and a left atrial
coil electrode; a left atrial connection port that couples to a
left atrial lead with terminals associated with a left atrial tip
electrode and a left atrial ring electrode; a right ventricular
connection port that couples to a right ventricular lead with
terminals associated with a right ventricular tip electrode, a
right ventricular ring electrode, a right ventricular shocking
coil, and a right ventricular coil electrode; and a right atrial
connection port that couples to a right atrial lead with terminals
associated with a right atrial tip electrode and a right atrial
ring electrode.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a division of copending U.S. application
Ser. No. 09/835,006, filed Apr. 12, 2001, titled "System and Method
for Automatically Selecting Electrode Polarity During Sensing and
Stimulation."
FIELD OF THE INVENTION
[0002] This invention relates generally to programmable cardiac
stimulating devices. More specifically, the present invention is
directed to an implantable stimulation device and associated method
for controlling the electrode sensing and stimulation
configurations and the activation sequence in a multi-chamber
cardiac stimulation device using noninvasive programming
techniques.
BACKGROUND OF THE INVENTION
[0003] In a normal human heart, the sinus node, generally located
near the junction of the superior vena cava and the right atrium,
constitutes the primary natural pacemaker initiating rhythmic
electrical excitation of the heart chambers. The cardiac impulse
arising from the sinus node is transmitted to the two atrial
chambers, causing a depolarization known as a P-wave and the
resulting atrial chamber contractions. The excitation pulse is
further transmitted to and through the ventricles via the
atrioventricular (A-V) node and a ventricular conduction system
causing a depolarization known as an R-wave and the resulting
ventricular chamber contractions.
[0004] Disruption of this natural pacemaking and conduction system
as a result of aging or disease can be successfully treated by
artificial cardiac pacing using implantable cardiac stimulation
devices, including pacemakers and implantable defibrillators, which
deliver rhythmic electrical pulses or other anti-arrhythmia
therapies to the heart at a desired energy and rate. One or more
heart chambers may be electrically stimulated depending on the
location and severity of the conduction disorder.
[0005] Cardiac pacemakers conventionally stimulate a heart chamber
by applying current pulses to cardiac tissues via two electrodes, a
cathode and an anode. Standard pacing leads are available in either
of two configurations, unipolar leads or bipolar leads, depending
on the arrangement of the electrodes of a particular lead. A
unipolar pacing lead contains a single electrode, normally the
cathode, which extends pervenously distal from the pacemaker in an
insulating enclosure until it is adjacent to the tip of the lead
where the insulation is terminated to provide for electrical
contact of the cathode with the heart tissue. The anode provides a
return path for the pacing electrical circuit. For a unipolar lead,
the anode is the pacemaker case.
[0006] A bipolar lead contains two electrodes within an insulating
sheath, an anode that extends distal from the pacemaker to a
position adjacent to, but spaced from, the electrode tip, and a
cathode that also extends distal from the pacemaker, but terminates
a short distance distal of the anode, at the lead tip. The anode
commonly takes the form of a ring having greater surface area than
the cathode tip. An insulating barrier separates the cathode and
anode of a bipolar lead. In present-day pacemakers, circuits for
pacing and sensing, which determine tip, ring and case electrode
connections, are provided. Thus, the pacemakers can be programmed
via telemetry for either bipolar or unipolar operation with respect
to either sensing or pacing operations.
[0007] A single-chamber pacemaker delivers pacing pulses to one
chamber of the heart, either one atrium or one ventricle, via
either a unipolar or bipolar electrode. Single-chamber pacemakers
can operate in either a triggered mode or a demand mode. In a
triggered mode, a stimulation pulse is delivered to the desired
heart chamber at the end of a defined time-out interval to cause
depolarization of the heart tissue (myocardium) and it's
contraction. The stimulating pulse must be of sufficient energy to
cause depolarization of the heart chamber, a condition known as
"capture." The lowest pulse energy required to achieve capture is
termed "threshold." The pacemaker also delivers a stimulation pulse
in response to a sensed event arising from that chamber when
operating in a triggered mode.
[0008] When operating in a demand mode, sensing and detection
circuitry allow for the pacemaker to detect if an intrinsic cardiac
depolarization, either an R-wave or a P-wave, has occurred within
the defined time-out interval. If an intrinsic depolarization is
not detected, a pacing pulse is delivered at the end of the
time-out interval. However, if an intrinsic depolarization is
detected, the pacing pulse output is inhibited to allow the natural
heart rhythm to preside. The difference between a triggered and
demand mode of operation is the response of the pacemaker to a
detected native event.
[0009] Dual chamber pacemakers are now commonly available and can
provide either trigger or demand type pacing in both an atrial
chamber and a ventricular chamber, typically the right atrium and
the right ventricle. Both unipolar or bipolar dual chamber
pacemakers exist in which a unipolar or bipolar lead extends from
an atrial channel of the dual chamber device to the desired atrium
(e.g. the right atrium), and a separate unipolar or bipolar lead
extends from a ventricular channel to the corresponding ventricle
(e.g. the right ventricle). In dual chamber, demand-type
pacemakers, commonly referred to as DDD pacemakers, each atrial and
ventricular channel includes a sense amplifier to detect cardiac
activity in the respective chamber and an output circuit for
delivering stimulation pulses to the respective chamber.
[0010] If an intrinsic atrial depolarization signal (a P-wave) is
not detected by the atrial channel, a stimulating pulse will be
delivered to depolarize the atrium and cause contraction. Following
either a detected P-wave or an atrial pacing pulse, the ventricular
channel attempts to detect a depolarization signal in the
ventricle, known as an R-wave. If no R-wave is detected within a
defined atrial-ventricular interval (AV interval or delay), a
stimulation pulse is delivered to the ventricle to cause
ventricular contraction. In this way, rhythmic dual chamber pacing
is achieved by coordinating the delivery of ventricular output in
response to a sensed or paced atrial event.
[0011] Mounting clinical evidence supports the evolution of more
complex cardiac stimulating devices capable of stimulating three or
even all four heart chambers to stabilize arrhythmias or to
re-synchronize heart chamber contractions (Ref: Cazeau S. et al.,
"Four chamber pacing in dilated cardiomyopathy," Pacing Clin.
Electrophsyiol 1994 17(11 Pt 2):1974-9). Stimulation of multiple
sites within a heart chamber has also been found effective in
controlling arrhythmogenic depolarizations (Ref: Ramdat-Misier A.,
et al., "Multisite or alternate site pacing for the prevention of
atrial fibrillation," Am. J. Cardiol., 1999 11
;83(5b):237D-240D).
[0012] In order to achieve multi-chamber or multi-site stimulation
in a clinical setting, conventional dual-chamber pacemakers have
now been used in conjunction with adapters that couple together two
leads going to different pacing sites or heart chambers. Reference
is made to U.S. Pat. No. 5,514,161 to Limousin in which a triple
chamber cardiac pacemaker, with the right and left atrial combined
with a right ventricular lead, is described. Cazeau et al. (Pacing
Clin. Electrophsyiol 1994 17(11 Pt 2):1974-9) describe a four
chamber pacing system in which unipolar right and left atrial leads
are connected via a bifurcated bipolar adapter to the atrial port
of a bipolar dual chamber pacemaker. Likewise, unipolar right and
left ventricular leads are connected via a bifurcated bipolar
adapter to the ventricular channel. The left chamber leads were
connected to the anode terminals and the right chamber leads were
connected to the cathode terminals of the dual chamber device. In
this way, simultaneous bi-atrial or simultaneous bi-ventricular
pacing is achieved via bipolar stimulation but with several
limitations.
