U.S. patent application number 09/842879 was filed with the patent office on 2002-12-12 for control of pacing rate in mode switching implantable medical devices.
Invention is credited to Dunham, David, Struble, Chester L..
Application Number | 20020188328 09/842879 |
Document ID | / |
Family ID | 25288472 |
Filed Date | 2002-12-12 |
United States Patent
Application |
20020188328 |
Kind Code |
A1 |
Struble, Chester L. ; et
al. |
December 12, 2002 |
CONTROL OF PACING RATE IN MODE SWITCHING IMPLANTABLE MEDICAL
DEVICES
Abstract
An implantable medical device and method of pacing provide for
switching from a first pacing mode to second pacing mode upon
detection of a period of accelerated atrial arrhythmia. Generally,
the second pacing mode has an associated predetermined lower pacing
rate. At least initially, upon switching from the first pacing mode
to the second pacing mode, the predetermined lower pacing rate is
adjusted to an elevated adjusted lower rate. Further, this elevated
adjusted lower rate may then be decelerated towards a programmed
basic pacing rate during a deceleration period. Generally, the
programmed basic pacing rate is elevated relative to the
predetermined lower pacing rate.
Inventors: |
Struble, Chester L.;
(Eijsden, NL) ; Dunham, David; (Brackley,
GB) |
Correspondence
Address: |
MEDTRONIC, INC.
710 MEDTRONIC PARKWAY NE
MS-LC340
MINNEAPOLIS
MN
55432-5604
US
|
Family ID: |
25288472 |
Appl. No.: |
09/842879 |
Filed: |
April 27, 2001 |
Current U.S.
Class: |
607/9 |
Current CPC
Class: |
A61N 1/36843 20170801;
A61N 1/36542 20130101; A61N 1/36842 20170801; A61N 1/3622 20130101;
A61N 1/3684 20130101 |
Class at
Publication: |
607/9 |
International
Class: |
A61N 001/362 |
Claims
What is claimed is:
1. An implantable medical device method of pacing, the method
comprising: detecting a period of accelerated atrial arrhythmias;
switching from a first pacing mode to a second pacing mode upon
detection of the period of accelerated atrial arrhythmias, wherein
the first pacing mode paces at least one ventricle based on sensed
atrial activity, and further wherein the second pacing mode paces
the at least one ventricle based on sensed ventricular activity at
a predetermined lower rate with such pacing inhibited based on
intrinsic ventricular activity; and at least initially, upon
switching from the first pacing mode to the second pacing mode,
adjusting the lower rate to an elevated adjusted lower rate such
that pacing of the at least one ventricle is not inhibited based on
intrinsic ventricular activity.
2. The method of claim 1, wherein adjusting the lower rate to an
elevated adjusted lower rate comprises adjusting the lower rate to
an elevated adjusted lower rate based on R-R intervals measured
during a ventricular response detection time window associated with
switching from the first pacing mode to the second pacing mode.
3. The method of claim 2, wherein adjusting the lower rate to the
elevated adjusted lower rate comprises: measuring one or more R-R
intervals during the ventricular response detection time window;
detecting at least the fastest R-R interval occurring during the
ventricular response detection time window; and adjusting the lower
rate to the elevated adjusted lower rate based on at least the
fastest R-R interval measured during the ventricular response
detection time window.
4. The method of claim 2, wherein adjusting the lower rate to the
elevated adjusted lower rate comprises: determining the elevated
adjusted lower rate based on R-R intervals measured during the
ventricular response detection time window; and limiting the
elevated adjusted lower rate based on a programmed maximum pacing
rate.
5. The method of claim 2, wherein adjusting the lower rate to the
elevated adjusted lower rate comprises: determining the elevated
adjusted lower rate based on R-R intervals measured during the
ventricular response detection time window; comparing the elevated
adjusted lower rate to an activity sensor indicated pacing rate;
and using either the elevated adjusted lower rate or the activity
sensor indicated pacing rate based on the comparison.
6. The method of claim 1, wherein the method further comprises
decelerating from the elevated adjusted lower rate towards a
predetermined basic pacing rate that is as fast or faster than the
predetermined lower rate.
7. The method of claim 6, wherein decelerating from the elevated
adjusted lower rate towards the predetermined basic pacing rate
comprises: decelerating from the elevated adjusted lower rate
towards the predetermined basic pacing rate during a deceleration
period; monitoring ventricular activity to detect any intrinsic
ventricular events during the deceleration period; and readjusting
the elevated adjusted lower rate upon detection of an intrinsic
ventricular event during the deceleration period and decelerating
the readjusted elevated lower rate during a reinitiated
deceleration period.
8. The method of claim 6, wherein decelerating from the elevated
adjusted lower rate towards the predetermined basic pacing rate
further comprises continuing deceleration to the predetermined
basic pacing rate if no intrinsic ventricular events are detected
during the deceleration period and thereafter continuing to use the
predetermined basic pacing rate until either an intrinsic
ventricular event is detected and a readjusted elevated lower rate
is reset for deceleration during another deceleration period or
operation is switched from the second pacing mode back to the first
pacing mode.
9. The method of claim 6, wherein decelerating from the elevated
adjusted lower rate towards the predetermined basic pacing rate
comprises: comparing the decelerating elevated adjusted lower rate
to an activity sensor indicated pacing rate; and using either the
decelerating elevated adjusted lower rate or the activity sensor
indicated pacing rate based on the comparison.
10. The method of claim 1, wherein switching from the first pacing
mode to the second pacing mode comprises switching from a DDD,
DDDR, VDD, or VDDR pacing mode to a DDI, DDIR, VVI, or VVIR pacing
mode, respectively.
11. The method of claim 1, wherein the implantable medical device
comprises a bi-ventricular pacing apparatus, a dual chamber pacing
apparatus, and a pacemaker/cardioverter/defibrillator.
12. An implantable medical device method of pacing, the method
comprising: switching from a DDD, DDDR, VDD, or VDDR first pacing
mode to a DDI, DDIR, VVI, or VVIR second pacing mode, respectively,
upon detection of a period of accelerated atrial arrhythmia,
wherein the second pacing mode has an associated predetermined
lower pacing rate; at least initially, upon switching from the
first pacing mode to the second pacing mode, adjusting the
predetermined lower pacing rate to an elevated adjusted lower rate;
and decelerating from the elevated adjusted lower rate towards a
programmed basic pacing rate during a deceleration period, wherein
the programmed basic pacing rate is as fast or faster than the
predetermined lower pacing rate.
13. The method of claim 12, wherein adjusting the predetermined
lower pacing rate associated with the second pacing mode to the
elevated adjusted lower rate comprises adjusting the predetermined
lower pacing rate to an elevated adjusted lower rate based on R-R
intervals measured during a ventricular response detection time
window associated with switching from the first pacing mode to the
second pacing mode.
14. The method of claim 13, wherein adjusting the predetermined
lower pacing rate to the elevated adjusted lower rate comprises:
measuring one or more R-R intervals during the ventricular response
detection time window; detecting at least the fastest R-R interval
occurring during the ventricular response detection time window;
and adjusting the predetermined lower pacing rate to the elevated
adjusted lower rate based on at least the fastest R-R interval
measured during the ventricular response detection time window.
15. The method of claim 13, wherein adjusting the predetermined
lower pacing rate to the elevated adjusted lower rate comprises:
determining the elevated adjusted lower rate based on R-R intervals
measured during the ventricular response detection time window; and
limiting the elevated adjusted lower rate based on a programmed
maximum pacing rate.
16. The method of claim 12, wherein switching from the DDD, DDDR,
VDD, or VDDR first pacing mode to the DDI, DDIR, VVI, or VVIR
second pacing mode, respectively, upon detection of a period of
accelerated atrial arrhythmia comprises switching from a DDDR or
VDDR first pacing mode to a DDIR or VVIR second pacing mode,
respectively, upon detection of a period of accelerated atrial
arrhythmia, and further wherein adjusting the predetermined lower
pacing rate associated with the second pacing mode to an elevated
adjusted lower rate comprises: determining the elevated adjusted
lower rate based on R-R intervals measured during the ventricular
response detection time window; comparing the elevated adjusted
lower rate to an activity sensor indicated pacing rate; and using
either the elevated adjusted lower rate or the activity sensor
indicated pacing rate based on the comparison.
17. The method of claim 12, wherein decelerating from the elevated
adjusted lower rate towards the programmed basic pacing rate
comprises: monitoring to sense any intrinsic ventricular activity
during the deceleration period; and readjusting the elevated
adjusted lower rate upon detection of intrinsic ventricular
activity during the deceleration period and decelerating the
readjusted elevated lower rate during a reinitiated deceleration
period.
18. The method of claim 12, wherein decelerating from the elevated
adjusted lower rate towards the programmed basic pacing rate
further comprises continuing deceleration to the programmed basic
pacing rate if no intrinsic ventricular activity is detected during
the deceleration period and thereafter continuing use of the
programmed basic pacing rate until either intrinsic ventricular
activity is detected and a new readjusted elevated lower rate is
reset for deceleration during another deceleration period or
operation is switched from the second pacing mode back to the first
pacing mode.
19. The method of claim 12, wherein switching from the DDD, DDDR,
VDD, or VDDR first pacing mode to the DDI, DDIR, VVI, or VVIR
second pacing mode, respectively, upon detection of a period of
accelerated atrial arrhythmia comprises switching from a DDDR or
VDDR first pacing mode to a DDIR or VVIR second pacing mode,
respectively, upon detection of a period of accelerated atrial
arrhythmia, and further wherein decelerating from the elevated
adjusted lower rate towards the programmed basic pacing rate
comprises: comparing the decelerating elevated adjusted lower rate
to an activity sensor indicated pacing rate; and using either the
decelerating elevated adjusted lower rate or the activity sensor
indicated pacing rate based on the comparison.
20. The method of claim 12, wherein the implantable medical device
comprises a bi-ventricular pacing apparatus, a dual chamber pacing
apparatus, and a pacemaker/cardioverter/defibrillator.
21. An implantable medical device comprising: pacing generator
circuitry operable to generate pacing pulses at one or more pacing
rates during at least first and second pacing modes, wherein the
first pacing mode paces at least one ventricle based on sensed
atrial activity, and further wherein the second pacing mode paces
the at least one ventricle based on sensed ventricular activity at
a predetermined lower rate with such pacing inhibited based on
intrinsic ventricular activity; sensing circuitry operable to sense
atrial and ventricular activity; and a pacing controller operable
to switch from the first pacing mode to the second pacing mode upon
detecting a period of accelerated atrial arrhythmias based on
information from the sensing circuitry, wherein the pacing
controller is further operable to at least initially, upon
switching from the first pacing mode to the second pacing mode,
adjust the predetermined lower rate to an elevated adjusted lower
rate such that pacing of the at least one ventricle is not
inhibited based on detected intrinsic ventricular activity.
22. The device of claim 21, further wherein the pacing controller
is operable to adjust the predetermined lower rate to the elevated
adjusted lower rate based on R-R intervals measured during a
ventricular response detection time window associated with
switching from the first pacing mode to the second pacing mode.
