Defibrillation efficacy testing is a common procedure at defibrillator implantation, with the objective to ensure that each patient receives a system with adequate shock efficacy. In this study, defibrillation shock efficacy as a function of shock energy was modeled by a dose response relationship. The frequency distributions of the two parameters characterizing this relationship were estimated from a large clinical study on 634 patients. The estimated parameters were then compared to published data on defibrillation studies performing dose response measurements. After having identified the optimal parameter distributions for the whole population, a Monte Carlo method was used to compare the outcomes of two defibrillation efficacy testing protocols: a safety margin test requiring 2 successes out of 2 trials at 20 J, and the binary search protocol used in the clinical study. Results showed good correspondence with clinical observations. The probabilistic nature of defibrillation success and differences in acceptance and rejection rates of the two protocols were highlighted. The model developed in this study could be used to further understand the differences between various defibrillation testing protocols used in clinical practice.

The defibrillation test protocol greatly influences the probability of meeting implant criterion. Therefore, these test protocols should be standardized. The model developed in this study, could be used to further understand their impact and to derive recommendations.

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Transvenous unipolar active can defibrillation systems have proven to be effective in treating ventricular tachyarrhythmias. However, a further reduction of ventricular defibrillation thresholds (V-DFT) would increase the longevity, reduce the size of pulse generators, and help to avoid additional leads in patients with inacceptable high V-DFTs. In a finite difference computer model, the extension of the right ventricular (RV) defibrillation coil into the low right atrium led to a 40% reduction of unipolar V-DFT. To evaluate this finding, we conducted a prospective, randomized study in 11 patients receiving an ICD. Extension of the RV electrode was simulated by adding a second coil placed in the low right atrium with the same polarity. Using a binary search protocol, V-DFT was determined with and without the additional electrode in each patient. Total shock impedance was significantly lower in the two coil (low RA) configuration, compared to the single coil (RV) configuration. Corresponding values were 49.9 +/- 6.7 Ohm and 61.1 +/- 9.3 Ohm, respectively (P < 0.01, paired t-test). However, there was no reduction, but even a nonsignificant increase in V-DFTs. Mean V-DFT in the RV configuration was 12.0 +/- 5.6 J and 16.3 +/- 7.8 J in the low RA configuration (P = 0.09, paired t-test). Despite a reduction in total impedance, the addition of a defibrillation coil in the low right atrium does not reduce ventricular defibrillation thresholds.

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