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

Abstract

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.

Implantable Cardioverter Defibrillator

“…Simulations based on clinical data demonstrate both that the mean DFT depends on the specific testing method used (shock protocol, initial shock strength, and shock step size) and that the standard deviation of most clinical methods is wide. 6,7 Vulnerability testing is based on the close relationship between the ULV and the minimum shock strength that defibrillates reliably (see Figure 116-3, B). 8 The ULV is the weakest shock at which VF is not induced when delivered at the most vulnerable time point during the vulnerable period of the T wave.…”

“…6,7 Failure of a test shock at greater than or equal to 20 J and the subsequent maximum output rescue shock is sufficient confirmation if detection of VF is rapid. However, if a test shock fails but a maximum output shock succeeds, the test shock should be repeated.…”

“…However, confirmation of sensing during VF is important in specific circumstances, including in patients with other implanted electronic devices (device-device interactions) or programming of long or frequent ventricular blanking periods, which can occur with rate-smoothing pacing in dual-chamber ICDs (intradevice interactions). 6,8,11 …”

“…EMI is a greater problem for integrated bipolar leads because of the larger integrated bipolar antenna, 6 but T wave oversensing may be a greater problem for true bipolar leads.…”

Impact of Defibrillation Test Protocol and Test Repetition on the Probability of Meeting Implant Criteria

“…This study was based on clinical data from 564 patients who participated in the PainFREE Rx II clinical study 12 . Computer simulations using a Monte Carlo method were used to model the different clinical defibrillation test protocols and to simulate defibrillation test outcomes 13 . This method allowed the simulation of a high number of test shocks that would have been impossible to perform clinically, leading to a quantitative comparison of the different protocols based on a large population.…”