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Pacing at a Very Short Pulse Width
CORRESPONDENCE
Pacing at a Very Short Pulse Width To the Editor: I would like to compliment Dr. Tobias on his excellent article “Pacing at a Very Short Pulse Width” [2]. He has established that chronic pacing can be accomplished at a pulse width of 0.3 msec without special electrodes or techniques and has provided very useful actuarial survival figures for pacemaker patients, pacemakers, and electrodes. However, the final statement in the abstract-”a standard mercury-zinc pulse generator remains an acceptable alternative in selected patients”-is not supported by his data. Standard in this sense means nonhermetically sealed. The hit-and-miss reliability of nonhermetic mercury-zinc pacers is well illustrated by a comparison between Dr. Tobias’s results with the 5931, 5961 series and the disheartening results with the Xytron 5950, 5951 series, which are, to quote Tobias, “comparable in many respects” to the units he studied. Even the admittedly good results with the Medtronic 5931, 5961 series are significantly less satisfactory than the 99+ O/O monthly reliability rate achieved to date by the hermetically sealed solidstate lithium cell powered pacers of Cardiac Pacemakers, Inc., Intermedics, and Telectronics [4]. According to Dr. Tobias, “the patient mortality [yearly] of 6% speaks eloquently of the need for a long-lived pacing system.” Recently, it has been repeatedly and disastrously demonstrated that no nonhermetic pacemaker can meet this need [l,31, and Dr. Tobias’s aside to the contrary, prominently displayed at the end of his abstract, detracts from the otherwise fine quality of his paper. As a final point, nonhermetically sealed mercuryzinc pacers do initially cost less than hermetically sealed state-of-the-art units, but they are not “a lower-cost alternative,” as Dr. Tobias stated on page 31. First, predictability of patient longevity is always fraught with inaccuracy and moral and legal hazards. Who should have a “cheap” life support system? Second, the costs of follow-up monitoring, rehospitalization, and reoperation are all much higher with nonhermetic mercury-zinc systems (mean functional life of approximately two years) than with solid-state lithium systems (mean proven functional life in excess of five years). Nonhermetic pacing systems have necessitated the recall of more than 50,000 pacers in the last few years with disastrous costs, both financial (for the companies, taxpayers, and other third-party payees) and personal (for the patients, families, and physicians involved). The continued use of nonhermetically sealed pacemakers should not be recommended.
G . Frank 0. Tyers, M . D . Division of Cardiovascular and Thoracic Surgery The University of Texas Medical Branch Galveston, TX 77550 590
References 1. MacGregor DC, Noble EJ, Morrow JD, et al: Man-
agement of a pacemaker recall. J Thorac Cardiovasc Surg 74:657, 1977 2. Tobias JA: Pacing at a very short pulse width. Ann Thorac Surg 26:27, 1978 3. Tyers GFO, Brownlee RR: The non-hermetically sealed pacemaker myth or Navy-Ribicoff 22,000-FDA-Weinberger 0. J Thorac Cardiovasc Surg 71:253, 1976 4. Tyers GFO, Brownlee RR: Current status of pacemaker power sources. Ann Thorac Surg 25:571, 1978
Propranolol and Coronary Revascularization To the Editor: In a recent study (Ann Thorac Surg 26:222, 1978), Boudoulas and co-workers support the view that propranolol can be safely continued in patients with coronary artery disease during coronary revascularization. Although we have employed propranolol successfully before and during operation in selected patients, we are concerned about the proper selection of inotropic agents in the presence of beta blockade. Our laboratory investigations in chronically betablocked dogs indicate that none of the standard inotropic agents are satisfactory when used individually. Isoproterenol can produce beta effects if administered in amounts that are 5 to 30 times the standard doses, but also results in relative hypotension due to peripheral vasodilatation. Mixed alpha and beta agonists, such as dopamine, dobutamine, and epinephrine, are relatively unsatisfactory. Enhanced alpha adrenergic effects tend to cause hypertension and reduce cardiac output. In our laboratory studies, the most satisfactory combination of drugs tested to date is dopamine (10 pg per kilogram per minute) and isoproterenol (0.40 p g per kilogram per minute). This combination, in the presence of chronic beta blockade in dogs, has effects quite similar to dopamine alone in controls. Although we do not have extensive experience with the administration of catecholamine mixtures to beta-blocked patients, we believe the results of our studies are useful for surgeons who encounter severe heart failure in the presence of propranolol. Through relative titration of two drugs, it may be possible to achieve a salutary balance of alpha and beta effects that otherwise could not be achieved. G . lames A v e r y , 11, M . D . Alan 1. Benvenisty, M . D . Henry M . Spotnitz, M . D .
