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Abnormal left ventricular function in hyperthyroidism: evidence for a possible reversible cardiomyopathy
Insights
Hyperthyroidism impairs heart function during exercise, causing a paradoxical drop in left ventricular ejection fraction (LVEF). This abnormal cardiac response in hyperthyroid patients is reversible and not solely due to beta-adrenoceptor activity.
Area of Science:
- Cardiology
- Endocrinology
- Exercise Physiology
Background:
- Hyperthyroidism is associated with cardiovascular changes.
- Left ventricular ejection fraction (LVEF) may be altered in hyperthyroid patients.
Purpose of the Study:
- To investigate the effects of exercise and beta-adrenoceptor blockade on LVEF in hyperthyroid patients.
- To determine if abnormal cardiac function during exercise in hyperthyroidism is reversible and mediated by beta-adrenoceptors.
Main Methods:
- Assessed LVEF using radionuclide ventriculography in nine hyperthyroid patients.
- Studied patients in both hyperthyroid and euthyroid states during rest and exercise.
- Administered propranolol (a beta-blocker) to assess its effects.
Main Results:
- Hyperthyroid patients exhibited a high resting LVEF but a paradoxical fall during exercise.
- Euthyroid state restored the normal rise in LVEF during exercise.
- Propranolol reduced resting LVEF similarly in both states but did not alter the exercise-induced LVEF fall in hyperthyroidism.
Conclusions:
- Abnormal left ventricular function during exercise in hyperthyroidism suggests a reversible cardiomyopathy.
- This functional cardiomyopathy appears independent of beta-adrenoceptor activation.
- Excess circulating thyroid hormones may directly cause this cardiac dysfunction.
Abstract:
We assessed the effects of exercise and beta-adrenoceptor blockade on left ventricular ejection fraction (LVEF) measured by radionuclide ventriculography in nine patients with uncomplicated hyperthyroidism. Patients were studied in both the hyperthyroid and euthyroid states. The hyperthyroid state was characterized by a high LVEF at rest but--paradoxically--by a significant fall (P less than 0.01) in LVEF during exercise. At the same workload and at the same heart rate, patients had a restoration of the normal rise in LVEF during exercise when they were euthyroid. The LVEF was greater during exercise (P less than 0.02) when the patients were euthyroid than when they were hyperthyroid. Pretreatment with propranolol caused similar reductions in resting LVEF in the hyperthyroid and euthyroid states; the drug attenuated the rise in LVEF during exercise when the patients were euthyroid, but did not influence the exercise-induced reduction in LVEF in hyperthyroidism. The abnormal left ventricular function observed during exercise in hyperthyroidism suggests a reversible functional cardiomyopathy, independent of beta-adrenoceptor activation, that is presumably a direct effect of an excess in circulating thyroid hormones.