INFLUENCE OF POLARITY REVERSAL ON DEFIBRILLATION SUCCESS WITH BIPHASIC SHOCKS AND A TRANSVENOUS SUBCUTANEOUS DEFIBRILLATOR SYSTEM IN A PORCINE ANIMAL-MODEL/

Clinical studies show that polarity reversal affects defibrillation su ccess in transvenous monophasic defibrillators. Current devices use bi phasic shocks for defibrillation. We investigated in a porcine animal model whether polarity reversal influences defibrillation success with biphasic shocks. In nine anesthetized, ventilated pigs, the defibrill ation efficacy of biphasic shocks (14.3 ms and 10.8 ms pulse duration) with ''initial polarity'' (IP, distal electrode = cathode) and ''reve rsed polarity'' (RP, distal electrode = anode) delivered via a transve nous/subcutaneous lead system was compared. Voltage and current of eac h defibrillating pulse were recorded on an oscilloscope and impedance calculated as voltage divided by current. Cumulative defibrillation su ccess was significantly higher for RP than for ITP for both pulse dura tions (55% vs 44%, P = 0.019) for 14.3 ms (57% vs 45%, P < 0.05) and i nsignificantly higher for 10.8 ms (52 % vs 42 %, P = n.s.). Impedance was significantly lower with RP at the trailing edge of pulse 1 (IP: 4 4 +/- 8.4 vs RP: 37 +/- 9.3 with 14.3 ms, P < 0.001 and IP: 44 +/- 6.2 vs RP: 41 +/- 7.6 Ohm with 10.8 ms, P < 0.001) and the leading edge o f pulse 2 (IP: 37 +/- 5 vs RP: 35 +/- 4.2 Ohm with 14.3 ms, P = 0.05 a nd IF: 37.5 +/- 3.7 vs RP: 36 +/- 5 Ohm with 10.8 ms, P = 0.02). In co nclusion, in this animal model, internal defibrillation using the dist al coil as anode results in higher defibrillation efficacy than using the distal coil as cathode. Calculated impedances show different cours es throughout the shock pulses suggesting differences in current flow during the shock.