U.S. patent application number 10/870402 was filed with the patent office on 2004-12-30 for implantable cardiac stimulator wherein the atrial stimulation time interval is set dependent on the evoked response amplitude.
This patent application is currently assigned to St. Jude Medical AB. Invention is credited to Lindgren, Anders.
Application Number | 20040267327 10/870402 |
Document ID | / |
Family ID | 27656650 |
Filed Date | 2004-12-30 |
United States Patent
Application |
20040267327 |
Kind Code |
A1 |
Lindgren, Anders |
December 30, 2004 |
Implantable cardiac stimulator wherein the atrial stimulation time
interval is set dependent on the evoked response amplitude
Abstract
An implantable heart stimulating device with atrial overdrive
capability has an atrial stimulation unit for stimulating the
atrium via stimulation electrode(s), an atrial evoked response
detector adapted to determine an atrial evoked response amplitude,
and an atrial control unit to control an atrial timing unit to set
an atrial stimulation time interval length between consecutively
applied atrial stimulation pulses. The atrial stimulation time
interval length is set in dependent on the determined atrial evoked
response amplitude such that the next time interval length is a
predetermined percentage of the present time interval length. If
the ER signal amplitude decreases, the stimulating interval has to
be decreased. The pacemaker can also try to increase the
stimulating interval back to back until a decrease in ER signal
amplitude is seen in order to avoid too high stimulating rate.
Inventors: |
Lindgren, Anders; (Taby,
SE) |
Correspondence
Address: |
SCHIFF HARDIN LLP
Patent Department
6600 Sears Tower
233 South Wacker Drive
Chicago
IL
60606
US
|
Assignee: |
St. Jude Medical AB
|
Family ID: |
27656650 |
Appl. No.: |
10/870402 |
Filed: |
June 17, 2004 |
Current U.S.
Class: |
607/9 ;
607/27 |
Current CPC
Class: |
A61N 1/368 20130101;
A61N 1/3712 20130101 |
Class at
Publication: |
607/009 ;
607/027 |
International
Class: |
A61N 001/362 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 30, 2003 |
SE |
0301919-7 |
Claims
I claim as my invention:
1. An implantable cardiac stimulator comprising: an atrial pulse
generator; stimulation electrode(s) connected to the atrial pulse
generator and adapted for interaction with the atrium to deliver
pulses from the atrial pulse generator to the atrium; an atrial
evoked response detector connected to said stimulation electrode(s)
for determining an atrial evoked response amplitude for at least
one of said stimulation pulses; and an atrial control unit
connected to the atrial pulse generator and to the atrial evoked
response detector, and having an atrial timer for setting an atrial
stimulation time interval length between consecutive pulses from
said atrial pulse generator, said control unit operating said
atrial timer to set the atrial stimulation time interval length for
a next time interval length, dependent on said atrial evoked
response amplitude, as a predetermined percentage of a current time
interval length.
2. An implantable cardiac stimulator as claimed in claim 1 wherein
said control unit employs a predetermined percentage in a range
between 85% and 95%.
3. An implantable cardiac stimulator as claimed in claim 1 for
stimulating a heart having an intrinsic atrial time interval
length, and wherein said control unit control said timer to set
said time interval length for said next time interval to be as long
as possible with respect to said intrinsic atrial time interval
length.
4. An implantable cardiac stimulator as claimed in claim 1 wherein
said atrial evoked response detector operates with a plurality of
amplitude thresholds for identifying a decrease of said atrial
evoked response amplitude, and wherein said control unit operates
said atrial timer to decrease said atrial stimulation time interval
length for said next time interval if a decreasing atrial evoked
response amplitude is identified.
5. An implantable cardiac stimulator as claimed in claim 1 wherein
said atrial evoked response detector determines if said atrial
evoked response amplitude is less than a minimum evoked response
amplitude threshold and, if so, said control unit operates said
atrial timer to decrease said atrial stimulation time interval
length for said next time interval by said predetermined
percentage.
6. An implantable cardiac stimulator as claimed in claim 1 wherein
said atrial evoked response detector operates with a plurality of
amplitude thresholds to identify an increasing atrial evoked
response amplitude, and wherein said control unit operates said
atrial timer to increase said atrial stimulation time interval
length for said next time interval length by said predetermined
percentage if an increasing atrial evoked response amplitude is
identified.