23. The device of claim 22, further wherein the pacing controller
is operable to: measure one or more R-R intervals during the
ventricular response detection time window based on information
from the sensing circuitry; determine at least the fastest R-R
interval occurring during the ventricular response detection time
window; and adjust the predetermined lower rate to the elevated
adjusted lower rate based on at least the fastest R-R interval
measured during the ventricular response detection time window.
24. The device of claim 22, further wherein the pacing controller
is operable to: determine the elevated adjusted lower rate based on
R-R intervals measured during the ventricular response detection
time window; and limit the elevated adjusted lower rate based on a
programmed maximum pacing rate.
25. The device of claim 24, further wherein the pacing controller
is operable to: determine the elevated adjusted lower rate based on
R-R intervals measured during the ventricular response detection
time window; compare the elevated adjusted basic pacing rate to an
activity sensor indicated pacing rate; and control the pacing rate
by using either the elevated adjusted lower rate or the activity
sensor indicated pacing rate based on the comparison.
26. The device of claim 21, wherein the pacing controller is
further operable to decelerate the elevated adjusted lower rate
towards a predetermined basic pacing rate that is as fast or faster
than the predetermined lower rate.
27. The device of claim 26, further wherein the pacing controller
is operable to: control deceleration from the elevated adjusted
lower rate towards the predetermined basic pacing rate during a
deceleration period; and readjust the elevated adjusted lower rate
during the deceleration period based on intrinsic ventricular
activity sensed by the sensing circuitry and control deceleration
of the readjusted elevated lower rate during a reinitiated
deceleration period.
28. The device of claim 26, wherein the pacing controller is
further operable to continue deceleration to the predetermined
basic pacing rate if no intrinsic ventricular activity is sensed
during the deceleration window and thereafter continue to use the
predetermined basic pacing rate until either intrinsic ventricular
activity is sensed and a new readjusted elevated lower rate is
reset for deceleration during another deceleration period or
operation is switched from the second pacing mode back to the first
pacing mode.
29. The device of claim 26, further wherein the pacing controller
is operable to: compare the decelerating elevated adjusted lower
rate to an activity sensor indicated pacing rate; and use either
the decelerating elevated adjusted lower rate or the activity
sensor indicated pacing rate based on the comparison.
30. The device of claim 21, wherein the pacing controller is
operable to switch from a DDD, DDDR, VDD, or VDDR first pacing mode
to a DDI, DDIR, VVI, or VVIR second pacing mode, respectively.
31. The device of claim 21, wherein the implantable medical device
comprises a bi-ventricular pacing apparatus, a dual chamber pacing
apparatus, and a pacemaker/cardioverter/defibrillator.
32. An implantable medical device comprising: pacing generator
circuitry operable to generate pacing pulses at one or more pacing
rates during at least first and second pacing modes, wherein the
first pacing mode comprises a DDD, DDDR, VDD, or VDDR pacing mode
and wherein the second pacing mode comprises a DDI, DDIR, VVI, or
VVIR pacing mode, and further wherein the DDI, DDIR, VVI, or VVIR
second pacing mode has an associated programmed lower pacing rate;
sensing circuitry operable to sense atrial and ventricular
activity; and a pacing controller operable to switch from the DDD,
DDDR, VDD, or VDDR first pacing mode to the DDI, DDIR, VVI, or VVIR
second pacing mode, respectively, upon detecting a period of
accelerated atrial arrhythmias based on information from the
sensing circuitry, wherein the pacing controller is further
operable to at least initially, upon switching from the first
pacing mode to the second pacing mode, adjust the programmed lower
pacing rate to an elevated adjusted lower rate, and further wherein
the pacing controller is operable to decelerate the elevated
adjusted lower rate towards a predetermined basic pacing rate that
is as fast or faster than the programmed lower pacing rate during a
deceleration period.
33. The device of claim 32, further wherein the pacing controller
is operable to adjust the programmed lower pacing rate to an
elevated adjusted lower rate based on R-R intervals measured during
a ventricular response detection time window associated with
switching from the first pacing mode to the second pacing mode.
34. The device of claim 33, wherein the pacing controller is
further operable to: measure one or more R-R intervals during the
ventricular response detection time window based on information
from the sensing circuitry; determine at least the fastest R-R
interval occurring during the ventricular response detection time
window; and adjust the programmed lower pacing rate to the elevated
adjusted lower rate based on at least the fastest R-R interval
measured during the ventricular response detection time window.
35. The device of claim 32, further wherein the pacing controller
is operable to: determine the elevated adjusted lower rate based on
R-R intervals measured during the ventricular response detection
time window; and limit the elevated adjusted lower rate based on a
programmed maximum pacing rate.
36. The device of claim 32, wherein the pacing controller is
operable to switch from a DDDR or VDDR first pacing mode to a DDIR
or VVIR second pacing mode, respectively, upon detection of a
period of accelerated atrial arrhythmia, and further wherein the
pacing controller is further operable to: determine the elevated
adjusted lower rate based on R-R intervals measured during a
ventricular response detection time window; compare the elevated
adjusted lower rate to an activity sensor indicated pacing rate;
and use either the elevated adjusted lower rate or the activity
sensor indicated pacing rate based on the comparison.
37. The device of claim 32, wherein the pacing controller is
further operable to readjust the elevated adjusted lower rate
during the deceleration period based on intrinsic ventricular
activity sensed by the sensing circuitry and control deceleration
of the readjusted elevated lower rate during a reinitiated
deceleration period.
38. The device of claim 32, further wherein the pacing controller
is operable to continue deceleration towards the programmed basic
pacing rate if no intrinsic ventricular activity is sensed during
the deceleration period and thereafter continue use of the
programmed basic pacing rate until either intrinsic ventricular
activity is sensed and a new readjusted elevated lower rate is
reset for deceleration during another deceleration period or
operation is switched from the second pacing mode back to the first
pacing mode.
39. The device of claim 32, wherein the pacing controller is
further operable to switch from a DDDR or VDDR first pacing mode to
a DDIR or VVIR second pacing mode, respectively, upon detection of
a period of accelerated atrial arrhythmia, and further wherein the
pacing controller is operable to: compare the decelerating elevated
adjusted lower rate to an activity sensor indicated pacing rate;
and use either the decelerating elevated adjusted lower rate or the
activity sensor indicated pacing rate based on the comparison.
40. The device of claim 32, wherein the implantable medical device
comprises a bi-ventricular pacing apparatus, a dual chamber pacing
apparatus, and a pacemaker/cardioverter/defibrillator.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to implantable
medical devices and methods for cardiac stimulation. More
particularly, the present invention pertains to implantable medical
devices and methods that employ mode switching in cardiac
stimulation.
BACKGROUND OF THE INVENTION
[0002] Generally, in the human heart, the sinus (or sinoatrial (SA)
node typically located near the junction of the superior vena cava
and the right atrium) constitutes the primary natural pacemaker by
which rhythmic electrical excitation is developed. The cardiac
impulse arising from the sinus node is transmitted to the two
atrial chambers (or atria) at the right and left sides of the
heart. In response to excitation from the SA node, the atria
contract, pumping blood from those chambers into the respective
ventricular chambers (or ventricles). The impulse is transmitted to
the ventricles through the atrio-ventricular (AV) node, and via a
conduction system comprising the bundle of His, or common bundle,
the right and left bundle branches, and the Purkinje fibers. The
transmitted impulse causes the ventricles to contract with the
right ventricle pumping unoxygenated blood through the pulmonary
artery to the lungs and the left ventricle pumping oxygenated
(arterial) blood through the aorta and the lesser arteries to the
body. The right atrium receives the unoxygenated (venous) blood.
The blood oxygenated by the lungs is carried via the pulmonary
veins to the left atrium.
[0003] The above action is repeated in a rhythmic cardiac cycle in
which the atrial and ventricular chambers alternately contract and
pump, and then relax and fill. One-way valves, between the atrial
and ventricular chambers on the right and left sides of the heart,
and at the exits of the right and left ventricles, prevent backflow
of the blood as it moves through the heart and the circulatory
system. This sinus node is spontaneously rhythmic, and the cardiac
rhythm it generates is termed sinus rhythm. This capacity to
produce spontaneous cardiac impulse is called rhythmicity. Some
other cardiac tissues possess rhythmicity and hence constitute
secondary natural pacemakers, but the sinus node is the primary
natural pacemaker because it spontaneously generates electrical
pulses at a faster rate. The secondary pacemakers tend to be
inhibited by the more rapid rate at which impulses are generated by
the sinus node.
[0004] Disruption of the natural pacemaking and propagation system
as a result of aging or disease is commonly treated by artificial
cardiac pacing, by which rhythmic electrical discharges are applied
to the heart at a desired rate from an artificial pacemaker. A
pacemaker is a medical device which delivers electrical pulses to
an electrode that is implanted adjacent to or in the patient's
heart to stimulate the heart so that it will contract and beat at a
desired rate. If the body's natural pacemaker performs correctly,
blood is oxygenated in the lungs and efficiently pumped by the
heart to the body's oxygen-demanding tissues. However, when the
body's natural pacemaker malfunctions, an implantable pacemaker
often is required to properly stimulate the heart.
[0005] Implantable pacemakers are typically designed to operate
using various different response methodologies, such as, for
example, nonsynchronous or asynchronous (fixed rate), inhibited
(stimulus generated in the absence of a specified cardiac
activity), or triggered (stimulus delivered in response to a
specific hemodynamic parameter). Generally, inhibited and triggered
pacemakers may be grouped as "demand"-type pacemakers, in which a
pacing pulse is only generated when demanded by the heart. To
determine when pacing is required by the pacemaker, demand
pacemakers may sense various conditions such as heart rate,
physical exertion, temperature, and the like. Moreover, pacemaker
implementations range from the simple fixed rate, single chamber
device that provides pacing with no sensing function, to highly
complex models that provide fully-automatic dual chamber pacing and
sensing functions. For example, such multiple chamber pacemakers
are described in U.S. Pat. No. 4,928,688 to Mower entitled "Method
and Apparatus for Treating Hemodynamic Dysfunction," issued May 29,
1990; U.S. Pat. No. 5,792,203 to Schroeppel entitled "Universal
Programmable Cardiac Stimulation Device," issued Aug. 11, 1998;
U.S. Pat. No. 5,893,882 to Peterson et al. entitled "Method and
Apparatus for Diagnosis and Treatment of Arrhythmias," issued Apr.
13, 1999; and U.S. Pat. No. 6,081,748 to Struble et al. entitled
"Multiple Channel, Sequential Cardiac Pacing Systems," issued Jun.
27, 2000.
