U.S. patent application number 12/396267 was filed with the patent office on 2009-06-25 for cardiac signal template generation using waveform clustering.
Invention is credited to Yanting Dong, Scott A. Meyer.
Application Number | 20090163973 12/396267 |
Document ID | / |
Family ID | 36968959 |
Filed Date | 2009-06-25 |
United States Patent
Application |
20090163973 |
Kind Code |
A1 |
Meyer; Scott A. ; et
al. |
June 25, 2009 |
Cardiac Signal Template Generation Using Waveform Clustering
Abstract
Cardiac devices and methods using cardiac waveform clustering
for template generation are described. A method of characterizing a
cardiac response involves delivering pacing pulses to heart, the
pulses having an energy greater than a capture threshold. Cardiac
signals are sensed following the pulses. Cardiac signal
characteristics, waveforms, and/or features are clustered into a
plurality of clusters. A cardiac response template is formed using
one or more of the plurality of clusters.
Inventors: |
Meyer; Scott A.; (Lakeville,
MN) ; Dong; Yanting; (Shoreview, MN) |
Correspondence
Address: |
HOLLINGSWORTH & FUNK, LLC
8009 34TH AVE S., SUITE 125
MINNEAPOLIS
MN
55425
US
|
Family ID: |
36968959 |
Appl. No.: |
12/396267 |
Filed: |
March 2, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11116544 |
Apr 28, 2005 |
7499751 |
|
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12396267 |
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Current U.S.
Class: |
607/17 |
Current CPC
Class: |
A61B 5/35 20210101; A61N
1/371 20130101 |
Class at
Publication: |
607/17 |
International
Class: |
A61N 1/362 20060101
A61N001/362 |
Claims
1. A method of operating an implantable device to characterize a
cardiac response to pacing, comprising: delivering pacing pulses to
a heart sufficient in energy to effect capture; sensing cardiac
signals respectively following delivery of the pacing pulses;
extracting one more features from the cardiac signals; clustering
the features to define a plurality of clusters; identifying one or
more predominant clusters of the plurality of clusters and one or
more less predominant clusters of the plurality of clusters; and
forming a captured response template using the predominant
clusters.
2. The method of claim 1, wherein the one or more features
comprises one or more cardiac signal peaks.
3. The method of claim 1, wherein clustering the one or more
features of the cardiac signals comprises clustering the one or
more features in batch mode.
4. The method of claim 1, wherein clustering the one or more
features of the cardiac signals comprises clustering the one or
more features beat-by-beat.
5. The method of claim 1, wherein clustering the features comprises
clustering each feature of a cardiac signal independently from
clustering other features of the cardiac signal.
6. The method of claim 1, wherein forming the captured response
template comprises forming one or more detection windows of the
captured response template, each detection window having maximum
and minimum time limits and maximum and minimum amplitude
limits.
7. The method of claim 1, further comprising forming a fusion
template using the one or more less predominant clusters.
8. The method of claim 1, further comprising forming an intrinsic
activation template using the one or more less predominant
clusters.
9. The method of claim 1, further comprising forming a noise
template using the one or more less predominant clusters.
10. The method of claim 1, wherein at least one of the predominant
clusters used to form the captured response template includes
features extracted from cardiac signals of fusion beats.
11. The method of claim 1, wherein clustering the features
comprises clustering the features using one or both of K-means
clustering and a self-organizing map algorithm.
12. The method of claim 1, further comprising storing additional
information related to one or more of pacing energy, pacing rate,
and pacing interval with the captured response template.
13. The method of claim 1, wherein: forming the captured response
template comprises determining detection windows based on the
cardiac feature clusters; and further comprising adapting the
detection windows to accommodate changes in a patient's cardiac
waveform morphology.
14. The method of claim 13, wherein adapting the detection windows
comprises adapting the detection windows using features of a
cardiac signal associated with a captured response.
15. The method of claim 13, wherein adapting the detection windows
comprises changing at least maximum amplitude of a detection
window.
16. A method of operating an implantable device to determine a
template used to characterize a cardiac response to pacing,
comprising: delivering pacing pulses to a heart sufficient in
energy to effect capture; sensing cardiac signals respectively
following delivery of the pacing pulses; extracting peak values
from the cardiac signals; clustering the peak values to define a
plurality of clusters; identifying one or more predominant clusters
of the plurality of clusters and one or more less predominant
clusters of the plurality of clusters; and forming a captured
response template using the predominant clusters.
17. The method of claim 16, wherein: extracting the peak values
comprises extracting positive peak values and negative peak values;
clustering the peak values to define a plurality of clusters
comprises: clustering the positive peak values to define a
plurality of positive peak clusters; and clustering the negative
peak values to define a plurality of negative peak clusters;
identifying the one or more predominant clusters comprises:
identifying one or more predominant positive peak clusters; and
identifying one or more predominant negative peak clusters; and
forming the captured response template comprises forming the
captured response template using the one or more predominant
positive peak clusters and the one or more predominant negative
peak clusters.
18. The method of claim 17, wherein forming the captured response
template comprises: forming a positive peak detection window using
the positive peak clusters; and forming a negative peak detection
window using the negative peak clusters.
19. The method of claim 18, wherein the positive peak detection
window has a first shape and the negative peak detection window has
a second shape, different from the first shape.
20. The method of claim 16, further comprising forming one or more
of a fusion template, an intrinsic activation template, and a noise
template using the one or more less predominant clusters.
Description
RELATED PATENT DOCUMENTS
[0001] This is a divisional of U.S. patent application Ser. No.
11/116,544, filed on Apr. 28, 2005, to issue as U.S. Pat. No.
7,499,751 on Mar. 3, 2009, to which Applicant claims priority under
35 U.S.C. .sctn.120, and which is incorporated herein by
reference.
FIELD OF THE INVENTION
[0002] The present invention relates generally to implantable
medical devices and, more particularly, to cardiac devices and
methods using cardiac waveform clustering for template
generation.
BACKGROUND OF THE INVENTION
[0003] 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 comprise 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.
[0004] 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.
[0005] 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.
[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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.
[0010] Capture detection, for example, involves discriminating
captured beats from fusion/pseudofusion beats, intrinsic beats,
noise, and noncapture. Discriminating between various cardiac
responses can be accomplished by comparing cardiac signals to
templates representative of various response types. The present
invention involves methods and systems for creating templates used
in connection with recognizing various cardiac responses.
SUMMARY OF THE INVENTION
[0011] The present invention involves various cardiac devices and
methods using cardiac waveform clustering for template generation.
