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United States Patent iw
Raddi et al.
[in 3,738,371  June 12, 1973
 CARDIAC PACERS WITH SOURCE CONDITION-RESPONSIVE RATE
 Inventors: William J. Raddi; Robert W.
Johnson; Joseph W. Smithmyer, all
of Philadelphia, Pa.
 Assignee: ESB Incorporated, Philadelphia, Pa.  Filed: Dec. 11, 1970  Appl. No.: 97,254
 U.S. CI 128/419 P, 128/422, 307/48,
 Int. CI A61n 1/36
 Field of Search 128/419 P, 419 R,
128/421, 422; 320/29, 40; 307/48, 53, 55
 References Cited
UNITED STATES PATENTS 3,474,353 10/1069 Keller, Jr 128/419 P
3,620,220 U/1971 Murphy, Jr 128/419 P
3,454,012 7/1969 Raddi 128/419 P
FOREIGN PATENTS OR APPLICATIONS 225,033 12/1958 Australia 128/419 R
Primary Examiner—William E. Kamm
Attorney—Robert H. Robinson, Raymond L.
Balfour, Anthony J. Rossi and Thomas A. Lennox
In a pulse generating circuit, such as an implantable cardiac pacer having parallel connected batteries as its power supply, additional resistors are connected between the power supply and the pulse generating circuit of the pacer and form a part of the pulse generating circuit to indicate by a change in pulse rate when one or more cells of the batteries of the power supply fail prematurely.
7 Claims, 4 Drawing Figures
CARDIAC PACERS WITH SOURCE
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to pulse generating devices, and more particularly to pulse generating devices where it is desired to determine the state of the batteries of the power supply of the device from the rate of operation of the device. The invention will here be described in most detail in association with battery powered electronic organ stimulation device or cardiac pacer since the apparatus according to the invention has been particularly developed for use with such pacers, however, the apparatus may be used in other battery powered pulse generating devices. It might perhaps be used in conjunction with stimulators for the brain, bladder and other organs as well, and with pacers other than the type hereinafter described without departing from the scope of the invention.
2. Description of the Prior Art
It may be explained that cardiac pacing has become the standard mode of therapy for heart block and its complications. Briefly, heart block is the reduction or complete lack of coordination in the beating of the atria and ventricles of the heart. In the human body, blood is pumped primarily by the contractions of the ventricles of the heart which are triggered by natural electrical signals originating in the atrium of the heart. Physiological conditions which weaken or eliminate these natural signals result in a lack of coordination between the atria and ventricles and consequently, the natural pumping action of the heart is affected, at times resulting in death.
In order to overcome this condition, cardiac pacer have been developed to artifically stimulate the contraction of the ventricles with electrical pulses generated by the pacer. These pacers are implanted in the body of a patient along with batteries for powering the pacer and electrical leads attached to the heart.
At present, most commercial cardiac pacers utilize a set of five or six primary mercury cells connected in series as their power source. With such pacers, a change in pace or pulse rate reflects a change in battery voltage, for example, a rate decrease of several pulses per minute will indicate a drop in battery voltage, suggesting pacer replacement.
Accordingly, a pulse rate decrease in pacers that use five or six cells connected in series is an indication of battery exhaustion. A disadvantage of such a configuration is that should an individual cell of the power source fail prematurely, it is possible for the failed cell to be driven by the other cells of the battery into potential reversal and thus generate internal gas pressure from the electrolysis of the electrolyte in the failed cell. Furthermore, performance and reliability of such pacers are also affected as a result of reduced battery voltage. Consequently, when one or two cells fail in a conventional pacer utilizing a power supply of five or six series connected cells, future operation of the pacer becomes doubtful and the unit is preferably replaced. Pacer longevity, therefore, is not necessarily determined by the average cell life but instead it can and often times is limited by the performance of the weakest cell in the battery forming the power supply of the pacer.
Because battery failure or premature battery exhaustion has been determined to be the principal cause of failure in cardiac pacers, it has become desirable to use several batteries connected in a parallel redundant con
5 figuration as the pacer power source.
The parallel connection of the cells or batteries is generally made through diodes or transistors such that when a cell or battery in one parallel branch fails prematurely the diode associated with that battery reverse
10 biases thereby automatically disconnecting that battery from the load. Thus, the voltage of the power supply supplying the pacer remains relatively unchanged and the operation of the pacer remains virtually unchanged. As with the type pacers having a single battery com
15 prised of series connected primary cells as the power source, pacers having parallel connected batteries as a power source will, near the end of life of the batteries of the power source, manifest a change in operation due to lower voltage which is reflected in a change in the pulse rate.
There is* however, a major disadvantage of using redundant batteries in that when one of the batteries or cells in one of the parallel branches prematurely fails
25 there is no outward indication of such failure. In pacers having a battery comprised of series connected cells, as set forth above, the usual indication of battery failure is reduced pulse rate which, generally is proportional to battery terminal voltage. Consequently, with a three
3q cell redundant system as for example, the pacer could be operating on one third power very shortly after implant if cells of two parallel branches fail, with no outward indication to either patient or attending physician. The danger of this situation is obvious since it is
35 assumed that after implantation the pacer will operate safely for a predicted period of time when, in fact, in only one third or less of that time the pacer will certainly fail.
SUMMARY OF THE INVENTION
Briefly, the invention provides apparatus that will indicate when one or more of the electro-chemical cells powering a pulse generating devices fails.
In accordance with the invention, a pulse generating 45 device is provided having a power supply comprising a plurality of batteries connected in parallel wherein each battery is comprised of at least one electrochemical cell. A pulse generating circuit is provided operatively connected across the power supply to translate 50 the power supplied by the power supply into electrical impulses. Means are provided adapting the pulse generating circuit to generate pulses at a first frequency and, upon failure of at least one of the electrochemical cells of the power supply, to generate pulses at a second fre55 quency different from the first frequency.
The apparatus, in accordance with the invention, is essentially free of the defects of the prior art devices having parallel connected batteries in that it provides an outward indication of cell or battery failure in the power supply when such failure occurs. The apparatus of the invention is an improvement over devices having five or six series connected cells as a power supply in that if a cell or battery of the power supply of the appa65 ratus of the invention fails, there is an ample reserve of energy to permit continued operation of the pacer.
A more complete understanding of the invention will become apparent from the following description, taken