Short Biphasic Pulses from 90 Microfarad Capacitors Lower Defibrillation Threshold

For defibrillation between right ventricular and retropectoral patch electrodes using truncated exponential pulses, the stored energy defibrillation threshold (DFT) is lower for short pulses from small 60‐μF capacitors than for conventional pulses from 120‐μF capacitors, but 60‐μF pulses frequently require higher voltages than are currently used. The goal of this study was to determine if DFT could be reduced by intermediate size 90‐μF capacitors. This study compared biphasic waveform DFTs for 120μF‐65% tilt pulses, 90μF‐65% tilt pulses, and 90 μF‐50% tilt pulses in 20 patients at defibrillator implantation. The 90μF‐50% tilt pulses were selected because their duration is half that of 120μF‐65% tilt pulses. The stored energy DFT for 90 μF‐50% tilt pulses (9.1 ± 4.3 J) was less than both the DFT for 120 μF‐65% tilt pulses (12.0 ± 5.5 J, P < 0.005) and the DFT for 90μF‐65% tilt pulses (11.6 ± 5.8 J, P < 0.005). There was no significant difference between the latter two values. The voltage DFTs for 90 μF‐50% pulses (436 ± 113 V) and 120 μF‐65% tilt pulses (436 ± 104 V) were not statistically different; the voltage DFT for 90 μF‐65% tilt pulses was higher than for either of the other two pulses (490 ± 131, P < 0.005). The DFT was 20 } or greater in three patients for both 120 μF‐65% tilt pulses and 90 μF‐65% tilt pulses, but it was 16 J or less in all patients for 90 μF‐50% tilt pulses. When pathways were dichotomized by the median resistance of 71 Ω, 90 μF‐50% tilt pulses significantly reduced DFTs compared to 120 μF‐65% tilt pulses for higher resistance pathways (9.2 ± 4.0 J vs 13.0 ± 6.2 J, P = 0.002), but not lower resistance pathways (9.0 ± 4.8 J vs 10.9 ± 4.6 J, P = NS). For the electrode configuration tested, biphasic 90 μF‐50% tilt pulses reduce stored energy DFT in comparison with 120 μF‐65% tilt pulses without increasing voltage DFT. However, 90 μF‐65% tilt pulses provide no benefit.