 |
Claims  |
|
|
What we claim is:
1. A cardiac rhythm management pulse generator device for generating
electric pulses and coupleable to an electrode which senses electrical
activity of the heart and carries the electrical pulses to the heart, the
pulse generator device comprising:
an input/output terminal connectable to the electrode to receive the sensed
electrical activity of the heart from the electrode and provide the
electrical pulses to the electrode;
a lowpass filter coupled to the input/output terminal for filtering the
sensed electrical activity;
a highpass filter coupled to the lowpass filter for further filtering the
electrical activity passed from the lowpass filter, the highpass filter
including a resistive portion coupled to a ground node;
a switch operable to effectively remove the resistive portion from the
highpass filter;
a sense amplifier coupled to the highpass filter for amplifying the
electrical activity of the heart passed from the highpass filter;
a cardiac depolarization detector coupled to the sense amplifier for
detecting depolarizations in the amplified electrical activity of the
heart and providing a depolarization signal indicative of the
depolarizations; and
a pulse circuit coupled to the input/output terminal and the cardiac
depolarization detector for generating the electrical pulses based on the
depolarization signal.
2. The pulse generator device of claim 1 further comprising control means
for operating the switch to effectively remove the resistive portion for a
selected period of time following each electrical pulse generated by the
pulse circuit.
3. The pulse generator device of claim 1 wherein the pulse circuit
generates pacing pulses for pacing the heart.
4. The pulse generator device of claim 1 wherein the pulse circuit is
capable of generating high voltage pulses to halt tachyarrhythmia
conditions in the heart.
5. The pulse generator device of claim 4 further comprising a second switch
operable to disconnect the sense amplifier from the highpass filter.
6. The pulse generator device of claim 5 further comprising control means
for operating the second switch to disconnect the sense amplifier from the
highpass filter prior to an electrical pulse being generated by the pulse
circuit.
7. The pulse generator device of claim 4 wherein the lowpass filter
includes a capacitor coupled to the ground node.
8. The pulse generator device of claim 7 further comprising a second switch
operable to effectively remove the capacitor from the lowpass filter.
9. The pulse generator device of claim 8 further comprising control means
for operating the second switch to effectively remove the capacitor for a
selected period of time ranging from before an electrical pulse is
generated by the pulse circuit until after the electrical pulse
dissipates.
10. The pulse generator device of claim 1 wherein the sense amplifier
comprises a differential sense amplifier.
11. A cardiac pacemaker for generating electrical pacing pulses and
coupleable to an electrode which senses electrical activity of the heart
and carries the electrical pacing pulses to the heart, the cardiac
pacemaker comprising:
input/output terminal connectable to the electrode to receive the sensed
electrical activity of the heart from the electrode and provide the
electrical pacing pulses to the electrode;
a bandpass filter coupled to the input/output terminal for filtering the
sensed electrical activity, the bandpass filter including a resistive
portion coupled to a ground node;
a switch operable to effectively remove the resistive portion from the
bandpass filter;
a sense amplifier coupled to the bandpass filter for amplifying the
electrical activity of the heart passed from the bandpass filter;
a cardiac depolarization detector coupled to the sense amplifier for
detecting depolarizations in the amplified electrical activity of the
heart and providing a depolarization signal indicative of the
depolarizations; and
a pulse circuit coupled to the input/output terminal and the cardiac
depolarization detector for generating the electrical pacing pulses based
on the depolarization signal.
12. The cardiac pacemaker of claim 11 further comprising control means for
operating the switch to effectively remove the resistive portion for a
selected period of time following each electrical pacing pulse generated
by the pulse circuit.
13. The cardiac pacemaker of claim 11 wherein the bandpass filter includes:
a lowpass filter coupled to the input/output terminal for filtering the
sensed electrical activity and the electrical pacing pulses; and
a highpass filter coupled to the lowpass filter and the sense amplifier for
further filtering the electrical activity passed from the lowpass filter,
the highpass filter including the resistive portion.
