ICD waveform optimization: A randomized, prospective, pair-sampled multicenter study

The theoretical tissue model-based estimates of phase 1 and phase 2 duratio n of biphasic waveforms are considerably shorter than the pulse widths curr ently used in ICDs with standard tilt. This study used a tissue resistance/ capacitance (RC) model to identify optimal biphasic pulse widths. By paired step-down defibrillation threshold (DFT) testing, the efficacy of standard versus "tuned" biphasic waveforms was evaluated in 91 patients. Standard w aveforms consisted of a phase 1 set to 65% tilt and phase 2 = phase 1. The tuned waveform was based on an RC model of membrane characteristics with a time constant of 3.5 ms. The optimal phase 2 truncation point is at the pea k of membrane response. The optimal phase 2 duration ends with a membrane r esponse near or just below 0. In paired analysis, no significant difference s were found in DFT or impedance between standard and tuned waveforms. In p atients with DFTs > 400 V, the tuned waveform lowered the DFT by an average of 38 V (P < 0.05). Multivariate analyses showed a significant inverse rel ationship between DFT and impedance (P < 0.001). As impedance increased, th e tuned waveform was associated with DFTs comparable to the standard wavefo rm with shorter pulse duration and lower delivered energy. No single tilt v alue allowing an easy calculation of delivered energy was related to ICD wa veform efficacy. The use of ICDs with tuned optimal pulse durations offer a greater flexibility of choice for patients with high DFTs.