U.S. patent application number 10/605476 was filed with the patent office on 2004-06-03 for multi-electrode apparatus and method for treatment of congestive heart failure.
This patent application is currently assigned to QUETZAL BIOMEDICAL INC.. Invention is credited to Mathis, Scott, Prentice, John K., Rottenberg, William B., Schmidt, John.
Application Number | 20040106958 10/605476 |
Document ID | / |
Family ID | 23023051 |
Filed Date | 2004-06-03 |
United States Patent
Application |
20040106958 |
Kind Code |
A1 |
Mathis, Scott ; et
al. |
June 3, 2004 |
MULTI-ELECTRODE APPARATUS AND METHOD FOR TREATMENT OF CONGESTIVE
HEART FAILURE
Abstract
An apparatus and method for treatment of congestive heart
failure from the right side of the heart. An implantable cardiac
stimulation system with a multi-electrode lead having three or more
selectable electrodes, together with apparatus for identifying an
optimal subset of electrodes, apparatus for shaping a propagating
wave front, and apparatus for modifying the intrinsic ventricular
cardiac activation sequence, or generating simultaneous or near
simultaneous pacing pulses to the septum or right ventricular
outflow tract during ventricular systole in order to improve left
ventricular cardiac efficiency and reduce mitral regurgitation in
patients with dilated cardiomyopathy. A three dimensional map of
electrode placement may be calculated. A sub set of the available
electrodes in the right side of the heart is selected for
stimulation such that septal motion during systole is reduced or
the mitral valve area is stiffened to reduce mitral
regurgitation.
Inventors: |
Mathis, Scott; (Durango,
CO) ; Prentice, John K.; (Boulder, CO) ;
Schmidt, John; (Leesburg, VA) ; Rottenberg, William
B.; (Durango, CO) |
Correspondence
Address: |
JOHN RICHARD MERKLING
11171 WEST EXPOSITION DIRVE
LAKEWOOD
CO
80226
US
|
Assignee: |
QUETZAL BIOMEDICAL INC.
P.O. Box 3576
Boulder
CO
|
Family ID: |
23023051 |
Appl. No.: |
10/605476 |
Filed: |
October 1, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10605476 |
Oct 1, 2003 |
|
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|
10075808 |
Feb 13, 2002 |
|
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|
6643546 |
|
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60268449 |
Feb 13, 2001 |
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Current U.S.
Class: |
607/11 |
Current CPC
Class: |
A61N 1/368 20130101;
A61N 1/36842 20170801; A61N 1/3686 20130101; A61N 1/3684 20130101;
A61N 1/3627 20130101 |
Class at
Publication: |
607/011 |
International
Class: |
A61N 001/18 |
Claims
1. An apparatus for treating congestive heart failure comprising a
multi-electrode lead, said multi-electrode lead having at least
three selectable electrodes, a cardiac stimulator in the body of
said patient, said cardiac stimulator being connected to said
multi-electrode lead, means for selecting a subset of said
electrodes for stimulating the heart such that stimulation through
said set of electrodes improves cardiac performance, and means for
stimulating the heart through said subset of electrodes.
2. The apparatus of claim 1 further comprising means for selecting
a set of electrodes lying on the right septal wall.
3. The apparatus of claim 3 further comprising means for
stimulating substantially all of the ventricular septum within at
least the first 10 per cent of ventricular contraction time.
4. The apparatus of claim 2 further comprising means for
stimulating at said set of electrodes to stiffen the septum in a
sequence such that substantially all of the septum stiffens
substantially simultaneously.
5. The apparatus of claim 2 further comprising means for selecting
a set of electrodes lying on the septal wall by identifying a set
of electrodes close to a line connecting two electrodes that are
known to lie on the septal wall.
6. The apparatus of claim 1 wherein said multi-electrode lead has
sufficient electrodes deployable on the right ventricular septal
wall such that at least fifty per cent of the right ventricular
wall could be stimulated within the first ten percent of the
ventricular contraction time.
7. The apparatus of claim 6 wherein said electrodes are within 8 mm
of each other.
8. The apparatus of claim 6 wherein the electrodes are within 4 mm
of each other.
9. The apparatus of claim 1 further comprising means for
determining a three dimensional position for each electrode.
10. The apparatus of claim 1 further comprising means for
developing a plurality of template patterns of wave fronts passing
said electrodes and means for distinguishing between intrinsic and
ectopic wave fronts by comparing sensed wave fronts to said
template patterns.
11. An implantable cardiac stimulator for treating congestive heart
failure comprising an implantable lead having at least three
electrodes, a cardiac stimulator connectable to said lead to place
said electrodes in electrical communication with said stimulator;
at least one detector coupled to said electrodes for detecting
electrical phenomenon in the patient's body; a timer connected to
said detector for timing at least one elapsed time between
electrical phenomena detected at said electrodes; at least one
logical template of an expected pattern of detected electrical
phenomenon at said electrodes, a comparator comparing said detected
electrical phenomenon and said elapsed times associated with said
phenomenon to said logical template, and an output circuit
providing a therapy to said patient in response to said
comparison.
12. The implantable cardiac stimulator of claim 11 further
comprising a logical model in said cardiac stimulator representing
locations of said electrodes in a patient's body.
13. The implantable cardiac stimulator of claim 11 further
comprising a time-out circuit, said time out circuit turning off
said timer whenever a second electrical phenomenon has not occurred
within a selected period of time after a first phenomenon.
14. The implantable cardiac stimulator of claim 13 wherein the
selected period of time is set based on electrode spacing and on
expected conduction velocities.
15. The implantable cardiac stimulator according to claim 11
further comprising a logical template of a normal pattern and at
least one logical template of an ectopic pattern.
16. The implantable cardiac stimulator according to claim 15
further comprising a circuit identifying an ectopic beat whenever a
series of electric phenomenon is first detected at an electrode
other than a selected first electrode.
17. The implantable cardiac stimulator according to claim 16
further comprising memory storing a template for identified ectopic
beats.
18. The implantable cardiac stimulator of claim 11 further
comprising circuit means for stimulating the heart through at least
some of said at least three electrodes and means for selecting as a
stimulating electrode that electrode which produces a pattern of
electric phenomenon most closely resembling a normal template.
19. The implantable cardiac stimulator of claim 18 further
comprising means for identifying fast conduction associated with
stimulation through a patient's Purkinje system.
20. The implantable cardiac stimulator of claim 18 further
comprising means for measuring cardiac output and means for
comparing relative cardiac output resulting from stimulation at
each of said at least some electrodes and wherein said means for
selecting a stimulating electrode is responsive to said means for
measuring cardiac output to select as stimulating electrode the
electrode optimizing cardiac output.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is a divisional application of U.S. patent application
Ser. No. 10/075,808, filed Feb. 13, 2002, now U.S. Pat. No.
______.
BACKGROUND OF INVENTION
[0002] This invention pertains to a method and apparatus for
applying cardiac stimulation using multiple electrodes, and more
particularly, to a method and apparatus for treatment of congestive
heart failure.
[0003] The heart is a mechanical pump that is stimulated by
electrical impulses. The mechanical action of the heart results in
the flow of blood. During a normal heartbeat, the right atrium (RA)
fills with blood from the returning veins. The RA then contracts
and this blood is moved into the right ventricle (RV). When the RV
contracts it pumps that blood to the lungs. Blood returning from
the lungs moves into the left atrium (LA), and after LA
contraction, is pumped into the left ventricle (LV), which then
pumps it throughout the body. Four heart valves keep the blood
flowing in the proper directions.
[0004] The electrical signal that drives this mechanical
contraction starts in the sinus node, a collection of specialized
heart cells in the right atrium that automatically depolarize
(change their voltage potential). This depolarization wave front
passes across all the cells of both atria and results in atrial
contraction. When the advancing wave front reaches the A-V node it
is delayed so that the contracting atria have time to fill the
ventricles. The depolarizing wave front then passes over the
ventricles, causing them to contract and pump blood to the lungs
and body. This electrical activity occurs approximately 72 times a
minute in a normal individual and is called normal sinus
rhythm.
[0005] The corresponding electrical signals identifying these
events are usually referred to as the P, QRS (or R) and T waves or
beats. More particularly, an atrial contraction is represented on
an ECG by a P wave, a ventricular contraction is represented by an
R wave and a ventricular repolarization is represented by a T wave.
