Ultrasonic myocardial textural analysis in subclinical hypothyroidism

Background: In subclinical hypothyroidism (sHT), a condition in which impai red hormone synthesis is compensated by thyroid-stimulating hormone (TSH) h ypersecretion, previous studies have suggested the presence of disturbances in left ventricular (LV) function. Objectives: Our goal was to investigate LV structure and function through t he combined use of conventional Doppler echocardiography and ultrasonic vid eodensitometry. Methods: We studied 16 patients with sHT (aged 32 +/- 12 [mean +/- SD] year s) who had raised TSH levels (> 3.6 mIU/L) but normal levels of free thyroi d hormones (free thyroxine [FT4] and free triiodothyronine [FT3]) and 16 ca refully age- and sex-matched euthyroid subjects. Transmitral now Doppler an alysis and quantitative analysis of the echocardiographic digitized images were performed in all study subjects. Textural parameters of the septum and posterior wall were obtained as mean gray levels, which were then used to calculate the cyclic variation index (CVI), that is, the percent change in mean gray levels between diastole and systole. Results: Patients with sHT had a significantly higher LV mass index (92 +/- 16 versus 76 +/- 16 g.m(2), P < .01) and isovolumic relaxation time correc ted for heart rate (IVRTc) (2.9 +/- 0.6 versus 2.5 +/- 0.6, P < .04) than d id controls. On videodensitometry, patients had lower CVIs both for the sep tum (-5% +/- 22% versus 33% +/- 9%, P < .0001) and the posterior wall (10% +/- 26% versus 49% +/- 18%, P < .0001). IVRTc discriminated only 25% of the patients from the controls, whereas CVI analysis correctly identified 85% of the patients with sHT (P < .002). Furthermore, CVI values were found to be significantly related to serum FT4 and FT3 concentrations in a direct fa shion, and to serum TSH levels in an inverse fashion. Conclusions: Subclinical hypothyroidism is associated with changes in video densitometric myocardial structure. These changes, which are not accurately detected by conventional or Doppler echocardiography, are quantitatively r elated to loss of thyroid function and could represent an early sign of myo cardial damage in hypothyroidism.