[Mechanism of the occurrence of ventricular bigeminy]

Twenty-seven patients, aged 15 to 77, with a variety of cardiovascular diseases and bigeminy, and 3 normal subjects were investigated, using exercise and atropin tests. Electrocardiograms were recorded at pre-ectopic intervals of no more than 0.55 sec in bigeminy and polygeminy. The common divisor for interectopic intervals, ectopic complex interpolation, P-Q and Q-T intervals of the main complex and the presence of a wave on the ascending or descending slope of the R wave in sinus QRS complex were determined. Three mechanisms were identified to explain ventricular bigeminy developing during the third phase of action potential and the supernormal myocardial excitation period. A risk group was identified with respect to persistent bigeminy, incorporating patients with the short P-Q syndrome and signs of the typical or atypical Wolff-Parkinson-White syndrome.