The atrium also repolarizes but this event (the U wave) is masked
by activity in the ventricle and consequently it is not observable
on an ECG.
[0006] Congestive heart failure is a condition that causes many
deaths annually. The condition is characterized by weakness,
breathlessness, abdominal discomfort, edema in the lungs and the
lower portions of the body resulting from venous statis and reduced
outflow of blood. These symptoms are associated with the inability
of the heart to pump sufficient blood. Insufficiency may be
associated with either the left ventricle, the right ventricle, or
both. Cardiac output insufficiency may be caused by the failure of
the heart to contract in an efficient way. If the physiologic
conduction system has broken down, the chambers of the heart may
not contract in a coordinated or effective manner. It is believed
that cardiac efficiency could be improved by cardiac pacing that
commences at or near physiologically optimum locations, or that can
control or modify a cardiac wave front as the wave front passes
through a chamber of the heart. In addition, dilated cardiomyopathy
associated with heart failure often leads to a dysynchrony between
the contraction of the left and right ventricles and to mitral
regurgitation. Ventricular dysynchrony results in paradoxical
septal wall motion and in reduction of cardiac output. Mitral
regurgitation also results in a reduction in cardiac output. Both
conditions increase myocardial strain that in turn leads to
progression of the dilated cardiomyopathy via the expression of
myocardial stretch proteins. Reduction in myocardial strain is
thought to result in down regulation of these stretch proteins and
a consequent slowing of the progression of or reversal of the
dilated cardiomyopathy via reverse myocardial remodeling. Cardiac
pacing to resynchronize ventricular contractions has been shown to
increase cardiac output and reduce myocardial wall strain and it
has been observed to produce reverse cardiac remodeling in human
clinical studies. It is believed that cardiac pacing to directly
control the contraction of the septal wall could also increase
output, reduce mitral regurgitation, and reduce myocardial strain,
leading to increased cardiac efficiency and potentially reverse
remodeling. Cardiac pacing to modify the left ventricular
base-to-apex activation sequence could also reduce mitral
regurgitation, and again produce increased cardiac efficiency and
potentially reverse remodeling.
[0007] Conventional pacemakers utilize a single or dual leads to
apply pacing pulses. The dual (bipolar) lead typically includes a
tip and a ring electrode. The lead is inserted in such a manner
that the tip is imbedded into the cardiac muscle. A pacing pulse is
then applied between the tip and the ring electrodes, thereby
causing the cardiac muscle to contract. If a single unipolar
electrode lead is used, the electric pulse is applied between the
tip electrode and another electrode outside the heart, for example,
the housing of the pacemaker. Bradycardia pacing therapy has
usually been delivered through a pacing electrode implanted near
the ventricular apex, that is, near the bottom of the heart. This
location has been preferred not for physiologic reasons, but
because most lead designs favor implantation at this site. A lead
entering the right ventricle from the right atrium tends to extend
into the lower apex of the ventricle where an active fixation
apparatus, such as a helical corkscrew, may be used to secure the
lead to the heart wall. Even if the distal tip of the lead is
implanted at another location, it may be difficult or impossible to
move the electrode to another location within the heart after
initial implantation. The physician is thus limited to a single
site for applying treatment. Bradycardia pacing therapy can be
improved by delivering the stimulating pulse to a more efficient
location than the ventricular apex. Studies have indicated that the
abnormal contraction that results from apical pacing has long-term
deleterious effects. Short-term studies using conventional pacing
leads implanted in alternative locations have shown clinical
improvements, but the long-term reliability of conventional pacing
leads in these alternative locations is questionable and lead
placement is difficult.
[0008] A single stimulating electrode, such as one available on a
conventional lead, may not be implanted close enough to a
physiologically preferred location in the patient's heart to cause
improved cardiac efficiency when the pacemaker stimulates the
heart. In fact, stimulating at the bottom end of the ventricle may
diminish cardiac efficiency as compared to a wave propagated from
the top of the ventricle. Moreover, an apparatus with a single
electrode cannot control cardiac contraction, guide the propagation
of a wave front, force a selected path for a stimulating wave
front, or create a coordinated simultaneous or near simultaneous
cardiac contraction of large sections of the myocardium. Such
controlled contractions may result in more efficient cardiac
contraction, thereby reducing the overall demand on the heart,
allowing the body to alleviate the symptoms associated with
inefficient blood flow.
SUMMARY OF INVENTION
[0009] In view of the above disadvantages of the prior art, it is
an objective of the present invention to provide an implantable
cardiac stimulation system, such as a pacemaker, in which three or
more electrodes are positioned in a chamber of the heart and an
optimum electrode or electrodes are selected for pacing.
[0010] A further objective is to provide an implantable cardiac
stimulation system with apparatus for shaping or modifying a
propagating wave front, modifying the intrinsic ventricular cardiac
activation sequence, or generating simultaneous or near
simultaneous pacing pulses to the septum or right ventricular
outflow tract during ventricular systole in order to improve left
ventricular cardiac efficiency and reduce mitral regurgitation in
patients with dilated cardiomyopathy.
[0011] Another object of the invention is to provide a cardiac
stimulator system that uses multiple electrodes that can pace
simultaneously or sequentially through any or all of the
electrodes.
[0012] Other objectives and advantages of the invention shall
become apparent from the following description.
[0013] Briefly, the subject invention pertains to an implantable
cardiac stimulation system having a cardiac stimulator having
electronic circuitry for the stimulation and a multi-electrode lead
attached to the stimulator and inserted into one or more body
cavities. (The term cardiac stimulator will be used herein to cover
pacemakers as well as other cardiac devices such as internal
cardioversion devices and defibrillators.) The lead is inserted
into the cardiac cavity into a predetermined position.
Alternatively the lead may be positioned in the veins, or it may be
positioned externally of the heart. Since the lead has many
electrodes, then an appropriate subset of electrodes is selected
for stimulation.
[0014] More specifically, an implantable cardiac stimulation system
is disclosed with a stimulator adapted to sense intrinsic cardiac
activity and to generate a stimulation pulse or pulses responsive
to intrinsic cardiac activity, said stimulation pulse or pulses
having an amplitude associated with a stimulation threshold; and a
plurality of implanted electrodes including at least one optimum
electrode selected based on a physiologic parameter related to
cardiac efficiency. Stimulation of the heart for a selected chamber
usually begins at the optimum electrode or electrodes. Additional
electrodes are implanted in a patient's heart. These electrodes may
be along a wave front propagation path, such that a wave front may
be modified or reshaped by additional stimulation at selected
electrodes, they may be at sites to be stimulated simultaneously or
nearly simultaneously to cause a regional contraction of portions
of the ventricular septum, or they may be positioned to induce a
specific left ventricular activation sequence. Means are provided
to identify the optimum electrode or set of electrodes and to
identify the pattern in which cardiac tissue should be stimulated
by the additional electrodes. Such means may involve stimulating
pulses. A three dimensional map of electrode placement may be
calculated. The relative locations of the electrodes may be
determined by sensing an artificial wave front, emanating from a
known electrode, such as the distal tip electrode or by field
mapping techniques involving high frequency signals.
[0015] In a preferred embodiment, a lead having an elongated member
is provided with the electrodes being formed on said elongated
member. The electrodes comprise axially spaced electrodes disposed
on said elongated member, each electrode being connected by a wire
extending though said elongated member. The electrodes may be
circumferential coils integral or continuous with the wires or may
be rings connected to the wires by crimping or laser welding, for
example. An electrode may also be provided at the distal end of the
lead. The elongated member may be a tube housing the wires. The
electrodes can be angularly spaced with respect to each about the
elongated member. The tube may include an elongated cavity adapted
to receive a removable stylet. The stylet may be more rigid then
the lead and may be used for the implantation of the lead. After
the lead is implanted, the stylet is removed.
[0016] In another aspect of the invention, a method is presented
for treating congestive heart failure by implanting a lead having
at least three electrodes, identifying an optimum electrode or
electrodes for stimulation based on cardiac efficiency, and
stimulating the heart through the optimum electrode or
electrodes.
