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The lithium iodide-powered cardiac pacemaker
The lithium iodide-powered cardiac pacemaker Clinical experience with 250 implantations A long-life cardiac pulse generator powered by the lithium-iodide fuel cell is described and our experience with 250 implantations is documented. The compact, hermetically sealed pulse generator unit is easily implanted, is reliable, and is well accepted by patients. There have been no pacemaker-related deaths and only minimal morbidity. There was a single instance of electrical circuit failure of the pulse generator early in our experience; however, to date, after 15.9 months' average follow-up representing 3,988 patient months of cardiac pacing, there have been no battery failures and no further electrical component failures. The pulse generator unit is now guaranteed by the manufacturer for 6 years. We believe that the lithium-iodide powered pacemaker represents a significant advance in pacemaker generator technology and is recommended for long-term cardiac pacing.
Lawrence H. Burr, M.D., F.R.C.S. (C), Vancouver, British Columbia,
V-^ardiac pacemakers were first developed by Bigelow and associates1 in Canada and by Zoll2 in the United States during the early 1950's; in 1960, Chardack, Gage, and Greatbatch3 reported the insertion of the first totally implantable cardiac pacemaker for use in man, powered by standard hydrogen-generating mercury batteries. The electrical circuitry of the cardiac pacemaker has been improved, modified, and refined, but many units are still powered by standard batteries and require replacement every 2 to 4 years. In September, 1973, a new cardiac pacemaker,* powered with a lithium-iodide fuel cell developed by Wilson Greatbach, Ltd., was introduced in Canada. This report documents the first 250 implantations of the original lithium-iodide pacemaker at the Vancouver General Hospital between September, 1973, and February, 1976. Early in 1976 the manufacturer introduced two From the Division of Cardiothoracic Surgery, Department of Surgery, University of British Columbia, 700 West 10th. Ave., Vancouver, British Columbia, Canada. This work was supported by a Fellowship from the R. S. McLaughlin Foundation of Canada. Received for publication Aug. 27, 1976. Accepted for publication Sept. 30, 1976. Requests for reprints should be sent to Dr. Lawrence H. Burr at the above address. *CPI Maxilith, Cardiac Pacemakers, St. Paul, Minn.
Canada
new, smaller lithium iodide-powered pulse generators. Data from these pacemakers will be reported separately. Pulse generator characteristics The lithium-iodide fuel cell is a solid-state battery in which metallic lithium chemically combines with iodine to produce crystalline lithium iodide plus energy.4 Since there is no production of hydrogen gas, the power unit is hermetically sealed against intrusion by body fluids. There are two metallic lithium anodes inside the cell: The doubled anode surface area reduces ceU resistance by half and decreases electrolyte buildup. The iodide-containing compound is also in two sections and, since the two cells are arranged in parallel, failure of one side of the unit will shift the load to the other half without any need for electronic switching devices. The battery is incorporated into a compact R wave-inhibited demand pulse generator unit measuring 79 by 57 by 16 mm., weighing 165 Gm., and displacing a volume of 69.7 ml. The pulse circuitry is potted in epoxy resin, coated with silicone, and hermetically welded onto the stainless steel battery case. The pulse generator produces a signal width of 1.0 msec, amplitude 5 v., and refractory period 330 msec. The rated current is 30 microamperes, with a capacity of over 3.5 ampere hours; battery life is predicted at 3,760 milliampere hours, equivalent to 13.98 years of 421
The Journal of Thoracic and Cardiovascular Surgery
4 2 2 Burr
Table I. Indications for cardiac pacing Complete heart block Intermittent complete heart block Second-degree heart block Bifascicular block Sinus arrest/bradycardia Postsurgical heart block Ventricular tachyarrhythmia Congenital heart disease Unstable rheumatic heart disease Carotid sinus syncope
Table III. Pacing lead complications 101 53 18 8 55 7 3 2 2 1
Table II. Wound complications Infection of generator site Dehiscence (sterile) Hematoma Delayed wound healing (sterile, intact) Catgut allergy (proved: wound reopened and resutured) Pain in pulse generator site Local muscle stimulation
clinical use at a current drain of 30 microamperes. Pacemaker function is not affected by television sets, electrical motors, household appliances, or weapons detectors. Caution must be used near microwave ovens and with surgical electrocautery. Electric razors should not be used on the skin directly over the pulse generator site. The standard pre-set factory rate of this model is 72 ± 3 beats per minute: A test magnet applied over the implanted pulse generator will increase the rate by 15 beats per minute for monitoring of the electrocardiogram. Battery output maintains a steady, high, slowly decaying level until the chemicals are becoming depleted; the pacing rate slows by 6 beats per minute as the battery reaches elective replacement time. The manufacturer currently warrants the pacemaker for 6 years' full replacement. Clinical experience Our first 250 CPI lithium iodide-powered pacemakers were implanted in 147 male and 103 female patients. The average age was 71.6 years (range 12 to 93 years). Transvenous endocardial pacing electrodes were used in 214 patients, myocardial electrodes in 17, and the sutureless electrode in 19 patients. A bipolar pacemaking system was used in 159 patients and a unipolar system in 91. Ninety-four patients received the lithium-iodide pacemaker as their first pulse generator and 156 as a replacement unit. The indications for cardiac pacing are given in Table I.
