Thyrotropin Over-suppression and Heart

Inclusion criteria

• ✓. age less than 45 years old when receiving total or near-total thyroidectomy,
• ✓. serum level of TSH\<0.1 mU/L in the intermediate -risk or TSH\<0.3 mU/L in the low recurrence-risk group over 2 years before study entry,
• ✓. receiving TSH suppressive therapy for 5 to 9 years with fixed dose of LT4 more than 2 years before study entry, and
• ✓. no history of structural heart disease, arrhythmia, or cardiac symptoms (palpitation, exertional dyspnea and chest discomfort) during therapy.
• ✓. the subject matched to a patient by age (±2 years), sex, and body mass index (BMI) (±2 kg/m2),
• ✓. within the reference range of serum TSH (0.3-4.6 mU/L),
• ✓. no history of structural heart disease, arrhythmia, or cardiac symptoms,
• ✓. no history of comorbid diseases which affect thyroxine metabolism and cardiac structure, including hepatic or renal disease, anemia, and hypertension.