Evidence and controversies regarding the screening for subclinical hypothyroidism in patients with cardiovascular disease

Subclinical hypothyroidism is defined as thyroid-stimulating hormone (TSH) level above the upper limit of the reference ranges with normal free thyroxine (T4) concentrations (1). Current data suggest that the prevalence of subclinical hypothyroidism can reach up to 10% in the elderly (2) and around 30% of subject can progress to overt hypothyroidism (low levels of T4) depending on the initial serum TSH concentrations and the presence of anti-thyroid peroxidase (anti-TPO) antibodies (3). Thyroid hormones have different effects on the cardiovascular system (4). Subclinical hypothyroidism is a well-known secondary reversible cause of hypercholesterolemia. Unspecific cardiac alterations have been associated with overt and subclinical hypothyroidism, such as impaired systolic function and left ventricular diastolic filling, increased peripheral vascular resistance, diastolic hypertension, increased arterial stiffness, endothelial dysfunction, pericardial effusion and arrhythmia (5-8). These findings are more likely to be observed in patients with higher TSH levels and in elderly.