U.S. patent application number 11/312874 was filed with the patent office on 2006-07-13 for bi-ventricular ventricular capture management in cardiac resyncronization therapy delivery devices.
Invention is credited to Karen J. Kleckner, Luc R. Mongeon, John C. Rueter.
Application Number | 20060155338 11/312874 |
Document ID | / |
Family ID | 36654246 |
Filed Date | 2006-07-13 |
United States Patent
Application |
20060155338 |
Kind Code |
A1 |
Mongeon; Luc R. ; et
al. |
July 13, 2006 |
Bi-ventricular ventricular capture management in cardiac
resyncronization therapy delivery devices
Abstract
The present invention provides a technique for verifying pacing
capture of a ventricular chamber, particularly to ensure desired
delivery of a ventricular pacing regime (e.g., "CRT"). The
invention also provides ventricular capture management by
delivering a single ventricular pacing stimulus and checking
inter-ventricular conduction during a temporal window to determine
if the stimulus captured. If a loss-of-capture (LOC) signal results
from the capture management testing, then the applied pacing pulses
are modified and the conduction test repeated. If LOC, an alert
message can issue. Other aspects include: use of a trend of A-RV/LV
and LV-RV timing intervals to monitor changes in the patient's
heart conduction properties; bi-ventricular verification test and
search--while still pacing BiV by detecting latent sense; single-V
pacing threshold search, use of timing of sense in other V chamber
to establish capture and LOC windows; (iv) use of a premature V
pace rather than short AV interval if VV cannot be discriminated
from AV; (v) option to run a threshold search only if the
Bi-ventricular verification test fails.
Inventors: |
Mongeon; Luc R.;
(Minneapolis, MN) ; Kleckner; Karen J.; (New
Brighton, MN) ; Rueter; John C.; (Woodbury,
MN) |
Correspondence
Address: |
MEDTRONIC, INC.
710 MEDTRONIC PARK
MINNEAPOLIS
MN
55432-9924
US
|
Family ID: |
36654246 |
Appl. No.: |
11/312874 |
Filed: |
December 20, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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60637633 |
Dec 20, 2004 |
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60637620 |
Dec 20, 2004 |
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60637571 |
Dec 20, 2004 |
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60637532 |
Dec 20, 2004 |
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Current U.S.
Class: |
607/9 |
Current CPC
Class: |
A61N 1/3684 20130101;
A61N 1/3627 20130101; A61N 1/371 20130101; A61N 1/36843 20170801;
A61N 1/36842 20170801; A61N 1/36592 20130101 |
Class at
Publication: |
607/009 |
International
Class: |
A61N 1/36 20060101
A61N001/36 |
Claims
1. A method of monitoring and/or adjusting therapy delivery via a
ventricular cardiac resynchronization therapy (CRT) delivery
device, comprising: monitoring at least one of an atrial-left
ventricular (A-LV) interval, an atrial-right ventricular (A-RV)
interval, a LV to RV interval; storing in a memory structure said
at least one of the A-LV interval, the A-RV interval, the left
ventricular (LV) to right ventricular (RV) interval (LV-RV); and
performing a temporal trend analysis upon said at least one of the
foregoing stored intervals over a discrete period of time,
utilizing a plurality of discrete values of said stored
intervals.
2. A method according to claim 1, further comprising: performing an
automated ventricular chamber capture management pacing threshold
test for at least one of the LV and the RV.
3. A method according to claim 1, wherein said trend analysis
includes one of: a percentage of time wherein at least one of the
LV and the RV were deemed to have loss of capture (LOC), a
percentage of time when one of the LV and the RV were deemed to
have successfully captured, a percentage of time when one of the LV
and the RV were deemed to have unknown or uncertain capture
status.
4. A method according to claim 2, wherein said capture management
pacing threshold test further comprises: delivering bi-ventricular
pacing therapy for at least one cardiac cycle; and sensing in at
least one of the LV and the RV for a latent ventricular event
indicative of loss of capture in one of said LV and RV.
5. A method according to claim 4, wherein an LV-RV interval used to
deliver the bi-ventricular pacing therapy comprises a substantially
null value.
6. A method according to claim 4, wherein said sensing for said
latent ventricular event occurs during a temporal window about 40
milliseconds (ms) to 280 ms subsequent to the delivery of the
bi-ventricular pacing therapy and further comprising: declaring one
of loss of capture (LOC) and suspected cardiac lead dislodgement in
each of the LV and RV that recorded the latent ventricular event
during the temporal window.
7. A method according to claim 4, wherein said sensing for said
latent ventricular event occurs during a window about 40
milliseconds (ms) to 280 ms subsequent to the delivery of the
bi-ventricular pacing therapy and further comprising: declaring
capture in each chamber that failed to record the latent
ventricular event during the temporal window.
8. A method according to claim 4, further comprising independently
adjusting the pacing energy of one of the LV and RV so that each of
the LV and RV capture during bi-ventricular pacing therapy
delivery.
9. A method according to claim 7, further comprising in the event
that a latent sense does not occur, then performing one of the
following to establish that a sensed event would have occurred in
the event of loss of capture; namely: performing one of: a.
delivering bi-ventricular pacing therapy having a prolonged A-RV
interval or A-LV interval to verify the occurrence of
atrio-ventricular conduction; b. delivering single ventricular
pacing therapy with a shortened A-RV or A-LV interval to verify the
occurrence of inter-ventricular conduction and c. delivering a
premature ventricular pacing stimulus to a first ventricle in lieu
of a shortened A-RV or A-LV interval to verify the occurrence of
inter-ventricular conduction if the stimulus captures; and
declaring capture only if both atrio-ventricular conduction and
inter-ventricular conduction are verified.
10. A method according to claim 6, further comprising: performing a
pacing threshold search by one of incrementing an decrementing the
magnitude of pacing energy delivery until pacing capture is
confirmed at both the LV and the RV; and performing at least one of
storing information regarding the confirmed pacing capture and
communicating to a remote patient management network regarding the
confirmed pacing capture.
11. A method according to claim 10, further comprising storing the
value of the magnitude of pacing energy used to confirm capture in
each of said LV and the RV in a computer memory.
12. A method according to claim 10, further comprising incrementing
the pacing energy level a predetermined amount and chronically
delivering pacing therapy at said incremented pacing energy
level.
13. An apparatus for monitoring, delivering and/or adjusting
cardiac therapy delivery, comprising: means for monitoring at least
one of an atrial-left ventricular (A-LV) interval, an atrial-right
ventricular (A-RV) interval, a left ventricular (LV) to right
ventricular (RV) interval; means for storing in a memory structure
said at least one of the A-LV interval, the A-RV interval, the LV
to RV interval; and means for performing a temporal trend analysis
upon said at least one of the foregoing stored intervals over a
discrete period of time, utilizing a plurality of discrete values
of said stored intervals.
14. An apparatus according to claim 1, further comprising: means
for performing an automated ventricular chamber capture management
pacing threshold test for at least one of the LV and the RV,
wherein said automated threshold test is triggered by one of: a
clinician, a relatively longer duration QRS complex, a
morphologically relatively different QRS complex.
15. An apparatus according to claim 14, wherein said trend analysis
includes one of: a percentage of time wherein at least one of the
LV and the RV were deemed to have loss of capture (LOC), a
percentage of time when one of the LV and the RV were deemed to
have successfully captured, a percentage of time when one of the LV
and the RV were deemed to have unknown or uncertain capture
status.
16. An apparatus according to claim 14, further comprising: means
for delivering bi-ventricular pacing therapy for at least one
cardiac cycle; and means for sensing in at least one of the LV and
the RV for a latent ventricular event indicative of loss of capture
in one of said LV and RV.
17. An apparatus according to claim 16, wherein an LV-RV interval
used to deliver the bi-ventricular pacing therapy comprises a
substantially null value.
18. An apparatus according to claim 16, wherein said sensing for
said latent ventricular event occurs during a temporal window about
40 milliseconds (ms) to 280 ms subsequent to the delivery of the
bi-ventricular pacing therapy and further comprising: declaring one
of loss of capture (LOC) and suspected cardiac lead dislodgement in
each of the LV and RV that recorded the latent ventricular event
during the temporal window; and performing a pacing threshold
search for each of the LV and RV that recorded the latent
ventricular event during the temporal window.
19. An apparatus according to claim 16, wherein said sensing for
said latent ventricular event occurs during a window about 40
milliseconds (ms) to 280 ms subsequent to the delivery of the
bi-ventricular pacing therapy and further comprising: declaring
capture in each chamber that failed to record the latent
ventricular event during the temporal window.
20. An apparatus according to claim 16, further comprising means
for independently adjusting the pacing energy of one of the LV and
RV so that each of the LV and RV capture during bi-ventricular
pacing therapy delivery.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This non-provisional U.S. patent application claims the
benefit of prior U.S. provisional patent application Ser. No.
60/637,633 of common title, filed 20 Dec. 2004 and also relates to
a co-pending provisional U.S. patent application by Sheth et al.;
namely Ser. No. 60/637,620 (Atty. Dkt. P-10798.00) filed 20 Dec.
2004, and entitled, "AUTOMATIC LV/RV CAPTURE VERIFICATION AND
DIAGNOSTICS;" a co-pending provisional U.S. patent application by
Sheldon et al.; namely Ser. No. 60/637,571 (Atty. Dkt. P-20777.00)
filed 20 Dec. 2004, and entitled, "METHOD OF CONTINUOUS CAPTURE
VERIFICATIONS IN CARDIAC RESYNCHRONIZATION DEVICES," and a
co-pending provisional U.S. patent application by Kleckner et al.,
namely Ser. No. 60/637,532 (Atty. Dkt. No. P-21289.00) filed 20
Dec. 2004 and entitled "LV THRESHOLD MEASUREMENT AND CAPTURE
MANAGEMENT," the entire contents of each, including all exhibits
thereof, are hereby incorporated by reference herein.