A method of characterizing a cardiac response in accordance with
the present invention involves delivering pacing pulses to heart,
the pacing pulses having an energy greater than a capture
threshold. Cardiac signals are sensed following the pacing pulses.
One or more initial templates may be selectively updated using the
sensed cardiac signals. A cardiac response template may be formed
using one or more selected templates. Selectively updating the
initial templates may involve using selected ones of the sensed
cardiac signals to update a particular template. Embodiments may
further involve selectively updating the templates by comparing the
sensed cardiac signals to each of the templates, and selectively
updating the templates using the cardiac signals based on the
comparison, such as by comparing cardiac signal features to
template features and/or by determining a similarity between each
template and each cardiac signal and selectively updating a
particular template having a particular similarity to a particular
cardiac signal.
[0012] Selectively updating the templates may involve associating a
counter with each template and incrementing the counter associated
with a particular template if the particular template is updated.
Characterizing the cardiac response using the selected template may
involve characterizing the cardiac response using a particular
template correlated to a higher number of cardiac signals than
other templates. The selected template may be used to classify a
cardiac response to pacing beat by beat, during capture threshold
testing, and/or for automatic capture verification.
[0013] Other methods of characterizing a cardiac response to pacing
in accordance with the present invention involve delivering pacing
pulses to a heart sufficient in energy to effect capture and
sensing cardiac signals respectively following delivery of the
pacing pulses. The cardiac signals are clustered, defining a
plurality of clusters, so that cardiac response templates may be
formed using a selected one or more of the plurality of clusters.
One or more features of the cardiac signals may be used to define
the plurality of clusters, such as peak times of the cardiac
signals, peak times associated with negative polarity peaks and/or
positive polarity peaks, peak-amplitudes of the cardiac signals, or
other features or signal attributes. A cardiac response template
may be formed using selected clusters by forming the cardiac
response template using a cluster associated with a greatest number
of cardiac signals having similar characteristics.
[0014] Further embodiments of the present invention are directed to
devices for characterizing a cardiac response to pacing. The device
may include a sensing system configured to sense cardiac signals
following pacing pulses delivered to a heart, having a processor
coupled to the sensing system. The processor may be configured to
selectively update a plurality of templates using the cardiac
signals, and to characterize the cardiac response to pacing using a
selected template of the templates. The processor may further be
configured to provide one or more initial templates and selectively
update the initial templates. The processor may be configured to
compare the cardiac signals from a paced response to each of the
templates and to selectively update the templates using the cardiac
signals based on the comparison.
[0015] Other embodiments provide for the processor to be configured
to determine a similarity between each template and each cardiac
signal, and to update a particular template having a particular
similarity to a particular cardiac signal. The processor may be
configured to characterize the cardiac response using a template
selected by a criterion, such as by matching a predetermined number
cardiac signals before other templates are matched to the
predetermined number of cardiac signals.
[0016] Yet another embodiment involves system for characterizing a
cardiac response to pacing. The system includes a pulse generator
configured to deliver pacing pulses to a heart sufficient in energy
to effect capture. A sensor system is configured to sense cardiac
signals respectively following delivery of the pacing pulses. A
processor is coupled to the sensor system and is configured to
cluster the cardiac signals to define a plurality of clusters and
to form a cardiac response template using a selected one or more of
the plurality of clusters.
[0017] 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
[0018] FIGS. 1A and 1B are flowcharts illustrating methods using
cardiac waveform clustering for template generation in accordance
with embodiments of the invention;
[0019] FIG. 2A is a concept diagram illustrating the use of
clustering for template creation in accordance with embodiments of
the invention;
[0020] FIG. 2B is a flowchart of a method of using cardiac waveform
clustering for template generation in accordance with embodiments
of the invention;
[0021] FIGS. 2C and 2D are flowcharts illustrating methods of
generating templates in accordance with embodiments of the
invention;
[0022] FIG. 3 is a graph illustrating a number of cardiac signals
representing captured responses, fusion responses, and an intrinsic
response that may be utilized for cardiac response template
generation in accordance with embodiments of the invention;
[0023] FIG. 4 is a graph that depicts the peaks of the captured
signals, the fusion beats, and the intrinsic response illustrated
in FIG. 3;
[0024] FIG. 5 illustrates cardiac response detection windows that
may be used to form templates in accordance with embodiments of the
invention;
[0025] FIGS. 6 and 7 illustrate how detection windows formed by
clustering can be used to detect various types of cardiac responses
to pacing in accordance with embodiments of the invention;
[0026] FIGS. 8A-8D illustrate adjustment of a detection window to
accommodate for changes in cardiac signal morphology in accordance
with embodiments of the invention;
[0027] FIG. 9 illustrates a cardiac rhythm management device that
may be used to implement template generation in accordance with
embodiments of the present invention; and
[0028] FIG. 10 illustrates a block diagram of a cardiac rhythm
management (CRM) device suitable for implementing template
formation and adaptation in accordance with embodiments of the
present invention.
[0029] 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 EMBODIMENTS
[0030] 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.
[0031] Recognition of various cardiac conditions may rely on the
consistent morphology of the type of cardiac signal associated with
that condition. For example, morphology templates may be formed
based on samples and/or characteristic features of a cardiac signal
associated with a particular cardiac condition. A cardiac device
may later compare a sensed cardiac signal to a morphology template
and determine that the cardiac condition associated with the
morphology template exists if the sensed cardiac signal is
sufficiently similar to the morphology template. Similarly, if the
sensed cardiac signal is sufficiently different from the morphology
template, a condition exclusive of the cardiac condition associated
with the morphology template can be determined.
[0032] Determination of the cardiac response to a pacing pulse
applied to a heart chamber may be based on morphological features
of the cardiac signal sensed in the heart chamber after pacing. The
cardiac response to a pacing pulse may include noncapture without
intrinsic activity, capture, fusion, pseudofusion, and noncapture
with intrinsic activity, for example. Morphology templates can be
used to represent one or more of these types of cardiac pacing
responses. Cardiac signals sensed after pacing may be compared to
one or more morphology templates. In one implementation, samples
and/or characteristic features of a cardiac signal are extracted
from the cardiac signal and are compared to samples and/or features
associated with one or more of morphology templates characterizing
a particular type of cardiac pacing response. The type of cardiac
pacing response may be determined based on the similarity of the
samples and/or characteristic features of the sensed cardiac signal
to one of the morphology templates.
[0033] Cardiac response classification may be implemented by a
pacemaker, defibrillator, or other cardiac rhythm management (CRM)
device to determine the cardiac response to an applied electrical
pacing stimulus. Embodiments of the invention are directed to
cardiac devices and methods using clustering of the cardiac signals
or signal features to generate templates characterizing various
types of cardiac responses to pacing.
