Influence of excitability on the ventricular fibrillation threshold in dogs.

The influence of the excitability threshold on the ventricular fibrillation threshold was studied in dogs during myocardial ischemia and potassium and aprindine infusion. Interventions that influenced excitability threshold were associated with similar changes in ventricular fibrillation threshold although the percent change in both values differed. Although it is possible that the interventions studied caused parallel but independent changes in excitability threshold and ventricular fibrillation threshold, it is likely that the excitability threshold influences the ventricular fibrillation threshold. An increase in excitability threshold could result in an increase in ventricular fibrillation threshold in spite of an increase in the actual tendency of the heart to fibrillate spontaneously. Such discordance between the "electrical stability of the heart" and the ventricular fibrillation threshold was found during myocardial ischemia.