Depressant effect on the retrograde atrioventricular nodal conduction of beta-adrenergic blockade by propranolol in humans.

Propranolol is known to have a depressant effect on anterograde atrioventricular (AV) nodal conduction in normal subjects and in those with AV nodal reentrant tachycardia. Using His bundle recording and programmed ventricular stimulation, the effect of propranolol-induced beta-adrenergic blockade (1 mg/kg intravenously) on retrograde AV nodal conduction was studied in 17 patients without (group I) and nine with (group II) AV nodal reentrant tachycardia. During baseline studies the ventricular pacing cycle length that induced ventriculoatrial block was 338 +/- 60 ms (range 260 to 450 ms) in group I and 305 +/- 39 ms (range 260 to 375 ms) in group II patients (not significant). After injection of propranolol, the ventricular pacing cycle length that induced ventriculoatrial block in group I patients was 416 +/- 97 ms (range 300 to 550 ms) (P less than 0.001, compared to baseline state) in 15 patients, and complete block occurred in two patients. In group II patients ventriculoatrial block occurred at a ventricular pacing cycle length of 375 +/- 97 ms (range 260 to 510 ms) (P less than 0.02 compared to baseline value) in eight patients, and complete block occurred in one patient. Retrograde AV nodal conduction expressed as the H2A2 interval was 75 +/- 33 ms (range 35 to 150 ms) in group I and 49 +/- 16 ms (range 20 to 80 ms) in group II patients (P less than 0.05). Following the administration of propranolol, the H2A2 interval was prolonged in group I patients by 10 to 45 ms in 11 patients, no retrograde AV nodal conduction was observed in three patients, and there was no effect in two patients.(ABSTRACT TRUNCATED AT 250 WORDS)