[0034] Several functions of CRM devices may rely on the consistency
of cardiac beats to detect certain conditions. For example, cardiac
pacing response characterization algorithms may rely on templates
of the heart's response as the basis for determining whether a
pacing pulse produces a captured response or other response.
However, the morphology of the captured response signal may vary
across patients, and change over time. Therefore, templates
characterizing the captured response (or other types of cardiac
signals) may need to be regularly generated or updated for every
patient.
[0035] A flowchart illustrating a method of forming templates in
accordance with embodiments of the invention is illustrated in FIG.
1A. A plurality of pacing pulses is delivered 112 to the heart. The
cardiac signals associated with the pacing pulses are sensed 114.
Clusters of similar cardiac signals are formed 116. The clusters
may be used to generate 120 templates characterizing one or more
types of cardiac pacing responses. Clustering the cardiac signals
may be performed using a variety of techniques, including analog
and/or digital processing techniques. Several exemplary embodiments
directed to clustering processes are described herein, however,
other processes may additionally or alternatively used and are
considered to be within the scope of the present invention.
[0036] FIG. 1B illustrates another method of forming a template in
accordance with embodiments of the invention. A plurality of pacing
pulses are delivered 130 to the heart and cardiac signals are
sensed 140 following each pacing pulse. Features of the cardiac
signals are extracted 150. The cardiac signal features are used to
form 160 a plurality of clusters. A cardiac pacing response is
characterized 170 using one or more of the plurality of
clusters.
[0037] Consider generating a template for a captured response as an
example. One goal is to generate the template for a captured
response, and at the same time, avoid the influence of
fusion/pseudofusion beats, noise or other types of responses.
Including fusion beats in the response template generation adds an
error component to the template. Templates that include information
from responses other than the desired response may result in less
than optimal template correlation to future captured beats, and
contribute to impaired discrimination capability.
[0038] Template generating in accordance with the present invention
reduces the inclusion of undesired response signals. Reducing
undesired signals from inclusion to a particular template may be
accomplished by recognizing that captured responses have consistent
morphology. Clustering signal features according to similarities
provides a signal exclusion criterion for template generation.
Clustering may be performed using techniques such as a K-Means
clustering algorithm, self-organizing map algorithms, or other data
clustering algorithms.
[0039] Continuing with the example of generating a captured
response template, suppose that a sequence of N supra-threshold
paces are delivered, N being a positive integer. A clustering
algorithm, which may be applied after all N paces are delivered, or
applied during response signal collection, may be applied to the
extracted features of the pace response signals in accordance with
the present invention. After N paces are delivered, a template may
be generated using only the response signals with features within a
cluster, and exclude all other signals from the template
generation. Applied during response signal collection, a template
may be generated using only the response signals with features
within a cluster, thereby building confidence in the cluster,
adjusting the template with each select response signal, and
excluding all other signals from the template generation. Multiple
templates may be created concurrently by creating a template for
each cluster, or selected clusters.
[0040] For example, responses to all N paces may be recorded, and
processed through a clustering algorithm that separates the signals
into three clusters, captured response, fusion response, and other
response. If all the pace pulses are known a-priori to be above the
capture threshold and the pacing parameters are chosen to promote
capture, then it would be expected that the number of captured
responses would be predominant, followed by the number of
fusion/pseudofusion beats, and possibly include some other
responses such as noise or unknown responses. A capture template
may be generated using the signals in the predominant cluster. For
example, the cluster with the largest number of similar pace
responses may be selected as the cluster used to generate the
captured response template.
[0041] Other criteria may also be imposed, such as a cluster is
only used if a predetermined number of signals are associated with
the cluster, such as a number P, where P is a positive integer less
than N, using the above example. Cardiac waveform clustering for
template generation in accordance with the present invention
provides an accurate template of heart response, and reduces the
influence of undesirable beats on the estimate of the template.
[0042] The use of clustering for template creation is illustrated
by the concept diagram of FIG. 2A. In FIG. 2A, the measured cardiac
signals responsive to thirteen successive paces are illustrated as
circles 201-213. Each circle 201-213 may correspond to a feature of
the cardiac signals responsive to the thirteen paces, a sequence of
features points, or the entire cardiac waveform. The circle 201 may
correspond to a feature, feature points or waveform of a first
paced response, the second circle 202 may correspond to a feature,
feature points or waveform of a second paced response. In some
embodiments, the pacing and response measurement process continues
until the circle 213 is measured, corresponding to a feature,
feature points or waveform of the thirteenth paced response. In
other embodiments, clustering may be performed after each
measurement in a beat by beat manner.
[0043] Responses 201, 202, 204, 205, 209, 210, 212, and 213 are
grouped into a cluster 220 based on the similarity of responses
201, 202, 204, 205, 209, 210, 212, and 213. Responses 203, 206, and
211 are grouped into a cluster 230. Responses 207 and 208 are
grouped into a cluster 240. The responses 201, 202, 204, 205, 209,
210, 212, and 213 of cluster 220 may be determined to include
captured responses, the responses 203, 206, and 211 of cluster 230
may be determined to represent fusion/pseudofusion beats, and the
responses 207 and 208 of cluster 240 may be noisy signals or
unknown cardiac responses.
[0044] The similarity of responses in a cluster may be determined
based on one or more morphological features of the cardiac signal.
In one implementation, the system may determine the similarity of
one or more of a peak width, peak amplitude and peak timing. In
another implementation, a sequence of samples from one cardiac
signal may be compared to a corresponding sequence of samples from
another cardiac signal to determine if the signals are similar.
[0045] Clustering the cardiac waveform features, sequence of
feature points or cardiac waveforms involves grouping the features,
sequence of feature points or cardiac waveforms that are
similar.
[0046] According to one implementation, the process of using
clustering to form a template may involve determining corresponding
cardiac signal features of a number of cardiac signals associated
with a particular type of cardiac pacing response and clustering
the cardiac signal features to form a template. The clustering may
be performed by determining the relationships between the cardiac
signal feature points and forming clusters of the feature points
based on the relationships. Clustering in this manner may be
performed using a variety of clustering algorithms, including
K-means algorithms, self-organizing map algorithms, or other data
clustering algorithms.
[0047] According to another implementation, clustering may be
performed by forming an initial template, for example, using one or
more feature points of a first detected cardiac signal and
clustering additional feature points of additional cardiac signals
with the initial feature point based on a set of rules. For
example, an additional feature point may be clustered with a
feature point of the initial template if it is sufficiently similar
to the corresponding feature point of the initial template.
