The susceptibility of infarcted right ventricular myocardium to inducible ventricular tachyarrhythmias was serially evaluated in 18 conscious dogs during the first 2 weeks after permanent right coronary artery occlusion. Properly timed double premature stimuli applied to the right ventricular outflow tract induced sustained (longer than 1 minute) ventricular tachycardia at rates of 190 to 400 beats/min in nine dogs, and ventricular fibrillation in six dogs. No ventricular arrhythmias could be induced in the remaining three dogs. The zone of premature coupling intervals within which ventricular tachyarrhythmias could be induced decreased in each dog as the infarct aged, and by day 12 after occlusion, no ventricular arrhythmias could be induced in any of the dogs studied. Both the size and the degree of patchiness (graded from 0 for no patchiness to +4 for patchiness throughout the infarct) of the infarct appear to be related to the nature of the induced rhythm. Infarcts with greater heterogeneity and those that were larger than 8% of the right ventricular volume were associated with a higher incidence of ventricular fibrillation, and infarcts with a lesser degree of patchiness were more suitable for sustained ventricular tachycardia (3.4 +/- 1.2 versus 1.4 +/- 0.4, p less than 0.05). These findings indicate that the infarcted right ventricular myocardium, independent of left ventricular involvement, can be associated with malignant ventricular tachyarrhythmias, ventricular tachyarrhythmias can be induced only during a well defined postinfarction period; and both the size and geometry of the right ventricular infarct determine the nature of the induced ventricular rhythm.
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