Transchest electrical ventricular defibrillation

L e t t e r s to the E d i t o r

states where the right atrium attempts to augment right ventricular filling. In this case the prominent A-wave and the $4 may be due to right ventricular overload secondary to decreased right ventricular compliance which may occur following pulmonary embolism or obstruction to right ventricular outflow due to the tumor. Contrariwise, if the S, did not follow a prominent A-wave in the jugular venous pulse then we would be at a loss to explain its etiology and would have to assume it was due to disturbance of the tumor position by "normal" atrial systole. We agree with Dr. Levisman's observation t h a t Sakakibara and associates (his Reference 1) did not present data to suggest a specific relationship of the early diastolic sound to pulmonic closure but we were influenced by their statement that although the abnormal vibratory phenomena was recorded over the entire precordial area it did have it "maximal intensity at the pulmonary focus" as was also present in our case. Because of the location of the miximum intensity of the sound we could not dispel a possible relationship between it and pulmonic valve closure. I hope that the above comments will answer some of Dr. Levisman's questions. Stanley N. Snyder, M.D. Francis Y. K. Lau, M.D. 9209 Colima Rd. Whittier, Calif. 90605

Transchest electrical ventricular defibrillation To the Editor: The statement that "defibrillators presently available cannot deliver a dose that is adequate to defibrillate consistently the ventricles of most patients who weigh 80 kilograms or more ''1 is based primarily on data derived from animal experimentation~ and on a single retrospective study in patients2 The interpretation of the human study is open to question, since the reason for a lower success rate in subjects weighing more than 50 kilograms might well be the higher incidence of significant pre-existing cardiovascular disease in adults. Furthermore, the number of very heavy patients (more than 90 kilograms) was quite small. A prospective study was published more recently by the Belfast group, with a comparable number of patients weighing more than 50 kilograms and in particular a larger number of patients in the crucial group weighing more than 90 kilograms. They used a very low delivered energy o f 150 to 165 wattseconds with a very respectable rate of success.* The clinical data indicating the need for high-energy defibrillation are at best controversial. The data indicating that low energies are adequate is much more compatible with our experience at UCLA. In 1975, in our capacity as a Paramedic Base Station, we participated in the care of 302 patients who experienced sudden cardiac arrest outside the hospital. The paramedic squads are equipped with commercially available defibrillators producing a Lown wave form, and uniformly employ the 400 watt-second energy setting for defibrillation. The delivered energy is probably in the 250 to 320 watt-second range. It is our distinct impression that our rate of successful defibrillation is high, even in heavy patients. Therefore, it would seem premature to recommend the manufacture and sale of defibrillators with very large energy

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output, since such a trend would lead to heavier, more expensive, less portable defibrillators and to increased potential for myocardial damage due to the delivery of excessive electrical doses to some patients? Additional clinical studies should be undertaken to verify the need for higher energy outputs in human ventricular defibrillation.

Marshall T. Morgan, M.D. Charles R. McElroy, M.D. Emergency Medicine Center UCLA Medical Center Los Angeles, Calif. 90024

REFERENCES 1. Ewy, G. A., and Tacker, W. A.: Transchest electrical ventricular defibrillation, AM. HEART J. 91:403, 1976. 2. Geddes, L. A., Tacker, W. A., Rosborough, J. P., et al.: Electrical dose for ventricular defibrillation of large and small animals using precordial electrodes, J. Clin. Invest. 53:310, 1974. 3. Tacker, W. A., Galioto, F., Guiliani, E., et al.: Energy dosage for human transchest electrical ventricular deftbrillation, N. Engl. J. Med. 290:214, 1974. 4. Pantridge, J. F., Adgey, A. A. J., Webb, S. W., et al.: Electrical requirements for ventricular defibrillation, Br. Me(]. J. 2:313, 1975. 5. Dahl, C. F., Ewy, G. A., and Warner, E. D.: Myocardial necrosis from direct current countershock, Circulation 50:956, 1974.

Reply To the Editor: We appreciate the response from Drs. Morgan and McElroy and fully agree that additional clinical, studies should be undertaken to verify the need for higher energy output for human ventricular defibrillation. A group such as theirs might be ideal to gather these data by noting defibrillatory energy settings, weight of the patient, and the success and or failure of the first few defibrillatory countershocks. Since the transthoracic impedance to direct-current countershock decreases with successive defibrillatory discharges,' a unit that delivers borderline energy might be successful after a few or several countershocks. The goal should be to deliver adequate energy for defibrillation with the first countershock. The prospective study by the Belfast group ~ has been expanded in their book, The acute coronary attack. ~ Their latest data indicate that, of 144 episodes of ventricular fibrillation, 124 (86 per cent) were converted to another rhythm by a single low-energy countershock, whereas in 11 a second and in 2 a third countershock was necessary. Their results can be summarized as follows: Patient wt. Success rate Kg. (%) < 60 100 < 80 98 > 80 85 100 70 This experience suggests that the energy level needed for human ventrieular defibrillation might well be lower than that for ventricular defibrillation of animals. However, the

N o v e m b e r , 1976, Vol. 92, No. 5