BIPHASIC TRANSTHORACIC DEFIBRILLATION CAUSES FEWER ECG ST-SEGMNENT CHANGES AFTER SHOCK

Study objective: Electrocardiographic abnormalities are common after t ransthoracic defibrillation. ECG ST-segment changes are especially pro blematic after defibrillation and may indicate ischemic or shock-induc ed cardiac dysfunction after resuscitation. Biphasic defibrillation wa veforms, compared with monophasic waveforms, diminish shock-induced ca rdiac dysfunction in laboratory preparations. This effect has not been validated in human subjects. We therefore evaluated in a prospective, blinded fashion the effect of biphasic and monophasic transthoracic d efibrillation on the ECG ST segment in 30 consecutive patients during surgery for the implantation of a cardioverter-defibrillator. Methods: In each patient two low-energy truncated biphasic transthoracic defib rillation shocks (115 and 130 J) were compared with a standard clinica l 200 J monophasic damped-sine wave shock. The biphasic shocks and the damped-sine wave shock have been demonstrated to have equal defibrill ation efficacy of 97%. Fifteen-second ECG signals recorded across tran sthoracic defibrillation electrodes were digitized before ventricular fibrillation induction and immediately after each defibrillation attem pt. The ST segments 80 msec after the J point were analyzed in a blind ed fashion by two reviewers. The ST-segment deflection, QRS-interval d uration, QT interval, and heart rate after each therapy were compared with baseline values. Results: ECG ST-segment elevation was significan tly greater with the 200-J damped-sine waveform than with either bipha sic waveform. The ECG ST-segment levels were -.55+/-.36 at baseline, . 76+/-.36 mm after internal shock, -.02-.36 mm after 115-J biphasic sho ck, .21+/-.38 mm after 130-J biphasic shock, and 2.09+/-.37 mm after 2 00-J damped-sine wave shock (P<.0001). QRS-interval duration, QT inter val, and heart rate did not change significantly with any waveform. Co nclusion: Transthoracic defibrillation with biphasic waveforms results in less postshock ECG evidence of myocardial dysfunction (injury or i schemia) than standard monophasic damped sine waveforms without compro mise of defibrillation efficacy.