Background: In subclinical hypothyroidism (sHT), a condition in which impaired hormone synthesis is compensated by thyroid-stimulating hormone (TSH) hypersecretion, previous studies have suggested the presence of disturbances in left ventricular (LV) function.
Objectives: Our goal was to investigate LV structure and function through the combined use of conventional Doppler echocardiography and ultrasonic videodensitometry.
Methods: We studied 16 patients with sHT (aged 32+/-12 [mean +/- SD] years) who had raised TSH levels (> 3.6 mIU/L) but normal levels of free thyroid hormones (free thyroxine [FT(4)] and free triiodothyro-nine [FT(3)]), and 16 carefully age- and sex-matched euthyroid subjects. Transmitral flow Doppler analysis 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 corrected for heart rate (IVRTc) (2.9 +/- 0.6 versus 2.5 +/- 0.6, P<.04) than did controls. On videodensitometry, patients had lower CVIs both for the septum (-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 FT(4) and FT(3) concentrations in a direct fashion, and to serum TSH levels in an inverse fashion.
Conclusions: Subclinical hypothyroidism is associated with changes in videodensitometric myocardial structure. These changes, which are not accurately detected by conventional or Doppler echocardiography, are quantitatively related to loss of thyroid function and could represent an early sign of myocardial damage in hypothyroidism.