A Different Point of View*

Sudden cardiac death resulting from ventricular arrhythmia is one of the leading public health problems of most developed countries. Despite intense research in the areas of ionic channels and pharmacological interventions, a panacea has not been found to control life-threatening arrhythmia and improve survival. In addition, the results of the Cardiac Arrhythmia Suppression Trial' demonstrated that some routinely used antiarrhythmic drugs are proarrhythmic and in certain cases can make the cure worse than the disease. An alternative approach, the implantable defibrillator, has been more successful and has been reported to extend life.2 Such devices could probably be improved if more were known about the mechanisms by which a defibrillation shock fails or succeeds. Many studies have investigated the mechanism of defibrillation by directly recording cardiac activations before and after successful and unsuccessful defibrillation shocks.3-7 These studies have resulted in the proposal of two completely opposite hypotheses. One of the hypotheses is the critical mass hypothesis of defibrillation,3'4 which states that a shock can fail to halt activation fronts within a region smaller than a certain critical