Detection of subclinical atrial dysfunction by two-dimensional echocardiography in patients with overt hyperthyroidism.

BACKGROUND: Hyperthyroidism is an important cardiovascular risk factor in the development of atrial fibrillation and heart failure. Increased atrial electromechanical intervals are used to predict atrial fibrillation, measured by tissue Doppler imaging (TDI).

AIMS: To evaluate atrial electromechanical delay (EMD) and left atrial (LA) mechanical function in patients with overt hyperthyroidism.

METHODS: Thirty-four patients with overt hyperthyroidism and 34 controls were included. A diagnosis of overt hyperthyroidism was reached with decreased serum thyroid-stimulating hormone (TSH) and increased free T4 (fT4) concentrations. Using TDI, atrial electromechanical coupling (PA) was obtained from the lateral mitral annulus (PA lateral), septal mitral annulus (PA septum) and right ventricular tricuspid annulus (PA tricuspid). LA volumes (maximum, minimum and presystolic) were measured by the disks method in apical four-chamber view and indexed to body surface area. LA active and passive emptying volumes and fractions were calculated.

RESULTS: LA diameter was significantly higher in hyperthyroid patients (P=0.001). LA passive emptying volume and fraction were significantly decreased in hyperthyroid patients (P=0.038 and P<0.001). LA active emptying volume and fraction were significantly increased in hyperthyroid patients (P<0.001 and P<0.001). Left and right intra-atrial (PA lateral-PA septum and PA septum-PA tricuspid) and interatrial (PA lateral-PA tricuspid) EMDs were significantly higher in hyperthyroid patients (29.2 ± 4.4 vs 18.1 ± 2.6, P<0.001; 18.7 ± 4.3 vs 10.6 ± 2.0, P<0.001; and 10.5 ± 2.9 vs 7.1 ± 1.2, P<0.001, respectively). Stepwise linear regression analysis demonstrated that fT4 and TSH concentrations were independent predictors of interatrial EMD (β=0.436, P<0.001 and β=-0.310, P=0.005, respectively).

CONCLUSION: This study showed prolonged atrial electromechanical intervals and impaired LA mechanical function in patients with overt hyperthyroidism, which may be an early sign of subclinical cardiac involvement and dysrhythmias in overt hyperthyroidism.