U.S. patent number 4,549,548 [Application Number 06/532,184] was granted by the patent office on 1985-10-29 for pacemaker system with automatic event-programmed switching between unipolar and bipolar operation.
This patent grant is currently assigned to Vitafin N.V.. Invention is credited to Willem Boute, Frederik H. M. Wittkampf.
United States Patent |
4,549,548 |
Wittkampf , et al. |
October 29, 1985 |
**Please see images for:
( Certificate of Correction ) ** |
Pacemaker system with automatic event-programmed switching between
unipolar and bipolar operation
Abstract
A pacemaker system incorporates an implantable pacemaker and a
plurality of electrodes, electrodes preferably being on a pacing
lead for a single chamber pacemaker, or a pair of such leads for a
dual chamber pacemaker. Programmable connection means are provided
for connecting the pacemaker output to a selected combination of
lead electrodes, the selection being changed during each pacer
cycle to optimize the choice of unipolar and bipolar operation for
given pacemaker events. In one mode, the system employs bipolar QRS
sensing and unipolar pacing and T-wave sensing. In another mode,
the system employs bipolar QRS sensing and pacing, and unipolar
T-wave sensing.
Inventors: |
Wittkampf; Frederik H. M.
(Brummen, NL), Boute; Willem (Doesburg,
NL) |
Assignee: |
Vitafin N.V. (Curacao,
NL)
|
Family
ID: |
24120707 |
Appl.
No.: |
06/532,184 |
Filed: |
September 14, 1983 |
Current U.S.
Class: |
607/27; 607/25;
607/36; 607/38 |
Current CPC
Class: |
A61N
1/36185 (20130101); A61N 1/368 (20130101); A61N
1/3686 (20130101); A61N 1/37211 (20130101); A61N
1/3688 (20130101) |
Current International
Class: |
A61N
1/368 (20060101); A61N 1/372 (20060101); A61N
001/36 () |
Field of
Search: |
;128/419PG |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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30897 |
|
Jun 1981 |
|
EP |
|
2026870 |
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Feb 1980 |
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GB |
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Other References
"Bipolar Versus Unipolar Issues in DDD Pacing"; Ross G. Baker, Jr.
and Eric N. Falkenberg, Nov.-Dec. 1984, Pace, Part II, vol. 7, pp.
1178-1182. .
"Long-Term Comparison of Unipolar and Bipolar Pacing and Sensing
Using a New Multiprogrammable Pacemaker System", Pace, vol. 6,
May-Jun. 1983, Part I..
|
Primary Examiner: Kamm; William E.
Attorney, Agent or Firm: Woodcock Washburn Kurtz Mackiewicz
& Norris
Claims
We claim:
1. Pacemaker apparatus having an implantable pacemaker, said
pacemaker having stimulus means for generating stimulus pulses,
sensing means for sensing heart signals, and cyclic means for
controlling said pacemaker to carry out cyclic operation, a lead
with at least two spaced lead electrodes thereon, and an
indifferent electrode, comprising:
connection means for controllably connecting said sensing means and
said stimulus means to respective selected ones of a plurality of
combinations of said lead electrodes and said indifferent
electrode;
selection means for selecting respective first and second ones of
said combinations for sensing of respective heart signals at
different times during a cycle of pacemaker operation; and
control means for controlling said connection means in accordance
with said selected combinations
2. The apparatus as described in claim 1, wherein a first of said
combinations comprises one of said lead electrodes and said
indifferent electrode, and a second of said combinations comprises
two of said lead electrodes, thereby providing selection between
unipolar and bipolar operation.
3. The apparatus as described in claim 2, wherein said pacemaker is
housed in a housing, said housing having at least a portion of the
outside of which comprises said indifferent electrode.
4. The apparatus as described in claim 1, said sensing means having
first sensing means for sensing a first selected heartbeat signal
and second sensing means for sensing a second selected heartbeat
signal, and wherein said selection means has first selection means
for selecting said unipolar connection for sensing of said first
selected heartbeat signal once each pacing cycle, and second
selection means for selecting said bipolar connection for sensing
of said second selected heartbeat signal once each cycle.
