991-72 Effect of Polarity Reversal Using Clinical Defibrillation Waveforms and a Tranvenous Lead System

There have been conflicting reports over the years about the effects of waveform polarity on defibrillation efficacy. The development of the tranvenous lead system has led to an increase in defibrillation thresholds when compared to epicardial patches when using the same pulse generator. Reversing waveform polarity might lower defibrillation thresholds enough to allow implantation of a tranvenous lead system while maintaining an adequate safety margin. This study was undertaken to determine the effects of waveform polarity on monophasic and biphasic waveforms using a tranvenous lead system and three clinically available defibrillation waveforms.Six 25kg swine underwent placement of an ENDOTAK® catheter with the distal electrode in the RV apex (RVA) and the proximal electrode at the junction of the SCV and RA. Three defibrillation waveforms were studied: the CPI Ventak 65% fixed tilt monophasic waveform (CPI-M), the CPI Ventak, 60% tilt phase 1, 50% tilt phase 2 biphasic waveform (CPI-Bi), and the Ventritex HVS-02 6ms/6ms biphasic waveform (V-Si). Defibrillation thresholds (DFT) using an up/down technique were determined for each waveform for RVA electrode as cathode (-) for CPI-M and phase 1 of CPI-BI and V-Bi or as anode (+).When RVA was (+), CPI-M defibrillated with a lower leading edge voltage (LEV) and energy (E) than when RVA was (-). LEV and E were not significantly different when RVA was (+) vs RVA as (-) for either biphasic waveform tested.CPI-MCPI-BiV-BI(+)470±51317±36345±23(-)546±66†296±34339±25†CPI-M(+) sig lower than CPI-M(-) (p<0.05)These results show that biphasic waveforms defibrillate better than monophasic waveforms regardless of polarity. It also suggests that when implanting a monophasic waveform device, that the RVA electrode should be anode, but that when implanting a biphasic device, that the RVA electrode can be either anode or cathode