Human ventricular refractoriness. II. Effects of procainamide.

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Abstract
The effects of procainamide (PA) on the ventricular effective refractory period (ERP-V) and on the relationship of refractoriness to recovery of excitability were evaluated in 8 patients during ventricular pacing. Measurements of ERP-V and plasma levels of PA were taken before and after i.v. administration of 500 mg of PA. The ERP-V was prolonged from a group mean value of 237 .+-. 7 msec (SE) to 279 .+-. 16 msec (P < 0.05). Peak increase occurred at maximal drug levels 5 min after administration of PA. The QT intervals increased from a group mean value of 421 .+-. 8 ms to 461 .+-. 9 ms after PA (P < 0.01). The ratio ERP-V/QT increased in 7 of 8 patients from 0.56 .+-. 0.01 to 0.62 .+-. 0.04 after infusion of PA (0.1 < P < 0.2). The ratio remained unchanged in 1 patient. PA increases ERP-V in man and usually increases the ratio ERP-V/QT. A longer portion of the ventricular recovery period is refractory after administration of the drug. The data, which correlate with animal studies, help to explain how PA may suppress human re-entrant ventricular arrhythmias.