U.S. patent application number 13/076250 was filed with the patent office on 2011-07-21 for techniques for promoting biventricular synchrony and stimulation device efficiency using intentional fusion.
This patent application is currently assigned to PACESETTER, INC.. Invention is credited to Paul A. Levine, Xing Pei.
Application Number | 20110178567 13/076250 |
Document ID | / |
Family ID | 43928334 |
Filed Date | 2011-07-21 |
United States Patent
Application |
20110178567 |
Kind Code |
A1 |
Pei; Xing ; et al. |
July 21, 2011 |
TECHNIQUES FOR PROMOTING BIVENTRICULAR SYNCHRONY AND STIMULATION
DEVICE EFFICIENCY USING INTENTIONAL FUSION
Abstract
A method includes providing an optimal interventricular
interval, determining an atrio-ventricular conduction delay for the
ventricle having faster atrio-ventricular conduction, determining
an interventricular conduction delay and determining an advance
atrio-ventricular pacing interval, for use in pacing the ventricle
having slower atrio-ventricular conduction, based at least in part
on the optimal interventricular interval and the interventricular
conduction delay.
Inventors: |
Pei; Xing; (Thousand Oaks,
CA) ; Levine; Paul A.; (Santa Clarita, CA) |
Assignee: |
PACESETTER, INC.
Sylmar
CA
|
Family ID: |
43928334 |
Appl. No.: |
13/076250 |
Filed: |
March 30, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12055166 |
Mar 25, 2008 |
7941217 |
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13076250 |
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Current U.S.
Class: |
607/25 |
Current CPC
Class: |
A61N 1/365 20130101;
A61N 1/3622 20130101 |
Class at
Publication: |
607/25 |
International
Class: |
A61N 1/365 20060101
A61N001/365 |
Claims
1. A method comprising: providing an optimal interventricular
interval (VV.sub.Opt); setting an atrio-ventricular interval for
the right ventricle (AV.sub.RV or PV.sub.RV); delivering
stimulation to the right ventricle and sensing cardiac activity of
the left ventricle; extending an atrio-ventricular interval for the
left ventricle (AV.sub.LV or PV.sub.LV); and if the extending
results in atrio-ventricular conduction of an atrial event that
causes depolarization of the left ventricle, then determining an
advance atrio-ventricular pacing interval for the right ventricle
(AV.sub.RV advance or PV.sub.RV advance) based on the optimal
interventricular interval (VV.sub.Opt), the delivering and the
sensing, and the extending.
2. The method of claim 1 further comprising diagnosing left bundle
branch block (LBBB) if the extending does not result in
atrio-ventricular conduction of an atrial event that causes
depolarization of the left ventricle.
3. The method of claim 1 wherein delivery of stimulation to the
right ventricle according to the advance atrio-ventricular pacing
interval (AV.sub.RV advance or PV.sub.RV advance) fuses with
depolarization of the left ventricle.
4. The method of claim 1 further comprising sensing cardiac
activity and preventing delivery of stimulation to the right
ventricle if the sensing detects depolarization of the right
ventricle during the advance atrio-ventricular pacing interval
(AV.sub.RV advance or PV.sub.RV advance).
5. A method comprising: providing an optimal interventricular
interval (VV.sub.Opt); setting an atrio-ventricular interval for
the left ventricle (AV.sub.LV or PV.sub.LV); delivering stimulation
to the left ventricle and sensing cardiac activity of the right
ventricle; extending an atrio-ventricular interval for the right
ventricle (AV.sub.RV or PV.sub.RV); if the extending results in
atrio-ventricular conduction of an atrial event that causes
depolarization of the right ventricle, then determining an advance
atrio-ventricular pacing interval for the left ventricle (AV.sub.LV
advance or PV.sub.LV advance) based on the optimal interventricular
interval (VV.sub.Opt), the delivering and the sensing, and the
extending.
6. The method of claim 5 further comprising diagnosing right bundle
branch block (RBBB) if the extending does not result in
atrio-ventricular conduction of an atrial event that causes
depolarization of the right ventricle.
7. The method of claim 5 wherein delivery of stimulation to the
left ventricle according to the advance atrio-ventricular pacing
interval (AV.sub.LV advance or PV.sub.LV advance) fuses with
depolarization of the right ventricle.
8. The method of claim 5 further comprising sensing cardiac
activity and preventing delivery of stimulation to the left
ventricle if the sensing detects depolarization of the left
ventricle during the advance atrio-ventricular pacing interval
(AV.sub.LV advance or PV.sub.LV advance).
9. A method comprising: overdriving the intrinsic atrial rate at an
atrial overdrive rate; shortening an atrio-ventricular interval for
a ventricle with at least some degree of atrio-ventricular
conduction block until shortening of the atrio-ventricular delay
for the other ventricle occurs; determining an interventricular
conduction delay (IVCD) from the ventricle with at least some
degree of atrio-ventricular conduction block to the other ventricle
for the atrial overdrive rate; lengthening the atrio-ventricular
interval for the ventricle with at least some degree of
atrio-ventricular conduction block until a change occurs in the
atrio-ventricular delay for the other ventricle to thereby
determine an atrio-ventricular delay for that ventricle for the
atrial overdrive rate; decreasing the atrial rate until majority
sensing occurs to determine an intrinsic atrial rate; and
determining an advance atrio-ventricular pacing interval (AV
advance or PV advance) for the ventricle with at least some degree
of atrio-ventricular conduction block.
10. The method of claim 9 further comprising performing a
sensitivity analysis prior to the determining an advance
atrio-ventricular pacing interval (AV advance or PV advance).
11. The method of claim 10 wherein the sensitivity analysis
shortens and then lengthens an atrio-ventricular interval for the
ventricle with at least some degree of atrio-ventricular conduction
block and, in response, measures the atrio-ventricular interval for
the other ventricle.
12. The method of claim 10 wherein the sensitivity analysis seeks
an atrio-ventricular interval for the ventricle with at least some
degree of atrio-ventricular conduction block where adjustments to
the atrio-ventricular interval have minimal effect on the
atrio-ventricular interval of the other ventricle.
13. The method of claim 9 wherein delivery of stimulation to the
ventricle according to the advance atrio-ventricular pacing
interval fuses (AV advance or PV advance) with depolarization of
the other ventricle.
14. The method of claim 9 further comprising sensing cardiac
activity and preventing delivery of stimulation to the ventricle
with at least some degree of atrio-ventricular conduction block if
the sensing detects depolarization of that ventricle during the
advance atrio-ventricular pacing interval (AV advance or PV
advance).
Description
RELATED APPLICATIONS
[0001] This application is a division of U.S. patent application
Ser. No. 12/055,166, filed Mar. 25, 2008, entitled "Techniques for
Promoting Biventricular Synchrony and Stimulation Device Efficiency
Using Intentional Fusion," now U.S. Pat. No. ______, which is
related to U.S. patent application Ser. No. 10/703,070, filed Nov.
5, 2003, entitled "Method for Ventricular Pacing," now abandoned,
and to U.S. patent application Ser. No. 10/980,140, filed Nov. 1,
2004, entitled "Methods for Ventricular Pacing Using Interference,"
now abandoned.
TECHNICAL FIELD
[0002] Subject matter presented herein generally relates to cardiac
pacing therapy and, in particular, to optimizing ventricular
pacing.
BACKGROUND
[0003] Clinical studies related to cardiac pacing have shown that
an optimal atrio-ventricular delay (e.g., AV delay) and/or an
optimal interventricular delay (e.g., VV delay) can improve cardiac
performance. For example, given an optimal VV delay, cardiac
resynchronization therapy (CRT) can deliver electrical stimulation
to the heart at a right ventricular site (e.g., apex or
interventricular septum) and then deliver electrical stimulation to
the heart at a left ventricular site (e.g., postero-lateral wall)
to improve mechanical dyssynchrony associated with an intrinsic
abnormal ventricular activation pattern (e.g., due to left bundle
branch block). With respect to AV delay, simply setting a CRT
device's AV delay to a value less than a patient's intrinsic
conduction time (i.e., to reduce competition from intrinsic
activity with delivered electrical stimuli to the ventricles) is
not necessarily optimal as results from the DAVID trial indicate
that an excessively short AV delay can cause potentially
detrimental, unnecessary ventricular pacing. Similarly, an overly
long AV delay can be as counterproductive as an overly short AV
delay for patients with intact nodal AV condition. Indeed, a truly
optimal AV delay may cause CRT to deliver optimal intermittent
ventricular pacing (i.e., an AV delay that is not too short and not
too long).
[0004] Optimization of an AV delay and/or a VV delay often occurs
at implantation. However, what is "optimal" for an AV delay and/or
a VV delay depends on a variety of factors that may vary over time.
Hence, sometimes, re-optimization of a delay or delays occurs
during a follow-up consultation. While such optimizations are
beneficial, the benefits may not be long lasting due to changes in
various factors related to device condition, cardiac function,
patient behavior, etc. Such factors may change unpredictably
between consultations. Further, as the period between consultations
increases, the chances that a patient's CRT is using suboptimal
delays increases.
[0005] As described herein, various exemplary methods, devices,
systems, etc., aim to determine and/or adjust AV delay, VV delay
and/or other inter-chamber delays. Particular techniques involving
such delays are presented for intentional fusion where one
ventricle can be activated via an atrial to ventricular conducted
depolarization and where the other ventricle is activated via
artificially delivered electrical stimulation. Such techniques may
use an optimal AV delay that is neither too short nor too long and
that allows for intermittent ventricular pacing.
SUMMARY
[0006] An exemplary method includes providing an optimal
interventricular interval, determining an atrio-ventricular
conduction delay for the ventricle having faster atrio-ventricular
conduction, determining an interventricular conduction delay and
determining an advance atrio-ventricular pacing interval, for use
in pacing the ventricle having slower atrio-ventricular conduction,
based at least in part on the optimal interventricular interval and
the interventricular conduction delay. Other exemplary methods,
devices, systems, etc., are also disclosed. In general, the various
methods, devices, systems, etc., described herein, and equivalents
thereof, are suitable for use in a variety of pacing therapies
and/or other cardiac related therapies.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] Features and advantages of the described implementations can
be more readily understood by reference to the following
description taken in conjunction with the accompanying
drawings.
[0008] FIG. 1 is a simplified diagram illustrating an exemplary
implantable stimulation device in electrical communication with at
least three leads implanted into a patient's heart and at least one
other lead for delivering stimulation and/or shock therapy. Other
devices with fewer leads may also be suitable in some
circumstances.
[0009] FIG. 2 is a functional block diagram of an exemplary
implantable stimulation device illustrating basic elements that are
configured to provide cardioversion, defibrillation, pacing
stimulation and/or other tissue and/or nerve stimulation. The
implantable stimulation device is further configured to sense
information and administer stimulation pulses responsive to such
information.
[0010] FIG. 3 is a series of waveforms related to native cardiac
activity and cardiac activity responsive to artificial electrical
stimulation.
[0011] FIG. 4 is an approximate anatomical diagram of a heart and
two waveforms that exhibit a paced interventricular conduction
delay (PIVCD).
[0012] FIG. 5 is an intracardiac electrogram (IEGM) that includes a
waveform associated with the right ventricle and a waveform
associated with the left ventricle that may be used to determine a
paced interventricular conduction delay (PIVCD) or an
interventricular delay (A). The IEGM was acquired using a unipolar
sensing arrangement for a right ventricular tip electrode and a
left ventricular tip electrode having a common electrode.
[0013] FIG. 6 is an intracardiac electrogram (IEGM) acquired in a
study using an implantable device that included a switchable
channel for RV and LV sensing and/or pacing. The IEGM shows
activation of one ventricle in response to stimulation delivered to
the other ventricle; such an IEGM may be used to measure a paced
interventricular conduction delay (PIVCD).
[0014] FIG. 7 is a series of electrograms for native conduction and
for various atrio-ventricular delays (AV delay) where fusion occurs
at one of the AV delays.
[0015] FIG. 8 is a series of electrograms for intrinsic activity,
for right ventricular pacing and for intentional fusion.
[0016] FIG. 9 is a block diagram of an exemplary method for
determining an AV or PV delay.
[0017] FIG. 10 is a block diagram of an exemplary method for
delivering a stimulation therapy that aims to promote
bi-ventricular synchrony.
[0018] FIG. 11 is a block diagram of an exemplary method for
determining various values for use in determining a rate adaptive,
advance AV or PV delay.
[0019] FIG. 12 is a block diagram of an exemplary method that
includes various scenarios where therapy may delivery stimulation
to both ventricle or to only a single ventricle.
[0020] FIG. 13 is a block diagram of an exemplary method that
relies on information sensed during an alert period to determine
whether bi-ventricular pacing or single ventricle pacing should
occur.
[0021] FIG. 14 is a block diagram of various exemplary methods for
adjusting one or more parameters with respect to patient activity
state.
DETAILED DESCRIPTION
Overview
[0022] Exemplary methods, devices, systems, etc., described herein
pertain generally to ventricular pacing. For example, various
exemplary methods include deciding whether to use ventricular
pacing and, if so, whether to pace in a single ventricle or in both
ventricles. If such a method decides that ventricular pacing is
appropriate, then the method may also determine an
atrio-ventricular delay for one or both ventricles. For the case of
bi-ventricular pacing, the method may determine an
atrio-ventricular delay for each ventricle and/or an
interventricular delay (e.g., which may be inherent in the use of
two atrio-ventricular delay times). For the case where a single
ventricle is paced, a method may determine values for one or more
pacing parameters to cause intentional fusion. Such techniques may
reduce frequency of ventricular or bi-ventricular pacing and/or
enhance cardiac performance. Further, such techniques may optimize
pacing as a function of time or in response to changes in any of a
variety of factors related to cardiac and/or device
performance.
