U.S. patent application number 11/116558 was filed with the patent office on 2006-11-02 for non-captured intrinsic discrimination in cardiac pacing response classification.
Invention is credited to Yanting Dong, Scott A. Meyer, Kevin John Stalsberg.
Application Number | 20060247693 11/116558 |
Document ID | / |
Family ID | 37235467 |
Filed Date | 2006-11-02 |
United States Patent
Application |
20060247693 |
Kind Code |
A1 |
Dong; Yanting ; et
al. |
November 2, 2006 |
Non-captured intrinsic discrimination in cardiac pacing response
classification
Abstract
Cardiac devices and methods discriminate non-captured intrinsic
beats during evoked response detection and classification by
comparing the features of a post-pace cardiac signal with expected
features associated with a non-captured response with intrinsic
activation. Detection of a non-captured response with intrinsic
activation may be based on the peak amplitude and timing of the
cardiac signal. The methods may be used to discriminate between a
fusion or capture beat and a non-captured intrinsic beat.
Discriminating between possible cardiac responses to the pacing
pulse may be useful, for example, during automatic capture
verification and/or a capture threshold test.
Inventors: |
Dong; Yanting; (Shoreview,
MN) ; Meyer; Scott A.; (Rochester, MN) ;
Stalsberg; Kevin John; (White Bear Lake, MN) |
Correspondence
Address: |
Crawford Maunu PLLC
Suite 390
1270 Northland Drive
St. Paul
MN
55120
US
|
Family ID: |
37235467 |
Appl. No.: |
11/116558 |
Filed: |
April 28, 2005 |
Current U.S.
Class: |
607/9 |
Current CPC
Class: |
A61N 1/371 20130101;
A61B 5/35 20210101 |
Class at
Publication: |
607/009 |
International
Class: |
A61N 1/362 20060101
A61N001/362 |
Claims
1. A method of classifying a cardiac response to a pacing pulse,
comprising: delivering the pacing pulse to a heart; sensing a
cardiac signal following delivery of the pacing pulse; comparing
one or more characteristics of the cardiac signal to one or more
expected cardiac signal characteristics associated with a
non-captured response with intrinsic activity; and classifying the
cardiac response to the pacing pulse as the noncaptured response
with intrinsic activation based on the comparison.
2. The method of claim 1, wherein comparing the cardiac signal
characteristics to the expected characteristics comprises
extracting features of the cardiac signal and comparing the
features to expected cardiac signal features associated with the
non-captured response with intrinsic activity.
3. The method of claim 2, wherein comparing the one or more
features of the cardiac signal to the one or more expected features
associated with the non-captured response with intrinsic activation
comprises determining if one or more peaks of the cardiac signal
respectively fall within one or more intrinsic detection windows,
each of the one or more intrinsic detection windows associated with
an intrinsic peak amplitude range and an intrinsic peak timing
interval.
4. The method of claim 1, wherein classifying the cardiac response
further comprises discriminating the non-captured response with
intrinsic activation from unknown cardiac activity.
5. The method of claim 1, wherein classifying the cardiac response
further comprises discriminating between a captured response and
the non-captured response with intrinsic activation.
6. The method of claim 5, wherein discriminating between the
captured response and the non-captured response with intrinsic
activation comprises classifying the cardiac response as the
captured response if one or more features of the cardiac signal are
consistent with expected features associated with the captured
response.
7. The method of claim 1, wherein classifying the cardiac response
further comprises discriminating the cardiac response as a fusion
beat if the cardiac response does not comprise a captured beat or a
non-captured intrinsic beat.
8. The method of claim 1, wherein classifying the cardiac response
to the pacing pulse comprises classifying the cardiac response to
the pacing pulse during automatic capture verification.
9. The method of claim 1, wherein classifying the cardiac response
to the pacing pulse comprises classifying the cardiac response to
the pacing pulse during a capture threshold test.
10. The method of claim 1, further comprising: sensing for a
cardiac signal peak in at least two capture detection windows, each
of the at least two capture detection windows associated with a
captured response peak amplitude range and a captured response peak
time interval; and classifying the cardiac response as a captured
response if the cardiac signal peaks are detected in the at least
two capture detection windows.
11. The method of claim 10, further comprising classifying the
cardiac response as fusion if the cardiac response does not
comprise a non-captured intrinsic response or a captured
response.
12. The method of claim 1, further comprising: sensing for the
cardiac signal peak in at least one noise detection window, the at
least one noise detection window associated with a noise window
amplitude range and a noise window time interval; and classifying
the cardiac response as unknown cardiac signal behavior if the
cardiac signal peak is detected in the at least one noise detection
window.
13. A system for classifying a cardiac response to a pacing pulse,
comprising: a sensor system, comprising a plurality of electrodes
electrically coupled to a heart, the sensor system configured to
sense a cardiac signal following delivery of the pacing pulse; and
a processor coupled to the sensing system, the processor configured
to compare one or more characteristics of the cardiac signal to one
or more expected cardiac signal characteristics associated with a
non-captured intrinsic beat, and to classify the cardiac response
to the pacing pulse as the non-captured intrinsic beat based on the
comparison.
14. The system of claim 13, wherein the one or more characteristics
of the cardiac signal comprise one or more features of the cardiac
signal and the one or more expected characteristics comprise one or
more expected characteristics and the processor is configured to
extract the one or more features from the cardiac signal and to
compare the extracted features to the one or more expected
features.
15. The system of claim 14, wherein the one or more extracted
features comprises a peak time of the cardiac signal and the one or
more expected features comprises an expected peak timing range.
16. The system of claim 14, wherein the one or more extracted
features comprises a peak amplitude of the cardiac signal and the
one or more expected features comprises an expected peak amplitude
range.
17. The system of claim 13, wherein the processor is configured to
discriminate the non-captured intrinsic beat from other cardiac
activation based on the one or more characteristics of the cardiac
signal.
18. The system of claim 13, wherein the processor is configured to
classify the cardiac response as the non-captured intrinsic beat if
a cardiac signal peak is detected in at least one intrinsic
detection window, the at least one intrinsic detection window
associated with an intrinsic beat amplitude range and an intrinsic
beat time interval relative to the cardiac signal.
19. The system of claim 18, wherein parameters of the at least one
intrinsic detection window are selected based on an expected timing
of a cardiac signal feature associated with a captured
response.