5. The apparatus as described in claim 4, wherein said first
sensing means senses T waves.
6. The apparatus as described in claim 5, wherein said second
sensing means senses QRS signals.
7. The apparatus as described in claim 1, said sensing means having
QRS means for sensing QRS signals and T wave sensing means for
sensing T waves, and wherein said selection means selects said
unipolar connection each pacing cycle for T wave sensing and
delivery of a stimulus pulse, and selects said bipolar connection
each cycle for QRS sensing.
8. The apparatus as described in claim 1, wherein said selection
means further comprises means for selecting one of said
combinations for delivery of a stimulus pulse during said
cycle.
9. Pacemaker apparatus for delivering stimulus pulses, said
apparatus having pacing means for generating said stimulus pulses
and sensing means for sensing patient heartbeat signals, a housing
which houses at least said pacing means, at least a portion of
which housing comprises an indifferent electrode, and a lead having
at least two electrodes, said pacing means having program means for
carrying out cyclical operation, characterized further by
connecting means for selectively connecting said pacing means to
two of said lead electrodes for bipolar operation or to said
indifferent electrode and one of said lead electrodes for unipolar
operation,
first control means operable each pacemaker cycle to control said
connection means to make a selected connection during delivery of a
stimulus pulse, and
second control means operable twice each pacemaker cycle to control
said connection means to make predetermined selected connections
for sensing of patient heartbeat signals at two respective times
during said each cycle.
10. The apparatus as described in claim 9, wherein said connection
means comprises a switching circuit which is controllable to
connect said pacing means alternately to one of said lead
electrodes or to said indifferent electrode.
11. The apparatus as described in claim 9, further characterized by
having a second lead having at least two electrodes and second
connection means for connecting said pacing means to said second
lead for unipolar or bipolar operation.
12. Pacemaker apparatus for delivering stimulus pulses, said
apparatus having pacing means for generating said stimulus pulses
and sensing means for sensing patient heartbeat signals, a housing
which houses at least said pacing means, at least a portion of
which housing comprises an indifferent electrode, and a lead having
at least two electrodes, said pacing means having program means for
carrying out cyclical operation, characterized further by
connection means for selectively connecting said pacing means to
two of said lead electrodes for bipolar operation or to said
indifferent electrode and one of said lead electrodes for unipolar
operation,
monitoring means for monitoring the occurrence and absence of
occurrence of at least one said sensed heartbeat signal during each
pacemaker cycle, and
control means for controlling said connection means during each
said cycle as a function of said monitoring.
13. The apparatus as described in claim 12, wherein said sensing
means has QRS timing means for timing out a QRS period for sensing
a QRS signal, said control means controlling said connection means
for bipolar operation during said QRS period and for unipolar
operation at about the end of said period.
14. Pacemaker apparatus having a pacemaker with program means for
controlling repetitive cycles of pacemaker operation and a
plurality of electrodes for delivering stimulus pulses and sensing
heart activity, said pacemaker comprising:
connection means for controllably connecting said pacemaker to a
selected combination of said electrodes;
determining means for determining pacemaker data over a plurality
of said cycles, and
control means for controlling said connection means as a function
of said determined pacemaker data.
15. The apparatus as described in claim 8, wherein said determining
means comprises means for cyclically sensing heart signals and for
generating values representative of a feature of said sensed
signals, means for accumulating said values over a predetermined
number of cycles to derive summation values, and means for
comparing respective summation values.
Description
BACKGROUND OF THE INVENTION
This invention lies in the area of cardiac pacers and the method of
operation of same, with programmed means for varying pacemaker
operation and, in particular, pacemaker systems and other
implantable systems with microprocessor control for switching
between unipolar and bipolar operation in accordance with
programmed events such as sensing of patient signals and stimulus
delivery.
In the field of cardiac pacemakers, there is a need to provide an
efficient electrode system for the operations of delivery of
stimulus pulses and sensing patient heartbeat signals. In a
conventional single chamber demand pacemaker, of the demand type,
the electrode system must provide for efficient delivery of
ventricular stimulus signals, and also provide efficient pick up of
natural QRS signals. In dual chamber pacemakers, there is
additionally a need to be able to sense atrial signals, and to
deliver atrial stimulus pulses from the pacemaker. In another type
of pacemaker, as set forth in U.S. Pat. No. 4,228,803, assigned to
the same assignee, there is a need to sense T-waves.