[0023] The following description begins with a discussion of
exemplary implantable devices and associated components followed by
a discussion of heart rhythms and associated waveforms. Next, a
discussion of cardiac performance follows, and the detailed
description continues with a discussion of various exemplary
methods, devices, systems, etc.
Exemplary Stimulation Device
[0024] The techniques described below are intended to be
implemented in connection with any stimulation device that is
configured or configurable to stimulate nerves and/or stimulate
and/or shock a patient's heart.
[0025] FIG. 1 shows an exemplary stimulation device 100 in
electrical communication with a patient's heart 102 by way of three
leads 104, 106, 108, suitable for delivering multi-chamber
stimulation and shock therapy. The leads 104, 106, 108 are
optionally configurable for delivery of stimulation pulses suitable
for stimulation of autonomic nerves. In addition, the device 100
includes a fourth lead 110 having, in this implementation, three
electrodes 144, 144', 144'' suitable for stimulation and/or
sensing. Such a lead may be positioned epicardially for cardiac
stimulation and/or sensing.
[0026] The right atrial lead 104, as the name implies, is
positioned in and/or passes through a patient's right atrium. The
right atrial lead 104 optionally senses atrial cardiac signals
and/or provide right atrial chamber stimulation therapy. As shown
in FIG. 1, the stimulation device 100 is coupled to an implantable
right atrial lead 104 having, for example, an atrial tip electrode
120, which typically is implanted in the patient's right atrial
appendage. The lead 104, as shown in FIG. 1, also includes an
atrial ring electrode 121. Of course, the lead 104 may have other
electrodes as well.
[0027] To sense atrial cardiac signals, ventricular cardiac signals
and/or to provide chamber pacing therapy, particularly on the left
side of a patient's heart, the stimulation device 100 is coupled to
a coronary sinus lead 106 designed for placement in the coronary
sinus and/or tributary veins of the coronary sinus. Thus, the
coronary sinus lead 106 is optionally suitable for positioning at
least one distal electrode adjacent to the left ventricle and/or
additional electrode(s) adjacent to the left atrium. In a normal
heart, tributary veins of the coronary sinus include, but may not
be limited to, the great cardiac vein, the left marginal vein, the
left posterior ventricular vein, the middle cardiac vein, and the
small cardiac vein.
[0028] Accordingly, an exemplary coronary sinus lead 106 is
optionally designed to receive atrial and ventricular cardiac
signals and to deliver left ventricular pacing therapy using, for
example, at least a left ventricular tip electrode 122, left atrial
pacing therapy using at least a left atrial ring electrode 124, and
shocking therapy using at least a left atrial coil electrode 126.
For a complete description of a coronary sinus lead, the reader is
directed to U.S. Pat. No. 5,466,254, "Coronary Sinus Lead with
Atrial Sensing Capability" (Helland), which is incorporated herein
by reference.
[0029] Stimulation device 100 is also shown in electrical
communication with the patient's heart 102 by way of an implantable
right ventricular lead 108 having, in this exemplary
implementation, a right ventricular tip electrode 128, a right
ventricular ring electrode 130, a right ventricular (RV) coil
electrode 132, and an SVC coil electrode 134. Typically, the right
ventricular lead 108 is transvenously inserted into the heart 102
to place the right ventricular tip electrode 128 in the right
ventricular apex so that the RV coil electrode 132 will be
positioned in the right ventricle and the SVC coil electrode 134
will be positioned in the superior vena cava. Accordingly, the
right ventricular lead 108 is capable of sensing or receiving
cardiac signals, and delivering stimulation in the form of pacing
and shock therapy to the right ventricle.
[0030] FIG. 2 shows an exemplary, simplified block diagram
depicting various components of stimulation device 100. The
stimulation device 100 can be capable of treating both fast and
slow arrhythmias with stimulation therapy, including cardioversion,
defibrillation, and pacing stimulation. While a particular
multi-chamber device is shown, it is to be appreciated and
understood that this is done for illustration purposes only. For
example, various methods may be implemented on a pacing device
suited for single ventricular stimulation and not bi-ventricular
stimulation. Thus, the techniques and methods described below can
be implemented in connection with any suitably configured or
configurable stimulation device.
[0031] Housing 200 for stimulation device 100 is often referred to
as the "can", "case" or "case electrode", and may be programmably
selected to act as the return electrode for all "unipolar" modes.
Housing 200 may further be used as a return electrode alone or in
combination with one or more of the coil electrodes 126, 132 and
134 for shocking purposes. Housing 200 further includes a connector
(not shown) having a plurality of terminals 201, 202, 204, 206,
208, 212, 214, 216, 218, 221 (shown schematically and, for
convenience, the names of the electrodes to which they are
connected are shown next to the terminals).
[0032] To achieve right atrial sensing and/or pacing, the connector
includes at least a right atrial tip terminal (A.sub.R TIP) 202
adapted for connection to the atrial tip electrode 120. A right
atrial ring terminal (A.sub.R RING) 201 is also shown, which is
adapted for connection to the atrial ring electrode 121. To achieve
left chamber sensing, pacing and/or shocking, the connector
includes at least a left ventricular tip terminal (V.sub.L TIP)
204, a left atrial ring terminal (A.sub.L RING) 206, and a left
atrial shocking terminal (A.sub.L COIL) 208, which are adapted for
connection to the left ventricular tip electrode 122, the left
atrial ring electrode 124, and the left atrial coil electrode 126,
respectively. In instances where the device is configured to
stimulate nerve or non-cardiac tissue (e.g., via lead 110), an
electrode (e.g., 144, 144', 144'') may be connected to the device
via any suitable terminal (e.g., the terminal S ELEC 221 may
provide for nerve stimulation).
[0033] To support right chamber sensing, pacing and/or shocking,
the connector further includes a right ventricular tip terminal
(V.sub.R TIP) 212, a right ventricular ring terminal (V.sub.R RING)
214, a right ventricular shocking terminal (RV COIL) 216, and a
superior vena cava shocking terminal (SVC COIL) 218, which are
adapted for connection to the right ventricular tip electrode 128,
right ventricular ring electrode 130, the RV coil electrode 132,
and the SVC coil electrode 134, respectively.
[0034] At the core of the stimulation device 100 is a programmable
microcontroller 220 that controls the various modes of stimulation
therapy. In the example of FIG. 2, the microcontroller 220 includes
a microprocessor, or equivalent control circuitry, designed
specifically for controlling the delivery of stimulation therapy,
and may further include RAM or ROM memory, logic and timing
circuitry, state machine circuitry, and I/O circuitry. Typically,
the microcontroller 220 includes the ability to process or monitor
input signals (data or information) as controlled by a program code
stored in a designated block of memory. The type of microcontroller
is not critical to the described implementations. Rather, any
suitable microcontroller may be used that carries out the functions
associated with one or more of the exemplary methods described
herein.
[0035] Representative types of control circuitry that may be used
in connection with the described embodiments can include the
microprocessor-based control system of U.S. Pat. No. 4,940,052
(Mann et al.), the state-machine of U.S. Pat. Nos. 4,712,555
(Thornander) and 4,944,298 (Sholder), all of which are incorporated
by reference herein. For a more detailed description of the various
timing intervals used within the stimulation device and their
inter-relationship, see U.S. Pat. No. 4,788,980 (Mann et al.), also
incorporated herein by reference.
[0036] FIG. 2 also shows an atrial pulse generator 222 and a
ventricular pulse generator 224 that generate pacing stimulation
pulses for delivery by the right atrial lead 104, the coronary
sinus lead 106, and/or the right ventricular lead 108 via an
electrode configuration switch 226. It is understood that in order
to provide stimulation therapy in each of the four chambers of the
heart (or to autonomic nerves or other tissue) the atrial and
ventricular pulse generators, 222 and 224, may include dedicated,
independent pulse generators, multiplexed pulse generators, or
shared pulse generators. The pulse generators 222 and 224 are
controlled by the microcontroller 220 via appropriate control
signals 228 and 230, respectively, to trigger or inhibit the
stimulation pulses.
[0037] Microcontroller 220 further includes timing control
circuitry 232 to control the timing of the stimulation pulses
(e.g., pacing rate, atrio-ventricular (e.g., AV) delay, atrial
interconduction (AA) delay, or ventricular interconduction (VV)
delay, etc.) as well as to keep track of the timing of refractory
periods, blanking intervals, noise detection windows, evoked
response windows, alert intervals, marker channel timing, etc.,
which is well known in the art.
[0038] Microcontroller 220 further includes an arrhythmia detector
234, a morphology detector 236, and optionally an orthostatic
compensator and a sensor module such as but not limited to minute
ventilation (MV) response, the latter two are not shown in FIG. 2.
These components can be utilized by the stimulation device 100 for
determining desirable times to administer various therapies,
including those to reduce the effects of orthostatic hypotension.
The aforementioned components may be implemented in hardware as
part of the microcontroller 220, or as software/firmware
instructions programmed into the device and executed on the
microcontroller 220 during certain modes of operation.
[0039] Microcontroller 220 further includes a synchronization
module 238 for performing a variety of tasks related to ventricular
synchrony. This component can be utilized by the stimulation device
100 for determining desirable times to administer various
therapies, including, but not limited to, ventricular stimulation
therapy, biventricular stimulation therapy, resynchronization
therapy, atrial stimulation therapy, etc. The synchronization
module 238 may be implemented in hardware as part of the
microcontroller 220, or as software/firmware instructions
programmed into the device and executed on the microcontroller 220
during certain modes of operation. Of course, such a module may be
limited to one or more of the particular functions of AA delay, AV
delay and/or VV delay. Such a module may include other capabilities
related to other functions that may be germane to the delays. Such
a module may help make determinations as to interference or fusion,
as described in more detail below.
[0040] The electronic configuration switch 226 includes a plurality
of switches for connecting the desired electrodes to the
appropriate I/O circuits, thereby providing complete electrode
programmability. Accordingly, switch 226, in response to a control
signal 242 from the microcontroller 220, determines the polarity of
the stimulation pulses (e.g., unipolar, bipolar, combipolar, etc.)
by selectively closing the appropriate combination of switches (not
shown) as is known in the art.
[0041] Atrial sensing circuits 244 and ventricular sensing circuits
246 may also be selectively coupled to the right atrial lead 104,
coronary sinus lead 106, and the right ventricular lead 108,
through the switch 226 for detecting the presence of cardiac
activity in each of the four chambers of the heart. Accordingly,
the atrial (ATR. SENSE) and ventricular (VTR. SENSE) sensing
circuits, 244 and 246, may include dedicated sense amplifiers,
multiplexed amplifiers, or shared amplifiers. Switch 226 determines
the "sensing polarity" of the cardiac signal by selectively closing
the appropriate switches, as is also known in the art. In this way,
the clinician may program the sensing polarity independent of the
stimulation polarity. The sensing circuits (e.g., 244 and 246) are
optionally capable of obtaining information indicative of tissue
capture (e.g., for detecting evoked responses).
[0042] Each sensing circuit 244 and 246 preferably employs one or
more low power, precision amplifiers with programmable gain and/or
automatic gain control, bandpass filtering, and a threshold
detection circuit, as known in the art, to selectively sense the
cardiac signal of interest. Automatic gain control can allow the
device 100 to deal effectively with the difficult problem of
sensing the low amplitude signal characteristics of atrial or
ventricular fibrillation.
[0043] The outputs of the atrial and ventricular sensing circuits
244 and 246 are connected to the microcontroller 220, which, in
turn, is able to trigger or inhibit the atrial and ventricular
pulse generators 222 and 224, respectively, in a demand fashion in
response to the absence or presence of cardiac activity in the
appropriate chambers of the heart. Furthermore, as described
herein, the microcontroller 220 is also capable of analyzing
information output from the sensing circuits 244 and 246 and/or the
data acquisition system 252 to determine or detect whether and to
what degree tissue capture has occurred and to program a pulse, or
pulses, in response to such determinations. The sensing circuits
244 and 246, in turn, receive control signals over signal lines 248
and 250 from the microcontroller 220 for purposes of controlling
the gain, threshold, polarization charge removal circuitry (not
shown), and the timing of any blocking circuitry (not shown)
coupled to the inputs of the sensing circuits, 244 and 246, as is
known in the art.
[0044] For arrhythmia detection, the device 100 utilizes the atrial
and ventricular sensing circuits, 244 and 246, to sense cardiac
signals to determine whether a rhythm is physiologic or pathologic.
In reference to arrhythmias, as used herein, "sensing" is reserved
for the noting of an electrical signal or obtaining data
(information), and "detection" is the processing (analysis) of
these sensed signals and noting the presence of an arrhythmia. In
some instances, detection or detecting includes sensing and in some
instances sensing of a particular signal alone is sufficient for
detection (e.g., presence/absence, etc.).
[0045] The timing intervals between sensed events can be classified
by the arrhythmia detector 234 of the microcontroller 220 by
comparing them to a predefined rate zone limit (i.e., bradycardia,
normal, low rate VT, high rate VT, and fibrillation rate zones) and
various other characteristics (e.g., sudden onset, stability,
physiologic sensors, and morphology, etc.) in order to determine
the type of remedial therapy that is needed (e.g., bradycardia
pacing, anti-tachycardia pacing, cardioversion shocks or
defibrillation shocks, collectively referred to as "tiered
therapy").
