Title:
Portable electronic cardiac stimulator
United States Patent 3866615


Abstract:
A light weight portable electronic cardiac emergency stimulator which includes separate defibrillation and pacemaking electronic circuits and a self-contained battery pack. The defibrillation and pacing circuits are selectively connectable, through a switch, to a pair of electrodes of special design which may be introduced rapidly into the patient's heart by a needle through his chest wall. The electrodes are self-spreading within the heart to establish firm electrical contact with opposite sides of its inner surface. After the electrodes have been introduced to the heart, as into the left ventricle, the circuits can be selectively connected to the electrodes through a switch to controllably apply either defibrillation or pacemaking electric pulses to the heart without delay.



Inventors:
HEWSON JOHN R
Application Number:
05/323972
Publication Date:
02/18/1975
Filing Date:
01/15/1973
Assignee:
DAIGLE; CLAUDE W.
Primary Class:
Other Classes:
607/7, 607/10, 607/34, 607/122
International Classes:
A61N1/05; A61N1/362; A61N1/39; (IPC1-7): A61N1/36
Field of Search:
128/404,418,419C,419D,419E,419P,421,422,423
View Patent Images:



Primary Examiner:
Kamm, William E.
Attorney, Agent or Firm:
Wolf, Greenfield & Sacks
Claims:
1. A portable emergency cardiac stimulator comprising:

2. A device defined in claim 1 further comprising:

3. A bipolar cardiac electrode comprising:

4. A bipolar cardiac electrode as defined in claim 3 further comprising:

5. An electrode arrangement as defined in claim 4 wherein said window is

6. A bipolar cardiac electrode as defined in claim 3 further comprising:

7. A bipolar cardiac electrode as defined in claim 4 wherein the leading ends further comprise:

Description:
BACKGROUND OF THE INVENTION

Cardiac disorders are believed to be among the major causes of death. Usually, acute disorders appear with no warning and where the patient is remote from medical assistance. While in some less severe cardiac disorders there is sufficient time to transport the patient to a hospital for treatment, in other more severe types of cardiac disorders, such as an acute myocardial infarction, immediate aid is often required. For example, in the United States, it is estimated that approximately 1,200,000 persons suffer an acute myocardial infarction each year. Of these, 200,000 people die within 15 minutes of the onset of their myocardial infarction, and another 50,000 die in the time interval between 15 minutes and 2 hours of the onset of their myocardial infarction. The death of a great proportion of the people in the latter group of 50,000 could largely be prevented by administering suitable medical aid quickly and without a delay. As to those persons who die of acute myocardial infarction within fifteen minutes of its onset, a great proportion could likewise be saved if proper medical attention could be employed immediately. Treatment of such acute cardiac disorders typically requires apparatus which is bulky and does not lend itself to portability. Thus, it has been necessary to transport the patient to a hopsital or other facility where such apparatus is available. The time interval ordinarily is too great and the patient dies.

In the great proportion (95 percent) of acute cardiac deaths, the patient is suffering from ventricular fibrillation. The remaining patients are in asystole, in which all heart activity has stopped. In each of these instances, there is no detectable arterial pulsation. As a result, the patient can deteriorate rapidly. For example, permanent brain damage can begin to occur approximately three minutes after pulsation stops.