Generally there are two types of electrode systems which are used
in cardiac pacing. In the bipolar system of operation, two
electrodes are positioned near the tip of a lead which is placed
into the heart, the electrodes typically being rings which conduct
the stimulus pulse and sense natural cardiac signals. In a unipolar
electrode arrangement, a single electrode is placed on the lead,
preferrably out or near the tip, and an indifferent electrode is
utilized at a location remote from the electrode tip. Most
typically, in unipolar, or monopolar arrangements, the indifferent
electrode is a portion of the pacemaker housing, which is a
convenient way of obtaining a large surface indifferent electrode.
Alternately, the indifferent electrode may be positioned on the
lead itself, at a point proximal to the tip, as is known in the
art.
The pacemaker industry has not resolved, and indeed cannot resolve
the question of whether unipolar or bipolar operation is generally
preferrable. Some physicians adhere to one or the other modes of
operation, having their own reasons for doing so. Most pacemaker
manufacturers have provided pacing systems for operation in each of
the modes, such that the physician can choose a unipolar or a
bipolar system. Bipolar leads and systems have the advantages of
reduced pick up of electromagnetic interference, and they avoid the
problem of unipolar systems wherein the pectoral muscle can be
inadvertantly excited. Unipolar systems are generally recognized to
have the advantage of better sensitivity for sensing heart signals,
and to have reduced polarization problems due to the relatively
large indifferent electrode and the relatively small lead
electrode. In special applications, such as searching for an evoked
response signal (QRS wave) following delivery of a stimulus pulse,
or in measuring T-waves, the unipolar system is definitely
preferable. There could be a problem if, in a bipolar system, the
heart muscle is captured at both electrodes, in which case the
sensed T-wave and QRS wave would be simply the difference of the
two signals and would be very small.
In view of the above, it is seen that there is a need to provide
increased flexibility, by which the pacer system can utilize the
advantages of each of the bipolar and unipolar modes of operation
for the particular events that are taking place. Thus, there is a
need for a system which automatically switches between unipolar and
bipolar forms of operation, the switching being programmed for
optimal operation of the different pacer events which take place
during each pacing cycle. The desirability for switching applies to
both single chamber and dual chamber pacing systems. In dual
chamber systems, it may be desirable, for example, to have bipolar
operation in the atrium to reduce the need for blanking following
delivery of the ventricular stimulus, while at the same time having
a unipolar electrode arrangement for sensing P waves. Generally,
considerations for unipolar and bipolar sensing vary at different
times in the pacing cycle, dependent upon the next anticipated
event.
While this invention is described in terms of switching between
unipolar and bipolar operation in a pacemaker system, it is to be
understood that it generally applies to optimized switching of
various electrode systems, for pacemakers and other types of
devices for delivering stimuli to a patient and/or sensing patient
signals. For example, electrode configurations may be used which
are not termed unipolar or bipolar, as those terms are understood
in the pacemaker art, but which electrode configurations are
changed during cycles of operation of the system.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a stimulus delivery
system having an implantable device and an electrode configuration
with a plurality of electrodes, and a controllable connection
circuit for connecting the electrodes to the stimulus/device in
various configurations, the circuit being switchable during each
device cycle so as to optimize the electrode configuration in terms
of system events.
It is another object of this invention to provide a pacing system
with microprocessor control for changing the system operation
between unipolar and bipolar operation within each pacing cycle, in
accordance with programmed events.
It is another object of this invention to provide an implantable
device system with programmed means for automatically changing the
electrode configuration in accordance with the programmed system
operation.
It is a further object of this invention to provide a pacemaker
system with program means for cyclically switching the pacemaker
sensing means and electrode configuration, to optimize sensing of
patient cardiac signals.
It is a further object of this invention to provide a pacemaker
system with means for automatically accumulating data corresponding
to system operation, and for automatically switching the system
electrode configuration in accordance with such accumulated patient
data.
