Apparatus and method employing plural electrode configurations for cardioversion of atrial fibrillation in an arrhythmia control system

An implantable device and a method for the automatic detection of atrial arrhythmias and for providing low energy atrial cardioversion therapy for such arrhythmias, with minimal tissue damage and power drain, is disclosed. The device is capable of being incorporated within, and is disclosed as part of, an implantable automatic pacemaker defibrillator/cardioverter having the ability to also provide high energy ventricular defibrillation therapy, as well as dual chamber antitachycardia pacing therapy and bradycardia support pacing. Tripolar atrial and ventricular endocardial leads, each including tip and ring pacing electrodes and a braid cardioverting electrode therein, are employed in conjunction with a subcutaneous electrode lead in delivering therapy from the device to the patient, allowing the device to be implanted in and used by a patient without the need to open the patient's chest cavity. A number of different cardioverting electrode configurations are selectable for the multiple implantable electrodes, and automatic switching from one electrode configuration to another is employed if cardioversion is not achieved using the first configuration.

TECHNICAL FIELD 
This invention relates to implantable medical devices which monitor the 
cardiac state of a patient by sensing the patient's intrinsic rhythm, 
atrial and ventricular tachycardia and atrial and ventricular 
fibrillation/flutter, and which deliver therapy in the form of electrical 
energy to cardiac tissue in an attempt to revert tachycardia and restore a 
normal sinus rhythm. More particularly, the invention relates to an 
apparatus and method for cardioversion of atrial fibrillation/flutter in a 
dual chamber arrhythmia control system. Although the invention may be 
incorporated in a cardioversion device alone, it is described herein as 
operating in a combined implantable antitachycardia pacing, bradycardia 
pacing, defibrillating/cardioverting arrhythmia control system. 
As used herein, the term ventricular tachycardia refers to any fast 
abnormal rhythm of the ventricle which may be amenable to treatment by 
electrical discharges and specifically includes ventricular tachycardia 
(VT), ventricular flutter and ventricular fibrillation (VF), while atrial 
tachycardia refers to atrial fibrillation (AF) and atrial flutter. 
The term cardioversion refers to the discharge of electrical energy into 
the cardiac tissue in an attempt to terminate or revert a tachycardia and 
may range from a high (40 Joules or more) to a low (less than 1 Joule) 
energy discharge. Cardioversion usually refers to a low energy discharge 
such as the discharge delivered to the atrium according to the present 
invention. Defibrillation, however, usually refers to higher energy shocks 
such as are delivered to the ventricles. By definition, as used herein 
both in the description of the invention and in the claims, the two terms 
may be considered as interchangeable. 
BACKGROUND OF THE INVENTION 
Atrial fibrillations have been observed after termination of ventricular 
arrhythmias by cardioversion, as described in an article entitled 
"Comparative Efficacy of Transvenous Cardioversion and Pacing in Patients 
with Sustained Ventricular Tachycardia: A Prospective, Randomized, 
Crossover Study," by Saksena et al., in Circulation 72, No. 1, pages 
153-160, 1985. Termination with transvenous cardioversion was followed by 
occurrences of atrial fibrillation, atrial flutter and sinus tachycardia. 
See, also, an article entitled "Transvenous Cardioversion and 
Defibrillation of Ventricular Tachyarrhythmias: Current Status and Future 
Directions," by Saksena et al., in E, Vol 8, pages 715-731, 1985. In 
this study, the incidence of supraventricular tachyarrhythmias after 
transvenous cardioversion was substantial. Such problems continue to 
exist. 
In patients receiving cardioversion shocks using prior art devices, it has 
been observed in some cases that such post-therapy arrhythmias have been 
attributable to the shock being delivered during the vulnerable zone of 
the atrium. In those cases where atrial arrhythmias occur at a 
sufficiently fast rate, there is a likelihood of this arrhythmia being 
detected as VT/VF, resulting in the patient receiving an unnecessary shock 
to the ventricles of the patient's heart. This highlights the need for an 
implantable device having the capability of effectively sensing atrial 
fibrillation, and having the ability both to switch to an atrial 
cardioversion configuration and to synchronize atrial cardioversion shocks 
to the ventricular rhythm of the patient, thereby to successfully treat 
atrial arrhythmias such as atrial fibrillation and atrial flutter. 
An article entitled "Atrial Fibrillation and Embolic Complications in Paced 
Patients," by H. Langenfeld et al., in E, Vol. 11, pages 1667-1672, 
1985, shows the high incidence of atrial fibrillation in patients with VVI 
pacemakers. This is said to be attributable to irritation of the atrial 
rhythm caused by retrograde conduction. Thus, certain combined implantable 
defibrillator/pacemakers not only may contribute to the cause of the 
problem of atrial fibrillation, but also have been found to lack the 
facilities to deal successfully with atrial arrhythmias. Thus, there is a 
need for implantable devices capable of successfully treating atrial 
arrhythmias. 
U.S. Pat. No. 3,857,398 to Rubin describes a combined pacer/defibrillator. 
This device performs either a pacing or a defibrillation function, 
depending on the detection of a VT/VF. If a VT/VF is detected, the device 
is switched to the defibrillating mode. After a period of time to charge 
the capacitor, a defibrillation shock is delivered to the patient. 
A multiprogrammable, telemetric, implantable defibrillator is disclosed in 
the co-pending U.S. patent application Ser. No. 576,178 of Norma L. Gilli 
et al., entitled "Reconfirmation Prior to Shock for Implantable 
Defibrillation." The device contains a bradycardia support system as well 
as a high energy defibrillation shock system to revert ventricular 
tachycardias to normal sinus rhythm. On reconfirmation of the presence of 
a tachycardia, a shock is delivered to the ventricle of a patient at a 
predetermined time or when the desired energy level is reached. This 
device is not capable of delivering atrial cardioversion in order to 
alleviate the condition of atrial fibrillation. 