FIELD OF THE INVENTION
[0002] The invention pertains to cardiac pacing systems and relates
to apparatus and methods for triggering automatic verification of
pacing capture of ventricular chambers and for managing pacing
therapy delivery to ensure continued pacing capture. In particular,
the invention relates to verification of pacing capture for both
ventricular chambers during bi-ventricular pacing, including
various forms of cardiac resynchronization therapy (CRT) delivery,
such uni-ventricular, fusion-type CRT delivery.
BACKGROUND OF THE INVENTION
[0003] Cardiac resynchronization cardiac pacing devices operate by
either delivering pacing stimulus to both ventricles or to one
ventricle with the desired result of a more or less simultaneous
mechanical contraction and ejection of blood from the ventricles.
However, due to a number of factors for a variety of patients such
cardiac pacing systems may not always effectively delivery CRT. For
example, varying capture thresholds, pacing lead and/or electrode
migration or dislodgement, time required for appropriate signal
processing, confounding conduction delays or conduction blockages,
diverse electrode placement locations, and the like.
[0004] In either form of CRT delivery, whether fusion-based or the
more traditional bi-ventricular stimulation, confirming that pacing
stimulus captures each paced ventricle is a very important clinical
issue so that the desired benefits of the CRT are in fact delivered
to a patient.
[0005] Assuming that the reader is familiar with bi-ventricular
pacing, the following should provide additional insight into the
importance of capture detection in a fusion-based bi-ventricular
pacing engine. One premise underlying fusion-based pacing is the
notion that a fusion-based evoked left ventricular (LV)
depolarization enhances stroke volume in hearts where the right
ventricle (RV) depolarizes first. This is commonly due to intact
atrio-ventricular (AV) conduction to the RV of a preceding
intrinsic or evoked atrial depolarization wave front, and wherein
the AV conducted depolarization of the LV is unduly delayed. The
fusion depolarization of the LV is attained by timing the delivery
of the LV pace (LVp) pulse to follow the intrinsic depolarization
of the RV but to precede the intrinsic depolarization of the LV.
Specifically, an RV pace (RVp) pulse is not delivered due to the
inhibition of the RVp event upon the sensing of RV depolarization
(RVs), allowing natural propagation of the wave front and
depolarization of the intraventricular septum, while an LVp pulse
is delivered in fusion with the RV depolarization. For supporting
mode switches to alternate pacing modalities, fusion-based CRT
delivery engines typically include at least one electrode in each
ventricle which allows such engines to be used in conjunction with
the present invention, as will be apparent upon review of the
following written description and drawings of the invention.
[0006] Left ventricular capture in particular is a clinical issue
with present-generation (and foreseeable) CRT systems, due to
acknowledged difficulty of maintaining stable lead situation in the
cardiac venous anatomy. Since CRT delivery becomes ineffective
(possibly even deleterious) if LV capture is lost, diagnosis of
dislodgment and maintenance of capture are high priorities.
[0007] Cardiac Resynchronization Therapy (CRT) devices have been
shown to improve quality of life (QOL), exercise capacity and New
York Heart Association (NYHA) heart failure class. The NYHA rating
varies from Class I to Class IV, as follows: Class I: patients with
no limitation of activities; they suffer no symptoms from ordinary
activities. Class II: patients with slight, mild limitation of
activity; they are comfortable with rest or with mild exertion.
Class III: patients with marked limitation of activity; they are
comfortable only at rest. Class IV: patients who should be at
complete rest, confined to bed or chair; any physical activity
brings on discomfort and symptoms occur at rest.
[0008] Currently approved CRT devices incorporate bi-ventricular
pacing technology with simultaneous pacing in the right ventricle
(RV) and the left ventricle (LV). Since the devices are implanted
essentially only to provide continuous bi-ventricular pacing
therapy, it is imperative that each pacing pulse stimulus delivered
to the two LV and RV provide an evoked response (i.e., each
stimulus delivered to a ventricle "captures" the ventricle). Thus,
if electrodes disposed in electrical communication with a ventricle
rapidly sense depolarization wavefronts a control sequence for the
pacing engine will inhibit ventricular pacing. For example, such a
situation occurs during rapidly conducted atrial fibrillation (AF).
When bi-ventricular pacing is inhibited the patient's symptoms of
heart failure return, and can sometimes even worsen as compared to
their pre-implant status. Similarly, if one of the pacing sites
loses capture (e.g., the LV) the subsequent RV-only pacing will
prevent the patient from receiving the intended benefit of CRT
delivery. To that end the inventors have addressed a need in the
art regarding capture verification in heart failure devices, such
as bi-ventricular CRT devices that indicates when capture is
occurring in both the LV and the RV.
[0009] Presently, the only somewhat similar diagnostic available in
CRT devices is percent-ventricular pacing (%Vpacing), which
indicates the percentage of time bi-ventricular pacing therapy is
being delivered; however, a limitation of the %Vpacing metric is
that bi-ventricular pacing may be "occurring" close to 100% of the
time but the LV chamber may not be captured at all. Currently,
cardiac device specialists assess LV capture acutely during office
visits by looking at the morphology of an electrogram (EGM) or by
temporarily setting pacing to RV-only and LV-only pacing. Current
state of the art pacemakers (e.g., the Kappa.RTM. brand family of
pacemakers provided by Medtronic, Inc.) incorporate ventricular
capture management algorithms. However, such algorithms require
specific circuitry and sensing capabilities to be able to perform
this function that are not currently available in the CRT products.
Also, the feasibility of this technology for LV capture management
has yet to be established. The present invention advantageously
contributes to both capture verification and management.
[0010] Previously others addressed issues related to capture
management; for example, Ventricular Capture Management (VCM) has
been successfully implemented in the Kappa.RTM. 700 dual-chamber
pacemaker sold by Medtronic, Inc. by measuring evoked responses on
the bipolar pair of electrodes in the right ventricle (RV). In this
device the pacing output energy is monitored and automatically
adjusted as required by the patient. This pacing threshold search
(PTS) measures the rheobase and chronaxie of the current pacing
threshold. The following can be used to determine rheobase and
chronaxie: 1--determine the rheobase, which is the minimum Stimulus
Strength that will produce a response (his is the voltage to which
the Strength-Duration curve asymptotes). Step 2--calculate
2.times.rheobase and step 3--determine chronaxie, which is the
Stimulus Duration that yields a response when the Stimulus Strength
is set to exactly 2.times.rheobase.
[0011] Then, a pulse width and amplitude safety margin is
calculated and the output of the device is set to that new value.
The PTS is conducted on a programmable periodic basis, commonly set
up to measure the thresholds once a day (typically at night).
[0012] Currently in the bi-ventricular pacing CRT devices like the
InSync.RTM. family of implantable pulse generators, including
ICDs), no capture verification or threshold management scheme
exists. Instead, pacing thresholds are manually measured at the
right ventricular and the left ventricular pacing sites. The site
with the highest pacing threshold requirement dictates the
programmed output of the device to assure proper capture at both
ventricular sites for devices with a single ventricular pacing
stimulus energy output.
[0013] A need therefore exists in the art to effectively
chronically deliver ventricular pacing therapies (including CRT) to
patients who might not otherwise receive the full benefit of such
therapies.
SUMMARY
[0014] Among other contributions to the art, the present invention
addresses the issues identified above of not providing adequate
metrics (or diagnostics) to a physician regarding LV (and therefore
bi-ventricular) capture. The invention addresses this significant
need where capture management functionality is not available in a
CRT device. According to the invention, the bi-ventricular capture
management as described here measures and monitors pacing
thresholds at each of pacing sites being used in CRT delivery while
the patient is ambulatory. The ability to obtain the LV and RV
thresholds and modulate these outputs helps assure greater
likelihood of bi-ventricular capture. Such dual site capture is
critical in order for a patient to benefit from CRT. Bi-ventricular
capture verification and capture management is also an important
element to enable remote follow-up (e.g., via a patient management
network or the like) and to provide a triage tool for understanding
whether worsening heart failure is due to a device pacing-capture
problem versus a manifestation of worsening heart failure. The
clinically important aspect of managing pacing capture thresholds
in these patients is that an HF decompensation event that might
have been related to bi-ventricular capture problems are eliminated
due to the dynamic nature of the (left-sided) pacing stimulus
output energy. In the event that the capture detection and
management scheme detects a situation of failed LV capture (e.g.,
left side lead dislodgement), a clinician or physician can be
notified via a network such as the Medtronic CareLink.RTM. network
alert system utilizing e-mail, fax, phone calls, paging networks
and the like.
[0015] Currently no bi-ventricular capture management scheme has
been implemented in any pacing therapy delivery device, such as an
IPG. As stated hereinabove, the advantages are both from a
clinician ease-of-use perspective, for example a clinically
significant aspect of assuring CRT is being effectively delivered
as planned, and a timesaving triage tool which would help identify
left-lead issues that comprise a significant issue for patients who
are scheduled to receive chronic CRT delivery.
[0016] Thus, at least on exemplary algorithm is described for rapid
incorporation into next-generation CRT devices that actively
performs LV capture verification and threshold test(s) on a daily
(or other) basis with automatic retry and wireless communication of
testing results, trends and the like (including any testing
anomalies). The results of the test(s) can be stored and/or
provided to the user, a clinician, or other entity. The results of
the tests can be provided remotely or via a programming head at a
next programmer-based session, as is known in the art. The data
regarding LV capture can be used, for example, to record or
demonstrate whether an intended CRT delivery is occurring and the
amount of time or percentage that a patient in fact received CRT.
If LV capture verification is NOT confirmed, in addition to the
stored diagnostic metrics, a patient alert can be triggered to warn
the patient (and/or a clinician) that the device is not functioning
as intended and the patient should consider consulting a
physician.
