R on T or R on P phenomenon? Relation to the genesis of ventricular tachycardia.

Continuous electrocardiographic monitoring of 225 patients with acute myocardial infarction was performed during the initial 48 hours after admission. Two hundred twelve episodes of ventricular tachycardia occurred in 49 subjects, and 8 patients had primary ventricular fibrillation. Most cases of ventricular tachycardia were associated with late coupling of premature ventricular complexes. Of the 212 instances of ventricular tachycardia, 42 (20 percent) were initiated by a premature complex on the T wave (R on T) (R-R'/Q-T less than 1), and 93 (44 percent) had initiating premature complexes that occurred directly after onset of the sinus P wave (R on P). Of eight episodes of ventricular fibrillation, seven were initiated by a premature ventricular complex and in four of these there was associated R on T phenomenon. The influence of atrial contraction and myocardial stretch on reentry or ectopy is proposed as a possible explanation for the relatively high incidence rate of ventricular tachycardia observed after the onset of the sinus P wave.