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THE INCORPORATION OF A MAGNETIC SWITCH INTO AN IMPLANTED PACEMAKER
T H E I N C O R P O R A T I O N OF A MAGNETIC SWITCH I N T O A N I M P L A N T E D PACEMAKER /. Weinman,
Jerusalem,
Israel
T
HERE are situations in which one would like to be able to stop at will and with ease without a surgical procedure, the working of an implanted pace maker for shorter or longer periods of time. The incorporation of such a feature into an implanted pacemaker could be, in case of an intermittent or temporary atrioventricular block, of crucial importance. The reappearance of the sinus rhythm, while the pacemaker is working, enables pacemaker impulses to enter the myocardium during the vulnerable phase for initiating fibrillation, thus creating a highly dangerous situation, as was lately pointed out by Lillehei and his associates.2 Widman (discussion of Lillehei et al. 2 ) justifies his preference for radiofrequency-driven pacemakers by the ease with which their functioning can be interrupted at will and he illustrates the importance of this possibility with a case history. Most of the clinically used pacemakers are not radiofrequency driven but are fully implanted blocking oscillators and, once in situ, cannot be switched off without surgical intervention. One can, however, convert them into "switchable" pacemakers without decreasing their reliability and without the necessity of surgery by using the small magnetic switch shown in Fig. 1. Such switches are manufactured by RCA (1962) under the trade name of Minireed and by Hivac (1964) as Dry Reed Relay Inserts. They consist of two reeds made of a metal of low magnetic reluctance enclosed hermetically in a gas-filled glass capsule. The switch is normally open and will close when the two reeds are placed in the axis of a magnetic field, which polarizes the two ends oppositely. A commercially available permanent Alnico bar magnet will close the switch from a distance up to 4 cm. When the field is removed, the switch will remain open even when exposed to violent movements and vibrations (RCA [1962]). The switch was used for the first time on my advice on a patient with a complete atrioventricular block, who, some time after the implantation of a pace maker, developed a sinus rhythm suddenly, followed after a few days by a heart standstill, due probably to fibrillation. After resuscitation* and removal of the Prom the Rogoff Laboratory for Medical Electronics, Hebrew University, Hadassah Medical School, Jerusalem, Israel. Received for publication March 19, 1964. *Dr. Rogel, Cardiovascular Department, University-Hadassah Hospital, Jerusalem, Israel. 690
Vol. 48, No. 4 October, 1964
MAGNETIC SWITCH I N I M P L A N T E D PACEMAKER
691
pacemaker, the sinus rhythm continued, but the danger of the reappearance of a complete atrioventricular block persisted. In order to be able to deal with such an emergency, the pacemaker was again implanted, this time, however, together with the magnetic switch. The magnetic switch (Hivac XS6) was embedded in silicone rubber (Dow Corning, Medical Silastic 382) and connected in series with one of the pacemaker electrodes.* The spot on the skin, where one has to put the bar magnet t in order to actuate the magnetic switch, was marked with an undilutable dye. By sticking the magnet with tape to the marked spot, one can immediately close the magnetic switch and supply, by reconnecting the electrode, the heart muscle with impulses from the pacemaker 4
Fig. 1.—Magnetic Switch Minireed RCA 2100 SN. Scale in centimeters (subdivision millimeters).
Another mode of using the magnetic switch would be to connect it across the output of the pacemaker. In this case, the pacemaker would stimulate the heart continuously and the placing of the magnetic bar on the marked spot will close the switch, shorten the pacemaker output, and, thus, stop the stimulation. Most of the commercial pacemakers are constant current generators and, there fore, such a procedure is permissible and will not increase the drain on the pacemaker batteries. The ideal solution would be the incorporation of the magnetic switch into the electronics of the pacemaker by the manufacturer. This could be done in such a way that the closing of the switch would stop the oscillatory circuit of the pacemaker when, due to the reappearance of the sinus rhythm, one would like to stop the artificial stimulation. Such a feature would give the additional possibility of stopping the pacemaker for short intervals in order to enable one to cheek the rate of the idioventricular rhythm and to record the existing spontaneous activity of the heart muscle. •Performed by J. Mahler. tEclipse, bar magnet 2 inches long, weight 2% ounces, manufactured by James Neill, Napier St., Sheffield, England. It is most probable that a much smaller and lighter magnet would suffice. JThe pacemaker used was manufactured by Electrodyne.
WEINMAN
692
J. Thoracic and Cardiovas. Surg.
For the sake of completeness, I would like to draw the attention to a report by Sykosh and his co-workers4 which (1963) describes a pacemaker which will be automatically stopped when the sinus rhythm reappears. In order to perform this function, two ECG electrodes are used. These electrodes detect the reappearance of the sinus rhythm by the increased heart rate. This information, converted into a DC signal, switches a small radiofrequency transmitter, which is coupled, through the skin, to an implanted receiving coil. The rectified receiver signal stops the implanted pacemaker. One would hesitate, for the time being, to make use of such a complicated solution in clinical practice. REFERENCES
1. Hivac Ltd., Stonefield Way, South Euislip, Middlesex, England. D r y Keed Eelay Insert Type XS6 (Subminiature). Leaflet, January, 1964. 2. Lillehei, C. W., Sellers, E . D., Bonnabeau, E . C , and Elliot, E. S.: Chronic Postsurgical Complete Heart Block: With Particular Reference to Prognosis, Management, and a New P-Wave Pacemaker, J . THORACIC & CARDIOVAS. SURG. 46: 436, 1963.
3. RCA., Cat. R E 2100 Minireed, RCA 2100 VL, March, 1962. 4. Sykosh, S., Efert, S., Pulver, K . G., and F. Zaconto: Zur Theraphie mit elektrisohem Schrittmachern. E i n implantierbarer induktiv ausschaltbarer elektriseher Schrittmacher, Elektromedizin 8: 139, 1963.