[0006] Because of the large number of options available for pacer
operation, an industry convention has been established whereby
specific pacer configurations are identified according to a code
comprising multiple letters (generally, three to four letters,
although a fifth coded position may also be used). The most common
configuration codes comprise either three or four letters, as shown
in Table I below. For simplicity, the fifth coded position is
omitted. Each code can be interpreted as follows:
1 TABLE 1 Code Position 1 2 3 4 function chamber chamber response
to programmability rate identified paced sensed sensing modulation
options 0 - none 0 - none 0 - none 0 - none available A - atrium A
- atrium T - triggered P - programmable V - ventricle V - ventricle
I - inhibited M - multi- D - dual D - dual D - dual programmable (A
+ V) (A + V) (T + I) C - communica- ting R - rate modula- ting
[0007] For example, a DDD pacer paces either chamber (atrium or
ventricle) and senses in either chamber. Thus, a pacer in DDD mode,
may pace the ventricle in response to electrical activity sensed in
the atrium. A VVI pacer paces and senses in the ventricle, but its
pacing is inhibited by spontaneous electrical activity of the
ventricle, also referred to as intrinsic ventricular activity
(i.e., the ventricle paces itself naturally). In VVIR mode,
ventricle pacing is similarly inhibited upon determining that the
ventricle is naturally contracting. With the VVIR mode, the pacer's
pacing rate, however, in the absence of naturally occurring pacing,
is modulated by the physical activity level of the patient. Pacers
commonly include accelerometers to provide an indication of the
patient's level of physical activity.
[0008] As illustrated in the table above, it may be desirable to
sense in one cardiac chamber (e.g., detect electrical activity
represented of contraction of the chamber and referred to as a
"sensed event") and, in response, pace (referred to as a "paced
event") in the same or different chamber. It also may be desirable
to pace at two electrode locations following a sensed event. For
example, patients with abnormally fast atrial rhythms (referred to
as atrial tachyarrhythmias) are often treated with pacemakers that
include an electrode in each of the two atrial chambers and a third
electrode in the right ventricle. Both atrial chambers usually are
paced following a sensed event in either chamber. Various pacemaker
protocols may be used.
[0009] Further, for example, some patients, like heart failure
patients, are often treated with bi-ventricular pacemakers that
include an electrode in each of the two ventricular chambers, and
also possible a third electrode in the right atrium. Both
ventricular chambers usually are paced following a sensed or paced
atrial event.
[0010] In the context of dual chamber pacing, a variety of mode
switching features have been developed which detect an excessively
rapid atrial rhythm and in response cause the pacemaker to switch
from an atrial synchronized pacing mode such as DDD to a
nonsynchronized mode such as VVI or DDI. Such mode switching
features are disclosed in U.S. Pat. No. 5,144,949 to Olson entitled
"Dual Chamber Rate Responsive Pacemaker With Automatic Mode
Switching," issued Sep. 8, 1992; U.S. Pat. No. 5,318,594 to
Limousin et al. entitled "DDD Type Cardiac Pacemaker Having
Automatic Operating Mode Switching," issued Jun. 7, 1994; U.S. Pat.
No. 4,944,298 to Sholder entitled "Atrial Rate Based Programmable
Pacemaker With Automatic Mode Switching Means," issued Jul. 31,
1990; U.S. Pat. No. 4,932,406 to Berkovits entitled "Dual Chamber
Rate Responsive Pacemaker," issued Jun. 12, 1990; and U.S. Pat. No.
5,292,340 to Crosby et al. entitled "Physiologically-Calibrated
Rate Adaptive, Dual Chamber Pacemaker," issued Mar. 8, 1994. In
such devices, the primary purpose of the mode switch is to prevent
the pacemaker from tracking a non-physiologic atrial rate.
[0011] Generally, mode switching is generally in most dual chamber
pacemakers. Such mode switching typically changes the mode of
pacing therapy during periods of accelerated atrial arrhythmias
such as, for example, SVT (supra ventricular tachycardia), PAF
(paroxysmal atrial flutter), and AF (atrial fibrillation). For
example, mode switching may change the dual chamber pacing mode
from DDD to DDI, DDDR to DDIR, VDD to VVI, or VDDR to VVIR.
[0012] During such episodes of mode switching due to periods of
accelerated atrial arrhythmias such as SVT/PAF/AF, the pacemaker
will revert to a lower rate (LR) of pacing (or a sensor-driven
pacing rate or frequency in rate modulating operating modes such as
DDIR or VVIR). In many cases, the LR is programmed below that of
the intrinsic rate of the patient's sinus rhythm. For example, the
LR may be 60 ppm when the sinus rhythm of the patient is 70 bpm. As
such, with regard to patients with ventricular dysfunction (e.g.,
heart failure), because such patients are inactive due to their
severe conditions, the heart rate may be paced at an insufficient
low pacing rate, i.e., LR.
[0013] Therefore, such mode switching may result in insufficient
pacing rate and cardiac output. For example, during mode switching
periods, as described above, the pacemaker may pace the heart at
the LR in a mode such as DDI(R) or VVI(R). DDIR behaves much like
VVIR in the case of atrial tachyarrhythmias. This pacing LR is
typically too slow to guarantee sufficient cardiac output in heart
failure patients.
[0014] In addition to the potential lower cardiac output due to
pacing at the LR, reduced cardiac output may also occur due to the
atrial arrhythmia and loss of atrial contribution to ventricular
filling. For example, all atrial contribution (e.g., "atrial kick")
to ventricular filling may be lost during atrial arrhythmia. As
such, stroke volume becomes reduced, e.g., reduced by 20-25%,
because cardiac output=(heart rate)(stroke volume). Due to the
above, such reduced cardiac output may be inadequate for the
patient.
[0015] Further, during periods of accelerated atrial arrhythmias
(e.g., SVT/PAF/AF), AV conduction often occurs irregularly. Such
irregular AV conduction may result in irregular intrinsic
ventricular response (e.g., ventricular response rates of 100 bpm
due to the attempt of the ventricular chamber to respond
intrinsically to the accelerated arrhythmias to the LR of 60 ppm
when no intrinsic ventricular response is detected and the
ventricular chamber is paced at LR).
[0016] Yet further, in bi-ventricular pacing for heart failure
patients, continuous pacing therapy should be maintained. During
mode switching, there may be a loss of such continuous
bi-ventricular pacing therapy.
[0017] Table II below lists U.S. Patents relating to multiple
chamber pacing apparatus and mode switching techniques and
methods.
2TABLE II U.S. Pat. No. Inventor Issue Date 4,928,688 Mower 29 May
1990 4,932,406 Berkovits 12 June 1990 4,944,298 Sholder 31 July
1990 5,144,949 Olson 8 September 1992 5,292,340 Crosby et al. 8
March 1994 5,318,594 Limousin et al. 7 June 1994 5,792,203
Schroeppel 11 August 1998 5,893,882 Peterson et al. 13 April 1999
5,902,324 Thompson et al. 11 May 1999 6,070,101 Struble et al. 30
May 2000 6,081,748 Struble et al. 27 June 2000
[0018] All references listed in Table II, and elsewhere herein, are
incorporated by reference in their respective entireties. As those
of ordinary skill in the art will appreciate readily upon reading
the Summary of the Invention, Detailed Description of the
Embodiments, and claims set forth below, at least some of the
devices and methods disclosed in the references of Table II and
elsewhere herein may be modified advantageously by using the
teachings of the present invention. However, the listing of any
such references in Table II, or elsewhere herein, is by no means an
indication that such references are prior art to the present
invention.
SUMMARY OF THE INVENTION
[0019] The present invention has certain objects. That is, various
embodiments of the present invention provide solutions to one or
more problems existing in the prior art with respect to implantable
medical device pacing techniques and, in particular, mode switching
used in conjunction with such pacing techniques. One of such
problems involves the provision of insufficient pacing rate and
cardiac output during mode switching periods. Further, for example,
other problems involve the occurrence of irregular AV conduction
during accelerated atrial arrhythmias and mode switching periods
that often result in irregular intrinsic ventricular response. In
addition, for example, in bi-ventricular pacing for heart failure
patients, during mode switching periods upon detection of
accelerated atrial arrhythmias, pacing therapy may not be
continuous.
[0020] In comparison to known mode switching techniques, various
embodiments of the present invention may provide one or more of the
following advantages. For example, the highest level of continued
ventricular therapy, e.g., bi-ventricular pacing therapy, during
mode switching periods due to accelerated atrial arrhythmias, is
ensured. Further, an elevated pacing rate counteracts the absence
of atrial contribution to ventricular filling in patients during
periods of atrial arrhythmias. Yet further, the present invention
provides for interaction in the mode switching period with a rate
response activity sensor indicated rate to provide for more
appropriate pacing rates when a patient is undertaking greater
activity, e.g., exercise. In general, by making adjustments to
lower rate pacing during mode switching, such that an elevated
compensatory rate is provided, the present invention provides the
advantage of providing sufficient cardiac output during episodes of
accelerated atrial arrhythmias.
[0021] Some embodiments of the present invention include one or
more of the following features: detection of a period of
accelerated atrial arrhythmias; switching from a first pacing mode
to a second pacing mode upon detection of a period of accelerated
atrial arrhythmias; provision of a first pacing mode (e.g., DDD,
DDDR, VDD, or VDDR pacing mode) that paces at least one ventricle
based on sensed atrial activity and a second pacing mode (e.g.,
DDI, DDIR, VVI, or VVIR pacing mode) that paces the at least one
ventricle based on sensed ventricular activity at a predetermined
lower rate with such pacing inhibited based on intrinsic
ventricular activity; adjusting a lower rate to an elevated
adjusted lower rate upon switching from a first pacing mode to a
second pacing mode such that pacing of the at least one ventricle
is not inhibited based on intrinsic ventricular activity; adjusting
a lower rate to an elevated adjusted lower rate based on R-R
intervals measured during a ventricular response detection time
window associated with mode switching; adjusting a lower rate based
on at least the fastest R-R interval measured during a ventricular
response detection time window; limiting the elevated adjusted
lower rate based on a programmed maximum pacing rate; taking into
consideration an activity sensor indicated pacing rate when
determining an appropriate rate; decelerating from an elevated
adjusted lower rate towards a predetermined basic pacing rate that
is as fast or faster than the predetermined or programmed lower
rate; monitoring ventricular activity during the deceleration
period and readjusting the elevated adjusted lower rate upon
detection of an intrinsic ventricular event and further
decelerating the readjusted elevated lower rate during a
reinitiated deceleration period; and continuing deceleration to a
predetermined pacing rate if no intrinsic ventricular events are
detected and thereafter continuing to use a predetermined basic
pacing rate until either an intrinsic ventricular event is detected
and a readjusted elevated lower rate is reset for deceleration or
mode of operation is switched back.