[0017] In one form of the invention, such a patent alert can be
triggered on a remote patient management network (e.g., the
Medtronic Medtronic CareLink.RTM. remote monitoring service for
patients with Medtronic cardiac devices) to notify third parties of
the lack of CRT delivery. This test and the resultant diagnostic
metric values (e.g., percentage of actual CRT delivery in temporal
terms, by the number of cardiac cycles with and without CRT
delivery, or by time of day and the like) simply and accurately
depicts actual CRT delivery. The values also provide assurance to
the physician, patient and/or care-giver that the device is not
only pacing in both ventricular chambers, but capturing, thereby
providing maximal therapeutic benefit to the patient. The values
also help in the early identification of a situation where, for
some reason a pacing lead is not capturing in the associated
ventricle thereby minimizing patient discomfort and restoration of
the desired therapeutic regime. Also, a test according to the
invention can be applied to verify RV capture and for in-office,
easy-to-use acute confirmation of capture verification of the LV
and RV.
[0018] Multiple approaches can be used for measuring the pacing
threshold at the left and right ventricular sites.
[0019] For example, evoked response measurement at each site: this
involves measuring the pacing threshold using the evoked response
approach previously used in the Kappa devices of Medtronic, Inc.
The capture management feature provides automatic monitoring of
ventricular pacing thresholds and automatic adjustment of amplitude
and pulse width to maintain capture. When capture management is
programmed to monitor only, the pacemaker periodically causes paces
to be delivered (affecting pacemaker timing temporarily if
necessary). The pacemaker then monitors the paces by changing first
amplitude and then pulse width to find two points that lie on the
strength duration curve that define the boundary between settings
that capture and those that do not. How often the pacemaker
performs this pacing threshold search is determined by the
programmable Capture Test Frequency parameter. This parameter
determines how often the pacing threshold search will be initiated
and provides for retry if the test is delayed. When Capture
Management is programmed to Adaptive, the pacemaker responds to
monitoring by adapting ventricular amplitude and pulse width using
the following programmable parameters:
[0020] Amplitude Margin and Pulse Width Margin--the pacemaker
determined threshold multiplied by a selected safety factor.
[0021] Minimum Adapted Amplitude and Minimum Adapted Pulse
Width--the lower limit to which Amplitude and Pulse Width can be
set by the pacemaker during adaptation.
[0022] Acute Phase Days Remaining--time in days during which the
pacemaker will not decrease output settings below the initially
programmed settings. This parameter is used during the lead
maturation period.
[0023] The LV threshold can thus be measured using evoked response
as on the left side. Pacing threshold measurements using evoked
responses can require that each pacing site be individually
evaluated.
[0024] Another way to accomplish LVCM according to the invention
involves intrinsic deflection detection at each site: According to
this aspect of the invention uses the detection of an intrinsic
deflection within a certain window that is generated from a pacing
pulse at the other ventricular electrode. The advantage to using
such an algorithmic approach is that it can be implemented on a
pacing engine that has independent ventricular channels. This
approach could be initiated via the device programmer or a remote
monitor, such as the Medtronic CareLink network supported by
Medtronic, Inc. So, for example, if a clinician wants to collect
data on pacing thresholds they could readily access the data
remotely.
[0025] Yet another technique according to the invention involves a
hybrid of intrinsic at one site and evoked at the other: The use of
the intrinsic deflection sensing on the one side only may provide
an advantage as the evoked response sensing circuitry for the
second site would be unnecessary.
[0026] Another aspect of the invention is that a variety of
verification test protocols can be implemented that increase in
aggressiveness if a prior test fails or is inconclusive. According
to this aspect of the invention, a "level 1" verification test
might only confirm that capture is occurring at the currently
programmed settings. It could also evaluate if a sensed event can
actually occur at each electrode to eliminate lead dislodgement as
a reason for a failure to sense cardiac events. According to this
level of verification, the pacing output channels would not be
reprogrammed nor is any therapy delivery modified (e.g., no pacing
mode switches).
[0027] Another somewhat indirect capture management technique
involves periodic measurement of QRS durations and comparison
between a prior duration wherein capture was confirmed. Such a
comparison also provides some evidence of the state of heart
failure and/or conduction defects of a patient.
[0028] Some applications of the invention without limitation
include: (1) ambulatory, automatic LV capture verification; (2)
ambulatory, automatic RV capture verification; (3) diagnostic data
display on trends of capture performance; (4) alerts to clinics,
physicians and patients when LV capture is suspect or lost; (5)
in-office easy-to-use LV/RV capture verification testing; (6)
automatic ambulatory LV and RV capture management (e.g., adjustment
of pacing outputs to maintain capture); and (7) providing capture
verification and/or pacing threshold search (PTS) testing with
atrial-tracking and non-tracking modalities. The latter use can
include aspects of the following: the present inventive method
provides an effective avenue for providing device intelligence and
automatic adjustment of operating parameters to ensure pacing
capture of the ventricles (LV and/or RV). In the event that pacing
capture is lost, or is suspect, the patient or a clinic (or
clinician) can be notified and/or certain pacing or sensed
parameters of the medical device stored and/or sent via telemetry
to a remote location for later review. The stored parameters
provide a clinician with diagnostic data for a patient that can be
stored in a graphical format, histogram or the like for convenient
review.
[0029] According to the present invention a ventricular pacing
device (including CRT delivery devices) analyzes myocardial
electrogram signals in one ventricle can be used to infer capture
or loss-of-capture (LOC) of an earlier stimulus pulse in the same
ventricle, on a continuous (every pacing cycle), aperiodic or
periodic basis. Rather than using an evoked-response principle as
has been the basis of capture detection in prior art systems, a
principle employed via the present invention uses evidence of
inter-ventricular conduction (i.e., from the opposite chamber) as
evidence of LOC, since a non-capturing pacing stimulus will allow
myocardial tissue to remain non-refractory and thus
inter-ventricular wavefront propagation (i.e., conduction) and
organized myocardial contractions to commence.
[0030] Using existing sense amplifiers and associated circuitry,
simple and efficient signal analysis, and discrimination of the
conducted signal of interest (from unwanted signals of cardiac
activity such as T-waves, premature ventricular contractions, or
"PVCs," far-field R-waves, and the like) can be enhanced as needed
based on the timing the sensed signal, its magnitude or other
morphology characteristics, as registered by suitable
circuitry.
[0031] Ventricular sensing of intrinsic (not evoked) depolarization
signal can thus be used to infer LOC, as a basis for diagnostic and
auto-adjustment of stimulus output, in CRT or multi-site
bradycardia therapy devices.
[0032] Other aspects of the invention include, without limitation,
some or all of the following: (i) Use of a trend of A-RV/LV and
LV-RV timing intervals to monitor changes in the patient's heart
conduction properties; (ii) BiV verification test and
search--verifying capture in RV and LV while still pacing BiV by
looking for a latent sense following the BiV pace; (iii) single V
pacing threshold search, use of timing of sense in other V chamber
to establish capture and LOC windows; (iv) use of a premature V
pace rather than short AV interval if VV cannot be discriminated
from AV; (v) option to run a threshold search only if the
Bi-ventricular verification test fails.
[0033] The foregoing and other aspects and features of the present
invention will be more readily understood from the following
detailed description of the embodiments thereof, when considered in
conjunction with the drawings, in which like reference numerals
indicate similar structures throughout the several views.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] FIG. 1 is an illustration of transmission of a normal
cardiac conduction system through which depolarization waves are
propagated through the heart in a normal intrinsic electrical
activation sequence.
[0035] FIG. 2 is a schematic diagram depicting a three channel,
atrial and bi-ventricular, pacing system for implementing the
present invention.
[0036] FIG. 3 is a simplified block diagram of one embodiment of
IPG circuitry and associated leads employed in the system of FIG. 2
for providing three sensing channels and corresponding pacing
channels that selectively functions in an energy efficient,
single-pacing stimulus, ventricular pre-excitation pacing mode
according to the present invention.
[0037] FIG. 4 is a flow chart depicting an embodiment of
ventricular capture verification and pacing threshold testing
regimen according to the present invention.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
[0038] In the following detailed description, references are made
to illustrative embodiments for carrying out methods of confirming
pacing capture of ventricular pacing stimulation. It is understood
that other embodiments may be utilized without departing from the
scope of the invention. For example, the invention is disclosed in
detail herein in the context of a bi-ventricular CRT delivery. In
one form of the invention, a pacing regimen is modified to
single-ventricle pacing therapy delivery wherein ventricular
sensing in a first ventricle of a pacing stimulus delivered to a
second ventricle is used to verify pacing capture in said first
ventricular chamber. Thus, loss-of-capture (LOC) can be declared,
verified or managed and one of several possible responses
initiated. For example, the pacing pulse stimulus can be adjusted
(e.g., modified pulse amplitude, pulse width, polarity, etc.), a
pacing mode-switch can be implemented, and/or in relatively extreme
cases a clinician can attempt to adjust the system, including
electrode location, to improve pacing capture.
[0039] A cardiac pacing apparatus, according to the invention,
comprises a programmable implantable pulse generator (IPG) that can
be operated as a dual- or triple-chamber pacing system having an AV
synchronous operating mode for restoring upper and lower heart
chamber synchronization and/or right and left atrial and/or
ventricular chamber depolarization synchrony. A system according to
the invention efficiently provides cardiac resynchronization
therapy (CRT) with a single ventricular stimulus per cardiac cycle
in a fusion-inducing CRT delivery or with a pair of synchronized
bi-ventricular pacing stimulus per cardiac cycle.
[0040] The present invention provides enhanced hemodynamic
performance for patients that benefit from CRT delivery due to
various forms of heart failure, ventricular dysfunctions and/or
ventricular conduction abnormalities. Pacing systems according to
the present invention can also include rate responsive features and
anti-tachyarrhythmia pacing and the like. In addition, a system
according to the invention can include cardioversion and/or
defibrillation therapy delivery.
