Effects of thyroid hormones on cardiac structure: A tissue characterization study in patients with thyroid disorders before and after treatment

Experimental evidence suggests an involvement of thyroid hormones in myocar dial nonmyocyte component growth. We evaluated the possible role of thyroid hormones in myocardial remodeling by ultrasonic tissue characterization (v ideodensitometry) in 8 hyperthyroid patients, in 10 hypothyroid patients, a nd in 2 patients with thyroid hormone resistance syndrome (RTH), before, 60 , and 120 days after treatment (TO, T60, T120), and in 10 age-matched euthy roids. According to a previously described procedure, the derived collagen volume fraction (dCVF%, an echocardiographic index estimating the collagen content) was predicted from the pixel-level frequency distribution width (b roadband, Bb) of the selected echocardiographic images. Thyrotropin (TSH), fret thyroxine (FT4), and free triiodothyronine (FT3) were assessed by immu nometric method. QT interval dispersion (QTd) on basal electrocardiogram wa s measured as a marker of dyshomogeneous ventricular repolarization. At TO, Bb and dCVF% were normal in hyperthyroid and euthyroid patients, and sligh tly increased in RTH patients, whereas significantly higher values were fou nd in hypothyroids. At T60, a significant reduction in Bb was observed in h ypothyroids, with nearly normal dCVF% values. This trend was confirmed at T 120 with complete normalization of echoreflectivity. No echoreflectivity ch anges were observed in hyperthyroid and RTH patients during treatment. QTd was significantly increased in hypothyroids at TO, while no significant dif ferences were found among groups at T60 and T120. Because the different vid eodeonsitometric myocardial properties observed in hypothyroid versus hyper thyroid patients correspond to an increase of dCVF%, this study suggests th at thyroid hormones exert an inhibitory effect on myocardial collagen synth esis in humans.