[0022] Still further, some embodiments of the present invention
include one or more of the following features: pacing generator
circuitry operable to generate pacing pulses at one or more pacing
rates during at least first and second pacing modes; a first pacing
mode that paces at least one ventricle based on sensed atrial
activity (e.g., DDD, DDR, VDD, or VDDR); a second pacing mode that
paces the at least one ventricle based on sensed ventricular
activity at a predetermined lower rate (e.g., a programmed rate)
with such pacing inhibited based on intrinsic ventricular activity
(e.g., DDI, DDIR, VVI, or VVIR pacing mode); sensing circuitry
operable to sense atrial and ventricular activity; a pacing
controller operable to switch from a first pacing mode to a second
pacing mode upon detection of a period of accelerated atrial
arrhythmia based on information from sensing circuitry; a pacing
controller operable to at least initially upon switching from a
first pacing mode to a second pacing mode adjust a predetermined
lower rate to an elevated adjusted lower rate such that pacing of
at least one ventricle is not inhibited based on detected intrinsic
ventricular activity; a pacing controller that is operable to
adjust a predetermined lower rate to an elevated adjusted rate
based on R-R intervals measured during a ventricular response
detection time window associated with mode switching; a pacing
controller that is operable to limit an elevated adjusted lower
rate based on a programmed maximum pacing rate; a pacing controller
that is operable to control the pacing rate based on an activity
sensor indicated pacing rate; a pacing controller that is operable
to decelerate an elevated adjusted lower rate towards a
predetermined basic pacing rate (e.g., a programmed rate) that is
as fast or faster than the predetermined lower rate; a pacing
controller that is operable to readjust an elevated adjusted lower
rate during a deceleration window based on intrinsic ventricular
activity and to control deceleration of the readjusted elevated
lower rate during a reinitiated deceleration period; and a pacing
controller that is operable to continue deceleration to a
predetermined basic pacing rate if no intrinsic ventricular
activity is sensed during a deceleration window and thereafter
continue to use the predetermined basic pacing rate until either
intrinsic ventricular activity is sensed and a new readjusted
elevated lower rate is reset for deceleration during another
reinitiated deceleration period or the mode of operation is
switched back.
[0023] The above summary of the present invention is not intended
to describe each embodiment or every implementation of the present
invention. Advantages, together with a more complete understanding
of the invention, will become apparent and appreciated by referring
to the following detailed description and claims taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The present invention will be further described with
reference to the drawings, wherein:
[0025] FIG. 1 is an implantable medical device (IMD) in accordance
with one embodiment of the invention, wherein the IMD is implanted
within a body of a patient;
[0026] FIG. 2 is an enlarged view of the IMD of FIG. 1
diagrammatically illustrating coupling with the patient's heart in
accordance with one embodiment of the invention;
[0027] FIG. 3 is a functional block diagram of an IMD in accordance
with one embodiment of the present invention;
[0028] FIG. 4 is an IMD in accordance with another embodiment of
the invention, wherein the IMD is an implantable
pacemaker-cardioverter-defib- rillator (PCD);
[0029] FIG. 5 is a functional block diagram of the IMD of FIG.
4;
[0030] FIG. 6 is a diagram depicting a three or four channel,
biatrial and/or bi-ventricular, pacing system according to one
embodiment of the present invention;
[0031] FIG. 7 is a flow diagram illustrating accelerated
ventricular lower rate pacing according to the present
invention;
[0032] FIG. 8 is a flow diagram illustrating one illustrative
embodiment of performing the adjustment of the lower rate as shown
in FIG. 7 according to the present invention;
[0033] FIG. 9 is a timing diagram for use in illustrating the
accelerated lower rate pacing shown in FIG. 7; and
[0034] FIGS. 10-12 show flow diagrams illustrating the interaction
of activity sensor indicated rates in conjunction with the
accelerated lower rate pacing of FIG. 7.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0035] FIG. 1 is a simplified schematic view of one embodiment of
implantable medical device ("IMD") 10 of the present invention. IMD
10 shown in FIG. 1 is a pacemaker comprising at least one of pacing
and sensing leads 16 and 18 attached to hermetically sealed
enclosure 14 and implanted near human or mammalian heart 8. Pacing
and sensing leads 16 and 18, sense electrical signals attendant to
the depolarization and re-polarization of the heart 8, and further
provide pacing pulses for causing depolarization of cardiac tissue
in the vicinity of the distal ends thereof. Leads 16 and 18 may
have, for example, unipolar or bipolar electrodes disposed thereon,
as is well known in the art. Examples of IMD 10 include implantable
cardiac pacemakers disclosed in U.S. Pat. No. 5,158,078 to Bennett
et al., U.S. Pat. No. 5,312,453 to Shelton et al. or U.S. Pat. No.
5,144,949 to Olson.
[0036] FIG. 2 shows connector module 12 and hermetically sealed
enclosure 14 of IMD 10 located near human or mammalian heart 8.
Atrial and ventricular pacing leads 16 and 18 extend from connector
header module 12 to the right atrium and ventricle, respectively,
of heart 8. Atrial electrodes 20 and 21 disposed at the distal end
of atrial pacing lead 16 are located in the right atrium.
Ventricular electrodes 28 and 29 at the distal end of ventricular
pacing lead 18 are located in the right ventricle.
[0037] FIG. 3 is a block diagram illustrating the constituent
components of IMD 10 in accordance with one embodiment of the
present invention, where IMD 10 is a pacemaker having a
microprocessor-based architecture. IMD 10 is shown as including
activity sensor or accelerometer 11, which is preferably a
piezoceramic accelerometer bonded to a hybrid circuit located
inside enclosure 14. Activity sensor 11 typically (although not
necessarily) provides a sensor output that varies as a function of
a measured parameter relating to a patient's metabolic
requirements. For the sake of convenience, IMD 10 in FIG. 3 is
shown with lead 18 only connected thereto; similar circuitry and
connections not explicitly shown in FIG. 3 apply to lead 16.
[0038] IMD 10 in FIG. 3 is most preferably programmable by means of
an external programming unit (not shown in the Figures). One such
programmer is the commercially available Medtronic Model 9790
programmer, which is microprocessor-based and provides a series of
encoded signals to IMD 10, typically through a programming head
which transmits or telemeters radio-frequency (RF) encoded signals
to IMD 10. Such a telemetry system is described in U.S. Pat. No.
5,354,319 to Wyborny et al. The programming methodology disclosed
in Wyborny et al.'s '319 patent is identified herein for
illustrative purposes only. Any of a number of suitable programming
and telemetry methodologies known in the art may be employed so
long as the desired information is transmitted to and from IMD
10.
[0039] As shown in FIG. 3, lead 18 is coupled to node 50 in IMD 10
through input capacitor 52. Activity sensor or accelerometer 11 is
most preferably attached to a hybrid circuit located inside
hermetically sealed enclosure 14 of IMD 10. The output signal
provided by activity sensor 11 is coupled to input/output circuit
54. Input/output circuit 54 contains analog circuits for
interfacing to heart 8, activity sensor 11, antenna 56 and circuits
for the application of stimulating pulses to heart 8. The rate of
heart 8 is controlled by software-implemented algorithms stored in
microcomputer circuit 58.
[0040] Microcomputer circuit 58 preferably comprises on-board
circuit 60 and off-board circuit 62. Circuit 58 may correspond to a
microcomputer circuit disclosed in U.S. Pat. No. 5,312,453 to
Shelton et al. On-board circuit 60 preferably includes
microprocessor 64, system clock circuit 66 and on-board RAM 68 and
ROM 70. Off-board circuit 62 preferably comprises a RAM/ROM unit.
On-board circuit 60 and off-board circuit 62 are each coupled by
data communication bus 72 to digital controller/timer circuit 74.
Microcomputer circuit 58 may comprise a custom integrated circuit
device augmented by standard RAM/ROM components.
[0041] Electrical components shown in FIG. 3 are powered by an
appropriate implantable battery power source 76 in accordance with
common practice in the art. For the sake of clarity, the coupling
of battery power to the various components of IMD 10 is not shown
in the Figures. Antenna 56 is connected to input/output circuit 54
to permit uplink/downlink telemetry through RF transmitter and
receiver telemetry unit 78. By way of example, telemetry unit 78
may correspond to that disclosed in U.S. Pat. No. 4,556,063 issued
to Thompson et al., or to that disclosed in the above-referenced
'319 patent to Wyborny et al. It is generally preferred that the
particular programming and telemetry scheme selected permit the
entry and storage of cardiac rate-response parameters. The specific
embodiments of antenna 56, input/output circuit 54 and telemetry
unit 78 presented herein are shown for illustrative purposes only,
and are not intended to limit the scope of the present
invention.
[0042] V.sub.REF and Bias circuit 82 (see FIG. 3) most preferably
generates stable voltage reference and bias currents for analog
circuits included in input/output circuit 54. Analog-to-digital
converter (ADC) and multiplexer unit 84 digitizes analog signals
and voltages to provide "real-time" telemetry intracardiac signals
and battery end-of-life (EOL) replacement functions. Operating
commands for controlling the timing of IMD 10 are coupled by data
bus 72 to digital controller/timer circuit 74, where digital timers
and counters establish the overall escape interval of the IMD 10 as
well as various refractory, blanking and other timing windows, such
as those described herein, for controlling the operation of
peripheral components disposed within input/output circuit 54.
[0043] Digital controller/timer circuit 74 is preferably coupled to
sensing circuitry, including sense amplifier 88, peak sense and
threshold measurement unit 90 and comparator/threshold detector 92.
Circuit 74 is further preferably coupled to electrogram (EGM)
amplifier 94 for receiving amplified and processed signals sensed
by lead 18. Sense amplifier 88 amplifies sensed electrical cardiac
signals and provides an amplified signal to peak sense and
threshold measurement circuitry 90, which in turn provides an
indication of peak sensed voltages and measured sense amplifier
threshold voltages on multiple conductor signal path 67 to digital
controller/timer circuit 74. An amplified sense amplifier signal is
then provided to comparator/threshold detector 92. By way of
example, sense amplifier 88 may correspond to that disclosed in
U.S. Pat. No. 4,379,459 to Stein.
[0044] The electrogram signal provided by EGM amplifier 94 is
employed when IMD 10 is being interrogated by an external
programmer to transmit a representation of a cardiac analog
electrogram. See, for example, U.S. Pat. No. 4,556,063 to Thompson
et al. Output pulse generator 96 provides pacing stimuli to
patient's heart 8 through coupling capacitor 98, for example, in
response to a pacing trigger signal provided by digital
controller/timer circuit 74 each time the escape interval times
out, in response to an externally transmitted pacing command or in
response to other stored commands as is well known in the pacing
art and as is described herein. By way of example, output amplifier
96 may correspond generally to an output amplifier disclosed in
U.S. Pat. No. 4,476,868 to Thompson.
[0045] The specific embodiments of input amplifier 88, output
amplifier 96 and EGM amplifier 94 identified herein are presented
for illustrative purposes only, and are not intended to be limiting
in respect of the scope of the present invention. The specific
embodiments of such circuits may not be critical to practicing some
embodiments of the present invention so long as they provide means
for generating a stimulating pulse and are capable of providing
signals indicative of natural or stimulated contractions of heart
8.
[0046] In some embodiments of the present invention, IMD 10 may
operate in various non-rate-responsive modes, including, but not
limited to, DDD, DDI, VVI, VOO and VVT modes. In other embodiments
of the present invention, IMD 10 may operate in various
rate-responsive modes, including, but not limited to, DDDR, DDIR,
VVIR, VOOR and VVTR modes. Some embodiments of the present
invention are capable of operating in both non-rate-responsive and
rate-responsive modes. Moreover, in various embodiments of the
present invention, IMD 10 may be programmably configured to operate
so that it varies the rate at which it delivers stimulating pulses
to heart 8 only in response to one or more selected sensor outputs
being generated. Numerous pacemaker features and functions not
explicitly mentioned herein may be incorporated into IMD 10 while
remaining within the scope of the present invention.