[0041] In accordance with an aspect of the present invention, a
method and apparatus is provided to mimic the normal
depolarization-repolarization cardiac cycle sequence (nominally
depicted in FIG. 1) and restore cardiac intra- and/or
inter-ventricular synchrony between the RV and LV that contributes
to adequate cardiac output related to the synchronized
electromechanical performance of the RV and LV. The foregoing and
other advantages of the invention are realized through confirmed
delivery of cardiac pacing stimulation to the ventricles. For
example, a number of physiologic factors can influence the ability
of delivered pacing stimulus to capture a cardiac chamber. For
instance, conduction delays through the A-V node and/or the
His-Purkinje fibers, electrical conduction delay for sensing
intra-cardiac events (from electrodes through threshold sensing
circuitry of a medical device), electrical conduction delay for
pacing therapy delivery circuitry, electromechanical delay
associated with the delivery of a pace and the ensuing mechanical
contraction, ischemic episodes temporarily tempering conduction
pathways, myocardial infarction(s) zones, all can deleteriously
impact cardiac conduction and thereby affect an operating pacing
therapy delivery regime. Because the conduction status of a patient
can vary over time and/or vary based on other factors such as heart
rate, autonomic tone and metabolic status, the present invention
provides a dynamically controllable resynchronization pacing
modality.
[0042] According to the invention verification of capture can be
triggered so that a desired amount of dual- or single-chamber
(fusion-based) CRT delivery ensues. Some of the factors include,
(i) completion of a pre-set number of cardiac cycles, (ii) pre-set
time limit, (iii) loss of capture of a paced ventricle, (iv)
physiologic response triggers (e.g., systemic or intra-cardiac
pressure fluctuation, heart rate excursion, metabolic demand
increase, decrease in heart wall acceleration, intra-cardiac
electrogram morphology or timing, etc.) and/or (v) time of day, and
the like. The present invention provides a cardiac pacing system
that can readily compensate for the particular implantation sites
of the pace/sense electrode pair operatively coupled to a
ventricular chamber. When implemented in a triple-chamber
embodiment, a pacing system according to the present invention can
quickly mode-switch in the event that loss-of-capture (LOC) is
declared.
[0043] FIG. 2 is a schematic representation of an implanted,
triple-chamber cardiac pacemaker comprising a pacemaker IPG 14 and
associated leads 16,32,52 in which the present invention may be
practiced. The pacemaker IPG 14 is implanted subcutaneously in a
patient's body between the skin and the ribs. The three endocardial
leads 16,32,52 operatively couple the IPG 14 with the RA, the RV
and the LV, respectively. Each lead has at least one electrical
conductor and pace/sense electrode, and a remote indifferent can
electrode 20 is formed as part of the outer surface of the housing
of the IPG 14. As described further below, the pace/sense
electrodes and the remote indifferent can electrode 20 (IND_CAN
electrode) can be selectively employed to provide a number of
unipolar and bipolar pace/sense electrode combinations for pacing
and sensing functions, particularly sensing far field signals (e.g.
far field R-waves). The depicted positions in or about the right
and left heart chambers are also merely exemplary. Moreover other
leads and pace/sense electrodes may be used instead of the depicted
leads and pace/sense electrodes that are adapted to be placed at
electrode sites on or in or relative to the RA, LA, RV and LV.
Also, as noted previously, multiple electrodes and/or leads may be
deployed into operative communication with the relatively "late"
depolarizing ventricle to pace at multiple sites with varying
degrees of pre-excitation. In addition, mechanical and/or metabolic
sensors can be deployed independent of, or in tandem with, one or
more of the depicted leads. In the event that multiple pacing
electrodes are operatively deployed into communication with a
single chamber, a capture detection for each such electrode may be
individually performed. That is, different pacing stimulus can be
implemented for each discrete pacing location and said pacing
stimulus delivery can thus be tuned for capture and/or conduction
anomalies (e.g., due to infarct or ischemia or the like).
[0044] As depicted, a bipolar endocardial RA lead 16 passes through
a vein into the RA chamber of the heart 10, and the distal end of
the RA lead 16 is attached to the RA wall by an attachment
mechanism 17. The bipolar endocardial RA lead 16 is formed with an
in-line connector 13 fitting into a bipolar bore of IPG connector
block 12 that is coupled to a pair of electrically insulated
conductors within lead body 15 and connected with distal tip RA
pace/sense electrode 19 and proximal ring RA pace/sense electrode
21. Delivery of atrial pace pulses and sensing of atrial sense
events is effected between the distal tip RA pace/sense electrode
19 and proximal ring RA pace/sense electrode 21, wherein the
proximal ring RA pace/sense electrode 21 functions as an
indifferent electrode (IND_RA). Alternatively, a unipolar
endocardial RA lead could be substituted for the depicted bipolar
endocardial RA lead 16 and be employed with the IND_CAN electrode
20. Or, one of the distal tip RA pace/sense electrode 19 and
proximal ring RA pace/sense electrode 21 can be employed with the
IND_CAN electrode 20 for unipolar pacing and/or sensing.
[0045] Bipolar, endocardial RV lead 32 is passed through the vein
and the RA chamber of the heart 10 and into the RV where its distal
ring and tip RV pace/sense electrodes 38 and 40 are fixed in place
in the apex by a conventional distal attachment mechanism 41. The
RV lead 32 is formed with an in-line connector 34 fitting into a
bipolar bore of IPG connector block 12 that is coupled to a pair of
electrically insulated conductors within lead body 36 and connected
with distal tip RV pace/sense electrode 40 and proximal ring RV
pace/sense electrode 38, wherein the proximal ring RV pace/sense
electrode 38 functions as an indifferent electrode (IND_RV).
Alternatively, a unipolar endocardial RV lead could be substituted
for the depicted bipolar endocardial RV lead 32 and be employed
with the IND_CAN electrode 20. Or, one of the distal tip RV
pace/sense electrode 40 and proximal ring RV pace/sense electrode
38 can be employed with the IND_CAN electrode 20 for unipolar
pacing and/or sensing.
[0046] Further referring to FIG. 2, a bipolar, endocardial coronary
sinus (CS) lead 52 is passed through a vein and the RA chamber of
the heart 10, into the coronary sinus and then inferiorly in a
branching vessel of the great cardiac vein to extend the proximal
and distal LV CS pace/sense electrodes 48 and 50 alongside the LV
chamber. The distal end of such a CS lead is advanced through the
superior vena cava, the right atrium, the ostium of the coronary
sinus, the coronary sinus, and into a coronary vein descending from
the coronary sinus, such as the lateral or posteriolateral vein. In
addition, while not depicted in FIG. 2 the atrial, ventricular,
and/or CS-deployed pacing leads can couple to the exterior of a
heart via a pericardial or epicardial attachment mechanism.
[0047] In a four chamber or channel embodiment, LV CS lead 52 bears
proximal LA CS pace/sense electrodes 28 and 30 positioned along the
CS lead body to lie in the larger diameter CS adjacent the LA.
Typically, LV CS leads and LA CS leads do not employ any fixation
mechanism and instead rely on the close confinement within these
vessels to maintain the pace/sense electrode or electrodes at a
desired site. The LV CS lead 52 is formed with a multiple conductor
lead body 56 coupled at the proximal end connector 54 fitting into
a bore of IPG connector block 12. A small diameter lead body 56 is
selected in order to lodge the distal LV CS pace/sense electrode 50
deeply in a vein branching from the great vein (GV).
[0048] In this case, the CS lead body 56 would encase four
electrically insulated lead conductors extending proximally from
the more proximal LA CS pace/sense electrode(s) and terminating in
a dual bipolar connector 54. The LV CS lead body would be smaller
between the LA CS pace/sense electrodes 28 and 30 and the LV CS
pace/sense electrodes 48 and 50. It will be understood that LV CS
lead 52 could bear a single LA CS pace/sense electrode 28 and/or a
single LV CS pace/sense electrode 50 that are paired with the
IND_CAN electrode 20 or the ring electrodes 21 and 38, respectively
for pacing and sensing in the LA and LV, respectively.
[0049] In this regard, FIG. 3 depicts bipolar RA lead 16, bipolar
RV lead 32, and bipolar LV CS lead 52 without the LA CS pace/sense
electrodes 28 and 30 coupled with an IPG circuit 300 having
programmable modes and parameters of a bi-ventricular DDD/R type
known in the pacing art. In turn the sensor signal processing
circuit 43 indirectly couples to the timing circuit 330 and via bus
306 to microcomputer circuitry 302. The IPG circuit 300 is
illustrated in a functional block diagram divided generally into a
microcomputer circuit 302 and a pacing circuit 320. The pacing
circuit 320 includes the digital controller/timer circuit 330, the
output amplifiers circuit 340, the sense amplifiers circuit 360,
the RF telemetry transceiver 322, the activity sensor circuit 322
as well as a number of other circuits and components described
below.
[0050] Crystal oscillator circuit 338 provides the basic timing
clock for the pacing circuit 320, while battery 318 provides power.
Power-on-reset circuit 336 responds to initial connection of the
circuit to the battery for defining an initial operating condition
and similarly, resets the operative state of the device in response
to detection of a low battery condition. Reference mode circuit 326
generates stable voltage reference and currents for the analog
circuits within the pacing circuit 320, while analog to digital
converter ADC and multiplexer circuit 328 digitizes analog signals
and voltage to provide real time telemetry if a cardiac signals
from sense amplifiers 360, for uplink transmission via RF
transmitter and receiver circuit 332. Voltage reference and bias
circuit 326, ADC and multiplexer 328, power-on-reset circuit 336
and crystal oscillator circuit 338 may correspond to any of those
presently used in current marketed implantable cardiac
pacemakers.
[0051] If the IPG is programmed to a rate responsive mode, the
signals output by one or more physiologic sensor are employed as a
rate control parameter (RCP) to derive a physiologic escape
interval. For example, the escape interval is adjusted
proportionally the patient's activity level developed in the
patient activity sensor (PAS) circuit 322 in the depicted,
exemplary IPG circuit 300. The patient activity sensor 316 is
coupled to the IPG housing and may take the form of a piezoelectric
crystal transducer as is well known in the art and its output
signal is processed and used as the RCP. Sensor 316 generates
electrical signals in response to sensed physical activity that are
processed by activity circuit 322 and provided to digital
controller/timer circuit 330. Activity circuit 332 and associated
sensor 316 may correspond to the circuitry disclosed in U.S. Pat.