Repositioning of transvenous lead Fracture of old lead Pacing lead change* TV-TV TV-SL SL-TV SL-SL Intermittent postural diaphragm stimulation
19 7 16* 5 9 1 1 2
Legend: TV, Transvenous electrode. SL, Sutureless electrode. •Includes 8 patients in whom lead repositioning failed, included with the 19 patients mentioned above.
In the 156 patients in whom the lithium-iodide pulse generator was a replacement unit, the indications for replacement of the previous generating units were as follows: elective replacement, 97 cases; pulse generator failure, 34 cases; change of pacing lead, 18 cases; and wound complications, 7 cases. The implantations have been followed for 3,988 patient months of cardiac pacing, an average of 15.9 months (range 4 to 32 months). During this time we have documented the following complications: pulse generator failure, one case; wound complications, 12 cases; lead repositioning, 19 cases; lead changes, 16 cases; and miscellaneous, 2 cases. There have been nine deaths during this time. Six occurred within 3 months of the insertion of the pacemaker; three of these were from the inexorable progression of congestive heart failure, and three were from myocardial infarction. Three patients died later from cerebrovascular accident, thrombosis of the superior mesenteric artery, and cardiac arrest. In all patients the pacemaker was working perfectly at the time of death. There was one pulse generator failure early in our clinical experience. Intermittent failure of pacing in the immediate postinsertion period was noted, and the newly implanted lithium-iodide power pack and bipolar transvenous lead were both replaced during the first week. Subsequent testing by the manufacturer proved the pulse generator to be defective owing to random failure of an electrical circuit component, which resulted in variable R-wave sensing. Wound complications have occurred in 12 of the 250 patients (Table II). The pulse generator site became infected in 2 cases, 3 and 5 months after implantation. Sterile dehiscence necessitated resuturing in 2 cases, as did proved catgut allergy in one case. There were 4 cases of wound hematoma following surgery; 2 patients were receiving anticoagulants and required surgical evacuation of the hematoma. One patient had delayed wound healing, but the wound remained sterile and
Volume 73 Number 3 March, 1977
intact. One patient experienced pain in the pulse generator site 8 weeks postoperatively and finally required a new pulse generator in a different site. Local muscle stimulation occurred in one patient with a unipolar pacemaking system; this unit was later replaced with a bipolar system without complications. Pacing lead complications occurred in 31 of the 250 implantations (Table III). Repositioning of the transvenous lead was necessary in 19 patients; in 15 cases this was performed during the first 3 months. Fracture of two previously placed endocardial leads occurred after almost one year of pacing with the lithium iodidepowered pulse generator and necessitated lead replacement. Among the 16 patients with pacing lead changes, 8 had previous repositionings of their transvenous leads and are included in the group of 19 patients just mentioned, as are the 2 who had lead fracture. Two patients had intermittent postural stimulation of the diaphragm but declined treatment of this condition. The lithium-iodide generator was removed in 15 patients; in 12 cases it was removed at the time of lead change and in one case at the time of lead repositioning, once for muscle stimulation and once because of infection at the pulse generator site. Each pulse generator was tested by the manufacturer after removal and was found to be functioning normally. Discussion Our initial experience with 250 lithium iodide-powered pulse generators is most gratifying. The smaller, thinner, rectangular unit has required less generator pouch dissection, has aided in the tension-free tissue closure over the pack, and has resulted in less pack migration. Patient acceptance has been excellent. Patients with previous pulse generators comment favorably on the lighter, smaller unit. The combined wound breakdown and infection rate of 2 per cent (five of 250 implantations) is less than with the previous, larger sized, standard battery units in our Cardiothoracic Surgery Unit. There have been no pacemaker-related deaths to date in our series, although 9 patients have died from cardiovascular causes. We do not think that the problems of lead complications documented in this report are related to the lithium-iodide pulse generator. We have prefered the transvenous pacemaker system with the simplicity of electrode insertion but recognize that 11 of the 214 transvenous leads required repositioning and a further 8 required a change of pacing lead system to sutureless electrodes after failure of transvenous electrode adjustment. In the 16 cases of pacing lead