Where the patient is suffering from ventricular fibrillation, it is essential first that the fibrillation be stopped before the heart can resume more regular activity. The usual emergency procedure for treating a pulseless patient is to check his air passages and perhaps attempt mouth-to-mouth resuscitation. If that fails to restart the heart, a sharp blow is applied to the chest generally in the region of the heart. That failing, closed chest cardiac message is initiated primarily in order to maintain a semblance of blood circulation in an attempt to avoid or minimize brain damage. These techniques are rarely effective to defibrillate a fibrillating heart and do not generally restart the heart. They are employed primarily as supportive therapy until the patient can be brought to a hospital or facility where fibrillation or asystole can be more effectively treated. When the patient has reached the hospital the vigorous closed chest massage is continued until the electric defibrillation apparatus has been readied. Such apparatus generates a substantial electrical pulse which is applied to the patient by means of a pair of paddle-like electrodes which are applied to the patient's chest. In general, it has been found that the most effective way to defibrillate is by applying such an electric pulse to the patient. The urgency of immediate defibrillation cannot be overstated. When the patient has no apparent pulse, closed chest massage is at best a poor substitute for a normally beating heart. Thus, even with vigorous closed chest massage the patient's brain and heart deteriorate quickly. Lactic acid builds up due to poor oxygenation of tissue which is the direct result of poor cardiac output. Thus, even when the patient reaches the hospital where he can be defibrillated electrically, the degree of deterioration which he may have suffered often is such that the defibrillation apparatus is ineffective and the patient dies. Because of the relatively nonportable bulky nature of defibrillation apparatus, many people have died within the time interval necessary to transport the patient to the hospital.

In addition to the foregoing difficulties, even if a patient has been defibrillated, he may still remain pulseless, in asystole. Among the most effective treatments for this condition is the application of electrical pulses of a smaller magnitude to the heart at a rate approximating that of a normal heart beat. Application of such pacing pulses is of considerable assistance in restarting an asystolic heart and maintaining regular operation of that heart. However, even in a hospital environment this takes some time which may add further to the interval so critical to the patient. This is true even though the electrodes for the heart pacing arrangement are applied through a transthoracic catheter of the type shown in the Ackerman patent or through a major vein into the heart. These procedures take time in addition to the time already elapsed. Although closed chest massage is maintained throughout these intervals the patient deteriorates further. Moreover, it may be noted that ventricular fibrillation is recurrent and can begin again even after the heart has been defibrillated but before the pacing electrodes have properly placed in operation. In such instance, the procedure may have to be restarted with the attendant loss in time. It is among the primary objects of my invention to provide a device and technique which minimizes greatly any interval between the time at which medical or paramedical personnel reach the patient and the time in which proper electrical stimulation of his heart is provided.

SUMMARY OF THE INVENTION

My invention includes independent defibrillation and pacing circuits which are assembled in a compact portable housing. The housing also contains a battery power pack and a switching arrangement to enable either of the circuits to be connected to the power pack. The output from the device is connectable to an arrangement of electrodes which are adapted to be introduced directly into the heart by a transthoracic needle. The electrodes are arranged to make good electrical contact with the inner surface of the heart, such as within the left ventricle. After the electrodes are disposed properly within the heart, the defibrillation or pacing pulse can be applied immediately. Further aspect of the invention relates to the bipolar configuration of the electrodes. The electrodes are highly flexible and normally tend to assume a spread apart configuration. When introduced into the heart they spread apart and against opposite sides of the inner surface of the left ventricle. The portions of the electrodes which contact the wall of the ventricle are of a broad and curved configuration. The electrodes are arranged so that there is little tendency for the electrical pulse to short circuit through the blood in the heart. This ensures that the electrical pulse will be applied directly to the myocardium. Because of the direct contact of the electrodes with the heart, there is significantly less impedance to the electrical pulse than that which is presented by the usual bulky defibrillation apparatus in which the pulse is applied to the exterior of the chest. As a result, there is a substantially smaller power requirement necessary which facilitates the portability of the device so that it may be carried easily to the patient thus saving time. Additionally, the electrode configuration is highly flexible and presents substantially no resistance to contraction of the heart.

It is among the objects of my invention to provide a portable cardiac stimulator capable of immediately applying defibrillation pulses to a cardiac victim.

Another object of the invention is to provide a portable defibrillation device which can selectively be employed to apply pacing pulses to the patient.

A further object of the invention is to provide a portable apparatus which avoids the critical lag in time incurred in the usual emergency treatment of such heart disorders.

Another object of the invention is to provide a portable cardiac stimulator which is capable of immediately and selectively applying either of a defibrillation pulse or a repetitive series of pacing pulses.