BRIEF DESCRIPTION OF DRAWINGS
[0017] FIG. 1 shows a diagrammatic front view of a patient with a
cardiac stimulation system, including a programmer used to program
the cardiac stimulator.
[0018] FIG. 2 shows a block diagram of the cardiac stimulator or
FIG. 1.
[0019] FIG. 3 is a block diagram of a portion of the circuits of
FIG. 2.
[0020] FIG. 4 is a second embodiment of the circuit portion of FIG.
3.
[0021] FIG. 5 is a block diagram of another portion of the circuits
of FIG. 2.
[0022] FIG. 6 is a second embodiment of the other circuit portion
of FIG. 5.
[0023] FIG. 7 is a block diagram of an adapter for connecting a
multi-electrode lead to an IS-1 connector.
[0024] FIG. 8 is a view of a multi-electrode lead implanted in a
heart.
[0025] FIG. 9 is a view of a second configuration of the
multi-electrode lead in the heart.
[0026] FIG. 10 is a view of a third configuration of the
multi-electrode lead in the heart.
[0027] FIG. 11 is a view of a fourth configuration of the
multi-electrode lead in the heart.
[0028] FIG. 12 is a cross section of the multi-electrode lead of
FIG. 8.
[0029] FIG. 13 is a flow chart for the development of a 3-D model
of electrode position.
[0030] FIG. 14 is a flow chart for characterizing electrodes from
intrinsic wave fronts.
[0031] FIG. 15 is a flow chart for characterizing electrodes from
wave fronts produced by stimulation.
[0032] FIG. 16 is a graphical representation of a cardiac
contraction as sensed by a plurality of electrodes and by an
external ECG machine.
[0033] FIG. 17 is a graphical representation of an ectopic cardiac
contraction as sensed by a plurality of electrodes and by an
external ECG machine.
[0034] FIG. 18 is a graphical representation of a cardiac
contraction caused by pacing at a sub-optimal electrode as sensed
by a plurality of electrodes and by an external ECG machine.
[0035] FIG. 19 is a graphical representation of a cardiac
contraction caused by pacing at an optimal electrode as sensed by a
plurality of electrodes and by an external ECG machine.
[0036] FIG. 20 is a graphical representation of a cardiac
contraction caused by sequential pulse train pacing at a plurality
of electrodes as sensed by a plurality of electrodes and by an
external ECG machine.
[0037] FIG. 21 is a flow chart of a program for providing a therapy
for congestive heart failure.
[0038] FIG. 22 is a flow chart of a program for identifying a set
of electrodes on or near the right ventricular septal wall.
[0039] FIG. 23 is a graphical representation of electrodes selected
in connection with the program of FIG. 22.
[0040] FIG. 24 is a flow chart of a program for gathering data
concerning cardiac wave fronts and providing therapy.
DETAILED DESCRIPTION
[0041] The subject invention pertains to an implantable cardiac
stimulation system 10 including a cardiac stimulator 12 with
various electronic circuits, and a multi-electrode lead 14 attached
to the stimulator 12, as shown. The lead 14 has a distal end 16
disposed, for example, in one of the cardiac chambers such as the
right ventricle 18 of heart 20. In FIG. 1, end 16 is shown having a
general spiral shape. The system 10 is adapted to deliver therapy
in the form of electrical pulses. The therapy may include GCV
(greater cardiac vein) resynchronization therapy, treatment of
conduction pathway abnormalities, bardycardia pacing, etc. The
cardiac stimulator 12 contains electronic components common to
current cardiac stimulators such as a battery, microprocessor
control circuit, ROM, RAM, an oscillator, reed switch and antenna
for communication, output circuits, and sense circuits. These
components are well known to those of skill in the art. In addition
the cardiac stimulator 12 has a plurality of independent sensing
and stimulating circuits for each heart chamber, as will be
explained below.
[0042] Cardiac Stimulator FIG. 2 illustrates important elements of
the cardiac stimulator 12 in block diagram. The cardiac stimulator
12 comprises a logic control and timing circuit 22, which may
include a microprocessor and memory, but which could also be
implemented in a specialized circuit. The logic control and timing
circuit 22 receives input from a sense detection circuit 24 and
issues control instructions to an output control circuit 26. To
accommodate the many electrodes used in the apparatus, multiple
sense amplifiers 28a, 28b . . . 28n are provided, each in
electrical communication with an electrode through the lead 14 and
with the sense detection circuit 24. Similarly, the output control
circuit 26 is electrically connected to a plurality of output
circuits 30a, 30b . . . 30n. The output circuits 30a, 30b . . . 30n
produce stimulating pulses or high frequency, non-simulating
signals at electrodes in the heart through the lead 14. The logic
control and timing circuit 22 may operate in accordance with a
program stored into memory. The programming in memory is received
through a transceiver 25 (for instance from programmer 100). As
part of this programming, the electrodes designated for
stimulation, as described below, are stored in memory. During its
operation, the microprocessor of the logic control and timing
circuit 22 sets the output control circuit 26 and the sense
detection circuit 24 in accordance with the appropriate electrode
designations. Thereafter, the sensing detection circuit 24 senses
intrinsic activity and other signals within the heart 20 and
provides corresponding indication signals to the microprocessor.
The Logic control and timing circuit 22 then issues appropriate
commands to the output control circuit 26. The output control
circuit 26 generates appropriate stimulation pulses. These pulses
are steered to the designated electrode or electrodes.
[0043] Output Circuits. FIGS. 3 and 4 show two embodiments of
output control circuits 26 and output circuits 30a, 30b . . . 30n.
The embodiment of FIG. 3 comprises a communications controller that
receives control signals from the logic control and timing circuit
22 (FIG. 2). Output of the communications controller 32 is sent to
an amplitude controller 34 that controls the voltages produced by a
plurality of voltage amplifiers 36a, 36b . . . 36n. In parallel,
the communications controller 32 also regulates a pulse timing
controller 38. Signals from the pulse timing controller 38 close
and open switches 40a, 40b . . . 40n, thereby delivering
stimulation pulses or high frequency signals to the heart through
electrodes on the lead 14. The embodiment of FIG. 4 also uses a
communication controller 32 and pulse timing controller 38, but the
amplitude controller 34 and plurality of voltage amplifiers 36a,
36b . . . 36n are replaced by a single voltage amplifier 42. To
achieve the same effect of multiple pulses to selected electrodes,
the signals from the pulse timing controller are sent to a
multiplexer 44, comprising a switch matrix controller 46 and a
plurality of switches 48a, 48b . . . 48n. The switches 48a, 48b . .
. 48n must be opened and closed in a synchronized manner. It may be
necessary to open all switches before and after closing a selected
switch. Thus the embodiment of FIG. 4 gains simplicity and energy
efficiency by minimizing the number of voltage amplifiers, but
sacrifices flexibility in potential output patterns.
[0044] Sense Circuits A variety of apparatus may also be used to
sense signals from multiple electrodes through the sense detection
circuit 24. A first embodiment is illustrated in FIG. 5. In the
embodiment of FIG. 5, a communication controller 50 in the sense
detection circuit 24 communicates with the logic control and timing
circuit 22 (FIG. 2). The communication controller 50 is in
electrical communication with a sense amp controller 52 and a sense
event timing analysis unit 54. The sense amp controller 52
regulates amplification levels on the sense amps 36a, 36b . . . 36n
such that significant signals are detected and noise is rejected.
Each amplifier has independent sensitivity (gain) and filter
characteristics. The sense event timing analysis unit 54 receives
output from the sense amps 36a, 36b . . . 36n and collects that
information into a description of a moving wave front. Both
intervals between sensed events and the sequence of channels or
electrodes are used to describe the wave front. The description of
the wave front is communicated to the logic control and timing
circuit 22 for use in determining the appropriate therapy. A second
embodiment, illustrated in FIG. 6, employs a multiplexer in a
manner similar to the second embodiment of the output control
circuit, described in connection with FIG. 4, above. In this second
embodiment of the sense detection circuit 24, the sense amp
controller 52 controls a single amplifier 56. The sense event
timing analysis unit 54 analyses the output of the single amplifier
56 and produces the description of the moving wave front. A sense
timing controller 58, in electrical communication with both the
communication controller 50 and the sense event timing analysis
unit 54, controls a multiplexer 60 through a switch matrix
controller 62. The switch matrix controller 62 opens and closes a
plurality of switches 64a, 64b . . . 64n, selectively connecting
the electrodes of the lead 14 to the sense amplifier 56. As
explained above, replacing multiple dedicated sense amplifiers 36a,
36b . . . 36n with a single amplifier 56 exchanges flexibility and
simplified control for energy efficiency.
