ICD Waveform Optimization: A Randomized, Prospective, Pair‐Sampled Multicenter Study

Abstract

MOUCHAWAR, G., ET AL.: ICD Waveform Optimization: A Randomized, Prospective, Pair-Sampled Mul ticenter Study. The theoretical tissue model-based estimates of phase 1 and phase 2 duration of biphasic waveforms are considerably shorter than the pulse widths currently 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 waveforms 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 1 truncation point is at the peak of membrane response. The optimal phase 2 duration ends with a membrane response near or just below 0. In paired analysis, no sig nificant differences were found in DFT or impedance between standard and tuned waveforms. In patients 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 relationship between DFT and impedance (P < 0.001). As impedance increased, the tuned waveform was associated with DFTs comparable to the standard wave form with shorter pulse duration and lower delivered energy. No single tilt value allowing an easy calcu lation of delivered energy was related to ICD waveform efficacy. The use of ICDs with tuned optimal pulse durations offer a greater flexibility of choice for patients with high DFTs. (PACE 2000; 23:[Pt. II]:1992-1995

Does defibrillation threshold increase as left ventricular ejection fraction decreases?

“…Fixed pulse-width waveforms have been shown to provide lower voltage and energy DFTs than fixed-tilt waveforms, particularly when DFT is higher than 400 V. This might explain our lower DFT per LVEF range as well as our lower incidence of ‘high DFT’. 21,22 It should be noted that concerns regarding DFTs between 20 and 26 J may not be as great when a device with maximum delivered energy capability of 36 J is used because a 10 J safety margin would be available.…”

Frequency Characteristics and Associations with the Defibrillation Threshold of Ventricular Fibrillation in Patients with Implantable Cardioverter Defibrillators

“…In this study, the frequency analyses were performed using induced VF under general anesthesia, the electrophysiological characteristics of which may differ from those of spontaneous VF (31). The defibrillation threshold is affected by variables of the ICD system, such as the number of defibrillation coils and position of the defibrillation lead and ICD (32)(33)(34). However, in the current study, the ICDs and leads were positioned similarly in all patients, and the number of defibrillation coils did not affect the DF or defibrillation threshold.…”

Achieving low defibrillation thresholds at implant: pharmacological influences, RV coil polarity and position, SVC coil usage and positioning, pulse width settings, and the azygous vein

“…There is inter‐patient variability in the critical membrane time constant (τ) for defibrillation [106]. Most studies of optimized waveforms use phase durations based on an assumed typical human critical membrane time constant of 3.5 ms. Human studies have now confirmed the superiority of fixed duration waveforms over tilt‐based duration waveforms [107–110].…”