Further object of the invention is to provide an improved electrode arrangement employing a pair of poles which are self-spreading into contact with the opposite sides of the patient's ventricle.

Still another object of the invention is to provide an improved electrode arrangement in which each of the poles of the electrode contact the inner surface of the ventricle along a substantial area and not just point contact.

A further object of the invention is to provide an electrode configuration which presents substantially no resistance or damage to the heart in the event of contraction of the heart.

DESCRIPTION OF THE DRAWINGS

The foregoing and other objects and advantages of the invention will be understood more fully from the following detailed description thereof, with reference to the accompanying drawings wherein:

FIG. 1 is a diagrammatic cross section through a patient's thorax at the level of the fifth intercostal space, showing the invention with the self-spreading bipolar electrode inserted into the left ventricle of the heart;

FIG. 2 is an illustration of the electrode arrangement when in its spread configuration and having portions thereof broken away to illustrate its internal configuration;

FIG. 3A-3F are cross sections of the lead to the bipolar electrode and the bipolar electrodes themselves showing the internal arrangement of the electrode leads along successive portions of the electrode and as seen along the lines 3A--3A, 3B--3B, 3C--3C, 3D--3D, 3E--3E and 3F--3F of FIG. 2;

FIG. 4 is a longitudinal sectional illustration of the transthoracic needle by which the bipolar electrode may be inserted into the patient's left ventricle and showing the configuration of it in the manner in which the bipolar electrode is disposed within the needle in readiness to be inserted into the patient;

FIG. 5 is an enlarged illustration of the arrangement by which the electrode may be connected to the circuitry of the device;

FIG. 6 is a diagrammatic illustration of the circuitry of the invention; and

FIG. 7 is an illustration of the face of the control panel and housing for the circuitry.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows the invention in readiness to apply electric stimulating pulses to the patient. It includes the bipolar electrode 10 which has been inserted, in the manner described herein, through the patient's chest wall 12 at the level of the fifth intercostal space, to the left of the sternum 14. When properly located, the bipolar electrode 10 is disposed within the left ventricular lumen 16 of the heart. The electrode leads are connected by a connector 18 to the output leads 20 from a compact integral and controllable pulse generator 22. As described more fully below, the pulse generator includes independent circuits adapted to generate a defibrillating pulse and pacemaking pulses which can be selectively applied to the bipolar electrodes 10.

The bipolar electrode 10 is formed from a pair of thin flexible electrically conductive wires 24 made from a metal which is biologically non-reactive such as No. 316 extra low carbon stainless steel wire. In the illustrative embodiment, the wires approximate 0.012 inches in diameter. A pair of such wires is embedded in a flexible insulative sheath which, in the preferred embodiment, has an external diameter of approximately 0.034 inches. The sheath should be made from an appropriate material which is similarly biologically non-reactive such as silastic.

The parallel insulated wires 24 and surrounding sheath 26 are bifurcated at the end of thee electrode to define a generally T-shaped configuration in which the ends of the wires 24 extend generally in opposite directions. The sheath 26 continues integrally along the separated electrode portions of the wires 24 to define electrode sheaths 28 which insulate the bifurcated electrodes 30. The insulative sheaths 28 extend fully to and about the tips of the electrodes 30 except for cutout segments 32 through which the inner electrodes 30 are exposed.