20. The system of claim 18, wherein parameters of the at least one
intrinsic detection window are selected based on patient
conditions.
21. A cardiac device, comprising: a pulse generator configured to
deliver a pacing pulse to a heart; a sensing system configured to
sense a cardiac signal following delivery of the pacing pulse;
means for comparing one or more features of the cardiac signal to
one or more expected features associated with a non-captured
response with intrinsic activation; and means for classifying the
cardiac response to the pacing pulse as the non-captured response
with intrinsic activation based on the comparison.
22. The cardiac device of claim 21, further comprising means for
determining if a peak amplitude of the cardiac signal falls within
an intrinsic detection window, the intrinsic detection window
associated with an intrinsic peak amplitude range and an intrinsic
peak timing interval.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to implantable
medical devices and, more particularly, to cardiac devices and
methods that discriminate non-captured intrinsic beats during
evoked response detection.
BACKGROUND OF THE INVENTION
[0002] When functioning normally, the heart produces rhythmic
contractions and is capable of pumping blood throughout the body.
However, due to disease or injury, the heart rhythm may become
irregular resulting in diminished pumping efficiency. Arrhythmia is
a general term used to describe heart rhythm irregularities arising
from a variety of physical conditions and disease processes.
Cardiac rhythm management systems, such as implantable pacemakers
and cardiac defibrillators, have been used as an effective
treatment for patients with serious arrhythmias. These systems
typically include circuitry to sense electrical signals from the
heart and a pulse generator for delivering electrical stimulation
pulses to the heart. Leads extending into the patient's heart are
connected to electrodes that contact the myocardium for sensing the
heart's electrical signals and for delivering stimulation pulses to
the heart in accordance with various therapies for treating the
arrhythmias.
[0003] Cardiac rhythm management systems operate to stimulate the
heart tissue adjacent to the electrodes to produce a contraction of
the tissue. Pacemakers are cardiac rhythm management systems that
deliver a series of low energy pace pulses timed to assist the
heart in producing a contractile rhythm that maintains cardiac
pumping efficiency. Pace pulses may be intermittent or continuous,
depending on the needs of the patient. There exist a number of
categories of pacemaker devices, with various modes for sensing and
pacing one or more heart chambers.
[0004] When a pace pulse produces a contraction in the heart
tissue, the electrical cardiac signal preceding the contraction is
denoted the captured response (CR). The captured response typically
includes an electrical signal, denoted the evoked response signal,
associated with the heart contraction, along with a superimposed
signal associated with residual post pace polarization at the
electrode-tissue interface. The magnitude of the residual post pace
polarization signal, or pacing artifact, may be affected by a
variety of factors including lead polarization, after-potential
from the pace pulse, lead impedance, patient impedance, pace pulse
width, and pace pulse amplitude, for example.
[0005] A pace pulse must exceed a minimum energy value, or capture
threshold, to produce a contraction. It is desirable for a pace
pulse to have sufficient energy to stimulate capture of the heart
without expending energy significantly in excess of the capture
threshold. Thus, accurate determination of the capture threshold is
required for efficient pace energy management. If the pace pulse
energy is too low, the pace pulses may not reliably produce a
contractile response in the heart and may result in ineffective
pacing. If the pace pulse energy is too high, the patient may
experience discomfort and the battery life of the device will be
shorter.
[0006] Detecting if a pacing pulse "captures" the heart and
produces a contraction allows the cardiac rhythm management system
to adjust the energy level of pace pulses to correspond to the
optimum energy expenditure that reliably produces capture. Further,
capture detection allows the cardiac rhythm management system to
initiate a back-up pulse at a higher energy level whenever a pace
pulse does not produce a contraction.
[0007] A fusion beat is a cardiac contraction that occurs when two
cardiac depolarizations of a particular chamber, but from separate
initiation sites, merge. At times, a depolarization initiated by a
pacing pulse may merge with an intrinsic beat, producing a fusion
beat. Fusion beats, as seen on electrocardiographic recordings,
exhibit various morphologies. The merging depolarizations of a
fusion beat do not contribute evenly to the total
depolarization.
[0008] Pseudofusion occurs when a pacing stimulus is delivered on a
spontaneous P wave during atrial pacing or on a spontaneous QRS
complex during ventricular pacing. In pseudofusion, the pacing
stimulus may be ineffective because the tissue around the electrode
has already spontaneously depolarized and is in its refractory
period.
[0009] Noise presents a problem in evoked response detection
processes when the pacemaker mistakenly identifies noise as
capture, fusion/pseudofusion, or intrinsic activity. Noise
mistakenly identified as capture or fusion/pseudofusion may cause a
pacemaker to erroneously withhold backup pacing under loss of
capture conditions. Noise mistakenly identified as non-captured
intrinsic activity may lead to a premature loss of capture
determination during threshold testing.
[0010] In the event that the pace does not capture the heart and
capture or fusion/pseudofusion would then not occur, intrinsic
activity may occur early enough in the cardiac cycle to appear as
an evoked response when the pace did not actually capture the
heart. These non-captured intrinsic beats represent a loss of
capture. The misclassification of non-captured intrinsic beat to
capture or fusion beats may result in low threshold measurement
during threshold testing.
SUMMARY OF THE INVENTION
[0011] The present invention involves various cardiac devices and
methods that discriminate non-captured intrinsic beats during
evoked response detection and classification. An embodiment of a
method of classifying a cardiac response to a pacing pulse in
accordance with the present invention involves delivering pacing
pulse to a heart and sensing a cardiac signal following delivery of
the pacing pulse. The cardiac response to the pacing pulse is
classified as a non-captured intrinsic beat based on one or more
characteristics of the cardiac signal. Classifying the cardiac
response may involve detecting one or both of a peak time and peak
amplitude of the cardiac signal, and may be based on one or both of
the peak time and peak amplitude.
[0012] Other embodiments of methods of classifying a cardiac
response to a pacing pulse in accordance with the present invention
involve sensing for a cardiac signal peak in at least one intrinsic
beat detection window associated with an intrinsic beat amplitude
range and an intrinsic beat time interval. The cardiac response may
be classified as a non-captured intrinsic beat if the cardiac
signal peak is detected in at least one intrinsic beat detection
window. Methods may further involve sensing for a cardiac signal
peak in at least two capture detection windows, each associated
with a captured response amplitude range and a captured response
time interval. The cardiac response may be classified as a captured
response if the cardiac signal peaks are detected in at least two
capture detection windows. Further, the cardiac response may be
classified as fusion if the cardiac signal peak is not detected in
at least one capture detection window, and the cardiac signal peak
is not detected in the at least one intrinsic detection window.