Lithium iodide-powered cardiac pacemaker
423
change, 9 patients had the transvenous lead replaced with a sutureless electrode; 5 patients simply had a new transvenous electrode implanted, one a new sutureless electrode, and one a transvenous lead after failure of a sutureless lead. There have been no battery or electrical failures in our series with the sole exception of the one patient with immediate post-implantation failure. The 15 generators that have been removed during our follow-up period have all been removed when the cause of intermittent pacing was uncertain. It is pertinent to re-emphasize that none of these pulse generators was faulty and that all were functioning normally when extensively tested upon return to the manufacturer. Crude preliminary analysis of cost of cardiac pacing with the lithium-iodide pulse generator has been made in our 250 patients. With the actual observed complications, removals, and deaths, it is calculated that over a 2 year period the yearly cost of cardiac pacing with the lithium-iodide generator is $ 1,272 as compared to a cost of $ 1,610 for the standard battery generator. Extrapolation of the data markedly lowers the yearly cost of cardiac pacing, but we cannot confirm this extrapolation with hard data. The long-life lithium-iodide pacemaker represents a significant advance in pacemaker technology and allows cardiac pacing without the restrictions consequent to the use of nuclear energy, the uncertainties of biological power sources, or the biweekly commitment of recharging the batteries. We unhesitatingly recommend the lithium-iodide powered pacemaker in all age groups for long-term cardiac pacing. May I gratefully thank Miss Sheila Stickney, R.N., for her help in collecting the patient data. I also acknowledge the kind permission of Drs. Peter Allen, P. G. Ashmore, A. I. Munro, C. L. N. Robinson, and W. G. Trapp to include their patients in this series. The work was supported by a Fellowship from the R. S. McLaughlin Foundation of Canada. REFERENCES 1 Bigelow, W. G., Callaghan, J. C , and Hopps, J. A.: An Artificial Pacemaker for Cardiac Standstill, Ann. Surg. 132: 531, 1950. 2 Zoll, P. M.: Resuscitation of the Heart in Ventricular Standstill by External Electrical Stimulation, N. Engl. J. Med. 247: 768, 1952. 3 Chardack, W. M., Gage, A. A., and Greatbatch, W.: A Transistorized, Self-Contained, Implantable Pacemaker for the Long-Term Correction of Complete Heart Block, Surgery 48: 643, 1960. 4 Lillehei, R. C , Romero, L. H., Beckman, C. B., Burrows, J., and Friedberg, H. D.: A New Solid-State, Long-Life, Lithium-Powered Pulse Generator, Ann. Thorac. Surg. 18: 479, 1974.
Lawrence H. Burr, M.D., F.R.C.S. (C), Vancouver, British Columbia,
V-^ardiac pacemakers were first developed by Bigelow and associates1 in Canada and by Zoll2 in the United States during the early 1950's; in 1960, Chardack, Gage, and Greatbatch3 reported the insertion of the first totally implantable cardiac pacemaker for use in man, powered by standard hydrogen-generating mercury batteries. The electrical circuitry of the cardiac pacemaker has been improved, modified, and refined, but many units are still powered by standard batteries and require replacement every 2 to 4 years. In September, 1973, a new cardiac pacemaker,* powered with a lithium-iodide fuel cell developed by Wilson Greatbach, Ltd., was introduced in Canada. This report documents the first 250 implantations of the original lithium-iodide pacemaker at the Vancouver General Hospital between September, 1973, and February, 1976. Early in 1976 the manufacturer introduced two From the Division of Cardiothoracic Surgery, Department of Surgery, University of British Columbia, 700 West 10th. Ave., Vancouver, British Columbia, Canada. This work was supported by a Fellowship from the R. S. McLaughlin Foundation of Canada. Received for publication Aug. 27, 1976. Accepted for publication Sept. 30, 1976. Requests for reprints should be sent to Dr. Lawrence H. Burr at the above address. *CPI Maxilith, Cardiac Pacemakers, St. Paul, Minn.