U.S. Pat. No. 4,572,191 to Mirowski et al. describes an atrial 
cardioverting device that is externally driven by either the physician or 
the patient. The detection of an arrhythmia requires the patient to 
recognize it, which is disadvantageous for a number of reasons including 
medical clinic visits, carrying expensive equipment around, or just the 
failure to recognize a tachycardia. Furthermore, the device is incapable 
of automatic detection and reconfirmation, as well as failing in the 
capacity to defibrillate the ventricles of a patient in the event an 
atrial shock accelerates the rhythm into VT/VF. This patent also describes 
the delivery of cardioversion shocks using a single pacing lead. A single 
pacing lead has been found, by recent research, to be inadequate in 
effectively discharging a cardioversion shock. Significantly, the main 
reason for this problem is that pacing leads possess a very low surface 
area, giving rise to a high impedance at the area of discharge. Aside from 
the device using too much power, the patient is subjected to a risk of 
tissue damage at the electrode interface. 
Another problem exists with the Mirowski et al. device as there are no 
provisions therein for sensing R-waves and for pacing the patient's 
ventricle. Therefore the device is unable to synchronize the cardioversion 
shock to the ventricle. As a result, the unsynchronized atrial 
cardioversions delivered to a patient may cause VF, resulting in a further 
hazardous situation. 
A further disadvantage of the above device is that it is turned off except 
when it is externally engaged by a magnet that allows the power source to 
charge. Thus the device is inadequate as an automatic implantable 
therapeutic device. Also, since the device is not capable of being 
instituted within a pacemaker defibrillator system, it does not have 
provisions for allowing bradycardia pacing, single or dual chamber 
antitachycardia pacing and defibrillation therapy to the ventricle. 
Therefore, aside from failing to adequately cardiovert the atrium 
successfully and automatically, the device fails as an all round 
therapeutic medical device offering a variety of treatments to the 
patient. 
It is an object of the present invention to provide an improved implantable 
device for the automatic detection of atrial arrhythmias and for providing 
atrial cardioversion therapy therefor. 
It is also an object of the invention to achieve effective cardioversion of 
atrial fibrillation with minimal power drain, and to prevent tissue damage 
due to high voltages being discharged over a small area, such as results 
from the use of a single pacing electrode. 
It is a further object of the invention to provide a device having at least 
two defibrillation endocardial electrodes or other suitable electrodes of 
surface area substantially greater than that of a normal pacing lead, and 
of substantially lower impedance than the latter, and including at least 
one subcutaneous patch, which device does not require a magnet or any 
other external manual switching system for turning on the power source to 
charge its capacitor. 
Another object of the invention is to provide an improved device which is 
on call at all times, and which is capable of being incorporated within an 
implantable automatic pacemaker defibrillator/cardioverter having the 
ability to provide defibrillation therapy to a patient's ventricle, as 
well as antitachycardia pacing therapy and bradycardia support pacing to 
either or both chambers of the heart when required. 
It is yet another object of the invention to provide an automatic 
implantable device capable of delivering low energy cardioversion therapy 
into the atrium in order to improve the health and safety of patients by 
returning atrial arrhythmias to normal rhythms, thereby obviating the need 
for unnecessary high energy shocks. 
A still further object of the invention is to minimize complications 
associated with atrial arrhythmias, since patients who have experienced 
atrial fibrillation have been reported to have a higher mortality rate due 
to embolism development. 
An additional object of the invention is to provide a device which has the 
ability to achieve atrial cardioversion, either with R-wave 
synchronization or during a device-initiated ventricular refractory 
period, to insure that the vulnerable zone of the ventricle is avoided, 
thereby minimizing post-shock arrhythmias attributable to shock delivery 
during the ventricular vulnerable zone and degeneration of the arrhythmia 
into VT/VF. 
It is a further object of the invention to provide an atrial cardioversion 
device having a plurality of electrode configurations, and having the 
ability to switch from one electrode configuration to another prior to the 
delivery of a shock or between deliveries of consecutive shocks. 
Further objects and advantages of this invention will become apparent as 
the following description proceeds. 
SUMMARY OF THE INVENTION 
Briefly stated, and in accordance with one embodiment of the invention, 
there is provided an implantable atrial cardioverting device for the 
reversion of atrial tachycardias, comprising: means for storing electrical 
energy; means for detecting the presence of an atrial tachycardia; an 
electrode lead system including a plurality of electrode leads therein, 
each of the leads including a cardioverting electrode having a 
substantially larger electrode surface area and lower electrode impedance 
than the surface area and impedance of a pacing lead electrode, at least 
one of the leads being an atrial endocardial electrode lead; a plurality 
of atrial cardioversion electrode configurations, each of the 
configurations including at least two of the electrode leads; switching 
means responsive to the detection of an atrial tachycardia by the 
detecting means for selectively connecting the energy storage means to one 
of the atrial cardioversion electrode configuration; means for setting the 
level of electrical energy stored in the electrical energy storing means 
to an appropriate level for an atrial cardioversion shock; and, means for 
discharging the stored electrical energy across the selected atrial 
cardioversion electrode configuration. 