[0013] Firstly, this configuration of bipolar stimulation is
distinctly different from a conventional bipolar lead configuration
wherein both the cathode and anode are located a short distance
apart, approximately one centimeter, on the same lead. In the
bi-chamber pacing configuration described above, the anode and
cathode are in fact located on two different leads positioned in
two different locations, several centimeters apart. In addition,
since the tip electrode of one lead is forced to be the anode, and
this has a significantly smaller surface area than the anode of a
classic bipolar lead, the relative resistance or impedance is
higher with this lead system. In such a bipolar, bi-chamber pacing
configuration, the threshold energy is likely to be relatively
higher than in conventional bipolar stimulation in part because of
the higher impedance of the electrode system. In addition, the
electrode used for stimulation in the left heart chamber is usually
within the coronary sinus or a cardiac vein, not making direct
contact with the myocardium. As such, the energy needed to
accommodate bi-chamber stimulation will usually be higher than that
which is commonly required for single chamber stimulation using
bipolar leads.
[0014] A potential risk that exists when higher output settings are
used, as may be needed to ensure bi-chamber stimulation, is
cross-chamber capture, also known as cross-stimulation (Ref: Levine
P A, et al., Cross-stimulation: the unexpected stimulation of the
unpaced chamber, PACE 1985: 8: 600-606). If bi-atrial stimulation
is delivered in a bipolar configuration across one electrode
located in the right atrium and another electrode located in the
left atrium, which in actuality is the coronary sinus which lies
between the left atrium and left ventricle, the stimulation energy
could conceivably be high enough to inadvertently capture one or
both ventricles simultaneously. Such cross-chamber capture is a
highly undesirable situation in that the upper and lower chambers
would contract against each other causing severe cardiac output
perturbation. This is also likely to occur with bipolar
bi-ventricular stimulation with respect to cross-stimulation of the
atrial chambers if the left ventricular lead located within a
cardiac vein is in close anatomic proximity to the left atrium and
high outputs are required to assure capture.
[0015] Another limitation of the multi-chamber stimulation systems
described above is that simultaneous stimulation of left and right
chambers, as required when two leads are coupled together by one
adapter, is not always necessary nor desirable. For example, in
some patients conduction between the two atria may be compromised,
however the pacemaking function of the sinus node in the right
atrium may still be normal. Hence, detection of an intrinsic
depolarization in the right atrium could be used to trigger
delivery of a pacing pulse in the left atrium. Since an intrinsic
depolarization has occurred in one chamber, simultaneous
stimulation of both chambers in this situation is unnecessary.
[0016] In another example, when inter-atrial or inter-ventricular
conduction is intact, stimulation in one chamber may be conducted
naturally to depolarize the second chamber. A stimulation pulse
delivered in one chamber, using the minimum energy required to
depolarize that chamber, will be conducted to the opposing chamber
thus depolarizing both chambers. In this case, stimulation of both
chambers simultaneously would be wasteful of battery energy.
[0017] Another limitation is that, in the presence of an
inter-atrial or inter-ventricular conduction defect, one may want
to control the interval between a sensed or paced event in one
chamber and delivery of a stimulation pulse to the other chamber.
If pacing is required in both chambers, the control of the sequence
of the stimulation pulse delivery to each chamber, rather than the
simultaneous delivery of stimulation pulses, may be desirable in
order to achieve a specific activation sequence that has
hemodynamic benefit.
[0018] Yet another limitation is that, once implanted, the
designation of cathode and anode assignments is fixed and cannot be
reassigned in order to determine the polarity that results in the
lowest stimulation thresholds, to achieve a desired directionality
of the stimulation delivery or to obtain the optimal sequencing of
stimulation and/or sensing to optimize hemodynamic function.
Typically, the electrode in the right chamber is connected to the
cathode terminal and the electrode in the left chamber is connected
to the anode terminal. In other cases, the electrode in the left
chamber is connected to the cathode terminal while the right
chamber electrode is connected to the anode. In some patients, a
lower stimulation threshold or an improved excitation pattern or
perhaps even hemodynamic benefit might be achieved by reversing the
cathode and anode locations yet this cannot be done without
operative intervention.
[0019] In the first generation of multi-chamber devices, an adapter
was required to connect multiple leads to a conventional dual
chamber device, a requirement that adds cost and time to the
implant procedure. Adapters can be cumbersome and an additional
site for potential lead breakage or discontinuity, essentially
adding bulk and a "weak link" to the implanted system. In certain
current devices, adapters are no longer required. The connection
between leads is hardwired internally in the connector block
coupling the ventricular leads to the ventricular channel and the
atrial leads to the atrial channel. While this design
advantageously eliminates the need for adapters, the hardwire
connections preclude the potential to non-invasively adjust the
polarity orientation. This also prevents introducing separate
timing between stimulation pulses delivered to each chamber or
responding with any programmable delays to a sensed event by
delivery of an output pulse to the other chamber.
[0020] To address some of these limitations, Verboven-Nelissen
proposes a method and apparatus that includes a multiple-chamber
electrode arrangement having at least two electrodes placed to
sense and/or pace different chambers or areas of the heart.
Reference is made to U.S. Pat. No. 5,720,518. The proposed method
involves switching from a bipolar to a unipolar configuration
during sensing for determining the origination site of a detected
depolarization signal. If the signal is determined to have arisen
from the SA node in the right atrium, a conduction interval is
applied to allow the cardiac signal to properly propagate to the
other heart chambers. If no cardiac signal is detected in another
cardiac chamber, for example, the left atrium, then pacing is
initiated in that chamber at the end of the conduction interval. In
this example, the interval is equal to the inter-atrial conduction
time (i.e. the time required for a P-wave cardiac signal to
propagate from right atrium to left atrium). However the
inter-atrial conduction time may vary over time and the time for an
excitation pulse to propagate from the right chamber to the left
chamber may be different than the propagation time from the left
chamber to the right chamber. In addition, the conduction time from
the right atrium to the left atrium may vary from that required to
go from the left atrium to the right atrium. Depending on the site
of origin of the detected depolarization, it may be hemodynamically
beneficial to control the coupling interval between the detected
depolarization and the triggered output to the other chamber. U.S.
Pat. No. 5,720,518 does not address the ability to control the
interval between detection and stimulation within the atria or
ventricles in the setting of multisite stimulation.
[0021] Reference is also made to U.S. Pat. No. 5,902,324 to
Thompson et al. in which a multi-channel pacing system having two,
three or four pacing channels, each including a sense amplifier and
pace output pulse generator, is described. A pacing pulse or
detection of a spontaneous depolarization in one of the right or
left heart chambers is followed by a short conduction delay window.
A pacing pulse that would otherwise be delivered at the termination
of the conduction delay window in the opposing heart chamber is
inhibited if the conducted depolarization wave is sensed within the
conduction delay window. While the duration of the conduction delay
window can be programmed, no method is provided by which to select
the optimal interval between chamber depolarizations.
[0022] Patients with marked hemodynamic abnormalities may benefit
from multi-site or multi-chamber pacing that controls the
activation sequence of the heart chambers. Precise control of the
activation sequence may improve the coordination of heart chamber
contractions resulting in more effective filling and ejection of
blood from the heart. Patients with hemodynamic abnormalities often
have conduction defects due to dilation of the heart or other
causes. Yet, even in patients with intact conduction, precise
control of the timing and synchronicity of heart chamber
contractions may provide hemodynamic benefit.
[0023] There remains an unmet need, therefore, for a multi-chamber
or multi-site cardiac stimulation device that allows independent
stimulation and sensing at multiple sites within the heart as well
as flexible selection of stimulation sequence and timing intervals
between these stimulation sites. It would thus be desirable to
provide a multisite or multichamber cardiac stimulation device
having independent sensing and output circuitry for each pacing
site. It would further be desirable to allow flexible selection of
sensing and stimulation polarity for each stimulation site,
including the designation of cathode and anode assignment during
bichamber stimulation. Further, it would be desirable to provide
flexible programming of the stimulation sequence and timing
intervals associated with multisite or multichamber pacing.
Different timing intervals should be advantageously selectable
depending on the origination site of a detected depolarization wave
or a desired directionality of depolarization in order to achieve
optimal hemodynamic or electrophysiological benefit for the
patient.
SUMMARY OF THE INVENTION
[0024] The present invention addresses this need by providing an
implantable multichamber or multisite cardiac stimulation device in
which the electrode configurations for sensing and stimulation are
flexibly programmable, and the stimulation sequence between
multiple sites can be precisely controlled.
