Impaired cardiac reserve and exercise capacity in patients receiving long-term thyrotropin suppressive therapy with levothyroxine.
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.
Biondi
B
B
Department of Internal Medicine, University Federico II Medical School, Naples, Italy.
Fazio
S
S
Cuocolo
A
A
Sabatini
D
D
Nicolai
E
E
Lombardi
G
G
Salvatore
M
M
Saccà
L
L
D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000328:Adult; D015444:Exercise; D005260:Female; D006321:Heart / Q000187:drug effects*; D006801:Humans; D008297:Male; D008875:Middle Aged; D013972:Thyrotropin / Q000378:metabolism*; D013974:Thyroxine / Q000009:adverse effects*; D016277:Ventricular Function, Left / Q000187:drug effects
D000319:Adrenergic beta-Antagonists; D013972:Thyrotropin; D013974:Thyroxine