A PROSPECTIVE RANDOMIZED COMPARISON IN HUMANS OF 90-MU-F AND 120-MU-FBIPHASIC PULSE DEFIBRILLATION USING A UNIPOLAR DEFIBRILLATION SYSTEM

Introduction: Capacitance is known to influence defibrillation, Optima l biphasic waveform capacitance for transvenous unipolar defibrillatio n systems in man is currently being defined, In an effort to improve d efibrillation efficacy, we examined the relative defibrillation effica cy of a 65% tilt biphasic pulse from a 90-mu F capacitor compared to a 65% tilt biphasic pulse from a 120-mu F capacitor in a prospective, r andomized fashion in 16 consecutive cardiac arrest survivors undergoin g defibrillator surgery. Methods and Results: The transvenous unipolar pectoral defibrillation system uses a single endocardial RV anodal de fibrillation coil and the shell of an 80-cc volume (88 cm(2) surface a rea) pulse generator (Medtronic Model 7219C PCD ''active CAN'') as the cathode for the first phase of the biphasic shock: RV(+) --> CAN(-). Defibrillation thresholds for each capacitance were determined prospec tively in a randomized fashion, The defibrillation threshold results f or the 90-mu F capacitance were: leading edge voltage 383 +/- 132 V; s tored energy 7.4 +/- 5.0 J; and resistance 57 +/- 10 Omega. The result s for the 120-mu F capacitance were: leading edge voltage 315 +/- 93 V (P = 0.002); stored energy 6.5 +/- 3.7 J (P = 0.21); and resistance 5 7.0 +/- 11 Omega (P = 0.87). Conclusions: We conclude that 90-mu F, 65 % tilt biphasic pulses used with unipolar pectoral defibrillation syst ems have equivalent stored energy defibrillation efficacy compared to 120-mu F, 65% tilt pulses, Use of lower capacitance is possible in pre sent implantable defibrillators without compromising defibrillation.