[0025] One aspect of the present invention is to provide a
plurality of connection ports, preferably two through four
connection ports, that allow independent connection to the
stimulation device of each electrical lead associated with a
particular stimulation site in the heart. Each connection port
further provides a unique terminal for making electrical contact
with only one electrode such that no two electrodes are required to
be electrically coupled. Furthermore, each electrode, whether
residing on a unipolar, bipolar or multipolar lead, may be
selectively connected or disconnected through programmable
switching circuitry that determines the electrode configurations to
be used for sensing and for stimulating at each stimulation
site.
[0026] Another aspect of the present invention is a unique sensing
circuit associated with each stimulation site such that
depolarizations occurring at each stimulation site can be detected
independently of events occurring at other sites within the heart.
This independent sensing advantageously allows the location of a
detected depolarization to be recognized by the stimulation device.
The desired electrodes to be used for sensing in a specific heart
chamber or at a specific site within a heart chamber are connected
to the input of the sensing circuit via programmable switching
circuitry.
[0027] Still another aspect of the present invention is a unique
output circuit associated with each stimulation site such that each
site can be stimulated independently of other sites or on a
precisely timed basis triggered by events occurring at other sites.
The electrodes used for stimulation at a specific site may be
different than those used for sensing at the same site.
[0028] Yet another aspect of the present invention is the ability
to program unique coupling intervals for precisely controlling the
activation sequence of stimulated sites. Coupling intervals may be
defined in relation to the originating location of a detected
depolarization or in relation to stimulus delivery at another
location. Coupling intervals are advantageously selected in a way
that provides optimal hemodynamic benefit to the patient by
overcoming various conduction disorders or improving coordination
of heart chambers in patients suffering from heart failure. One
embodiment of the present invention includes a method for
automatically determining the optimal coupling intervals and
adjusting the programmed settings based on measurements related to
the hemodynamic state of the heart.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] Further features and advantages of the present invention may
be more readily understood by reference to the following
description taken in conjunction with the accompanying drawings, in
which:
[0030] FIG. 1 is a simplified, partly cutaway view illustrating an
implantable stimulation device in electrical communication with at
least three leads implanted into a patient's heart for delivering
multi-chamber stimulation and shock therapy;
[0031] FIG. 2 is a functional block diagram of the multi-chamber
implantable stimulation device of FIG. 1, illustrating the basic
elements that provide pacing stimulation, cardioversion, and
defibrillation in four chambers of the heart;
[0032] FIG. 3 is a simplified, partly cutaway view illustrating an
implantable stimulation device in electrical communication with at
least four bipolar leads implanted into a patient's heart
representing a preferred embodiment of the present invention;
[0033] FIG. 4 is a block diagram of the stimulation device of FIG.
3, illustrating a switch with four ports for connection to four
leads;
[0034] FIG. 5 depicts a flow chart describing an overview of a
method for automatically configuring sensing electrodes for use in
the cardiac stimulation device of the present invention;
[0035] FIGS. 6 through 9 depict flow chart describing a method for
automatically configuring stimulation electrodes for use in the
cardiac stimulation device of the present invention; and
[0036] FIG. 10 is a flow chart describing an overview of a method
implemented by the stimulation device of FIG. 2, for automatically
adjusting the coupling intervals used in the methods of FIGS. 5 -
9, to achieve an optimal physiological response to a multichamber
stimulation therapy.
DETAILED DESCRIPTION OF THE INVENTION
[0037] The following description is of a best mode presently
contemplated for practicing the invention. This description is not
to be taken in a limiting sense but is made merely for the purpose
of describing the 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.
[0038] The present invention relates to a cardiac stimulation
device capable of delivering precisely ordered stimulation pulses
to multiple chambers of the heart, referred to herein as
multi-chamber stimulation, or to multiple sites within a chamber of
the heart, referred to herein as multi-site stimulation. As used
herein, the shape of the stimulation pulses is not limited to an
exact square or rectangular shape, but may assume any one of a
plurality of shapes which is adequate for the delivery of an energy
packet or stimulus.
[0039] The stimulation device is intended for use in patients
suffering from hemodynamic dysfunction, which may or may not be
accompanied by conduction disorders. Precisely controlled
stimulation at multiple sites or in multiple chambers is provided
to intentionally make use of the pacing function of the heart in
order to improve cardiac hemodynamics by re-coordinating heart
chamber contractions and/or preventing arrhythmogenic
depolarizations from occurring. Thus, the cardiac stimulation
device is capable of delivering at least low-voltage stimulation
pulses to multiple stimulation sites for providing pacing therapy,
and may include high-voltage stimulation shocks for providing
cardioversion therapy and defibrillation therapy.
[0040] FIG. 1 illustrates a stimulation device 10 in electrical
communication with a patient's heart 12 by way of three leads 20,
24 and 30 suitable for delivering multi-chamber stimulation and
shock therapy. To sense right atrial cardiac signals and to provide
right atrial chamber stimulation therapy, the stimulation device 10
is coupled to an implantable right atrial lead 20 having at least
an atrial tip electrode 22, which typically is implanted in the
patient's right atrial appendage.
[0041] To sense left atrial and/or left ventricular cardiac signals
and to provide left-chamber pacing therapy, the stimulation device
10 is coupled to a "coronary sinus" lead 24 designed for placement
in the "coronary sinus region" via the coronary sinus os so as to
place a distal electrode adjacent to the left ventricle and
additional electrode(s) adjacent to the left atrium. As used
herein, the phrase "coronary sinus region" refers to the
vasculature of the left ventricle, including any portion of the
coronary sinus, 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 coronary
sinus. It could also be an epicardial lead placed at the time of
thoracotomy or thorascopy.
[0042] Accordingly, the coronary sinus lead 24 is designed to
receive atrial and/or ventricular cardiac signals and to deliver:
left ventricular pacing therapy using at least a left ventricular
tip electrode 26, left atrial pacing therapy using at least a left
atrial ring electrode 27, and shocking therapy using at least a
left atrial coil electrode 28. For a more detailed description of a
coronary sinus lead, refer to U.S. patent application Ser. No.
09/196,898, titled "A Self-Anchoring Coronary Sinus Lead" (Pianca
et. al), and U.S. Pat. No. 5,466,254, titled "Coronary Sinus Lead
with Atrial Sensing Capability" (Helland) that are incorporated
herein by reference.
[0043] The stimulation device 10 is also shown in electrical
communication with the patient's heart 12 by way of an implantable
right ventricular lead 30 having, in this embodiment, a right
ventricular tip electrode 32, a right ventricular ring electrode
34, a right ventricular (RV) coil electrode 36, and an SVC coil
electrode 38. Typically, the right ventricular lead 30 is
transvenously inserted into the heart 12 so as to place the right
ventricular tip electrode 32 in the right ventricular apex so that
the RV coil electrode 36 will be positioned in the right ventricle
and the SVC coil electrode 38 will be positioned in the superior
vena cava. Accordingly, the right ventricular lead 30 is capable of
receiving cardiac signals, and delivering stimulation in the form
of pacing and shock therapy to the right ventricle.
[0044] FIG. 2 illustrates a simplified block diagram of the
multi-chamber implantable stimulation device 10, which is capable
of treating both fast and slow arrhythmias with stimulation
therapy, including cardioversion, defibrillation, and pacing
stimulation. While a particular multi-chamber device 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/or pacing stimulation.
[0045] The stimulation device 10 includes a housing 40 which is
often referred to as "can", "case" or "case electrode", and which
may be programmably selected to act as the return electrode for all
"unipolar" modes. The housing 40 may further be used as a return
electrode alone or in combination with one or more coil electrodes
28, 36, or 38, for shocking purposes. The housing 40 further
includes a connector having a plurality of terminals, 42, 44, 46,
48, 52, 54, 56, and 58 (shown schematically and, for convenience,
the names of the electrodes to which they are connected are shown
next to the terminals). In accordance with the present invention,
the connector will provide a unique connection port for each lead
in communication with the heart so as to avoid the necessity of
adapters. Furthermore, the connector will provide a unique terminal
for electrical connection to each electrode(s) associated with each
stimulation site within the heart 12. In this way, coupling of more
than one stimulation site using adaptors, or hardwiring between
terminals inside the connector, is avoided allowing independent
stimulation and sensing at each stimulation site.