Nos. 5,052,388 and 4,428,378. Similarly, the present invention may
be practiced in conjunction with alternate types of sensors such as
oxygenation sensors, pressure sensors, pH sensors and respiration
sensors, all well known for use in providing rate responsive pacing
capabilities. Alternately, QT time may be used as the rate
indicating parameter, in which case no extra sensor is required.
Similarly, the present invention may also be practiced in non-rate
responsive pacemakers.
[0052] Data transmission to and from the external programmer is
accomplished by means of the telemetry antenna 334 and an
associated RF transceiver 332, which serves both to demodulate
received downlink telemetry and to transmit uplink telemetry.
Uplink telemetry capabilities will typically include the ability to
transmit stored digital information, e.g. operating modes and
parameters, EGM histograms, and other events, as well as real time
EGMs of atrial and/or ventricular electrical activity and Marker
Channel pulses indicating the occurrence of sensed and paced
depolarizations in the atrium and ventricle, as are well known in
the pacing art.
[0053] Microcomputer 302 contains a microprocessor 304 and
associated system clock 308 and on-processor RAM and ROM chips 310
and 312, respectively. In addition, microcomputer circuit 302
includes a separate RAM/ROM chip 314 to provide additional memory
capacity. Microprocessor 304 normally operates in a reduced power
consumption mode and is interrupt driven. Microprocessor 304 is
awakened in response to defined interrupt events, which may include
A-TRIG, RV-TRIG, LV-TRIG signals generated by timers in digital
timer/controller circuit 330 and A-EVENT, RV-EVENT, and LV-EVENT
signals generated by sense amplifiers circuit 360, among others.
The specific values of the intervals and delays timed out by
digital controller/timer circuit 330 are controlled by the
microcomputer circuit 302 by means of data and control bus 306 from
programmed-in parameter values and operating modes. In addition, if
programmed to operate as a rate responsive pacemaker, a timed
interrupt, e.g., every cycle or every two seconds, may be provided
in order to allow the microprocessor to analyze the activity sensor
data and update the basic A-A, V-A, or V-V escape interval, as
applicable. In addition, the microprocessor 304 may also serve to
define variable, operative AV delay intervals and the energy
delivered to each ventricle.
[0054] In one embodiment of the invention, microprocessor 304 is a
custom microprocessor adapted to fetch and execute instructions
stored in RAM/ROM unit 314 in a conventional manner. It is
contemplated, however, that other implementations may be suitable
to practice the present invention. For example, an off-the-shelf,
commercially available microprocessor or microcontroller, or custom
application-specific, hardwired logic, or state-machine type
circuit may perform the functions of microprocessor 304.
[0055] Digital controller/timer circuit 330 operates under the
general control of the microcomputer 302 to control timing and
other functions within the pacing circuit 320 and includes a set of
timing and associated logic circuits of which certain ones
pertinent to the present invention are depicted. The depicted
timing circuits include URI/LRI timers 364, V-V delay timer 366,
intrinsic interval timers 368 for timing elapsed V-EVENT to V-EVENT
intervals or V-EVENT to A-EVENT intervals or the V-V conduction
interval, escape interval timers 370 for timing A-A, V-A, and/or
V-V pacing escape intervals, an AV delay interval timer 372 for
timing the A-LVp delay (or A-RVp delay) from a preceding A-EVENT or
A-TRIG, a post-ventricular timer 374 for timing post-ventricular
time periods, and a date/time clock 376.
[0056] According to the invention, the AV delay interval timer 372
is loaded with an appropriate delay interval for one ventricular
chamber (i.e., either an A-RVp delay or an A-LVp delay) to time-out
starting from a preceding A-PACE or A-EVENT. The interval timer 372
triggers pacing stimulus delivery, and can based on one or more
prior cardiac cycles (or from a data set empirically derived for a
given patient)
[0057] The post-event timers 374 time out the post-ventricular time
periods following an RV-EVENT or LV-EVENT or a RV-TRIG or LV-TRIG
and post-atrial time periods following an A-EVENT or A-TRIG. The
durations of the post-event time periods may also be selected as
programmable parameters stored in the microcomputer 302. The
post-ventricular time periods include the PVARP, a post-atrial
ventricular blanking period (PAVBP), a ventricular blanking period
(VBP), and a ventricular refractory period (VRP). The post-atrial
time periods include an atrial refractory period (ARP) during which
an A-EVENT is ignored for the purpose of resetting any AV delay,
and an atrial blanking period (ABP) during which atrial sensing is
disabled. It should be noted that the starting of the post-atrial
time periods and the AV delays can be commenced substantially
simultaneously with the start or end of each A-EVENT or A-TRIG or,
in the latter case, upon the end of the A-PACE which may follow the
A-TRIG. Similarly, the starting of the post-ventricular time
periods and the V-A escape interval can be commenced substantially
simultaneously with the start or end of the V-EVENT or V-TRIG or,
in the latter case, upon the end of the V-PACE which may follow the
V-TRIG. The microprocessor 304 also optionally calculates AV
delays, post-ventricular time periods, and post-atrial time periods
that vary with the sensor based escape interval established in
response to the RCP(s) and/or with the intrinsic atrial rate.
[0058] The output amplifiers circuit 340 contains a RA pace pulse
generator (and a LA pace pulse generator if LA pacing is provided),
a RV pace pulse generator, and a LV pace pulse generator or
corresponding to any of those presently employed in commercially
marketed cardiac pacemakers providing atrial and ventricular
pacing. In order to trigger generation of an RV-PACE or LV-PACE
pulse, digital controller/timer circuit 330 generates the RV-TRIG
signal at the time-out of the A-RVp delay (in the case of RV
pre-excitation) or the LV-TRIG at the time-out of the A-LVp delay
(in the case of LV pre-excitation) provided by AV delay interval
timer 372 (or the V-V delay timer 366). Similarly, digital
controller/timer circuit 330 generates an RA-TRIG signal that
triggers output of an RA-PACE pulse (or an LA-TRIG signal that
triggers output of an LA-PACE pulse, if provided) at the end of the
V-A escape interval timed by escape interval timers 370.
[0059] The output amplifiers circuit 340 includes switching
circuits for coupling selected pace electrode pairs from among the
lead conductors and the IND_CAN electrode 20 to the RA pace pulse
generator (and LA pace pulse Pace/sense electrode pair selection
and control circuit 350 selects lead conductors and associated pace
electrode pairs to be coupled with the atrial and ventricular
output amplifiers within output amplifiers circuit 340 for
accomplishing RA, LA, RV and LV pacing.
[0060] The sense amplifiers circuit 360 contains sense amplifiers
corresponding to any of those presently employed in contemporary
cardiac pacemakers for atrial and ventricular pacing and sensing.
As is known, it has been common in the prior art to use very high
impedance P-wave and R-wave sense amplifiers to amplify the voltage
difference signal which is generated across the sense electrode
pairs by the passage of cardiac depolarization wavefronts. The high
impedance sense amplifiers use high gain to amplify the low
amplitude signals and rely on pass band filters, time domain
filtering and amplitude threshold comparison to discriminate a
P-wave or R-wave from background electrical noise. Digital
controller/timer circuit 330 controls sensitivity settings of the
atrial and ventricular sense amplifiers 360.
[0061] The sense amplifiers are typically uncoupled from the sense
electrodes during the blanking periods before, during, and after
delivery of a pace pulse to any of the pace electrodes of the
pacing system to avoid saturation of the sense amplifiers. The
sense amplifiers circuit 360 includes blanking circuits for
uncoupling the selected pairs of the lead conductors and the
IND_CAN electrode 20 from the inputs of the RA sense amplifier (and
LA sense amplifier if provided), RV sense amplifier and LV sense
amplifier during the ABP, PVABP and VBP. The sense amplifiers
circuit 360 also includes switching circuits for coupling selected
sense electrode lead conductors and the IND_CAN electrode 20 to the
RA sense amplifier (and LA sense amplifier if provided), RV sense
amplifier and LV sense amplifier. Again, sense electrode selection
and control circuit 350 selects conductors and associated sense
electrode pairs to be coupled with the atrial and ventricular sense
amplifiers within the output amplifiers circuit 340 and sense
amplifiers circuit 360 for accomplishing RA, LA, RV and LV sensing
along desired unipolar and bipolar sensing vectors.
[0062] Right atrial depolarizations or P-waves in the RA-SENSE
signal that are sensed by the RA sense amplifier result in a
RA-EVENT signal that is communicated to the digital
controller/timer circuit 330. Similarly, left atrial
depolarizations or P-waves in the LA-SENSE signal that are sensed
by the LA sense amplifier, if provided, result in a LA-EVENT signal
that is communicated to the digital controller/timer circuit 330.
Ventricular depolarizations or R-waves in the RV-SENSE signal are
sensed by a ventricular sense amplifier result in an RV-EVENT
signal that is communicated to the digital controller/timer circuit
330. Similarly, ventricular depolarizations or R-waves in the
LV-SENSE signal are sensed by a ventricular sense amplifier result
in an LV-EVENT signal that is communicated to the digital
controller/timer circuit 330. The RV-EVENT, LV-EVENT, and RA-EVENT,
LA-SENSE signals may be refractory or non-refractory, and can
inadvertently be triggered by electrical noise signals or
aberrantly conducted depolarization waves rather than true R-waves
or P-waves.
