Effect of Cardiac Resynchronization Therapy on Thyroid Function

BACKGROUND: Heart failure patients frequently have thyroid function abnormalities. Cardiac resynchronization therapy (CRT) is a major treatment for patients with advanced chronic heart failure. We aimed to investigate the effects of CRT on thyroid functions. HYPOTHESIS: CRT improves thyroid functions. METHODS: Fifty-seven patients (42 male, 15 female; mean age 58 ± 13 y) undergoing CRT were included in the study. Serum levels of thyroid hormones and echocardiographic parameters were measured before and 6 months after CRT. A response to CRT was defined as a reverse remodeling detected by a relative increase of ≥15% in left ventricular ejection fraction. RESULTS: The clinical status and functional capacity of the patients in the remodeling group were improved significantly. The mean New York Heart Association class was reduced from 3.2 ± 0.4 to 2.2 ± 0.4 (P<0.001). The free triiodothyronine (fT3) level increased from 2.67 pg/mL to 2.97 pg/mL in the reverse remodeling group (P = 0.005). The fT3/fT4 ratio increased from 1.81 to 2.34 (P = 0.006). CONCLUSIONS: CRT improves fT3 levels and fT3/fT4 ratio, which may play an important role in reverse remodeling.