[0046] As such, in the embodiment of FIG. 2, the connector includes
at least a right atrial tip terminal 42 adapted for connection to
the atrial (A.sub.R) tip electrode 22 in order to achieve right
atrial sensing and pacing.
[0047] To achieve left chamber sensing, pacing and/or shocking, the
connector includes at least a left ventricular (V.sub.L) tip
terminal 44, a left atrial (A.sub.L) ring terminal 46, and a left
ventricular (V.sub.L) shocking terminal (coil) 48, which are
adapted for connection to the left ventricular tip electrode 26,
the left atrial ring electrode 27, and the left atrial coil
electrode 28, respectively.
[0048] To support right ventricular sensing, pacing and/or
shocking, the connector further includes a right ventricular
(V.sub.R) tip terminal 52, a right ventricular (V.sub.R) ring
terminal 54, a right ventricular (RV) shocking terminal (coil) 56,
and an SVC shocking terminal (coil) 58, which are adapted for
connection to the right ventricular tip electrode 32, right
ventricular ring electrode 34, the RV coil electrode 36, and the
SVC coil electrode 38, respectively. Thus, the embodiment of FIG. I
includes one connection port for the right atrial lead 20 and two
bipolar, high-voltage connection ports for the right ventricular
lead 30 and the coronary sinus lead 24, allowing sensing and
stimulation in all four chambers of the heart.
[0049] In alternative embodiments, the stimulation device 10 may
include a multi-port connector capable of accommodating any
combination of three, four or more uni-polar, bi-polar or
multi-polar leads. The arrangement and type of leads used may vary
depending on the type of stimulation therapy to be delivered and
individual patient need. In a preferred embodiment, to be described
later in conjunction with FIG. 3, four bipolar connection ports are
provided to accommodate a programmable selection of unipolar,
bipolar or combination stimulation and sensing in any or all four
chambers of the heart, or at four sites within the heart 12.
[0050] At the core of the stimulation device 10 is a programmable
microcontroller 60 that controls the various modes of stimulation
therapy. As is well known in the art, the microcontroller 60
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 60 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 60 are not critical
to the present invention. Rather, any suitable microcontroller 60
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.
[0051] As shown in FIG. 2, an atrial pulse generator 70 and a
ventricular pulse generator 72 generate pacing stimulation pulses
for delivery by the right atrial lead 20, the right ventricular
lead 30 and/or the coronary sinus lead 24, via the switch bank 74.
It is understood that in order to provide stimulation therapy in
each of the four chambers of the heart, or at multiple sites within
one or more chambers, the atrial pulse generator 70 and the
ventricular pulse generator 72 include dedicated, independent pulse
generators, multiplexed pulse generators, or shared pulse
generators. However, in order to provide independent stimulation at
each stimulation site, atrial pulse generator 70 and ventricular
pulse generator 72 include independent output circuits for each
stimulation site that allow delivery of unique stimulation pulses
to each site.
[0052] The atrial pulse generator 70 in FIG. 2 thus includes a
right atrial output circuit for delivering stimulation pulses to
the right atrium via right atrial lead 20, and further includes a
left atrial output circuit for delivering stimulation pulses to the
left atrium via coronary sinus lead 24. The ventricular pulse
generator 72 includes a right ventricular output circuit for
delivering stimulation pulses to the right ventricle via right
ventricular lead 30, and further includes a left ventricular output
circuit for delivering stimulation pulses to the left ventricle via
the coronary sinus lead 24. The atrial pulse generator 70 and the
ventricular pulse generator 72 are controlled by the
microcontroller 60 via appropriate control signals 76 and 78,
respectively, to trigger or inhibit the stimulation pulses.
[0053] The microcontroller 60 further includes timing control
circuitry 79 which is used to control the timing of such
stimulation pulses (e.g. pacing rate, atrio-ventricular (AV) delay,
interatrial conduction (A-A) delay, or interventricular conduction
(V-V) delay, etc.), as well as to keep track of the timing of
refractory periods, PVARP intervals, noise detection windows,
evoked response windows, alert intervals, marker channel timing,
etc.
[0054] In accordance with one embodiment of the present invention,
the timing control circuitry 79 is also used to control coupling
intervals, which precisely control the stimulation sequence during
multi-chamber or multi-site stimulation. For example, the
interatrial conduction (A-A) delay may be determined by
programmable selection of coupling intervals defined according to
whether an intrinsic atrial depolarization is first sensed in the
right atrium or in the left atrium. A right-to-left atrial coupling
interval may be programmed to control the time between a right
atrial detected event (P-wave) and the delivery of a left atrial
stimulation pulse. A different left-to-right atrial coupling
interval may be programmed to control the time between a left
atrial detected P-wave and right atrial stimulation pulse
delivery.
[0055] Furthermore, different coupling intervals may be defined in
relation to paced events than detected events. Hence, the coupling
interval between a right atrial paced event and a left atrial paced
event may be different than the coupling interval between a right
atrial detected event (intrinsic P-wave) and a left atrial paced
event. In other words, for each stimulation site, a unique coupling
interval between it and all other stimulation sites may be defined
in relation to both paced events and detected events occurring at
that site. Details regarding the application of coupling intervals
as provided by the present invention will be described later in
conjunction with FIGS. 5 through 10.
[0056] The switch bank 74 includes a plurality of switches for
connecting the desired electrodes to the appropriate I/O circuits,
thereby providing complete electrode programmability. Accordingly,
the switch bank 74, in response to a control signal 80 from the
microcontroller 60, determines the polarity of the stimulation
pulses (e.g. unipolar, bipolar, combined manner, etc.) by
selectively closing the appropriate combination of switches (not
shown).
[0057] In addition to providing programmable stimulation polarity,
the stimulation device 10 includes the programmable polar
assignments of each electrode during bipolar or unipolar
stimulation. For example, bi-ventricular stimulation may be
provided in a combined manner between the right ventricular tip
electrode 32 and left ventricular tip electrode 26 by connecting
these two tip electrodes to ventricular pulse generator 72 via
switch bank 74.
[0058] The stimulation device 10 provides the programmable
assignment of cathode and anode poles in the following stimulation
configuration. The left ventricular tip electrode 26 may be
selected as the cathode with the right ventricular tip electrode 32
selected as the anode, to achieve one directionality and
stimulation threshold. Alternatively, the left ventricular tip
electrode 26 may be selected as the anode and the right ventricular
tip electrode 32 may be selected as the cathode, to achieve a
different directionality and stimulation threshold. In this way,
the selection of cathode and anode assignments during bi-atrial or
bi-ventricle stimulation, or within a chamber during multisite
stimulation, may be tailored to meet the individual patient's
need.
[0059] In some patients it may be advantageous to provide anodal
stimulation rather than cathodal stimulation. Hence, it is one
feature of the present invention to further allow assignment of the
active electrode used in unipolar stimulation to be the anode with
the housing 40 assigned as the cathode. For example, unipolar
anodal stimulation of the right ventricle may be achieved by
designating the right ventricular ring electrode 54 as the anode
and the housing 40 as the cathode.
[0060] The programmable designation of electrode poles is
preferably accomplished via electronic switching devices controlled
by logic gates receiving high or low signals under the control of
microprocessor 60. For details regarding a switching circuitry that
may be used for providing programmable selection of stimulation and
sensing electrode configurations, refer to U.S. Pat. No. 4,991,583
to Silvian, hereby incorporated herein by reference.