[0063] Multiple approaches can be used for measuring the pacing
threshold at the left and right ventricular sites according to the
invention. For example, evoked response measurements at each pacing
site. This approach involves continuing to measure the ventricular
thresholds using the evoked response approach. According to this
approach, each of the RV and LV thresholds are measured using an
evoked response approach. That is, pacing threshold measurements
using evoked responses generally require that each pacing site
(e.g., each pacing stimulus vector, uni-polar and/or bi-polar,
etc.) be individually evaluated. According to this approach, the
pacing stimulus energy delivered to each ventricle can be
iteratively reduced until LOC is declared. The LOC declaration can
be obtained from temporal EGM signal traces, temporal ECG signal
traces, mechanical sensors (e.g., accelerometer, fluid pressure
sensor, and the like). Once LOC is declared the pacing stimulus
energy can be increased to a chamber-capturing threshold. This
threshold can be used chronically, although typically the chronic
pacing energy is increased by a small, so-called safety margin so
that capture is more likely to be maintained.
[0064] Another approach involves intrinsic deflection detection at
each site wherein detection of an intrinsic deflection within a
certain temporal window. The temporal window is generated from a
pacing pulse using another ventricular electrode (or vector). The
advantage to using such an evoked response algorithmic approach is
that no need exists to Implement the evoked response detection
circuitry on a new, or modified, device platform, and the features
of the invention could be implemented on the future devices which
have independent ventricular pacing circuitry and channels. This
approach can also be used for a remote monitoring scheme both
ambulatory (or at least at a patient's residence) or used in the
office or clinic by a clinician that wants to measure pacing
thresholds. The test could be initiated via the programmer or the
Medtronic CareLink.RTM. network instruments developed and supported
by Medtronic, Inc. In addition, a hybrid approach of both intrinsic
threshold testing at one site and evoked response testing at the
other involves use of intrinsic deflection sensing on one side only
(i.e., LV or RV) can provide advantages since the evoked response
sensing circuitry for the second side would be unnecessary.
Moreover, both approaches at each site (or for each side, LV and
RV) can be advantageously applied in order to cross check results
or in the event that one technique is ineffective at one or both
sites. The foregoing appears to represent a better approach--or the
best of both--since it provides redundant systems for performing
the same function.
[0065] As implied above, the use of multiple electrode locations
could also be used to conduct the threshold tests and/or to monitor
the intraventricular delay between two or more pacing sites. Such
multiple electrodes can comprise an chronically implanted
multi-polar pacing lead or an acute interventional procedure using
an electrophysiology catheter, such as a decapolar diagnostic
catheter. Such multi-polar testing can be used to optimize CRT
delivery and monitor the patients for any clinically relevant
prolongation or shortening of the intra-ventricular delay.
[0066] The capture management features according to the invention
verify that existing pacing outputs are capturing. Such tests
include calculated ventricular threshold amplitude at the
programmed pacing stimulus pulse width; strength duration curve
showing the results with a 2.times. amplitude over the programmed
amplitude (including the so-called safety margin); status of
capture management (adaptive or monitor only); capture management
parameters include some or all of the following: Ventricular
Amplitude, Ventricular Pulse Width, Amplitude Margin, Pulse Width
Margin, Minimum Adapted Amplitude, Minimum Adapted Pulse Width,
Date when an acute phase test was completed or time remaining to
next acute phase test.
[0067] The information or data gathered and used by the inventive
algorithm also provides diagnostic information and trend data on
the timing between the RV and LV pacing stimulus delivery and the
A-RV and A-LV pacing intervals. Such timing data can be used to
monitor the changes in the patient's heart conduction properties,
used to detect a lead dislodgement, used to trigger a
firmware-initiated PTS, and used to activate a patient alert,
clinic or clinician notification or the like.
[0068] A verification test or a PTS test can be initiated by
several mechanisms which include a firmware initiation, a
programmer initiation and a remote monitor initiation.
[0069] In the case of a remote follow-up initiation, the clinician
sets up the system to conduct a verification test followed by a PTS
(if necessary) upon having a patient interrogate and download
device data to a patient management-type network (e.g., the
Medtronic CareLink.RTM. network). The test can be conducted
asynchronously (automatically) or during an interactive remote
programming session. The remote nature of the test will allow for
early warning of lead issues and allow appropriate triage of
patients to the EP or the Heart Failure specialist.
[0070] A template of a normal bi-v paced electrogram can be stored
for template matching purposes. If the implanted device supports
far-field, endocardial electrograms (EGM) or pseudo/subcutaneous
ECG, a control template will also be captured from these vectors
and stored far later comparison. If the QRS width is prolonged, it
is likely that a capture issue exists. Periodic QRS widths can be
measured by the device and if it fails out of a range defined by
the control template, a firmware verification of capture can be
initiated.
[0071] In an in-office programmer initiated test, similar to the
remote test, the clinical user can define if a full PTS will be
executed or if only a verification test will be done. This aspect
of the capture management feature of the invention allows
clinicians to easily conduct an in-office measurement of the pacing
thresholds at each of the pacing sites.
[0072] A third case is initiation of the test via the implanted
device firmware. The firmware can use a time of day approach or a
detected condition from either a verification test result, the
timing information, or a change in the ventricular EGM morphology
(near or far-field) and QRS duration that may indicate a change in
capture or a dislodgement to trigger the start of a test. A control
template is stored for comparison purposes.
[0073] In the event that a remote test or a firmware-initiated test
discovers a LOC event at any of the pacing sites, a patient alert
will be generated via the system as is known and used in the
art.
[0074] The default setting will be for the algorithm to run a
verification test first and run a PTS only if indicated by the
results of the verification test. The aggressiveness of the test is
tiered, wherein the verification test is relatively less aggressive
(e.g., by not changing any therapy delivery and only looking at
sensing events) as compared to the PTS where pacing outputs are
changed (at one, both or additional electrodes) while pacing can be
suspended on one or the other electrodes. The sequence of tests can
be programmable, thus can be set up for a different sequence as
preferred by the clinician. For example, the in-office test may be
a PTS only.
[0075] Once a test is initiated, the first step is to assure that
the underlying conditions permit the test to run successfully. For
the initial verification test that looks for sense events during
bi-ventricular pacing with a few previously defined abort
conditions. As the test grows in aggressiveness, new or more
stringent requirements for the patient's intrinsic rhythm threshold
or criteria can be required before the test begins. In general,
however, the intrinsic heart rate (HR) must be low enough to permit
overdrive pacing of the heart (e.g., HR at or below 100 bpm). Any
detected heart rate variability (HRV) should also be of
sufficiently low magnitude to allow overdrive pacing. For example,
HRV can be represented as a departure from a nominal P-P, R-R
interval or the like. The algorithm also should be able to define a
test window that will discriminate between test beats and fusion
beats. If the AV interval Is very short, or very long, premature
ventricular beats may be used to allow differentiation between
fusion and test pacing stimulus delivery. Also, atrial overdrive
pacing may be necessary in the case of threshold testing. In the
case of using EGM senses in the 40-280 ms window for confirmation,
atrial overdrive pacing is likely not needed.
[0076] Once all of the predefined criteria are met, the selected
test starts.
[0077] A verification test (level 1) will only confirm that capture
is occurring at the currently programmed settings. It will also
evaluate if a sense event can actually occur at each electrode to
eliminate possible lead dislodgement as a reason for not detecting
a depolarization event. Typically, the pacing outputs are not be
reprogrammed nor is therapy altered as a result of this level of
the test. The verification test (level 1) can be used to evaluate
sense events on each of the EGMs obtained during bi-ventricular
pacing, although less than all EGMs can be utilized. If there is a
sense event in a window of approximately 40 to 280 ms after a
bi-ventricular pacing stimulus delivery, loss of capture is
suspected on the electrode that recorded the sense event. The user
can then program the response of the sense system at this point to
decide if a PTS is to be conducted. An alert is then set to occur
in a given manner and at a given time. In an analysis of
preexisting patient EGM data, the presence of a sense event within
this temporal window was completely (i.e., 100%) both sensitive and
specific to a lead problem related to either a higher threshold
being required, LOC, or lead dislodgement from a prior operable
location.
[0078] However, if an intrinsic deflection (a sensed event not
resulting from pacing therapy delivery) is not detected during the
bi-v portion of the test, confirmation of the ability to detect
such sensed events will be sought by looking for an intrinsic
deflection (a sensed event) on one of the pacing electrodes from a
pace generated on the other electrode (i.e., inter-ventricular
conduction) or by trying to determine if a conducted beat from the
atria is detected at each of the pacing sites. The intrinsic
conduction test is nominally conducted first. The AV interval is
temporarily prolonged (e.g., to approximately 300 ms) and sensed
events are sought. If sensing is not achievable at one of the
sites, then dislodgement is suspected and an alert is set. If there
is no intrinsic conduction within 300 ms, then the alternate
approach of single site pacing will be used. A sensed event on one
electrode will be sought from pacing at the other electrode. If no
sensed event is detected, then a maximum output pace is generated
at the pacing site. If no sense is yet detected, an alert is set
indicating a possible lead dislodgement on the sense electrode or a
possible threshold increase on the pace electrode. Each of the
electrode combinations will be evaluated, if necessary or
desirable. During this portion of the test there will be some
temporary changes to the therapy delivered to the patient.
[0079] In the event that both electrodes show the ability to detect
a sensed event (Le. no lead dislodgement) then a bi-ventricular
capture is confirmed by lack of a sense in the 40-280 ms temporal
window. The verification is complete. All parameters will be
restored after a completion of the verification test. A
bi-ventricular PTS can be conducted using the 40-280 ms sensing
window as a detector for the output that fails to capture at one of
the sites.
[0080] The PTS.
[0081] The PTS is an active test that seeks to define the capture
threshold in either the bi-v mode or at individual electrodes.
[0082] Bi-V test.
[0083] For a bi-ventricle test PTS, the output of both electrodes
are swept at the same time and a sensed event in the LOC window on
either of the electrodes would indicate the bi-V threshold. This
test works best in the case where the outputs are tied together and
the V-V pacing time is set to null (0).
[0084] Individual Electrodes.