[0013] Other embodiments of a method of classifying a cardiac
response to a pacing pulse in accordance with the present invention
involve sensing for the cardiac signal peak in at least one noise
detection window associated with a noise window amplitude range and
a noise window time interval. The cardiac response may be
classified as an unknown cardiac signal behavior if the cardiac
signal peak is detected in the at least one noise detection
window.
[0014] Further embodiments in accordance with the present invention
are directed to systems for classifying a cardiac response to a
pacing pulse. Systems in accordance with the present invention may
include a sensor system configured to sense a cardiac signal
following delivery of the pacing pulse with a processor coupled to
the sensing system. The processor may be configured to detect one
or more features of the cardiac signal and to classify the cardiac
response to the pacing pulse as a non-captured intrinsic beat based
on the one or more cardiac signal features. The processor may be
configured to detect one or more peak times and/or amplitudes of
the cardiac signal and to classify the cardiac response based on
the peak time(s) and/or amplitude(s). The processor may
discriminate the non-captured intrinsic beat from other cardiac
activity based on the one or more features of the cardiac signal.
The processor may classify the cardiac response as the non-captured
intrinsic beat if a feature value associated with a particular
cardiac signal feature is consistent with an expected feature value
associated with a non-captured intrinsic beat.
[0015] The above summary of the present invention is not intended
to describe each embodiment or every implementation of the present
invention. Advantages and attainments, 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
[0016] FIG. 1 is a flowchart of a method that discriminates
non-captured intrinsic beats during evoked response detection and
classification in accordance with embodiments of the invention;
[0017] FIG. 2 is a diagram illustrating time intervals that may be
used for discriminating non-captured intrinsic beats during evoked
response detection and classification in accordance with
embodiments of the invention;
[0018] FIG. 3 is a graph including cardiac response classification
windows and noise detection windows that may be utilized for
cardiac devices and methods that discriminate non-captured
intrinsic beats during evoked response detection and classification
in accordance with embodiments of the invention;
[0019] FIG. 4 illustrates cardiac response waveform portions
superimposed over the graph in FIG. 3 in accordance with
embodiments of the invention;
[0020] FIG. 5 is a partial view of one embodiment of an implantable
medical device in accordance with embodiments of the invention;
[0021] FIG. 6 is a block diagram of an implantable medical device
that may be use for discrimination of non-captured intrinsic beats
during evoked response detection and classification in accordance
with embodiments of the invention; and
[0022] FIG. 7 is a schematic diagram of a circuit that may be used
to sense a cardiac signal following the delivery of a pacing
stimulation and to classify the cardiac response to the pacing
stimulation according to embodiments of the invention.
[0023] While the invention is amenable to various modifications and
alternative forms, specifics thereof have been shown by way of
example in the drawings and will be described in detail below. It
is to be understood, however, that the intention is not to limit
the invention to the particular embodiments described. On the
contrary, the invention is intended to cover all modifications,
equivalents, and alternatives falling within the scope of the
invention as defined by the appended claims.
DETAILED DESCRIPTION OF VARIOUS EMBODIMETS
[0024] In the following description of the illustrated embodiments,
references are made to the accompanying drawings forming a part
hereof, and in which are shown by way of illustration, various
embodiments by which the invention may be practiced. It is to be
understood that other embodiments may be utilized, and structural
and functional changes may be made without departing from the scope
of the present invention.
[0025] Cardiac response classification may be implemented by a
pacemaker or other cardiac rhythm management (CRM) device to
determine whether an applied electrical pacing stimulus captures
the heart. Embodiments of the invention are directed to cardiac
devices and methods that discriminate non-captured intrinsic beats
during cardiac pacing response determination. The methods described
herein use one or more characteristics of the cardiac signal, e.g.,
cardiac signal features, samples, discrete and/or analog
morphological waveform characteristics, to discriminate between
various responses to pacing and may be used during automatic
capture verification or capture threshold testing. Cardiac pacing
responses may include, for example, noncapture, capture,
fusion/pseudofusion, and noncapture with intrinsic activity.
[0026] Processes for recognizing the cardiac response to pacing may
rely on one or more templates characterizing various types of
possible responses. The system may compare a cardiac signal sensed
after delivery of the pacing pulse to the templates. If the cardiac
signal is sufficiently similar to a particular template, then the
cardiac response may be classified as the type of response
characterized by the template.
[0027] In some embodiments, a template characterizing a particular
type of cardiac pacing response may comprise one or more detection
windows that represent an expected range of values of a cardiac
signal associated with particular type of cardiac response. For
example, if the cardiac signal following the pacing pulse is
detected within the detection regions, then the system classifies
the cardiac response as the particular type of cardiac response
characterized by the template.
[0028] Automatic threshold and automatic capture verification are
algorithms that may be used by cardiac rhythm management (CRM)
devices. These algorithms attempt to discriminate captured beats
from non-captured beats. Detection of non-capture may be
complicated by non-capture beats that include intrinsic activation.
For some patients, for example, patients with intact AV conduction,
a non-captured beat with intrinsic activation may have a morphology
somewhat similar to a captured response. Thus, templates used to
discriminate between a captured response and a noncaptured response
with intrinsic activation must be formed and used accurately to
discriminate between the two types of responses. In automatic
threshold testing, erroneous classification of a noncaptured
intrinsic beat as a captured response may cause the capture
threshold to be incorrectly identified.
[0029] Embodiments of the present invention are directed to
detection and classification of non-captured beats with intrinsic
activation. Detection and classification of such beats may be
accomplished by recognizing the characteristic signal features of
such non-captured intrinsic beats. In accordance with one aspect of
the invention, detection and classification of non-captured,
intrinsic beats is accomplished based on the determination of one
or more features of the cardiac signal, for example, one or more
peak amplitudes and associated peak times.
