Effects of propranolol on anomalous pathway refractoriness and circus movement tachycardias in patients with preexcitation

Electrophysiologic effects of intravenous propranolol, 0.1 mg/kg, were evaluated in 18 patients with anomalous pathways utilizing intracardiac stimulation and recording. Fourteen patients had Wolff-Parkinson-White syndrome and four had concealed ventricular preexcitation. Anomalous pathway effective refractory period could be measured during the control period and after propranolol administration in nine patients and was 304 ± 7.5 (mean ± standard error of the mean) and 304 ± 8.3 msec, respectively (difference not significant). Ventricular paced 1:1 ventriculoatrial (V-A) conduction (reflecting retrograde anomalous pathway conduction) measured in 12 patients was intact during both the control period and after propranolol at rates of 170 to 200/min. Sustained paroxysmal supraventricular tachycardia was induced in 14 patients during the control period and in 10 after propranolol (in 4 of whom the tachycardia could not be sustained because of atrioventricular [A-V] nodal refractoriness). Mean cycle length of tachycardia in these 10 patients was 328 ± 18 (control) and 352 ± 19 msec (propranolol) (P < 0.01). The increase in tachycardia cycle length reflected an increase in A-V nodal conduction time (A-H interval). In conclusion: (1) Propranolol has an insignificant effect on both anterograde and retrograde anomalous pathway properties. (2) In most cases, propranolol does not interfere with induction of sustained circus movement tachycardia. However, it does produce a statistically significant but slight slowing of the rate of tachycardia. (3) In a minority of cases, propranolol inhibits induction of sustained paroxysmal supraventricular tachycardia by increasing A-V nodal refractoriness.