Estimating the Parameter Distributions of Defibrillation Shock Efficacy Curves in a Large Population

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.