Background: Impaired left ventricular (LV) diastolic function is a common pathophysiological feature of patients with hypertrophic
cardiomyopathy (HCM). High-normal thyrotropin (thyroid-stimulating hormone, TSH) levels may alter the performance
of the left ventricle.

Aim: To ascertain whether the severity of impaired LV diastolic function in HCM patients might worsen with elevating TSH
levels within the reference range.

Methods: This study included 152 HCM patients and 119 healthy controls with euthyroidism. Blood samples were taken to test
for serum TSH, free triiodothyronine (FT3) and free thyroxine (FT4) levels. LV diastolic function was quantified by determining
the ratio of the transmitral early LV filling velocity to the early diastolic mitral annulus velocity (E/Ea ratio).

Results: The E/Ea ratio was significantly higher in patients with high-normal TSH levels (25.7 ± 5.6 vs. 17.7 ± 4.9, p < 0.001).
There was a significant correlation between the E/Ea ratio and the TSH levels within the high reference range (β = 0.268,
p = 0.021). Univariate logistic regression showed that high-normal TSH levels were predictors of severe heart failure. However,
after adjusting for the effect of LV diastolic dysfunction, high-normal TSH levels were no longer independent predictors
of severe heart failure.

Conclusions: The HCM patients with high-normal TSH levels had a higher degree of LV diastolic dysfunction. Mild TSH
level changes within the high reference range can influence the severity of impaired LV diastolic function. In HCM patients,
high-normal TSH levels may affect the development of heart failure through their association with LV diastolic impairment.