COMPARISON OF BIPHASIC AND MONOPHASIC PULSES - DOES THE ADVANTAGE OF BIPHASIC SHOCKS DEPEND ON THE WAVESHAPE

With present implantable defibrillators, the ability to vary the defib rillation technique has been shown to increase the number of patients suitable for transvenous system. As newer waveforms become available, the need for a flexible device may change. In addition, although it ha s been shown that the option of biphasic waveform may increase the def ibrillation efficacy, this may depend upon the shape of the biphasic w aveform used. Thirty patients undergoing transvenous defibrillator imp lant were included in the study. In 20 patients (group I), defibrillat ion efficacy of simultaneous monophasic, sequential monophasic, and bi phasic waveform with 50% tilt was determined randomly. Similarly, in t en patients (group II) testing of simultaneous monophasic shocks and b iphasic waveforms with 65% and 80% tilt was performed in random order. The electrode system used consisted of two transvenous leads and a su bcutaneous patch in all 30 patients. In group I, 50% tilt biphasic wav eform consistently provided similar or better defibrillation efficacy compared to monophasic waveforms (biphasic 7.5 +/- 5.1 joules vs simul taneous 17 +/- 7.8 joules, P < 0.02; and vs sequential 17 +/- 8.4 joul es, P < 0.01). In group II, 65% tilt biphasic pulse required less ener gy for defibrillation as compared with simultaneous monophasic shocks (9.6 +/- 4.5 joules vs 15.6 +/- 5.2 joules, P = 0.04). No significant difference was observed in terms of defibrillation thresh old between 80% tilt biphasic shocks and simultaneous monophasic pulses (11.8 +/- 6 joules vs 15.6 +/- 5.1 joules, P = NS). Biphasic shocks with smaller tilt delivered using a triple lead system more uniformly improved def ibrillation threshold over standard monophasic waveforms.