[0046] Through appropriate switching, cardiac signals can be
applied to inputs of an analog-to-digital (ND) data acquisition
system 252. In the example of FIG. 2, the data acquisition system
252 is configured to acquire intracardiac electrogram signals,
convert the raw analog data into a digital signal, and store the
digital signals for later processing and/or telemetric transmission
to an external device 254. The data acquisition system 252 is
coupled to the right atrial lead 104, the coronary sinus lead 106,
the right ventricular lead 108 and/or the lead 110 through the
switch 226 to sample signals across any pair of desired
electrodes.
[0047] The microcontroller 220 is further coupled to a memory 260
by a suitable data/address bus 262, where the programmable
operating parameters used by the microcontroller 220 are stored and
modified, as required, in order to customize the operation of the
stimulation device 100 to suit the needs of a particular patient.
Such operating parameters define, for example, pacing pulse
amplitude, pulse duration, electrode polarity, rate, sensitivity,
automatic features, arrhythmia detection criteria, and the
amplitude, wave shape, number of pulses, and vector of each
shocking pulse to be delivered to the patient's heart 102 within
each respective tier of therapy. The device 100 can be configured
to sense and store a relatively large amount of data (e.g., from
the data acquisition system 252), which data may then be used for
subsequent analysis to guide the programming of the device.
[0048] Advantageously, the operating parameters of the implantable
device 100 may be non-invasively programmed into the memory 260
through a telemetry circuit 264 in telemetric communication via
communication link 266 with the external device 254, such as a
programmer, transtelephonic transceiver, or a diagnostic system
analyzer. The microcontroller 220 activates the telemetry circuit
264 with a control signal 268. The telemetry circuit 264
advantageously allows intracardiac electrograms and status
information relating to the operation of the device 100 (as
contained in the microcontroller 220 or memory 260) to be sent to
the external device 254 through an established communication link
266.
[0049] The stimulation device 100 can further include one or more
physiological sensors 270. For example, the device 100 may include
a sensor commonly referred to as a "rate-responsive" sensor for use
in adjusting pacing stimulation rate according to the activity
state of a patient. The one or more physiological sensors 270 may
include a sensor to detect changes in cardiac output (see, e.g.,
U.S. Pat. No. 6,314,323, entitled "Heart stimulator determining
cardiac output, by measuring the systolic pressure, for controlling
the stimulation," to Ekwall, issued Nov. 6, 2001, which discusses a
pressure sensor adapted to sense pressure in a right ventricle and
to generate an electrical pressure signal corresponding to the
sensed pressure, an integrator supplied with the pressure signal
which integrates the pressure signal between a start time and a
stop time to produce an integration result that corresponds to
cardiac output), a sensor to detect changes in the physiological
condition of the heart and/or a sensor to detect diurnal changes in
activity (e.g., detecting sleep and wake states). Accordingly, the
microcontroller 220 can respond to sensed information by adjusting
one or more of the various pacing parameters (such as rate, AA
delay, AV delay, VV delay, etc.).
[0050] While the aforementioned pressure sensor is configured for
right ventricular pressure, pressure may be sensed in other
chambers. For example, the device 100 may acquire information from
a pressure sensor for left atrial pressure (see, e.g., U.S. Pat.
No. 6,970,742, to Mann et al., "Method for detecting, diagnosing,
and treating cardiovascular disease," issued Nov. 29, 2005, which
discusses a sensor package deployed across the atrial septum to
sense left atrial pressure). Increased pressure in the left atrium
is a predictor of pulmonary congestion, which is the leading cause
of hospitalization for congestive heart failure patients.
[0051] While shown as being included within the stimulation device
100, it is to be understood that the one or more of the one or more
physiological sensors 270 may be external to the stimulation device
100, yet still be implanted within or carried by the patient.
Examples of physiological sensors that may be implemented in device
100 include known sensors that, for example, sense respiration
rate, pH of blood, ventricular gradient, cardiac output, preload,
afterload, contractility, hemodynamics, pressure, and so forth.
Another sensor that may be used is one that detects activity
variance, wherein an activity sensor is monitored diurnally to
detect the low variance in the measurement corresponding to the
sleep state. For a complete description of the activity variance
sensor, the reader is directed to U.S. Pat. No. 5,476,483, entitled
"System and method for modulating the base rate during sleep for a
rate-responsive cardiac pacemaker," to Bornzin et al., issued Dec.
19, 1995, which patent is hereby incorporated by reference.
[0052] The one or more physiological sensors 270 may include a
position sensor and/or a minute ventilation (MV) sensor to sense
minute ventilation, which is defined as the total volume of air
that moves in and out of a patient's lungs in a minute. Signals
generated by such sensors can be passed to the microcontroller 220
for analysis for any of a variety of purposes (e.g., to determine
whether to adjust the pacing rate, etc.). The microcontroller 220
can monitor signals from appropriate sensors for indications of the
patient's position and activity status, such as whether the patient
is climbing upstairs or descending downstairs or whether the
patient is sitting up after lying down.
[0053] The stimulation device additionally includes a battery 276
that provides operating power to all of the circuits shown in FIG.
2. For the stimulation device 100, which employs shocking therapy,
the battery 276 is capable of operating at low current drains for
long periods of time (e.g., preferably less than 10 .mu.A), and is
capable of providing high-current pulses (for capacitor charging)
when the patient requires a shock pulse (e.g., preferably, in
excess of 2 A, at voltages above 2 V, for periods of 10 seconds or
more). The battery 276 also desirably has a predictable discharge
characteristic so that elective replacement time can be
detected.
[0054] The stimulation device 100 can further include magnet
detection circuitry (not shown), coupled to the microcontroller
220, to detect when a magnet is placed over the stimulation device
100. A magnet may be used by a clinician to perform various test
functions of the stimulation device 100 and/or to signal the
microcontroller 220 that the external programmer 254 is in place to
receive or transmit data to the microcontroller 220 through the
telemetry circuits 264.
[0055] The stimulation device 100 further includes an impedance
measuring circuit 278 that is enabled by the microcontroller 220
via a control signal 280. The known uses for an impedance measuring
circuit 278 include, but are not limited to, lead impedance
surveillance during the acute and chronic phases for proper lead
positioning or dislodgement; detecting operable electrodes and
automatically switching to an operable pair if dislodgement occurs;
measuring respiration or minute ventilation; measuring thoracic
impedance for determining shock thresholds; detecting when the
device has been implanted; measuring stroke volume; and detecting
the opening of heart valves, etc. The impedance measuring circuit
278 is advantageously coupled to the switch 226 so that any desired
electrode may be used.
[0056] In the case where the stimulation device 100 is intended to
operate as an implantable cardioverter/defibrillator (ICD) device,
it detects the occurrence of an arrhythmia, and automatically
applies an appropriate therapy to the heart aimed at terminating
the detected arrhythmia. To this end, the microcontroller 220
further controls a shocking circuit 282 by way of a control signal
284. The shocking circuit 282 generates shocking pulses of low
(e.g., up to approximately 0.5 J), moderate (e.g., approximately
0.5 J to approximately 10 J), or high energy (e.g., approximately
11 J to approximately 40 J), as controlled by the microcontroller
220. Such shocking pulses are applied to the patient's heart 102
through at least two shocking electrodes, and as shown in this
embodiment, selected from the left atrial coil electrode 126, the
RV coil electrode 132, and/or the SVC coil electrode 134. As noted
above, the housing 200 may act as an active electrode in
combination with the RV electrode 132, or as part of a split
electrical vector using the SVC coil electrode 134 or the left
atrial coil electrode 126 (i.e., using the RV electrode as a common
electrode). Other exemplary devices may include one or more other
coil electrodes or suitable shock electrodes (e.g., a LV coil,
etc.).
[0057] Cardioversion level shocks are generally considered to be of
low to moderate energy level (where possible, so as to minimize
pain felt by the patient), and/or synchronized with an R-wave
and/or pertaining to the treatment of tachycardia. Defibrillation
shocks are generally of moderate to high energy level (i.e.,
corresponding to thresholds in the range of approximately 5 J to
approximately 40 J), delivered asynchronously (since R-waves may be
too disorganized), and pertaining exclusively to the treatment of
fibrillation. Accordingly, the microcontroller 220 is capable of
controlling the synchronous or asynchronous delivery of the
shocking pulses.
[0058] Referring to FIG. 3, various exemplary waveforms 300 are
shown. As discussed herein, a ventricular waveform caused by a
ventricular stimulus (V) is generally referred to as an evoked
response (ER) while a ventricular waveform caused by a native
stimulus (e.g., conducted via the atrioventricular node or bundle
(AVN)) is generally referred to as an R wave or native QRS complex.
Another type of ventricular waveform discussed herein is caused by
a stimulus in one ventricle traveling to the other ventricle and
then causing depolarization of the other ventricle. Such a waveform
is referred to as an R.sub.V wave, i.e., an R wave caused by
ventricle to ventricle conduction, or referred to as a conducted
evoked response (ER.sub.c), i.e., an evoked response in one
ventricle due to stimulation and depolarization of the other
ventricle.
[0059] As described herein, and shown in Table 1, the terms
primary) (1.degree.), secondary (2.degree. and tertiary (3.degree.)
simply refer to an order of events that help to define the symbols:
P, A, R, R.sub.c, R.sub.v, V, ER and ER.sub.c. For example,
contraction of a ventricle (R) normally occurs after and in
response to sinus activity (P); hence, the sinus activity (P) may
be referred to as a primary event (1.degree.) and contraction of
the ventricle (R) may be referred to as a secondary event
(2.degree.) caused by the primary event (1.degree.). In this
example, if the ventricle was paced (V) prior to conduction of the
sinus activity (P), then contraction of the ventricle (ER) would be
a primary event (1.degree.).
[0060] For a patient with left bundle branch block (LBBB), sinus
activity (P), a primary event (1.degree.), causes depolarization of
the right ventricle (R), a secondary event (2.degree.), which then
causes, by conduction, depolarization of the left ventricle
(R.sub.c), which may be referred to as a tertiary event (3.degree.)
of the sinus activity (P). Subscripts may be added to V, ER, R,
R.sub.c, RV, or ER.sub.c to denote association with the right
ventricle (RV) or the left ventricle (LV).
[0061] The various events can be used to determine intervals. For
example, a PR interval, a PR.sub.c interval, an RR.sub.c interval,
an AV interval, a V.sub.RV interval, etc. Where ventricle
designators are used, these examples may become for the right
ventricle PR.sub.RV, PR.sub.C-RV, R.sub.RVR.sub.C-LV, AV.sub.RV,
V.sub.RVR.sub.V-LV, etc., and for the left ventricle PR.sub.LV,
PR.sub.C-LV, R.sub.LVR.sub.C-RV, AV.sub.LV, V.sub.LVR.sub.V-RV,
etc.
TABLE-US-00001 TABLE 1 Classification of Activity Other (e.g.,
Origin Sinus Paced PAC, PVC) Right Atrium 1.degree. (P) 1.degree.
(A) 1.degree. Right Ventricle 2.degree. (R) 1.degree. (V, ER)
1.degree., 2.degree., 3.degree. 3.degree. (R.sub.C) 2.degree. (R,
R.sub.V, ER.sub.C) 3.degree. (R.sub.C) Left Ventricle 2.degree. (R)
1.degree. (V, ER) 1.degree., 2.degree., 3.degree. 3.degree.
(R.sub.C) 2.degree. (R, R.sub.V, ER.sub.C) 3.degree. (R.sub.C)
[0062] Referring to FIG. 3, the exemplary waveforms 300 include a
native waveform 310 (e.g., per an ECG), which exhibits a distinct
QRS complex and a distinct T wave. A paced ventricular waveform 320
that results in capture (i.e., an evoked response) differs from the
native waveform 310. If the ventricles are refractory or if the
stimulus energy is insufficient, then a non-capture waveform
results 330. The particular non-capture waveform 330 corresponds to
a scenario lacking native or intrinsic activity; the stylized
waveform exhibits a stimulus artifact only. Of course, intracardiac
electrograms (IEGMs) acquired with use of a blanking interval may
not exhibit such an artifact.
[0063] Fusion is typically characterized by a wave complex formed
by depolarization of the myocardium initiated by both a non-native
stimulus and a native stimulus or two native pacemaker foci
activating a given chamber at virtually the same time. As shown in
FIG. 3, a fusion waveform 340 includes characteristics of a native
waveform and a paced ventricular waveform. In particular, the
waveform 340 includes depolarization due to an administered
stimulus. In contrast, pseudofusion is typically characterized by a
wave complex formed by depolarization of the myocardium initiated
by a native activation; however, a non-native activation, that does
not contribute to depolarization, is present that distorts the wave
complex. The exemplary waveforms 300 include a pseudofusion
waveform 350, which exhibits a native waveform and a stimulus
artifact wherein the stimulus does not contribute to
depolarization. As described herein, a waveform indicative of
fusion may be referred to as a "fusion beat" and a waveform
indicative of pseudofusion may be referred to as a "pseudofusion
beat".