In accordance with another aspect of the invention there is provided an 
implantable cardioverting/defibrillating device for the reversion of 
tachycardias, comprising: means for storing electrical energy; means for 
detecting the presence of an atrial tachycardia; means for detecting the 
presence of a ventricular tachycardia; an electrode lead system including 
a plurality of electrode leads therein, each of the leads including a 
cardioverting electrode having a substantially larger electrode surface 
area and a substantially lower electrode impedance than the surface area 
and impedance of a pacing lead electrode, at least a first one of the 
leads being an atrial endocardial electrode lead and a second one of the 
leads being a ventricular endocardial electrode lead; a plurality of 
atrial cardioversion electrode configurations, each of the configurations 
including at least two of the elctrode leads; a plurality of ventricular 
defibrillating electrode configurations, each of the configurations 
including at least two of the electrode leads; first switching means 
responsive to the detection of an atrial tachycardia by said atrial 
tachycardia detecting means for selectively connecting the energy storage 
means to one of said atrial cardioversion electrode configurations; second 
switching means responsive to the detection of a ventricular tachycardia 
by said ventricular tachycardia detecting means for selectively connecting 
the energy storage means to one of the ventricular defibrillating 
electrode configurations; means for setting the level of electrical energy 
stored in the electrical energy storing means to an appropriate level for 
atrial cardioversion shock; means for setting the level of electrical 
energy stored in the electrical energy storing means to an appropriate 
level for a ventricular defibrillation shock; and, means for discharging 
the stored electrical energy across a selected one of the atrial and 
ventricular electrode configurations. Preferably, the foregoing device 
also includes means for delivering atrial and ventricular bradycardia and 
antitachycardia pacing therapy. 
In accordance with a further aspect of the invention the foregoing device 
may also preferably include means for sensing R-waves and delivering 
ventricular pacing pulses; means responsive both to the detection of an 
atrial tachycardia and to the absence of an R-wave during a predetermined 
period of time following such detection of an atrial tachycardia for 
delivering a ventricular pacing pulse to produce a temporary ventricular 
refractory condition; and means for timing the delivery of the atrial 
cardioversion shock to occur during such temporary refractory condition. 
Additionally, it may also preferably include means responsive both to the 
detection of an atrial tachycardia and to the detection of an R-wave 
during a predetermined period of time following such detection of an 
atrial tachycardia for timing the discharging of the stored electrical 
energy to synchronously occur during an absolute ventricular refractory 
period which occurs following the R-wave. 
In accordance with another aspect of the invention there is provided a 
method of operating an implantable atrial tachycardia cardioverting 
device, the device including an electrode lead system having a plurality 
of electrode leads therein, each of which leads includes a cardioverting 
electrode having a substantially larger surface area and lower electrode 
impedance than the surface area and impedance of a pacing lead electrode, 
at least one of the leads being an atrial electrode, the device further 
including a plurality of atrial cardioversion electrode configurations, 
each of the configurations including at least two of the electrode leads, 
the method comprising the steps of: 
A) detecting the presence of an atrial tachycardia; 
B) storing a charge of electrical energy at an appropriate level for an 
atrial cardioversion shock; 
C) connecting the stored charge of electrical energy to one of the 
electrode configurations; 
D) delivering cardioversion shock therapy across such one of such electrode 
configurations; 
E) determining whether the shock therapy has reverted the atrial 
tachycardia, and if it has not, 
F) storing another charge of electrical energy at an appropriate level for 
an atrial cardioversion shock; 
G) connecting the stored other charge of electrical energy to another one 
of the electrode configurations; and 
H) delivering cardioversion shock therapy across such other one of the 
electrode configurations. 
The device and method may further include provisions for antitachycardia 
pacing when a tachycardia is detected. The antitachycardia pacing may take 
the form of either a single chamber or a dual chamber algorithm such as is 
described in U.S. Pat. No. 4,998,974, entitled "Apparatus and method for 
Antitachycardia Pacing in Dual Chamber Arrhythmia Control System", to N. 
L. Gilli, the present inventor, which patent is assigned to the assignee 
of the present invention. The antitachycardia pacing is preferably issued 
prior to cardioversion or other treatment of a secondary arrhythmia. Also, 
should the atrial cardioverting shock accelerate or degenerate the 
arrhythmia to a VF or VT, defibrillator shock therapy is preferably 
available. In such a situation the device uses the switching configuration 
to switch to the defibrillator electrode system at an appropriate energy 
level. However, to prevent the occurrence of a cardioverting shock causing 
a ventricular arrhythmia when the ventricles are non-refractory, and in 
the absence of a sensed R-wave, a ventricular pace may be used just prior 
to the time that the shock is delivered to the atrium. If an R-wave is 
present, the atrial cardioversion is synchronized with it to prevent VF 
development. The invention is effectively achieved with endocardial 
defibrillating leads, or other leads in which the electrodes are much 
larger in surface area and lower in impedance than are the electrodes in 
pacing leads. Alternatively, subcutaneous defibrillation patches as well 
as epicardial patches, or any combination, thereof may be used in 
conjunction with the endocardial leads.

BEST MODE OF THE INVENTION 
Referring to FIG. 1, there is depicted a block diagram of an implanted dual 
chamber arrhythmia control system or device 10, which comprises: an atrial 
cardiac lead 21 for sensing and pacing in the atrium and a ventricular 
cardiac lead 31 for sensing and pacing in the ventricle, the distal end 
portions of both of which are positioned in the patient's heart 11; a 
pacemaker 17 for the detection of analog signals representing cardiac 
electrical activity, and for the delivery of pacing pulses to the heart; a 
microprocessor 19 which, in response to various inputs received from the 
pacemaker 17 as well as from a defibrillator 16, performs various 
operations so as to generate different control and data outputs to both 
the pacemaker 17 and the defibrillator 16; a power supply 18 for the 
provision of a reliable voltage level; defibrillator 16 which produces a 
high voltage to charge its capacitors and then discharges them in response 
to control signals from the microprocessor 19; and an atrial endocardial 
cardioversion electrode lead 150, a ventricular endocardial defibrillation 
electrode lead 151 and a subcutaneous electrode lead 152, for transferring 
the energy of a cardioversion/defibrillator shock 15 from the implanted 
device 10 to either the atrium or the ventricle of the heart 11. Further 
details in regard to leads 150, 151 and 152 are hereinafter provided in 
connection with discussions of FIGS. 2A, 7A-7F, and 8-11. 