14. A cardioverter/defibrillator with pacing capability for generating
electrical pulses including shock pulses and pacing pulses and coupleable
to an electrode which senses electrical activity of the heart and carries
the electrical pulses to the heart, the cardioverter/defibrillator
comprising:
an input/output terminal connectable to the electrode to receive the sensed
electrical activity of the heart from the electrode and provide the
electrical pulses to the electrode;
a bandpass filter coupled to the input/output terminal for filtering the
sensed electrical activity, the bandpass filter including a resistive
portion coupled to a ground node;
a first switch operable to effectively remove the resistive portion from
the bandpass filter;
a sense amplifier coupled to the bandpass filter for amplifying the
electrical activity of the heart passed from the bandpass filter;
a second switch operable to disconnect the sense amplifier from the
bandpass filter;
a cardiac depolarization detector coupled to the sense amplifier for
detecting depolarizations in the amplified electrical activity of the
heart and providing a depolarization signal indicative of the
depolarizations;
a shock pulse circuit coupled to the input/output terminal and the cardiac
depolarization detector for generating the shock pulses based on the
depolarization signal; and
a pace pulse circuit coupled to the input/output terminal and the cardiac
depolarization detector for generating the pacing pulses based on the
depolarization signal.
15. The cardioverter/defibrillator of claim 14 further comprising control
means for operating the first switch to effectively remove the resistive
portion for a selected period of time following each electrical pulse.
16. The cardioverter/defibrillator of claim 14 further comprising control
means for operating the second switch to disconnect the sense amplifier
from the bandpass filter prior to each shock pulse being generated by the
shock pulse circuit.
17. The cardioverter/defibrillator of claim 16 wherein the control means
further operates the second switch to connect the sense amplifier to the
bandpass filter when each pacing pulse is being generated by the pace
pulse circuit.
18. The cardioverter/defibrillator of claim 14 wherein the bandpass filter
includes:
a lowpass filter coupled to the input/output terminal for filtering the
sensed electrical activity; and
a highpass filter coupled to the lowpass filter and the sense amplifier for
further filtering the electrical activity passed from the lowpass filter,
the highpass filter including the resistive portion.
19. The cardioverter/defibrillator of claim 18 wherein the lowpass filter
includes a capacitor coupled to the ground node.
20. The cardioverter/defibrillator of claim 19 further comprising a third
switch operable to effectively remove the capacitor from the lowpass
filter.
21. The cardioverter/defibrillator of claim 20 further comprising control
means for operating the third switch to effectively remove the capacitor
for a selected period of time ranging from before each shock pulse is
generated by the shock pulse circuit until after each shock pulse
dissipates.
22. The cardioverter/defibrillator of claim 21 wherein the control means
further operates the third switch to keep the capacitor in the lowpass
filter when each pacing pulse is being generated by the pace pulse
circuit.
23. An apparatus for effectively removing the after potential occurring
after a shock pulse is delivered in a cardioverter/defibrillator system
having an electrode for sensing electrical activity of the heart and
carrying the shock pulse to the heart and a sense amplifier for detecting
the electrical activity from the electrode, the system comprising:
switch means for disconnecting the sense amplifier from the electrode
during the delivery of the shock pulse;
a lowpass filter coupled to the electrode and having filter components
including a capacitive component for filtering the sensed electrical
activity;
a highpass filter coupled to the lowpass filter and the sense amplifier and
having filter components for further filtering the electrical activity
passed from the lowpass filter;
clamping means for limiting a charge in the capacitive component of the
lowpass filter resulting from the after potential; and
equilibrium means for allowing the filter components of the lowpass filter
and the highpass filter to return to an equilibrium state following the
delivery of the shock pulse.
24. The apparatus of claim 23 wherein the filter components of the highpass
filter include a resistive component coupled to a ground node, and wherein
the equilibrium means operates to effectively remove the resistive
component from the highpass filter for a selected period of time following
the delivery of the shock pulse.
25. The apparatus of claim 23 wherein the cardioverter/defibrillator system
includes pacing means for generating pacing pulses and the electrode
further carries the pacing pulses to the heart, wherein the apparatus
effectively removes the after potential occurring after each pacing pulse
is delivered by the pacing means, wherein the switch means couples the
sense amplifier to the electrode during the delivery of each pacing pulse,
but the equilibrium means couples the second amplifier to a ground node
during the delivery of each pacing pulse and the equilibrium means allows
the filter components of the lowpass filter and the highpass filter to
return to an equilibrium state following the delivery of each pacing
pulse.
26. The apparatus of claim 25 wherein the filter components of the highpass
filter include a resistive component coupled to a ground node, and wherein
the equilibrium means operates to effectively remove the resistive
component from the highpass filter for a selected period of time following
the delivery of each pacing pulse.
