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Effect of antihypertensive therapy on left ventricular function and myocardial perfusion at rest and during exercise
Insights
Beta-blocker therapy, like propranolol, reduces exercise heart rate and cardiac output in hypertensive patients. This, not coronary insufficiency, limits exercise tolerance by increasing peripheral resistance.
Area of Science:
- Cardiology
- Pharmacology
- Exercise Physiology
Background:
- Hypertension management often involves medications impacting cardiovascular function.
- Understanding the effects of different antihypertensive drugs on cardiac performance during exercise is crucial for patient management.
Purpose of the Study:
- To compare the effects of methyldopa, propranolol, hydrochlorothiazide, and enalapril on left ventricular function and perfusion during exercise in hypertensive patients.
- To investigate the mechanisms behind exercise intolerance in patients treated with beta-blockers.
Main Methods:
- Equilibrium-gated technetium-99m ejection fraction and thallium-201 scintigraphy were used to assess left ventricular function and perfusion.
- 43 patients with mild to moderate hypertension were studied at rest and during exercise, off and on four different therapies for 16 weeks.
Main Results:
- Propranolol significantly lowered resting and exercise heart rates compared to other agents.
- In the propranolol group, ejection fraction decreased during exercise, suggesting reduced cardiac output and increased peripheral resistance.
- No significant differences in coronary perfusion or its ratio to rate-pressure product were observed across treatment groups.
Conclusions:
- Exercise limitation in patients on beta-blockers is primarily due to attenuated cardiac output response and increased peripheral vascular resistance during exercise.
- The findings suggest that coronary insufficiency is not the cause of reduced exercise tolerance in this context.
Abstract:
We 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 VO2 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.