Similarity in this implementation may be determined by an
externally determined set of rules that are not necessarily based
on the relationships between feature points.
[0048] FIG. 2B is a flowchart of a method 170 of using cardiac
waveform clustering for template generation in accordance with
embodiments of the invention. Two or more pacing pulses 172 are
delivered to a patient's heart, at a level that exceeds the capture
threshold. Cardiac response signals 174 are sensed, and
measurements are made of cardiac signal features. One or more
initial templates are provided. The one or more initial templates
may be generated using one or more cardiac signals, may be
estimated, retrieved from memory, formed according to a rules-based
process, or formed by other methods. One or more of the initial
templates 176 are incrementally adjusted using select cardiac
response signals. Each sensed cardiac signal may be used to adjust
176 a particular template of the one or more templates. Adjustment
of the templates may be implemented using a clustering algorithm
and may be based on the measurements of the cardiac signal
features. One or more of the templates 178 may be selected for
characterizing cardiac responses. In one example, one of the
templates may be selected to characterize a captured response. In
another example, a first template formed via the clustering process
may be used to characterize a captured response and a second
template may be used to characterize a fusion/pseudofusion
response.
[0049] FIG. 2C is a flowchart of a method 139 of generating
templates in accordance with embodiments of the present invention.
An integer number NT of pacing cycles are selected to begin 140 the
template generation process using a NT pacing cycle loop 140-162. A
pace 142 is delivered to the heart, and the cardiac signal
associated with the pacing pulse is sensed. Features or samples of
the cardiac signal associated with the pacing pulse are acquired.
If no template has been created or otherwise provided, then the
cardiac signal is used to generate a template. The initial template
156 is saved, and the pacing cycle continues after incrementing the
NT count at pacing cycle loop end 162. Information related to the
cardiac signal may also be stored and associated with the template,
such as the pacing energy (voltage and/or pulse width) of the
pacing pulse, pace rate, AV delay, VV interval and/or any other
pacing parameter settings or measurements. If a template has
already been formed or provided, then the process continues to the
loop represented by blocks 146-152. In loop 146-152, the cardiac
signal is compared to any existing templates at a check 148. If the
check 148 finds that the cardiac signal matches an existing
template, the template is adjusted 150 to improve the estimate of
the template, and the loop 146-152 continues. Adjusting the
template may be accomplished, for example, by averaging feature
values or performing a weighted average of feature values.
Characteristics represented by the stored information that is
related to the cardiac signal and associated with the template,
such as pacing parameter settings or measurements, may also be
adjusted.
[0050] If no template matches at check 148 after all existing
templates have been compared to the cardiac signal, a decision 158
is made to add or replace a template 160. A new template may be
created, either by adding or estimating a new template, or
replacing an old template. In various implementations, the replaced
template may comprise the oldest template or the template with the
least number of matched beats. If all templates have at least a
minimum number of matched beats, e.g., about one beat, then the
cardiac cycle may be ignored with no template replaced. The maximum
number of templates used by method 139 may be limited to a
predetermined number.
[0051] In one implementation, the NT pacing cycle loop 140-162
continues until all NT paces are completed or when some other
criteria are satisfied. For example, the NT pacing cycle loop may
terminate successfully (with a template recommendation) if a
template has been matched to more than NT-M beats, where M
represents the number of allowed mismatched beats. In another
embodiment, the pacing cycle loop 140-162 may terminate
unsuccessfully (without a template recommendation) if the maximum
number of template matches is below a predetermined number after a
certain number of pacing cycles. More specifically, the pacing
cycle loop 140-162 may terminate unsuccessfully if the maximum
number of template matches is below about one after about three
pacing cycles.
[0052] After all NT paces are completed in the NT pacing cycle loop
140-162, a decision 164 is made to determine if one or more of the
templates meets criteria for saving as templates representative of
particular types of cardiac pacing responses. For example, if a
template is desired to characterize a captured response, a
criterion may comprise: out of NT paced beats of the NT pacing
cycle loop 140-152, if a template has been updated (NT-M) times,
where M represents the designated number of mismatched beats that
form a failed attempt at template generation, then the template is
accepted as an captured response template, and the captured
response template generation is successful 166. Using this
criterion, if a template has not been updated (NT-M) times, then
the template is not accepted as a captured response template, and
the template generation is not successful 154. Additional criteria
may be applied to terminate template generation early. If at check
148, a designated M mismatches are realized before NT pacing cycles
complete, or the first cycle after the initial saved template, 156,
does not match, then a failed attempt at template generation
results.
[0053] Each pacing cycle loop 140-162 represents an attempt to
generate a template. After a predetermined number of pacing cycle
loops 140-162 are performed, attempts to generate the template may
be suspended for a period of time or abandoned.
[0054] FIG. 2D is a flowchart illustrating a method for generating
a template during threshold testing according to embodiments of the
invention. After beginning 251 the template generation process, a
check is performed 252 to see if a maximum number of attempts to
generate the template have been tried. If so, the process exits 253
and a threshold test may be rescheduled for a later time.
[0055] If the maximum number of attempts have not been attempted
252, then a loop 254-265 of NT pacing cycles is initiated 254. A
pacing pulse 255 is delivered and the cardiac signal following the
pacing pulse is sensed. Features are extracted from the sensed
cardiac signal. If it is the first cycle 256 in the loop 254-265 of
NT pacing cycles, then the extracted features are saved 257 as an
initial template. If it is not the first cycle 256 in the loop
254-265 of NT pacing cycles, then a check is performed 258 to
determine if the features of the sensed cardiac signal for the
cycle are similar to the stored template features. If the features
of the sensed cardiac signal are 258 sufficiently similar to the
stored template features, then the template features are updated
259 using the features of the sensed cardiac signal.
[0056] If the cardiac signal features of NT-M cycles are similar to
263 the template features, then the template generation is
successful 264.
[0057] If the cardiac signal features of the cardiac cycle are not
similar 258 to the template features, then a check is performed 260
based on the number of cardiac cycles following formation of the
initial template. If the cardiac signal features of a predetermined
number of cycles following formation of the initial template are
not 260 similar to the template, or if there have been M cardiac
signal that are not 262 similar to the template then the template
generation attempt is terminated 261 unsuccessfully.
[0058] The graphs of FIGS. 3 through 5 illustrate the process of
forming templates according to the methods of the present
invention. FIG. 3 is a graph illustrating a number of cardiac
signals representing captured responses, identified by the letter
C, fusion responses, identified by the letter F, and a
non-captured, intrinsic response, identified by the letters NC.