A number of control signals pass between the microprocessor 19 and 
defibrillator 16. These control signals include an atrial endocardial 
charge control signal in line 201, and a switching control signal on line 
202. The switching control signal on line 202 switches the defibrillator 
16 (which in addition to providing ventricular defibrillation shocks also 
provides atrial cardioversion shocks) among various electrode 
configurations available to it for providing either defibrillation to the 
ventricles, by means of a ventricular defibrillation lead configuration 
(see, e.g., FIG. 7D), or cardioversion to the atrium, by means of an 
atrial cardioversion lead configuration (see, e.g., FIG. 7B). These lead 
configurations are described in greater detail hereinafter in connection 
with a discussion of FIGS. 7A to 7F. Other control signals passing from 
the microprocessor 19 to the defibrillator 16 include those on a 
communication bus 203, an atrial endocardial shock control signal on line 
204, a ventricular endocardial shock control signal on line 205, a 
ventricular endocardial charge control signal on line 206, a subcutaneous 
electrode charge control signal on line 207, a ventricular endocardial 
shock energy control signal on line 208, an atrial endocardial shock 
energy control signal on line 209, and a dump control signal on line 58. 
Referring to FIG. 2A there is depicted a block diagram of the defibrillator 
16 of FIG. 1. Circuitry for providing an atrial cardioversion shock is 
shown at 213; circuitry for providing a ventricular defibrillation shock 
is shown at 214; and circuitry for providing a subcutaneous electrode 
shock is shown at 215. The atrial endocardial lead 150 connects the atrial 
shock circuitry 213 to the atrium of the heart 11. The ventricular 
endocardial lead 151 connects the ventricular shock circuitry 214 to the 
ventricle of the heart 11. The subcutaneous electrode lead 152 connects 
the subcutaneous electrode shock circuitry 215 to a subcutaneous electrode 
at the distal end of lead 152. Preferably, the endocardial leads 150 and 
151 and the subcutaneous electrode lead 152 are provided with large 
surface area, low impedance electrodes adjacent their distal ends such as 
the braid electrodes, described briefly herein in connection with FIGS. 8, 
9 and 11, and described in greater detail in U.S. Pat. No. 5,005,587 to S. 
E. Scott, entitled "Braid Electrode Leads and Catheters and Methods for 
Using the Same," which patent is assigned to the assignee of the present 
invention. Alternatively, in another embodiment, the subcutaneous 
electrode lead 152 may be provided with a conventional patch electrode, as 
shown in FIG. 10. 
Telemetry circuitry, shown at 30, provides a bidirectional link between a 
defibrillator control block 239 and an external device such as a 
programmer (not shown). It allows data such as the operating parameters to 
be read from or altered in the implanted device 10. 
The defibrillator control block 239 is connected to the atrial shock 
circuitry 213 by means of an atrial endocardial control line 210. The 
control block 239 is connected to the ventricular shock circuitry 214 by 
means of a ventricular endocardial control line 211. The subcutaneous 
electrode shock circuitry 215 is connected to control block 239 by means 
of a subcutaneous electrode control line 212. A number of control signals 
pass between microprocessor 19 and defibrillator control block 239. These 
control signals include the aforementioned atrial endocardial charge 
control signal on line 201, the switching control signal on line 202, the 
various signals on communication bus 203, the atrial endocardial shock 
control signal on line 204, the ventricular endocardial shock control 
signal on line 205, the ventricular endocardial charge control signal on 
line 206, the subcutaneous electrode charge control signal on line 207, 
the ventricular endocardial shock energy control signal on line 208, the 
atrial endocardial shock energy control signal on line 209, and the dump 
control signal on line 58. 
Referring to FIG. 2B, there is depicted a block diagram of the pacemaker 17 
of FIG. 1. Pacemaker 17 comprises atrial pacing circuitry 24, ventricular 
pacing circuitry 34, atrial sensing circuitry 25, ventricular sensing 
circuitry 35, and the aforementioned telemetry circuitry 30. In addition, 
pacemaker 17 includes a pacemaker control block 39. 
In operation, the sensing circuits 25 and 35 detect atrial and ventricular 
analog signals 23 and 33, respectively, from the heart 11 and convert the 
detected signals to digital signals. The sensing circuits 25 and 35 
respectively receive an input atrial sense control signal via line 27 and 
an input ventricular sense control signal via line 37 from the control 
block 39, which signals determine the sensitivity applied to the detection 
circuits. A change in this sensitivity will affect the voltage deviation 
required at the sensing electrode for a sense to be registered. The 
operation of the logic which changes the sensitivity is described in more 
detail in U.S. Pat. No. 4,940,054 to Richard Grevis and Norma L. Gilli, 
entitled "Apparatus and Method for Controlling Multiple Sensitivities in 
Arrhythmia Control System Including Post Therapy Pacing Delay." 
The pacing circuits 24 and 34 also respectively receive an input atrial 
pacing control signal and an input atrial pacing energy control signal via 
line 28, and an input ventricular pacing control signal and an input 
ventricular pacing energy control signal via line 38, from the pacemaker 
control block 39. The pacing control signals determine the type of pacing 
to occur, while the magnitude of the pulse energy is determined by the 
pacing energy control signals. The operation of the logic which changes 
the pulse energy is described in more detail in U.S. Pat. No. 4,869,252, 
entitled "Apparatus and Method for Controlling Pulse Energy in 
Antitachyarrhythmia and Bradycardia Pacing Devices," to Normal L. Gilli. 
The pacing circuits 24 and 34 generate the atrial pacing pulse 22 and the 
ventricular pacing pulse 32 which are delivered to the patient's heart 11 
by means of the atrial cardiac lead 21 and the ventricular cardiac lead 
31, respectively. 
