| Abstract: | Clinical studies show that polarity reversal affects de-fibrillation success in transvenous monophasic defibrillators. Current devices use biphasic shocks for de-fibrillation. We investigated in a porcine animal model whether polarity reversal influences de-fibrillation success with biphasic shocks. In nine anesthetized, ventilated pigs, the de-fibrillation efficacy of biphasic shocks (14.3 ms and 10.8 ms pulse duration) with “initial polarity” (IP, distal electrode = cathode) and “reversed polarity” (RP, distal electrode = anode) delivered via a transvenous/subcutaneous lead system was compared. Voltage and current of each defibrillating pulse were recorded on an oscilloscope and impedance calculated as voltage divided by current. Cumulative de-fibrillation success was significantly higher for RP than for IP for both pulse durations (55% vs 44%, P = 0.019) for 14.3 ms (57% vs 45%, P < 0.05) and insignificantly 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: 44 ± 8.4 vs RP: 37 ± 9.3 with 14.3 ms, P < 0.001 and IP: 44 ± 6.2 vs RP: 41 ± 7.6 Ω with 10.8 ms, P < 0.001) and the leading edge of pulse 2 (IP: 37 ± 5 vs RP: 35 ± 4.2 Ω with 14.3 ms, P = 0.05 and IP: 37.5 ± 3.7 vs RP: 36 ± 5 Ω with 10.8 ms, P = 0.02). In conclusion, in this animal model, internal de-fibrillation using the distal coil as anode results in higher de-fibrillation efficacy than using the distal coil as cathode. Calculated impedances show different courses throughout the shock pulses suggesting differences in current flow during the shock. |
