Myocardial ultrasonic reflectivity in patients with thyroid dysfunction: a tissue characterization study

In order to evaluate the role of thyroid hormones on myocardial collagen synthesis we studied the echoreflectivity of left ventricular wall in 6 hyperthyroid patients (fT3 = 21.7 ± 8.1 pmol/l) and 4 hypothyroid patients(fT3 = 2.9 ± 1.1 pmol/l), aged 38 ± 19 years, with recent (20 @? 90 days) symptoms of thyroid dysfunction, matched with 7 euthyroid controls (fT3 = 6.1 ± 0.8 pmol/l). The echo patterns were assessed by analyzing standard two-dimensional long-axis echocardiograms digitized off-line (standard TV phase alternation line) onto a personal computer, color-coded at 256 levels. The region for the analysis (5 x 5 mm) was set at end diastole in each patient in the mid portion of the interventricular septum. For each selection a color-level histogram representing the frequency distribution of pixels was derived using a software developed in our laboratory with estimates of the average pixel intensity (mean color scale) and broad band of the histogram that supports an index of fibrosis (derived collagen volume fraction; normal values up to 2%) directly correlated with the histologic assessed collagen content. Echo-derived parameters obtained were compared with corresponding values of TSH, fT3, fT4. A significant correlation was found between fT3 and mean color scale (r = 0.61), broad band (r = 0.78) and derived collagen volume fraction (r = 0.78); in particular with the decrease of fT3 an increase in echoreflectivity parameters and a leftward shift of the color histogram were observed with a significant increase of the derived indexes of fibrosis. These results suggest a direct inhibitory effect of triidothyironine on myocardial collagen synthesis confirming the observations made in animal models of hypothyroidism.