Echocardiography in monitoring the therapeutic effect of levothyroxine replacement therapy in subclinical hypothyroidism
Authors: Pandrc M , Ristic A , Kostovski V , Ciric J 
Published: January 2025

Abstract

Introduction
Hypothyroidism (SCH) is defined as the elevated serum thyroid-stimulating hormone (TSH) and normal serum free thyroxine (FT4). According to the prospective Whickam survey's data, SCH occurs in 7.5 % women and 2.8% men, with the highest incidence in women aged over 60 years.

Purpose
Of our study is to quantify the effect of LT4 treatment on cardiac morphology and function in individuals with SCH in which TSH elevation persists more than 3 months together with other risk factors for developing overt hypothyroidism, in order to support its early introduction.

Materials and Methods
This was a pilot study within a prospective open-label study. Weight, height, BMI, waist circumference (WC) and blood pressure as well as electro and echocardiographic parameters were measured before intervention with thyroxine and 3 months after the euthyroid state had been achieved.

Results
Our study included 35 patients, in the age range of 51.6±15.4 years, 29 females (82.9%) and 6 males (17.1%). The reduction in systolic and diastolic blood pressure were recorded (p=0.024, p=0.019). There was a significant increase in heart rate (p=0.001) and the decreases in PR (p&lt;0.001), QT (p&lt;0.001) and QT corrected (p&lt;0.001) intervals. The significant drop of the following parameters of the left ventricle was recorded: septum in diastole (p=0.012), LV mass and mass index (p=0.003, p&lt;0.001 respectively), ESV (M-mode) (p&lt;0.001). The increase was registrated in EF (Simpson) (p=0.001), EF (Teicholz) (p&lt;0.001), and fractional shortening (Teicholz) (p&lt;0.001). After the therapy there was a significant increase in the following parameters: E /A (p=0.004), E /e (p=0.017), PEP (p=0.001) and ET (p=0.009), dP/dt (p&lt;0.001), and reduction in mitral valve area (p=0.013), e (p=0.001), e/a (p=0.001), IVCT (p&lt;0.001), IVRT (p&lt;0.001), IVCT/ET (p&lt;0.001), PEP/ ET (p&lt;0.001). After the treatment decrease in the frequency of criteria for diastolic dysfunction, as well as in the frequency of diastolic dysfunction was recorded, but with no significance (p=0.625, p=0.500, p=1.000, p=0.625 respectively). After LT4 substitution, there was a reduction of the following parameters: ESA (p&lt;0.001), TEI (p&lt;0.001). The significant increase was recorded in RA long and short axis (p&lt;0.001, p&lt;0.001 respectively), wall thickness (p&lt;0.001), FS (p=0.002) and ET (p=0.044). There was a positive correlation among changes in the average dose of levothyroxine with change in right ventricular TEI index (r= 0.517, p= 0.001) and change in EDV (Simpson) (r=0.355, p=0.036). Change in tAbs positive, moderately correlated with the change in IVCT / ET.

Conclusion
Future studies with a greater number of participants will be needed to ascertain the clinical and hemodynamic significance of those findings. The improvement of cardiac structure and function, measured by electrocardiographic and echocardiographic indicators should be weighty factor in monitoring the therapeutic effect.