Features of these responses may be clustered to form templates
representative of each the different types of responses, or
templates representative of some of the responses and exclusive of
others; in either case, allowing discrimination of the various
responses. In this example, the particular features that are
clustered include peak amplitudes and peak timings of the cardiac
signals. The clustered peaks are used to form templates comprising
one or more classification windows defined in terms of amplitude
and time.
[0059] FIG. 4 is a graph that depicts the peaks of the captured,
fusion, and non-captured intrinsic responses illustrated in FIG. 3.
The peaks of the captured signals are designated with the letter c,
the peaks of the fusion beats are designated with the letter f, and
the intrinsic response is designated with the letter i. The peaks
of the cardiac signals are clustered to form templates comprising
one or more detection windows 430, 460, 470. Inclusion or exclusion
of peaks from a detection window, or combinations of the detection
windows 430, 460, 470 can be used to discriminate between the
different cardiac responses.
[0060] FIG. 5 illustrates a first capture detection window 550, a
second capture detection window 540 and an intrinsic detection
window 560. In this example, midpoints 515, 525, 535 of the
detection windows 550, 540, 560 are illustrated. The boundaries of
the detection windows 550, 540, 560 may be calculated, for example,
based on coordinates of characteristic features of the clustered
cardiac signals.
[0061] In one implementation, an average of the characteristic
feature coordinates may be defined as a point, such as a center, or
other location, within a detection window. In this example, the
boundaries of a detection window may be established according to a
predetermined shape, for example, a circle, square, rectangle,
rhombus, or other quadrilateral. Additionally or alternatively, a
detection window may be created to enclose a predetermined area.
After initialization of the detection windows 550, 540, 560, the
detection windows may be used to detect a captured response,
fusion/pseudofusion response and/or noncapture with intrinsic
activation.
[0062] FIGS. 6 and 7 illustrate how detection windows formed by
clustering can be used to detect various types of cardiac responses
to pacing. A cardiac signal of a heart chamber sensed in one or
multiple time intervals following a pacing pulse to the heart
chamber may be used for determination of the cardiac pacing
response in accordance with embodiments of the invention. As
illustrated in FIG. 6, a pacing stimulation 610 is delivered to the
heart, for example, to the right ventricle. The sensed cardiac
signal is blanked for a period of time 620, typically about 0
milliseconds to about 40 milliseconds, following the delivery of
the pacing pulse 610.
[0063] After the blanking period 620, the cardiac signal may be
sensed in a first time interval 630. The duration of the first time
interval 630 may be a programmable duration, for example, less than
about 325 milliseconds. If the cardiac signal does not exceed a
threshold in the first time interval 630, then the cardiac response
may be classified as noncapture. If the cardiac signal exceeds a
threshold value, then various characteristics or features of the
cardiac signal may be extracted and compared to cardiac response
templates for determining the type of cardiac pacing response. In
some cases, sensing of the cardiac signal, associated feature
extraction and template comparison may be extended to additional
time intervals, such as the second time interval 640. The second
time interval 640 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. Alternatively, the durations of the first and the
second time intervals may be the same.
[0064] A delay period 650 may be established between the end of one
time interval 230 and the beginning of another time interval 640.
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 610 may be classified based on
the characteristics or features of the cardiac signal sensed in the
first and/or the additional time intervals 630, 640, regarding
their comparison to cardiac response templates.
[0065] FIG. 7 is a graph illustrating how templates formed using
cardiac response detection windows, such as those illustrated in
FIG. 5, may be used for capture detection. FIG. 7 illustrates
includes superimposed graphs illustrating a captured response
signal 784, a fusion response signal 782, and a non-captured
intrinsic signal 780. Following delivery of a pace 710, the sensing
channel is blanked, e.g., the sense electrodes are disconnected
from sense amplifiers or the sense amplifiers are rendered
inoperative, during a blanking period 715. Following the blanking
period, the cardiac signal is sensed in one or more time intervals
720, 750. As illustrated in FIG. 6, sensing may occur in two time
intervals following the pacing pulse. In some scenarios, the second
750 and subsequent time intervals (not shown) may be triggered by
events occurring in one or more previous intervals.
[0066] 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. 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.
[0067] During the first time interval 720, the system senses for a
positive or negative cardiac signal magnitude exceeding a threshold
level 740. If the cardiac signal magnitude does not exceed the
threshold 740 during the first time interval 720, then the cardiac
response is classified as noncapture and a backup pace 770 may be
delivered. The backup pace 770 is typically a high energy pace that
is delivered following a backup interval (BPI) 730. For example,
the backup interval 730 may comprise an interval of about 100 ms
timed from the delivery of the primary pace 710.
[0068] The system may utilize one or more cardiac response
classification windows 755, 756, 760 for detecting various cardiac
pacing responses. The template creation methods in accordance with
embodiments of the invention may be used to form one or more of the
classification windows 755, 756, 760. The cardiac response
classification windows 755, 756, 760 are areas defined in terms of
amplitude and time.
[0069] The system may classify a cardiac response as capture if a
first peak value of the cardiac signal is detected in the first
detection window 755 and a second peak value of the cardiac signal
is detected in the second detection window 756. If a cardiac signal
peak is detected in the intrinsic detection window 760, but not in
the first or second capture detection windows 755, 756, the cardiac
response may be classified as noncapture with early intrinsic
activation. Otherwise, the cardiac response may be classified as a
fusion/pseudofusion beat.
[0070] A template characterizing a particular type of cardiac
pacing response may be adapted to accommodate gradual morphological
changes in the cardiac pacing response. A cardiac signal waveform,
e.g., a cardiac signal waveform representative of a captured
response, may exhibit natural variations in its morphology over
time. Unless the template is adjusted, the cardiac waveform
morphology may gradually drift away from the originally established
template.
[0071] In accordance with embodiments of the invention, one or more
of the detection windows may be adjusted to accommodate changes in
cardiac waveform morphology. A particular detection window may be
adjusted according to a relationship, e.g., a spatial relationship,
between the particular detection window and its associated waveform
feature, for example a peak of the cardiac signal. Adjustment of
the detection windows may involve, for example changing the size,
shape, or location of the detection window.
[0072] A cardiac feature location, such as a peak, may be
identified by a timing coordinate (usually represented as an x-axis
coordinate) and an amplitude coordinate (y-axis coordinate). A
detection window may be adjusted based on a relationship between a
detected feature's amplitude coordinate and the associated
detection window's amplitude range. A detection window may also be
adjusted based on a relationship between an associated detected
feature's timing coordinate and the detection window's timing
range. In other examples, the detection window may be adjusted
based on a variability of an associated detected feature's timing
and/or amplitude coordinates.
