The effects of ajmaline in experimental and clinical arrhythmias and their relation to some electrophysiological parameters of the heart.

The antiarrhythmic efficacy of ajmaline has been evaluated in three experimental models of cardiac arrhythmias in the dog. These data have been related to the actions of the compound on several parameters of heart function and compared to results obtained in various clinical arrhythmias. Ajmaline was more effective in arrhythmias of the ectopic focus type than in the circus movement model. These results agreed with the pattern of clinical activity. The compound produced decreases in excitability and conduction and increased the functional refractory period in all heart tissues. These effects were most marked in the atrium. The drug also showed a moderate degree of anticholinergic activity. Both in the dogs and in the clinical cases, the agent showed an important hypotensive effect. In a group of experiments in which transmembrane potentials were recorded, the compound produced in all tissues a decrease in upstroke velocity and amplitude of the action potential; it also increased the duration of the action potential in atrial and ventricular muscle, but it decreased it in Purkinje fibers. The possible mechanism(s) of action of the drug is discussed in terms of the different hypotheses for cardiac arrhythmias.