POLARITY REVERSAL IMPROVES DEFIBRILLATION EFFICACY IN PATIENTS UNDERGOING TRANSVENOUS CARDIOVERTER-DEFIBRILLATOR IMPLANTATION WITH BIPHASICSHOCKS

The purpose of this study was to determine the influence of polarity r eversal on DFT in patients undergoing implantation of nonthoracotomy d efibrillators with biphasic shocks. Previous studies have shown higher defibrillation efficacy with using the distal electrode as anode in i mplantation of nonthoracotomy defibrillators and monophasic shocks. Ho wever, it is as yet unclear whether biphasic shock defibrillation will also be influenced by polarity reversal. Using a transvenous lead sys tem with a proximal electrode in the superior caval vein and a distal electrode in the RV apex, 27 patients undergoing defibrillator implant ation were randomized to DFT testing with ''initial'' (distal electrod e = cathode) or ''reversed'' polarity (distal electrode = anode). Defi brillation energy was reduced stepwise until defibrillation failure oc curred. At this point, polarity at as switched and testing continued u ntil the lon est energy requirement was determined for both polarities . With reversed polarity, DFT was 11.1 +/- 5.7 J versus 13.3 +/- 5.8 J with initial polarity (P = 0.033). This means a 17% reduction of the DFT. In 10 patients, the threshold was was lower with reversed, wherea s in 3 patients it was lower with initial polarity. in conclusion, cha nging electrode polarity in transvenous implantable defibrillators wit h biphasic shocks may significantly influence defibrillation energy re quirements. Therefore, polarity reversal should always be attempted be fore considering patch implantation.