[0045] The multiplexers 44, 60 of the embodiments of the output
control circuit of FIG. 4 and of the sense detection circuit of
FIG. 6 may be combined externally to the cardiac stimulator 12 in
an alternative configuration, illustrated in part in FIG. 7. FIG. 7
shows an adapter 66 for a connecting a multi-electrode lead to a
cardiac stimulator having an IS-1 connector in the header of the
stimulator 12. IS-1 connectors are well known and many physicians
are familiar with their operation and use. For the adapter 68 a
male IS-1 connector 68 is connected to the multiplexers 44, 60 in
an independent package. The multiplexers are connected either
directly to the lead 14 or indirectly through a multi-electrode
connector 70. Dual chamber pacemakers having two IS-1 connectors in
a single header are well known. In cardiac stimulators 12 according
to the present invention using IS-1 connectors rather than a
specialized multi-electrode connector, a first IS-1 connector might
be used to carry both the voltage from the voltage amp 42 and
signals from the pulse timing circuit 38 and a second IS-1
connector might be used to carry both the signals to the sense
amplifier 56 and the control signals from the sense timing
controller 58. Alternatively, one IS-1 connector might be dedicated
to the control signals from the sense timing controller 58 and the
pulse timing circuit 38 while another IS-1 connector might be
dedicated to the signals delivered to and received from the heart,
that is, to pulses from the voltage amp 42 and to sensed
events.
[0046] Multi-electrode Lead Details of the multi-electrode lead 14
are shown in FIG. 8. In a second embodiment, the lead 14 includes
an external biocompatible polymer tube 72 having a straight portion
74 and a shaped portion 76. The tube may be made of polyurethane or
other similar materials that may be thermally shaped so that the
shaped portion 76 retains any desired configuration. In FIGS. 1 and
8, the shaped portion 76 is shown as having a spiral shape, but
many other shapes may be selected as well. The spiral or coil
shaped lead of FIGS. 1 and 8 places electrodes around the entire
chamber of the heart. This embodiment allows complete sensing and
stimulating control around the entire chamber.
[0047] Another embodiment illustrated in FIG. 9 may provide a
folded lead that places electrodes along the ventricular septum and
up into the right ventricular outflow tract. This embodiment may be
particularly useful where the applied therapy seeks to stiffen the
septum, as further described below.
[0048] Yet another possible embodiment of FIG. 10 uses a serpentine
shape to place electrodes along a wall of a chamber of the heart.
These and other configurations may be combined and used in one or
more chambers of the heart. FIG. 11, for example, shows a lead
having a folded configuration in the right ventricle and a coiled
or spiral configuration in the atrium. Such a configuration may
have particular advantages for so-called single pass, dual chamber
applications.
[0049] It will be apparent that numerous shapes could be selected
to address the clinical needs of a particular patient. Moreover,
because the position of the electrodes in the heart is determined
as much by physiology and implantation technique as by the
characteristics of the lead, the effectiveness of the electrodes is
best determined after implantation and is substantially independent
from the location of a given electrode along the lead. Apparatus
and methods for identifying optimum electrodes are therefore
described hereinafter.
[0050] Attached to tube 72 of the lead 14 of any configuration,
there are provided a plurality of electrodes E1, E2, E3, E4, E5, .
. . En. Preferably electrodes E1 . . . En are formed of coils of
bare wire or cable wound about the tube 72. Each electrode is
connected to corresponding wires W1, W2, W3 . . . Wn which extend
through the length of tube 72 and which are shown exiting through
end 80 for the sake of clarity. Wires W1, W2, W3 . . . Wn are
insulated, so that they are not shorted to each other within the
tube 72. The electrode 14 and its method of manufacture are
disclosed in co-pending commonly assigned application Ser. No.
09/245,246 filed Feb. 5, 1999, and incorporated herein by
reference. Preferably the end 80 of tube 72 and the ends of wires
W1, W2, W3, etc. are coupled to a connector 82 for attaching the
lead 14 to the cardiac stimulator 12. The connector 82 may have a
plurality of pins Pi. Each wire W1 . . . Wn is associated with a
pin. As explained below, however, it is not necessary to connect
the electrodes E1 . . . En through the wires W1 . . . Wn to any
specific pin. Because the lead may assume different configurations
in the heart, it is the relative location of the electrodes in the
heart that is important for application of an appropriate therapy,
not the placement of the electrodes along the lead. This apparatus,
therefore, assigns a functionality to an electrode and its pin
after implantation of the lead.
[0051] In addition to spiral coil or ring electrodes E1 . . . En, a
distal tip electrode Ed may also be provided. The distal tip
electrode Ed may also have an active fixation mechanism, for
example a helical screw 84 or tines, to secure the lead to the
interior wall of the heart.
[0052] The lead 14 can be constructed with the tube 72 extending
relatively straight or can be customized to any shape to fit any
pre-selected location within the heart 20 dependent on each
particular patient's pathology. For example, if the lead 14 is to
be placed in the greater cardiac vein, then its end 16 (consisting
of tube portion 76 and electrodes E1, E2, E3 . . . etc.) is shaped
to form a small helix, so that it will fit into the grater cardiac
vein.
[0053] The tube 72 can be formed with a longitudinal cavity 86, as
shown in the cross sectional view of FIG. 12. Cavity 86 holds the
wires W1, W2, W3 etc. The lead 14 could be straightened by
inserting a substantially straight stylet 90 into cavity 86. The
stylet 90 is also flexible but is less flexible than the lead 14 so
that as it is inserted into the cavity 86, it forces the tube 72 to
straighten. The lead 14 is then inserted into the heart or into a
vein near the heart. After implantation of the lead 14, the stylet
90 is withdrawn and the lead 14 flexes back and takes a
configuration shown, for example, in FIG. 8, 9, 10, or 11.
[0054] Programmer A programmer 100 may be used to program the
cardiac stimulator 12, usually by electromagnetic signals. In
particular for use with this system, the programmer may be
temporarily connected directly to the lead 14, as shown in FIG. 1
by dotted line 102. This connection may be made to the lead alone,
or it may be made through the cardiac stimulator 12. This
connection is used after the lead has been implanted to
characterize the location of the electrodes, as explained in detail
below. The programmer 100 comprises a microprocessor 104 for
performing various functions in connection with programming the
cardiac stimulator. In addition, in order to characterize the
electrodes of the lead, and provide sufficient information for
selecting therapies suitable for treating congestive heart failure,
the programmer may be provided with certain sensors and pulse or
frequency generators. The programmer may have an external ECG
detector coupled to electrodes 110, 112, which may be external
electrodes. In addition, a physiologic sensing circuit 114 may be
provided with an associated sensor 116. Physiologic parameters
associated with cardiac performance may be sensed to provide
information for characterizing the lead or programming the cardiac
stimulator. Such physiologic parameters may include blood pressure,
temperature, blood oxygenation, and so on. Similar sensors may be
connected to the cardiac stimulator 12 for chronic implantation and
may be mounted on the stimulator itself or on the lead 14, for
example. The programmer may also be provided with a pulse generator
for generating temporary stimulating pulses, if desired or if
pulses are not generated by control of the cardiac stimulator and
the cardiac stimulator is not connected to the lead during
characterization of the lead. In this context, the programmer may
also have sensing circuits 120 for sensing electrical events in the
heart where the cardiac stimulator 12 is not used for this purpose.
Finally, the programmer may have a high frequency generator 122 and
high frequency sensor circuit 124, for providing non-stimulating
high frequency signals that may be used to calculate the three
dimensional positions of the electrodes within the patient's
heart.
[0055] A cardiac visualization device 101 may also be provided. The
device 101 may be a fluoroscope or ultra sonogram apparatus. The
device may be capable of visualizing Doppler flow of blood through
the valves of the heart and in particular through the mitral valve.