27. The apparatus of claim 23 wherein the capacitive component of the
lowpass filter is coupled to a ground node, and wherein the clamping means
includes means for effectively removing the capacitive component for a
selected period of time ranging from before a shock pulse is delivered
until after the shock pulse dissipates.
28. The apparatus of claim 23 wherein the filter components of the lowpass
filter further include a resistive component having a first terminal
coupled to the electrode and a second terminal coupled to the highpass
filter, and wherein the capacitive component has a first terminal coupled
to the second terminal of the resistive component and the highpass filter
and a second terminal coupled to a ground node.
29. The apparatus of claim 28 wherein the clamping means includes shorting
means for connecting the second terminal of the resistive component to the
ground node for a selected period of time ranging from before a shock
pulse is delivered until after the shock pulse dissipates.
30. The apparatus of claim 23 wherein the filter components of the highpass
filter include:
a capacitive component having a first terminal coupled to the lowpass
filter and a second terminal coupled to the sense amplifier; and
a resistive component having a first terminal coupled to the second
terminal of the capacitive component and the sense amplifier and a second
terminal coupled to a ground node.
31. The apparatus of claim 30 wherein the equilibrium means includes
shorting means for connecting the second terminal of the capacitive
component to the ground node for a selected period of time following the
delivery of the shock pulse.
32. The apparatus of claim 30 wherein the cardioverter/defibrillator system
includes pacing means for generating pacing pulses and the electrode
further carries the pacing pulses to the heart, and wherein the
equilibrium means includes shorting means for connecting the second
terminal of the capacitive component to the ground node for a selected
period of time following the delivery of a pacing pulse.
33. The apparatus of claim 23 wherein the clamping means includes means for
bypassing through a ground node a shock current created by the delivery of
the shock pulse.
34. An apparatus for effectively removing the after potential occurring
after a pace pulse is delivered in a cardiac pacemaker system having an
electrode for sensing electrical activity of the heart and carrying the
pace pulse to the heart and a sense amplifier for detecting the electrical
activity from the electrode, the apparatus comprising:
a lowpass filter coupled to the electrode and having filter components for
filtering the sensed electrical activity and the pace pulse;
a highpass filter coupled to the lowpass filter and the sense amplifier and
having filter components for further filtering the electrical activity
passed from the lowpass filter; and
equilibrium means for allowing the filter components of the lowpass filter
and the highpass filter to return to an equilibrium state following the
delivery of the pace pulse.
35. The apparatus of claim 34 wherein the filter components of the highpass
filter include a resistive component coupled to a ground node, and wherein
the equilibrium means operates to effectively remove the resistive
component from the highpass filter for a selected period of time following
the delivery of the pacing pulse.
36. The apparatus of claim 34 wherein the filter components of the lowpass
filter include:
a resistive component having a first terminal coupled to the electrode and
a second terminal coupled to the highpass filter; and
a capacitive component having a first terminal coupled to the second
terminal of the resistive component and the highpass filter and a second
terminal coupled to a ground node.
37. The apparatus of claim 34 wherein the filter components of the highpass
filter include:
a capacitive component having a first terminal coupled to the lowpass
filter and a second terminal coupled to the sense amplifier; and
a resistive component having a first terminal coupled to the second
terminal of the capacitive component and the sense amplifier and a second
terminal coupled to a ground node.
38. The apparatus of claim 37 wherein the equilibrium means includes
shorting means for connecting the second terminal of the capacitive
component to the ground node for a selected period of time following the
delivery of the pacing pulse.
39. A method of effectively removing the after potential occurring after a
shock pulse is delivered in a cardioverter/defibrillator system including
an electrode for sensing electrical activity of the heart and for carrying
the shock pulse to the heart, and including a sense amplifier for
detecting the electrical activity from the electrode, the sensed
electrical activity having a plurality of signal components, each signal
component having a distinct frequency in a range of relatively high and
low frequencies, the method comprising the steps of:
disconnecting the sense amplifier from the electrode during the delivery of
the shock pulse;
bypassing through a ground node a shock current created by the delivery of
the shock pulse;
filtering, with at least one first filter component, signal components of
relatively high frequency from the sensed electrical activity;
filtering, with at least one second filter component, signal components of
relatively low frequency from the filtered electrical activity; and
allowing the at least one first filter component and the at least one
second filter component to return to an equilibrium state following the
delivery of the shock pulse.