7. An implantable cardiac stimulator as claimed in claim 1 wherein
said evoked response detector detects an electrical evoked response
signal, and wherein said atrial evoked response amplitude is an
amplitude of said electrical evoked response signal.
8. An implantable cardiac stimulator as claimed in claim 1 wherein
said evoked response detector operates with amplitude thresholds to
identify a decreasing atrial evoked response amplitude, and wherein
said control unit operates said timer to decrease said atrial
stimulation time interval length for said next time interval by
said predetermined percentage if a decreasing evoked response
amplitude is identified and, if said atrial stimulation time
interval length for said next time interval was decreased in any of
a predetermined number of preceding heart cycles, and if said
atrial evoked response amplitude is above a predetermined
threshold, said control unit operates said atrial timer to increase
said atrial stimulation time interval length for said next time
interval length.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an implantable cardiac
stimulator of the type having atrial overdrive capability, and
having an atrial stimulator for stimulating the atrium via
stimulation electrode(s), an atrial evoked response detector for
determining an atrial evoked response amplitude, and an atrial
control unit that controls an atrial timer to set an atrial
stimulation time interval length between consecutive atrial
stimulation pulses.
[0003] 2. Description of the Prior Art
[0004] A healthy heart pumps blood through the circulatory system
in successive, periodic cycles each including an atrial contraction
followed shortly thereafter by a ventricular contraction. The
successive atrial and ventricular contractions occur upon being
triggered by the heart's natural pacemaker, which causes electrical
wave fronts to propagate through cardiac tissue, causing the tissue
cells to be momentarily depolarized, thereby initiating the
contractions. If a patient's natural pacemaker, through disease,
ceases to function or functions only erratically, artificial pacing
therapy can be provided by an implanted pacemaker, which delivers
low-energy pacing pulses to the atrium, or to the ventricle, or to
both the atrium and the ventricle in a properly synchronized
sequence. Depending on the needs of a particular patient, the
pacemaker can be programmed to continuously supply such pacing
pulses without interruption, or can operate to sense when the
patient's natural pacemaker has failed to deliver a signal
resulting in contraction, and only then does the implanted
pacemaker deliver a pacing pulse. Pacemakers of this latter type
are known as demand pacemakers.
[0005] Fibrillation, in general, characterizes abnormal operation
of the heart, which can spontaneously occur, wherein the normal
initiation of the electrical wave fronts becomes chaotic and
therefore the cardiac tissue never receives a clear or coherent
signal triggering contraction, and pumping therefore ceases.
Ventricular fibrillation is a life-threatening condition, and when
it occurs must be treated rapidly and effectively. For this
purpose, implantable defibrillators are well-known in the art,
which deliver one or more high-energy electrical pulses to the
cardiac tissue, at selected locations and in a selected timing
sequence, so as to momentarily depolarize substantially all of the
cardiac tissue, thereby rendering virtually all of the cardiac
tissue momentarily unable to propagate the chaotic wave fronts. If
defibrillation is successful, when the cells again become capable
of propagating a pacing wave front, they will do so in a normal,
non-chaotic manner.
[0006] Atrial fibrillation is usually not an immediately
life-threatening pathology, and can be tolerated for a certain
amount of time without significant adverse consequences to the
patient. This means that upon the occurrence of atrial
fibrillation, there is usually a relatively long time during which
an effective therapy can be developed, and subsequently
administered. Although implantable defibrillator technology,
primarily intended for treating ventricular fibrillation, can be
adapted also to treat atrial fibrillation, the delivery of high
energy shocks to the patient is painful and moreover, such drastic
therapy is usually not necessary in the case of atrial
fibrillation. Atrial fibrillation is also treated by extracorporeal
delivery of the shocks to the heart through the skin of the patient
by an external defibrillator of the type well-known in the art,
also being extremely uncomfortable for the patient. Moreover, this
type of treatment generally results only in temporary relief for
patients, and must be repeated.
[0007] In treating atrial fibrillation by means of electrical
shocks supplied to the heart, such shocks must be applied in
synchronism with the ventricular electrical activity, otherwise
ventricular fibrillation may be induced.
[0008] Another treatment regimen for atrial fibrillation is the
administration of suitable drugs for reducing the occurrences of
atrial fibrillation. Drugs suitable for this purpose which are
currently available, however, have many undesirable side effects,
and many patients become resistant to their atrial fibrillation
suppressing properties, thereby significantly reducing the
therapeutic effect of such drugs.
