MON-587 Thyroid Hormones within the Normal Range and Cardiac Function in the General Population: The Epiporto Study

Introduction: Thyroid hormones have a central role in cardiovascular homeostasis. Both hypothyroidism and hyperthyroidism are associated with specific cardiovascular changes. However, the association of thyroid hormone levels within the normal range with cardiac function in general population remains largely unknown. Methods: 835 subjects with ≥45 years from EPIPorto population-based cohort study were analyzed. We excluded participants with TSH, FT4 or FT3 outside the reference range and participants with history of myocardial infarction, coronary revascularization, cardiac surgery, valvular heart disease, history of thyroid disease or treatment with drugs that interfere with thyroid function. All participants were submitted to detailed echocardiographic evaluation. The association of TSH, FT4 and FT3 with heart rate, blood pressure (BP), cardiac structure and cardiac function was evaluated with linear regression models unadjusted and adjusted for sex and age (model 1), and for sex, age, BMI, diabetes and hypertension (model 2). We assessed nonlinear associations using restricted cubic splines (3 knots). Results: The mean age of the population was 61.5±10.5 years, with 61.1% female participants. Eleven percent had diabetes, 47.8% dyslipidemia and 54.8% hypertension. Heart rate was positively associated with FT3 levels (model 2: β=1.78 [0.04 to 3.51], p=0.045). Diastolic BP was positively associated with TSH levels (model 2: β=1.50 [0.10 to 2.89], p=0.035). Regarding left ventricle (LV) structure, there was a nonlinear association of FT4 with posterior wall thickness, with lower thickness in the middle of the reference range. Both LV end-diastolic and end-systolic diameters were inversely associated with TSH (β=-3.62 (-5.89 to -1.35), p=0.002; and β=-2.03 (-3.31 to -0.77), p=0.002 in model 2). FT3 was nonlinearly associated with ejection fraction, with higher ejection fractions near the extremes of the normal range of FT3. Concerning diastolic function, FT3 was positively associated with E', and FT4 was negatively associated with E', although these associations were no longer significant in the adjusted models. Conclusions: Variations of thyroid function within the reference range are associated with heart rate, blood pressure, cardiac structure and cardiac function in the general population. Our results suggest that increasing thyroid function (lower TSH, higher FT4 or higher FT3) is associated with higher heart rate, lower diastolic BP and larger LV cavity volumes. On the other hand, both LV wall thickness and LV ejection fraction are non-linearly associated with thyroid hormones, with greater wall thickness and higher ejection fraction near the extremes of normal range of thyroid hormones concentration.