40. The method of claim 39 wherein the cardioverter/defibrillator system
includes pacing circuitry for generating pacing pulses and the electrode
further carries the pacing pulses to the heart, wherein the method further
performs the step of effectively removing the after potential occurring
after each pacing pulse is delivered by further comprising the steps of:
connecting the sense amplifier to the electrode and a ground node during
the delivery of the pacing pulse; and
allowing the at least one first filter component and the at least one
second filter component to return to an equilibrium state following the
delivery of the pacing pulse.
41. A cardiac rhythm management system comprising:
an electrode for sensing electrical activity of the heart and carrying
electrical pulses to the heart;
a lowpass filter coupled to the electrode for filtering the sensed
electrical activity;
a highpass filter coupled to the lowpass filter for further filtering the
electrical activity passed from the lowpass filter, the highpass filter
including a resistive portion coupled to a ground node;
a switch operable to effectively remove the resistive portion from the
highpass filter;
a sense amplifier coupled to the highpass filter for amplifying the
electrical activity of the heart passed from the highpass filter;
a cardiac depolarization detector coupled to the sense amplifier for
detecting depolarizations in the amplified electrical activity of the
heart and providing a depolarization signal indicative of the
depolarizations; and
pulse circuit coupled to the electrode and the cardiac depolarization
detector for providing the electrical pulses to the electrode based on the
depolarization signal.
42. The cardiac rhythm management system of claim 41 further comprising
control means for operating the switch to effectively remove the resistive
portion for a selected period of time following each electrical pulse
provided by the pulse circuit.
43. The cardiac rhythm management system of claim 42 wherein the control
means comprises a microprocessor. |
|
 |
|
 |
Claims |
|
|
|
Description |
|
|
FIELD OF THE INVENTION
The present invention generally relates to implantable medical devices, and
more particularly, to after potential removal circuitry for a cardiac
rhythm management device such as a cardiac pacemaker and/or
cardioverter/defibrillator.
BACKGROUND OF THE INVENTION
Cardiac rhythm management systems include leads or electrodes disposed in
at least one of the chambers of the heart to sense electrical activity
occurring in the chamber. For example, leads disposed in the atrial
chamber of the heart sense electrical activity representative of a P-wave
portion of the PQRST complex of a surface electrogram (EGM) indicating
depolarizations in the atrium or leads disposed in the ventricular chamber
of the heart sense electrical activity representative of a R-wave portion
of the PQRST complex of a surface EGM indicating depolarizations in the
ventricle. An implantable cardiac rhythm management system also includes a
pulse generator device, such as a cardiac pacemaker, a
cardioverter/defibrillator, or a cardioverter/defibrillator with pacing
capability, used to treat certain arrhythmia conditions in the heart such
as bradycardia and tachyarrhythmia (including ventricular fibrillation and
ventricular tachycardia) based on the sensed electrical activity. There
are a variety of well known methods and apparatus for detecting,
analyzing, and storing depolarization information related to the sensed
electrical activity of the heart for the purpose of detecting and treating
arrhythmia conditions with implantable cardiac rhythm management systems.
Present cardiac pacemakers and cardioverter/defibrillators create
after-potentials following a pacing pulse or shock pulse which are much
greater than the invoked potentials of the myocardium. As a result,
immediate detection of depolarizations in the heart is very difficult, if
not impossible, due to the after-potential effect. Prior systems have
attempted to reduce the effects of such after-potentials by various
methods.
One such method utilized in some cardiac rhythm management systems is to
use separate leads or electrodes for pulse delivery and sensing. In fact,
some cardioverter/defibrillator systems with pacing capability use
separate leads for pacing, shock delivery, and sensing. However, surgical
procedures for implanting cardiac rhythm management systems are much more
complex with the extra leads required to have separate electrodes for
pulse delivery and sensing. In addition, the extra electrodes tend to
produce additional failures in the implanted system.
Other cardiac rhythm management systems deliver a pulse to the heart and
sense on the same leads or electrodes. Some cardioverter/defibrillator
systems with pacing capability pace, deliver high energy shock pulses, and
sense through the same electrodes. When the same electrodes are used to
deliver a pulse to the heart and for sensing, a standard practice in the
art is to blank for many milliseconds the sense amplifier connected to the
lead over which the pacing pulse or shock pulse is generated. There have
been many attempts to shorten the blanking periods by speeding up the
charge dissipation process of the after potential.