Telemetry circuitry 30, which was discussed earlier in connection with a 
discussion of the defibrillator 16, also provides a bi-directional link 
between the pacemaker control block 39 and an external device such as a 
programmer (not shown). It allows data such as the operating parameters to 
be read from or altered in the implanted device 10. 
An atrial sense signal and a ventricular sense signal pass via respective 
lines 45 and 49 from the pacemaker control block 39 to the microprocessor 
19. Passing from the microprocessor 19 to the control block 39 are an 
atrial pace control signal on line 46, an atrial sensitivity control 
signal on line 43, an atrial pacing energy control signal on line 44, a 
ventricular pace control signal on line 50, a ventricular sensitivity 
control signal on line 47, and a ventricular pacing energy control signal 
on line 48. A communication bus 42 is employed for communicating various 
other signals between the control block 39 and the microprocessor 19. 
Referring to FIG. 3, there is shown a block diagram of the microprocessor 
19 of FIG. 1. It comprises two 16-bit timers 51 and 52, a central 
processing unit or CPU 53, a vectored interrupts block 54, a read only 
memory or ROM 55, a random access memory or RAM 56, an external memory 57, 
a ports block 41 and an internal communication bus 40. 
Microprocessor 19 receives various status and/or control inputs from 
pacemaker 17 and defibrillator 16 such as the sense signals on lines 45 
and 49, performs operations such as arrhythmia detection, and produces 
outputs such as the atrial pace control signal on line 46 and the 
ventricular pace control signal on line 50, which determine the type of 
pacing to take place. Other control outputs generated by microprocessor 19 
include the atrial and ventricular pacing energy control signals on 
respective lines 44 and 48 which determine the magnitude of the pulse 
energy, the dump control signal on line 58 which indicates that a shock is 
to be dumped at an internal load within the defibrillator, and the various 
charge control signals on lines 201, 206, and 207 which determine the 
voltage level of the shock to be delivered. Other output signals pass from 
microprocessor 19 to the defibrillator control block 239. These control 
signals, mentioned earlier herein, include the switching control signal on 
line 202, the various signals on communication bus 203, the atrial 
endocardial shock control signal on line 204, the ventricular endocardial 
shock control signal on line 205, the ventricular endocardial shock energy 
control signal on line 208, and the atrial endocardial shock energy 
control signal on line 209. Other control outputs from the microprocessor 
include the atrial and ventricular sensitivity control signals on lines 43 
and 47, respectively, which determine the sensitivity settings of the 
pacemaker sensing circuits. 
Referring to FIG. 4A in conjunction with FIG. 1, there is depicted an 
electrocardiogram or ECG trace outlining the application of the device 10 
in treating a VF, shown at 180. The device 10 charges a capacitor (not 
shown) in defibrillator 16 to an appropriate high energy level for 
defibrillation, switches to a programmed electrode configuration (e.g. the 
configuration of FIG. 7D) and delivers a defibrillation shock 181 to the 
ventricle of the patient's heart 11. Normal sinus rhythm (NSR) 182 
results, indicating effective therapy. 
Referring to FIG. 4B in conjunction with FIG. 1, there is depicted an ECG 
trace outlining a low energy cardioversion shock sequence of device 10. As 
shown, an AF has developed at 183. Prior to the delivery of low energy 
cardioversion shock therapy at 185, the device switches to a programmed 
electrode configuration at 184 (e.g., the configuration of FIG. 7A) and 
checks for the presence of R-waves in the ventricle. The capacitor (not 
shown) in defibrillator 16 is charged to an appropriate low energy level 
for atrial cardioversion and when ready to deliver, it waits for a 
programmable time period such as a normal pacing standby interval of 857 
ms. If during this time an R-wave is not detected, then prior to the 
atrial cardioversion shock, a pacing pulse is delivered to the ventricle. 
The timing of the pacing pulse is such that it renders the ventricle 
depolarized during the subsequent delivery of the low energy shock. The 
interval between the delivery of the ventricular pacing pulse and the 
delivery of the shock is usually short. In the preferred embodiment, this 
interval is 100 ms but it may be longer or shorter than this value 
provided that the ventricle is depolarized at the time of delivery of the 
low energy cardioversion shock. If during the 857 ms standby period an 
R-wave is detected, then the cardioversion therapy is delivered within 100 
ms. This results in a synchronized atrial cardioversion (i.e., it is 
synchronized with the last inherent R-wave) so that at the moment of 
delivery the ventricles are refractory. This has the purpose of preventing 
VF's from developing. As shown, the cardioversion shock at 185 has 
succeeded in reverting the atrial arrhythmia, and normal sinus rhythm 186 
is now present in the patient. 
Referring to FIG. 4C in conjunction with FIG. 1, there is depicted an ECG 
trace outlining another low energy cardioversion shock sequence of device 
10. As shown, an AF has developed at 187. As described with reference to 
FIG. 4B, and assuming the device is in a first programmed electrode 
configuration (e.g., the configuration of FIG. 7A), a check is made for 
R-waves and a pacing pulse is delivered to the ventricle 100 ms prior to 
the delivery of low energy cardioversion shock therapy at 188. The 
ventricular pacing pulse renders the ventricle depolarized during the 
subsequent delivery of the cardioversion shock. Following cardioversion 
shock delivery, an AF is still shown to be present at 189, with 
reconfirmation of the AF shown at 190. At this point, as shown at 191, 
there is a change or switch in the electrode configuration, according to 
programmed instructions and the electrode configuration combinations 
available, to a second programmed electrode configuration (e.g., the 
configuration of FIG. 7B). As described with reference to FIG. 4B, and 
above, a test for R-waves again occurs and within 100 ms of detection of 
the R-wave, a cardioversion shock is delivered, at 192, utilizing the 
changed electrode configuration to improve cardioversion effectiveness. 
Reversion of the atrial fibrillation and resultant establishment of normal 
sinus rhythm is shown at 193. 