Canada
new, smaller lithium iodide-powered pulse generators. Data from these pacemakers will be reported separately. Pulse generator characteristics The lithium-iodide fuel cell is a solid-state battery in which metallic lithium chemically combines with iodine to produce crystalline lithium iodide plus energy.4 Since there is no production of hydrogen gas, the power unit is hermetically sealed against intrusion by body fluids. There are two metallic lithium anodes inside the cell: The doubled anode surface area reduces ceU resistance by half and decreases electrolyte buildup. The iodide-containing compound is also in two sections and, since the two cells are arranged in parallel, failure of one side of the unit will shift the load to the other half without any need for electronic switching devices. The battery is incorporated into a compact R wave-inhibited demand pulse generator unit measuring 79 by 57 by 16 mm., weighing 165 Gm., and displacing a volume of 69.7 ml. The pulse circuitry is potted in epoxy resin, coated with silicone, and hermetically welded onto the stainless steel battery case. The pulse generator produces a signal width of 1.0 msec, amplitude 5 v., and refractory period 330 msec. The rated current is 30 microamperes, with a capacity of over 3.5 ampere hours; battery life is predicted at 3,760 milliampere hours, equivalent to 13.98 years of 421
The Journal of Thoracic and Cardiovascular Surgery
4 2 2 Burr
Table I. Indications for cardiac pacing Complete heart block Intermittent complete heart block Second-degree heart block Bifascicular block Sinus arrest/bradycardia Postsurgical heart block Ventricular tachyarrhythmia Congenital heart disease Unstable rheumatic heart disease Carotid sinus syncope
Table III. Pacing lead complications 101 53 18 8 55 7 3 2 2 1
Table II. Wound complications Infection of generator site Dehiscence (sterile) Hematoma Delayed wound healing (sterile, intact) Catgut allergy (proved: wound reopened and resutured) Pain in pulse generator site Local muscle stimulation
clinical use at a current drain of 30 microamperes. Pacemaker function is not affected by television sets, electrical motors, household appliances, or weapons detectors. Caution must be used near microwave ovens and with surgical electrocautery. Electric razors should not be used on the skin directly over the pulse generator site. The standard pre-set factory rate of this model is 72 ± 3 beats per minute: A test magnet applied over the implanted pulse generator will increase the rate by 15 beats per minute for monitoring of the electrocardiogram. Battery output maintains a steady, high, slowly decaying level until the chemicals are becoming depleted; the pacing rate slows by 6 beats per minute as the battery reaches elective replacement time. The manufacturer currently warrants the pacemaker for 6 years' full replacement. Clinical experience Our first 250 CPI lithium iodide-powered pacemakers were implanted in 147 male and 103 female patients. The average age was 71.6 years (range 12 to 93 years). Transvenous endocardial pacing electrodes were used in 214 patients, myocardial electrodes in 17, and the sutureless electrode in 19 patients. A bipolar pacemaking system was used in 159 patients and a unipolar system in 91. Ninety-four patients received the lithium-iodide pacemaker as their first pulse generator and 156 as a replacement unit. The indications for cardiac pacing are given in Table I.
Repositioning of transvenous lead Fracture of old lead Pacing lead change* TV-TV TV-SL SL-TV SL-SL Intermittent postural diaphragm stimulation
19 7 16* 5 9 1 1 2
Legend: TV, Transvenous electrode. SL, Sutureless electrode. •Includes 8 patients in whom lead repositioning failed, included with the 19 patients mentioned above.
In the 156 patients in whom the lithium-iodide pulse generator was a replacement unit, the indications for replacement of the previous generating units were as follows: elective replacement, 97 cases; pulse generator failure, 34 cases; change of pacing lead, 18 cases; and wound complications, 7 cases. The implantations have been followed for 3,988 patient months of cardiac pacing, an average of 15.9 months (range 4 to 32 months). During this time we have documented the following complications: pulse generator failure, one case; wound complications, 12 cases; lead repositioning, 19 cases; lead changes, 16 cases; and miscellaneous, 2 cases. There have been nine deaths during this time. Six occurred within 3 months of the insertion of the pacemaker; three of these were from the inexorable progression of congestive heart failure, and three were from myocardial infarction. Three patients died later from cerebrovascular accident, thrombosis of the superior mesenteric artery, and cardiac arrest. In all patients the pacemaker was working perfectly at the time of death. There was one pulse generator failure early in our clinical experience. Intermittent failure of pacing in the immediate postinsertion period was noted, and the newly implanted lithium-iodide power pack and bipolar transvenous lead were both replaced during the first week. Subsequent testing by the manufacturer proved the pulse generator to be defective owing to random failure of an electrical circuit component, which resulted in variable R-wave sensing. Wound complications have occurred in 12 of the 250 patients (Table II). The pulse generator site became infected in 2 cases, 3 and 5 months after implantation. Sterile dehiscence necessitated resuturing in 2 cases, as did proved catgut allergy in one case. There were 4 cases of wound hematoma following surgery; 2 patients were receiving anticoagulants and required surgical evacuation of the hematoma. One patient had delayed wound healing, but the wound remained sterile and
