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Changes of Cardiac Functions in Athyreotic Patients with and without Suppressive Thyroxine Treatment

Objectives: Thyroid hormone (TH) exerts profound effects on the heart. The presence of cardiac hypertrophy in patients receiving long term L-T4 therapy is associated with a marked diastolic dysfunction. The study was performed to investigate the possible effect of suppressive thyroxine treatment (STT) on cardiac functions in athyreotic patients. Methods: Forty-three athyreotic patients (mean age 42 ± 9 years old, and range from 25 to 56 years old) who received STT to suppress thyrotropin synthesis after surgery and 131I ablation for differentiated thyroid carcinoma were studied. Scintigraphic evaluation of cardiac functions including left ventricle (LV) ejection fraction (EF), peak filling rate (PFR) and peak ejection rate (PER) was performed during STT [Eltroxin (T4), 4-5 pg/kg/day for 6-12 (mean, 9) months] and 4 weeks after discontinuing treatment. The concomitant blood samples were drawn and were analyzed simultaneously for concentrations of serum TH including T3, T4, TSH and free T4. Results: The thyroid profiles showed that patients were subclinically hyperthyroid with STT and hypothyroid 4 wk after STT withdrawal. The values of PFR and resting heart rate were significantly increased in the STT group as compared to that of T4 withdrawal (3.18±0.06 vs. 2.91 ±0.06 EDV/sec and 82 ± 10 vs. 72 ± 11 beats/mm, P＜0.05 and P＜0.01, respectively). However, no significant changes of mean EF and PER values were found. There were weekly significant negative correlations between PFR and serum TSH values in the STT withdrawal group (P= 0.045). Conclusion: Our results support the view that LV diastolic function may be affected in athyreotic patients with thyroidal dysfunction. However, its long-term effect, especially to the aged and with preexisting cardiovascular disorders patients, needs further clarified.