As will be explained hereafter, motion of the septal wall may be
visualized for treatment of congestive heart failure and in
particular for the selection of an optimal set of stimulating
electrodes. A sensor 103 emits and detects radiation such as
ultrasound or electromagnetic radiation. The resulting images may
be digitized and communicated to the microprocessor 104 by a
communications link 105. Alternatively, an operator may select
optimal electrodes through the microprocessor based in part on data
displayed by the visualization device.
[0056] Electrode Identification The process of identifying the
optimum electrode or electrodes or a pattern of electrodes may be
performed using several different approaches. For treatment of
congestive heart failure, as well as for more traditional pacing
modalities for bradycardia and tachycardia, the location of the
electrode in the heart is important, not necessarily the position
of any given electrode along the lead. As is apparent from FIGS. 8,
9, 10 and 11, an implanted lead may assume many configurations. The
lead may overlap itself, whereby electrodes proximal on the lead
are closer to the ventricular apex than are more distal electrodes.
However, in many cases, the relative location of the electrodes in
the heart may be determined by inspection under fluoroscopy by
visual approximation. This information or mapping would be used
either in the programmer or the cardiac stimulator or both. The
mapping could be used as a starting point for additional location
algorithms or as a model for measuring cardiac performance or
providing appropriate therapy.
[0057] The connection between electrodes and pins may be determined
either by manufacturing such that the first electrode is connected
to the first pin, the second electrode to the second pin, and so
on, or by measurements. A test apparatus may be provided wherein an
electrical signal is supplied to each electrode in turn and the
pins sampled to identify the pin receiving the signal. The mapping
of electrodes to pins would then be communicated to a cardiac
stimulator at the time of implantation so that the lead and cardiac
stimulator could function together as a unit.
[0058] The relative position of the electrodes can also be
determined by measuring certain phenomenon and calculating a three
dimensional position for each electrode, or by sensing the
progression of an intrinsic wave front propagating through the
heart, or by sensing the progression of a stimulated wave front,
moving through the heart, as described below.
[0059] To determine the relative positions of the electrodes in
three-dimensional space, calculations can be performed either in an
external device such as the programmer 100, or in the cardiac
stimulator 12. Because such calculations may be relatively energy
expensive, calculation in an external device may be preferred. As
described above, after implantation, the free end of lead 14 is
connected to programmer 100, as shown in dotted line 102 in FIG. 1.
Next, in step 300 (See FIG. 13) a high frequency test signal is fed
to one of the electrodes, Ei, such as the electrode disposed at the
tip of the lead 14. Preferably this test signal has a frequency in
a range that is known to have no effect on the heart 20. For
example, the test signal may have a frequency of about 200 kHz.
This test signal is generated by a high frequency or HF generator
124 and applied to the lead 14 by a multiplexer 126 that selects
different electrodes. While this HF test signal is applied to the
one lead electrode, a sensor 124 within the programmer 100 is used
to detect 302 the HF signals in the remaining electrodes. In step
304, a microprocessor 104 is used to determine the voltage
amplitude of the detected signals at each electrode. If a signal
has not been injected at each of the n electrodes (step 306), a new
electrode i is selected (step 308), and a new set of data is
recorded. Selecting all n electrodes will produce a more accurate
determination of the position of the electrodes, however, positions
can be determined by selecting as few a five electrodes (step 308).
Using this information, the microprocessor 1 04 then determines
(step 310) the position of each electrode in step 300. Details of
the algorithms used to make this determination are provided in
commonly assigned co-pending application Ser. No. 60/288,358 filed
May 3, 2001 and entitled "Implantable Electrode System To Map
Electrical Activity In 3-Dimensions And Deliver Multifocal Pacing
Therapy For Atrial Fibrillation", incorporated herein by reference.
Briefly, as described in that application, a 3D electrode
positioning system operates by applying a periodic voltage to
several subgroups of the electrodes and measuring the signal
induced on selected remaining electrodes. The number of subgroups
employed is sufficient to over-determine a system of non-linear
equations representing the distribution of the voltage (or
potential) at each of the electrodes and in the surrounding tissue.
Several means are available to extract the electrode positions
relative to tissue boundaries from such models. One of these, the
method of non-linear least squares, is well known in the
literature. (e.g. Golub and Van Loan, Matrix Computations, 1989,
Johns Hopkins) In step 312, families of sensing and pacing
electrodes are designated. This may be done automatically, using
predetermined rules provided in programmer 100. Alternatively, a
physician using an input device 106 may designate electrodes based
on the position of the electrodes and other criteria. Using this
process, it may be determined for example, that the electrodes
E1-E6 of FIG. 8 should be used for ventricular pacing.
[0060] After the optimum stimulating electrode has been designated,
the cardiac stimulator or the programmer 100 may stimulate 314 the
heart and sense 316 the propagating wave front at each of the
remaining N-1 electrodes. The time delay from the origin of the
inserted signal until the signal is sensed at an electrode provides
a set of delta times representative of the preferred propagation of
a wave front across the heart. The time delays and position for an
electrode permits calculation of a wave velocity 318 across the
heart. A physiologic sensor, such as a sensor for cardiac
contraction, or for core temperature, or blood oxygenation can be
used to determine if the selected electrode is physiologically
optimum. Alternatively, an external cardiac sensor, such as heart
monitor 108, may be used to detect the external electrocardiogram
resulting from the stimulation at the optimum electrode. Comparing
the detected ECG with an ideal ECG, an attending physician may
attempt to modify 320 the stimulation pattern. This may be done in
conjunction with the programmer 100. The physician, for example,
may indicate through a graphical interface, a portion of the ECG
that should be modified. The programmer may then seek to stimulate
the heart at selected other electrodes after the primary
stimulation. Thus, by shortening the allowed Delta Time between the
origin electrode and another electrode, an advancing wave front
could be accelerated or otherwise modified. Improved cardiac
performance may be detected on the physiologic sensors or through
the detected external ECG. When a satisfactory stimulation pattern
has been identified, the parameters representing the stimulation
pattern may be communicated 322 to the implantable cardiac
stimulator. Parameters may include time delays (Delta T), wave
front velocities, three-dimensional coordinates, and pin
assignments. Pin assignments tell the implanted device which pin in
the lead connector is associated with an electrode at a particular
location in the heart. As noted above, the location of the
electrode along the lead is not important.
[0061] Information on the relative three dimensional location of
electrodes in the heart and with relationship to the heart wall may
be valuable in specifying a therapy for the diseased heart or for
interpreting phenomenon detected in the heart. Such information is
not absolutely necessary for providing therapy for congestive heart
failure. A set of ordered time delays as a function of the n
electrodes implanted in the heart may be sufficient to provide a
clinical benefit. The order of the electrodes and their associated
time delays may be determined in several ways. Two such ways are
illustrated in FIGS. 14 and 15.
[0062] In FIG. 14, a system 330 is illustrated, for patients with
at least some intrinsic cardiac function, that is, wherein a
relatively normal contraction wave front is expected to propagate
across the heart. As above, although this functional system could
be implemented on the implanted device, for reasons of energy
conservation, implementation on the programmer 100 is preferred. To
initialize the system, the patient's intrinsic cardiac contraction
is sensed 332 at all n electrodes implanted in the heart. Ordered
pairs of an electrode and a time delay Delta T are stored 334 for
each of the n electrodes. As pointed out above, this may involve
the identification of a pin number in the lead connector. Because
the pins are not necessarily sequentially associated with adjacent
electrodes on the lead, and further because the position of the
lead in the heart is somewhat random, no information can be drawn
from the physical order of the pins in the connector as distinct
from the logical order of the pins (and electrodes) determined from
sensing the wave form in the heart. In may be expected that the
wave front pattern in a diseased heart varies considerably.
Therefore, a sample 336 of a pre-selected number M of contractions
may be taken. A counter 338 may be incremented until the sample has
been filed. Thereafter, the most physiological appropriate
occurrence may be selected 340. This may involve comparing the
samples to an ideal template, statistically averaging the samples,
or presenting the stored data to a physician through a
communication device or programmer 100, and allowing the physician
to select an intrinsic waveform among the M recorded waves. The
physician may be assisted in the selection by additional sensor
information associated with the wave forms, for example, the
external ECG, blood oxygenation, blood pressure, and so on.