[0064] An example of the aforementioned R.sub.V wave or conducted
evoked response (ER.sub.c) is presented in FIG. 4 (Interventricular
Conduction 400), which shows waveform sets (410 and 420), an
approximate anatomical diagram and equations associated with a
delay time referred to as an interventricular conduction delay
(IVCD) and, in this example, a paced interventricular conduction
delay (PIVCD). The approximate anatomical diagram includes a right
bundle branch (RBB) and a left bundle branch (LBB), as discussed
herein, one of the branches may have conduction problems such as a
conduction block (e.g., RBBB or LBBB). Such problems can cause
contraction of the ventricles to become asynchronous.
[0065] An interventricular conduction delay (IVCD) may be a sensed
interventricular conduction delay (SIVCD) where an intrinsic event
in one ventricle conducts to the other ventricle. For example,
where atrial activity occurs in the presence of a bundle branch
block, the ventricle without block may be expected to depolarize
(2.degree. event) followed by the ventricle with block (3.degree.
event). Thus, a sensed interventricular conduction delay may be the
interval R to R.sub.c (e.g., SIVCD=R.sub.c-R).
[0066] Referring to the delay time PIVCD-RL of FIG. 4, this
parameter is the difference between the delivery time (e.g.,
V.sub.RV) of a ventricular stimulus in one ventricle and
contraction of the other ventricle due to interventricular
conduction of the delivered ventricular stimulus (e.g., R.sub.V).
This delay may also be measured from the detection of an evoked
response (e.g., ER.sub.RV) in the ventricle where the stimulus is
delivered to the detection of an R.sub.V wave (or ER.sub.c) in the
other ventricle. Appropriate adjustments may be made depending on
the specific technique used.
[0067] The scenario of FIG. 4 pertains to pacing in a right
ventricle (e.g., V.sub.RV) and sensing in a left ventricle (e.g.,
LV.sub.Sense location to sense R.sub.V-LV) where the time between
pacing and sensing is referred to as a right to left PIVCD or
PIVCD-RL, which equals R.sub.V-LV-V.sub.RV, wherein V.sub.RV is a
pace time of a pacing stimulus in the right ventricle and
R.sub.V-LV is a sense time of a "right ventricle, evoked response
wavefront" in the left ventricle due to the paced stimulus in the
right ventricle. In general, this wavefront is co-extensive with
depolarization of the left ventricle and hence referred to as an
R.sub.V wave or ER.sub.c, as already discussed.
[0068] The parameter PIVCD-RL is normally greater than zero. To
ensure that the pacing stimulus in the right ventricle results in
an evoked response, a capture routine or algorithm may be
implemented. Thus, various exemplary methods, devices and/or
systems optionally include a capture algorithm (e.g., consider the
AUTOCAPTURE.TM. algorithm of St. Jude Medical, Sylmar, Calif.).
[0069] In FIG. 4, the set of waveforms 410 include an atrial event
(while labeled "A", this could be a native event e.g., "P"), an
atrial to ventricular paced delay AV.sub.RV, a ventricular pace
time V.sub.RV and a sensed evoked response in the right ventricle
ER.sub.RV. The other set of waveforms 420 pertains primarily to the
left ventricle and includes an atrial event (e.g., A or P), an AVN
delay and a sensed evoked response in the left ventricle R.sub.V-LV
which is a result of the stimulus V.sub.RV in the right ventricle.
To ensure that the sensed evoked response in the left ventricle
R.sub.V-LV is not due to conducted electrical activity from the
atria, a sufficiently short ventricular paced delay AV.sub.RV may
be used. For example, a paced delay AV.sub.RV of approximately 30
ms to approximately 70 ms may suffice. In one example, AV.sub.RV is
set to approximately 50 ms to approximately 80 ms. AV.sub.RV may
also be set sufficiently short to avoid fusion, if conduction
exists from the atria to the right ventricle. While AV is referred
to, PV may also apply where appropriate.
[0070] In general, bipolar sensing (or other multipolar/combipolar
sensing) may increase signal to noise of the sensed activation in
the left ventricle when compared to unipolar sensing that includes
use of an in vivo, yet non-local electrode such as a pulse
generator can. The latter technique is more often used in detection
of evoked response or applications utilizing far-field signals.
Further, bipolar sensing that includes two electrodes positioned in
proximity to each other (e.g., less than approximately 4 cm), may
increase signal to noise and sensitivity and better sense timing of
an activation wave front proximate to the electrodes.
[0071] Various delays and other parameters are discussed herein
such as the following delays that are related to pacing in the
right ventricle and/or the left ventricle:
[0072] PV Delay between an atrial event and a paced ventricular
event
[0073] PV.sub.optimal Optimal PV delay
[0074] PV.sub.RV PV delay for right ventricle
[0075] PV.sub.LV PV delay for left ventricle
[0076] AV Delay for a paced atrial event and a paced ventricular
event
[0077] AV.sub.optimal Optimal AV delay
[0078] AV.sub.RV AV delay for right ventricle
[0079] AV.sub.LV AV delay for left ventricle
[0080] .DELTA. Estimated interventricular delay, e.g., via IEGM,
etc.
[0081] .DELTA..sub.programmed Programmed interventricular delay
(e.g., a programmed VV delay)
[0082] .DELTA..sub.optimal Optimal interventricular delay, e.g.,
via hemodynamic sensing/sensor or other cardiac sensing
[0083] IVCD-RL Delay between paced/sensed RV and sensed LV
[0084] IVCD-LR Delay between paced/sensed LV and sensed RV
[0085] .DELTA..sub.IVCD Interventricular conduction delay (paced,
sensed, hybrid)
[0086] Other parameters include those already mentioned (e.g.,
R.sub.V or ER.sub.c) as well as those conventionally used in
conjunction with cardiac activity (e.g., AR, PR, etc.). In
addition, parameters such as AR.sub.V or PR.sub.V and yet others,
described below, may be used.
[0087] FIG. 5 shows an exemplary IEGM plot 500 acquired in a study
using a unipolar sensing arrangement for a right ventricular tip
electrode and a left ventricular tip electrode having a common
electrode (e.g., can, device sensing circuit, etc.). In this
unipolar arrangement, an electrical connection exists between right
and left ventricular sensing circuits. In particular,
depolarization due to atrio-ventricular intrinsic conduction was
sensed at the right ventricle and then sensed at the left ventricle
as the activation propagated (i.e., conducted) from the right
ventricle to the left ventricle. Even without an electrical
connection between RV and LV sensing circuits, an implantable
device may provide such IEGM information where depolarization of
the RV inscribes a waveform complex and then, upon depolarization
of the LV, a second waveform complex is inscribed.
[0088] In the example of FIG. 5, a trough-to-trough time delay
typically approximates .DELTA.; noting that peak-to-peak or other
feature(s) may be used to approximate .DELTA.. For purposes of
discussion, "peak-to-peak" will refer to any of the possibilities
for approximating .DELTA.. Referring again to FIG. 5, the delay may
approximate PIVCD-RL as in the case of FIG. 4. If RV is paced at a
short AV interval, the time delay from pacing RV to the peak of the
conduction to the left ventricle approximates PIVCD-RL. In an
alternative example, not shown in FIG. 5, a pacing stimulus was
delivered to the right ventricle at a time of approximately 0 ms.
This pacing stimulus resulted in capture of the right ventricle and
the IEGM showed a corresponding right ventricular evoked response.
In this example, the left ventricle was not paced or initially
captured by the pace to the right ventricle but after a short
delay, the left ventricle depolarized spontaneously due to
conduction of the paced event from the right ventricle
(R.sub.V-LV). Hence, the delay between the right ventricular peak
(RV) and the left ventricular peak (LV) approximates a paced
interventricular conduction delay from right ventricle to left
ventricle (see, e.g., PIVCD-RL of FIG. 4). Thus, the plot 500 helps
to demonstrate a particular exemplary manner in which an
implantable device that uses a single sensing amplifier for right
and left ventricular sensing channels can determine paced
interventricular conduction delay and thus, various parameters. In
addition, such a sensing arrangement may be used to determine a VV
delay (e.g., .DELTA., etc.) based on an intrinsic or a paced atrial
event that is then conducted to the left ventricle and the right
ventricle. This situation is predicated upon the sensing circuit
have an extremely short or virtually zero refractory period,
particularly an absolute refractory period (i.e., blanking period)
such that the circuitry can sense shortly after delivery of a paced
stimulus to the RV for sensing of the RV depolarization.
[0089] Further, some implantable devices having sensing and pacing
capabilities can deliver a stimulus to one ventricle and then
switch to sensing of both ventricles. For example, in the plot 500,
the RV stimulus may have been delivered in an open configuration
(e.g., RV and LV leads/electrodes not "connected") and, thereafter,
leads/electrodes "shorted" to allow for sensing from both
ventricles. Of course, where appropriate, pacing in one ventricle
and sensing in the other ventricle may occur according to various
arrangements.
[0090] FIG. 6 shows an exemplary IEGM plot 600 wherein the
ventricular IEGM was acquired in a study using an implantable
device including a switchable channel for RV and LV sensing; an
equation for PVICD-RL 610 is also shown. Such a device may allow
for measurement of AR.sub.RV/PR.sub.RV and AR.sub.LV/PR.sub.LV, by
switching between RV sensing to LV sensing. Accordingly, .DELTA.
may be ascertained. Such a device may also allow for pacing in the
right ventricle and/or left ventricle. Further, such a device may
ascertain PIVCD-RL and/or PIVCD-LR and optionally .DELTA..sub.IVCD
(the difference between PIVCD-RL and PIVCD-LR). For example, if an
AV.sub.RV or PV.sub.RV interval is set short enough to avoid fusion
(i.e., from conduction of an atrial event), then AR.sub.V-LV or
PR.sub.V-LV may be determined on the basis of LV sensing wherein
the LV sensing sense electrical activity in the left ventricle
(e.g., R.sub.V-LV) stemming from the right ventricular stimulus
(e.g., V.sub.RV). In this example, PIVCD-RL may equal
AR.sub.V-LV-AV.sub.RV or PR.sub.V-LV-PV.sub.RV. While various
examples mention PIVCD, where suitable, SIVCD may be used. Further,
in some instances .DELTA..sub.IVCD may be a hybrid of a PIVCD time
and a SIVCD time.
[0091] Other implantable devices may include RV and LV sensing
channels that can operate at the same time. Such devices may allow
for measurement of AR.sub.RV/PR.sub.RV and AR.sub.RV/PR.sub.LV on a
beat-by-beat basis. For example, for a single beat, an atrial to
right ventricular delay and an atrial to left ventricular delay may
be ascertained. Such an exemplary method can reduce measurement
error by determining such variable for a single beat as compared to
determining one variable for one beat and another variable for a
different beat. Detection of an event may be based on sensitivity
programmed in devices or a criterion such as an amplitude value
greater than approximately 40% of an expected QRS amplitude
value.
[0092] Various exemplary methods, devices and/or systems may help
to avoid cross ventricular sensing. For example, if an
interventricular delay is less than interventricular conduction
(e.g., PIVCD-RL and PIVCD-LR), the incidence of sensing paced
ventricular events in an alert interval is reduced. Further, this
incidence may be further reduced through use of an automatic
capture algorithm.
[0093] As already mentioned, fusion is typically characterized by a
wave complex formed by depolarization of the myocardium initiated
by two different foci, commonly a non-intrinsic stimulus as from a
pacemaker or ICD and an intrinsic stimulus. Table 2, below, sets
forth various fusion scenarios where stimuli and/or consequences
thereof may cause fusion.
TABLE-US-00002 TABLE 2 Exemplary Fusion Scenarios Fusion Scenario
Stimulus Chamber Parameters 1 P or A to RV; pace RV RV
AVF.sub.RV/PVF.sub.RV 2 P or A to LV; pace LV LV
AVF.sub.LV/PVF.sub.LV 3 P or A to RV conduct to LV; LV Various pace
LV 4 P or A to LV conduct to RV; RV Various pace RV 5 RV pace
conduct to LV; LV/RV VVF-RL pace LV AVF.sub.RV/PVF.sub.RV 6 LV pace
conduct to RV; RV/LV VVF-LR Pace RV AVF.sub.LV/PVF.sub.LV
In Table 2, Scenario 1 is for fusion in the right ventricle where a
paced stimulus to the right ventricle (V.sub.RV) fuses with an
intrinsic or non-intrinsic atrial stimulus conducted to the right
ventricle (R.sub.RV); Scenario 2 is for fusion in the left
ventricle where a paced stimulus to the left ventricle (V.sub.LV)
fuses with an intrinsic or non-intrinsic atrial stimulus conducted
to the left ventricle (R.sub.N); Scenario 3 is for fusion in the
left ventricle where a paced stimulus to the left ventricle
(V.sub.LV) fuses with an intrinsic or non-intrinsic atrial stimulus
conducted to the right ventricle (R.sub.RV) and is delayed in
conduction to the left ventricle (R.sub.c-LV) (e.g., where left
bundle branch block may exist and delay conduction of the atrial
stimulus to the left ventricle); Scenario 4 is for fusion in the
right ventricle where a paced stimulus to the right ventricle
(V.sub.RV) fuses with an intrinsic or non-intrinsic atrial stimulus
conducted to the left ventricle (R.sub.LV) and is delayed in
conduction to the right ventricle (R.sub.C-RV) (e.g., where right
bundle branch block may exist and delay conduction of the atrial
stimulus to the right ventricle); Scenario 5 is for fusion in the
left ventricle where a paced stimulus to the left ventricle
(V.sub.LV) fuses with a paced stimulus to the right ventricle
(V.sub.RV) that subsequently conducts to the left ventricle
(ER.sub.C-LV) and optionally for fusion in the right ventricle
where the paced stimulus to the right ventricle (V.sub.RV) fuses
with an intrinsic or non-intrinsic atrial stimulus; and Scenario 6
is for fusion in the right ventricle where a paced stimulus to the
right ventricle (V.sub.RV) fuses with a paced stimulus to the left
ventricle (V.sub.LV) that subsequently conducts to the right
ventricle (ER.sub.C-RV) and optionally for fusion in the left
ventricle where the paced stimulus to the left ventricle (V.sub.LV)
fuses with an intrinsic or non-intrinsic atrial stimulus. Thus,
Scenarios 5 and 6 can allow for detection of fusion in both
ventricles.
