Diastolic dysfunction in patients on thyroid-stimulating hormone suppressive therapy with levothyroxine: beneficial effect of beta-blockade.

Thyroid-stimulating hormone (TSH) suppressive therapy with levothyroxine (L-T4) may cause adverse cardiac effects such as rhythm disturbances and ventricular hypertrophy. The latter is a predisposing condition to diastolic dysfunction. Thus, this study was designed to assess the effect of long-term TSH suppressive therapy on cardiac diastolic function. Because beta-blockade is known to reduce ventricular hypertrophy in patients on L-T4 therapy, we also tried to determine whether the addition of a beta-blocker to L-T4 improved diastolic function. Twenty-five patients (21 female and 4 male; mean age 41 +/- 10 yr) on TSH suppressive therapy for 3-9 yr (9 for differentiated carcinoma and 16 for nontoxic goiter) and 20 control subjects were studied. A subgroup of 10 patients, selected for the presence of symptoms and signs of adrenergic overactivity, was treated for 4 months with the beta-blocker bisoprolol (4.25 +/- 1.2 mg/day), and their maintaining L-T4 therapy was unchanged. In the patient group, left ventricular mass was significantly increased (P < 0.001), isovolumic relaxation time was prolonged (P < 0.001), and early diastolic filling velocity was markedly reduced (P < 0.001), whereas late diastolic filling was increased (P < 0.005). Consequently, the early-to-late diastolic flow velocity ratio was markedly decreased (P < 0.001). These alterations were more pronounced in the subgroup of patients with evidence of adrenergic overactivity. In these patients, beta-blockade induced a significant regression of cardiac hypertrophy and improved diastolic dysfunction. In particular, isovolumic relaxation time decreased (P < 0.01) and the early-to-late flow velocity ratio increased significantly (P < 0.01). Both indices reached values after beta-blockade that were no longer different from those of asymptomatic patients. It is concluded that long-term L-T4 therapy increases myocardial mass and causes relevant diastolic dysfunction, particularly in those patients with evidence of mild hyperthyroidism and adrenergic overactivity. Both myocardial hypertrophy and diastolic dysfunction are significantly improved by adrenergic beta-blockade.