A Model to Evaluate Alternative Methods of Defibrillation Threshold Determination

The voltage (or, equivalently, energy) at which defibrillation occurs for a specific episode of fibrillation can be represented by specifying or estimating the probability of successful defibrillation for each voltage or energy. This relation of voltage to probability is the probability function. For a series of attempts, the probability function predicts the frequency with which defibrillation will occur at a given voltage. By defining the defibrillation threshold (DFT) as the voltage at which the probability function takes on a specific value, say 50%, a method of defibrillation threshold determination can be evaluated by how accurately and precisely it estimates the "true" defibrillation threshold. By utilizing estimated probability functions from animals and humans, the relative performance of different methods of defibrillation threshold determination can be evaluated. Three methods were evaluated using published animal data and human clinical data: (1) stepping down to the first voltage that fails; (2) stepping up to the first voltage that succeeds; and (3) doing both 1 and 2 and averaging. In all cases, Method 3 has lower total error. Definitions of defibrillation threshold other than the 50% level can also be evaluated in this fashion.