[0085] In newer devices, outputs on each of the electrodes will be
set individually. In this case one electrode can be used as the
sensing electrode for capture at the other electrode. Other sensors
can also be used such as pressure, an accelerometer,
sonomicrometry, evoked response, etc. This a reasonably complex
portion of the algorithm and requires a host of criteria to be met
in order to have a test performed. It is in this case that a fusion
window ought to be defined in order to not mistaken an intrinsic
deflection as a pacing-capture event. The window of confirmation
needs to take into account that a fusion contraction (or beat) is
conducted from the atria. If the AV interval is very short or of
the same duration as the V-V interval, a premature ventricular pace
(approximately 100 ms early) can be used as the test pulse. The
test pulse is optionally, but not required, preceded by a train of
at least three paces. In this case, a detection of an intrinsic
deflection (a sensed event) in the window of 0 ms to the expiration
of the AV interval from a pace on the other electrode indicates a
capture confirmation. An output sweep conducted until a LOC is
detected. The pacing output of last capture is recorded and the
output of that electrode is set to that value plus, optionally, a
safety margin. The second electrode has the same test performed on
it as just described. During this portion of the search, the atrium
would be paced at the same time as the ventricles in order to
increase the detection window size and reduce the likelihood of a
conducted beat from the atrium being sensed as a successful capture
on one of the ventricular leads. Timing information related to the
conduction time between electrodes can be stored by the device and
used for reporting patient myocardial conduction status. Trends of
these conduction times will be maintained in order to detect any
clinically important changes in the patient's myocardial conduction
properties.
[0086] The PTS described herein allows for temporary alteration of
bi-ventricular pacing during performance of the PTS, pacing at one
of the ventricular sites will be turned off while the output sweep
on the other electrode is conducted.
[0087] A premature V test pace can be used if the AV interval is of
the same duration as the V-V interval. The capture detector can be
evoked response if this circuitry is available in the device or it
can be the sensing of an intrinsic deflection on the other
ventricular electrode combined with the appropriate timing
information which takes into account any conducted beats from the
atrium. Capture detectors can range from the evoked response
detector, the intrinsic deflection on another vector or electrode,
pressure changes due to a contraction, accelerometer disposed on or
about one or both ventricles, piezoelectric crystal, intra-cardiac
impedance, sonomicrometry, or any sensor which can detect a
mechanical or electrical activation.
[0088] As mentioned, a PTS test can also be triggered by the
clinician during an in-office evaluation and in this case the
verification test can be bypassed.
[0089] At least in part, some of the novel features of this present
invention relate to using the other electrode as a means to confirm
capture on the first electrode. The technique also uses an
algorithmic approach to sense and verify capture with different
level tests which have an increasing level of aggressiveness and
intervention.
[0090] The particular operating mode of the present invention is a
programmed or hard-wired sub-set of possible CRT delivery operating
modes, including bi-ventricular pacing whether involving
simultaneous V-V pacing stimulation (i.e., synchronized ventricular
pacing therapy delivery) or offset V-V pacing stimulation (e.g., in
an attempt to compensate for various cardiac conduction and/or
contractile defects). In addition, the invention can be used to
verify pacing capture of either one of an RV or an LV (and RA and
LA). As noted, the inventive algorithm advantageously helps confirm
the capture status of a pacing regimen by providing one of: a LOC
signal, a capture signal, or a "capture suspect" signal. Of course,
the methods according to the present invention are intended to be
stored as executable instructions on any appropriate computer
readable medium that provides control signals to effect the
technical result of the invention herein described and depicted,
although certain of the steps of the inventive methods may be
performed manually as well.
[0091] In the presently described and depicted embodiment of the
invention capture verification testing occurs on a daily basis,
however, the testing may occur based on a triggering signal (e.g.,
from a patient or clinician, from a hand-held programmer or the
like locally or remotely spaced from said patient). Upon
confirmation of capture of a cardiac chamber, a desired pacing
therapy delivery can be re-enabled and continue until: a loss of
capture occurs, a predetermined period of time elapses, a
mode-switch occurs to another pacing regimen (e.g., due to a
automated physiologic trigger, a programming change, etc.) or the
like. If a loss of capture in a ventricular chamber is detected it
could indicate one or more possible problems requiring remedial
action. For example, the pacing stimulus might be arriving too late
(e.g., during the refractory period of the chamber), the pacing
electrodes might have malfunctioned or become dislodged, an
elongated conductor within a medical electrical lead might have
been damaged, open- or short-circuited. Accordingly, in addition to
verifying pacing capture, the present invention optionally includes
capability for alerting a physician, clinician, patient, health
care provider or the like that pacing system interrogation might be
required. In addition, the configuration of the pacing system,
including collected patient data and physiologic parameters can be
stored for later retrieval thereby enhancing the likelihood of an
accurate assessment of the operating condition of the pacing
system.
[0092] In one form of the invention, following detection of
inappropriate or non-programmed operating conditions (e.g.,
including receipt of a LOC signal during CRT delivery) the pacing
therapy can be adjusted, discontinued or a mode switch performed to
another pacing modality which, for example might exclude the pacing
lead that produced the LOC signal. One aspect of this form of the
invention, upon receipt of a ventricular LOC signal an intended
bi-ventricular or uni-ventricular CRT delivery regimen is suspended
and an atrial-pacing only therapy is implemented (e.g., an AAI,
ADI, AAI/R, ADI/R and the like). That is, assuming that a patient's
A-V conduction remains relatively intact until such time as the
patient is able to receive qualified medical attention or until a
subsequent ventricular capture verification test indicates that
non-suspect capture has been achieved. In this regard, U.S. Pat.
No. 6,772,005 to Casavant et al. entitled "Preferred ADI/R: a
Permanent Pacing Mode to Eliminate Ventricular Pacing While
Maintaining Backup Support" which is assigned to Medtronic, Inc. is
hereby incorporated herein by reference in its entirety.
[0093] In addition, the present invention can operate in
non-tracking modes wherein for example, with a patient at rest
(based on a nominal activity sensor signal) a supraventricular
tachycardia (SVT) episode occurs. The SVT episode causes the atrial
channel of a dual-chamber IPG to sense a rapid (atrial) rate while
the input to ventricular sensor(s) indicates physical inactivity
and therefore no need to increase the pacing rate. The pacemaker
can use this information to make the diagnosis of SVT and activate
automatic mode switching to a nontracking mode (to control the
paced ventricular rate). Thus, the PTS and verification testing can
occur without relying on a stable HR, although the abort criteria
typically will preclude the operation of the PTS and verification
testing absent a stable HR and absence of HRV.
[0094] The patient may, in the best scenario, be relieved of pacing
therapy delivery altogether (programming the pacing circuitry to an
ODO monitoring-only "pacing modality"). Assuming the patient is not
chronotropically incompetent, normal sinus rhythm may emerge
permanently for all the activities of daily living. Additionally,
the process 600 may be employed to search for a change in
conduction status (e.g., wherein a later-to-depolarize ventricle
changes from the LV to the RV).
[0095] A few salient features of the automatic, ambulatory LV/RV
capture verification test according to the invention are described
below:
[0096] (1) The feature (e.g., "Automatic LV/RV Capture
Verification") will be selectably programmable by the user and no
other programmable parameters associated with the conduction test
sequences.
[0097] (2) A "patient alert" type selection can be optionally
provided (selectable on or off) associated with the results of the
LV/RV Capture Verification test sequences. Such an alert feature
includes a range of selectable options regarding when to sound the
alert (e.g., immediately after a negative test, based on diurnal
cycles such as in the morning or upon detection of patient activity
after a lengthy sedentary period, etc.) are within the purview of
the invention.
[0098] (3) In one form of the invention, the conduction test
sequences are applied at approximately the same (whether on a
daily-, weekly-, monthly-basis, etc.) for example at night when the
patient is sleeping. For the example described, the tests are
applied at 3:00 a.m.
[0099] (4) The conduction test sequence with generally be withheld
in the event that the patient's then-current heart rhythm supports
running the test (e.g., no atrial or ventricular tachycardia
episodes in progress at the time when the test starts or while the
test sequences are running, the atrial rate is relatively low, and
the patient is currently paced in the ventricle).
[0100] (5) For example, every night at approximately 3:00 a.m. the
device initiates the conduction test sequence. The first step is to
measure the time interval between an atrial event to an
antegrade-conducted RV sense (referred to as "PR interval" herein).
This is done by setting a relatively long AV interval (e.g., 400
ms) for one cardiac cycle and measuring the time between said
A-event and the associated v-event (i.e., an RV sensed event). If a
ventricular pace (VP) occurs, it indicates that the patient likely
has some degree of AV block. The PR interval used for an algorithm
according to the invention (see below) will be set to the
programmed AV interval in this case.
[0101] (6) The device is then programmed to LV-only pacing for one
cardiac cycle with a relatively short, or minimum, AV interval.
Then, one of the following two results are obtained, with the
concomitant response(s).
[0102] a. No sense RV-event: If an RV-event is not sensed prior to
the next scheduled ventricular pace (VP), it implies "loss of
capture" (LOC) because there is no conduction from the LV paced
event to the RV--assuming that RV sensing components and circuitry
are not an issue. For completeness, other cardiac pacing system
features are available and will be provided to alert the clinician
to this possibility (but such features are not relevant to the
present invention). However, the inventors posit that there exists
a rare possibility that a premature ventricular contraction (PVC)
may have occurred around the time of the LV pace event (pacing
stimulus delivery to the LV) in which case no RV sense event can
occur due to the LV pace event (and, in particular, the associated
sensing-channel blanking typically imposed upon delivery of the LV
pacing stimulus). To address this unlikely situation step (6) is
again performed. If an RV sense event is still not recorded, then a
"loss of capture" (LOC) output signal is issued as the test result.
If an RV-sense event is recorded, then the method proceeds to
option b. (immediately below).
[0103] b.) RV sense event recorded: If an RV sense event is
recorded prior to the next LV pace, it could mean that it came from
(A) an intrinsically-conducted PR interval (from an A-event), or
(B) a conducted inter-ventricular event (i.e., a conducted LV pace
event that conducts to the RV), or (C) a PVC.