[0063] When the preferred sample is identified, the associated set
of ordered pairs of electrodes and time delays is set 342 as an
initial preferred condition. This set of electrodes will usually
approximate a desirable wave front preceding from the sino-atrial
node down through the heart to the apex of the ventricle. In
particular, the first electrode E1 in this series located in a
given chamber of the heart, for example, in the right ventricle, is
taken as the first approximation of the optimum electrode for
stimulation in that chamber. Under appropriate circumstances, the
heart is stimulated at E1 (step 344). The resulting contraction is
sensed at the remaining n-1 electrodes, and the resulting vector
(that is, set of ordered pairs of electrodes and time delays) is
compared 346 to the stored pattern. A search is performed to
confirm that stimulation at E1 is superior to any electrodes within
a predetermined proximity to E1. Since the actual physical location
of the electrodes is unknown, this is a logical proximity, that is,
for example, the first P electrodes in order of time delay from E1.
If stimulation at one (Ei) of these P electrodes is superior to E1
(step 348), Ei replaces E1 as the preferred electrode E[Best] (step
350). The counter is reset 352 and the search proceeds in the
proximity of the new preferred electrode. Otherwise, the counter is
incremented 354. When the counter reaches the pre-selected number P
(step 356) the search halts and E[Best] has been identified
360.
[0064] It may also be necessary to identify the optimum electrode
E[Best] when there is no intrinsic waveform or when the intrinsic
waveform is so unpredictable or sporadic that meaningful
information cannot be derived from it. In such conditions, a system
380 illustrated in FIG. 15 may be used. As mentioned above, a
multi-electrode lead used with this apparatus may be constructed
such that the electrical communication between an electrode and a
pin in the lead connector is essentially randomly determined at the
time of manufacture. That is, the electrodes may be connected to
the pins in any order. However, if the distal tip of the lead is
both a fixation device, such as a helical screw, and an electrode,
the distal tip will preferably be provided with an identifiable
electrical connection, probably physically different from the other
wires in the lead. For example, the other electrodes may be
mechanically continuous with their electrical connector or wire,
while the distal tip or distal electrode may be connected to a
conducting wire through a mechanical connection, such as a crimp
joint or laser weld. This difference would allow the distal
electrode to be electrically connected to a specific pin in the
lead connector. Inserting the electrical conductor for the distal
electrode into the lead either first or last could also aide in
identifying this connection. In addition, the conductor connected
to the distal tip could be physically different from other
conductors, for example in type, color or thickness of wire or
insulation. The conductor connected to the distal tip might also be
identified electrically.
[0065] When the lead is implanted, the distal tip or distal
electrode can usually be located physically in the heart. For
instance, the distal electrode may be implanted low in the heart at
the apex of the right ventricle. The system 380 can begin 382 to
identify an optimum stimulation pattern. A signal may be emitted
384 through the distal electrode E[Distal]. The signal may be
either a high frequency, non-stimulating signal, or a stimulating
pulse that causes the ventricle to contract. The propagation of
this signal through the heart is sensed 386 at all electrodes and
elapsed times Delta T for each electrode are recorded 388. It may
be expected that the electrode associated with the largest Delta T
would be located relatively high in the ventricle. It may not be
the optimum electrode, but it represents a good candidate for
beginning a search for the optimum electrode. Therefore, Ei is set
390 equal to E[max T], and the heart is stimulated at step 392. The
resulting waveform is sensed 394 either by the implantable device
or externally. A physiologic performance parameter is also sensed
396 during the cardiac contractions affected by the stimulation.
The sensed parameter Pi is compared 398 with a standard P[Best]. If
Pi exceeds P[Best], P[Best] is replaced by Pi in step 400. The next
potential electrode is identified by incrementing i [step 402]. A
new set of ordered pairs associating each electrode (or pin) to a
Delta T resulting from the stimulation. If i has been incremented
to Q (step 404) the set of ordered pairs or Delta T values is
stored 406. Q is a pre-selected number equal to of less than the
total number of electrodes. If i is less than Q, a new stimulation
392 is produced at the next Ei electrode. When the optimum
electrode E[Best] has been electrode, a physician may choose to
modify the shape of the waveform by adding additional stimulations
at other electrodes, in the manner described above.
[0066] The selection of optimal electrodes has been described in
conjunction with pacing of the right ventricle. However, the same
techniques may be used for other types of stimulations as well,
including atrial pacing, dual chamber pacing, atrial and
ventricular cardioversion, atrial defibrillation, etc. Moreover,
while the techniques are described in conjunction with a single
multi-electrode lead, they are applicable for leads having other
configurations, such as several single or multi-electrode
leads.
[0067] Therapies for Congestive Heart Failure. When the cardiac
stimulator is in operation, the sense detection circuit 24 and
sense amplifiers 28 collect information about wave fronts moving
through the heart. This information can be compared to optimized
patterns or templates, such as those developed above, and used to
provide therapy. The information can also be stored for diagnostic
purposes.
[0068] For example, the cardiac stimulator 12 can distinguish
between intrinsic contractions and ectopic contractions by
distinguishing events that originate near the normal focus, that
is, near the SA node in the atrium or near the AV node in the
ventricle. Where an optimum or best electrode has been identified
as near one of these foci, as described above, a sense event may be
first detected by the optimum electrode or by an electrode within a
predetermined proximity of the optimum electrode. Such a sensed
event would be considered intrinsic if sensed first at the optimum
or best electrode or by one of a pre-selected set of nearby
electrodes. Events initiating from locations remote from the foci,
that is, relatively far away from the optimum electrode or its
adjacent set of electrodes, would be considered ectopic. A list of
frequency of initiation at each electrode can be maintained in
memory in the cardiac stimulator as a useful diagnostic.
[0069] Using the multi-electrode lead and capabilities of the
apparatus described above, it is possible to map cardiac electrical
activity. For example, in FIG. 16, a series of sense events is
illustrated at electrodes numbered in order of physical location
within the heart from electrode 1, which is the electrode nearest
the relevant focus for a particular chamber of the heart. The wave
front proceeds across the heart in an orderly fashion,
corresponding to the surface ECG also shown in FIG. 16. The
progress and shape of the wave front may be represented by a series
of ordered pairs, each pair comprising a number of an electrode and
a time delay in milliseconds, representing elapsed time from the
prior sensing point or electrode. As an example, the wave front
series or matrix for the samples of FIG. 16 might be:
[0070] In contrast, an ectopic event might produce a pattern,
similar to the pattern illustrated in FIG. 17. The contraction
commences near electrode 4, and propagates towards both electrode 3
and electrode 5. The matrix may appear as follows:
[0071] In ectopic contractions, the surface ECG may be longer or
less well-defined, reflecting the decreased efficiency of such
contractions. As will be explained below, the cardiac stimulator 12
can count intrinsic and ectopic contractions and, by recording the
ordered pairs or matrix for a contraction, can record the pattern
of ectopic events for diagnostic purposes.
[0072] The pattern of FIG. 16 represents the wave front of a
normally conducted ventricular contraction. In patients suffering
congestive heart failure, the wave front and contraction may differ
from the normal pattern. The wave front may commence at an ectopic
site. The wave front may be delayed or may be ineffectual in
certain locations, or it may not propagate uniformly through the
heart. In any event, the heart chamber does not contract
efficiently, and the heart has to work harder, for less effect.
Controlled pacing through multiple electrodes can treat these
conditions. The cardiac stimulator and multiple electrode lead
described herein can deliver effective therapy for alleviating
congestive heart failure.
[0073] Sweet-spot pacing involves the determination of the optimal
stimulating location within the heart chamber. As described above,
the optimum electrode may be determined at the time of
implantation. After implantation, similar search algorithms may be
used either through the cardiac stimulator 12 or with the
programmer 100 to confirm or modify the selection of the optimum
electrode, as conditions change over time. Current pulse generators
stimulate from an electro-physiologically arbitrary point
determined by implant technique. Stimulation at a conventionally
implanted electrode may produce a wave front similar to that
illustrated in FIG. 18. Like the ectopic wave of FIG. 17, the wave
front propagates across the heart in a less natural manner. Longer
intervals between sensed events and an extended QRS signature may
be due to the fact that the wave front follows cellular conduction
rather than the faster Purkinje fibers. Where the optimum electrode
has been identified, as described above, pacing at the optimum
electrode may produce the more natural and efficient contraction
illustrated in FIG. 19.