Referring to FIG. 4D in conjunction with FIG. 1, there is depicted an ECG 
trace outlining a VF 194 for which a high energy defibrillation shock 195 
is delivered in an attempt to revert the VF. Although the high energy 
shock 195 in this instance has successfully reverted the ventricular 
fibrillation, utilizing the electrode configuration of FIG. 7D for 
example, an atrial fibrillation 196 has developed post-shock. The AF is 
reconfirmed at 197. A change in the electrode switching configuration is 
then given at 198 (e.g. to the electrode configuration of FIG. 7B), and 
atrial cardioversion therapy is applied at 199. The AF is shown as having 
been successfully reverted to normal sinus rhythm at 200. 
Referring now to FIG. 5 there is depicted a flow chart showing the sequence 
of events occurring during operation of the implantable arrhythmia control 
system. The start or standby mode is shown at block 160. A tachycardia 
detection decision occurs at block 161. If no tachycardia is present, as 
indicated at 162, there is a return to the standby mode of block 160. If a 
tachycardia is detected, as indicated at 163, it is examined to determine 
whether or not it is an AF at block 164. If it is not an AF, as indicated 
at 165, then it is examined to determine whether or not it is a VT/VF at 
block 175. If it is not a VT/VF, as indicated at 176, there is a return to 
the standby mode of block 160. If a VT/VF is present, as indicated at 177, 
then at block 178 defibrillation therapy is applied by the device to the 
ventricle of the patient. 
In the particular embodiment illustrated in FIG. 5, there is only one 
electrode configuration available at block 178 for defibrillating the 
ventricles, and that is the one shown in FIG. 7D. Thus the device 
automatically switches to this configuration at VT/VF detection. Hence, 
there is no need to pass via block 167, which specifically relates to 
changing electrode configurations in connection with atrial cardioversion. 
If an AF is classified at block 164, as indicated at 166, then the 
electrode configuration is switched to the appropriate setting at block 
167. At block 168, the AF is reconfirmed. 
When the device is ready to deliver a cardioversion shock, it waits at 
block 179 for a programmed standby interval such as 857 ms to detect the 
presence of an R-wave. If no R-wave is detected during the programmed 
standby interval, then a ventricular pace is provided by the device at 
block 169 to depolarize the ventricle at a programmed time interval such 
as 100 ms before the shock is delivered. If an R-wave is detected during 
the programmed standby interval, then at block 170 the device synchronizes 
the shock delivery with the patient's R-wave and, within 100 ms of the 
R-wave, delivers the atrial cardioversion therapy at block 171. 
At block 172, the device checks for the success of the therapy. If 
successful, as shown at 173, there is a return to the standby mode of 
block 160. If the cardioversion therapy is not successful, as shown at 
174, there is a return to the AF classifier at block 164. If an AF is 
still present at block 166, there is a change in the electrode 
configuration at block 167 and a repeat of cardioversion therapy with the 
new electrode configuration. 
FIG. 6 shows a prior art lead configuration for an externally controlled 
atrial cardioverting device (not shown). It comprises a two-electrode 
single pacing lead 153 positioned in the atrium of the heart 11, as shown. 
FIG. 7A depicts a unidirectional lead configuration according to the 
invention, including atrial endocardial J-lead 150 in the atrium, 
ventricular endocardial lead 151 in the ventricle and subcutaneous 
electrode lead 152. In this configuration the atrial endocardial lead 150 
is charged negatively and the endocardial ventricular lead 151 is charged 
positively. No charge is applied to the subcutaneous electrode lead 152. 
Thus, at delivery there is a unidirectional discharge with the waveform 
direction as shown by arrow A, from the electrode of atrial lead 150 to 
the electrode of ventricular lead 151. 
FIG. 7B depicts a further unidirectional lead configuration according to 
the invention, including atrial endocardial lead 150 in the atrium, 
ventricular endocardial lead 151 in the ventricle and subcutaneous 
electrode lead 152. In this configuration the atrial endocardial lead 150 
is charged positively, the endocardial ventricular lead 151 is uncharged, 
and a positive charge is applied to the subcutaneous electrode lead 152. 
Thus, at delivery there is a unidirectional discharge with the waveform 
direction as shown by arrow B, from the electrode of ventricular lead 151 
to the electrode of subcutaneous electrode lead 152. 
FIG. 7C depicts a bidirectional lead configuration according to the 
invention, including atrial endocardial lead 150 in the atrium, 
ventricular endocardial lead 151 in the ventricle and subcutaneous 
electrode lead 152. In this configuration the atrial endocardial lead 150 
is charged positively, the ventricular endocardial lead 151 is charged 
negatively and a positive charge is applied to the subcutaneous electrode 
lead 152. Thus, at delivery there is a bidirectional discharge with the 
waveform directions as shown by arrows C1 and C2, from the electrode of 
ventricular lead 151 to both the electrode of atrial lead 150 and the 
electrode of subcutaneous electrode lead 152, respectively. 
FIG. 7D depicts a further unidirectional lead configuration according to 
the invention, including atrial endocardial lead 150 in the atrium, 
ventricular endocardial lead 151 in the ventricle and subcutaneous 
electrode lead 152. In this configuration the atrial endocardial lead 150 
is uncharged, the endocardial ventricular lead 151 is charged negatively 
and a positive charge is applied to the subcutaneous electrode lead 152. 
Thus, at delivery there is a unidirectional discharge with the waveform 
direction as shown by arrow D, from the electrode of ventricular lead 151 
to the electrode of subcutaneous electrode lead 152. 
The electrode configuration of FIG. 7D is suitably used in the preferred 
embodiment for defibrillation therapy to the ventricle in the case of VT. 