The bifurcated electrodes 30 are fabricated so that they tend to assume the spread configuration shown in FIG. 2 which is somewhat S-shaped. The outer ends of the sheathed electrodes 30 are curved with their tips tending to extend inwardly. The arrangement is such that the lateral regions of the electrodes define a substantial convex configuration. It may be noted that the outer diameter of the electrode sheaths 28 is approximately 0.017 inches. At the outwardly facing side of each of the outer arcuate segments 36, the electrode sheaths 28 are cut away at 32 to define outwardly exposed semicircular sections of the electrodes 30. The cutout segments 32 preferably are approximately 3/16 of an inch long and begin approximately 3/16 of an inch from the tip 34 of each electrode 30. The cutout segments 32 expose the electrode only laterally outwardly and over approximately 180° of the cross sectional circumference of the electrode. The portions of the electrodes 30 which are so exposed serve as the conductive terminal ends of the electrode and are intended to bear against and establish electrical communication with the opposite inner surfaces of the ventricle wall. The electrode configuration shown in FIG. 2 is that in its completely relaxed condition. The bifurcated end of the electrode is dimensioned so as to be somewhat greater than the inner diameter of the ventricle. When the electrode arrangement is disposed within the ventricle and expands against diametrically opposite sides of the inner surface of the ventricle, the lateral arcuate segments 36 and, particularly the exposed surfaces of the electrodes 30 will bear against the ventricle wall snugly to establish firm electrical connection. When properly disposed within the ventricle, the electrodes assume a more T-shaped configuration than that shown in FIG. 2 with the reversely curved segments 38 of the electrodes being somewhat less curved than shown in FIG. 2. This is suggested somewhat in FIG. 1. While the dimensions of the electrode wire are such to enable it to be biased with sufficient firmness against the ventricle wall, it is sufficiently light as to present substantially no resistance to contraction or flexure of the myocardium. The foregoing arrangement ensures that electrical contact will be maintained with the ventricle during contraction or other movement of the heart.

The foregoing electrode arrangement provides a number of advantages. The exposed portions of the electrodes define a relatively substantial area of electrical contact thus tending to reduce the magnitude of impedance presented. It also reduces significantly the possibility of short circuiting through the relatively conductive blood within the left ventricle. The electrodes 30 are exposed only laterally and are biased firmly against the slightly into the ventricle wall which tends to cooperate with the insulative sheathing to isolate the electrode from the blood within the ventricle. This enhances the likelihood of the electrical pulse being applied to the ventricle wall and not being short circuited through the blood. In addition, the engagement of the electrodes with diametrically opposite portions of the ventricle further reduces the possibility of short-circuiting by maximizing the distance between the exposed portions of the electrodes. Still another significant advantage of the electrode configuration is that by applying the electrodes at opposite internal surfaces of the ventricle it is more effectively ensured that a substantial portion, if not all of the ventricle wall will be subjected to the electrical pulse. The arrangement of the insulated tips 34 by which they extend inwardly toward each other and away from the ventricle wall affords a further safety feature by eliminating the possiblity of accidental puncture of the ventricle wall. In this regard it may be noted that when the electrodes are properly disposed within the ventricle, the tips 34 extend inwardly toward each other even to a greater extent than that shown in FIG. 2.

FIGS. 3A-3F show the cross section of the electrode leads at various locations along their length and the manner in which the leads may be connected to the pulse generator 22. The wires 24 extend within the sheath and are connected to a pair of conductive sleeves 40 which are spaced along the distal end of the leads and are exposed about the circumference of the sheath 26. The wires 24 are connected by appropriate means to the sleeves 40 as shown in FIGS. 3B and 3D.

The sleeved end of the sheath 26 is connected to the pulse generator 22 by a connector 18 in the manner described below.

The electrode is introduced transthoracically into the left ventricle of the heart before its trailing end is electrically connected to the pulse generator and by means of an arrangement shown in FIG. 4. This arrangement includes a plastic tube 42 having an internal diameter of approximately 0.040 inches which encloses the bipolar electrodes as shown. The electrodes are sufficiently resilient as to be able to be slipped into the tube 42 with its normally S-shaped bifurcations being constrained in the substantially straight configuration shown. The outer diameter of the tube 42 is dimensioned to fit within the hub 44 of a 17 gage cardiac needle indicated generally at 46. The electrodes are introduced by inserting the cardiac needle 46 into the ventricle then removing the obturator (not shown) normally within the needle and thereafter inserting the plastic tube 42 into the hub 44 of the cardiac needle 46. The needle 46 and tube 42 are approximately each five inches long. The electrode then is advanced along the tube into and through the needle until the trailing end of the electrode sheath is flush with the end of the plastic sleeve. The length of the electrodes and sheath are related to the combined length of the cardiac needle 46 and tube 42 so that when the trailing end of the sheath is flush with the end of the tube 42 the electrode end of the sheath will have extended approximately 1 3/4 inches past the inner end of the cardiac needle 46 and will have spread into its generally T-shaped configuration. The needle and tube then may be withdrawn with the electrode properly disposed within the left ventricle and with its leads extending outwardly from the patient.