[0061] Atrial sensing circuit 82 and ventricular sensing circuit 84
may also be selectively coupled to the right atrial lead 20,
coronary sinus lead 24, and the right ventricular lead 30, through
the switch bank 74, for detecting the presence of cardiac activity
in each of the four chambers of the heart. In order to detect
events occurring within each chamber or at each stimulation site
independently, the atrial and ventricular sensing circuits 82 and
84 include dedicated independent sense amplifiers associated with
each stimulation site within the heart 12. As used herein, each of
the atrial sensing circuit 82 and the ventricular sensing circuit
84 includes a discriminator, which is a circuit that senses and can
indicate or discriminate the origin of a cardiac signal in each of
the cardiac chambers.
[0062] The inputs to each sense amplifier are programmable and may
be selected in any combination of available electrode terminals in
order to provide independent unipolar or bipolar sensing at each
stimulation site. In this way, a detected atrial event may be
distinguished as being a right atrial event or a left atrial event.
Likewise, a detected ventricular event may be distinguished as a
right ventricular event or a left ventricular event.
[0063] If the stimulation device 10 is being used for multisite
stimulation within a chamber of the heart, one electrode might be
positioned in the upper area of the chamber and a second electrode
might be positioned in a lower area of the same chamber or any two
distinct locations within that chamber. Unique sensing circuitry
for each electrode allows discrimination of a detected event as
occurring in either the upper area or the lower area of the
chamber. The stimulation response provided by the device 10 may
then be determined based on the location of a detected event.
[0064] Additionally, combination sensing for bi-atrial or
bi-ventricular sensing during multichamber stimulation or
combipolar sensing within a single chamber during multisite
stimulation may be selected by programming the appropriate inputs
to the individual sense amplifiers. The switch bank 74 determines
the "sensing polarity" of the cardiac signal by selectively closing
the appropriate switches. In this way, the clinician may program
the sensing polarity independent of the stimulation polarity.
[0065] Each of the atrial sensing circuit 82 or the ventricular
sensing circuit 84 preferably employs one or more low power,
precision amplifiers with programmable gain and/or automatic gain
control, bandpass filtering, and a threshold detection circuit, to
selectively sense the cardiac signal of interest. The automatic
gain control enables the stimulation device 10 to deal effectively
with the difficult problem of sensing the low amplitude signal
characteristics of atrial or ventricular fibrillation. The outputs
of the atrial and ventricular sensing circuits 82 and 84 are
connected to the microcontroller 60 for triggering or inhibiting
the atrial and ventricular pulse generators 70 and 72,
respectively, in a demand fashion, in response to the absence or
presence of cardiac activity, respectively, in the appropriate
chambers of the heart.
[0066] One feature of the present invention is to provide precise
control of the activation sequence of the stimulation sites. To
this end, the stimulation device 10 may act only in a trigger mode
thereby gaining complete control of the heart rhythm in an attempt
to provide a more hemodynamically effective contraction sequence of
the heart chambers than that produced by the natural heart
rhythm.
[0067] Preferably, the stimulation device 10 operates in a trigger
mode in controlling the timing of contraction at all the
stimulation sites. Alternatively, it may operate in a demand mode
in delivering or inhibiting stimulation pulses to at least one
site, and may operate in a trigger mode in delivering stimulation
pulses to all other stimulation sites. For example, atrial pulse
generator 70 may be inhibited from delivering a right atrial
stimulation pulse when atrial sensing circuit 82 detects an
intrinsic P-wave in the right atrium within a given escape
interval. However, this detection may cause microcontroller 60 to
trigger atrial pulse generator 70 and ventricular pulse generator
72 to deliver stimulation pulses at prescribed intervals of time to
the left atrium and the right and left ventricles, respectively,
regardless of any events detected in these chambers. In this way,
the activation sequence of all four heart chambers is precisely
controlled by the natural pacemaking activity of the sinus node.
Hence, in the present invention, the pacing mode of stimulation
device 10, that is demand or trigger mode, for each stimulation
site is preferably programmable.
[0068] If the cardiac stimulation device 10 is also intended for
delivering cardioversion and defibrillation therapy, arrhythmia
detection by the stimulation device 10 utilizes the atrial and
ventricular sensing circuits 82 and 84 to sense cardiac signals,
for determining 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. P-waves, R-waves, and depolarization
signals associated with fibrillation which are sometimes referred
to as "F-waves" or "Fib-waves") are then classified by the
microcontroller 60 by comparing them to a predefined rate zone
limit (e.g. bradycardia, normal, low rate VT, high rate VT, 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, anti-tachycardia pacing, cardioversion
shocks or defibrillation shocks, collectively referred to as
"tiered therapy").
[0069] Cardiac signals are also applied to the inputs of an
analog-to-digital (A/D) data acquisition system 90. The data
acquisition system 90 is configured to acquire intracardiac
electrogram (EGM) signals, convert the raw analog data into digital
signals, and store the digital signals for later processing and/or
telemetric transmission to an external device 102. The data
acquisition system 90 is coupled to the right atrial lead 20, the
coronary sinus lead 24, and the right ventricular lead 30 through
the switch bank 74 to sample cardiac signals across any pair of
desired electrodes.
[0070] The microcontroller 60 is further coupled to a memory 94 by
a suitable data/address bus 96, wherein the programmable operating
parameters used by the microcontroller 60 are stored and modified,
as required, in order to customize the operation of the stimulation
device 10 to suit the needs of a particular patient. Such operating
parameters define, for example, pacing pulse amplitude, pulse
duration, electrode polarity, rate, sensitivity, automatic
features, arrhythmia detection criteria, and the amplitude, wave
shape and vector of each shocking pulse to be delivered to the
patient's heart 12 within each respective tier of therapy.
[0071] Advantageously, the operating parameters of the stimulation
device 10 may be non-invasively programmed into the memory 94
through a telemetry circuit 100 in telemetric communication with
the external device 102, such as a programmer, transtelephonic
transceiver, or a diagnostic system analyzer. The telemetry circuit
100 is activated by the microcontroller 60 by a control signal 106.
The telemetry circuit 100 advantageously allows intracardiac
electrograms and status information relating to the operation of
the stimulation device 10 (as contained in the microcontroller 60
or memory 94) to be sent to the external device 102 through the
established communication link 104.
[0072] The stimulation device 10 may further include a physiologic
sensor 108, 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 108 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). Accordingly, the microcontroller 60 responds by
adjusting the various pacing parameters (such as rate, AV Delay,
V-V Delay, etc.) at which the atrial and ventricular pulse
generators 70 and 72 generate stimulation pulses.
[0073] In accordance with one feature of the present invention,
coupling intervals that determine the activation sequence of
stimulated chambers or sites, may be adjusted based on changes
detected by the physiologic sensor 108. Preferably physiologic
sensor 108 includes detection of changes related to the hemodynamic
state of the patient and thereby allows adjustment of the coupling
intervals to be made in a way that optimizes the hemodynamic
response to multisite or multichamber stimulation. One method for
accomplishing automatic adjustment of coupling intervals based on
physiologic sensor 108 data will be described in detail in
conjunction with FIG. 10.
[0074] While the physiologic sensor 108 is shown as being included
within the stimulation device 10, it is to be understood that the
physiologic sensor 108 may alternatively be external to the
stimulation device 10, yet still be implanted within, or carried by
the patient. A common type of rate responsive sensor is an activity
sensor, such as an accelerometer or a piezoelectric crystal, which
is mounted within the housing 40 of the stimulation device 10.
Other types of physiologic sensors are also known, for example,
sensors which sense the oxygen content of blood, cardiac output,
respiration rate and/or minute ventilation, pH of blood,
ventricular gradient, etc. However, any sensor may be used which is
capable of sensing a physiological parameter, which corresponds to
the exercise or hemodynamic state of the patient.
[0075] The stimulation device 10 additionally includes a power
source such as a battery 110 that provides operating power to all
the circuits shown in FIG. 2. For the stimulation device 10, which
employs shocking therapy, the battery 110 must be capable of
operating at low current drains for long periods of time, and also
be capable of providing high-current pulses (for capacitor
charging) when the patient requires a shock pulse. The battery 110
must preferably have a predictable discharge characteristic so that
elective replacement time can be detected. Accordingly, the
stimulation device 10 can employ, for example, lithium/silver
vanadium oxide batteries.