[0009] Recent pacemakers include an overdrive capability adapted to
control the mechanisms responsible for atrial fibrillation (AF).
Herein, overdrive is defined as a pacing regime that suppresses the
initiation of atrial fibrillation by stimulating the atrium at a
rate higher than the patient's own intrinsic atrial rate. St Jude
Medical has designed an AF suppression algorithm, known as the
Dynamic Atrial Overdrive (DAO) algorithm for that purpose, see e.g.
the brochure "AF Suppression Algorithm: A New Tool for Reducing
Atrial Fibrillation in Pacemaker Recipients" .COPYRGT. 2001 St Jude
Medical Cardiac Rhythm Management Division. It accomplishes this by
continually monitoring the intrinsic atrial rhythm, promptly
increasing the stimulation rate when the intrinsic atrial rhythm
emerges, and periodically reducing the stimulation rate gradually
to search for intrinsic atrial activity. This process ensures that
the stimulation rate is not inappropriately rapid when the patient
is at rest, yet is sufficiently high when the patient is
active.
[0010] With AF suppression turned on, detection of two intrinsic
atrial events within a 16-cycle window causes an increase in the
atrial stimulation rate. The magnitude of the increase depends
among others on the current stimulation rate. The increased rate is
maintained for a programmed number of overdrive cycles, after which
the system begins to search for the intrinsic rate by gradually
extending the atrial stimulation interval (8 ms for rates>100
ppm; 12 ms for rates<100 ppm).
[0011] The described algorithm is illustrated by the ECG shown in
FIG. 1. In FIG. 1, while overdrive pacing the atrium at a rate of
84 ppm, the device detects two intrinsic atrial events and
immediately responds with a rate increase (by overdrive pacing at a
rate of 93 ppm). After stimulating the atrium for the selected
number of overdrive pacing cycles (15 cycles at a rate of 93 ppm),
the device begins to extend the pacing cycle lengths to search for
intrinsic atrial activity (rate recovery). Detection of two
intrinsic atrial events would again initiate a prompt rate increase
and reset the cycle length counter.
[0012] In the presently used AF suppression algorithm, which
briefly has been described above, the paced atrial rate is
decreased until two spontaneous P-waves are seen within a 16-cycle
window. The algorithm then increases the paced atrial rate to
regain a paced atrial rhythm, where after it again starts to
decrease its pace rate until two spontaneous P-waves are seen
within a 16-cycle window.
SUMMARY OF THE INVENTION
[0013] Thus, in some cases spontaneous P-waves interrupt the AF
suppression algorithm at regular intervals, and an object of the
present invention is to further improve the algorithm so that the
paced atrial rhythm is maintained and not interrupted by
spontaneous sinus rhythm.
[0014] Thus, the object is generally achieved by monitoring the
changes of the atrial evoked response (ER) signal amplitudes. It
has been observed that the ER signal amplitude decreases by
increased degree of atrial fusion (and the amplitude will vanish
completely during atrial inhibition.)
[0015] Atrial fusion is herein defined as the ECG waveform that
typically results when an intrinsic atrial depolarization and an
atrial stimulation pulse occur simultaneously and both contribute
to the electrical activation of the atrium.
[0016] This change in the amplitude is used to set the atrial
stimulation time interval length in dependence of the determined
atrial evoked response amplitude such that said time interval
length is a predetermined percentage of an intrinsic atrial time
interval length.
[0017] The pacemaker tries to keep the paced atrial intervals as
long as possible. However, if a decreasing ER signal amplitude is
seen, this indicates that the atrial pacing interval is becoming
too long and thus has to be decreased somewhat to maintain a paced
atrial rhythm. The pacemaker can also try to increase the
stimulating intervals until a decrease in ER signal amplitude is
seen.
DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 shows an ECG that illustrates the conventional AF
suppression algorithm.
[0019] FIG. 2 is a schematic illustration of an implantable heart
stimulating device in which the present invention is
applicable.
[0020] FIG. 3 is a block diagram illustrating the present
invention.
[0021] FIG. 4 is a simplified chart of a number of heart cycles
showing the relationship of the determined ER amplitude and the
atrial stimulation time interval length according to the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] FIG. 2 shows a schematic illustration of an implantable
heart stimulating device where the present invention is applicable.