[0047] The present invention is not limited in scope to dual-sensor
pacemakers, and is not limited to IMD's comprising activity or
pressure sensors only. Further, the present invention is not
limited in scope to dual-chamber pacemakers, dual-chamber leads for
pacemakers or single-sensor or dual-sensor leads for pacemakers.
Thus, various embodiments of the present invention may be practiced
in conjunction with more than two leads or with multiple-chamber
pacemakers, for example. At least some embodiments of the present
invention may be applied equally well in the contexts of dual-,
triple- or quadruple-chamber pacemakers or other types of IMD's.
See, for example, U.S. Pat. No. 5,800,465 to Thompson et al. In one
preferred embodiment, the present invention is particularly
directed at pacing apparatus that provide bi-ventricular pacing
therapy.
[0048] IMD 10 may also be a pacemaker-cardioverter-defibrillator
("PCD") corresponding to any of numerous commercially available
implantable PCD's. Various embodiments of the present invention may
be practiced in conjunction with PCD's such as those disclosed in
U.S. Pat. No. 5,545,186 to Olson et al., U.S. Pat. No. 5,354,316 to
Keimel, U.S. Pat. No. 5,314,430 to Bardy, U.S. Pat. No. 5,131,388
to Pless and U.S. Pat. No. 4,821,723 to Baker, Jr. et al.
[0049] FIGS. 4 and 5 illustrate one embodiment of IMD 10 and a
corresponding lead set of the present invention, where IMD 10 is a
PCD. In FIG. 4, the ventricular lead takes the form of leads
disclosed in U.S. Pat. Nos. 5,099,838 and 5,314,430 to Bardy, and
includes an elongated insulative lead body 1 carrying three
concentric coiled conductors separated from one another by tubular
insulative sheaths. Located adjacent the distal end of lead 1 are
ring electrode 2, extendable helix electrode 3 mounted retractably
within insulative electrode head 4 and elongated coil electrode 5.
Each of the electrodes is coupled to one of the coiled conductors
within lead body 1. Electrodes 2 and 3 are employed for cardiac
pacing and for sensing ventricular depolarizations. At the proximal
end of the lead is bifurcated connector 6 which carries three
electrical connectors, each coupled to one of the coiled
conductors. Defibrillation electrode 5 may be fabricated from
platinum, platinum alloy or other materials known to be usable in
implantable defibrillation electrodes and may be about 5 cm in
length.
[0050] The atrial/SVC lead shown in FIG. 4 includes elongated
insulative lead body 7 carrying three concentric coiled conductors
separated from one another by tubular insulative sheaths
corresponding to the structure of the ventricular lead. Located
adjacent the J-shaped distal end of the lead are ring electrode 9
and extendable helix electrode 13 mounted retractably within an
insulative electrode head 15. Each of the electrodes is coupled to
one of the coiled conductors within lead body 7. Electrodes 13 and
9 are employed for atrial pacing and for sensing atrial
depolarizations. Elongated coil electrode 19 is provided proximal
to electrode 9 and coupled to the third conductor within lead body
7. Electrode 19 preferably is 10 cm in length or greater and is
configured to extend from the SVC toward the tricuspid valve. In
one embodiment of the present invention, approximately 5 cm of the
right atrium/SVC electrode is located in the right atrium with the
remaining 5 cm located in the SVC. At the proximal end of the lead
is bifurcated connector 17 carrying three electrical connectors,
each coupled to one of the coiled conductors.
[0051] The coronary sinus lead shown in FIG. 4 assumes the form of
a coronary sinus lead disclosed in the above cited '838 patent
issued to Bardy, and includes elongated insulative lead body 41
carrying one coiled conductor coupled to an elongated coiled
defibrillation electrode 21. Electrode 21, illustrated in broken
outline in FIG. 4, is located within the coronary sinus and great
vein of the heart. At the proximal end of the lead is connector
plug 23 carrying an electrical connector coupled to the coiled
conductor. The coronary sinus/great vein electrode 41 may be about
5 cm in length.
[0052] The implantable PCD is shown in FIG. 4 in combination with
leads 1, 7 and 41, and lead connector assemblies 23, 17 and 6
inserted into connector block 12. Optionally, insulation of the
outward facing portion of housing 14 of PCD 10 may be provided
using a plastic coating such as parylene or silicone rubber, as is
employed in some unipolar cardiac pacemakers. The outward facing
portion, however, may be left uninsulated or some other division
between insulated and uninsulated portions may be employed. The
uninsulated portion of housing 14 serves as a subcutaneous
defibrillation electrode to defibrillate either the atria or
ventricles. Lead configurations other than those shown in FIG. 4
may be practiced in conjunction with the present invention, such as
those shown in U.S. Pat. No. 5,690,686 to Min et al.
[0053] FIG. 5 is a functional schematic diagram of one embodiment
of an implantable PCD of the present invention. This diagram should
be taken as exemplary of the type of device in which various
embodiments of the present invention may be embodied, and not as
limiting, as it is believed that the invention may be practiced in
a wide variety of device implementations which provided pacing
therapies.
[0054] The PCD is provided with an electrode system. If the
electrode configuration of FIG. 4 is employed, the electrode
configuration correspondence may be as follows. Electrode 25 in
FIG. 5 includes the uninsulated portion of the housing of the PCD.
Electrodes 25, 15, 21 and 5 are coupled to high voltage output
circuit 27, which includes high voltage switches controlled by
CV/defib control logic 29 via control bus 31. Switches disposed
within circuit 27 determine which electrodes are employed and which
electrodes are coupled to the positive and negative terminals of
the capacitor bank (which includes capacitors 33 and 35) during
delivery of defibrillation pulses.
[0055] Electrodes 2 and 3 are located on or in the ventricle and
are coupled to the R-wave amplifier 37, which preferably takes the
form of an automatic gain controlled amplifier providing an
adjustable sensing threshold as a function of the measured R-wave
amplitude. A signal is generated on R-out line 39 whenever the
signal sensed between electrodes 2 and 3 exceeds the present
sensing threshold.
[0056] Electrodes 9 and 13 are located on or in the atrium and are
coupled to the P-wave amplifier 43, which preferably also takes the
form of an automatic gain controlled amplifier providing an
adjustable sensing threshold as a function of the measured P-wave
amplitude. A signal is generated on P-out line 45 whenever the
signal sensed between electrodes 9 and 13 exceeds the present
sensing threshold. The general operation of R-wave and P-wave
amplifiers 37 and 43 may correspond to that disclosed in U.S. Pat.
No. 5,117,824, to Keimel et al.
[0057] Switch matrix 47 is used to select which of the available
electrodes are coupled to wide band (0.5-200 Hz) amplifier 49 for
use in digital signal analysis. Selection of electrodes is
controlled by the microprocessor 51 via data/address bus 53, which
selection may be varied as desired. Signals from the electrodes
selected for coupling to bandpass amplifier 49 are provided to
multiplexer 55, and thereafter converted to multi-bit digital
signals by A/D converter 57, for storage in to random access memory
59 under control of direct memory access circuit 61. Microprocessor
51 may employ digital signal analysis techniques to characterize
the digitized signals stored in random access memory 59 to
recognize and classify the patient's heart rhythm employing any of
the numerous signal processing methodologies known in the art.
[0058] The remainder of the circuitry is dedicated to the provision
of cardiac pacing, cardioversion and defibrillation therapies, and,
for purposes of the present invention may correspond to circuitry
known to those skilled in the art. The following exemplary
apparatus is disclosed for accomplishing pacing, cardioversion and
defibrillation functions. Pacer timing/control circuitry 63
preferably includes programmable digital counters which control the
basic time intervals associated with DDD, VVI, DVI, VDD, AAI, DDI
and other modes of single and dual chamber pacing well known to the
art. Circuitry 63 also preferably controls escape intervals
associated with anti-tachyarrhythmia pacing in both the atrium and
the ventricle.
[0059] Intervals defined by pacing circuitry 63 include atrial and
ventricular pacing escape intervals, the refractory periods during
which sensed P-waves and R-waves are ineffective to restart timing
of the escape intervals and the pulse widths of the pacing pulses.
The durations of these intervals are determined by microprocessor
51, in response to stored data in memory 59 and are communicated to
pacing circuitry 63 via address/data bus 53. Pacer circuitry 63
also determines the amplitude of the cardiac pacing pulses under
control of microprocessor 51.
[0060] During pacing, escape interval counters within pacer
timing/control circuitry 63 are reset upon sensing of R-waves and
P-waves as indicated by signals on lines 39 and 45, and in
accordance with the selected mode of pacing on time-out trigger
generation of pacing pulses by pacer output circuitry 65 and 67,
which are coupled to electrodes 9, 13, 2 and 3. Escape interval
counters are also reset on generation of pacing pulses and thereby
control the basic timing of cardiac pacing functions, including
anti-tachyarrhythmia pacing. The durations of the intervals defined
by escape interval timers are determined by microprocessor 51 via
data/address bus 53. The value of the count present in the escape
interval counters when reset by sensed R-waves and P-waves may be
used to measure the durations of R-R intervals, P-P intervals, P-R
intervals and R-P intervals, which measurements are stored in
memory 59 and used to detect the presence of tachyarrhythmias.
[0061] Microprocessor 51 most preferably operates as an interrupt
driven device, and is responsive to interrupts from pacer
timing/control circuitry 63 corresponding to the occurrence of
sensed P-waves and R-waves and corresponding to the generation of
cardiac pacing pulses. Those interrupts are provided via
data/address bus 53. Any necessary mathematical calculations to be
performed by microprocessor 51 and any updating of the values or
intervals controlled by pacer timing/control circuitry 63 take
place following such interrupts.
[0062] Detection of atrial or ventricular tachyarrhythmias, as
employed in the present invention, may correspond to
tachyarrhythmia detection algorithms known in the art. For example,
the presence of an atrial or ventricular tachyarrhythmia may be
confirmed by detecting a sustained series of short R-R or P-P
intervals of an average rate indicative of tachyarrhythmia or an
unbroken series of short R-R or P-P intervals. The suddenness of
onset of the detected high rates, the stability of the high rates,
and a number of other factors known in the art may also be measured
at this time. Appropriate ventricular tachyarrhythmia detection
methodologies measuring such factors are described in U.S. Pat. No.
4,726,380 issued to Vollmann et al., U.S. Pat. No. 4,880,005 issued
to Pless et al. and U.S. Pat. No. 4,830,006 issued to Haluska et
al. An additional set of tachycardia recognition methodologies is
disclosed in the article "Onset and Stability for Ventricular
Tachyarrhythmia Detection in an Implantable
Pacer-Cardioverter-Defibrillator" by Olson et al., published in
Computers in Cardiology, Oct. 7-10, 1986, IEEE Computer Society
Press, pages 167-170. Atrial fibrillation detection methodologies
are disclosed in Published PCT Application Ser. No. US92/02829,
Publication No. WO92/18198, by Adams et al., and in the article
"Automatic Tachycardia Recognition", by Arzbaecher et al.,
published in PACE, May-June, 1984, pp. 541-547.
