Chronic thyrotropin-suppressive therapy with levothyroxine and short-term overt hypothyroidism after thyroxine withdrawal are associated with undesirable cardiovascular effects in patients with differentiated thyroid carcinoma.

To evaluate cardiovascular functionality in patients with thyroid cancer, we have performed echocardiography and ambulatory blood pressure monitoring in 19 women with differentiated thyroid carcinoma during thyroxine withdrawal, at three time points: the last day on TSH-suppressive thyroxine doses (subclinical or mild hyperthyroidism), 4-7 days after withdrawal (normal free thyroxine (FT4) and free triiodothyronine (FT3) levels), and before 131I whole body scanning (overt hypothyroidism). Twenty-one healthy euthyroid women served as controls. When compared with the values at visit 2, when patients had normal serum FT4 and FT3 levels, night-time systolic and mean blood pressure were increased when the patients were mildly hyperthyroid, and night-time systolic, diastolic and mean blood pressure were increased during overt hypothyroidism. The proportion of nondippers (absence of nocturnal decline in blood pressure) was markedly increased compared with healthy controls (7%), when patients were hyper- or hypothyroid (58% and 50% respectively), but not when patients had normal FT4 and FT3 levels (12%). No changes were observed in office blood pressure or in daytime ambulatory blood pressure readings. Diastolic function worsened during thyroxine withdrawal (E and A waves (early and late mitral flow) decreased, and the E/A ratio and the isovolumic relaxation time increased), and cardiac output decreased in parallel with the decrease in heart rate and systolic blood flow. In conclusion, the chronic administration of TSH-suppressive doses of thyroxine and the withdrawal of thyroxine frequently used for the management of differentiated thyroid carcinoma, are associated with undesirable cardiovascular effects.