[0073] According to embodiments of the invention, the adjustment of
a detection window involves modifying the detection window in the
direction of an associated cardiac feature location. In various
examples, a detected cardiac feature may fall within a particular
detection window, but be offset from the center of the detection
window. The location, size, and/or shape of the detection window
may be modified in the direction of re-centering or otherwise
re-orienting the detection window with respect to an associated
detected cardiac feature point falling within the detection window.
The detection window may be adjusted, for example, using a
function-based or rules-based technique.
[0074] According to one implementation, adjustment of the detection
windows may be accomplished using a function that is based on
present and past locations of an associated detected cardiac
waveform feature, e.g., a peak. According to one example, the
detection windows may be adjusted using an exponential average
based on the present location of the waveform feature and the
previous locations of the detection window. Adjustment of the
detection window may be implemented based on Equation 1 below.
Adjusted Location=.alpha.*past location of the waveform
feature+(1-.alpha.)*present location of the waveform feature
[1]
[0075] By selecting the values of .alpha., more emphasis may be
placed on the past location of the detection window, corresponding
to .alpha.>0.5, or more emphasis may be placed on the present
location of the waveform feature, corresponding to .alpha.<0.5.
The value of .alpha. may vary for different features or
characteristics. The location of the detection window may be
determined by re-centering or otherwise re-orienting the detection
window using the adjusted location.
[0076] In other implementations, a detection window may be adjusted
using a rules-based technique. For example, the detection window
may be adjusted in the direction of a detected associated feature
point based on one or more re-centering rules.
[0077] A cardiac beat may be required to meet certain
qualifications before it is used to adjust the detection windows. A
cardiac beat qualified to adjust a detection window may be required
to meet certain timing, rate, amplitude, regularity, or other
criteria. The cardiac beat may be compared, for example, to a
template representing a captured response. If the cardiac beat is
consistent with the template, then the cardiac beat may be used to
adjust one or more of the capture detection windows.
[0078] Adjustment of a detection window is illustrated in the
diagrams of FIGS. 8A-B. FIG. 8A illustrates a detection window 820
having a center 810 based on locations of the previously detected
cardiac waveform features associated with the detection window.
FIG. 8B illustrates the situation after the next cardiac signal is
sensed. The current cardiac waveform feature point 830 is detected.
The location of the current feature point 830 has drifted above and
to the right of the original center 810 illustrated in FIG. 8A. A
current detection window 840 centered on the new cardiac waveform
feature 830 would represent a significant change from the original
detection window 820. In one example embodiment, adjustment of the
detection window is performed so that modifications exhibit a
relatively smooth transition. The adjusted detection window 850 may
be determined, for example using Equation 1 or other method, to
smoothly accommodate the waveform feature drift based on both the
past detection window location 820 and the current detection window
location 840. The adjustment of the detection window may be limited
to predetermined upper and lower boundaries with respect to the
amplitude and time coordinates.
[0079] Although Equation 1 mathematically describes adjusting the
detection window location using an exponential average, other
methods of adjusting the detection window locations are also
possible. For example, in other embodiments, each of the one or
more detection windows may be adjusted according to a moving window
average, or another function representing the change in distance
between the original detection window and the waveform feature. In
a further embodiment, the detection windows may be adjusted
according to a rules-based process. A rules-based adjustment
process may involve adjusting the detection window location by an
amount based on the locations of subsequently detected cardiac
waveform features. For example, the detection window location may
be moved an incremental amount to the right if a predetermined
number, e.g., five, consecutive cardiac signals exhibit cardiac
waveform features located within the detection window, but to the
right of center of the original detection window. Adjustments in
other directions, i.e., left, up, and down, may be made using
similar criteria.
[0080] In yet other embodiments, adjustment of a detection window
may include adjusting the shape and/or size of the detection
window. FIGS. 8C-D are diagrams illustrating adjusting a detection
window by modifying the shape of the detection window. FIG. 8C
illustrates a detection window 820 having a center 810. FIG. 8D
illustrates the situation after the next cardiac signal is sensed.
The cardiac waveform feature 860 associated with the detection
window 820 is detected. The location of the current feature point
860 has drifted above the original center 810 of the detection
window 820. An adjusted detection window 870, having a different
shape from the original detection window 820, is defined. The
adjustment of the detection window may be limited to a
predetermined limit. Methods and systems for updating detection
windows, aspects of which may be used in connection with the
present invention, are described in commonly owned U.S. patent
application identified by Attorney Docket No. GUID.169PA, filed
concurrently with this patent application, and incorporated herein
by reference.
[0081] The embodiments of the present system illustrated herein are
generally described as being implemented in an implantable cardiac
defibrillator (ICD) 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 using cardiac
waveform clustering for template generation in accordance with the
present invention. The methods of the present invention may also be
implemented 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.
[0082] 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.
[0083] Referring now to FIG. 9 of the drawings, there is shown a
cardiac rhythm management system that may be used to implement
template generation methods of the present invention. The cardiac
rhythm management system in FIG. 9 includes an cardiac rhythm
management (CRM) device 900 electrically and physically coupled to
a lead system 902. The housing and/or header of the CRM device 900
may incorporate one or more electrodes 909 used to provide
electrical stimulation energy to the heart and to sense cardiac
electrical activity. The CRM device 900 may utilize all or a
portion of the CRM device housing as a can electrode 909. The CRM
device 900 may also include indifferent electrodes (not shown)
positioned, for example, on the header or the housing of the CRM
device 900. If the CRM device 900 includes both a can electrode 909
and indifferent electrodes, the electrodes typically are
electrically isolated from each other.
[0084] The lead system 902 is used to detect electric cardiac
signals produced by the heart 901 and to provide electrical energy
to the heart 901 under certain predetermined conditions to treat
cardiac arrhythmias. The lead system 902 may include one or more
electrodes used for pacing, sensing, and/or defibrillation. In the
embodiment shown in FIG. 9, the lead system 902 includes an
intracardiac right ventricular (RV) lead system 904, an
intracardiac right atrial (RA) lead system 905, an intracardiac
left ventricular (LV) lead system 906, and an extracardiac left
atrial (LA) lead system 908. The lead system 902 of FIG. 9
illustrates one embodiment that may be used in connection with the
template creation and cardiac response discrimination methodologies
described herein. Other leads and/or electrodes may additionally or
alternatively be used.
