767-2 Biphasic Shocks of “Reversed” Polarity are Superior to Those of “Initial” Polarity in Defibrillation of the Heart in Patients Undergoing Transvenous Cardioverter/Defibrillator Implantation

We previously reported that biphasic shocks of “reversed” polarity (RP: anode = distal coil, cathode = proximal coil) delivered through a transvenous/subcutaneous lead system are more effective in defibrillating the porcine heart than those of “initial” polarity (IP: anode = proximal coil, cathode = distal coil). The purpose of the study was to determine whether these findings could be confirmed in human implants of cardioverter/defibrillators (ICD) and a transvenous lead system.We randomly assigned 18 pts who underwent ICD implantation (Medtronic PCD “Jewel”® 13 pts, CPI Ventak P2® 4 pts, CPI Ventak PR×2® 1 pt) to IP or RP. Two different lead systems were used (Endotak C® or Transvene®). Defibrillation threshold (DFT) testing was performed by stepwise reduction of defibrillation energy from 20 Joules (J) to 1.5 J or the first unsuccessful shock. At this point, polarity was switched (IP → RP or RP → IP, respectively) and DFT testing continued with switched polarity starting at the previously unsuccessful energy level.ResultsIn 7 of 18 pts who RP was better than IP; DFT differed by 10 J in 3, by 6 J in 1, by 5 J in 2 and by 3 J in 1 pI. In 11 pts no difference was found. Mean DFT was 9.2±4.3 J with RP vs. 11.9±4.8 J with IP (p<0.01 in paired t test). There was no difference in shock impedance between both polarities (lP: 49.9±7.1Ω vs. RP: 51.1±8.1 Ω, p=n.s.)Conclusions1) Simple reversal of electrode polarity may result in DFTs equal or better than with IP in pts undergoing transvenous ICD implants with biphasic shock forms. Therefore RP should be tested first during ICD implantation. 2) The advantage of RP cannot be explained by differences in impedance