[0094] Table 2 also shows various parameters that may be determined
for the various scenarios. AVF and PVF refer to surrogates or
substitutes for AR and PR and VVF-RL and VVF-LR refer to surrogates
or substitutes for IVCD-RL and IVCD-LR, which are discussed above.
Where "various" is listed in Table 2, sensing and/or other
circumstances may determine which parameters may be determined or
estimated. In the scenarios 3 and 4, an AR or PR may be determined
for one ventricle and an AVF or PVF for the other ventricle.
[0095] Various exemplary methods, devices, systems, etc.,
optionally rely on occurrence of fusion or other interference to
determine one or more pacing parameters. In particular, a variety
of techniques may be used to analyze cardiac activity for fusion or
other interference. Such techniques include traditional fusion
detection techniques that rely on slope, amplitude, morphology,
etc. For example, morphology discrimination (see, e.g., block 236
of FIG. 2) may be used to detect fusion. Morphology discrimination
typically relies on "dynamic template matching" to discriminate
between normal and abnormal events (e.g., fusion, intrinsic
depolarization, non-intrinsic depolarization, etc.), which may be
present in sensed cardiac activity. Morphology discrimination
enables a device to examine multiple characteristics of an
electrogram (e.g., sensed cardiac activity), as opposed to
techniques which may look only at a complex's width, amplitude
and/or slew rate; however, such techniques may be used in
conjunction with or as alternatives to one or more morphology
discrimination techniques. Morphology discrimination allows for a
comparison between a complex, or portion thereof, and a template.
For example, morphology discrimination may compare a last acquired
complex with a predetermined physician-selected patient-specific
template. In commercially available implementations of morphology
discrimination (MD), a MD algorithm is normally disabled in the
setting of a delivered output pulse. In contrast, various exemplary
methods described herein may allow for morphology discrimination or
other signal characterization following delivery of an output
pulse.
[0096] Various exemplary methods, devices, systems, etc., described
herein pertain to scenarios 3 and 4. In particular, an exemplary
method aims to cause scenario 3 or scenario 4 to be present, thus,
fusion may be intentional. While the site of fusion is referred to
as "LV" or "RV", the site of fusion may be located and optionally
controlled. Fusion may optionally occur at the intraventricular
septum (IVS). Intentional or controlled fusion may provide
benefits, especially for patients subject to cardiac
resynchronization therapy (CRT).
[0097] FIG. 7 shows four ECGs 704, 708, 712, 716, which correspond
to different scenarios. The ECG 704 corresponds to no pacing where
native conduction controls, directly or indirectly, contraction of
the right ventricle and the left ventricle. The ECG 708 corresponds
to pacing with an AV interval of 100 ms, which is a nominal shipped
value for a commercially available biventricular pacemaker. The ECG
708 shows that, for an AV interval of 100 ms, there was total loss
of AV synchrony. The ECG 712 corresponds to pacing with an AV
interval of 160 ms. The ECG 712 shows that the P wave becomes
visible in front of the paced QRS and that the paced QRS narrows.
The narrowest paced QRS appears in the ECG 716, where an AV
interval of 210 ms provided the best velocity time integral (echo
measure of stroke volume), which also resulted in fusion with
native conduction down the right bundle.
[0098] A good percentage of heart patients can have a one sided
bundle branch block, i.e., right bundle branch block (RBBB) or left
bundle branch block (LBBB), or one sided conduction that is slow
whereby such conduction does not provide for adequate cardiac
performance. These conditions result in a large inter-ventricular
depolarization activation timing difference. For example, a LBBB
patient can still have a good conduction from atrium to right
ventricular through the AV node to the RBB to the Purkinje RBB.
However, starting from somewhere on the path of the Purkinje LBB
due to the blockage, the conduction has a larger delay. Thus, the
activation of the left ventricle will take an extra time for
natural conduction to fully depolarize chamber. In the setting of
complete block of the LBB, activation of the left ventricle comes
from the depolarization of the right ventricle and then crossing
over to the left ventricle by way of the interventricular septum.
Consequently, with LBBB, a patient's heart experiences
uncoordinated dyssynchronous contraction of the LV. As mentioned in
the Background section, CRT aims to address such issues. For
example, given an electrode arrangement that allows for pacing at a
RV site(s) (e.g., that causes depolarization of the
interventricular septum) and at a LV site(s) (e.g., lateral or
posterior wall), CRT can synchronize contraction of the LV.
[0099] Where pacing occurs, a paced beat takes an extra-time to
travel from the pacing site to the rest of heart. For a patient
with compromised LBB conduction, pacing at a left ventricular site
at correct timing will help synchronize depolarization of the
postero-lateral wall of the left ventricle with the
interventricular septum, which is depolarized by the naturally
conducted impulse. Correct timing may be set according to the time
difference of the conduction of RBB and LBB of the intrinsic
impulse since this is the time required for the paced
depolarization to travel back to the point to meet the
depolarization of the other chamber. The equivalent effect is the
true cross chamber triggered pacing. However, regular cross chamber
triggered pacing can not achieve desired VV synchrony because it
can not pre-pace in the chamber with slow conduction. In contrast,
"true" cross chamber triggered pacing with advanced pacing can
result in the VV synchrony. This phenomenon is demonstrated in the
FIG. 8 from data obtained from a patient who has intrinsic
RBBB.
[0100] FIG. 8 shows three ECGs 804, 808, 812, which correspond to
different scenarios. The ECG 804 shows electrical activity of the
heart where the LBB provides an intrinsic conduction pathway, as
the patient has RBBB. The ECG 808 shows electrical activity where
the right ventricle is paced and where intrinsic conduction causes
depolarization of the left ventricle. The ECG 812 shows electrical
activity where the timing of the pacing stimulus to the right
ventricle is timed such that fusion occurs between the evoked
response of the right ventricle and the depolarization of the left
ventricle.
[0101] Various exemplary methods determine upper and lower limits
or boundaries for VV interval or AV/PV interval. For example, an
optimal VV interval may be obtained via clinical testing where one
ventricle is paced and the other ventricle depolarizes due to
intrinsic bundle branch (BB) conduction. Accordingly, the VV
interval equals the time difference AR/PR-AV/PV, where
AV/PV<AR/PR due to advanced pacing. For a given set of
conditions, AR/PR may remain relatively constant and hence the
AV/PV time determined via clinical testing may be set as an upper
limit. Of course, some margin may be used such as X ms (e.g., a few
ms) or a percentage (e.g., 105%) to provide a more flexible
boundary; noting, however, that the condition that AV/PV<AR/PR
remains. With respect to a lower limit, the minimum AV/PV allowed
by an implantable device may be used.
[0102] An exemplary method may periodically (or upon occurrence of
an event) search for a rate adaptive, dynamic AV/PV where the
search extends and/or shortens the paced AV/PV interval so that the
paced depolarization will fuse with the sensed AR/PR in the
opposite chamber.
[0103] An exemplary method for determining an AV/PV interval uses
the following equation (Eqn. 1):
AV/PV.sub.programmed=AR/PR.sub.measured-VV.sub.optimal+C.sub.VV
(1)
where C.sub.VV is a correction factor (positive, negative or zero).
According to this method, the dynamic AV/PV time interval can be
further modulated by the instant heart rate, the immediate
atrioventricular conduction history, or other information. A
particular example uses instant heart rate and the immediate
atrioventricular conduction history to modulate a dynamic AV/PV
time. With respect to the conduction history, in general,
information acquired during the past 24 hours is used; however,
depending on patient specifics, this time may consider information
acquired past 24 hours.
[0104] With respect to detection of fusion or, in general, analysis
of electrical activity, techniques disclosed in U.S. Pat. No.
6,928,326 entitled "Diagnosis of Fusion or Pseudofusion," to
Levine, issued Aug. 9, 2005, which is incorporated by reference
herein ("the '326 patent"), may be used.
[0105] As stated in the '326 patent, while fusion and pseudofusion
avoidance can improve some pacing therapies, other pacing therapies
can benefit from algorithms that help promote fusion. For example,
some multisite pacing therapies for dilated cardiomyopathy and
congestive heart failure actually rely on fusion because the
resulting ventricular activation sequence provides the best
hemodynamic results. Therefore, various exemplary fusion and/or
pseudofusion recognition algorithms can enhance performance of
particular pacing therapies. Pacing therapies discussed herein can
benefit from the techniques presented in the '326 patent. In
particular, the techniques can help to detect fusion where fusion
is a goal.
[0106] An exemplary method may store AV/PV interval values or other
dynamic information related to synchrony verses parameters such as
heart rate and natural intrinsic conduction. Analysis of such
stored information can help track progression of conduction
problems (e.g., bundle branch block) and heart failure disease.
[0107] Various exemplary methods aim to promote the heart's natural
AV synchrony and reduce unnecessary ventricular pacing that may
exacerbate heart failure; promote VV synchrony with the heart's
natural activation in the intact chamber to achieve optimal VV
function; dynamically adjust VV timing delay to accommodate the
change of patient condition; provide information for disease
prognosis; and/or reducing energy consumption by reducing pacing
requirements (e.g., less pacing required to maintain VV synchrony)
and thus prolong battery life.
[0108] With respect to clinical testing, standard tissue Doppler
(TD) echocardiographic analysis can provide a wealth of information
such as septal wall thickness, posterior wall thickness, LV
internal diastolic diameter and systolic diameter, ejection
fraction, LV mass index, E peak velocity, A peak velocity, E/A peak
velocity, E deceleration time, isovolumic relaxation time, etc. A
study by Citro et al., ("Left bundle branch block with and without
coronary artery disease: which value for a tissue Doppler-derived
post-systolic motion?", Ital Heart J 2003; 4 (10): 706-712),
reported use of the following TD measurements as indexes of
regional myocardial function: myocardial systolic peak velocity
(S.sub.m, m/s), myocardial pre-contraction time (from the onset of
the ECG QRS to the beginning of S.sub.m) and contraction time (from
the beginning to the end of S.sub.m) as systolic indexes and
myocardial early (E.sub.m) and atrial (A.sub.m) peak velocities and
their ratios, and relaxation time (RT.sub.m)--corresponding to the
time interval elapsing between the end of S.sub.m and the onset of
E.sub.m--as diastolic measurements. The study of Citro et al., used
TD for analysis of the middle interventricular septum (or
"intra-ventricular" septum or "IVS") and left ventricular (LV)
mitral annulus. Various studies show that the earliest site of
activation of the normal ventricular wall occurs at the
mid-IVS.
[0109] As described herein, an exemplary method optionally aims to
locate fusion. In particular, data indicate that, for various
patients, optimal VV synchrony corresponds to fusion at a location
near the intra-ventricular septum. For example, such a method may
determine advanced pacing timing (e.g., an advance pacing interval)
such that the paced beat induced ventricular depolarization will
fuse with the natural conducted beat introduced ventricular
depolarization somewhere near the middle of the heart (e.g., at the
IVS). In this example, the two depolarization fronts meet together
to achieve the VV synchrony while AV synchrony may be optimized by
natural conduction. Thus, clinical testing may aim to uncover
mechanics of the IVS to determine optimal VV interval. Of course,
other regions of the heart may be examined (e.g., LV mitral
annulus, etc.) for purposes of optimizing synchrony.
[0110] FIG. 9 shows an exemplary method 900 for determining an AV
or PV interval. This particular example refers to delivering a
stimulus to the right ventricle as conduction to the right
ventricle is either faulty (e.g., RBBB) or otherwise too slow. In a
set block 904, the AV/PV interval for the right ventricle is set to
a value or gradually decreased to a value that allows for
conduction of a stimulus to the right ventricle to cause
depolarization of the left ventricle. In this example, conduction
from atria (or atrium) to the left ventricle is sufficient to cause
contraction of the left ventricle. Using the sufficiently short
AV/PV interval for the right ventricle, a determination block 906
determines a value for the parameter IVCD-RL (see, e.g., PIVCD-RL
of FIG. 4).
[0111] The method 900 includes a determination block 908 for
determining an optimal VV interval (e.g., VV.sub.optimal), which
may be determined using one or more techniques. A techniques block
910 refers to various techniques, which include clinical
techniques, algorithmic techniques, and data-based techniques. For
example, a clinical technique may rely wholly or primarily on
echocardiograms, an algorithmic technique may rely wholly or
primarily on a model that receives values for one or more
parameters, a data-based technique may rely wholly or primarily on
a database with patient or other data. The determination block 908
may rely on one or more of such techniques or other techniques.
