Effect of antihypertensive therapy on left ventricular function and myocardial perfusion at rest and during exercise

The authors studied left ventricular function by equilibrium-gated technetium-99m ejection fraction and global left ventricular perfusion by thallium-201 scintigraphy in 43 patients with mild to moderate hypertension. Patients were studied at rest and during submaximal (approximately 50% of V̇(O₂) max) supine bicycle exercise, off therapy and on four forms of therapy for 16 weeks: methyldopa (n = 9); propranolol (n = 9); hydrochlorothiazide (n = 9); and enalapril (n = 16). None of the patients had focal myocardial ischaemia or heart failure. There were no differences between methyldopa, propranolol, hydrochlorothiazide and enalapril in blood pressure responses to exercise. However, heart rate at rest (57 ± 4.6 beats/min) and during exercise (108 ± 8.0 beats/min) was significantly lower in patients on propranolol than in other groups (70 ± 3.9 and 117 ± 5.5 beats/min for methyldopa; 75 ± 3.3 and 119 ± 4.9 beats/min for hydrochlorothiazide; 74 ± 2.8 and 125 ± 2.6 beats/min for enalapril). In the propranolol-treated group, mean ejection fraction fell from 55% at rest to 49% during exercise. This suggests that cardiac output is likely to be lower and peripheral resistance higher during exercise in patients on propranolol than on other forms of treatment. There were no significant differences in coronary perfusion responses to exercise, however, or in the ratio of coronary perfusion to rate-pressure product, between any of the groups. These findings suggest that the limitation in exercise tolerance often reported by patients on beta-blockers is not due to coronary insufficiency during exercise, but to an attenuation of the cardiac output response to exercise, together with a raised peripheral vascular resistance.