SUMMARY OF THE INVENTION
The present invention provides a cardiac rhythm management pulse generator
device for generating electrical pulses. The pulse generator device is
coupleable to an electrode which senses electrical activity of the heart
and carries the electrical pulses to the heart. The pulse generator device
includes an input/output terminal connectable to the electrode to receive
the electrical activity from the electrode and to provide the electrical
pulses to the electrode. A lowpass filter is coupled to the input/output
terminal and filters the sensed electrical activity. A highpass filter is
coupled to the lowpass filter for further filtering the electrical
activity passed from the lowpass filter. The highpass filter includes a
resistive portion coupled to a ground node. A switch is operable to
effectively remove the resistive portion from the highpass filter. A sense
amplifier is coupled to the highpass filter for amplifying the electrical
activity of the heart passed from the highpass filter. A cardiac
depolarization detector is coupled to the sense amplifier and detects
cardiac depolarizations in the amplified electrical activity of the heart
to provide a depolarization signal indicative of the depolarizations. A
pulse circuit is coupled to the input/output terminal and the cardiac
depolarization detector for generating the electrical pulses based on the
depolarization signal.
The cardiac rhythm management pulse generator device of the present
invention can be embodied in a pacemaker, a cardioverter/defibrillator, or
a cardioverter/defibrillator with pacing capability. In any of these
embodiments, the pulse generator device preferably includes a switch
controller such as a microprocessor and/or state machine for operating the
switch to effectively remove the resistive portion from the highpass
filter for a selected period of time following an electrical pulse
provided by the pulse circuit. The removal of the resistive portion from
the highpass filter permits passive filter components of the lowpass
filter and the highpass filter to return more quickly to an equilibrium
state following the delivery of the electrical pulse.
When the cardiac rhythm management pulse generator device is embodied in a
cardioverter/defibrillator, the cardioverter/defibrillator includes a
second switch preferably controlled by the switch controller to disconnect
the sense amplifier from the highpass filter prior to a shock pulse being
generated by the cardioverter/defibrillator. In this way, the sense
amplifier and other sensing circuitry is protected from the shock pulse.
The lowpass filter of the pulse generator device according to the present
invention preferably includes a capacitor coupled to the ground node. When
the pulse generator device is embodied in a cardioverter/defibrillator, a
third switch is preferably included to be operable under microprocessor
and/or state machine control to effectively remove the capacitor from the
lowpass filter for a selected period of time ranging from before each
shock pulse is generated by the cardioverter/defibrillator until after
each shock pulse dissipates. In this way, a shock current created by the
after potential caused by the delivery of each shock pulse is bypassed
through the ground node.
When the cardiac rhythm management system of the present invention is
embodied in a pacemaker, the pacemaker preferably does not include
disconnecting circuitry such as the above-described second switch for
disconnecting the sense amplifier from the highpass filter prior to the
delivery of a shock pulse in a cardioverter/defibrillator system. The
disconnecting circuitry is not needed with the present invention because
of the effects of the combined lowpass and highpass filters and the switch
for effectively removing the resistor portion from the highpass filter for
the selected period of time following a pacing pulse provided by the
pacemaker.
When the cardiac rhythm management system is embodied in a
cardioverter/defibrillator with pacing capability, the three
above-described switches are controlled differently under microprocessor
and/or state machine control based on if the cardioverter/defibrillator is
pacing or providing a shock pulse. When delivering a shock pulse, the
three switches operate as described above for the
cardioverter/defibrillator embodiment. When delivering pacing pulses, the
first switch operates as above to remove the resistive portion for a
selected period of time following the pacing pulse. However, when
providing the pacing pulse, the system effectively removes the after
potential occurring after a pacing pulse is delivered with the second
switch operated to connect the sense amplifier to the highpass filter
during the entire pacing cycle, and with the third switch operated to keep
the capacitor in the lowpass filter during the entire pacing cycle.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a cardioverter/defibrillator with pacing
capability according to the present invention.
FIG. 2 is a schematic block diagram of a cardiac rhythm management system
according to the present invention.
FIG. 3 is a schematic diagram of filter and after potential removal
circuitry according to the present invention.
FIG. 4 is a timing diagram illustrating the operation of switches in the
circuitry of FIG. 3 operating under pacing conditions.