[0112] Another determination block 912 extends the AV/PV interval
to determine AR/PR interval for the ventricle having sufficient
conduction (e.g., the left ventricle). Yet another determination
block 916 determines a correction factor (see, e.g., C.sub.w of
Eqn. 1) for use in determining an advance AV/PV pacing interval for
the right ventricle. For example, the correction factor may be
determined using the following equation (Eqn. 2):
C.sub.VV=(IVCD-RL-VV.sub.optimal)/IVCD-RL (2)
[0113] Given the correction factor, the method 900 then enters a
determination block 920 to determine the AV/PV interval for advance
ventricular pacing of the right ventricle. This block may determine
the interval using, for example, the following equation (Eqns. 3A
and 3B):
AV advance=(AV interval)-(IVCD-RL)*(1-C.sub.VV) (3A)
PV advance=(PV interval)-(IVCD-RL)*(1-C.sub.VV) (3B)
[0114] An exemplary method includes providing an optimal
interventricular interval, setting an atrio-ventricular interval
for the left ventricle or the right ventricle, delivering
stimulation to the left ventricle or the right ventricle and
sensing cardiac activity of the right ventricle or the left
ventricle, respectively, extending an atrio-ventricular interval
for the right ventricle or the left ventricle and, if the extending
results in atrio-ventricular conduction of an atrial event that
causes depolarization of the right ventricle or the left ventricle,
respectively, then determining an advance atrio-ventricular pacing
interval for the left ventricle or the right ventricle based on the
optimal interventricular interval, the delivering and the sensing,
and the extending. Such an exemplary method may optionally diagnose
right or left bundle branch block if the extending does not result
in atrio-ventricular conduction of an atrial event that causes
depolarization of the right ventricle or the left ventricle,
respectively.
[0115] FIG. 10 shows an exemplary method 1000 for optimizing
ventricular synchrony. The method 1000 commences in a detection
block 1004, upon detection of an atrial event. In response to
detection of the atrial event, an implementation block 1006
implements an advance AV/PV interval. As described above, the
advance AV/PV interval aims to deliver stimulation to a ventricle
with faulty conduction (e.g., bundle branch block or otherwise slow
conduction). A decision block 1008 follows implementation of the
advance AV/PV interval that relies on sensing to decide if an
intrinsic event occurred in the "blocked" ventricle during the
advance AV/PV interval. If the decision block 1008 decides that an
intrinsic event occurred, then the method 1000 continues in the
detection block 1004, where sensing is used to help detect a
subsequent atrial event. However, if the decision block 1008
decides that no intrinsic event occurred during the advance
interval, then the method 1000 continues in a delivery block 1010
that calls for delivery of stimulation to the "blocked"
ventricle.
[0116] To proceed, the method 1000 relies on a VV interval, such as
the aforementioned VV.sub.optimal interval. In particular, a wait
block 1012 implements a wait period that waits for activation of
the other ventricle, i.e., the "unblocked" ventricle. During this
wait period, a detection algorithm relies on sensed information for
detection of activation of the other ventricle. The activation may
be intrinsic (e.g., of atrial origin) or it may be due to
conduction from the "blocked" ventricle. Again, the type of fusion
expected by the method 1000 for optimizing ventricular synchrony,
is between an artificial activation wavefront of one ventricle and
an atrial-to-ventricular activation wavefront of the other
ventricle.
[0117] A decision block 1014 relies on the detection algorithm to
decide if activation occurred during the wait period (e.g.,
VV.sub.optimal). If the decision block 1014 decides that activation
occurred, then the method 1000 continues at the detection block
1004. However, if it decides that activation did not occur, then
the method 1000 enters a deliver block 1016 that calls for delivery
of stimulation to the "unblocked" ventricle. Execution of the
delivery block 1016 may indicate that some aspect of cardiac
condition has changed. Hence, the method 1000 may enter an update
block 1018 that aims to update or re-optimize therapy. In instances
where the conduction to the "unblocked" ventricle becomes too slow
or blocked, then the update block 1018 may simply disable one or
more of the fusion-based techniques and revert to delivering
stimulation to both ventricles, according to some optimal set of
parameters (e.g., AV/PV, VV, etc.).
[0118] Referring again to the wait block 1012, the wait period may
be set to a value other than VV.sub.optimal. For example, the
following equation (Eqn. 4) may be used to determine the wait
period:
Wait=VV.sub.optimal.OMEGA.*(IVCD-XX-VV.sub.optimal) (4)
where IVCD-XX is the IVCD from the "blocked" ventricle to the
"unblocked" ventricle (e.g., PIVCD-RL, PIVCD-LR, SIVCD-RL,
SIVCD-LR) and where .beta. is a coefficient, for example between 0
and 1. Equation 4 allows for a wait period that is generally
greater than VV.sub.optimal. The coefficient .OMEGA. may be
adjusted based, for example, on patient condition, power store,
etc. Adjustments of the coefficient .beta. can be used to control
the frequency or likelihood of bi-ventricular pacing (and single
ventricle pacing). In some instances, the coefficient .OMEGA. may
be assigned a negative value.
[0119] FIG. 11 shows an exemplary method 1100 that performs various
searches for use in determining an advance AV/PV. The method 1100
commences in an initiation block 1104 that initiates a search for
various values. These values pertain to the following
parameters:
[0120] Rate_pacing (atrial rate for majority pacing);
[0121] IVCD-XX_delay-rate (where AR interval in "unblocked"
ventricle begins to shorten in response to shortening AV/PV of
"blocked" ventricle);
[0122] AV_delay-rate (where AR in "unblocked" ventricle no longer
changes in response to lengthening AV/PV in "blocked"
ventricle);
[0123] Rate_sensing (atrial rate for majority sensing, i.e., est.
intrinsic rate); and
[0124] PV_delay-rate (rate adaptive intrinsic conduction time based
on small changes in AV/PV and not change in AR of "unblocked"
ventricle).
[0125] The method 1100 continues in an override block 1106 that
sets the atrial pacing rate to a value that exceeds and, thus,
overdrive, the intrinsic rate. The parameter Rate_pacing is then
accorded the override rate. While pacing at the overdrive rate, an
action block 1108 acts to shorten the AV for the "blocked"
ventricle and, in response, an associated decision block 1110
decides if AR shortening occurs in the "unblocked" ventricle. A
loop exists between the decision block 1110 and the action block
1108 that may expire upon a certain amount of AR shortening or upon
a certain number of iterations (or other event).
[0126] Once AR shortening is noted, a value for the parameter
IVCD-XX_delay-rate is determined that corresponds to the
interventricular conduction interval from, for example, the paced,
"blocked" ventricle to the "unblocked" ventricle. The method 1100
continues in an action block 1114 that acts to lengthen the AV
interval for the "blocked" ventricle until a change in AR occurs
for the "unblocked" ventricle, as decided by a decision block 1116.
Once a change occurs, per the decision block 1116, then a
determination block 1118 sets the last unchanged AR, for the given
atrial rate, as the rate adaptive intrinsic conduction time
AV_delay-rate.
[0127] Following the determination block 1118, an action block 1120
acts to decrease the atrial rate until majority sensing occurs
(e.g., majority intrinsic atrial control), as decided by a decision
block 1122. A determination block 1124 then determines the
intrinsic atrial rate (the parameter Rate_sensing) based on the
atrial rate where majority sensing occurred. A sensitivity analysis
block 1126 follows that shortens and then lengthens the PV
(assuming intrinsic control) in small steps and, in response,
measures PR intervals in "unblocked" ventricle, until the PR
interval no longer changes. The value for the last unchanged PR is
then set to be the rate adaptive intrinsic conduction PR time,
i.e., the parameter PV delay_rate.
[0128] The determination block 1128 then uses the various values to
determine the rate adaptive advance AV/PV (ra-advance AV/PV). For
example, the following equations (Eqns. 5A and 5B) may be used to
determine the advance AV or advance PV:
ra-advance AV=(AV delay_rate)-(IVCD-XX_delay-rate)*(1-C.sub.VV)
(5A)
ra-advance PV=(PV delay_rate)-(IVCD-XX_delay-rate)*(1-C.sub.VV)
(5B)
[0129] The exemplary method 1100 or any associated search can be a
timer based periodic search, a search that occurs when there is a
cardiac rate change (when rate responsive adaptive VV is on) and
may be occur when the current rate has not been recorded
previously.
[0130] Information acquired during execution of the exemplary
method 1100 or a part thereof may be used for diagnostics. For
example, a method may record the rate adaptive IVCD-XX_delay-rate
and AV/PV interval in the form of histogram suitable for trend
analysis (e.g., rate, ra-adaptive AV/PV, IVCD-XX_delay-rate and
date may be recorded).
[0131] Another exemplary method uses sensing in both ventricles. In
this example, earliest sensing is expected to occur in chamber
which does not have bundle branch conduction delay (i.e., the
"unblocked" ventricle). Upon detection of activation in the
"unblocked" ventricle, that ventricle is labeled the "first"
ventricle or master ventricle. Then, a triggered output is
delivered after a programmable delay in the "second" ventricle or
slave ventricle. The programmable delay may be 0 ms or some other
programmable interval. In this example, synchrony is restored while
maintaining the native AV delay and eliminating ventricular pacing
to at least one chamber thus effectively reducing battery current
drain.
[0132] As already mentioned, various techniques may be used to
determine the particular pacing method to achieve optimal
synchrony. FIG. 12 shows a block diagram of an exemplary method
1200. While the method 1200 pertains to scenarios with atrial
pacing, such a method may omit atrial pacing (e.g., rely on an
intrinsic atrial activity, etc.) and/or include atrial pacing and
intrinsic atrial activity, etc. (e.g., PR, AR, AV, and/or PV). The
exemplary method 1200 includes three Scenarios I, II and III.
[0133] With respect to various "fusion" techniques described
herein, Scenarios IA and IB: "Single Ventricle Pacing" are of
particular interest. For example, the techniques of the methods
900, 1000, 1100 may be applied where single ventricle pacing
occurs. FIG. 13, described further below, also includes information
germane to single ventricle pacing. An exemplary device optionally
includes control logic for performing actions of the method 900,
1000, 1100, 1200 and/or 1300. For example, such a device may be
able to perform the actions of the method 1200 and, where single
ventricle pacing occurs (Scenarios IA and IB), actions may promote
ventricular synchrony via intentional "fusion". Intentional fusion
may be suitable for other scenarios as well (e.g., variants of
Scenario II, etc.). A discussion of various examples that can
include intentional fusion follows a brief description of the
method 1200.
[0134] According to the method 1200, in a decision block 1204, a
decision is made as to whether AR.sub.RV and/or AR.sub.LV have
exceeded a predetermined AR.sub.max value. If neither value exceeds
AR.sub.max, then Scenario III follows, which may disable
ventricular pacing or take other appropriate therapy per block
1208. Other appropriate therapy optionally includes therapy that
achieves a desirable VV delay by any of a variety of techniques. If
however one or both values exceed AR.sub.max, then the method 1200
continues in another decision block 1212. The decision block 1212
decides whether AR.sub.RV and AR.sub.LV have exceeded AR.sub.max.
If both values do not exceed AR.sub.max, then single ventricular
pacing occurs, for example, per Scenario IA or Scenario IB. If both
values exceed AR.sub.max, then bi-ventricular pacing occurs, for
example, Scenario II.
[0135] Scenario IA commences with a decision block 1216 that
decides if AR.sub.RV is greater than AR.sub.LV. If AR.sub.RV
exceeds AR.sub.RV, then single ventricular pacing occurs in the
right ventricle (e.g., right ventricle master). If AR.sub.RV does
not exceed AR.sub.RV, then single ventricular pacing occurs in the
left ventricle (e.g., left ventricle master).
[0136] For right ventricular pacing per Scenario IA, the method
1200 continues in a back-up pacing block 1218 where AV.sub.LV is
set to AR.sub.RV plus some back-up time (e.g., .DELTA..sub.BU). The
block 1218, while optional, acts to ensure that pacing will occur
in the left ventricle if no activity occurs within some given
interval. The method 1200 then continues in a set block 1228 where
the parameter .DELTA..sub.IVCD is used as a correction factor to
set the AV.sub.RV delay to
AV.sub.optimal-(|.DELTA.|-.DELTA..sub.IVCD).
[0137] For left ventricular pacing per the Scenario IA, the method
1200 continues in a back-up pacing block 1230 where AV.sub.LV is
set to AR.sub.LV plus some back-up time (e.g., .DELTA..sub.BU). The
block 1230, while optional, acts to ensure that pacing will occur
in the left ventricle if no activity occurs within some given
interval. The method 1200 then continues in a set block 1240 where
the parameter .DELTA..sub.IVCD is used as a correction factor to
set the AV.sub.LV delay to
AV.sub.optimal-(|.DELTA.|.DELTA..sub.IVCD).
[0138] Scenario IB commences with a decision block 1216' that
decides if AR.sub.RV is greater than AR.sub.LV. If AR.sub.RV
exceeds AR.sub.LV, then single ventricular pacing occurs in the
right ventricle (e.g., right ventricle master). If AR.sub.RV does
not exceed AR.sub.LV, then single ventricular pacing occurs in the
left ventricle (e.g., left ventricle master).
[0139] For right ventricular pacing per Scenario IB, the method
1200 continues in a back-up pacing block 1218' where AV.sub.LV is
set to AR.sub.LV plus some back-up time (e.g., .DELTA..sub.BU). The
block 1218', while optional, acts to ensure that pacing will occur
in the left ventricle if no activity occurs within some given
interval. The method 1200 then continues in a set block 1228' where
the parameter .DELTA..sub.IVCD is used as a correction factor to
set the AV.sub.RV delay to AR.sub.LV-(|.DELTA.|-.DELTA..sub.IVCD).