[0030] A template for recognizing the intrinsic beats may comprise
one or more intrinsic detection windows, having dimensions of time
and amplitude, into which peaks of the non-captured, intrinsic
signal are expected to fall. If the peaks of a sensed cardiac
signal fall into one or more of the intrinsic detection windows,
the cardiac response may be classified as a non-captured response
with intrinsic activation. Methods and systems for generating and
updating detection windows, aspects of which may be utilized in
connection with the embodiments of the present invention are
described in commonly owned U.S. patent applications identified by
Attorney Docket Nos.: GUID.168PA and GUID.169PA, both of which are
concurrently filed with this patent application, and incorporated
herein by reference.
[0031] One embodiment of the invention is based on the peak
amplitude and timing of non-captured intrinsic activity, relative
to those of captured beats. As will be described in more detail
below, non-captured intrinsic beats typically have a relatively
late peak relative to captured beats, while fusion beats typically
have earlier peaks. Devices and methods in accordance with the
present invention provide a non-captured intrinsic detection window
after a capture detection window, to discriminate these
non-captured intrinsic beats. In addition to the relatively late
peak, an intrinsic beat may also have a larger peak amplitude when
compared to the peak amplitude of a captured response. Therefore,
embodiments of the present invention may include a second
non-captured intrinsic detection window that may be used to
discriminate non-captured intrinsic beats with increased peak
amplitudes.
[0032] A further check may be performed to discriminate and manage
unusual intrinsic beats, such as premature ventricular contraction
(PVC). For example, one or more noise detection windows may also be
provided in accordance with the present invention to detect a
relatively large positive peak associated with PVC and uncommon to
the other cardiac responses.
[0033] FIG. 1 is a flowchart of a method 100 of detecting
non-captured beats with intrinsic activation in accordance with
embodiments of the invention. Pacing pulses 110 are delivered to a
patient's heart. For example, the pacing pulses may be delivered to
one or more of a right ventricle, right atrium, left ventricle,
and/or left atrium. Cardiac signals 120 following the pacing pulse
that are associated with, or in response to, the pacing pulse are
sensed, and measurements are made of one or more characteristics of
the cardiac signal, such as cardiac signal features that may
include amplitudes and timings associated with positive and/or
negative cardiac signal peaks. The one or more cardiac signal
characteristics are compared 130 to one or more expected
characteristics associated with a non-captured response with
intrinsic activation. If the one or more sensed cardiac signal
characteristics are consistent with the one or more expected
characteristics, the cardiac pacing response is classified 140 as a
non-captured response with intrinsic activation.
[0034] FIG. 2 is a diagram illustrating multiple time intervals
that may be used for discriminating non-captured intrinsic beats
during cardiac pacing response classification in accordance with
embodiments of the invention. A pacing stimulation 210 is delivered
to the heart, for example, to the right ventricle. The cardiac
signal is blanked for a period of time 220, typically about 0
milliseconds to about 40 milliseconds, following the delivery of
the pacing stimulation 210. After the blanking period 220, a first
time interval 230 is initiated. The duration of the first time
interval 230 may be a programmable duration, for example, less than
about 325 milliseconds. The cardiac signal associated with the
pacing pulse is sensed during the first time interval 230. If the
positive or negative amplitude of the cardiac signal does not
exceed a threshold in the first time interval 230, then the cardiac
response may be classified as a noncaptured response. If the
cardiac signal exceeds the threshold value, then various features
of the cardiac signal may be determined and used for cardiac pacing
response classification. In some cases, sensing of the cardiac
signal may be extended to additional time intervals, such as the
second time interval 240. The second time interval 240 may be
programmable, and may have a duration less than about 325
milliseconds. The durations of the additional time intervals may be
different or the same as the duration of the first time
interval.
[0035] A delay period 250 may be established between the end of one
time interval 230 and the beginning of another time interval 240.
The duration of the delay may be in a range of about 0 milliseconds
(no delay) to about 40 milliseconds, for example. The cardiac
response to the pacing stimulation 210 may be classified based on
characteristics of the cardiac signal determined in the first
and/or the additional time intervals 230, 240.
[0036] FIG. 3 illustrates detection windows that may be utilized in
cardiac devices and methods that discriminate non-captured
intrinsic beats during cardiac pacing response classification in
accordance with embodiments of the invention. Following delivery of
a pace 410, the sensing system is blanked, e.g., the sense
electrodes are disconnected from sense amplifiers or the sense
amplifiers are rendered inoperative, during a blanking period 415.
Following the blanking period, the cardiac signal is sensed in one
or more time intervals. As illustrated in FIG. 3, sensing may occur
in two time intervals 420, 450 following the pacing pulse 410. In
some scenarios, the second 450 and subsequent time intervals (not
shown) may be triggered by events occurring in one or more previous
intervals.
[0037] In various implementations, sensing may be performed using
the same electrode combination that was used to deliver the pacing
stimulation. In other implementations, the pacing stimulation may
be delivered using a first electrode configuration and sensing may
use a second electrode configuration. Use of a sensing vector that
is spatially removed from the pacing vector may be particularly
useful for diminishing the effect of a pacing artifact on the
cardiac signal following pacing. Systems and methods for
classifying a cardiac response to pacing using multiple time
intervals and various sensing and pacing vectors are described in
commonly owned U.S. Patent applications: Ser. No. 10/733,869, filed
Dec. 11, 2003, entitled "Cardiac Response Classification Using
Multiple Classification Windows"; Ser. No. 10/734,599 filed Dec.
12, 2003, entitled "Cardiac Response Classification Using
Retriggerable Classification Windows"; and Ser. No. 10/735,519
filed Dec. 12, 2003, entitled "Cardiac Response Classification
Using Multisite Sensing And Pacing"; which are hereby incorporated
herein by reference.
[0038] During the first time interval 420, the system senses for a
positive or negative cardiac signal amplitude beyond a threshold
level 440. If the cardiac signal amplitude falls within the
threshold 440 during the first time interval 420, then the cardiac
response is classified as noncapture and a backup pace 470 may be
delivered. The backup pace 470 is typically a high energy pace that
is delivered following a backup interval (BPI) 430. For example,
the BPI 430 may include an interval of about 100 ms timed from the
delivery of the primary pace 410.