[0063] In the event an atrial or ventricular tachyarrhythmia is
detected and an anti-tachyarrhythmia pacing regimen is desired,
appropriate timing intervals for controlling generation of
anti-tachyarrhythmia pacing therapies are loaded from
microprocessor 51 into the pacer timing and control circuitry 63,
to control the operation of the escape interval counters therein
and to define refractory periods during which detection of R-waves
and P-waves is ineffective to restart the escape interval
counters.
[0064] Alternatively, circuitry for controlling the timing and
generation of anti-tachycardia pacing pulses as described in U.S.
Pat. No. 4,577,633, issued to Berkovits et al., U.S. Pat. No.
4,880,005, issued to Pless et al., U.S. Pat. No. 4,726,380, issued
to Vollmann et al. and U.S. Pat. No. 4,587,970, issued to Holley et
al., may also be employed.
[0065] In the event that generation of a cardioversion or
defibrillation pulse is required, microprocessor 51 may employ an
escape interval counter to control timing of such cardioversion and
defibrillation pulses, as well as associated refractory periods. In
response to the detection of atrial or ventricular fibrillation or
tachyarrhythmia requiring a cardioversion pulse, microprocessor 51
activates cardioversion/defibrillation control circuitry 29, which
initiates charging of the high voltage capacitors 33 and 35 via
charging circuit 69, under the control of high voltage charging
control line 71. The voltage on the high voltage capacitors is
monitored via VCAP line 73, which is passed through multiplexer 55
and, in response to reaching a predetermined value set by
microprocessor 51, results in generation of a logic signal on Cap
Full (CF) line 77 to terminate charging. Thereafter, timing of the
delivery of the defibrillation or cardioversion pulse is controlled
by pacer timing/control circuitry 63. Following delivery of the
fibrillation or tachycardia therapy microprocessor 51 returns the
device to q cardiac pacing mode and awaits the next successive
interrupt due to pacing or the occurrence of a sensed atrial or
ventricular depolarization.
[0066] Several embodiments of appropriate systems for the delivery
and synchronization of ventricular cardioversion and defibrillation
pulses and for controlling the timing functions related to them are
disclosed in U.S. Pat. No. 5,188,105 to Keimel, U.S. Pat. No.
5,269,298 to Adams et al. and U.S. Pat. No. 4,316,472 to Mirowski
et al. However, any known cardioversion or defibrillation pulse
control circuitry is believed to be usable in conjunction with
various embodiments of the present invention. For example,
circuitry controlling the timing and generation of cardioversion
and defibrillation pulses such as that disclosed in U.S. Pat. No.
4,384,585 to Zipes, U.S. Pat. No. 4,949,719 to Pless et al., or
U.S. Pat. No. 4,375,817 to Engle et al., may also be employed.
[0067] Continuing to refer to FIG. 5, delivery of cardioversion or
defibrillation pulses is accomplished by output circuit 27 under
the control of control circuitry 29 via control bus 31. Output
circuit 27 determines whether a monophasic or biphasic pulse is
delivered, the polarity of the electrodes and which electrodes are
involved in delivery of the pulse. Output circuit 27 also includes
high voltage switches which control whether electrodes are coupled
together during delivery of the pulse. Alternatively, electrodes
intended to be coupled together during the pulse may simply be
permanently coupled to one another, either exterior to or interior
of the device housing, and polarity may similarly be pre-set, as in
current implantable defibrillators. Examples of output circuitry
for delivery of biphasic pulse regimens to multiple electrode
systems may be found in U.S. Pat. No. 4,953,551 to Mehra et al. and
in U.S. Pat. No. 4,727,877 to Kallock.
[0068] An example of circuitry which may be used to control
delivery of monophasic pulses is disclosed in U.S. Pat. No.
5,163,427 to Keimel. Output control circuitry similar to that
disclosed in the above-cited patent issued to Mehra et al. or U.S.
Pat. No. 4,800,883 to Winstrom, may also be used in conjunction
with various embodiments of the present invention to deliver
biphasic pulses.
[0069] FIG. 6 is a schematic representation of an implantable
medical device (IMD) 114 including an implantable four-channel
cardiac pacemaker such as that described in U.S. Pat. No. 6,070,101
to Struble et al. entitled "Multiple Channel, Sequential, Cardiac
Pacing Systems," issued May 30, 2000. For example, such a pacemaker
may provide bi-ventricular pacing therapy. The inline connector 113
of a right atrial lead 116 is fitted into a bipolar bore of IMD
connector block 112 and is coupled to a pair of electrically
insulated conductors within lead body 115 that are connected with
distal tip right atrial pace-sense electrode 119 and proximal ring
right atrial pace-sense electrode 121. The distal end of the right
atrial lead 116 is attached to the right atrial wall by a
conventional attachment mechanism 117. Bipolar endocardial right
ventricle lead 132 is passed through the vein into the right atrial
chamber of the heart 8 and into the right ventricle where its
distal ring and tip right ventricular pace-sense electrodes 138 and
140 are fixed in place in the apex by a conventional and distal
attachment mechanism 141. The right ventricular lead 132 is formed
with an inline connector 134 fitting into a bipolar bore of IMD
connector block 112 that is coupled to a pair of electrically
insulated conductors within lead body 136 and then connected with
distal tip right ventricular pace-sense electrode 140 and proximal
ring right ventricular pace-sense electrode 138.
[0070] In this particular illustrative embodiment, although other
types of leads may be used, a quadripolar, endocardial left
ventricular coronary sinus (CS) lead 152 is passed through a vein
into the right atrial chamber of the heart 8, into the CS, and then
inferiorly in the great vein to extend to a distal pair of left
ventricular CS pace-sense electrodes 148 and 150 alongside the left
ventricular chamber and leave a proximal pair of left atrial CS
pace-sense electrodes 128 and 130 adjacent the left atrial chamber.
The left ventricular CS lead 152 is formed with a four-conductor
lead body 156 coupled at the proximal end to a bifurcated inline
connector 154 fitting into a pair of bipolar bores of IMD connector
block 112. The four electrically insulated lead conductors in left
ventricular CS lead body 156 are separately connected with one of
the distal pair of left ventricular CS pace-sense electrodes 148
and 150 and the proximal pair of left atrial CS pace-sense
electrodes 128 and 130.
[0071] The IMD 114 may comprise, for example, similar circuitry and
connections as shown in FIG. 3 for each of the multiple leads to
establish the multiple pacing/sensing channels provided for each
respective pair of pace-sense electrodes associated with each
chamber of the heart as shown in FIG. 6. For the sake of
convenience, such circuitry is not described further. For example,
channel circuitry for pacing/sensing the left atrial chamber is
associated with pace-sense electrodes 28 and 30 adjacent the left
atrium. One skilled in the art will recognize that each
sensing/pacing channel may include a sense amplifier and pace
output pulse generator coupled through the respective
pacing/sensing lead. Although the pacing system shown in FIG. 6,
shall not be described in detail for simplicity purposes, it will
be recognized that multiple chambers may be paced/sensed via
respective channels for such chambers. As such, for example,
bi-atrial and/or bi-ventricular pacing may be performed as would be
readily apparent to one skilled in the art.
[0072] With various embodiments of IMDs described above, it will
become apparent from the description below that the present
invention may be applied to any dual chamber pacing apparatus. For
example, the present invention may be applied to a three-chamber
atrial-bi-ventricular pacer, a dual chamber defibrillator, etc.
Some devices that may be modified to include the techniques
according to the present invention may include, for example, the
InSync, InSync-ICD, or In Sync III three chamber
atrial-biventricular pacers; all VDD(R)/DDD(R) pacemakers including
dual chamber right atrial/left ventricular pacers; Jewel DR
DDD(R)-ICD; dual chamber (right atrial/left ventricular)
defibrillators, and three chamber DDD(R)-ICD pacing devices
available from Medtronic Inc.
[0073] More particularly, the present invention may be applied to
any implantable medical device capable of employing a mode
switching operation. As used herein, mode switching is generally
referred to as the switching from a first pacing mode that paces at
least one ventricle based on sensed atrial activity, to a second
pacing mode that paces the at least one ventricle based on sensed
ventricular activity at a predetermined lower rate with such pacing
inhibited based on intrinsic ventricular activity. Mode switching
from the first pacing mode to the second pacing mode occurs, when
atrial activity is detected above a predetermined/programmed mode
switching rate. For example, mode switching is generally a standard
feature in many dual chamber pacemakers. Generally, such mode
switching provides for changing the operating mode of pacing
therapy during periods of accelerated atrial arrhythmias such as
SVT, PAF, and AF. For example, upon detection of periods of
accelerated atrial arrhythmias, mode switching may change dual
chamber pacing modes from DDD to DDI, DDDR to DDIR, VDD to VVI, or
VDDR to VVIR.
[0074] During episodes of conventional mode switching due to
accelerated atrial arrhythmia, generally the dual chamber pacemaker
reverts to a lower rate (LR) pacing frequency in a standard DDI or
VVI functionality (or if a rate responsive mode such as standard
DDIR or VVIR is used, then the pacemaker reverts to either the
lower rate (LR) or a rate response sensor indicated (RRSI) rate).
As previously described herein, during such mode switching periods,
an insufficient pacing rate and cardiac output may result. Further,
in the case of bi-ventricular pacing for heart failure-type
patients, continuous pacing therapy may be lost.
[0075] FIG. 7 generally shows a flow diagram for providing
accelerated LR pacing during episodes of mode switching to provide
enhanced operation during such periods and alleviating or reducing
the potential undesirable effects of mode switching. Accordingly,
attention is directed to FIGS. 7-12.
[0076] Various embodiments of accelerated ventricular LR pacing
according to the present invention shall be described with
reference to such figures. The circuitry described previously
herein, e.g., controller/timer circuit 74 of FIG. 3, includes
programmable digital counters which control the basic timing
intervals associated with various modes of pacing, e.g., DDD, DDI,
VVI, VDD, as well as other modes of dual chamber pacing known in
the art. Such circuitry controls escape intervals associated with
anti-tachyarrhythmia pacing therapies employed as described herein
and others known in the art. For example, intervals defined by
pacing circuitry, e.g., input/output circuitry 54 of FIG. 3,
include atrial and ventricular pacing escape intervals, the
refractory periods during which sensed P-waves and R-waves are
ineffective to restart timing of escape intervals, and the pulse
widths of the pacing pulses. The durations of these intervals are
determined by processing circuitry, e.g., microcomputer circuitry
58 of FIG. 3, in response to stored data in memory and are
communicated to the pacing circuitry, e.g., digital
controller/timer circuitry 74 of FIG. 3.
[0077] The duration of intervals defined by the escape interval
timers are determined by processing circuitry. The value of the
count present in escape interval counters when reset by sensed
R-waves and P-waves may be used to measure the durations of R-R
intervals, P-P intervals, P-R intervals, and R-P intervals, which
measurements are stored in memory and can be used in conjunction
with the present invention for a variety of functions, including to
diagnose the occurrence of accelerated atrial arrhythmias.