In accordance with the above objects, there is provided a pacemaker
system having an implantable pacemaker with means for delivering
stimulus pulses and means for sensin patient signals, the pacemaker
being in programmable connection with an electrode configuration
having a plurality of electrodes, and controllable means for
switching the electrodes connected to the pacemaker so as to
provide alternately unipolar and bipolar operation. The pacemaker
system preferably contains microprocessor control for cyclically
programming switching between unipolar and bipolar operation to
optimize the electrode configuration for predetermined pacing
events such as stimulus delivery and sensing of given patient heart
signals. In another embodiment, the pacemaker monitors one or more
system events over one or more pacemaker cycles, and automatically
selects an optimum electrode configuration.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is a block diagram showing the main components of a demand
pacemaker system in accordance with this invention.
FIG. 1B is a block diagram showing the main components of a dual
chamber pacemaker in accordance with this invention.
FIG. 1C is a schematic illustration of a pacemaker and lead,
illustrating placement of electrodes to achieve bipolar and
unipolar modes of operation.
FIGS. 2A and 2B present a flow diagram of a programmable pacemaker
utilizing the subject invention.
FIG. 3 is a flow diagram of a routine for switching the electrode
configuration as a function of performance monitored over a
plurality of cycles of operation.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to FIG. 1A, a pacemaker is shown in a casing, or
housing 30. An indifferent electrode 43, as also shown in FIG. 1C,
forms a portion of the outside surface of the casing, as is
conventional in the pacemaker art. The pacemaker contains
circuitry, as shown at block 32, for generating and delivering
stimulus pulses, or stimulus signals, and circuitry as shown at
block 34 for sensing patient heart signals, e.g. QRS and T waves,
or atrial P waves. A microprocessor control, incorporating a
microprocessor chip or chips as well as associated control
circuitry, is shown at block 36. Communications as indicated
between the microprocessor control and the stimulus and sense
circuitry enable overall control of the pacer, in a known manner. A
power source as shown at 38 provides a voltage V.sub.B which is
applied to all of the circuitry. As illustrated, the negative side
of the power source is connected to the circuitry, and the positive
side is connected to the system ground. All of these features are
conventional and well known in the art. See, for example, European
Patent Application No. 81108940.8.
The output of the stimulus amplifier circuitry, as well as the
input to the sense circuitry are tied in common and fed through the
pacer housing and connected through a conventional lead to a first
electrode 41, designated electrode 1 in FIG. 1A. This electrode is
typically located at the end of the lead, as illustrated in FIG.
1C. A bipolar lead of conventional design carries a second
electrode, suitably a ring positioned proximally to the distal
first electrode, and electrically connected by a conductor running
the length of the lead. A third electrode is suitably provided by a
plate 43 which forms a portion or substantially all of the
pacemaker can, or housing, as also illustrated in FIG. 1C.
In the system of this invention, an electronically controlled
switch 40 is provided which operates to switch either the second
electrode or the indifferent electrode to the system ground. When
the switch connects the second electrode (42) to system ground,
then the two ring electrodes as seen in FIG. 1C are connected to
the pacemaker, and bipolar system operation is achieved. With this
mode of connection, a stimulus pulse may be delivered with the
voltage difference being directly across the two ring electrodes
41, 42. When the switch 40 is switched so that the indifferent
electrode 43 is connected to system ground, then ring electrode 42
is not connected to the pacemaker, and unipolar operation is
achieved. In unipolar operation, a delivered stimulus pulse
presents a voltage between the small electrode 41 at the tip of the
lead, and the large electrode 43 on the pacemaker casing. As is
known in the art, the indifferent electrode may be positioned other
than on the pacemaker housing, and could be positioned as shown at
43' in FIG. 1C, far proximal on the lead itself.
The operation of switch 40, as illustrated in FIG. 1A, is under
control of the microprocessor control circuitry 36. Switch 40 may
be any well known semiconductor switch, such as is easily provided
in the art, the switching operation being under the control of a
conventional microprocessor or other analog or digital controller.
In the preferred embodiment of microprocessor control, the switch
may be accurately controlled at programmed intervals of each pacing
cycle, as illustrated in FIGS. 2A and 2B below. It is to be
understood that the switch control may take any conventional design
form, including the use of analog circuitry in a well known
manner.
