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

The effect of initial phase polarity (IPP] reversal using biphasic shocks o n DFT at the time of implantation of implantable cardioverter defibrillator and the reproducibility of this effect during predischarge testing was eva luated in a randomized fashion. Twenty-two patients with ventricular tachyc ardia or ventricular fibrillation (VF) who received either the Medtronic 72 19D (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 proto col. Initial shock was delivered at 12 J. If successful, subsequent shock w as delivered at 6 J, following which the shock was incremented or decrement ed 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 ir 6 J, respectively, IP = ns) at predisch arge testing. Of the six patients who had better DFT with RV+ at implantati on, only one patient maintained the benefit during predischarge testing. Th e differences observed in IPP in individual patients may not be demonstrabl e during repeated testing. These findings may have implications on how thes e devices should be programmed.