Estimating the 95% effective defibrillation dose.

Abstract

Minimum squared error (MinSE) testing protocols and a MinSE estimator are presented which accurately estimate the voltage that defibrillates 95% of the time (the ED95). The MinSE experimental procedures, presented in the form of lookup tables, detail the response to successful and unsuccessful trials. The lookup tables also show the ED95 estimates calculated from the observed results using the MinSE estimator. Two assumptions are required to develop the look-up tables: 1) the dose-response curve, chosen using a statistical analysis of a retrospective sample, and 2) the distribution of the ED95's in the population. The MinSE estimator and experimental procedure are examined in a prospective study of five dogs (19-25 kg, heart weights 139.3-236.9 gm) using nonthoracotomy implantable defibrillator electrodes and a biphasic defibrillation waveform (3.5 ms first phase, 2.0 ms second phase). Employing an ED95 population distribution assumption applicable to most implantable defibrillator electrodes and waveforms, e.g., the ED95 is between 0.0 and 800.0 V, the measured rms error was 15% of the mean measured ED95 for the MinSE, four test shock, ED95 estimates. If the protocols are designed with an ED95 population distribution assumption for animals of the same species and size, and defibrillation is constrained to one electrode configuration and waveform, the estimates improve by 3.8%. Using techniques from the Bayesian statistics literature, the MinSE approach can be extended to a variety of defibrillation parameter estimation problems.