Comparison of Fixed Tilt and Tuned Defibrillation Waveforms: The PROMISE Study

Comparison of Defibrillation Waveforms. Background: All modern defibrillation systems use biphasic shock waveforms. Typically a fixed tilt waveform is used for implantable defibrillators (ICDs), but a tuned waveform with duration based on shock impedance may be superior based on theoretical calculations. Objective: The objective of this study was to compare defibrillation efficacy of fixed tilt and tuned waveforms. Methods: PROMISE was designed as a prospective, within-patient, randomized study of defibrillation thresholds (DFTs) comparing a tuned (assuming a 3.5 milliseconds membrane time constant) versus a 50/50% tilt waveform. All patients had a left pectoral implant (active can) and testing was performed with a single coil shocking configuration ("SVC coil OFF"). DFTs were measured in random order with a binary search method in 52 patients, using the high-voltage lead impedance to select the pulse widths for both waveforms. Results: At the DFT, the tuned waveform had similar delivered energy (10.5 +/- 6.3 vs 9.5 +/- 5.5 J, P = 0.47), stored energy (13.6 +/- 7.9 vs 11.3 +/- 6.3 J, P = 0.06), peak current (7.5 +/- 3.0 vs 6.8 +/- 2.2 A, P = 0.09), and delivered voltage (451.0 +/- 134.5 vs 411.5 +/- 120.7 V, P = 0.05) compared with the 50/50% tilt waveform. Conclusion: The DFTs for 3.5-millisecond time constant based tuned and 50/50% tilt waveforms are similar using a single coil, left pectoral active can. (J Cardiovasc Electrophysiol, Vol. 24, pp. 323-327, March 2013)