Effect of certain antiadrenergic agents on systolic time intervals in essential hypertension.

Systolic time intervals, including preejection period (PEP) and left ventricular ejection time (LVET), were studied in patients with permanent essential hypertension before and after intra-venous administration of propranolol 0.2 mg/kg (11 patients), clonidine 0.002 mg/kg (10 patients) and methyldopa 2 mg/kg (12 patients). With propranolol, diastolic blood pressure was unchanged and the heart rate decreased, whilst PEP and LVET were significantly prolonged (P less than 0.001). Clonidine caused a fall in blood pressure (P less than 0.001), heart rate was slightly reduced, PEP was prolonged (P less than 0.001) and there was a significant decrease in LVET at 5 min. With methyldopa, no significant effect was observed after intravenous injection, but 7 days oral administration produced the identical effect as clonidine. These observations suggest that certain antihypertensive drugs may impair left ventricular performance and depress myocardial contractility.