[0085] The lead system 902 may include intracardiac leads 904, 905,
906 implanted in a human body with portions of the intracardiac
leads 904, 905, 906 inserted into a heart 901. The intracardiac
leads 904, 905, 906 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.
[0086] As illustrated in FIG. 9, the lead system 902 may include
one or more extracardiac leads 908 having electrodes, e.g.,
epicardial electrodes, positioned at locations outside the heart
for sensing and pacing one or more heart chambers.
[0087] The right ventricular lead system 904 illustrated in FIG. 9
includes an SVC-coil 916, an RV-coil 914, an RV-ring electrode 911,
and an RV-tip electrode 912. The right ventricular lead system 904
extends through the right atrium 920 and into the right ventricle
919. In particular, the RV-tip electrode 912, RV-ring electrode
911, and RV-coil electrode 914 are positioned at appropriate
locations within the right ventricle 919 for sensing and delivering
electrical stimulation pulses to the heart. The SVC-coil 916 is
positioned at an appropriate location within the right atrium
chamber 920 of the heart 901 or a major vein leading to the right
atrial chamber 920 of the heart 901.
[0088] In one configuration, the RV-tip electrode 912 referenced to
the can electrode 909 may be used to implement unipolar pacing
and/or sensing in the right ventricle 919. Bipolar pacing and/or
sensing in the right ventricle may be implemented using the RV-tip
912 and RV-ring 911 electrodes. In yet another configuration, the
RV-ring 911 electrode may optionally be omitted, and bipolar pacing
and/or sensing may be accomplished using the RV-tip electrode 912
and the RV-coil 914, for example. The right ventricular lead system
904 may be configured as an integrated bipolar pace/shock lead. The
RV-coil 914 and the SVC-coil 916 are defibrillation electrodes.
[0089] The left ventricular lead 906 includes an LV distal
electrode 913 and an LV proximal electrode 917 located at
appropriate locations in or about the left ventricle 924 for pacing
and/or sensing the left ventricle 924. The left ventricular lead
906 may be guided into the right atrium 920 of the heart via the
superior vena cava. From the right atrium 920, the left ventricular
lead 906 may be deployed into the coronary sinus ostium, the
opening of the coronary sinus 950. The lead 906 may be guided
through the coronary sinus 950 to a coronary vein of the left
ventricle 924. This vein is used as an access pathway for leads to
reach the surfaces of the left ventricle 924 which are not directly
accessible from the right side of the heart. Lead placement for the
left ventricular lead 906 may be achieved via subclavian vein
access and a preformed guiding catheter for insertion of the LV
electrodes 913, 917 adjacent to the left ventricle.
[0090] 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 913 and the LV
proximal electrode 917 may be used together as bipolar sense and/or
pace electrodes for the left ventricle. The left ventricular lead
906 and the right ventricular lead 904, in conjunction with the CRM
device 900, 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.
[0091] The right atrial lead 905 includes a RA-tip electrode 956
and an RA-ring electrode 954 positioned at appropriate locations in
the right atrium 920 for sensing and pacing the right atrium 920.
In one configuration, the RA-tip 956 referenced to the can
electrode 909, for example, may be used to provide unipolar pacing
and/or sensing in the right atrium 920. In another configuration,
the RA-tip electrode 956 and the RA-ring electrode 954 may be used
to provide bipolar pacing and/or sensing.
[0092] FIG. 9 illustrates one embodiment of a left atrial lead
system 908. In this example, the left atrial lead 908 is
implemented as an extracardiac lead with LA distal 918 and LA
proximal 915 electrodes positioned at appropriate locations outside
the heart 901 for sensing and pacing the left atrium 922. Unipolar
pacing and/or sensing of the left atrium may be accomplished, for
example, using the LA distal electrode 918 to the can 909 pacing
vector. The LA proximal 915 and LA distal 918 electrodes may be
used together to implement bipolar pacing and/or sensing of the
left atrium 922.
[0093] Referring now to FIG. 10, there is shown block diagram of a
cardiac rhythm management (CRM) device 1000 suitable for
implementing template formation and adaptation in accordance with
embodiments of the present invention. FIG. 10 shows a CRM device
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. 10 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 defibrillator suitable for
implementing the methodologies for forming templates according to
the methodologies of the present invention. In addition, although
the CRM device 1000 depicted in FIG. 10 contemplates the use of a
programmable microprocessor-based logic circuit, other circuit
implementations may be utilized.
[0094] The CRM device 1000 depicted in FIG. 10 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 CRM device 1000 is encased and hermetically sealed in a
housing 1001 suitable for implanting in a human body. Power to the
CRM device 1000 is supplied by an electrochemical battery 1080. A
connector block (not shown) is attached to the housing 1001 of the
CRM device 1000 to allow for the physical and electrical attachment
of the lead system conductors to the circuitry of the CRM device
1000.
[0095] The CRM device 1000 may be a programmable
microprocessor-based system, including a control system 1020 and a
memory 1070. The memory 1070 may store parameters for various
pacing, defibrillation, and sensing modes, along with other
parameters. The memory 1070 may be used, for example, for storing
historical EGM and therapy data, and for retaining cardiac signals
and/or cardiac signal features before and after grouping them with
their associated clusters. The historical data storage may include,
for example, data obtained from long-term patient monitoring used
for trending or other diagnostic purposes. Historical data, as well
as other information, may be transmitted to an external programmer
unit 1090 as needed or desired.
[0096] The control system 1020 and memory 1070 may cooperate with
other components of the CRM device 1000 to control the operations
of the CRM device 1000. The control system depicted in FIG. 10
incorporates a template processor 1024 for forming cardiac response
templates in accordance with various embodiments of the present
invention. The control system 1020 may include additional
functional components including a pacemaker control circuit 1022, a
cardiac response classification processor 1025, and an arrhythmia
detector 1021 along with other components for controlling the
operations of the CRM device 1000.
[0097] Telemetry circuitry 1060 may be implemented to provide
communications between the CRM device 1000 and an external
programmer unit 1090. In one embodiment, the telemetry circuitry
1060 and the programmer unit 1090 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 1090 and the telemetry circuitry 1060. In this
manner, programming commands and other information may be
transferred to the control system 1020 of the CRM device 1000 from
the programmer unit 1090 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
1090 from the CRM device 1000.
[0098] The telemetry circuitry 1060 may provide for communication
between the CRM device 1000 and an advanced patient management
(APM) system. The advanced patient management system allows
physicians to remotely and automatically monitor cardiac and/or
other patient conditions. In one example, a CRM 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.