[0104] i.) Criteria for recording a relatively `early` RV sense
event: If the time interval from an A-event to an R-sense event
(referred to herein as a "Test PR") is less than or equal to the PR
Interval less about 40 milliseconds (i.e., PR Interval--40 ms),
then the event could either represent scenario (B) or (C) above. In
this situation, step (6) is again repeated. If the just-described
pattern manifests itself again, then ventricular pacing capture is
verified (i.e., case (B) is confirmed). Such a verification and
confirmation appears reasonable because the likelihood that a PVC
might occur again at the same exact time interval is highly
unlikely and can be safely ignored. However, if the pattern is not
repeated again, then the prior RV-sensed event in fact represents a
PVC and the current A event to RV sense interval requires attention
by applying the following criteria and steps.
[0105] ii.) Criteria for recording of an "on time" RV sense event:
If an RV sense event is recorded prior to the next LV pace (on the
same cardiac cycle) and the Test PR interval is greater than the PR
Interval less 40 milliseconds (i.e., PR Interval--40 ms), then the
RV sense event comprises either: (A) a situation wherein the LV has
lost pacing capture (LOC) or (A') where the LV-RV inter-ventricular
interval is greater than the PR interval or (B) a situation wherein
the LV-RV inter-ventricular interval is approximately the same as
the PR interval. Since the inventors recognize that empirically
(i.e., from data gathered from the MIRACLE ICD trial) data has
shown that interventricular intervals (e.g., LVP to RVS interval)
times are rarely, if ever, greater than about 280 milliseconds.
[0106] Applying these values, then in the event that the Test PR is
greater than 310 ms (i.e., equal to the programmed AV delay
interval plus the LVP-RVS interventricular conduction time), then
the result of the conduction test is a "loss of capture" (LOC)
conclusion.
[0107] Conversely, if the Test PR is less than or equal to 310
milliseconds then the results of the conduction test is a "capture
is suspect." Both the PR Interval and the Test PR Interval are then
optionally stored into a histogram, a trend log or the like.
[0108] (7) If the result of the conduction test sequence is
"capture is suspect," then the recent or previous recorded history
of the patient can be used to determine if the loss of capture
(LOC) result is more or less likely. Accordingly, if ventricular
capture has been verified in the recent past and the presently
applied Test PR Interval is much larger than previous Test PR
Interval (e.g., on the order of about 60 ms larger or different,
then "loss of capture" (LOC) is the result of the conduction test
sequence.
[0109] (8) If a patient alert feature has been programmed to issue
upon an LOC result, then an alert will be sounded at the programmed
time. Such a patient alert can comprise any of a variety of
apparatus and circuitry intended to gain the attention of a
patient. Some examples include a haptic or vibratory alert wherein
a crystal or other structure disposed within an implantable medical
device oscillates or moves, an audible alert, and/or activation of
visual cues signaling an alert event. The alert message can be sent
wirelessly to remote stations or adjacent hardware so that the
patient and/or other personnel also receive the alert message.
[0110] (9) the foregoing steps (5) through (7) can be repeated
every night or on an otherwise periodic or aperiodic basis.
[0111] Some of the key elements of the inventive algorithm just
described are depicted and described with reference to an exemplary
embodiment shown in the flowchart appended hereto (e.g., FIG. 4).
The exemplary embodiment illustrates LV capture verification and
pacing threshold search (PTS) testing. Of course, a similar
flowchart also applies for RV capture verification (e.g., by
switching to RV-only pacing in lieu of LV-only pacing) and can be
applied for at least one cardiac cycle. The inventive conduction
test sequence can be run during atrial overdrive pacing. Such
overdrive pacing is known in the art and results in an increase of
the length of the interval between a preceding A-event and an
associated, conducted V-sense event.
[0112] Now referring to FIG. 4, a method 400 according to an
embodiment of the invention is depicted. The method 400 includes
two major paths or branches; namely verification testing 402 and
the PTS test 404.
[0113] With respect to verification testing 402, following a test
initiation step 406 wherein the various components of a system for
carrying out the invention are checked (e.g., the operative
firmware and/or software, the device programming instrument for
wirelessly communicating with an implantable medical device such a
CRT delivery platform, any remote communication links, etc.).
Following step 406 the test module 402 of method 400 enters
decision step 408 wherein certain test abort criteria are checked.
As noted herein the abort criteria can include a variety of items
which ought to be satisfied before the test module 402 can proceed.
However, the abort criteria can depend at least in part on whether
the test is being triggered remotely (e.g., via the Medtronic
CareLink.RTM. network) or in a clinic-type setting. In addition, if
the test module 402 occurs in a nontracking CRT mode or pacing mode
(i.e., a mode which essentially ignores atrial events, usually due
to the presence of a high rate atrial tachycardia such as a
supraventricular tachycardia or SVT). If the abort criteria causes
a failure the test module 402 can revert to the initiate test step
406 with re-attempts to perform the test module 402 thereafter on a
periodic basis. If the abort criteria does not cause a failure then
at step 410 a primary, or level I, test occurs. In the level I test
substantially simultaneous bi-ventricular pacing therapy is
provided to each ventricle and each ventricle is monitored for
evoked activation during a window of time that reveals whether the
dual pacing stimulation captured both ventricles. The window is
nominally set of approximately 40 ms to about 280 ms and assuming
no sensed, or detected, ventricular events during that window the
result of step 410 is negative and the verification test ends at
414. If step 410 results in a sensed ventricular event during the
window then the level I test is affirmative and a level II test
commences at step 412.
[0114] In the level II test alternating LV and RV pacing
stimulation is provided (at relatively short AV intervals) while
the non-paced ventricle is monitored for inter-ventricular
conduction, which indicate capture of the paced ventricle. If
capture is declared at step 416 then the test ends at step 414. If
LOC is declared (or suspect capture is declared), then at step 418
an optional PTS test is invoked (at step 424). If the optional PTS
test is declined then an alert is set at step 420 and the test ends
at step 414. The alert can include all relevant present and/or
prior verification testing details and the settings of the IPG and
patient information, and the like.
[0115] Following or in lieu of performing verification test module
402, a PTS test module 404 can be performed beginning with a preset
abort (test) criteria step at 424. As before, if the PTS module 404
fails at 424 then the PTS test can be re-attempted or retried at a
later time. Assuming that abort criteria 424 are not satisfied then
an iterative threshold testing regimen begins at step 426 wherein
both or just one of the RV and LV can be tested to provide a pacing
threshold of sufficient energy to capture the RV and/or LV. If just
one of the LV or RV is to be tested then at step 428 the pacing
stimulation to the non-threshold testing ventricle is turned off
(with an appropriate time-out function). If both the LV and the RV
are to be tested then at step 430 the process flow causes steps
428-442 to be performed serially (for each ventricle). As depicted,
in FIG. 4 the process flow for LV threshold testing is illustrated
(with the RV shown in brackets [RV to indicate the switch for RV
threshold testing. At step 432 for LV [RV] testing at the
then-present pacing energy threshold the RV is monitored for
activation of the LV. If the LV activates then at step 434 the
pacing energy is decremented until LOC is declared and then
increased until capture is restored in an iterative series of
cardiac cycles. The decrement (or increment) can include any
reasonable magnitude of energy and can include one or more of pulse
width, pulse amplitude, polarity, frequency, and the like. In one
embodiment the pulse amplitude is incremented and each increment or
decrement equals a nominal 0.5V.
[0116] The so-called scan/sweep of pacing energy thus provides a
pacing threshold for one or both ventricles. The pacing energy can
differ between the ventricles due to a number of physiologic and
pacing electrode conditions. If step 434 fails to provide a pacing
threshold with a cognizable value then an out-of-range message is
logged and/or communicated at step 438 and an alert is set and
pacing output set to a maximum allowable value at step 440. On the
other hand, if the step 432 provides in-range values for pacing
thresholds for the LV and/or RV then at step 436 the pacing output
is set to a value (that can optionally include a so-called safety
margin) for chronic pacing therapy delivery and the PTS module 404
ends at step 442.
[0117] In addition, a programmable bi-ventricular parameter
defining V-V conduction time can be supplied to and used by the
inventive algorithm. Such a conduction time can be set to a
worst-case default value (e.g., 280 ms), and thereafter be
user-adjusted or programmable by the user or clinician to render
the test results more determinate for patients with relatively
"shorter" PR intervals and relatively "longer" V-V intervals.
[0118] Devices incorporating the methods according to the invention
can advantageously store and display trend, histogram and/or other
information regarding capture verification tests, failing test
results and results for the last few months and other data related
thereto. When such data is displayed in a histogram format a
clinician or patient can perhaps more readily comprehend the
meaning of the data, so this type of display is favored, especially
for patient display. This data would be transmitted over a
hospital-, clinic-, and/or patient-adapted information network
(e.g., such as the Medtronic Medtronic CareLink.RTM. network) with
triggers and alerts triggered by `Capture Verification Suspect` and
LOC results to alert one or more clinicians viewing the patient
data remotely.
[0119] The same algorithm can be adapted slightly and
advantageously applied for easy-to-use in and a clinic or physician
office to verify LV and RV capture or to facilitate ambulatory LV
and RV capture management (e.g., if ventricular capture is deemed
to be "lost," the same algorithm is then applied at different
pacing output strength to automatically determine, and program, a
new pacing output at which assures ventricular pacing capture).
[0120] It should be understood that, certain of the above-described
structures, functions and operations of the pacing systems of the
illustrated embodiments are not necessary to practice the present
invention and are included in the description simply for
completeness of an exemplary embodiment or embodiments. It will
also be understood that there may be other structures, functions
and operations ancillary to the typical operation of an implantable
pulse generator that are not disclosed and are not necessary to the
practice of the present invention. In addition, it will be
understood that specifically described structures, functions and
operations set forth in the above-referenced patents can be
practiced in conjunction with the present invention, but they are
not essential to its practice. It is therefore to be understood,
that within the scope of the appended claims, the invention may be
practiced otherwise than as specifically described without actually
departing from the spirit and scope of the present invention.
* * * * *