[0074] In patients whose natural conduction system is insufficient,
sequential pulse train pacing may be used to improve cardiac
performance. This kind of pacing is illustrated in FIG. 20.
Following the pattern of a normal wave front, FIG. 16, a train of
pulses proceeds through the electrodes in an order and at time
delays that track the path of the normal wave front. The
contraction of the heart is rendered more efficient, allowing the
heart to accomplish its task with less effort, thereby allowing the
symptoms of Congestive heart failure to be alleviated. It is not
always necessary to pace at each electrode in the series. Because
the apparatus provides for sensing at each of the electrodes as
well as pacing, the heart may be paced at a given electrode only if
the wave front does not reach that electrode within the delay time
set in the ordered pair associated with that electrode. As pointed
out above, the ordered pairs may be adjusted by a physician to
improve the efficiency of the contraction and set a desired
template for the wave front. The apparatus would then stimulate the
heart at one or more electrodes to bring the actual action of the
heart into conformity with the template, as far as possible.
[0075] An important aspect of this invention comprises modifying
the intrinsic ventricular cardiac activation sequence and
generating simultaneous or near simultaneous pacing pulses to the
septum or the right ventricular outflow tract during ventricular
systole in order to improve left ventricular cardiac efficiency and
reduce mitral regurgitation in patients with dilated
cardiomyopathy. It is asserted that specialized stimulation from
the right side of the heart can so improve left side performance
that left ventricular output can be improved. Cardiac remodeling
may also take place. One source of left ventricular inefficiency
may be increased mitral valve regurgitation. A second source may be
increased septal motion. In the weakened heart, the right and left
ventricles may become dysynchronus. In the healthy heart, the
septal wall remains relatively straight, balanced between pressures
of the contracting right ventricle and the contracting left
ventricle. In the ailing heart, the right ventricle may first push
the septum into the left ventricle and the left ventricle,
contracting later, may then push the septum back into the right
ventricle. The septum oscillates back and forth and the energy of
the heart is used up in this motion, rather than in pushing blood
out of the heart and through the circulatory system. Both sources
of left ventricular inefficiency may be treated by appropriate
stimulation to contract or stiffen heart muscles. Stimulation
through at least one and preferably two or more electrodes lying
along the septal wall in the right ventricle may so stiffen the
septum that flutter or oscillation is reduced and cardiac
performance is improved. Similarly, stimulation through at least
one electrode in or near the right ventricular outflow tract may
propagate into the base of the left ventricle, stiffening the
muscular structures around the mitral valve and increasing left
ventricular output. Achieving these results requires selecting an
electrode or set of electrodes from a set of electrodes located
along the right ventricular septal wall and extending into the
right ventricular outflow tract. Preferably the lead 14 is deployed
in the right ventricle as shown in FIG. 11. Preferably sufficient
electrodes are disposed along the septal wall a sufficient
probability of stimulating the heart at an effective region within
a selected period of time. The selected period of time is believed
to be the first 20% of right ventricular contraction time, more
preferably 10% or less of the right ventricular contraction time.
The probability of stimulating at or near an ideal sport should be
at least 25%, more preferably at least 50%, yet more preferably
100%. At least 3, more preferably 5, and yet more preferably 12,
electrodes are disposed along the lead in the region of the septal
wall.
[0076] The number of electrodes to be deployed for a given patient
may be determined as follows. It will be recognized that any number
of electrodes exceeding calculated number will meet the selected
conditions of stimulation time and coverage probability. The
conduction velocity of a contraction wave form through a ventricle
is on the order of 500 mm/sec or 0.5 mm/ms. The ventricular
contraction takes about 40 ms and it is desirable to have the
septum rigid within the first 10% of the contraction time, or
within 4 ms. At the given conduction velocity, the effects of
stimulation from a given electrode would travel about 2 mm in 4 ms.
For complete coverage, adjacent electrodes would be about 4 mm
apart.
[0077] The distance d from the center of one electrode to the
center of an adjacent electrode may be calculated as follows:
d=e+2*cv*t*(100/c)where e is the electrode length, cv is the
conduction velocity, t is the maximum conduction time and c is the
selected percent coverage. For example, if the electrode length is
2 mm, and 100% coverage is desired, the electrode center-to-center
distance is 6 mm. The number of electrodes deployed along a septum
5 cm (50 mm) long would be twelve. If 50% coverage were desired, 5
electrodes must be deployed on the same septum. If 25% coverage is
desired, 3 electrodes would be deployed on the 5 cm septum. The
distance d is not necessarily the spacing of the electrodes along
the lead 14, except in configurations such as shown in FIG. 9. In
lead configurations such as FIG. 10, additional electrodes must be
provided to increase the probability that electrodes that fall on
the septal wall are separated by the desired distance d.
[0078] The number and spacing of electrodes on the septal wall may
also be affected by the number (n) of desirable pacing locations on
a particular patient's septal wall. One or more "sweet" spots may
be located by selective stimulation as described herein. If there
are more than one sweet spots, but only one of the spots needs to
be stimulated within the desired time to achieve septal rigidity,
the probability or likelihood (L) of stimulation is
L=1-((100-c)/100).sup.n
[0079] where c is the percent covered and n is the number of
desired points or sweet spots. The likelihood of stimulation I is a
number between 0 and 1. If more than one of the sweet spots needs
to be stimulated to achieve septal rigidity, the likelihood (L)
is
L=(1-((100-c)/100).sup.n).sup.p
[0080] where p is the number of sweet spots that must be
stimulated.
[0081] These equations may be reversed to determine the desired
spacing of electrodes along the septal wall, which will aide the
physician in selecting the appropriate multi-electrode lead and
lead configuration. For example, if a particular patient is
expected to have 5 sweet spots on the septal wall, 2 of which must
be stimulated with a 75% certainty (I=0.75) to achieve septal
rigidity, then coverage c is
c-1-.sup.n{square root}{square root over (1-.sup.p)}
[0082] For the selected parameters this would be c=0.33 or 33%. The
center-to-center distance would be 14 mm, or 4 electrodes for a 50
cm septal wall. The number of electrodes would be rounded up to the
nearest whole number of electrodes.
[0083] Where multiple points are stimulated from multiple
electrodes, the timing of stimulating pulses may be simultaneous or
the pulses may be delivered at slightly varying times such that the
wave fronts propagating from the electrodes arrive at their
respective stimulation points at substantially simultaneous
times.
[0084] Where the preferred configuration of the lead 14 shown in
FIGS. 9 or 11 is used, most of the electrodes will fall on or near
the right ventricular septal wall or in the right ventricular
outflow tract. In other lead configurations, such as FIGS. 8 or 10,
the step 412 of identifying electrodes near the septum or RV
outflow tract may be more difficult. A line of electrodes lying on
the septum may be selected where two electrodes on the septum are
known. The most distal or tip electrode on the lead is usually
secured to the heart near the right ventricular outflow tract or
the septal wall near the base of the right ventricular chamber and
its location is known by reason of fluoroscopic observation during
implantation. A second electrode may be located by observation of a
radio opaque marker proximally on the lead. An electrode near the
radio opaque marker may be determined to lie sufficiently near the
apex of the heart and close to the septal wall. Alternatively, a
temporary lead may be inserted in the heart and a distal electrode
advanced to the septal wall near the apex of the right ventricular
chamber. A grid mapping of the electrodes may then be developed, as
described below. The desired set of electrodes on the septal wall
are those electrodes on the shortest path containing the two known
electrodes. As shown in FIG. 22 a program 460 begins by stimulating
462 the heart at a known electrode, preferably the distal electrode
on the lead 14. A set of adjacent electrodes 464 is identified,
comprising the first electrode sensing the stimulating pulse and
all electrodes sensing the pulse within a pre-selected time t
thereafter. In FIG. 23, this set comprises electrodes A, B and C,
adjacent electrode 1, which is the known distal electrode. The
apparatus then stimulates the heart from each electrode in the set
ABC, step 466 and forms (step 468) additional subsets, for example,
A1, A2 and B from electrode A; A2, B1 and C1 from electrode B; and
B, C1 and C2 from electrode C. Unless all electrodes have acted as
a stimulating electrode (step 470), this process is repeated until
a complete map ordering the electrodes has been developed, as
suggested in FIG. 23. The electrodes on or near the septum will be
selected (step 472) as those electrodes in the shortest temporal
path from electrode 1 to the other known electrode, electrode 2,
which may be an electrode on the lead 14 or an electrode on a
temporary lead, as explained above. In FIG. 23, this set of septal
electrodes would be electrodes 1, B, B1, and B2. Electrode 2 would
be included if it is an electrode on the multi-electrode lead. If
electrode 2 is on a temporary lead, it would not be included in the
set of septal electrodes. The set of septal electrodes is then set
474 for use in identifying the optimum electrodes for stiffening
the septum or the mitral valve, as explained above.