FIG. 5 is a timing diagram illustrating the operation of switches in the
circuitry of FIG. 3 operating under cardioverter/defibrillator conditions.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the following detailed description of the preferred embodiments,
reference is made to the accompanying drawings which form a part hereof,
and in which is shown by way of illustration specific embodiments in which
the invention may be practiced. It is to be understood that other
embodiments may be utilized and structural or logical changes may be made
without departing from the scope of the present invention. The following
detailed description, therefore, is not to be taken in a limiting sense,
and the scope of the present invention is defined by the appended claims.
A dual chamber cardioverter/defibrillator 20 with pacing capability is
illustrated in block diagram form in FIG. 1. Cardioverter/defibrillator 20
operates as a pulse generator device portion of a cardiac rhythm
management system which also includes leads or electrodes (not shown)
disposed in the ventricular chamber of the heart to sense electrical
activity representative of a R-wave portion of the PQRST complex of a
surface EGM indicating depolarizations in the ventricle.
Cardioverter/defibrillator 20 includes input/output terminals 22 which are
connectable to the ventricular leads to receive the ventricular electrical
activity of the heart sensed by the ventricular leads. A pace pulse
circuit 24 provides pacing pulses such as bradycardia and antitachycardia
pacing pulses to input/output terminals 22 to be provided to the
ventricular chamber of the heart via the ventricular leads to stimulate
excitable myocardial tissue to treat arrhythmia conditions such as
bradycardia and some tachycardia. A shock pulse circuit 26 provides shock
pulses to input/output terminals 22 to be provided to the ventricular
chamber of the heart via the ventricular leads to shock excitable
myocardial tissue to treat tachyarrhythmia conditions. The tachyarrhythmia
conditions may include either ventricle fibrillation or ventricle
tachycardia.
A filter and after potential removal circuit 28 according to the present
invention filters the ventricular electrical activity received by
input/output terminals 22 and the pacing pulses provided from pacing pulse
circuit 24. In addition, filter and after potential removal circuit 28
effectively removes after potential created by a pacing pulse from pacing
pulse circuit 24 or a shock pulse delivered by shock pulse circuit 26. An
amplifier 30 amplifies the filtered ventricular electrical activity
provided from the filter and after potential removal circuit 28. A gain
control circuit 32 automatically adjusts the gain of amplifier 30.
Amplifier 30 and gain control circuit 32 can be implemented in any well
known automatic gain control circuit. An R-wave detection circuit 34 is
coupled to amplifier 30 to detect depolarizations in the amplified
ventricular electrical activity representative of R-wave depolarizations.
Amplifier 30 preferably includes circuitry for digitizing the ventricular
electrical activity data for detection by R-wave detection circuit 34.
R-wave detection circuit 34 provides a R-wave depolarization signal,
indicative of the R-wave depolarizations, to a microprocessor and memory
36. Microprocessor and memory 36 operates using any well known algorithm
for detection of arrhythmia conditions. For example, microprocessor and
memory 36 can be used to analyze the occurrence of detected R-waves
including the rate, regularity, and onset of variations in the rate of the
reoccurrence of the detected R-wave, the morphology of the detected
R-wave, or the direction of propagation of the depolarization represented
by the R-wave in the heart. In addition, microprocessor and memory 36
stores R-wave data and uses known techniques for analysis of the detected
R-waves for controlling pace pulse circuit 24 and shock pulse circuit 26
for delivery of pace pulses and shock pulses, respectively. In addition,
microprocessor and memory 36 controls a state machine 38. State machine 38
places corresponding circuits of cardioverter/defibrillator 20 including
filter and after potential removal circuit 28 in desired logic states as
dictated by the microprocessor and memory 36 based on various conditions
such as when a pace pulse or a shock pulse occurs.
The cardiac rhythm management system also includes leads or electrodes (not
shown) disposed in the atrial chamber of the heart to sense electrical
activity representative of a P-wave portion of the PQRST complex of a
surface EGM indicating depolarizations in the atrium.
Cardioverter/defibrillator 20 correspondingly also includes input/output
terminals 42 which are connectable to the atrial leads to receive the
atrial electrical activity of the heart sensed by the atrial leads. A pace
pulse circuit 44 provides pacing pulses such as bradycardia pacing pulses
to input/output terminals 42 to be provided to the atrial chamber of the
heart via the atrial leads to stimulate excitable myocardial tissue to
treat arrhythmia conditions such as bradycardia. A filter and after
potential removal circuit 48 operates similar to filter and after
potential removal circuit 28 to filter the atrial electrical activity
received by input/output terminals 42 and the pacing pulses provided from
pacing pulse circuit 44. In addition, filter and after potential removal
circuit 48 effectively removes after potential created by a pacing pulse
from pacing pulse circuit 44.
