Defibrillatory Effects of Low Sodium Solutions on Ventricular Fibrillation in Isolated Hearts of Rabbits

Isolated hearts in ventricular fibrillation can be defibrillated without interfering with the conduction of normal impulses arriving from the atria by the perfusion of solutions containing only about half of the normal sodium content. Reversion to a sinus rhythm occurs without a pause. The action of these solutions, which closely resembles that of normal solutions containing an excess of KCl or procaine, supports the hypothesis that these agents defibrillate by interfering with the entrance of sodium ions in the rising phase of the action potential. Defibrillation by this mechanism would be possible if ventricular fibrillation were the result of the discharge of premature impulses having a low safety factor of propagation from one or more ectopic foci.