The effect of intravenously administered procainamide (0.5-1 g, mean 0.966 g) on the inducibility of sustained ventricular tachycardia by programmed ventricular stimulation was tested in 15 patients (12 men and 3 women, mean age 57.2 +/- 16.6 years) with confirmed sustained ventricular tachycardia. Eleven patients had a previous myocardial infarction and two had congestive heart failure. The programmed ventricular stimulation (1-3 premature stimuli following after ventricular stimulation at a rate of 100/120 and 140/min. and a number of quick stimuli with a rising frequency from the apex of the right ventricle at an intensity equal to twice the diastolic threshold) was administered before and after procainamide administration. Sustained ventricular tachycardia was induced during the controlled examination in all 15 patients (100% sensitivity). Induced ventricular tachycardia had a haemodynamically important course with a rapid onset of unconsciousness in three patients whose index of risk of ventricular tachycardia (ratio of its frequency and the ejection fraction at rest) was significantly higher than in the remaining 12 patients (9.0 +/- 2.2 as compared with 4.9 +/- 1.2). Procainamide prevented the induction of sustained ventricular tachycardia in six patients (group I), i. e. in 40%. In the remaining nine patients (group II) ventricular tachycardia induced after procainamide had a significantly lower frequency (192 +/- 34/min.), as compared with controls (214 +/- 42/min.), but its haemodynamic impact was not affected. Patients of group I had, as compared with group II, a significantly higher ejection fraction (47 +/- 14% as compared with 35 +/- 10%) and a significantly lower index of the risk of tachycardia (4.5 +/- 1.3 as compared with 6.5 +/- 2.4).(ABSTRACT TRUNCATED AT 250 WORDS)

Keywords: Cardiac Pacing, Artificial; Female; Heart Diseases /physiopathology/; Heart Rate /drug effects/; Heart Ventricles; Humans; Male; Middle Aged; Procainamide /pharmacology/; Stroke Volume /drug effects/; Tachycardia /etiology/