An amplifier 50 amplifies the filtered atrial electrical activity provided
from filter and after potential removal circuit 48. A gain control circuit
52 automatically adjusts the gain of amplifier 50. Gain control circuit 52
and amplifier 50 operate similar to gain control 32 and amplifier 30. A
P-wave detection circuit 54 is coupled to amplifier 50 to detect
depolarizations in the amplified atrial electrical activity representative
of P-wave depolarizations. Amplifier 50 preferably includes circuitry for
digitizing the atrial electrical activity data for detection by P-wave
detection circuit 54.
P-wave detection circuit 54 provides a P-wave depolarization signal,
indicative of the P-wave depolarizations, to microprocessor and memory 36.
Microprocessor and memory 36 analyzes the detected P-waves indicated in
the P-wave depolarization signal from P-wave detection circuit 54 along
with the R-wave depolarization signal provided from R-wave detection
circuit 34 for the detection of arrhythmia conditions based on known
algorithms. For example, microprocessor and memory 36 can be used to
analyze the rate, regularity, and onset of variations in the rate of the
reoccurrence of the detected P-wave and R-wave, the morphology of the
detected P-wave and R-wave, or the direction of propagation of the
depolarization represented by the detected P-wave and R-wave in the heart.
In addition, microprocessor and memory 36 stores P-wave data and uses
known techniques for analysis of the detected P-waves to control pace
pulse circuit 44 for proper delivery of pace pulses to the atrium. In
addition, microprocessor and memory 36 controls a state machine 38 which
places filter and after potential removal circuit 48 in desired logical
states based on various conditions such as when a pace pulse to the atrium
occurs.
The dual chamber cardioverter/defibrillator 20 with pacing capability
illustrated in FIG. 1 includes pacing and shocking capabilities for the
ventricle and pacing capability for the atrium. Nevertheless, the present
invention can be embodied in a single chamber cardiac rhythm management
device having a single one of these capabilities. For example, the present
invention can be embodied in a ventricle defibrillator device for
providing shock pulses to the ventricle only or in a cardiac pacemaker
device for providing pace pulses to the ventricle only.
Input/output terminals 22 and 42 are typically implemented to be
connectable to a single set of electrodes (not shown) used for pacing,
shock delivery, and sensing. The electrodes of a cardiac rhythm management
system are typically implemented as unipolar or bipolar electrodes.
A unipolar electrode configuration has one pole or electrode (i.e.,
negative pole or cathode electrode) located on or within the heart, and
the other pole or electrode (i.e., positive pole or anode electrode)
remotely located from the heart. With endocardial leads, for example, the
cathode is located at the distal end of a lead and typically in direct
contact with the endocardial tissue to be stimulated, thus forming a "tip"
electrode. Conversely, the anode is remotely located from the heart, such
as comprising a portion of the metallic enclosure which surrounds the
implanted device, thus forming a "can" electrode and is often referred to
as the "indifferent" electrode.
A bipolar electrode configuration has both poles or electrodes typically
located within the atrial or ventricular chamber of the heart. With
endocardial leads, for example, the cathode is located at the distal end
of the lead, referred to as the "tip" electrode. In the bipolar
configuration, the anode is usually located approximate to the "tip"
electrode spaced apart by 0.5 to 2.5 cm., and typically forming a
ring-like structure, referred to as the "ring" electrode.
With respect to sensing, it is well known that bipolar and unipolar
electrode configurations do not yield equivalent cardiac EGMs. Each
configuration has advantages and disadvantages, for example, with a
unipolar-sensing configuration, only the electrical events adjacent to the
"tip" electrode control the unipolar EGM, while the remote "indifferent"
electrode contributes negligible voltage due to its location being
extracardiac.
With a bipolar-sensing configuration, the magnitude of the cardiac signal
is similar for both the "ring" and the "tip" electrodes, but the resulting
EGM is highly dependent upon the orientation of the electrodes within the
heart. Optimal sensing will occur, for example, when the sensing vector
defined by the sensing electrodes is parallel with the dipole defined by
the depolarization signal. Since bipolar electrodes are more closely
sp | | |