[0085] FIG. 21 illustrates an algorithm 410 for providing a
stimulation therapy for congestive heart failure by stimulation
from the right ventricle and right ventricular outflow tract.
First, a set of electrodes on the multi-electrode lead is
identified 412. This set of electrodes lies on or near the right
ventricular septal wall or in the right ventricular outflow tract.
A first effort may be made to identify a subset of electrodes that
stimulate the heart at locations such that the muscles around the
mitral valve will stiffen and mitral regurgitation will be reduced.
The heart is stimulated 414 through an electrode located near the
right ventricular outflow tract. Data is acquired 416 indicative of
the effectiveness of the stimulation in reducing mitral
regurgitation. The cardiac imaging device 101 is usually employed.
Data acquired by Doppler echocardiogram may indicate a reduced or
eliminated backflow through the mitral valve. This data may be
communicated across the link 105 to the programmer 100.
Alternatively, an attending health care provider may observe the
output of the cardiac imaging device 101 and enter a determination
of the effect of a stimulus on mitral regurgitation into the
programmer 100. The programmer 100 (or cardiac stimulator 12)
compares 418 regurgitation information for the present stimulation
electrode or electrodes with information from previous electrode or
sets of electrodes. If no improvement is noted, the program
inquires 422 if there is another electrode or set of electrodes in
or near the right ventricular outflow tract that is a candidate for
stimulation. If there is another electrode or set of electrodes,
those electrodes are selected 420, and the heart is stimulated 414
again. If not, the program 410 will locate an electrode or set of
electrodes that stiffen the septum in such a way that septal motion
is reduced. If there is an improvement at step 418, the current set
of electrodes is set as optimum 419 and the test for other
candidate electrodes 420 is performed.
[0086] The program 410 begins its search by stimulating 424 the
heart at an electrode or set of electrodes on or near the right
ventricular septal wall. The program may serially select single
electrodes, than sets of two electrodes, then sets of three
electrodes, and so on until a sufficient number of combinations has
been tried. Data is acquired to indicate if septal motion has been
reduced 426 by the stimulation. This may be accomplished by
digitizing features of the images captured by the cardiac imaging
device 101 and transferring this information to the programmer 100
or cardiac stimulator 12. Alternatively, the attending health care
provider may observe the output of the cardiac imaging device 101
and enter a determination of the effect of a stimulus on septal
motion into the programmer 100. The programmer 100 (or cardiac
stimulator 12) compares 430 septal wall motion information for the
present stimulation electrode or electrodes with information from
previous electrode or sets of electrodes. If no improvement is
noted, and additional electrode candidates exist (step 432), then a
new electrode or set of electrodes is selected 428 and the heart is
stimulated again 424. If there is an improvement, program test if
the current set of electrodes is better than the previous optimal
set 430. If the new set is better than the previous optimal set,
the new set is set as optimum 427, and the program inquires 432 if
there is another electrode or set of electrodes in or near the
right ventricular outflow tract that is a candidate for
stimulation. If there is another electrode or set of electrodes,
those electrodes are selected 428, and the heart is stimulated 424
again.
[0087] After both test sequences for mitral regurgitation and
septal wall motion have been performed, a set of optimal electrodes
is specified 434. For any given patient, of course, an attending
physician may elect to treat only mitral regurgitation or
ventricular wall motion without departing from the teachings of
this invention. The set of optimal electrodes is identified in the
cardiac stimulator 12 and used for stimulating the heart. In the
treatment of congestive heart failure, it may be advantageous to
stimulate the right ventricle slightly ahead of an expected
physiologic contraction, thereby controlling the contraction of the
heart from the optimal sites. Thus modern conventional pacers may
sense cardiac events in the atrium and wait for a corresponding
propagation of the event into the ventricle, stimulating the heart
only if timely propagation fails to occur. To treat congestive
heart failure, the cardiac stimulator may sense in the atrium, but
stimulate in the ventricle at a time sooner than the expected
propagation of the intrinsic wave into the ventricles.
Alternatively, the ventricle may be stimulated at a rate slightly
faster than the patient's expected heart rate. The expected heart
rate may be estimated, may be determined by electrical sensing or
may be determined by rate responsive sensing, such as by sensing an
accelerometer. This anticipatory stimulation allows the cardiac
stimulator 12 to control not only the timing of contraction, but
also the shape of the contraction, including the preparatory
stiffening of the septal wall or muscles around the mitral valve.
The shaped contraction is believed to improve cardiac output, and
in particular, to allow improved left ventricular performance from
electrodes implanted in the right ventricle.
[0088] The apparatus of the cardiac stimulator 12 and the
multi-electrode lead 14 may also be adapted to perform the
diagnostic and therapeutic functions as illustrated in the program
440 of FIG. 24. Sensing 442 through the multiple electrodes, as
described above, monitors the heart for the occurrence of sense
events. If an event is not detected (step 444), the apparatus
checks for the expiration of an event timer 446. The event timer
times various periods during a cardiac cycle. For example, a
relatively long time may be set between the completion of one
complete cardiac contraction and associated QRS complex, and the
beginning of a second contraction. After an initial sense event
(electrode 1 in FIG. 16) or an initial pace (electrode 1 in FIG.
19), shorter Delta Time periods from the ordered pairs defined
above would be used. Thus the algorithm will follow the pattern set
by a matrix of ordered pairs comprising electrodes and times and
will try to create a more normal contraction wave front. If the
event timer for the state has not expired, the apparatus will
continue sensing 448. If an event is sensed on an appropriate
electrode (step 444), the apparatus checks 450 if the event timer
is running. If the timer is running, the elapsed time is stored,
together with the identification of the sensing electrode, and the
timer is reset 452. If the event timer is not running, the timer is
started 454 and the wave front matrix is initialized. This would
indicate the beginning of a new intrinsic cardiac contraction. The
programming will follow the progress of the wave front and, if
necessary, remodel the wave front to a more efficient form. The
process begins by returning 456 to sensing 442.
[0089] When the cardiac contraction takes a longer, less efficient
form, the event timer will expire at step 446 before the wave front
is sensed at the next electrode in series. The program checks 458
if the wave front is following an intrinsic pattern, as explained
above, that is that the wave front is proceeding generally from a
focus through a chamber of the heart. If not, the wave front and
contraction are considered ectopic, and the program compares the
pattern to previously detected ectopic beats or contractions, for
diagnostic purposes. If a new pattern is detected, a record is made
of the form of the ectopic contraction, and therapy is applied 462.
This may include stimulation at a particular electrode to drive the
wave front back into a more efficient form. If the ectopic pattern
has previously been recorded, a counter for that pattern is
incremented and therapy is applied 464. On the other hand, if the
wave front matches an intrinsic pattern (step 458), an intrinsic
wave front counter is incremented and therapy applied 466 as above.
After therapy in each of these three cases, the program returns
456, 468 to sensing 442.
[0090] Data acquired by the cardiac stimulator 12 on the frequency
and form of ectopic and intrinsic wave fronts can be used to refine
the form of therapy applied. The matrix of ordered pairs
representing the desired wave front for an efficient contraction
can be modified in response to the particular needs of a patient.
The apparatus described herein allows for stimulation of the heart
at a location likely to produce an efficient contraction and for
subordinate stimulation to reshape a contraction waveform that has
started spontaneously or from an initial stimulating pulse.
Improved cardiac efficiency reduces the effects of congestive heart
failure.
[0091] Numerous other modifications may be made to this invention
without departing from its scope as defined in the attached
claims.
* * * * *