The device switches to this electrode configuration by means of a 
switching control signal sent from microprocessor 19 to defibrillator 16 
on line 202 (FIG. 1), and the energy of the shock to be delivered is 
adjusted to the higher energy required for defibrillation by means of a 
ventricular endocardial shock energy control signal and a subcutaneous 
electrode charge control signal sent from microprocessor 19 to 
defibrillator 16 on lines 208 and 207, respectively. 
FIG. 7E depicts a further unidirectional lead configuration according to 
the invention, including atrial endocardial lead 150 in the atrium, 
ventricular endocardial lead 151 in the ventricle, and subcutaneous 
electrode lead 152. In this configuration the atrial endocardial lead 150 
is charged positively, the endocardial ventricular lead 151 is charged 
negatively and no charge is applied to the subcutaneous electrode lead 
152. Thus, at delivery there is a unidirectional discharge with the 
waveform direction as shown by arrow E, from the electrode of ventricular 
lead 151 to the electrode of atrial lead 150. 
FIG. 7F depicts another bidirectional lead configuration according to the 
invention, including atrial endocardial lead 150 in the atrium, 
ventricular endocardial lead 151 in the ventricle and subcutaneous 
electrode lead 152. In this configuration the atrial endocardial lead 150 
is charged negatively, the ventricular endocardial lead 151 is charged 
negatively and a positive charge is applied to the subcutaneous electrode 
lead 152. Thus, at delivery there is a bidirectional discharge with the 
waveform directions as shown by arrows F1 and F2, from the electrodes both 
of atrial lead 150 and ventricular lead 151, respectively, to the 
electrode of subtaneous electrode lead 152. 
Referring to FIG. 8, a ventricular endocardial defibrillation electrode 
lead 151 that may be used in connection with the present invention has 
there been illustrated as part of a tripolar endocardial ventricular 
defibrillation and pacing catheter or lead 110. Lead 110 includes a 
conventional tip assembly 112 having a distal tip electrode 114 and a band 
or ring electrode 116 for pacing and sensing, as is well known in the art. 
As is also well known, tip electrode 114 and ring electrode 116 may be 
formed of a 90% platinum-10% iridium alloy covered with porous platinum. 
The lead 110 comprises a polyurethane tube having two small lumens and one 
large lumen (not shown) therein. 
Electrical connection is made to tip electrode 114 and ring electrode 116 
by two separate wire conductors (not shown). Each conductor extends along 
the length of one of the lumens of lead 110 and terminates in a connector 
126 of a type well known in the art. Connector 126 includes pins 128 and 
130 which are electrically connected to terminals 114 and 116, 
respectively, by the aforesaid conductors. The pins 128 and 130 are 
received in the neck (not shown) of the implanted device 10 (FIG. 1) and, 
together with the aforesaid conductors, comprise the ventricular cardiac 
lead 31 that connects to the pacemaker 17 of FIG. 1 for providing 
ventricular pacing stimulation to the heart and for receiving sensed 
ventricular signals therefrom. 
Lead 110 includes a hub or a Y connector 132 from which separate 
polyurethane tubes 134 and 136 extend to connector 126. The aforesaid wire 
conductors extend through hub 132 and then through respective tubes 134 
and 136, thus providing electrical connection to corresponding ones of 
pins 128 and 130. 
Lead 110 has placed, externally along a portion of its length, a 
cylindrical, braid, cardioverting electrode 142. Electrical connection to 
electrode 142 is made by collapsing that portion of the braid not used as 
part of electrode 142 into a rope (not shown), and passing the rope 
through a small opening into the large lumen of the lead 110. This rope 
conductor extends into an insulating tube 138 having a first end 
terminating in hub 132 and a second end terminating in a defibrillator 
connector 140. The connector 140 has a connection pin 144 extending 
therefrom. Connection pin 144 is electrically connected to the end of the 
rope conductor and is received in the neck (not shown) of the device 10 
(FIG. 1). The rope conductor, connector 140 and pin 144 constitute the 
lead 151 which connects to the defibrillator 16 (FIG. 1) for conducting 
endocardial cardioverting/defibrillating shocks 15 to the ventricle of the 
heart. As is apparent from an inspection of FIG. 8, the 
cardioverting/defibrillating electrode 142 has a substantially larger 
electrode surface area, and consequently a lower electrode impedance, than 
the surface area and impedance of pacing lead electrodes 114 and 116. This 
facilitates the transmission of the cardioversion shock therapy to the 
heart. 
Referring now to FIG. 9, an atrial endocardial cardioverting lead 150 has 
there been illustrated as part of a J-type tripolar endocardial atrial 
cardioverting and pacing catheter or lead 110A. Lead 110A is generally 
similar to lead 110 of FIG. 8 and includes a tip assembly 112A having a 
pacing tip electrode 114A and a pacing ring electrode 116A. The lead 110A 
includes a polyurethane tube having two small lumens and one large lumen. 
Electrical connection is made to tip electrode 114A and ring electrode 
116A by two separate wire conductors (not shown) each of which extends 
along the length of one of the lumens of lead 110A and terminates in a 
connector 126A having pins 128A and 130A which are electrically connected 
to terminals 114A and 116A, respectively, by the aforesaid conductors. The 
pins 128A and 130A are received by the pacemaker 17 (FIG. 1) and, together 
with the aforesaid conductors, constitute the atrial cardiac lead 21 of 
FIG. 1 that connects to the pacemaker 17 of FIG. 1 for providing atrial 
pacing stimulation to the heart and for receiving sensed atrial signals 
therefrom. 
As in the case of the lead 110 of FIG. 8, lead 110A of FIG. 9 includes a 
hub or Y-connector 132A from which separate polyurethane tubes 134A and 
136A extend to connector 126A. The aforesaid wire conductors extend 
through hub 132A and then through respective tubes 134A and 136A, thus 
providing electrical connection to corresponding ones of the pins 128A and 
130A. 