Referring to FIG. 1B, there is shown a block diagram illustrating a
more general system encompassed by this invention, as applied as a
dual chamber pacemaker. Microprocessor control circuitry 36 is
shown in two-way communication with pacer stimulus and sense
circuits as shown in block 45, and switch means as shown in block
46. The switch means provide the function of connecting a plurality
of electrodes, in different combinations, to the pacer stimulus and
sense circuits. As illustrated, five electrodes may be used, two
atrial electrodes 47, two ventricular electrodes 48, and an
indifferent electrode 43. It is to be understood that in the
general application of this invention, for pacemaker systems or
other similar implantable systems, the number of electrodes that
may be utilized is unlimited. The invention covers the automatic
switching of different electrode configurations during repetitive
cycles, the electrode configurations being chosen for use with one
or more predetermined programmed events. In the pacemaker system
embodiment, the programmed events include sensing of different
natural and/or evoked heart signals, and delivery of stimulus
pulses to one or more heart locations. As illustrated in FIG. 1B,
the switch means may also controllably connect to an extra sensor
52, which may be an additional cardiac electrode or a sensor for
sensing another patient parameter.
Referring now to FIGS. 2A and 2B, there is illustrated a flow
diagram covering a cycle of pacer operation. The flow diagram is
repeated continuously each pacer cycle.
Referring to FIG. 2A, there is illustrated an example of a
microprocessor controlled cardiac pacemaker system which changes
its electrode configuration, as well as filter characteristics,
within the pacer cycle. The program, as illustrated, is for a
ventricular demand pacer, and starts at a time just after the time
out of the pacer refractory period. At block 207, the filter of the
input amplifier, connected to receive a patient cardiac signal, is
set to an appropriate QRS setting, i.e., set to an appropriate
bandpass for detecting a patient QRS signal. At block 208, a
bipolar connection is set, for bipolar QRS sensing. At block 233,
the microprocessor enables sensing through the input amplifier,
and, for example, sets the sensitivity at 2 mV. At block 234, the
microprocessor is stopped to await either timeout or a sensed QRS.
When either of these events occurs, the microprocessor picks up at
block 236 and records the time T of the last cycle, and then
determines whether a timeout has occurred, at block 238.
If a timeout has occurred, meaning there has been no natural
patient beat, the program block branches to the right. In
preparation for generating the stimulus, the filter of the input
amplifier is first set to a high frequency characteristic, at block
239, in order to quickly damp out any artifacts produced by the
generated stimulus. If unipolar pacing is desired, a unipolar
connection is also set at this point. Thereafter the pacer timer is
set to zero at block 240, and the stimulus is generated at block
241. Bookkeeping type operations are done at 242-245 and 201; an
end-of-life (EOL) test may be done at 202-204, and at 205 the
program exits either to the "on-demand" path of FIG. 2B, or to a
fixed rate path. If the "NO" branch is taken at block 238, no
stimulus is generated, and bookkeeping functions 250-252 are
carried out.
Referring to FIG. 2B, the program continues after the stimulus
delivery provided in FIG. 2A. The program as illustrated provides
for controlling the rate of delivered stimulus pulses as a function
of stimulus T time intervals. A time delay is introduced at block
260, corresponding to the delay between the stimulus and the start
of evoked response sensing. The sense amplifier is disabled at
block 261, and the microprocessor is stopped to wait for the delay
T.sub.1. At block 262, the microprocessor determines whether the
timer has timed out. If yes, and the last cycle was a pace cycle,
as determined at 210, the pacer control branches to the right. At
block 263, a switchable filter such as disclosed in U.S.