[0076] As further shown in FIG. 2, the stimulation device 10 is
shown as having an impedance measuring circuit 112 which is enabled
by the microcontroller 60 by a control signal 114. The known uses
for an impedance measuring circuit 120 include, but are not limited
to, lead impedance surveillance during the acute and chronic phases
for assessing the mechanical integrity of the lead; detecting
operable electrodes and automatically switching to an operable pair
if mechanical disruption occurs in one lead; measuring respiration
or minute ventilation; detecting when the device has been
implanted; and a variety of hemodynamic variables such as measuring
stroke volume; and detecting the opening of the valves, etc. The
impedance measuring circuit 120 is advantageously coupled to the
switch bank 74 so that any desired electrode may be used.
[0077] The impedance measuring circuit 112 may be used
advantageously in the present invention for monitoring hemodynamic
indicators, such as ventricular impedance as an indication of
cardiac output, to provide feedback in the selection of optimal
coupling intervals. Impedance measuring circuit 112 may be used
alone or in conjunction with physiological sensor 108 for providing
such feedback. This data may be periodically stored in memory 94
such that a physician may then access this data during patient
follow-up visits to obtain useful information in manually selecting
and programming coupling intervals. Preferably, this data may be
used by the stimulation device 10 to automatically adjust coupling
intervals as will be described in conjunction with FIG. 10.
[0078] In cases where a primary function of the stimulation device
10 is to operate as an implantable cardioverter/defibrillator (ICD)
device, it must detect the occurrence of an arrhythmia, and
automatically apply an appropriate antitachycardia pacing (ATP)
and/or electrical shock therapy to the heart aimed at terminating
the detected arrhythmia. To this end, the microcontroller 60
further controls a shocking circuit 116 by way of a control signal
118. The shocking circuit 116 generates shocking pulses of low (up
to 0.5 Joules), moderate (0.5-10 Joules), or high (11 to 40 Joules)
energy, as controlled by the microcontroller 60. Such shocking
pulses are applied to the patient's heart through at least two
shocking electrodes, and as shown in this embodiment, selected from
the left atrial coil electrode 28, the RV coil electrode 36, and/or
the SVC coil electrode 38 (FIG. 1). As noted earlier, the housing
40 may act as an active electrode in combination with the RV
electrode 36, or as part of a split electrical vector using the SVC
coil electrode 38 or the left atrial coil electrode 28 (i.e., using
the RV electrode as common electrode).
[0079] 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 an R-wave 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 asychronously (since
R-waves may be too disorganized), and pertaining exclusively to the
treatment of fibrillation. Accordingly, the microcontroller 60 is
capable of controlling the synchronous or asynchronous delivery of
the shocking pulses.
[0080] FIG. 3 illustrates a preferred embodiment of the present
invention showing one bipolar lead 20 implanted in the right
atrium, one bipolar lead 21 implanted in the coronary sinus region
adjacent to left atrium, one bipolar high-voltage lead 30 implanted
in the right ventricle, and another bipolar high-voltage lead 31
implanted in the coronary sinus region adjacent to the left
ventricle. Using this electrode configuration with the stimulation
device 10, independent unipolar or bipolar stimulation and sensing
of either or both atria is possible, or, alternatively, combination
bi-atrial stimulation or sensing can be performed with the cathode
and anode assignments applied to the right atrial tip electrode 22,
right atrial ring electrode 23, left atrial ring electrode 27, and
left atrial tip electrode 29 as desired.
[0081] In addition, independent unipolar or bipolar stimulation and
sensing can be provided separately in the right and left ventricles
or, alternatively, combination bi-ventricular stimulation or
sensing can be performed with the cathode and anode assignments
applied to the right ventricular tip electrode 32, right
ventricular ring electrode 34, left ventricular ring electrode 25,
and left ventricular tip electrode 26 as desired.
[0082] In this embodiment, and as further illustrated in FIG. 4,
the stimulation device 10 of FIG. 3 includes four bipolar
connection ports 200, 210, 220 and 230. A left ventricular
connection port (LV connection port) 200 accommodates the left
ventricular lead (LV lead) 24 with terminals 44, 45, 48 that are
associated with the left ventricular tip electrode (LV tip
electrode) 26, the left ventricular ring electrode (LV ring
electrode) 25, and the left atrial coil electrode (LA coil
electrode) 28, respectively.
[0083] A left atrial connection port (LA connection port) 210
accommodates the left atrial lead (LA lead) 21 with terminals 49,
47 that are associated with the left atrial tip electrode (LA tip
electrode) 29 and the left atrial ring electrode (LA ring
electrode) 27, respectively. A right ventricular connection port
(RV connection port) 220 accommodates the right ventricular lead
(RV lead) 30 with terminals 52, 54, 56, 58 that are associated with
the right ventricular tip electrode (RV tip electrode) 32, the
right ventricular ring electrode (RV ring electrode) 34, the right
ventricular coil electrode (RVCE) 36 and the right ventricular SVC
coil electrode (RV SVC coil electrode) 38, respectively. A right
atrial connection port (RA connection port) 230 accommodates the
right atrial lead (RA lead) 20 with terminals that are associated
with the right atrial tip electrode (RA tip electrode) 22 and the
right atrial ring electrode (RA ring electrode) 23,
respectively.
[0084] It is recognized that numerous variations exist in which
combinations of unipolar, bipolar and/or multipolar leads may be
positioned at desired locations within the heart in order to
provide multichamber or multisite stimulation. The present
invention provides for the flexibility of independent stimulation
and/or sensing at multiple sites by providing a cardiac stimulation
device that includes multiple connection ports with unique
terminals for the electrode(s) associated with each stimulation
site as well as independent sensing and output circuitry for each
stimulation site. As such, stimulation and sensing sites are not
obligatorily coupled together by adapters or hardwiring within the
stimulation device that would otherwise preclude independent
sensing and stimulation at each pacing site during either
multichamber or multisite pacing.
[0085] FIGS. 5 and 6 illustrate a flow chart describing methods of
operation 200 and 300, respectively, that are implemented in one
embodiment of the stimulation device 10 in which defined coupling
intervals are applied by microcontroller 60 for controlling the
sequence of stimulation pulse delivery by the atrial pulse
generator 70 and the ventricular pulse generator 72. In this flow
chart, and the other flow charts described herein, the various
algorithmic steps are summarized in individual "blocks". Such
blocks describe specific actions or decisions that must be made or
carried out as the algorithm proceeds. Where a microcontroller (or
equivalent) is employed, the flow charts presented herein provide
the basis for a "control program" that may be used by such a
microcontroller (or equivalent) to effectuate the desired control
of the stimulation device. Those skilled in the art may readily
write such a control program based on the flow charts and other
descriptions presented herein.
[0086] The methods 200 and 300 will be described in relation to the
implant configuration of FIG. 3, where sensing and pacing are
performed in the right atrium, left atrium, right ventricle and
left ventricle. It is recognized that the algorithmic steps
illustrated in FIGS. 5 and 6 may easily be modified to control the
stimulation sequence during any multichamber or multi-site
stimulation configuration.
[0087] At the time of implant, coupling intervals are programmed by
the physician to precisely control the activation sequence of all
four chambers whenever pacing is required. Default nominal values
stored in the stimulation device 10 may also be selected. Coupling
intervals are defined in association with paced and sensed events
occurring at each stimulation site. For example, the delivery of a
right atrial stimulation pulse by the atrial pulse generator 70
will cause microcontroller 60 to initiate three coupling intervals:
one associated with the left atrium; another associated with the
right ventricle; and yet another associated with the left
ventricle. These coupling intervals control the time between the
delivery of the right atrial stimulation pulse and the delivery of
the left atrial, right ventricular, and left ventricular
stimulation pulses, respectively.
