Comparative effects of propranolol, pindolol, and practolol after excision of the sinoatrial node in dogs

We studied the effects of intravenous injections of three beta-adrenoceptor antagonists on cardiac automaticity in conscious dogs after sinoatrial node (SAN) excision. Injections were repeated for 60 days postoperatively. In controls, mean corrected sinoatrial node recovery time (CSNRT) was 535 +/- 24 ms. One milligram per kilogram of dl-propranolol did not modify heart rate but raised CSNRT (p less than 0.01). One-half milligram per kilogram of dl-pindolol raised heart rate (p less than 0.05) and reduced CSNRT (p less than 0.05). Ten milligrams per kilogram of dl-practolol were needed to significantly reduce heart rate and raise CSNRT (p less than 0.01). In dogs after SAN excision, 0.1 mg/kg and 0.5 mg/kg of dl-propranolol lowered heart rate on days 3, 30, 43, and 60. Corrected recovery time (CRT) at a cumulative dose of 0.5 mg/kg rose to 9015 +/- 1028 ms on day 3 and to 3064 +/- 810 ms on day 30 (p less than 0.001). dl-Pindolol stabilized the rhythm. With 0.1 mg/kg, heart rate and CRT were not modified significantly on days 9 and 46. dl-Practolol at cumulative doses of 1 and 5 mg/kg lowered heart rate significantly on days 7 and 46. On day 12, the same doses did not modify heart rate but raised CRT (p less than 0.05). This suggests that of the beta-adrenoceptor antagonists studied here pindolol may be preferable in treatment of certain supraventricular arrhythmias.