application Ser. No. 475,024 is set to the evoked QRS setting,
i.e., to a filter characteristic optimally designed to detect an
evoked QRS. A period T2 is put into the timer at 264, during which
the pacer looks for the evoked response. At block 265, the
electrodes are connected for unipolar operation, e.g., switch 40 is
set to connect the indifferent electrode to ground, leaving ring
electrode 42 unconnected. The sense amplifier is enabled at block
266, for example with a sensitivity of 8 mV. At block 268, it is
determined whether the timer has timed out. If no, meaning that an
evoked response was detected, the ERS flag is set at block 271. If
yes, meaning that there was no evoked response, the non-ERS flag is
set at 270. Following this, at block 273, the microprocessor goes
through an output processing subroutine, to change the stimulus
magnitude if required to achieve heart capture. At block 274, the
filter characteristic of the input amplifier is modified to a
characteristic adapted for detecting the T wave portion of the
heart signal. Following this, at block 276, a time interval TPT
corresponding to the T wave time is set into the timer, and at
block 277 the sense amplifier is enabled at a sensitivity of, for
example, 1 mV. The microprocessor is stopped at 280, and is started
again at 281 either by a sensed T wave or by timing out. If it is
not timed out, meaning that a T wave was sensed, the time of this T
wave in relation of the delivered pulse stimulus is stored at 283.
At block 284, the microprocessor goes through a rate subprocessing
routine to change the pacer rate, as set forth in U.S. Pat. No.
4,228,803. If, at block 210, it is determined that the last cycle
was ended by a sensed natural QRS, the program branches to block
226, where the refractory interval is established by setting the
timer to Ter. The sense amplifier is disabled at block 277, and the
microprocessor is stopped to await the time out of the refractory
period as shown at block 228.
As illustrated, FIGS. 2A and 2B show an example of cyclic bipolar
operation for sensing QRS and for stimulation, and monopolar
(unipolar) T wave sensing. Unipolar pacing can be achieved by
setting the unipolar connection after QRS sensing (or time out) and
before delivery of the stimulus pulse. Dual chamber operation
employs additional such switching steps in accordance with desired
electrode modes for atrial sensing and stimulating.
Referring to FIG. 3, there is illustrated a routine which can be
utilized in a pacemaker or other implantable device, for monitoring
performance and reprogramming a desired switch connection as a
function of monitored performance. The reprogramming can be done
with respect to cyclical switching, e.g., for the embodiment of
FIGS. 2A and 2B periodic signal sensing can be changed from bipolar
to unipolar, or vice versa. Alternately, the reprogramming can be
done on a permanent or fixed basis, e.g., the pacemaker may switch
from fixed unipolar operation to fixed bipolar, or vice versa.
The program of FIG. 3 illustrates monitoring a sensed heartbeat
signal to obtain a measure of whether the sensing operation would
be performed better in the unipolar or bipolar mode. The amplitude
of a received input signal, e.g. QRS or P wave, is stored at block
285. At block 286, a new sum designated A SUM is accumulated by
adding the just received amplitude A to the prior sum. At block
287, the number of iterations I is incremented by 1. In the
illustration, the routine iterates 10 times in order to accumulate
a sum, but it is to be understood that one or more measurements can
be made, and that the number of iterations is a matter of choice.
At block 288, it is determined whether I is less than 10. If yes,
more cycles are to be measured, and the routine branches directly
to the end. If no, meaning that 10 measurements have now been
accumulated, the program proceeds to block 289 where it is
determined whether A SUM is less than the prior, or old A SUM. If
no, meaning that A SUM has increased, reflecting improved
performance, the routine branches to block 292. If yes, meaning
that performance has deteriorated, the routine first performs the
operation at block 290 of changing the switch connection, i.e.,
changing the electrode mode for the sensing activity from bipolar
to unipolar, or vice versa. Thereafter, at block 292, the
microprocessor stores the accumulated A SUM as A SUM OLD. At block
294, the present values of A SUM and I are set to zero, and the
program exists.
The subroutine of FIG. 3 may be run continuously initiated
periodically by a counter in the pacemaker; or initiated by an
external program signal. It is presented as an illustration of
utilizing device-accumulated information to make the choice of mode
setting. While the illustration given relates to sensing a received
heart signal, patient information relative to stimulus delivery can
likewise be accumulated. With evoked response sensing, a patient
threshold can be determined by known means, and threshold compared
for unipolar versus bipolar stimulus delivery. It is to be
understood that the routine for cyclic switching between unipolar
and bipolar operation can be re-programmed from an external source,
by means well known in the art.
* * * * *