The outwardly disposed lead of the electrode is connected to the output leads 20 from the pulse generator 22 by means of an appropriate connector such as that shown in FIG. 5. The illustrated connector is formed integrally with the end of the output leads 20 and has an enlarged cylindrical portion 48 formed from insulative material integral with the insulative material surrounding the output leads 20. The cylindrical portion 48 has a center bore formed therethrough approximately 0.040 inches in diameter. The bore 50 is defined in part, at spaced locations along its length, by conductive sleeves 52. Sleeves 52 are electrically connected to the conductive leads 20 and are spaced identically to the sleeves 40 disposed at the trailing end of the electrode leads. The trailing end of the electrode leads may be inserted into the bore 50 to align the sleeves 52 with the sleeves 40 and can be secured therein by a number of arrangements such as the screws 54. The set screws 54 are of non-conductive material. Transthoracic insertion of the electrode arrangement into the ventricle and subsequent connection of the trailing end of the electrode arrangement to the pulse generator can be accomplished quickly and simply and requires no moving of the patient to a hospital or the like. After the electrodes have been connected, the pulse generator may be operated immediately either to apply a defibrillating pulse or a pacing pulse to the patient.

The circuitry shown in FIG. 6 generally includes switch 60, defibrillator circuit 62, pacemaker circuit 64, and energy supply means. The source of electrical energy comprises battery banks 66 and 68 which are mutually exclusively connectable by switch 60 to mode switch 70. Each of the battery banks includes a pair of commercially available 8.4 volt mercury batteries connected in series. When the unit is to be operated the switch 60 is thrown to select either bank 66 or 68. The unused battery bank remains readily available as a spare power source.

A battery failure indicator 72 couples to the common contact of switch 60 and indicates when the battery output falls to 85 percent of the full battery power, thus indicating the need to switch to the spare set of batteries by throwing switch 60 to its alternate position.

The mode switch 70 is a four position/double throw switch having a set of common contacts 70C and two sets of fixed contacts 70A and 70B. With switch 60 connected to either of the battery banks 66, 68, switch 70 can either be in its neutral position with its movable contacts 70C open, or it can be moved to either the "defib" position where the movable contacts 70C couple to the fixed contacts 70A, or the "pace" position where the movable contacts 70C connect to the fixed contacts 70B. When switch 70 is in the defib position energy is coupled to the defibrillator circuit 62 and an output signal is developed across output lines 74 and 76. In FIG. 6 the switch 70 is shown in the defib position. Alternatively, the switch can be moved to the pace position wherein energy is coupled to the pacemaker circuit 64 which develops its output across lines 74, 76.

