Impaired cardiac reserve and exercise capacity in patients receiving long-term thyrotropin suppressive therapy with levothyroxine

• Published in: The journal of clinical endocrinology and metabolism 1996-12, Vol.81 (12), p.4224-4228
• Main Authors: BIONDI, B, FAZIO, S, CUOCOLO, A, SABATINI, D, NICOLAI, E, LOMBARDI, G, SALVATORE, M, SACCA, L
• Format: Article
• Language: English
• Subjects: Adrenergic beta-Antagonists - pharmacology; Adult; Biological and medical sciences; Drug toxicity and drugs side effects treatment; Exercise; Female; Heart - drug effects; Humans; Male; Medical sciences; Middle Aged; Pharmacology. Drug treatments; Thyrotropin - secretion; Thyroxine - adverse effects; Toxicity: cardiovascular system; Ventricular Function, Left - drug effects
• ISSN: 0021-972X; 1945-7197
• DOI: 10.1210/jc.81.12.4224

To assess cardiac function and exercise tolerance in patients receiving long term TSH-suppressive therapy with levothyroxine (L-T4), we studied maximal exercise capacity with a bicycle ergometer and left ventricular function at rest and during physical exercise by radionuclide angiography. The evaluation was performed in 10 patients receiving L-T4 therapy (2.31 +/- 0.13 microgram/kg) for 5-9 yr, presenting with effort dyspnea and symptoms of adrenergic overactivity, and 10 matched control subjects. The patients were reassessed after 4 months of administration of the selective beta-adrenergic blocker bisoprolol (4.25 +/- 0.4 mg/day); L-T4 therapy remained unchanged. The results showed that at rest, left ventricular diastolic filling was impaired in the patients (P < 0.05), whereas systolic function was unaltered. During submaximal physical exercise, left ventricular ejection fraction increased in the controls from 58 +/- 2% to 65 +/- 2% (P < 0.001), whereas in the patients it fell from 63 +/- 2% to 53 +/- 2% (P < 0.01), mainly because of increased end-systolic left ventricular volume (P < 0.05). Exercise capacity was markedly reduced in the patients in terms of both peak workload (P < 0.001) and exercise duration (P < 0.001). beta-Adrenergic blockade prevented both the fall in ejection fraction and the increase in end-systolic volume during exercise, and improved exercise tolerance. In conclusion, our data show that long term TSH-suppressive therapy with L-T4 is not as harmless as believed, because it may cause marked impairment of cardiac functional reserve and physical exercise capacity. Administration of a beta-blocking drug for 4 months caused significant improvement of cardiac performance and exercise tolerance.