"Tuned" defibrillation waveforms outperform 50/50% tilt defibrillation waveforms: a randomized multi-center study.

Introduction: A superior performance of a tuned waveform based on duration using an assumed cardiac membrane time constant of 3.5 ms and of a 50/50% tilt waveform over a standard 65/65% tilt waveform has been documented before. However, there has been no direct comparison of the tuned versus the 50/50% tilt waveforms.

Methods: In 34 patients, defibrillation thresholds (DFTs) for tuned versus 50/50% tilt waveforms in a random order were measured by using the optimized binary search method. High voltage lead impedance was measured and used to select the pulse widths for tuned and 50/50% tilt defibrillation waveforms.

Results: Delivered energy (7.3 +/- 4.6 J vs 8.7 +/- 5.3 J, P = 0.01), stored energy (8.2 +/- 5.1 J vs 9.7 +/- 5.6 J, P = 0.01), and delivered voltage (405.9 +/- 121.7 V vs 445.0 +/- 122.6 V, P = 0.008) were significantly lower for the tuned than for the 50/50% tilt waveform. In four patients with DFT >/= 15 J, the tuned waveform lowered the mean energy DFT by 2.8 J and mean voltage DFT by 45 V. For all patients, the mean peak delivered energy DFT was reduced from 29 J to 22 J (24% decrease). Multiple regression analysis showed that a left ventricular ejection fraction < 20% is a significant predictor of this advantage.

Conclusion: Energy and voltage DFTs are lowered with an implantable cardioverter defibrillator that uses a tuned waveform compared to a standard 50% tilt biphasic waveform.