[0039] The system may utilize one or more cardiac response
detection windows 455, 456, 460, 461 as illustrated in FIG. 3. A
cardiac pacing response method that discriminates non-captured
intrinsic beats in accordance with embodiments of the invention
involves determining if one or more peak values of the cardiac
response signal falls, or does not fall, within one or more cardiac
response detection windows 455, 456, 460, 461. In this embodiment,
the cardiac response detection windows 455, 456, 460, 461 are areas
defined in terms of amplitude and time. In other embodiments,
different or additional parameters may be used in addition to, or
in place of the parameters of amplitude and time.
[0040] In the example of FIG. 3, the system may classify a cardiac
response as capture if a peak value of the cardiac signal is
detected in the first capture detection window 455 and a peak value
of the cardiac signal is detected in the second capture detection
window 456. If a cardiac signal peak is detected in the first
non-captured intrinsic detection window 460, or the second
non-captured intrinsic detection window 461, the cardiac response
may be classified as noncapture with non-captured intrinsic
activation. Otherwise, the beat may be classified as a
fusion/pseudofusion beat, or further discriminated.
[0041] Devices and methods that discriminate non-captured intrinsic
beats during evoked response detection and classification in
accordance with embodiments of the present invention may involve
the use of one or more noise detection windows 435, 436 for further
discrimination of cardiac waveforms. If signal peaks fall within
the cardiac response classification windows 455, 456, 460, 461 then
the system checks for peaks opposite in polarity and comparable in
magnitude to the cardiac response signal peaks. FIG. 3 illustrates
noise detection windows 435, 436. The noise detection windows 435,
436 may be any shape or size. For example, the noise detection
windows 435, 436 may be the same size and/or shape as a
corresponding capture detection window 455, 456 in a particular
time interval 420, 450, or may be a different size and/or shape.
Methods and systems involving noise detection windows, aspects of
which may be utilized in connection with the embodiments of the
present invention are described in commonly owned U.S. patent
application identified by Attorney Docket Number GUID.171PA,
concurrently filed with this patent application, and incorporated
herein by reference.
[0042] FIG. 4 illustrates three representative cardiac response
waveform portions superimposed over the graph illustrated in FIG.
3. A non-captured intrinsic beat 480, a PVC beat 482, and a
captured beat 484 are drawn, illustrating waveform parameters
useful for discriminating non-captured intrinsic beats during
cardiac pacing response classification in accordance with the
present invention. The waveform parameters of the PVC beat 482
illustrated in the graph of FIG. 4 include, but are not limited to,
a negative peak amplitude 481 within the second noise detection
window 436 during the second time interval 450, and a positive peak
489 within the first noise detection window 435 during the first
time interval 420.
[0043] The waveform parameters of the non-captured intrinsic beat
480 illustrated in the graph of FIG. 4 include, but are not limited
to, a negative peak amplitude 493 within the first intrinsic
detection window 460. The waveform parameters of the captured beat
484 illustrated in the graph of FIG. 4 include, but are not limited
to, a negative peak amplitude 487 within the first capture
detection window 455 during the first time interval 420, and a
positive peak 485 within the second capture detection window 456
during the second time interval 450.
[0044] As is evident in FIG. 4, the non-captured intrinsic beat 480
and the captured beat 484 have morphologies similar enough that
they may be confused if discrimination of non-captured intrinsic
beats during evoked response detection and classification is not
performed in accordance with embodiments of the present
invention.
[0045] First and second intrinsic detection windows 460, 461 are
provided in accordance with embodiments of the present invention to
perform intrinsic discrimination. In some scenarios, the
non-captured intrinsic beat 480 has a greater negative peak
amplitude than the captured beat 484. The second intrinsic
detection window 461 is defined in both time duration and amplitude
breadth to discriminate arrival of a non-captured intrinsic beat
480, having a relatively larger negative peak, within the time
frame of the capture detection window 455.
[0046] In some scenarios, as illustrated by the intrinsic waveform
480 of FIG. 4, the negative peak 493 of the intrinsic beat occurs
slightly later than the negative peak 487 of the captured beat
signal 484. A first intrinsic detection window 460 that begins
after the first capture detection window 455 discriminates
intrinsic beats from capture beats. Providing one or more
non-captured intrinsic beat capture detection windows in accordance
with the present invention improves the discrimination capabilities
of cardiac devices and reduces or eliminates the inclusion of
undesired response signals during capture threshold testing,
capture verification, template initialization and/or updating,
and/or for other purposes when non-captured intrinsic beat
discrimination is desirable.
[0047] The parameters of the intrinsic detection windows, including
shape, area, and/or position may be selected based on the estimated
or known morphology of cardiac signals associated with noncaptured
intrinsic beats. Determination of the detection window parameters
may be based on clinical data or on data acquired from the
patient.
[0048] In one embodiment, the intrinsic detection window parameters
are based on the relative timing of the capture detection window.
Intrinsic activity generally occurs slightly later than the
captured activity. Therefore, the intrinsic detection window may be
arranged to occur just after the capture detection window, for
example, in the first classification interval.
[0049] Patient conditions may affect the selected parameters of the
intrinsic detection windows. For patients with intact AV
conduction, for example, the intrinsic detection window parameters
may be selected based on this information. In one implementation,
for patients with known AV delay, the intrinsic detection window
may be positioned to occur a predetermined time following atrial
activity.
[0050] The embodiments of the present system illustrated herein are
generally described as being implemented in a patient implantable
medical device such as a pacemaker/defibrillator that may operate
in numerous pacing modes known in the art. Various types of single
and multiple chamber implantable cardiac defibrillators are known
in the art and may be used in connection with cardiac devices and
methods that discriminate non-captured intrinsic beats during
evoked response detection and classification in accordance with the
present invention. The methods of the present invention may also be
implemented in a variety of implantable or patient-external cardiac
rhythm management devices, including single and multi chamber
pacemakers, defibrillators, cardioverters, bi-ventricular
pacemakers, cardiac resynchronizers, and cardiac monitoring
systems, for example.
[0051] Although the present system is described in conjunction with
an implantable cardiac defibrillator having a microprocessor-based
architecture, it will be understood that the implantable cardiac
defibrillator (or other device) may be implemented in any
logic-based integrated circuit architecture, if desired.
