SHORT BIPHASIC PULSES FROM 90-MICROFARAD CAPACITORS LOWER DEFIBRILLATION THRESHOLD

For defibrillation between right ventricular and retropectoral patch e lectrodes using truncated exponential pulses, the stored energy defibr illation threshold (DFT) is lower for short pulses from small 60-mu F capacitors than for conventional pulses from 120-mu F capacitors, but 60-mu F pulses frequently require higher voltages than are currently u sed. The goal of this study was to determine if DFT could be reduced b y intermediate size 90-mu F capacitors. This study compared biphasic w aveform DFTs for 120 mu F-65% tilt pulses, 90 mu F-65% tilt pulses, an d 90 mu F-50% tilt pulses in 20 patients at defibrillator implantation . The 90 mu F-50% tilt pulses were selected because their duration is half that of 120 mu F-65% tilt pulses. The stored energy DFT for 90 mu F-50% tilt pulses (9.1 +/- 4.3 J) was less than both the DFT for 120 mu F-65% tilt pulses (12.0 +/- 5.5 J, P < 0.005) and the DFT for 90 mu F-65% tilt pulses (11.6 +/- 5.8 J, P < 0.005). There was no significa nt difference between the latter two values. The voltage DFTs for 90 m u F-50% pulses (436 +/- 113 V) and 120 mu F-65% tilt pulses (436 +/- 1 04 V) were not statistically different the voltage DFT for 90 mu F-65% tilt pulses was higher than for either of the other two pulses (490 /- 131, P ( 0.005). The DFT was 20 J or greater in three patients for both 120 mu F-65% tilt pulses and 90 mu F-65% tilt pulses, but it was 16 J or less in all patients for 90 mu F-50% tilt pulses. When pathway s were dichotomized by the median resistance of 71 Omega 90 mu F-50% t ilt pulses significantly reduced DFTs compared to 120 mu F-65% tilt pu lses 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 mu F-50% tilt pulses reduce stored energy DFT in comparison with 120 mu F-65% tilt pulses without increasing voltage DFT. However, 90 mu F- 65% tilt pulses provide no benefit.