The heart stimulating device 2 is provided with two heart electrode
leads 8 inserted into the heart 4. One of the electrode leads is
inserted into the right atrium and one is inserted into the right
ventricle for applying stimulation pulses to the respective heart
chambers. This is standard implantation locations in a dual chamber
pacemaker. The present invention is naturally also applicable when
using alternative placements of the heart electrodes. This may be,
for example, epicardial placements or locations in the coronary
veins, or in both atria, in both single (AAI) or dual chamber
pacemakers.
[0023] FIG. 3 is a block diagram illustrating the present
invention. Only components relevant for describing the present
invention are shown. Also included (but not shown) in a
conventional pacemaker are e.g. corresponding circuitry for the
ventricle channel, a ventricular electrode lead and power supply
means.
[0024] As shown in FIG. 3 the implantable heart stimulating device
2, provided with an atrial overdrive capability, has an atrial
stimulation means 6 for stimulating the atrium via stimulation
electrode(s) arranged at the distal end of an atrial heart
electrode lead 8, an atrial evoked response (ER) detector 10
adapted to determine an atrial evoked response amplitude and an
atrial control unit 12 to control an atrial timing unit 14 to set
an atrial stimulation time interval length between consecutively
applied atrial stimulation pulses. The atrial evoked response
amplitude preferably is determined as the amplitude of the
electrical evoked response signal.
[0025] The atrial stimulation time interval length is set dependent
on the determined atrial evoked response amplitude such that the
next time interval length is a predetermined percentage of the
present time interval length. Preferably, the predetermined
percentage is, when the interval is to be decreased, in the
interval 80-95% and may be set by an external programming means
(not shown) in steps of 5%.
[0026] In general, the atrial stimulation time interval length is
set as long as possible in relation to an intrinsic atrial time
interval length.
[0027] FIG. 4 is a simplified chart of a number of heart cycles
showing the relationship of the determined ER amplitude and the
atrial stimulation time interval length according to the present
invention. Atrial stimulation pulses are indicated by an "A".
[0028] FIG. 4 heart cycles 1-4 all have the same interval length T.
The ER amplitude is sensed by the atrial electrode, measured by the
atrial ER detector 10 and a measure of the amplitude is supplied to
the atrial control unit 12. These ER amplitude measures are
indicated in FIG. 4 as vertical bars. In the atrial control unit 12
the ER amplitude measure is compared to thresholds in order to
determine if the ER amplitude is increasing or decreasing and also
to determine if the ER amplitude is less than a minimum ER
threshold amplitude.
[0029] As can be seen from FIG. 4 the ER amplitude in heart cycle 4
is smaller than the previous ER amplitude and in heart cycle 5 the
ER amplitude is less than the minimum ER amplitude threshold. The
time interval length is then shortened a predetermined percentage
of the present time interval length, in FIG. 4 by 10%.
[0030] The shortened time interval length is kept until the ER
amplitude increases again and then the time interval length is
returned, e.g. to its previous length. In the figure the short time
interval length is kept for two heart cycles and is prolonged when
the ER amplitude is above a higher threshold.
[0031] As known to those skilled in the art the time interval
length may be decreased and increased in many different ways. In
this case the short time interval is kept for one heart cycle
despite the ER amplitude in heart cycle 6 is greater than the
minimum ER amplitude threshold. The return to the longer time
interval may naturally be instant or the shorter time interval may
be kept for a larger number of heart cycles.
[0032] The time interval changes may be in one step, as in the
illustrated example, or be more gradual over a number of heart
cycles under direct control of any detected changes of the ER
amplitudes.
[0033] As illustrated by FIG. 4, if said atrial stimulation time
interval length was decreased in any of a predetermined number of
preceding heart cycles (4 and 5) and the evoked response amplitude
is above the minimum ER amplitude threshold, the atrial stimulation
time interval length is increased (in heart cycle 7) under control
of the control unit 12.
[0034] It should be understood that the present invention is
primarily intended to be fully incorporated in the presently used
AF suppression algorithm designed by St Jude Medical.
[0035] Although modifications and changes may be suggested by those
skilled in the art, it is the intention of the inventor to embody
within the patent warranted hereon all changes and modifications as
reasonably and properly come within the scope of his contribution
to the art.
* * * * *