[0052] Referring now to FIG. 5 of the drawings, there is shown a
cardiac rhythm management system that may be used to implement
methods that discriminate non-captured intrinsic beats during
evoked response detection and cardiac pacing response
classification in accordance with the present invention. The
cardiac rhythm management system in FIG. 5 includes a
pacemaker/defibrillator 800 electrically and physically coupled to
a lead system 802. The housing and/or header of the
pacemaker/defibrillator 800 may incorporate one or more electrodes
908, 909 used to provide electrical stimulation energy to the heart
and to sense cardiac electrical activity. The
pacemaker/defibrillator 800 may utilize all or a portion of the
pacemaker/defibrillator housing as a can electrode 909. The
pacemaker/defibrillator 800 may include an indifferent electrode
908 positioned, for example, on the header or the housing of the
pacemaker/defibrillator 800. If the pacemaker/defibrillator 800
includes both a can electrode 909 and an indifferent electrode 908,
the electrodes 908, 909 typically are electrically isolated from
each other.
[0053] The lead system 802 is used to detect electric cardiac
signals produced by the heart 801 and to provide electrical energy
to the heart 801 under certain predetermined conditions to treat
cardiac arrhythmias. The lead system 802 may include one or more
electrodes used for pacing, sensing, and/or defibrillation. In the
embodiment shown in FIG. 5, the lead system 802 includes an
intracardiac right ventricular (RV) lead system 804, an
intracardiac right atrial (RA) lead system 805, an intracardiac
left ventricular (LV) lead system 806, and an extracardiac left
atrial (LA) lead system 808. The lead system 802 of FIG. 5
illustrates one embodiment that may be used in connection with the
feature determination methodologies described herein. Other leads
and/or electrodes may additionally or alternatively be used.
[0054] The lead system 802 may include intracardiac leads 804, 805,
806 implanted in a human body with portions of the intracardiac
leads 804, 805, 806 inserted into a heart 801. The intracardiac
leads 804, 805, 806 include various electrodes positionable within
the heart for sensing electrical activity of the heart and for
delivering electrical stimulation energy to the heart, for example,
pacing pulses and/or defibrillation shocks to treat various
arrhythmias of the heart.
[0055] As illustrated in FIG. 5, the lead system 802 may include
one or more extracardiac leads 808 having electrodes, e.g.,
epicardial electrodes, positioned at locations outside the heart
for sensing and pacing one or more heart chambers.
[0056] The right ventricular lead system 804 illustrated in FIG. 5
includes an SVC-coil 816, an RV-coil 814, an RV-ring electrode 811,
and an RV-tip electrode 812. The right ventricular lead system 804
extends through the right atrium 820 and into the right ventricle
819. In particular, the RV-tip electrode 812, RV-ring electrode
811, and RV-coil electrode 814 are positioned at appropriate
locations within the right ventricle 819 for sensing and delivering
electrical stimulation pulses to the heart 801. The SVC-coil 816 is
positioned at an appropriate location within the right atrium
chamber 820 of the heart 801 or a major vein leading to the right
atrial chamber 820 of the heart 801.
[0057] In one configuration, the RV-tip electrode 812 referenced to
the can electrode 909 may be used to implement unipolar pacing
and/or sensing in the right ventricle 819. Bipolar pacing and/or
sensing in the right ventricle may be implemented using the RV-tip
812 and RV-ring 811 electrodes. In yet another configuration, the
RV-ring 811 electrode may optionally be omitted, and bipolar pacing
and/or sensing may be accomplished using the RV-tip electrode 812
and the RV-coil 814, for example. The RV-coil 814 and the SVC-coil
816 are defibrillation electrodes.
[0058] The left ventricular lead 806 includes an LV distal
electrode 813 and an LV proximal electrode 817 located at
appropriate locations in or about the left ventricle 824 for pacing
and/or sensing the left ventricle 824. The left ventricular lead
806 may be guided into the right atrium 820 of the heart via the
superior vena cava. From the right atrium 820, the left ventricular
lead 806 may be deployed into the coronary sinus ostium, the
opening of the coronary sinus 850. The lead 806 may be guided
through the coronary sinus 850 to a coronary vein of the left
ventricle 824. This vein is used as an access pathway for leads to
reach the surfaces of the left ventricle 824 which are not directly
accessible from the right side of the heart. Lead placement for the
left ventricular lead 806 may be achieved via subclavian vein
access and a preformed guiding catheter for insertion of the LV
electrodes 813, 817 adjacent to the left ventricle.
[0059] Unipolar pacing and/or sensing in the left ventricle may be
implemented, for example, using the LV distal electrode referenced
to the can electrode 909. The LV distal electrode 813 and the LV
proximal electrode 817 may be used together as bipolar sense and/or
pace electrodes for the left ventricle. The left ventricular lead
806 and the right ventricular lead 804, in conjunction with the
pacemaker/defibrillator 800, may be used to provide cardiac
resynchronization therapy such that the ventricles of the heart are
paced substantially simultaneously, or in phased sequence, to
provide enhanced cardiac pumping efficiency for patients suffering
from chronic heart failure.
[0060] The right atrial lead 805 includes a RA-tip electrode 856
and an RA-ring electrode 854 positioned at appropriate locations in
the right atrium 820 for sensing and pacing the right atrium 820.
In one configuration, the RA-tip 856 referenced to the can
electrode 909, for example, may be used to provide unipolar pacing
and/or sensing in the right atrium 820. In another configuration,
the RA-tip electrode 856 and the RA-ring electrode 854 may be used
to provide bipolar pacing and/or sensing.
[0061] FIG. 5 illustrates one embodiment of a left atrial lead
system 808. In this example, the left atrial lead 808 is
implemented as an extracardiac lead with LA distal 818 and LA
proximal 815 electrodes positioned at appropriate locations outside
the heart 801 for sensing and pacing the left atrium 822. Unipolar
pacing and/or sensing of the left atrium may be accomplished, for
example, using the LA distal electrode 818 to the can 909 pacing
vector. The LA proximal 815 and LA distal 818 electrodes may be
used together to implement bipolar pacing and/or sensing of the
left atrium 822.
[0062] Referring now to FIG. 6, there is shown an embodiment of a
cardiac pacemaker/defibrillator 900 suitable for implementing
non-captured intrinsic cardiac response detection and
classification methods of the present invention. FIG. 6 shows a
cardiac pacemaker/defibrillator 900 divided into functional blocks.