[0078] Processor circuitry, e.g., microcomputer circuitry 58 as
shown in FIG. 3, includes associated memory that may be configured
for holding a series of measured intervals. Such measured intervals
may be analyzed to determine whether a patient's heart is presently
exhibiting atrial or ventricular tachyarrhythmia or to determine
the fastest R-R interval during a sample period as described
further below.
[0079] As shown in FIG. 7, the accelerated LR pacing method 200
includes the provision of atrial sensing (block 210) which is
monitored for a mode switching event (block 212). More
particularly, and preferably according to the present invention,
such a mode switching event includes the detection of periods of
accelerated atrial arrhythmia such as SVT, PAF, AF, etc.
[0080] The accelerated atrial arrhythmia detection method may
include the use of any prior art tachyarrhythmia detection
algorithms. Various atrial arrhythmia detection methods are
available in implantable medical devices, such as those available
from Medtronic. For example, many devices such as the InSync,
InSync-ICD, or InSync III three chamber atrial-biventricular
pacers; Jewel DR DDD(R)-ICD; and other pacing devices available
from Medtronic Inc. provide various algorithms for detecting such
accelerated atrial arrhythmias. However, any suitable arrhythmia
detection methodologies known in the art may be employed.
[0081] As used herein, a mode switching event is defined as a
period of accelerated atrial arrhythmia. Preferably, the detection
of such a mode switching event leads to the switching of pacing
modes in the pacing apparatus. Preferably, the pacing modes are
switched from a first mode wherein at least one ventricle is paced
based on sensed atrial activity, e.g., DDD, VDD, etc., to a second
mode that paces the at least one ventricle based on sensed
ventricular activity at the programmed LR with such pacing
inhibited based on intrinsic ventricular activity, e.g., DDI, VVI,
etc.
[0082] As shown in block 214, if no mode switching event is
detected, then further monitoring is performed (block 212).
However, according to the present invention, if a mode switching
event is detected, then the mode switch is initiated (block 216).
For example, if the dual chamber pacemaker was operating in DDD
mode, then a DDI mode would be initiated. Likewise, if the
pacemaker was operating in DDDR mode, then the mode may be switched
to DDIR mode. If the pacemaker is operating in VDD mode, then the
mode is switched to VVI, and, likewise, if the mode is operating in
VDDR mode, then the mode may be switched to VVIR.
[0083] In other words, for example, with respect to the switching
of the pacing mode from DDD to DDI upon the detection of a mode
switching event, i.e., a period of accelerated atrial arrhythmia,
pacing is no longer provided based on sensed atrial activity but
rather ventricular pacing is paced upon sensed ventricular activity
with pacing inhibited based on intrinsic ventricular events. In
other words, a pacer in DDD mode may pace the ventricle in response
to electrical activity sensed in the atrium. However, in DDI mode
(which is virtually equivalent to VVI mode), the pacer paces and
senses in the ventricle, but its pacing is inhibited by spontaneous
electrical activation of the ventricle (i.e., intrinsic ventricular
activity or events, or, in other words, the ventricle paces itself
naturally).
[0084] Generally, a programmed ventricular LR is considered (block
218) for use in determining rates used in the second pacing mode
upon initiation of a mode switch (block 216). At least in one
embodiment, the LR (block 218) is programmed below that of the
intrinsic rate of the patient's sinus rhythm, e.g., LR=60 ppm when
SR=70 bpm. This programmed LR is restricted from being set too fast
because if the LR is set too fast, it may compete with intrinsic
activity of the heart. Preferably, it is desirable that the
intrinsic activity control.
[0085] Therefore, as shown in FIG. 7, upon initiation of mode
switching (block 216), the ventricular LR is used. For example, if
no intrinsic ventricular activity is sensed in the ventricular
chamber, then the ventricle is paced at the LR. When sensed
ventricular events are detected, then pacing is inhibited and the
intrinsic ventricular activity controls.
[0086] Due to the problems previously described herein related to
the use of the LR (block 218) in the second pacing mode, e.g.,
insufficient pacing rate and reduced cardiac output, the present
invention provides accelerated LR pacing by activating a
ventricular response (R-R) detection window (block 220) at least
initially upon mode switching and adjusting the LR (block 218) at
least initially to an elevated adjusted LR based on measurements
taken during this window. The detection window may be a
programmable window of sampling in the range of, preferably, about
5 seconds to 10 seconds. As used herein, the term "at least
initially" refers to a time frame that does not necessarily mean
that the window or the adjustment of the LR to the elevated
adjusted LR is initiated or performed at the same time as the mode
is switched but rather is initiated or performed at least a short
time thereafter (e.g., preferably within 5 seconds to 10 seconds).
For example, the programmed lower rate is not adjusted until after
sampling is performed during the detection window which may be, for
example, 5-10 seconds. As such, although the LR is "at least
initially" adjusted to the elevated adjusted LR, this adjustment
does not generally occur until after the detection window.
[0087] Following activation of the window (block 220), the
programmed LR is then adjusted as a function of measured
ventricular activity within the window to an elevated adjusted LR
(block 222). The programmed LR is adjusted to an elevated adjusted
LR such that pacing of the at least one ventricle is not inhibited
based on intrinsic ventricular activity. In other words,
preferably, the elevated adjusted LR is at a rate faster than the
occurrence of intrinsic ventricular activity such that the
intrinsic ventricular activity does not inhibit the pacemaker from
pacing of the ventricle. In other words, as opposed to intrinsic
ventricular activity controlling heart activity, the pacemaker
takes control and at least one ventricle is paced at the elevated
adjusted LR.
[0088] FIG. 8 generally shows one illustrative embodiment of a
method 222 for adjusting the programmed LR as a function of
measured ventricular activity during the ventricular response
detection window. As shown therein, during the ventricular response
detection window (e.g., a 5 second to 10 second sampling window),
R-R intervals are measured and the elevated adjusted LR is
determined based thereon. For example, the fastest R-R interval may
be measured (block 300) for use in determining the initial elevated
adjusted LR to deliver ventricular therapy. Upon measurement of the
fastest R-R interval (block 300), the elevated adjusted LR is
calculated (block 302).
[0089] In one exemplary embodiment, as shown in FIG. 8, the
elevated adjusted LR may be determined by calculating the rate at
about 10% faster than the fastest R-R interval. This ensures that
continuous pre-excitation ventricular therapy is provided. For
example, if the fastest R-R interval is 600 milliseconds (or 100
bpm), then the elevated adjusted LR may be 110 ppm (i.e., 100+10%
thereof). One skilled in the art will recognize that the elevated
adjusted LR may be calculated using various other methods or any
other generally suitable percentage (for example, 9% faster than
the fastest R-R interval), as long as the resulting elevated
adjusted LR provides ventricular pacing that is not inhibited by
intrinsic ventricular activity.
[0090] Further, for patient safety, a programmed maximum rate is
also provided (block 304). This maximum rate for the elevated
adjusted LR is preferably provided by a physician to protect
patients in whom faster ventricular pacing is undesirable (e.g.,
ischaemic heart disease patients). For example, this maximum rate
may be in the range of about 120 ppm to about 160 ppm depending
upon the patient.
[0091] As shown in FIG. 8, upon calculation of the elevated
adjusted LR (block 302), the calculated elevated adjusted LR is
compared to the programmed maximum rate (block 303) to determine
whether the elevated adjusted LR must be limited by the programmed
maximum rate (block 304). As shown therein, if the elevated
adjusted LR is greater than the programmed maximum rate, then the
elevated adjusted LR is set at the programmed maximum rate (block
306). Otherwise, if the calculated elevated adjusted LR is less
than the maximum programmed rate, then the calculated elevated
adjusted LR is used (block 308). For example, if the maximum rate
is programmed for a patient at 130 ppm and the calculated elevated
adjusted LR is 140 ppm, then the calculated LR is limited by the
programmed maximum rate of 130 ppm.
[0092] Further, with reference to FIG. 7, upon adjustment of the LR
to the elevated adjusted LR (block 222) (e.g., following mode
switching due to detection of a period of accelerated atrial
arrhythmia), a deceleration period is provided during which the
elevated adjusted LR is decelerated to a predetermined basic pacing
rate (e.g., a programmed pacing rate) at a particular deceleration
rate. By overdrive pacing using the initial elevated adjusted LR
that ensures ventricular pacing therapy and thereafter decelerating
the elevated adjusted LR to a predetermined basic pacing rate that
is also preferably accelerated relative to the programmed LR (block
218), desirable cardiac output can be achieved.
[0093] The predetermined basic pacing rate is preferably as fast or
faster than the programmed LR (block 218). Further, preferably, the
programmed basic pacing rate is an elevated compensatory rate that
guarantees sufficient cardiac output. More preferably, this
predetermined or programmed basic pacing rate is programmed at the
LR as considered in block 218 plus 20 ppm, e.g., 80 ppm.
Preferably, the deceleration period is about 5 seconds to about 10
seconds and the elevated adjusted LR is gradually decelerated at a
rate of about 5% to about 10% per cycle during the deceleration
period.
[0094] Also during the deceleration period, ventricular response or
ventricular activity is monitored (block 228). If an intrinsic
ventricular event (R-R) is detected (block 230), then action must
be taken for continuing to ensure ventricular pacing therapy. In
other words, if intrinsic ventricular events are detected, then the
decelerating elevated adjusted LR is not fast enough to control
pacing of the heart. As such, upon detection of such intrinsic
ventricular events (block 230), a ventricular response detection
window is again re-activated or re-initiated (block 220) and the LR
is once again adjusted to a readjusted elevated LR based upon
measured activity in the detection window (block 222), e.g.,
adjusted based on the fastest R-R interval. Thereafter, the
readjusted elevated LR is then again decelerated (block 226) during
a reinitiated deceleration window, such as in the same manner as
described previously above.
[0095] If the elevated adjusted LR is decelerated to the
predetermined basic pacing rate with no intrinsic ventricular event
being detected (block 230), then pacing at the predetermined basic
pacing rate will continue until the end of the mode switching event
is detected (block 232). For example, until accelerated atrial
arrhythmias are no longer being detected, the ventricular pacing
therapy is continued at the predetermined basic pacing rate.
However, if a ventricular event is detected after the deceleration
period is over and while the pacing is being continued at the
predetermined basic pacing rate (block 233), then once again the
detection window is reactivated (block 220) and the rate is
readjusted to a new readjusted elevated LR (block 222) based on
information measured in the detection window.
[0096] Mode switching is a semi-permanent mode change driven by
sensed heart activity events and/or sensor derived events occurring
in a first relationship wherein the device dictates that it remain
in the mode it is changed to until those or others can satisfy a
second defined relationship. In other words, until the switching
back of the pacing device from the second pacing mode to the first
pacing mode (block 235), e.g., DDI back to DDD, ventricular pacing
therapy is performed at the predetermined basic pacing rate. In the
present invention, for the mode to switch back from the second mode
to the first mode, detected periods of accelerated atrial
arrhythmias must have terminated in the patient.
