Improved defibrillation efficacy with an ascending ramp waveform in humans

Objectives: The purpose of this study was to compare an ascending ramp waveform (RAMP) with a standard, clinically available biphasic truncated exponential waveform (BTE) for defibrillation in humans. Background: In animal studies, RAMP had a lower defibrillation threshold (DFT) than BTE. Methods: We studied 63 patients at implantable cardioverter-defibrillator placement using a dual-coil lead and left pectoral active can. The subjects were divided into two groups, one with a 12-ms ascending first phase and one with a 7-ms ascending first phase. Phase 2 of RAMP for both groups was a truncated exponential decay with 65% tilt and reversed polarity. The BTE had a 50% tilt in each phase. DFT and upper limit of vulnerability (ULV) were measured for both waveforms using a binary search protocol. Results: The patient population was 77% male, with a mean age of 63 ± 10 years and ejection fraction of 33 ± 13%. Delivered energy at DFT was lower with the 7-ms RAMP vs BTE (5.4 ± 2.6 J vs 6.5 ± 3.4 J; P < .01) but unchanged with the 12-ms RAMP (7.4 ± 4.5 J vs 7.1 ± 4.9 J). Maximal voltage at DFT was significantly lower with either RAMP compared to BTE (P < .01). There was a strong correlation between ULV and DFT for both RAMP and BTE (P < .01). Conclusions: The 7-ms ascending ramp waveform significantly reduced delivered energy (18%) and voltage (24%) at DFT, whereas the 12-ms RAMP reduced only DFT voltage. This is the first report of a waveform that is superior to a BTE for defibrillation in humans. ULV correlates with DFT for RAMP, supporting the use of ULV testing for implantation of devices.