The Association between Thyroid Hormone Levels, and Coronary Slow Flow Phenomenon and Coronary Artery Disease in Euthyroid Patients

Thyroid hormones are well-known for their various effects on the cardiovascular system. However, contradictory results have been obtained regarding the association between thyroid hormones within the Reference Range (RR) and Coronary Artery Disease (CAD). Moreover, scarce evidence is available regarding the association between thyroid hormones and Coronary Slow Flow Phenomenon (CSFP).

This study aimed to investigate the relationship between thyroid hormones in the RR, and CSFP and CAD.

A total of 1033 euthyroid patients who underwent coronary angiography were enrolled and divided into four groups based on their coronary angiography and Thrombolysis in Myocardial Infarction (TIMI) flow grade: Normal Coronary Artery (NCA), CSFP, Non-obstructive CAD (N-CAD), and Obstructive CAD (O-CAD). Multivariate multinomial regression analysis was conducted to assess the association between thyroid hormone levels and CSFP as well as CAD. Thereafter, the prediction accuracy of Free Triiodothyronine (FT3) levels for the presence of CSFP and CAD was evaluated by the Receiver Operating Characteristic (ROC) curve analysis.

FT3 serum level was significantly lower in the CSFP and both CAD groups compared to the NCA group (P < 0.001). FT3 level was inversely correlated to the presence of CSFP and CAD (both N-CAD and O-CAD) only in young females. Moreover, TSH was found to be an independent predictor of O-CAD in young individuals, regardless of their gender. Furthermore, FT3 levels ≤ 2.56 pg/mL predicted the presence of CSFP (78% sensitivity and 62% specificity) and FT3 levels ≤ 2.38 pg/mL predicted the presence of CAD (64% sensitivity and 75% specificity) in young females.

FT3 level was negatively associated with CSFP and CAD in young females. In addition, high levels of TSH were associated with O-CAD only in young patients. Further studies are required to shed more light upon the regarded associations.