Volume 73 Number 3 March, 1977
intact. One patient experienced pain in the pulse generator site 8 weeks postoperatively and finally required a new pulse generator in a different site. Local muscle stimulation occurred in one patient with a unipolar pacemaking system; this unit was later replaced with a bipolar system without complications. Pacing lead complications occurred in 31 of the 250 implantations (Table III). Repositioning of the transvenous lead was necessary in 19 patients; in 15 cases this was performed during the first 3 months. Fracture of two previously placed endocardial leads occurred after almost one year of pacing with the lithium iodidepowered pulse generator and necessitated lead replacement. Among the 16 patients with pacing lead changes, 8 had previous repositionings of their transvenous leads and are included in the group of 19 patients just mentioned, as are the 2 who had lead fracture. Two patients had intermittent postural stimulation of the diaphragm but declined treatment of this condition. The lithium-iodide generator was removed in 15 patients; in 12 cases it was removed at the time of lead change and in one case at the time of lead repositioning, once for muscle stimulation and once because of infection at the pulse generator site. Each pulse generator was tested by the manufacturer after removal and was found to be functioning normally. Discussion Our initial experience with 250 lithium iodide-powered pulse generators is most gratifying. The smaller, thinner, rectangular unit has required less generator pouch dissection, has aided in the tension-free tissue closure over the pack, and has resulted in less pack migration. Patient acceptance has been excellent. Patients with previous pulse generators comment favorably on the lighter, smaller unit. The combined wound breakdown and infection rate of 2 per cent (five of 250 implantations) is less than with the previous, larger sized, standard battery units in our Cardiothoracic Surgery Unit. There have been no pacemaker-related deaths to date in our series, although 9 patients have died from cardiovascular causes. We do not think that the problems of lead complications documented in this report are related to the lithium-iodide pulse generator. We have prefered the transvenous pacemaker system with the simplicity of electrode insertion but recognize that 11 of the 214 transvenous leads required repositioning and a further 8 required a change of pacing lead system to sutureless electrodes after failure of transvenous electrode adjustment. In the 16 cases of pacing lead
Lithium iodide-powered cardiac pacemaker
423
change, 9 patients had the transvenous lead replaced with a sutureless electrode; 5 patients simply had a new transvenous electrode implanted, one a new sutureless electrode, and one a transvenous lead after failure of a sutureless lead. There have been no battery or electrical failures in our series with the sole exception of the one patient with immediate post-implantation failure. The 15 generators that have been removed during our follow-up period have all been removed when the cause of intermittent pacing was uncertain. It is pertinent to re-emphasize that none of these pulse generators was faulty and that all were functioning normally when extensively tested upon return to the manufacturer. Crude preliminary analysis of cost of cardiac pacing with the lithium-iodide pulse generator has been made in our 250 patients. With the actual observed complications, removals, and deaths, it is calculated that over a 2 year period the yearly cost of cardiac pacing with the lithium-iodide generator is $ 1,272 as compared to a cost of $ 1,610 for the standard battery generator. Extrapolation of the data markedly lowers the yearly cost of cardiac pacing, but we cannot confirm this extrapolation with hard data. The long-life lithium-iodide pacemaker represents a significant advance in pacemaker technology and allows cardiac pacing without the restrictions consequent to the use of nuclear energy, the uncertainties of biological power sources, or the biweekly commitment of recharging the batteries. We unhesitatingly recommend the lithium-iodide powered pacemaker in all age groups for long-term cardiac pacing. May I gratefully thank Miss Sheila Stickney, R.N., for her help in collecting the patient data. I also acknowledge the kind permission of Drs. Peter Allen, P. G. Ashmore, A. I. Munro, C. L. N. Robinson, and W. G. Trapp to include their patients in this series. The work was supported by a Fellowship from the R. S. McLaughlin Foundation of Canada. REFERENCES 1 Bigelow, W. G., Callaghan, J. C , and Hopps, J. A.: An Artificial Pacemaker for Cardiac Standstill, Ann. Surg. 132: 531, 1950. 2 Zoll, P. M.: Resuscitation of the Heart in Ventricular Standstill by External Electrical Stimulation, N. Engl. J. Med. 247: 768, 1952. 3 Chardack, W. M., Gage, A. A., and Greatbatch, W.: A Transistorized, Self-Contained, Implantable Pacemaker for the Long-Term Correction of Complete Heart Block, Surgery 48: 643, 1960. 4 Lillehei, R. C , Romero, L. H., Beckman, C. B., Burrows, J., and Friedberg, H. D.: A New Solid-State, Long-Life, Lithium-Powered Pulse Generator, Ann. Thorac. Surg. 18: 479, 1974.