Experimental evidence suggests an involvement of
thyroid hormones in myocardial nonmyocyte component growth. We evaluated the possible role of
thyroid hormones in myocardial remodeling by ultrasonic tissue characterization (videodensitometry) in 8
hyperthyroid patients, in 10 hypothyroid patients, and in 2 patients with
thyroid hormone resistance syndrome (RTH), before, 60, and 120 days
after treatment (T0, T60, T120), and in 10 age-matched euthyroids. 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 (broadband, Bb) of the selected echocardiographic images.
Thyrotropin (TSH), free
thyroxine (FT4), and free
triiodothyronine (FT3) were assessed by immunometric method. QT interval dispersion (QTd) on basal electrocardiogram was measured as a marker of dyshomogeneous ventricular repolarization. At T0, Bb and dCVF% were normal in
hyperthyroid and euthyroid patients, and slightly increased in RTH patients, whereas significantly higher values were found in hypothyroids. At T60, a significant reduction in Bb was observed in hypothyroids, with nearly normal dCVF% values. This trend was confirmed at T120 with complete normalization of echoreflectivity. No echoreflectivity changes were observed in
hyperthyroid and RTH patients during treatment. QTd was significantly increased in hypothyroids at T0, while no significant differences were found among groups at T60 and T120. Because the different videodeonsitometric myocardial properties observed in hypothyroid versus
hyperthyroid patients correspond to an increase of dCVF%, this study suggests that
thyroid hormones exert an inhibitory effect on myocardial
collagen synthesis in humans.