It is understood by those skilled in the art that there exist many
possible configurations in which these functional blocks can be
arranged. The example depicted in FIG. 6 is one possible functional
arrangement. Other arrangements are also possible. For example,
more, fewer or different functional blocks may be used to describe
a cardiac pacemaker/defibrillator suitable for implementing the
methodologies for feature determination in accordance with the
present invention. In addition, although the cardiac
pacemaker/defibrillator 900 depicted in FIG. 6 contemplates the use
of a programmable microprocessor-based logic circuit, other circuit
implementations may be utilized.
[0063] The cardiac pacemaker/defibrillator 900 depicted in FIG. 6
includes circuitry for receiving cardiac signals from a heart and
delivering electrical stimulation energy to the heart in the form
of pacing pulses or defibrillation shocks. In one embodiment, the
circuitry of the cardiac pacemaker/defibrillator 900 is encased and
hermetically sealed in a housing 901 suitable for implanting in a
human body. Power to the cardiac pacemaker/defibrillator 900 is
supplied by an electrochemical battery 980. A connector block (not
shown) is attached to the housing 901 of the cardiac
pacemaker/defibrillator 900 to allow for the physical and
electrical attachment of the lead system conductors to the
circuitry of the cardiac pacemaker/defibrillator 900.
[0064] The cardiac pacemaker/defibrillator 900 may be a
programmable microprocessor-based system, including a control
system 920 and a memory 970. The memory 970 may store parameters
for various pacing, defibrillation, and sensing modes, along with
other parameters. Further, the memory 970 may store data indicative
of cardiac signals received by other components of the cardiac
pacemaker/defibrillator 900. The memory 970 may be used, for
example, for storing historical EGM and therapy data. The
historical data storage may include, for example, data obtained
from long-term patient monitoring used for trending and/or other
diagnostic purposes. Historical data, as well as other information,
may be transmitted to an external programmer unit 990 as needed or
desired.
[0065] The control system 920 and memory 970 may cooperate with
other components of the cardiac pacemaker/defibrillator 900 to
control the operations of the cardiac pacemaker/defibrillator 900.
The control system depicted in FIG. 5 incorporates a cardiac
response classification processor 925 for classifying cardiac
responses to pacing stimulation. The cardiac response
classification processor performs the function of discriminating
non-captured intrinsic responses for pacing response classification
in accordance with embodiments of the invention. The control system
920 may include additional functional components including a
pacemaker control circuit 922, an arrhythmia detector 921, along
with other components for controlling the operations of the cardiac
pacemaker/defibrillator 900.
[0066] Telemetry circuitry 960 may be implemented to provide
communications between the cardiac pacemaker/defibrillator 900 and
an external programmer unit 990. In one embodiment, the telemetry
circuitry 960 and the programmer unit 990 communicate using a wire
loop antenna and a radio frequency telemetric link, as is known in
the art, to receive and transmit signals and data between the
programmer unit 990 and the telemetry circuitry 960. In this
manner, programming commands and other information may be
transferred to the control system 920 of the cardiac
pacemaker/defibrillator 900 from the programmer unit 990 during and
after implant. In addition, stored cardiac data pertaining to
capture threshold, capture detection and/or cardiac response
classification, for example, along with other data, may be
transferred to the programmer unit 990 from the cardiac
pacemaker/defibrillator 900.
[0067] The telemetry circuitry 960 may provide for communication
between the cardiac pacemaker/defibrillator 900 and an advanced
patient management (APM) system. The advanced patient management
system allows physicians or other personnel to remotely and
automatically monitor cardiac and/or other patient conditions. In
one example, a cardiac pacemaker/defibrillator, or other device,
may be equipped with various telecommunications and information
technologies that enable real-time data collection, diagnosis, and
treatment of the patient. Various embodiments described herein may
be used in connection with advanced patient management. Methods,
structures, and/or techniques described herein, which may be
adapted to provide for remote patient/device monitoring, diagnosis,
therapy, or other APM related methodologies, may incorporate
features of one or more of the following references: U.S. Pat. Nos.
6,221,011; 6,270,457; 6,277,072; 6,280,380; 6,312,378; 6,336,903;
6,358,203; 6,368,284; 6,398,728; and 6,440,066, which are hereby
incorporated herein by reference.
[0068] In the embodiment of the cardiac pacemaker/defibrillator 900
illustrated in FIG. 5, electrodes RA-tip 856, RA-ring 854, RV-tip
812, RV-ring 811, RV-coil 814, SVC-coil 816, LV distal electrode
813, LV proximal electrode 817, LA distal electrode 818, LA
proximal electrode 815, indifferent electrode 908, and can
electrode 909 are coupled through a switch matrix 910 to sensing
circuits 931-937.
[0069] A right atrial sensing circuit 931 serves to detect and
amplify electrical signals from the right atrium of the heart.
Bipolar sensing in the right atrium may be implemented, for
example, by sensing voltages developed between the RA-tip 856 and
the RA-ring 854. Unipolar sensing may be implemented, for example,
by sensing voltages developed between the RA-tip 856 and the can
electrode 909. Outputs from the right atrial sensing circuit are
coupled to the control system 920.
[0070] A right ventricular sensing circuit 932 serves to detect and
amplify electrical signals from the right ventricle of the heart.
The right ventricular sensing circuit 932 may include, for example,
a right ventricular rate channel 933 and a right ventricular shock
channel 934. Right ventricular cardiac signals sensed through use
of the RV-tip 812 electrode are right ventricular near-field
signals and are denoted RV rate channel signals. A bipolar RV rate
channel signal may be sensed as a voltage developed between the
RV-tip 812 and the RV-ring 811. Alternatively, bipolar sensing in
the right ventricle may be implemented using the RV-tip electrode
812 and the RV-coil 814. Unipolar rate channel sensing in the right
ventricle may be implemented, for example, by sensing voltages
developed between the RV-tip 812 and the can electrode 909.
[0071] Right ventricular cardiac signals sensed through use of the
defibrillation electrodes are far-field signals, also referred to
as RV morphology or RV shock channel signals. More particularly, a
right ventricular shock channel signal may be detected as a voltage
developed between the RV-coil 814 and the SVC-coil 816. A right
ventricular shock channel signal may also be detected as a voltage
developed between the RV-coil 814 and the can electrode 909. In
another configuration the can electrode 909 and the SVC-coil
electrode 816 may be electrically shorted and a RV shock channel
signal may be detected as the voltage developed between the RV-coil
814 and the can electrode 909/SVC-coil 816 combination.
