Effect of rapid biphasic shock subpulse switching on ventricular defibrillation thresholds

The aim of this study was to demonstrate that significant reductions in defibrillation threshold (DFT) can be achieved by rapidly switching defibrillation pulses within an overall biphasic envelope between multiple endovascular electrode sets.

Defibrillation electrodes were implanted in four locations in nine anesthetized swine (41.7 +/- 8.7 kg). Electrodes were implanted into the right ventricular apex (RV), the superior vena cava (SVC), over the left pectoral region as a "hot can" (Can), and within the middle cardiac vein on the posterior left ventricular (LV) surface. The 50% DFT (level for which 50% of delivered shocks successfully defibrillated) for control shocks (7-ms first phase, 0.5-ms interpulse period, 4-ms second phase, RV- --> SVC+ + Can+) were determined to have energy of 20.5 +/- 5.5 J (mean +/- SD). Mean 50% DFTs were also determined for waveforms that split each phase of the same overall biphasic waveform between various electrode sets. Each phase was divided into 2, 3, 4, or 6 subpulses, the defibrillation shock was sequentially delivered to multiple electrode sets, and DFTs were determined (11.9 +/- 4.8 J, 11.7 +/- 2.9 J, 17.9 +/- 8.7 J, 16.7 +/- 6.1 J, respectively). DFT energy was statistically lower than the control (Wilcoxon sign rank test; P < 0.05) when each phase was divided into 2 or 3 subpulses.

Rapid shock switching within an overall biphasic waveform between electrode sets including an electrode in the middle cardiac vein potentially can lower DFT energy by 40% or more.