When switch 70 is in the defib position power is coupled to trigger button 78 which is a typical normally open momentary contact switch. When trigger button is depressed the high voltage defibrillatory shock pulse is generated and applied to the bipolar electrode thru lines 74, 76. The defibrillation circuit 62 illustrated may be considered as being of conventional design and generally comprises a DC to DC converter 80, transistor 82, neon tube 84, capacitor 86, SCR 88, and a series of resistors appropriately interconnected. The circuit 62 is substantially identical to the pulse circuit shown in U.S. Pat. No. 3,614,955 and operates as follows: When button 78 is depressed a relatively high voltage signal, approximately 2,500 volts, is established at the output of DC to DC converter 80. This voltage is developed across capacitor 86. The resistor chain and the tube 84 are interconnected in such a manner that when the voltage across capacitor 86 reaches a full 2,500 volts, the tube 84 conducts. When the capacitor 86 is fully charged, the transistor 82 becomes conductive, due to the now-conducting neon tube 84. When the tube conducts there is a sufficient conduction path by way of resistors 90, 92 and 94 to cause conduction of transistor 82. Concurrently therewith, a drive current is provided to the gate of SCR 88 and the SCR also conducts, applying the voltage from the capacitor 86 across the output lines 74, 76. The output of circuit 62 has a preferable pulse width of approximately 100 milliseconds as determined by the time constant of the network. The energy output is of the order of 15 joules at a current of approximately 25ma. This is significantly less than the energy requirements for previous defibrillation devices. The neon tube 84 serves the double function of being an integral part of the trigger circuit and, because it also lights up for an instant during voltage buildup in the converter 80 it also indicates that the circuit is in operation.

The device may be controlled to immediately apply lower voltage "pacing" pulses by operation of the switch 70 to the position in which the movable contacts 70C are connected to the fixed contacts 70B. The power from one of the battery banks 66 or 68 is coupled to the circuit 64 and the cyclic output of that circuit is coupled to the output lines 74, 76. A typical output from circuit 64 is a signal 0 to 30 milliamp, of 2.8 millisecond duration at a repetition rate of 70 pulses per minute.

The pacing circuit 64 comprises a conventional astable multivibrator including transistors 96 and 98, a pulse width regulator including transistors 100, 102, a voltage regulator including transistor 104 and a current source including transistor 106. The astable multivibrator is of conventional design and includes cross-coupling capacitors 108, 110 and collector resistors 112, 114. A potentiometer 116 is coupled to the base of transistor 96 for varying the frequency of operation of the astable multivibrator.

The output of the multivibrator couples by way of resistor 118 to transistor 100. The collector of transistor 100 couples through resistor 120 to the power source and also by way of capacitor 122 to resistor 124 and to the base of transistor 102. When transistor 100 is not conducting capacitor 122 is discharging and transistor 102 is non-conductive. When transistor 100 conducts because of a change of state of the astable multivibrator, capacitor 122 is charged by way of resistor 124 and after a predetermined time period transistor 102 conducts. Transistor 102 conducts in one embodiment for approximately 2.8 milliseconds before transistor 100 can change its state causing transistor 102 to stop conducting. During the brief time that transistor 100 conducts Zener diode 126 is shorted out and transistor 104 becomes conductive via Zener diode 128 to transistor 106. When this occurs, transistor 106 also conducts and a constant current is fed by way of switch 70 to output leads 74, 76. The potentiometer 130 is used to control the output current which may be varied from 0 to 30 milliamps. A pulse indicator 132 may be coupled from the collector of transistor 106 to the emitter of transistor 104 for verifying that the pacemaker circuit is functioning properly. The indicator 132 may also be coupled, in an alternate embodiment, directly to the astable multivibrator.

FIG. 7 shows the control panel with mode switch 70 which may be in any of its off, defib or pace positions. When the switch 70 is in its defib position, depression of the trigger button 78 causes almost instantaneous charging and discharging of the defibrillator circuit 62 and an attendant flashing of neon bulb 84 associated therewith. This indicates that the high voltage pulse has been coupled to the output leads 74 and 76. When the switch 70 is in the pace position, indicator 132 reveals a pulse rate of 70 beats per minute, for example. The milliamperage rating from the output of the pace circuit is adjusted by dial 134 shown in FIG. 7 which is coupled to the potentiometer 130.

Thus, I have described my invention which enables controlled electrical pulses to be selectively applied to a cardiac patient both as an emergency first aid measure as well as in a hospital environment. It should be understood, however, that the foregoing description of the invention is intended merely to be illustrative thereof, and that other modifications and embodiments may be apparent to those skilled in the art without departing from the spirit.