Hence, in this example, a pre-determined AV.sub.optimal is not
necessary.
[0140] For left ventricular pacing per the Scenario IB, the method
1200 continues in a back-up pacing block 1230' where AV.sub.LV is
set to AR.sub.LV plus some back-up time (e.g., .DELTA..sub.BU). The
block 1230', while optional, acts to ensure that pacing will occur
in the left ventricle if no activity occurs within some given
interval. The method 1200 then continues in a set block 1240' where
the parameter .DELTA..sub.IVCD is used as a correction factor to
set the AV.sub.LV delay to AR.sub.RV-(|.DELTA.|+.DELTA..sub.IVCD).
Again, in this example, a pre-determined AV.sub.optimal is not
necessary.
[0141] Referring again to the decision block 1212, if this block
decides that bi-ventricular pacing is appropriate, for example,
Scenario II, then the method 1200 continues in a decision block
1250, which that decides if AR.sub.RV is greater than AR.sub.LV. If
AR.sub.RV exceeds AR.sub.LV, then bi-ventricular pacing occurs
wherein the right ventricle is the master (e.g., paced prior to the
left ventricle or sometimes referred to as left ventricle slave).
If AR.sub.RV does not exceed AR.sub.LV, then bi-ventricular pacing
occurs wherein the left ventricle is the master (e.g., paced prior
to the right ventricle or sometimes referred to as right ventricle
slave).
[0142] For right ventricular master pacing, the method 1200
continues in a set block 1254 which sets AV.sub.LV to
AV.sub.optimal. The method 1200 then uses .DELTA..sub.IVCD as a
correction factor in a set block 1266, which sets AV.sub.RV delay
to AV.sub.LV-(|.DELTA.|-.DELTA..sub.IVCD).
[0143] For left ventricular master pacing, the method 1200
continues in a set block 1272 which sets AV.sub.RV to
AV.sub.optimal. The method 1200 then uses .DELTA..sub.IVCD as a
correction factor in a set block 1284, which sets AV.sub.LV delay
to AV.sub.RV-(|.DELTA.|+.DELTA..sub.IVCD).
[0144] As mentioned, conduction issues that affect left ventricle
synchrony can have a significant impact on cardiac performance.
With respect to the scenarios of FIG. 12, in the decision block
1204, LBBB may cause AR.sub.LV to exceed AR.sub.max. In response,
the method 1200 may call for Scenario IA, IB or II. However, an
intentional fusion technique may specify a maximum AR or PR for the
right and/or left ventricle. Further, such a criterion or criteria
for intentional fusion may be chosen in a manner that accounts for
the scenarios of FIG. 12. For example, if a cut-off value of 250 ms
is chosen for AR.sub.max and for intentional fusion, then block
1208 (i.e., Scenario III) may represent an intentional fusion
branch of the method 1200. Thus, if a patient (e.g., based on
surface ECG), has a PR/AR for the right ventricle and/or the left
ventricle less than 250 ms, then the appropriate therapy 1208 could
use intentional fusion.
[0145] In another example, consider a patient with LBBB, an
AR.sub.LV greater than the AR.sub.max value of the decision block
1204, and an AR.sub.RV less than an intentional fusion criterion.
In this example, intentional fusion may be used for Scenarios IA,
IB or II depending on whether AR.sub.RV is greater than AR.sub.max.
Where the cut-off criterion for intentional fusion is the same as
AR.sub.max, then fusion will be used in Scenarios IA or IB as
Scenario II would be excluded from intentional fusion. However, if
the LBBB conduction issue is intermittent, then an algorithm for
Scenario II may allow for intentional fusion where AR is
intermittently less than AR.sub.max (e.g., intermittent resort to
Scenario IA or IB, etc.). For a patient with LBBB, an intentional
fusion technique aims to pace the left ventricle in a manner that
causes fusion with conducted activity from the RV (or RV
pathway).
[0146] In yet another example, an AR criterion for intentional
fusion is greater than AR.sub.max of the decision blocks 1204 and
1212. In such an example, a patient with AR.sub.RV and AR.sub.LV
greater than AR.sub.max can use Scenario II with intentional fusion
if AR.sub.RV and/or AR.sub.LV is less than the intentional fusion
criterion.
[0147] As described herein, a cut-off value for intentional fusion
may be based at least in part on an optimal AV delay for a patient.
Further, as the optimal AV delay may change over time, a patient
may intermittently qualify for CRT that uses one or more
intentional fusion techniques. Noting that intentional fusion
techniques require AV conduction to at least one ventricle.
[0148] In some instances, a patient may have an AR/PR to a
ventricle that is quite short and not suitable for purposes of
intentional fusion. Accordingly, the method 1200 may include one or
more decision blocks for deciding whether AR/PR is too short for
implementing an intentional fusion technique. In general, such
blocks would normally be associated with Scenarios IA or IB (single
ventricle pacing) as decision block 1212 requires AR.sub.RV and
AR.sub.LV greater than AR.sub.max. However, as mentioned, values
can vary with respect to time. Hence, decisions in the method 1200
and other decisions could be repeated over time with different
outcomes. Further, a clinician may adjust decision criteria over
time.
[0149] While various examples pertain to a single RV site or a
single LV site for purposes of fusion, an example may include a
plurality of RV sites or a plurality of LV sites. For example, if a
CRT device includes a lead or leads configured for multiple LV
sites, then stimulation energy may be delivered in a coordinated
manner to the LV sites to achieve intentional fusion.
Alternatively, one site may be selected from the plurality of sites
for purposes of achieving intentional fusion. In another example, a
CRT may achieve intentional fusion by delivering stimulation energy
to one site for some beats and by delivering stimulation energy to
a different site for some other beats. In such an example, cardiac
performance may be assessed to determine patient condition,
effectiveness of CRT, etc.
[0150] A comparison between .DELTA. and .DELTA..sub.programmed or
.DELTA..sub.optimal can indicate a difference between a current
cardiac therapy or state and a potentially better cardiac therapy
or state. For example, consider the following equation:
.alpha.=.DELTA..sub.optimal/.DELTA. (6)
where .alpha. is an optimization parameter. Various echocardiogram
studies indicate that the parameter .alpha. is typically about 0.5.
The use of such an optimization parameter is optional. The
parameter .alpha. may be used as follows:
AV.sub.RV=AV.sub.optimal-.alpha.|.DELTA.| or (7A)
PV.sub.RV=PV.sub.optimal.alpha.|.DELTA.| (7B)
AV.sub.LV=AV.sub.optimal-.alpha.(|.DELTA.|+.DELTA..sub.IVCD) or
(8A)
PV.sub.LV=PV.sub.optimal-.alpha.(|.DELTA.|+.DELTA..sub.IVCD)
(8B)
[0151] If a parameter such as the aforementioned a parameter is
available, then such a parameter is optionally used to further
adjust and/or set one or more delays, as appropriate.
[0152] Various exemplary methods, devices, systems, etc., may
consider instances where normal atrio-ventricular conduction exists
for one ventricle. For example, if an atrio-ventricular conduction
time for the right ventricle does not exceed one or more limits
representative of normal conduction, then the atrio-ventricular
time for the right ventricle may serve as a basis for determining
an appropriate time for delivery of stimulation to the left
ventricle (or vice versa). The following equations (Eqn. 9A and 9B)
may be used in such a situation:
AC.sub.LV=AR.sub.RV-|.DELTA.| or (9A)
PV.sub.LV=PR.sub.RV-|.DELTA.| (9B)
[0153] Eqn. 9A is similar to the equation used in blocks 1228' and
1240' of Scenario IB of FIG. 12. With respect to backup pulses, a
backup pulse (e.g., for purposes of safety, etc.) may be set
according to the following equations (Eqn. 10A and 10B):
AV.sub.RV=AR.sub.RV+|.gamma.| or (10A)
PV.sub.RV=PR.sub.RV+|.gamma.| (10B)
[0154] Of course, administration of a backup pulse may occur upon
one or more conditions, for example, failure to detect activity in
the particular ventricle within a given period of time. In the
foregoing equation, the parameter .gamma. is a short time delay,
for example, of approximately 5 ms to approximately 10 ms. Eqn. 10A
is similar to the equation used in blocks 1218' and 1230' of
Scenario IB of FIG. 12.
[0155] FIG. 13 shows a block diagram of an exemplary method 1300.
While the method 1300 pertains generally to bi-ventricular pacing
to pace a master ventricle and a slave ventricle, under certain
circumstances, pacing is inhibited to the slave ventricle, which
results in single ventricle pacing. Specifically, the method 1300
addresses circumstances when an intrinsic beat occurs in an alert
period of a slave ventricle. Such an occurrence indicates that
intrinsic activity exists and that the timing of the intrinsic
activity may suffice for purposes of single ventricle pacing (e.g.,
including single ventricular pacing with intentional fusion).
[0156] According to the method 1300, an implementation block 1304
implements a bi-ventricular pacing scheme. A decision block 1308
follows wherein a decision is made as to whether an intrinsic event
has occurred in an alert period of a ventricular channel (e.g., a
slave channel). If the decision block 1308 decides that no activity
or event has occurred in an alert period, then the method 1300
proceeds to a continuation block 1310 where the bi-ventricular
pacing scheme continues where, as appropriate, the method 1300
flows back to the decision block (e.g., after certain programmed
events, etc.). However, if the decision block 1308 decides that an
intrinsic event occurred in an alert period, then another decision
block 1312 follows. The decision block 1312 decides if the activity
or event occurred prior to a VV delay period (e.g., a
.DELTA..sub.programmed). If the decision block 1312 decides that
the occurrence was not prior to a VV delay period then the method
1300 continues in an inhibition block 1314 that inhibits delivery
of a pace event to a ventricle. However, if the decision block 1312
decides that the occurrence was prior to a VV delay period then the
method 1300 continues in a trigger, blank and inhibition block
1316. The trigger, blank and inhibition block 1316 acts to trigger
delivery of a pace to a ventricle (e.g., the master ventricle), to
initiate one or more blanking periods (e.g., atrial and/or
ventricular), and to inhibit delivery of a pace to the other
ventricle (e.g., the slave ventricle).
[0157] Of course, an alert period for a master ventricular channel
may exist wherein an intrinsic event in the master ventricle causes
inhibition of a scheduled pace event in the master ventricle and
causes an update in the timing of a scheduled slave pace event. For
example, if an intrinsic event is sensed or detected in the master
ventricle, then the VV delay may commence in response thereto. Such
an exemplary method would act to preserve the VV delay (e.g.,
.DELTA..sub.programmed) to ensure appropriate timing of
contractions in left and right ventricles.
[0158] An exemplary method includes setting an interventricular
(VV) delay between a master ventricle and a slave ventricle (e.g.,
setting .DELTA..sub.programmed) and sensing for ventricular
activity. If activity is sensed in the slave ventricle prior to the
VV delay period and hence prior to delivery of a pace to the master
ventricle, then the method may immediately deliver stimulation to
the master ventricle and inhibit delivery of stimulation to the
slave ventricle. If activity is sensed in the slave ventricle after
delivery of stimulation to the master ventricle and prior to
expiration of the VV delay, then the exemplary method may inhibit
delivery of stimulation to the slave ventricle. Such a method
optionally includes adjusting the ventricular refractory period in
the slave ventricle channel to be greater than the appropriate IVCD
minus VV. IVCD could be either IVCD-LR or IVCD-RL or an average of
the two. Such a method optionally switches to single ventricular
pacing, where appropriate, and delivers single ventricular pacing
to achieve intentional fusion.
[0159] An exemplary implantable device includes a power supply, a
processor, a lead including one or more electrodes capable of being
positioned proximate to a master ventricle, a lead including one or
more electrodes capable of being positioned proximate to a slave
ventricle, and control logic, executable through use of the
processor, to set an interventricular delay between the master
ventricle and the slave ventricle and to call for immediate
delivery of stimulation to the master ventricle using the lead
proximate to the master ventricle upon detection of intrinsic
activity in the slave ventricle prior to the interventricular delay
(e.g., prior to delivery of stimulation to the master ventricle).
Such control logic optionally inhibits delivery of stimulation to
the slave ventricle. Such control logic optionally calls single
ventricular pacing, where appropriate, and delivers single
ventricular pacing to achieve intentional fusion.
[0160] An optimal interventricular delay can change as demand
and/or heart conditions change. Thus, an exemplary method may
determine an optimal interventricular delay during sleep on a
nightly, a weekly or some other basis. Such an exemplary method may
determine an optimal interventricular delay within a matter of
minutes (e.g., approximately 5 heart beats). Such an exemplary
method may be triggered according to a change in heart rate or some
other parameter related to heart condition. Over time or at time of
programming, an exemplary device may store one or more optimal
interventricular delays as a function of heart rate, heart
condition, etc., and then implement a selected delay from the
stored delays upon occurrence of a rate, condition, etc., or a
change in rate, condition, etc. Such dynamic control of
interventricular delay can improve cardiac performance and
potentially allow for an improvement in patient quality of life
(e.g., allow for a broader range of patient activity). If after
some predetermined period of time or upon occurrence of a
particular condition, an exemplary device may indicate a need for a
more rigorous determination, for example, via an
echocardiogram.
[0161] As described herein, various techniques include adjusting
one or more pacing parameters based at least in part on patient
activity. Such techniques may use variables such as P wave width
(AP), A wave width (AA), delay from end of a P wave to beginning of
a QRS complex (DD or DD interval) and/or delay from end of an A
wave to beginning of a QRS complex (AD or AD interval). Two
parameters, .delta. and .beta., are discussed in more detail below.
