Reversing the initial phase polarity in biphasic shocks: is the polarity benefit reproducible?

The effect of initial phase polarity (IPP) reversal using biphasic shocks on DFT at the time of implantation of implantable cardioverter defibrillator and the reproducibility of this effect during predischarge testing was evaluated in a randomized fashion. Twenty-two patients with ventricular tachycardia or ventricular fibrillation (VF) who received either the Medtronic 7219D (7 patients), 7219C (12 patients), 7223 (1 patient), or CPI Ventak MINI (2 patients) were studied. The DFT was determined in a randomized fashion at implantation and during predischarge testing using a binary search protocol. Initial shock was delivered at 12 J. If successful, subsequent shock was delivered at 6 J, following which the shock was incremented or decremented by 3 J depending upon the success. The DFT for right ventricular (RV)- and RV + IPP was 10.9 +/- 4.1 J and 11.1 +/- 4.0 J, respectively, at implant (P = ns) and 9.7 +/- 4.3 J and 8.4 +/- 6 J, respectively, (P = ns) at predischarge testing. Of the six patients who had better DFT with RV + at implantation, only one patient maintained the benefit during predischarge testing. The differences observed in IPP in individual patients may not be demonstrable during repeated testing. These findings may have implications on how these devices should be programmed.