As before, lead 110A has placed, externally along a portion of its length, 
a cylindrical, braid, cardioverting electrode 142A. Electrical connection 
to electrode 142A is made by collapsing that portion of the braid not used 
as part of electrode 142A into a rope (not shown), and passing the rope 
through a small opening into the large lumen of the lead 110A. This rope 
conductor extends into an insulating tube 138A having a first end 
terminating in hub 132A and a second end terminating in a defibrillator 
connector 140A. Connector 140A has a connection pin 144A extending 
therefrom. Connection pin 144A is electrically connected to the end of the 
rope conductor and is received in the neck (not shown) of the device 10 
(FIG. 1). The rope conductor, connector 140A and pin 144A constitute the 
lead 150 which connects to the defibrillator 16 (FIG. 1) for conducting 
endocardial cardioverting/defibrillating shocks 15 to the atrium of the 
heart. 
As in the case of the cardioverting electrode 142 of FIG. 8, the 
cardioverting electrode 142A of FIG. 9 has a substantially larger surface 
area, and consequently a lower electrode impedance, than the surface area 
and impedance of pacing lead electrodes 114A and 116A. This facilitates 
the transmission of the cardioversion shock therapy to the heart. 
Referring now to FIG. 11, a subcutaneous electrode lead 152 having a 
preferred form of multi-element, braided electrode, shown generally at 90, 
has there been illustrated. An inner tube 92 of, for example, polyurethane 
material is surrounded by a cylindrical braid 94 which extends to a distal 
end 96 of the tube to form a finger 97. Inner tube 92 and braid 94 are 
terminated by a polyurethane cap 98 which is provided with a reduced 
diameter plug portion (not shown) that fits into the distal end 96 of tube 
92 and is adhered in place by a suitable medical adhesive. An outer 
insulating tube 100, for example of polyurethane, fits snugly about the 
proximal portion of braid 94. 
The proximal ends of each of two braids 104A and 104B are cut to dimensions 
slightly longer than the distance from distal end 96 to connecting sleeve 
102 and are wrapped about and braised to metallic sleeve 102. Braising is 
used so as to firmly mechanically and electrically connect braid 94, 
metallic sleeve 102, braid 104A and braid 104B to one another. 
Respective tubes 106A and 106B, preferably formed of the same material as 
inner tube 92 and having a length somewhat shorter than the distance from 
distal end 96 to connecting sleeve 102, are fitted within braids 104A and 
104B, respectively, to form fingers 107A and 107B of stiffness comparable 
to that of finger 97. 
The distal ends of fingers 107A and 107B are terminated by caps 108A and 
108B, respectively, in the same manner as described above in connection 
with cap 98 and tube 92. A portion of the lead 90, including the distal 
end 99 of outer tube 100, extends distally to a region 105. Collapsed 
portions of braid 104A and 104B extend past the proximal ends of tubes 
106A and 106B, and therefore past the proximal ends 101A and 101B of 
fingers 107A and 107B. These components are all held in a mold (not 
shown), during manufacture, having a cavity into which polyurathane 
material is placed so as to form a trifurcation 103. The fingers 97, 107A 
and 107B have lateral spacing between them so that they may be fitted into 
adjacent intercostal spaces. To this end, a small taper angle may be 
established between outer tube 100 and fingers 107A and 107B. 
Although a multi-fingered subcutaneous braided electrode 90 has been 
illustrated in FIG. 11, it is to be understood that one or more 
single-fingered subcutaneous braided electrodes could be utilized in 
practicing the invention, or that more than one of such multi-fingered 
subcutaneous electrodes can be employed in utilizing this invention. In 
use, these electrodes are positioned subcutaneously, outside the chest 
cavity, in proximity to the heart. 
Referring now to FIG. 10, an alternative embodiment of a subcutaneous 
electrode lead 152 has there been illustrated. The electrode lead 152 in 
this embodiment is provided with a subcutaneous patch electrode 80 having 
an insulated back 82 and an active wire mesh electrode face 84. An 
insulated electrical conductor 86 extends from patch electrode 80 and 
terminates at a defibrillation connector (not shown), similar to connector 
140 of FIG. 8 and having a pin similar to pin 144 of FIG. 8 extending 
therefrom. The insulated electrical conductor 86 constitutes a portion of 
the subcutaneous electrode lead 152 in the embodiment of FIG. 10. 
It will be apparent from the foregoing description that the present 
invention provides an improved implantable device both for the automatic 
detection of atrial arrhythmias, and for providing low energy atrial 
cardioversion therapy for such arrhythmias with minimal tissue damage and 
power drain. The invention is capable of being incoporated within an 
implantable automatic pacemaker defibrillator/cardioverter having the 
ability to provide high energy ventricular defibrillation therapy, as well 
as antitachycardia pacing therapy and bradycardia support pacing to either 
or both chambers of the heart when required. 
Although the invention has been described herein with reference to 
particular embodiments, it is to be understood that such embodiments are 
merely illustrative of the application of the principles of the invention. 
For example, the delivery of a cardioversion shock following the detection 
of an atrial arrhythmia may be immediate, or it may be dependent on the 
charge time of the capacitor. Also shock waveforms may be monophasic, 
biphasic, multiphasic, or may have any waveform known in the art of pacing 
and defibrillating. Alternatively, the time to the delivery of a shock may 
depend on the hemodynamic condition of the patient, as described in U.S. 
Pat. No. 4,895,151 to R. Grevis et al., entitled "Apparatus and Method for 
Therapy Adjustment in Implantable Cardioverter." The device of the 
invention may also include means for delivering antitachycardia and/or 
bradycardia pacing therapy to either the atrium, or the ventricle, or to 
both the atrium and the ventricle. Hence numerous modifications may be 
made and other arrangements may be devised without departing from the true 
spirit and scope of the invention.