[0097] The accelerated LR pacing method 200 described above
generally with reference to FIG. 7, and also more particularly in
part with reference to FIG. 8, will be described in more detail
with respect to a particular illustrative delivered pacing therapy
method 240 shown in the timing diagram of FIG. 9. This pacing
therapy timing diagram 240 is representative of a pacing device
providing bi-ventricular stimulation therapy. One skilled in the
art will recognize that although this illustrative timing diagram
240 is provided with focus on bi-ventricular pacing in a heart
failure patient, the present invention can be applied to any dual
chamber pacing system with mode switching so as to accelerate the
mode switching LR (e.g., LR of block 218) during periods of
accelerated atrial arrhythmias. Such accelerated LR pacing
compensates for loss in cardiac output during mode switching
episodes, and is particularly important for patients who lose the
"atrial kick" at low levels of activity. It is at these low heart
rates that atrial kick has the greatest impact on ventricular
filling. As such, the accelerated LR pacing provided in accordance
with the present invention attempts to compensate for the loss of
atrial kick during episodes of atrial arrhythmias and/or episodes
of mode switching by elevating the ventricular pacing rate.
[0098] The timing diagram 240 shown in FIG. 9 includes a section
242 that is representative of the particular atrial sensed
conditions, e.g., sinus rhythm, accelerated atrial arrhythmias such
as SVT, PAF, etc.; a pacing section 244 that describes the type of
pacing that is occurring during the timing diagram 240 such as
atrial sensed bi-ventricular pacing (abiv), supraventricular
tachyarrhythmia (svt), and bi-ventricular pacing (biv); a section
246 that is indicative of ventricular response or R-R intervals; an
accelerated LR pacing section 250 that is illustrative of the
adjustment of pacing rates according to the present invention; and
a therapy identification section 252 that indicates the occurrence
and loss of therapy during the timing diagram 240.
[0099] As shown in FIG. 9, during a first period of time 260,
normal sinus rhythm is sensed. With the pacing apparatus operating
in DDD/VDD pacing mode, atrial bi-ventricular therapy 261 is
provided as shown by the atrial sensed bi-ventricular pacing 266
shown in section 244 along with a stable R-R interval pattern shown
in section 246. Following this episode of sinus rhythm 260,
accelerated atrial arrhythmia is detected in the form of PAF during
a subsequent period 262. Upon detection of the accelerated atrial
arrhythmia, i.e., PAF, mode switching 282 occurs and the first
pacing mode (i.e., DDD/VDD) is switched to the second pacing mode
(i.e., DDI/VVI). In this particular example, the programmed LR for
the second mode of pacing (i.e., DDI/VVI) is set at 1,000
milliseconds or an LR=60 ppm.
[0100] Upon the detection of the accelerated atrial arrhythmia, a
ventricular response detection window 284, e.g., a SVT fast rate
sample period, is initiated. As shown in FIG. 9, the ventricular
response detection window is about 5-10 seconds. During this
ventricular response detection window 284, there is a loss of
bi-ventricular stimulation therapy 263. In other words,
supra-ventricular tachycardia as shown in section 244 inhibits
bi-ventricular pacing, i.e., pacemaker stimulation. This is
directly evident from the changing R-R intervals shown in section
246 which follow the accelerated atrial arrhythmia. During two
particular cycles, bi-ventricular pacemaker stimulation or
bi-ventricular pacing (biv) occurs at the programmed LR of 1,000
milliseconds. This pacemaker bi-ventricular stimulation during
these two cycles 280 occurs due to the lack of ventricular activity
or intrinsic ventricular activity being sensed.
[0101] As can be seen by the regions of time represented by
reference numerals 268 representative of supraventricular
tachycardia, during most of the ventricular response detection
windows 284, cardiac output is substantially reduced. This would be
the case throughout the second mode of pacing without use of the
present invention. However, such reduced cardiac output only occurs
within the ventricular response detection window 284 as this
sampling period is used to determine an elevated adjusted LR to
capture the heart and be used to pace it thereafter.
[0102] During the ventricular response detection window 284, the
R-R intervals are measured, and the fastest R-R interval is
determined. In FIG. 9, the fastest R-R interval is equal to 600
milliseconds, as shown by reference numeral 278. The elevated
adjusted LR 286 is then determined based upon the measured fastest
R-R interval 278. In other words, the elevated adjusted LR may be
calculated as the fastest R-R interval plus 10%, which in FIG. 9 is
equal to 100 beats per minute plus 10%, or, in other words, 110 ppm
(i.e., a rate of about 550 milliseconds).
[0103] As such, at the end 287 of the ventricular response
detection window 284, the programmed LR is adjusted to the elevated
adjusted LR 286 equal to 110 ppm. Therefore, due to the elevated
nature of the LR (i.e., a LR greater than the intrinsic ventricular
R-R intervals) bi-ventricular stimulation therapy 265 is restored.
This is further shown by bi-ventricular pacing (biv) 272 (see
section 244) which in the initial portion thereof shows pacing at
the elevated adjusted LR 286 of about 550 milliseconds. As such,
this elevated adjusted LR 286 of 550 milliseconds ensures that
continuous bi-ventricular pacing therapy is delivered by the
pacemaker.
[0104] The elevated adjusted LR 286 is used initially at time
period 287 and then is decelerated during deceleration period 288.
As shown in the illustrative embodiment of FIG. 9, the deceleration
period may be in the range of about 5-10 seconds. Further, the
elevated adjusted LR 286 is decelerated at 5-10% per cycle. As
shown therein, the deceleration continues from the elevated
adjusted LR 286 of about 550 milliseconds to a predetermined (i.e.,
programmed) basic pacing rate 290 of 750 milliseconds.
[0105] As previously described herein, the predetermined basic
pacing rate 290 is programmed by the physician to preferably an
elevated compensatory rate that guarantees sufficient cardiac
output. As shown in FIG. 9, the programmed basic pacing rate 290 is
set at the LR rate (i.e., 1,000 milliseconds or 60 ppm) plus 20
ppm=80 ppm or a 750 millisecond basic pacing rate 290.
[0106] In the embodiment of FIG. 9, there were no intrinsic
ventricular events sensed during the restored bi-ventricular
stimulation therapy period 265, and therefore bi-ventricular
stimulation (biv) 272 occurs at the decelerating rate and
thereafter at the predetermined basic rate 290 for the remainder of
this period 265. However, if an intrinsic ventricular event would
have been detected, a ventricular response detection window 284
would have been reinitiated and a new readjusted LR set for
deceleration during a reinitiated deceleration period 288. However,
as no intrinsic ventricular event was detected, the elevated
programmed basic pacing rate 290 is used for bi-ventricular
stimulation therapy until sinus rhythm 264 is reestablished. As
such, upon the reestablishment of sinus rhythm, accelerated atria
arrhythmias are no longer being detected and the second pacing
mode, i.e., DDI/VVI mode, is switched back to first pacing mode,
i.e., DDD/VDD, and atrial sensed bi-ventricular pacing 274 is once
again provided for performing atrial bi-ventricular therapy
267.
[0107] As previously described herein, the elevated adjusted LR 286
determined using the measurements of R-R intervals during the
ventricular response detection window 284 may be limited by a
programmed maximum rate. For example, if the elevated adjusted LR
286 would have been determined to be 135 ppm and a programmed
maximum rate was 130 ppm, the elevated adjusted LR 286 would have
been limited to the maximum rate of 130 ppm.
[0108] FIGS. 10-12 are provided to show the interaction of the
present invention with pacing modes that also take into
consideration, or are rate modulated by, the physical activity
level of the patient. For example, pacing devices commonly use
accelerometers to provide an indication of the patient's level of
physical activity and which generally calculate a rate response
sensor indicated (RRSI) rate based thereon. For example, such RRSI
rates may be used in pacing apparatus operating in DDDR mode and
switching to a DDIR mode upon the detection of accelerated atrial
arrhythmias or, likewise, operating in a VDDR mode and switching to
a VVIR mode upon detection of accelerated atrial arrhythmias, i.e.,
detection of a mode switching event.
[0109] Generally, if the RRSI rate is greater than any of the
pacing rates determined according to the algorithms described with
reference to FIGS. 7-9, then the RRSI rate will have priority to
determine the pacing rate. This assumes that the activity sensor is
optimized for the patient, and therefore, that the RRSI rate is
more appropriate for the patient when the patient is undertaking
such activity, e.g., exercise.
[0110] As shown in FIG. 10, the programmed LR is provided (block
322) and an RRSI rate or an activity sensor indicated pacing rate
is also provided (block 324). During the ventricular response
detection window, e.g., 284 of FIG. 9, the RRSI rate is compared to
the programmed LR (block 326). If the programmed LR is greater than
the RRSI rate, then the programmed LR is utilized (block 328).
However, if the programmed LR is less than the RRSI rate, then the
RRSI rate or the activity sensing indicated pacing rate is used
(block 330). For example, in the illustrative embodiment shown in
FIG. 9, if the LR is equal to 1,000 milliseconds and the RRSI rate
provided per block 324 is equal to 750 milliseconds, then the RRSI
rate would have priority to determine the pacing rate during the
ventricular response detection window 284.
[0111] As shown in FIG. 11, an elevated adjusted LR or a
decelerated rate is provided (block 362) and, again, an RRSI rate
or activity sensor indicated pacing rate is provided (block 364).
Such rates are compared (block 366) to determine which rate is the
more appropriate rate to be used during the deceleration period. If
the elevated adjusted LR or decelerated rate is greater than the
RRSI rate, then the elevated adjusted LR or decelerated rate has
priority (block 368), whereas if the elevated adjusted LR or
decelerated rate is less than the RRSI rate, then the RRSI rate has
priority (block 370). For example, as shown in FIG. 9, if at the
time the decelerating rate is 625 milliseconds during the
deceleration period 288 and the RRSI rate is indicated to be 600
milliseconds, the RRSI rate will have priority to determine the
pacing rate.
[0112] Likewise, as shown in FIG. 12, the predetermined or
programmed basic pacing rate is provided (block 342) along with the
RRSI rate or activity sensor indicated pacing rate (block 344).
Again, such rates are compared (block 346) to determine which rate
has priority to determine the pacing rate. If the predetermined
programmed basic pacing rate is greater than the RRSI rate, then it
has priority (block 348). On the other hand, if the programmed
basic pacing rate is less than the RRSI rate, then the RRSI rate
has priority (block 350). For example, as shown in FIG. 9, the
adjusted programmed basic rate 290 is programmed at about 750
milliseconds. If the RRSI rate is 600 milliseconds, then the RRSI
rate of 600 milliseconds would have priority to determine the
pacing rate during the restored bi-ventricular stimulation therapy
265.
[0113] All patents and references cited herein are incorporated in
their entirety as if each were incorporated separately. This
invention has been described with reference to illustrative
embodiments and is not meant to be construed in a limiting sense.
As described previously, one skilled in the art will recognize that
various other illustrative applications may utilize the accelerated
LR pacing according to the present invention. Various modifications
of the illustrative embodiments, as well as additional embodiments
of the invention, will be apparent to persons skilled in the art
upon reference to this description.
* * * * *