[0088] Likewise, the detection of a P-wave in the right atrium by
the atrial sense circuitry 82 will also cause microcontroller 60 to
initiate three coupling intervals associated with the left atrium,
right ventricle, and left ventricle. However, these coupling
intervals may be different than the coupling intervals initiated
due to a right atrial paced event. Similarly, left atrial coupling
intervals are defined for the case of a left atrial event being
detected before a right atrial event for controlling the time
between the left atrial detection and right atrial stimulation,
right ventricular stimulation and left ventricular stimulation. In
addition, the system can be configured to deliver the left atrial
stimulus before the right atrial stimulus, or the left ventricular
stimulus before the right ventricular stimulus.
[0089] The method 200 and 300 of FIGS. 5 and 6 represent the
application of these coupling intervals over one cardiac cycle. It
is assumed in this example, that the stimulation device 10 is
programmed to operate in a demand mode in the atrial channels and
in a triggered mode in the ventricular channels although, it can be
set to operate in the triggered mode in both the atrium and
ventricle or the triggered mode in the atrium and the demand mode
in the ventricle.
[0090] Starting at step 202, a new escape interval is initiated.
The length of this escape interval is determined by the programmed
base pacing (or stimulation) rate. For example, if the base pacing
rate is programmed to be 60 beats per minute, then the escape
interval is 1000 msec. Method 200 waits for the detection of an
intrinsic P-wave by atrial sense circuit 82 prior to expiration of
the escape interval.
[0091] If at decision step 204 the method 200 determines that the
escape interval has expired before an intrinsic P-wave is detected,
microprocessor 60 triggers the right atrial output circuitry in the
atrial pulse generator 70 to deliver a stimulation pulse to the
right atrium at step 206, according to the programmed electrode
configuration for stimulation in the right atrium.
[0092] The delivery of a right atrial stimulation pulse causes
microprocessor 60 to trigger timing control circuitry 79 to start
three separate timers simultaneously at step 208. As it is
illustrated in FIG. 7, one timer initiates a right atrial pace to
left atrium (RApace to LA) coupling interval at step 325. Another
timer initiates a right atrial pace to right ventricle (RApace to
RV) coupling interval at step 335. The third timer simultaneously
initiates a right atrial pace to left ventricle (RApace to LV)
coupling interval at step 345. Upon expiration of the coupling
intervals, the stimulation device 10 delivers the required
stimulation pulses at step 310.
[0093] FIG. 7 illustrates further details of step 310. Upon
expiration of the right atrial pace to left atrium (RApace to LA)
coupling interval (step 325), method 300 inquires, at decision step
326, if an intrinsic left atrial depolarization (P-wave) is
detected. If it is, method 300 inhibits the delivery of a left
atrial stimulation pulse at step 328. If an intrinsic left atrial
depolarization is not detection at step 326, the microcontroller 60
triggers the left atrial output circuitry of atrial pulse generator
70 to deliver a left atrial (LA) stimulation pulse at step 327.
[0094] Similarly, upon expiration of the right atrial pace to left
atrium (RApace to RV) coupling interval at step 335, method 300
inquires, at decision step 336, if an intrinsic right ventricular
depolarization (R-wave) is detected. If it is, method 300 inhibits
the delivery of a right ventricular stimulation pulse at step 338.
If an intrinsic right ventricular depolarization is not detection
at step 336, the microcontroller 60 triggers the right atrial
output circuitry of the ventricular pulse generator 72 to deliver a
right ventricular (RV) stimulation pulse at step 337.
[0095] In a similar manner, upon expiration of the right atrial
pace to left ventricle (RApace to LV) coupling interval at step
345, method 300 inquires, at decision step 346, if an intrinsic
left ventricular depolarization (R-wave) is detected. If it is,
method 300 inhibits the delivery of a left ventricular stimulation
pulse at step 348. If an intrinsic left ventricular depolarization
is not detected at step 346, the microprocessor 60 triggers the
left atrial output circuitry of the ventricular pulse generator 72
to deliver a left ventricular (LV) stimulation pulse at step
347.
[0096] With respect to steps 328, 338, and 348, if a sensed event
occurs on the atrial channel or the ventricular channel, method 300
detects the chamber in which the sensed event originated and the
times the delivery of the output pulse to the other chamber in
accord with the automatic or physician set interval.
[0097] After the expiration of all these three coupling intervals
and the delivery of triggered stimulation to the designated
stimulation sites, method 300 returns to step 202 where the
microprocessor 60 initiates a new escape interval to start the next
cardiac pacing cycle.
[0098] Returning now to FIGS. 5 and 6, if a P-wave is detected by
the atrial sense circuitry 82 prior to the expiration of the escape
interval at decision step 204, methods 200 and 300 determine, at
decision step 216, if this detection has been made by the right
atrial sensing circuitry or the left atrial sensing circuitry of
the atrial sense circuit 82.
[0099] If a P-wave is detected at step 204 and the microprocessor
60 determines that the P-wave has been detected in the left atrial
sense circuitry of atrial sense circuitry 82 at decision step 216,
then the coupling intervals associated with a left atrial sense
event are initiated by timing the control circuitry 79 at step 217.
As it is illustrated in FIG. 8, a left atrial sense to right atrial
(LAsense to RA) coupling interval is initiated in one timer at step
425. This coupling interval may or may not be equal to the coupling
interval between the right and left atria associated with a
detected right atrial event.
[0100] On a separate timer, the timing control circuitry 79
simultaneously initiates a left atrial sense to right ventricle
(LAsense to RV) coupling interval at step 435. Another timer starts
the left atrial sense to left ventricle (LAsense to LV) coupling
interval at step 445. If a sensed event occurs within the
designated coupling intervals, the timing of the stimulus output to
the other chamber is based on the sensed event and not the output
pulse in the atrium. Upon expiration of the coupling intervals, the
stimulation device 10 delivers the required stimulation pulses at
step 318.
[0101] FIG. 8 illustrates further details of step 318. Upon
expiration of the left atrial sense to right atrial (LAsense to RA)
coupling interval at step 425, method 300 inquires, at decision
step 426, if an intrinsic right atrial depolarization (P-wave) is
detected. If it is, method 300 inhibits the delivery of a right
atrial stimulation pulse at step 428. If an intrinsic left atrial
depolarization is not detection at step 426, the microprocessor 60
triggers the right atrial output circuitry of the atrial pulse
generator 70 to deliver a stimulation pulse to the right atrium at
step 427.
[0102] Similarly, upon expiration of the left atrial to right
ventricular (LAsense to RV) coupling interval at step 435, method
300 inquires, at decision step 436, if an intrinsic right
ventricular depolarization (R-wave) is detected. If it is, method
300 inhibits the delivery of a right ventricular stimulation pulse
at step 438. If an intrinsic right ventricular depolarization is
not detection at step 436, the microcontroller 60 triggers right
ventricular output circuitry of the ventricular pulse generator 72
to deliver a stimulation pulse to the right ventricle at step
437.
[0103] In a similar manner, upon expiration of the left atrial to
left ventricular (LAsense to LV) coupling interval at step 445,
method 300 inquires, at decision step 446, if an intrinsic left
ventricular depolarization (R-wave) is detected. If it is, method
300 inhibits the delivery of a left ventricular stimulation pulse
at step 348. If an intrinsic left ventricular depolarization is not
detection at step 446, the microprocessor 60 triggers the left
ventricular output circuit of the ventricular pulse generator 72 to
deliver a stimulation pulse to the left ventricle at step 447.
[0104] Returning now to FIGS. 5 and 6, if the P-wave detection has
been made in the right atrium, the microprocessor 60 commands the
timing control circuitry 79 to simultaneously initiate three
different timers at step 220. As it is illustrated in FIG. 9, one
timer starts the right atrial sense to left atrium (RAsense to LA)
coupling interval (step 455). Another timer simultaneously starts
the right atrial sense to right ventricle (RAsense to RV) coupling
interval (step 465). The third timer starts the right atrial sense
to left ventricle (RAsense to LV) coupling interval (step 475).