[0072] Outputs from the right ventricular sensing circuit 932 are
coupled to the control system 920. In one embodiment of the
invention, rate channel signals and shock channel signals may be
used to develop morphology templates for analyzing cardiac signals.
In this embodiment, rate channel signals and shock channel signals
may be transferred from the right ventricular sensing circuit 932
to the control system 920 and analyzed for arrhythmia
detection.
[0073] Left atrial cardiac signals may be sensed through the use of
one or more left atrial electrodes 815, 818, which may be
configured as epicardial electrodes. A left atrial sensing circuit
935 serves to detect and amplify electrical signals from the left
atrium of the heart. Bipolar sensing and/or pacing in the left
atrium may be implemented, for example, using the LA distal
electrode 818 and the LA proximal electrode 815. Unipolar sensing
and/or pacing of the left atrium may be accomplished, for example,
using the LA distal electrode 818 to can vector 909 or the LA
proximal electrode 815 to can vector 909.
[0074] A left ventricular sensing circuit 936 serves to detect and
amplify electrical signals from the left ventricle of the heart.
Bipolar sensing in the left ventricle may be implemented, for
example, by sensing voltages developed between the LV distal
electrode 813 and the LV proximal electrode 817. Unipolar sensing
may be implemented, for example, by sensing voltages developed
between the LV distal electrode 813 or the LV proximal electrode
817 and the can electrode 909.
[0075] Optionally, an LV coil electrode (not shown) may be inserted
into the patient's cardiac vasculature, e.g., the coronary sinus,
adjacent the left heart. Signals detected using combinations of the
LV electrodes, 813, 817, LV coil electrode (not shown), and/or can
electrodes 909 may be sensed and amplified by the left ventricular
sensing circuitry 936. The output of the left ventricular sensing
circuit 936 is coupled to the control system 920.
[0076] The outputs of the switching matrix 910 may be operated to
couple selected combinations of electrodes 811, 812, 813, 814, 815,
816, 817, 818, 856, 854 to an evoked response sensing circuit 937.
The evoked response sensing circuit 937 serves to sense and amplify
voltages developed using various combinations of electrodes for
discrimination of various cardiac responses to pacing in accordance
with embodiments of the invention. The cardiac response
classification processor 925 may analyze the output of the evoked
response sensing circuit 937 to implement feature association and
cardiac pacing response classification in accordance with
embodiments of the invention.
[0077] Various combinations of pacing and sensing electrodes may be
utilized in connection with pacing and sensing the cardiac signal
following the pace pulse to classify the cardiac response to the
pacing pulse. For example, in some embodiments, a first electrode
combination is used for pacing a heart chamber and a second
electrode combination is used to sense the cardiac signal following
pacing. In other embodiments, the same electrode combination is
used for pacing and sensing. Use of different electrodes for pacing
and sensing in connection with capture verification is described in
commonly owned U.S. Pat. No. 6,128,535 which is incorporated herein
by reference.
[0078] The pacemaker control circuit 922, in combination with
pacing circuitry for the left atrium, right atrium, left ventricle,
and right ventricle 941, 942, 943, 944, may be implemented to
selectively generate and deliver pacing pulses to the heart using
various electrode combinations. The pacing electrode combinations
may be used to effect bipolar or unipolar pacing pulses to a heart
chamber using one of the pacing vectors as described above. In some
implementations, the cardiac pacemaker/defibrillator 900 may
include a sensor 961 that is used to sense the patient's
hemodynamic need. The pacing output of the cardiac
pacemaker/defibrillator may be adjusted based on the sensor 961
output.
[0079] The electrical signal following the delivery of the pacing
pulses may be sensed through various sensing vectors coupled
through the switch matrix 910 to the evoked response sensing
circuit 937 and used to classify the cardiac response to pacing.
The cardiac response may be classified as one of a captured
response, a non-captured response, a non-captured response with
intrinsic activation, and a fusion/pseudofusion beat, for
example.
[0080] Subcutaneous electrodes may provide additional sensing
vectors useable for cardiac response classification. In one
implementation, cardiac rhythm management system may involve a
hybrid system including an intracardiac device configured to pace
the heart and an extracardiac device, e.g., a subcutaneous
defibrillator, configured to perform functions other than pacing.
The extracardiac device may be employed to detect and classify
cardiac response to pacing based on signals sensed using
subcutaneous electrode arrays. The extracardiac and intracardiac
devices may operate cooperatively with communication between the
devices occurring over a wireless link, for example. Examples of
subcutaneous electrode systems and devices are described in
commonly owned U.S. patent application Ser. No. 10/462,001, filed
Jun. 13, 2003 and Ser. No. 10/465,520, filed Jun. 19, 2003, which
are hereby incorporated herein by reference in their respective
entireties.
[0081] FIG. 7 illustrates a block diagram of circuit 995 that may
be used to sense cardiac signals following the delivery of a pacing
stimulation and classify the cardiac response to the pacing
stimulation according to embodiments of the invention. A switch
matrix 984 is used to couple the cardiac electrodes 971, 972 in
various combinations discussed above to the sensing portion 970 of
the cardiac response classification circuit 995. The sensing
portion 970 includes filtering and blanking circuitry 975, 977,
sense amplifier 985, band pass filter 981, and window generation
and signal characteristic detector 982. The window generation and
signal characteristic detector 982 is coupled to a cardiac response
classification processor 983.
[0082] A control system, e.g., the control system 920 depicted in
FIG. 6, is operatively coupled to components of the cardiac sensing
circuit 995 and controls the operation of the circuit 995,
including the filtering and blanking circuits 975, 977. Following
delivery of the pacing stimulation, the blanking circuitry 975, 977
operates for a sufficient duration and then allows detection of a
cardiac signal responsive to the pacing stimulation. The cardiac
signal is filtered, amplified, and converted from analog to digital
form. The digitized signal is communicated to the cardiac response
classification processor 983, which operates in cooperation with
other components of the control system 920 (FIG. 6) to classify
cardiac responses to pacing according to embodiments of the
invention.
[0083] Various modifications and additions can be made to the
preferred embodiments discussed hereinabove without departing from
the scope of the present invention. Accordingly, the scope of the
present invention should not be limited by the particular
embodiments described above, but should be defined only by the
claims set forth below and equivalents thereof.
* * * * *