[0099] In the embodiment of the CRM device 1000 illustrated in FIG.
10, electrodes RA-tip 956, RA-ring 954, RV-tip 912, RV-ring 911,
RV-coil 914, SVC-coil 916, LV distal electrode 913, LV proximal
electrode 917, LA distal electrode 918, LA proximal electrode 915,
and can electrode 909 may be selectively coupled through a switch
matrix 1010 to sensing circuits 1031-1037.
[0100] A right atrial sensing circuit 1031 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 956 and
the RA-ring 954. Unipolar sensing may be implemented, for example,
by sensing voltages developed between the RA-tip 956 and the can
electrode 909. Outputs from the right atrial sensing circuit are
coupled to the control system 1020.
[0101] A right ventricular sensing circuit 1032 serves to detect
and amplify electrical signals from the right ventricle of the
heart. The right ventricular sensing circuit 1032 may include, for
example, a right ventricular rate channel 1033 and a right
ventricular shock channel 1034. Right ventricular cardiac signals
sensed through use of the RV-tip 912 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 912 and the RV-ring 911.
Alternatively, bipolar sensing in the right ventricle may be
implemented using the RV-tip electrode 912 and the RV-coil 914.
Unipolar rate channel sensing in the right ventricle may be
implemented, for example, by sensing voltages developed between the
RV-tip 912 and the can electrode 909.
[0102] Right ventricular cardiac signals sensed through use of the
RV-coil electrode 914 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 914 and the SVC-coil 916. A right
ventricular shock channel signal may also be detected as a voltage
developed between the RV-coil 914 and the can electrode 909. In
another configuration the can electrode 909 and the SVC-coil
electrode 916 may be electrically shorted and a RV shock channel
signal may be detected as the voltage developed between the RV-coil
914 and the can electrode 909/SVC-coil 916 combination.
[0103] Left atrial cardiac signals may be sensed through the use of
one or more left atrial electrodes 915, 918, which may be
configured as epicardial electrodes. A left atrial sensing circuit
1035 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 918 and the LA proximal electrode 915. Unipolar sensing
and/or pacing of the left atrium may be accomplished, for example,
using the LA distal electrode 918 to can vector 909 or the LA
proximal electrode 915 to can vector 909.
[0104] A left ventricular sensing circuit 1036 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 913 and the LV proximal electrode 917. Unipolar sensing
may be implemented, for example, by sensing voltages developed
between the LV distal electrode 913 or the LV proximal electrode
917 and the can electrode 909.
[0105] 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, 913, 917, LV coil electrode (not shown), and/or can
electrodes 909 may be sensed and amplified by the left ventricular
sensing circuitry 1036. The output of the left ventricular sensing
circuit 1036 is coupled to the control system 1020.
[0106] The outputs of the switching matrix 1010 may be operated to
couple selected combinations of electrodes 911, 912, 913, 914, 915,
916, 917, 918, 956, 954 to an evoked response sensing circuit 1037.
The evoked response sensing circuit 1037 serves to sense and
amplify voltages developed using various combinations of electrodes
for processes related to capture detection. For example, if the CRM
device is implementing the process of forming a cardiac pacing
response template, the evoked response sensing circuit may be
coupled to the template processor 1024. The cardiac signals sensed
by the evoked response sensing circuit 1037 may be used to form
templates by clustering signals or signal features indicative of
various cardiac pacing responses in accordance with embodiments of
the invention.
[0107] During capture verification and/or capture threshold testing
the evoked response sensing circuit 1037 may be coupled to the
cardiac response classification processor 1025. Signals sensed by
the evoked response sensing circuit 1037 via various electrode
combinations may be analyzed by the cardiac response classification
processor 1025 for detecting capture and/or other responses to
cardiac pacing as described herein. Other sensing circuits may
alternatively be used for template formation and/or detecting
cardiac pacing responses.
[0108] In the embodiments described below, 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.
[0109] The pacemaker control circuit 1022, in combination with
pacing circuitry for the left atrium, right atrium, left ventricle,
and right ventricle 1041, 1042, 1043, 1044, 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 of the heart
chambers as described above.
[0110] Bipolar or unipolar pacing pulses may be delivered to a
heart chamber via the pacing vectors described above. The
electrical signal following the delivery of the pacing pulses may
be sensed through various sensing vectors coupled through the
switch matrix 1010 to the evoked response sensing circuit 1037 or
other sensing circuits and used to classify the cardiac response to
pacing.
[0111] In one example, the cardiac signal following the pacing
pulse may be sensed using the same vector as was used for delivery
of the pacing pulse. In this scenario, the pacing artifact may be
canceled or otherwise removed or minimized from the sensed cardiac
signal. Following cancellation of the pacing artifact, one or more
time intervals and cardiac response classification windows may be
defined following the pacing pulse 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.
[0112] In another example, the vector used to sense the cardiac
signal following the pacing pulse may be different from the vector
that was used to deliver the pacing pulse. The sensing vector may
be selected to minimize the pacing artifact. Cancellation of the
pacing artifact may not be necessary if the pacing artifact is
sufficiently minimized using this technique.
[0113] In various embodiments, the pacing vector may be a
near-field vector and the sensing vector may be a far-field vector.
In an example of right ventricular pacing and cardiac response
sensing, the pacing vector may be the rate channel vector and the
sensing vector may be the shock channel vector.
[0114] Subcutaneous electrodes may provide additional sensing
vectors useable for template formation and 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. Nos. 10/462,001, filed
Jun. 13, 2003 and 10/465,520, filed Jun. 19, 2003, which are hereby
incorporated herein by reference in their respective
entireties.
[0115] The methods and systems described in the embodiments
provided herein use cardiac signal features to generate, update,
and/or use cardiac response templates. Although the examples
provided are described in terms of generating, updating, and using
morphology templates for cardiac pacing response determination, the
principles of the invention may be additionally or alternatively
applied to the generation and/or use of other types of cardiac
morphology templates.
[0116] For example, cardiac beats produced during an arrhythmic
episode may have characteristic features that can be discriminated
from the features of normal beats. In one scenario, the suspected
arrhythmic beats may be compared to a morphology template
characterizing a normal beat morphology. Arrhythmia is confirmed if
the sensed beat morphology is sufficiently different from the
normal beat morphology. In another scenario, a sensed arrhythmic
beat may be compared to one or more templates associated with
different types of monomorphic arrhythmias. The type of monomorphic
arrhythmia experienced by the patient may be determined based on
the similarity of the cardiac beats of the arrhythmia to one of the
morphology templates.
[0117] 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.
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