These coupling intervals triggered by a right atrial sense event
may be different than the coupling intervals triggered by a right
atrial pace event as described above in conjunction with steps 425,
435, and 445. Upon expiration of the coupling intervals, the
stimulation device 10 delivers the required stimulation pulses at
step 322.
[0105] FIG. 9 illustrates further details of step 322. Upon
expiration of the right atrial sense to left atrium (RAsense to LA)
coupling interval at step 455, method 300 inquires, at decision
step 456, if an intrinsic right atrial depolarization (P-wave) is
detected. If it is, method 300 inhibits the delivery of a left
atrial stimulation pulse at step 457. If an intrinsic left atrial
depolarization is not detection at step 456, the microprocessor 60
triggers the left atrial output circuitry of the atrial pulse
generator 70 to deliver a left atrial (LA) stimulation pulse at
step 457.
[0106] Similarly, upon expiration of the right atrial pace to right
ventricular (RApace to RV) coupling interval at step 465, method
300 inquires, at decision step 466, if an intrinsic right
ventricular depolarization (R-wave) is detected. If it is, method
300 inhibits the delivery of a right ventricular stimulation pulse
at step 468. If an intrinsic right ventricular depolarization is
not detection at step 436, the microcontroller 60 triggers the
ventricular pulse generator 72 to deliver a right ventricular (RV)
stimulation pulse at step 467.
[0107] In a similar manner, upon expiration of the right atrial
sense to left ventricular (RAsense to LV) coupling interval at step
475, method 300 inquires, at decision step 476, if an intrinsic
left ventricular depolarization (R-wave) is detected. If it is,
method 300 inhibits the delivery of a left ventricular stimulation
pulse at step 478. If an intrinsic left ventricular depolarization
is not detection at step 476, the microprocessor 60 triggers the
left atrial output circuitry of the ventricular pulse generator 72
to deliver a left ventricular (LV) stimulation pulse. After the
expiration of these three coupling intervals and the delivery of
triggered stimulation to the designated stimulation sites, method
300 returns to step 202 (FIG. 6) where the microprocessor 60
initiates a new escape interval to start the next cardiac
cycle.
[0108] In this way, the sequential delivery of stimulation pulses
to all four chambers of the heart is precisely controlled in order
to provide coordinated depolarization of the cardiac chambers. In
this example, the stimulation device 10 essentially operates in a
demand pacing mode in the right and left atria and in a triggered
pacing mode in the right and left ventricles, though other
possibilities are similarly feasible, as described herein. Sensing
within all of these chambers is still provided, however, in order
to accommodate the tachycardia detection features of the
stimulation device 10, and to utilize its ability to deliver
shocking therapy in addition to pacing therapy as needed.
[0109] The programmed settings of the coupling intervals described
in conjunction with FIG. 5 are preferably selected in a way that
provides optimal hemodynamic benefit to the patient. A medical
practitioner may manually program these settings based on clinical
measurements of cardiac performance. It is recognized that the
selection and programming of numerous coupling intervals associated
with numerous stimulation sites could become a time-consuming task.
Therefore, the selection of coupling intervals may be
semi-automatic or completely automatic. For example, after manual
programming of the most critical coupling intervals, the
microprocessor 60 might calculate other coupling intervals based on
mathematical relationships or patient's history stored in memory
90, or apply default values to other coupling intervals.
[0110] In an alternative embodiment of the present invention, the
optimal coupling intervals may be selected automatically based on
measurements of cardiac function or other physiological parameters
that relate to the clinical condition of the patient as measured by
physiological sensor 108 and/or impedance measuring circuit
112.
[0111] FIG. 10 illustrates a method 500 for automatically adjusting
the coupling intervals. The method 500 may be performed upon
delivery of an external command, or on a programmed periodic basis,
for example, daily. Method 500 starts at step 505 by verifying that
the patient is at rest. Preferably, physiological measurements made
for comparing cardiac state during different pacing modalities is
performed only at rest in order to avoid confounding variables that
may occur if the patient is engaged in varying levels of activity
during the test. Various methods may be used to verify resting
state, such as heart rate or other physiological sensor 108
measured parameters. For details regarding one method for verifying
resting state reference is made to U.S. Pat. No. 5,476,483 to
Bornzin.
[0112] At step 510, the microprocessor 60 determines the present
pacing state of the stimulation device 10. If the device 10 is
programmed to be operating in a demand mode in both the atrial and
ventricular chambers, it may be in one of four pacing states:
atrial pacing and ventricular pacing (AV pacing state), atrial
pacing and ventricular sensing (AR pacing state), atrial sensing
and ventricular pacing (PV pacing state) or atrial sensing and
ventricular sensing (PR pacing state).
[0113] If the stimulation device 10 is pacing in the ventricle,
that is in either the AV or PV pacing states, an attempt is made to
inhibit ventricular pacing by extending the atrial-ventricular (AV)
delay to allow more time for an intrinsic R-wave to occur at step
515. If the stimulation device 10 is pacing in the atrium, that is
in either the AV or AR pacing states, an attempt is made to inhibit
atrial pacing by reducing the base pacing rate in order to allow
the natural heart rate to predominate at step 520.
[0114] Preferably, all pacing is inhibited in order to obtain a
baseline physiologic measurement during the natural resting state
of the heart. If ventricular pacing cannot be inhibited, even at
the maximum AV delay setting, such as in the situation of total AV
block, no further attempt is made to inhibit ventricular pacing.
Atrial pacing may also not be inhibited even at a minimum pacing
rate due to sinus node dysfunction with either too slow a native
sinus rate or an unstable native sinus rate. In such cases, the
minimum base pacing rate and a nominal AV delay are applied.
[0115] At step 525, a measurement is made using the physiological
sensor 108 and/or impedance measurement circuit 112 to establish a
baseline cardiac function. At step 530, the coupling intervals are
modulated in a way that allows testing of numerous combinations of
coupling intervals, thus altering the activation sequence, in order
to determine the activation sequence and timing that allows optimal
improvement in cardiac state. Initially, coupling intervals between
the atria and coupling intervals between the ventricles may be
modulated. Next, the AV delay, herein referred to as the atrial to
ventricular coupling intervals, may be modulated. Pacing should be
sustained for any given set of "test" coupling intervals for a
defined minimum time period, such as one minute, to allow the
functional state of the heart to stabilize under the "test"
conditions before making physiological measurements at step
535.
[0116] Preferably, the stimulation device 10 operates in a trigger
mode throughout this test in order to provide a steady cardiac
rhythm at each set of coupling intervals. The physiological
measurement made by the sensor 108 and/or the impedance measurement
made by impedance measuring circuit 112 are stored in memory 94
(FIG. 2) with codes indicating the corresponding coupling interval
settings at step 540.
[0117] The coupling interval settings resulting in the greatest
improvement in cardiac function based on sensor 108 measurements
and/or impedance circuit 112 measurements are selected as the final
settings. At step 545, the optimal coupling interval settings are
automatically re-programmed. The physiologic sensor 108 measurement
and/or the impedance measuring circuit 112 measurement at these
final settings should be stored in histogram memory 94 to be
recalled and displayed graphically over time during patient
follow-up visits.
[0118] Thus, a multichamber or multisite cardiac stimulation device
has been provided which allows independent sensing and stimulation
at multiple sites within the heart according to programmed
electrode configurations. Furthermore, a method by which the
activation sequence of the stimulated sites may be precisely
controlled using programmable coupling intervals has been provided.
Thus, greater flexibility in sensing and stimulation during
multisite or multichamber stimulation therapies may be achieved
whereby pacing therapies may be individually tailored to patient
need so that optimal hemodynamic or electrophysiological results
may be realized.
[0119] While detailed descriptions of specific embodiments of the
present invention have been provided, it would be apparent to those
reasonably skilled in the art that numerous variations of
multi-site or multi-chamber stimulation configurations are possible
in which the concepts and methods of the present invention may
readily be applied. The descriptions provided herein, therefore,
are for the sake of illustration and are no way intended to be
limiting.
* * * * *