Effect of Shock Polarity on Defibrillation Thresholds with a Hybrid Patch-Coil Lead System

Introduction: Understanding the factors that affect defibrillation thresholds (DFTs) has important implications both for optimization of defibrillation efficacy and for the design of new lead systems. The objective of this prospective study was to evaluate the effect of shock polarity on defibrillation efficacy at the time of routine pulse generator replacement in patients with a hybrid patch-coil lead system. Methods: Each patient underwent 4 assessments of DFT: monophasic or biphasic shock with standard or reversed polarity, with the order of testing with respect to polarity randomized. In standard polarity, the right atrial coil is the anode and the left ventricular patch is the cathode. Results: The study population of 30 patients was 80% men with a mean age of 65±9 years and a mean left ventricular ejection fraction of 33 ± 12%. There was a significant 21% decrease in the mean monophasic DFT with reversed polarity shocks (13.1 ± 5.9 J vs. 16.6 ± 6.5 J, p < 0.01). Reversal of shock polarity did not have a significant effect on the mean biphasic DFT (8.0 ± 4.8 J vs. 8.5 ± 4.3 J for reversed and standard polarity respectively, p = NS). However, when an elevated biphasic DFT (≥15 J) was present in either standard or reversed polarity, a significant decrease in DFT was observed when the opposite polarity was used (16.7 ± 2.5 J vs. 9.1 ± 2.7 J, n = 9, p < 0.0001). Conclusion: Reversal of shock polarity markedly improves monophasic DFTs with the patch-coil lead configuration. The DFT should be determined with both shock polarities to optimize defibrillation efficacy for patients with high biphasic DFTs (≥15 J).