The parameter .delta. may depend on .DELTA.P or .DELTA.A while the
parameter .beta. may depend on .delta. and DD or AD, as indicated
by the following equations:
.delta.=f(.DELTA.P) or f(.DELTA.A) (11)
.beta.=.delta./DD or .delta./AD (12)
[0162] These parameters may be used to determine one or more pacing
parameters, for example, as indicated by the following
equations:
PV=.DELTA.P+.beta.*DD (13A)
AV=.DELTA.A+.beta.*AD (13B)
Variations of these four foregoing equations are presented with
respect to FIG. 14. The PV or AV forms may be used to determine an
optimal PV or AV. For example, AV.sub.opt may be determined and
then used in any of the various scenarios of FIG. 12. For VV delay,
techniques described above may be used. However, as discussed in
more detail below, VV may depend on activity and hence may change
when activity state changes. Where VV is used for bi-ventricular
pacing, the following equations may be used:
PV''=PV'+VV (14A)
AV''=AV'+VV (14B)
where PV' and AV' are for the master ventricle and where PV'' and
AV'' are for the slave ventricle.
[0163] Various exemplary method discussed herein include sensing
patient activity, for example, using an activity sensor (e.g.,
accelerometer, minute ventilation, etc.), and adjusting one or more
pacing parameters based at least in part on such sensing. An
exemplary method may select a pacing parameter for a pacing therapy
based on patient activity state. For example, an implantable device
may include a set of parameters for a rest state and a set of
parameters for an exercise state.
[0164] An exemplary method may include monitoring one or more
characteristics of atrial activity and adjusting one or more pacing
parameters based at least in part on such monitoring. For example,
a method may include monitoring P wave width (e.g., .DELTA.P) and
using P wave width to adjust one or more pacing parameters whereas
another method may include monitoring A wave width (e.g., .DELTA.A)
and using A wave width to adjust one or more pacing parameters. P
wave width or A wave width may increase as patient activity
increases. Thus, if the P wave width or the A wave width exceed a
limit, then an exemplary method may call for a change in one or
more pacing parameters.
[0165] An exemplary method may include disabling ventricular pacing
(for one or both ventricles) and measuring DD interval or AD
interval, respectively, and adjusting one or more pacing parameters
based at least in part on such measuring. DD interval or AD
interval may increase as patient activity increases. Thus, if the
DD interval (e.g., DD.sub.RV or DD.sub.LV) or the AD interval
(e.g., AD.sub.RV or AD.sub.LV) exceed a limit, then an exemplary
method may call for a change in one or more pacing parameters.
[0166] An exemplary method may include sensing PP interval as a
marker for the atrial rate (from P wave to P wave) which can serve
as a surrogate for patient activity and adjusting one or more
pacing parameters based at least in part on such sensing. In
general, PP interval will decrease as patient activity increases;
noting that certain conditions or drugs may make this technique
less useful (e.g., beta blockers, high NYHA class, etc.). While PP
interval is mentioned, other intervals may be used based on a
marker that occurs once per cardiac cycle (e.g., R.sub.RV,
R.sub.LV, etc.). An exemplary method may select a pacing parameter
for a pacing therapy based on an interval. For example, an
implantable device may include a set of parameters for a long
interval (e.g., a rest state) and a set of parameters for a short
interval (e.g., an exercise state).
[0167] While the foregoing discussion pertains to schemes
individually, an exemplary method may use any of the various
schemes, as appropriate. For example, an exemplary method may
include monitoring P wave width and disabling ventricular pacing
(to one or both ventricles) to measure DD interval based at least
in part on P wave width.
[0168] FIG. 14 shows various exemplary methods 1400. While
equations are presented in FIG. 14, implementation of techniques
described herein may be implemented using any of a variety of forms
of control logic. For example, look-up tables may be used together
with logic that stores and/or pulls data from the look-up table.
Control logic to achieve the overall goals achieved by the various
equations 1400 may be achieved by control logic that does not
explicitly rely on the equations, as presented.
[0169] A state block 1410 defines various activity states. The
activity states include a base state, for example, a rest state
denoted by a subscript "0". In other examples, the subscript "rest"
is used. The activity states include at least two states, for
example, a base state and another activity state. In FIG. 14, the
states range from the base state to activity state "N", which may
be an integer without any numeric limitation (e.g., N may equal 5,
10, 100, 1000, etc.). The number of activity states may depend on
patient condition and patient activity. For example, a patient that
is bedridden may have few activity states when compared to a young
patient (e.g., 40 years old) fitted with a pacemaker that leads an
active life with a regular exercise regimen.
[0170] A PV or AV states block 1420 presents equations for the
parameters .beta. and .delta. as well as for a base state PV and AV
and PV and AV for a state other than a base activity state,
referred to as AS.sub.x, where x=1, 2, . . . N. In addition, sets
of equations are presented that include a pacing latency term PL.
Pacing latency is generally defined as the time between delivery of
a cardiac stimulus and the onset of an evoked response caused by
the stimulus. More specifically, an implantable device may use the
time of delivery of a stimulus and the time at which a sensed,
evoked response signal deviates from a baseline, which is referred
to herein as PL.sub.I (e.g., to initiation of evoked response).
Such a signal is usually sensed using the lead that delivered the
stimulus, however, electrode configuration may differ (e.g.,
unipolar delivery and bipolar sensing, bipolar delivery and
unipolar sensing, etc.). In some instances, the pacing latency may
exceed 100 ms due to ischemia, scarring, infarct, etc. Thus, PV or
AV timing may be adjusted accordingly to call for earlier or later
delivery of a stimulus to a ventricle or ventricles.
[0171] An exemplary algorithm may determine PL for the right
ventricle (for a right ventricular lead) and for the left ventricle
(for a left ventricular lead) during measurement of IVCD-LR and
IVCD-RL (e.g., parameters that may be used to determine VV). While
pacing latency can be measured from the time of delivering a pacing
pulse to the time of an evoked response at the pacing lead
(PL.sub.I), pacing latency may be measured alternatively from the
time of the pulse to the peak of an evoked response (PL.sub.Peak).
In either instance, such techniques may shorten block and/or
discharge periods, optionally to a minimum (e.g., about 3 ms in
some commercial ICDs). An algorithm may also provide for detection
of capture, for example, using an integral (e.g., PDI) and/or a
derivative (e.g., D.sub.max). In general, pacing latencies for LV
and RV leads correspond to situations where capture occurs. In yet
another alternative, during P wave and PR measurement, a time delay
from a marker of a sensed R event to the peak of a QRS complex may
be measured and used as a correction term akin to pacing
latency.
[0172] A VV states block 1430 presents equations for the parameters
.alpha., .DELTA. and .DELTA..sub.IVCD and VV for a base activity
state (AS.sub.0) and another activity state (AS.sub.x). As
described herein, "VV" represents an interventricular interval that
occurs during a single "heartbeat" or cardiac cycle (e.g., from
delivery of stimulation energy to the RV to delivery of stimulation
energy to the LV for a cardiac cycle); whereas, "PP" represents an
interval for atrial activity from one cardiac cycle to a subsequent
cardiac cycle. These equations may be used in various scenarios of
the method 1200 of FIG. 12 or other methods. Noting that some
differences exist between the method 1200 and the equations of FIG.
14, for example, lack of absolute values for the parameter .DELTA..
To account for this variation, the value of .DELTA. is used to
determine whether the right ventricle or left ventricle is paced
for single ventricle pacing or is the master for bi-ventricular
pacing. If the .DELTA. is less than 0 ms, then the right ventricle
is paced (e.g., RV master) whereas if .DELTA. is greater than 0 ms,
then the left ventricle is paced (e.g., LV master). For
bi-ventricular pacing, the PV or AV state equation is used for the
master ventricle and then the VV equation is used to determine
timing of the slave ventricle. Hence, the control logic uses
.DELTA. to determine whether the PV or AV state equation will
correspond to the left ventricle or the right ventricle.
[0173] The block 1430 also includes equations for a pacing latency
differential, referred to as .DELTA.PL. This term may be
calculated, for example, as the difference between PL.sub.Peak and
a generic or average pacing latency (e.g., PL.sub.Ave based on a
sampling of "normal" pacing latencies). Hence, .DELTA.PL may
represent a difference from a normal pacing latency. A normal
pacing latency may be around 70 ms and hence APL may equal
PL.sub.Peak minus 70 ms. The parameter .DELTA.PL may be calculated
for both the right ventricle (e.g., .DELTA.PL-RV) and the left
ventricle (e.g., .DELTA.PL-LV). Where VV has positive sign that
indicates to pace LV first, then the correction term .DELTA.PL-LV
may be added while where VV has a negative sign that indicates to
pace RV first then the correction term .DELTA.PL-RV may be added.
In block 1230, the term .DELTA.PL is shown without indication of LV
or RV, noting that use of .DELTA.PL-LV or .DELTA.PL-RV may be
determined accordingly. A criterion or criteria may be used to
decide if a pacing latency correction term should be used in
determining PV, AV or VV. For example, if PL exceeds a certain
limit, then a pacing latency correction term or terms may be used.
Similarly, if .DELTA.PL exceeds a certain limit, then a pacing
latency correction term or terms may be used.
[0174] Recent clinical data indicates that during exercise, optimal
PV/AV delays are prolonged compared with those at rest in HF
patients. Various exemplary techniques described herein can account
for changes for HF patients during exercise and at rest through the
duration of P wave or A wave and an appropriate atrio-ventricular
conduction delay. During exercise some HF patients may have an
increase in width of atrial signals or atrio-ventricular conduction
delays or both that would lead to prolonged optimal AV and PV
delays. In patients with normal rate responses, AV or PV delays may
have negative hysteresis or remain the same as at rest.
[0175] While various examples mention use of a "rest" state, a rest
state may be a base state. Alternatively, a base state may be a
state other than a rest state. For example, a base state may
correspond to a low activity state where a patient performs certain
low energy movements (e.g., slow walking, swaying, etc.) that may
be encountered regularly throughout a patient's day. Thus, a base
state may be selected as a commonly encountered state in a
patient's waking day, which may act to minimize adjustments to PV,
AV or VV. Further, upon entering a sleep state, a device may turn
off adjustments to PV, AV or VV and assume sleep state values for
PV, AV or VV. Such decisions may be made according to a timer, a
schedule, an activity sensor, etc.
[0176] Various exemplary methods, devices, systems, etc., include
triggering of an algorithm to update optimal VV delay according to
a predetermined time or event period or activity sensors for
exercise, resting, etc. An exemplary device may include a learning
method that learns based on differences in conduction times (e.g.,
AR.sub.RV and AR.sub.LV, IVCD, etc.) such that parameters
associated with different heart demands can be stored. The
exemplary learning method may then extract such learned or other
parameters to set an optimal VV delay.
[0177] In the aforementioned learning example, if the device learns
on the basis of different cardiac demands, the device may adjust AV
delay and/or VV delay and/or learn a new AV delay and/or VV delay
upon a change in cardiac demand. According to this example, use of
external measurement or sensing equipment (e.g., echocardiogram,
etc.) is optional. Further, use of internal measurement or sensing
equipment for sensing pressure or other indicators of hemodynamic
performance is optional. Again, adjustment and learning may rely on
IEGM information and/or cardiac other rhythm information.
[0178] According to various exemplary methods, devices, systems,
etc., information acquired (e.g., sensed, detected and/or
determined) may be used to diagnose cardiac condition. For example,
an exemplary method may track AV delays and/or VV delays over time.
Such information may then be used to determine subsequent
therapy.
[0179] Various exemplary methods, devices, systems, etc., include
determining an optimal interventricular delay (e.g.,
.DELTA..sub.optimal) using a modality such as an echocardiogram.
While an internal echocardiogram or implantable hemodynamic sensors
may be available or become available and be able to measure such
optimal delays for a variety of patient circumstances (e.g., sleep,
exercise, etc.), an exemplary method, device, system, etc.,
includes use of one or more internal sensors to measure and/or
update such an optimal delay and/or to determine values for one or
more parameters related to an optimal delay. For example, a blood
pressure sensor (e.g., aortic arch, left atrium, etc.) may be used
to determine or to update an optimal delay. Further, information
may be collected over a period of time to determine heart condition
(e.g., deterioration, improvement, etc.).
[0180] Various exemplary methods, devices, systems, etc.,
optionally rely on interference between an intrinsic stimulus and a
non-intrinsic stimulus or between two non-intrinsic stimuli. A
common form of interference is known as "fusion". While various
aforementioned examples may aim to avoid fusion, other examples
deliberately seek the occurrence of fusion (i.e., intentional
fusion).
[0181] An exemplary method may alternate between a normally timed
pacing stimulus and one aimed at causing fusion. According to such
a method, if the normally timed pacing stimulus does not cause an
evoked response, then the capture threshold may have changed. Under
such circumstances, the "fusion" test should be halted until
capture is ensured. Alternatively, a fusion test may use a high
energy level (e.g., back-up level or other elevated level).
CONCLUSION
[0182] Although exemplary methods, devices, systems, etc., have
been described in language specific to structural features and/or
methodological acts, it is to be understood that the subject matter
defined in the appended claims is not necessarily limited to the
specific features or acts described. Rather, the specific features
and acts are disclosed as exemplary forms of implementing the
claimed methods, devices, systems, etc.
* * * * *