In this study, the duration of the QRS complex during ventricular pacing was used as an index of intraventricular conduction to quantitate the rate-dependent effects of intravenous lidocaine, procainamide and amiodarone. Right ventricular apical pacing (15 to 20 beats) was performed at cycle lengths of 600, 500, 400, 350, 300, 275 and 250 ms, before and 5 minutes after the intravenous administration of lidocaine in 11 patients (serum level 3.2 +/- 0.8 micrograms/ml [mean +/- SD] ), procainamide in 14 patients (serum level 8.2 +/- 1.9 micrograms/ml) and amiodarone in 12 patients (serum level 3.9 +/- 1.2 micrograms/ml). Electrocardiographic recordings were made at a paper speed of 150 mm/s. QRS duration was measured in a blinded fashion, with reproducibility within 5%. In the control state, QRS duration was the same at all paced cycle lengths. After lidocaine, procainamide and amiodarone administration, the shortest paced cycle length with complete ventricular capture was 250 +/- 0, 275 +/- 38 and 264 +/- 20 ms, respectively. At a paced cycle length of 600 ms, the increase in QRS duration compared with the control state was 1 +/- 2% with lidocaine (p greater than 0.05), 21 +/- 7% with procainamide (p less than 0.001) and 6 +/- 6% with amiodarone (p less than 0.05). At the shortest paced cycle length with complete capture, the increase in QRS duration compared with the control state was 20 +/- 6% with lidocaine (p less than 0.001), 42 +/- 11% with procainamide (p less than 0.001) and 26 +/- 4% with amiodarone (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)