Department of Surgery Columbia University College of Physicians and Surgeons 630 W 168th S t N e w York, N Y 10032
Pacing at a Very Short Pulse Width To the Editor: I would like to compliment Dr. Tobias on his excellent article “Pacing at a Very Short Pulse Width” [2]. He has established that chronic pacing can be accomplished at a pulse width of 0.3 msec without special electrodes or techniques and has provided very useful actuarial survival figures for pacemaker patients, pacemakers, and electrodes. However, the final statement in the abstract-”a standard mercury-zinc pulse generator remains an acceptable alternative in selected patients”-is not supported by his data. Standard in this sense means nonhermetically sealed. The hit-and-miss reliability of nonhermetic mercury-zinc pacers is well illustrated by a comparison between Dr. Tobias’s results with the 5931, 5961 series and the disheartening results with the Xytron 5950, 5951 series, which are, to quote Tobias, “comparable in many respects” to the units he studied. Even the admittedly good results with the Medtronic 5931, 5961 series are significantly less satisfactory than the 99+ O/O monthly reliability rate achieved to date by the hermetically sealed solidstate lithium cell powered pacers of Cardiac Pacemakers, Inc., Intermedics, and Telectronics [4]. According to Dr. Tobias, “the patient mortality [yearly] of 6% speaks eloquently of the need for a long-lived pacing system.” Recently, it has been repeatedly and disastrously demonstrated that no nonhermetic pacemaker can meet this need [l,31, and Dr. Tobias’s aside to the contrary, prominently displayed at the end of his abstract, detracts from the otherwise fine quality of his paper. As a final point, nonhermetically sealed mercuryzinc pacers do initially cost less than hermetically sealed state-of-the-art units, but they are not “a lower-cost alternative,” as Dr. Tobias stated on page 31. First, predictability of patient longevity is always fraught with inaccuracy and moral and legal hazards. Who should have a “cheap” life support system? Second, the costs of follow-up monitoring, rehospitalization, and reoperation are all much higher with nonhermetic mercury-zinc systems (mean functional life of approximately two years) than with solid-state lithium systems (mean proven functional life in excess of five years). Nonhermetic pacing systems have necessitated the recall of more than 50,000 pacers in the last few years with disastrous costs, both financial (for the companies, taxpayers, and other third-party payees) and personal (for the patients, families, and physicians involved). The continued use of nonhermetically sealed pacemakers should not be recommended.
G . Frank 0. Tyers, M . D . Division of Cardiovascular and Thoracic Surgery The University of Texas Medical Branch Galveston, TX 77550 590
References 1. MacGregor DC, Noble EJ, Morrow JD, et al: Man-
agement of a pacemaker recall. J Thorac Cardiovasc Surg 74:657, 1977 2. Tobias JA: Pacing at a very short pulse width. Ann Thorac Surg 26:27, 1978 3. Tyers GFO, Brownlee RR: The non-hermetically sealed pacemaker myth or Navy-Ribicoff 22,000-FDA-Weinberger 0. J Thorac Cardiovasc Surg 71:253, 1976 4. Tyers GFO, Brownlee RR: Current status of pacemaker power sources. Ann Thorac Surg 25:571, 1978
Propranolol and Coronary Revascularization To the Editor: In a recent study (Ann Thorac Surg 26:222, 1978), Boudoulas and co-workers support the view that propranolol can be safely continued in patients with coronary artery disease during coronary revascularization. Although we have employed propranolol successfully before and during operation in selected patients, we are concerned about the proper selection of inotropic agents in the presence of beta blockade. Our laboratory investigations in chronically betablocked dogs indicate that none of the standard inotropic agents are satisfactory when used individually. Isoproterenol can produce beta effects if administered in amounts that are 5 to 30 times the standard doses, but also results in relative hypotension due to peripheral vasodilatation. Mixed alpha and beta agonists, such as dopamine, dobutamine, and epinephrine, are relatively unsatisfactory. Enhanced alpha adrenergic effects tend to cause hypertension and reduce cardiac output. In our laboratory studies, the most satisfactory combination of drugs tested to date is dopamine (10 pg per kilogram per minute) and isoproterenol (0.40 p g per kilogram per minute). This combination, in the presence of chronic beta blockade in dogs, has effects quite similar to dopamine alone in controls. Although we do not have extensive experience with the administration of catecholamine mixtures to beta-blocked patients, we believe the results of our studies are useful for surgeons who encounter severe heart failure in the presence of propranolol. Through relative titration of two drugs, it may be possible to achieve a salutary balance of alpha and beta effects that otherwise could not be achieved. G . lames A v e r y , 11, M . D . Alan 1. Benvenisty, M . D . Henry M . Spotnitz, M . D .
Department of Surgery Columbia University College of Physicians and Surgeons 630 W 168th S t N e w York, N Y 10032