VENTRICULAR-FIBRILLATION AND DEFIBRILLATI ON - ELECTROPHYSIOLOGICAL BASES AND CLINICAL-APPLICATIONS

During sinus rhythm, the successive responses to the application of el ectrical stimuli of increasing intensity during the vulnerable period are cardiac stimulations followed by repetitive ventricular responses and then ventricular fibrillation. An impulse of even greater intensit y is not followed by ventricular fibrillation (shock at the upper limi t of vulnerability) suggesting that defibrillatory shock is effective only when it does not reinduce fibrillation. Two other hypotheses are also proposed in fibrillation, that of critical mass and that of exten sion of the refractory periods, in particular after biphasic shocks. C linically, the measurement of the threshold of defibrillation is diffi cult as it is a random process which does not obey the all or nothing principle. Ideally, a graph of efficacy versus energy should be constr ucted but this is only possible under experimental conditions. The eff ects of different antiarrhythmic drugs have been studied in this manne r; in general, the sodium channel blockers improve the energies of def ibrillation.