Jerusalem,
Israel
T
HERE are situations in which one would like to be able to stop at will and with ease without a surgical procedure, the working of an implanted pace maker for shorter or longer periods of time. The incorporation of such a feature into an implanted pacemaker could be, in case of an intermittent or temporary atrioventricular block, of crucial importance. The reappearance of the sinus rhythm, while the pacemaker is working, enables pacemaker impulses to enter the myocardium during the vulnerable phase for initiating fibrillation, thus creating a highly dangerous situation, as was lately pointed out by Lillehei and his associates.2 Widman (discussion of Lillehei et al. 2 ) justifies his preference for radiofrequency-driven pacemakers by the ease with which their functioning can be interrupted at will and he illustrates the importance of this possibility with a case history. Most of the clinically used pacemakers are not radiofrequency driven but are fully implanted blocking oscillators and, once in situ, cannot be switched off without surgical intervention. One can, however, convert them into "switchable" pacemakers without decreasing their reliability and without the necessity of surgery by using the small magnetic switch shown in Fig. 1. Such switches are manufactured by RCA (1962) under the trade name of Minireed and by Hivac (1964) as Dry Reed Relay Inserts. They consist of two reeds made of a metal of low magnetic reluctance enclosed hermetically in a gas-filled glass capsule. The switch is normally open and will close when the two reeds are placed in the axis of a magnetic field, which polarizes the two ends oppositely. A commercially available permanent Alnico bar magnet will close the switch from a distance up to 4 cm. When the field is removed, the switch will remain open even when exposed to violent movements and vibrations (RCA [1962]). The switch was used for the first time on my advice on a patient with a complete atrioventricular block, who, some time after the implantation of a pace maker, developed a sinus rhythm suddenly, followed after a few days by a heart standstill, due probably to fibrillation. After resuscitation* and removal of the Prom the Rogoff Laboratory for Medical Electronics, Hebrew University, Hadassah Medical School, Jerusalem, Israel. Received for publication March 19, 1964. *Dr. Rogel, Cardiovascular Department, University-Hadassah Hospital, Jerusalem, Israel. 690
Vol. 48, No. 4 October, 1964
MAGNETIC SWITCH I N I M P L A N T E D PACEMAKER
691
pacemaker, the sinus rhythm continued, but the danger of the reappearance of a complete atrioventricular block persisted. In order to be able to deal with such an emergency, the pacemaker was again implanted, this time, however, together with the magnetic switch. The magnetic switch (Hivac XS6) was embedded in silicone rubber (Dow Corning, Medical Silastic 382) and connected in series with one of the pacemaker electrodes.* The spot on the skin, where one has to put the bar magnet t in order to actuate the magnetic switch, was marked with an undilutable dye. By sticking the magnet with tape to the marked spot, one can immediately close the magnetic switch and supply, by reconnecting the electrode, the heart muscle with impulses from the pacemaker 4
Fig. 1.—Magnetic Switch Minireed RCA 2100 SN. Scale in centimeters (subdivision millimeters).
Another mode of using the magnetic switch would be to connect it across the output of the pacemaker. In this case, the pacemaker would stimulate the heart continuously and the placing of the magnetic bar on the marked spot will close the switch, shorten the pacemaker output, and, thus, stop the stimulation. Most of the commercial pacemakers are constant current generators and, there fore, such a procedure is permissible and will not increase the drain on the pacemaker batteries. The ideal solution would be the incorporation of the magnetic switch into the electronics of the pacemaker by the manufacturer. This could be done in such a way that the closing of the switch would stop the oscillatory circuit of the pacemaker when, due to the reappearance of the sinus rhythm, one would like to stop the artificial stimulation. Such a feature would give the additional possibility of stopping the pacemaker for short intervals in order to enable one to cheek the rate of the idioventricular rhythm and to record the existing spontaneous activity of the heart muscle. •Performed by J. Mahler. tEclipse, bar magnet 2 inches long, weight 2% ounces, manufactured by James Neill, Napier St., Sheffield, England. It is most probable that a much smaller and lighter magnet would suffice. JThe pacemaker used was manufactured by Electrodyne.
WEINMAN
692
J. Thoracic and Cardiovas. Surg.
For the sake of completeness, I would like to draw the attention to a report by Sykosh and his co-workers4 which (1963) describes a pacemaker which will be automatically stopped when the sinus rhythm reappears. In order to perform this function, two ECG electrodes are used. These electrodes detect the reappearance of the sinus rhythm by the increased heart rate. This information, converted into a DC signal, switches a small radiofrequency transmitter, which is coupled, through the skin, to an implanted receiving coil. The rectified receiver signal stops the implanted pacemaker. One would hesitate, for the time being, to make use of such a complicated solution in clinical practice. REFERENCES
1. Hivac Ltd., Stonefield Way, South Euislip, Middlesex, England. D r y Keed Eelay Insert Type XS6 (Subminiature). Leaflet, January, 1964. 2. Lillehei, C. W., Sellers, E . D., Bonnabeau, E . C , and Elliot, E. S.: Chronic Postsurgical Complete Heart Block: With Particular Reference to Prognosis, Management, and a New P-Wave Pacemaker, J . THORACIC & CARDIOVAS. SURG. 46: 436, 1963.
3. RCA., Cat. R E 2100 Minireed, RCA 2100 VL, March, 1962. 4. Sykosh, S., Efert, S., Pulver, K . G., and F. Zaconto: Zur Theraphie mit elektrisohem Schrittmachern. E i n implantierbarer induktiv ausschaltbarer elektriseher Schrittmacher, Elektromedizin 8: 139, 1963.