Subclinical Hypothyroidism as an Independent Determinant of Left Atrial Dysfunction in the General Population

Although subclinical hypothyroidism (SCH) is a common clinical entity and carries independent risk for incident heart failure (HF), its possible association with subclinical cardiac dysfunction is unclear. Left ventricular global longitudinal strain (LVGLS) and left atrial (LA) phasic strain can unmask subclinical left heart abnormalities and are excellent predictors for HF. This study aimed to investigate the association between the presence of SCH and subclinical left heart dysfunction in a sample of the general population without overt cardiac disease.

We examined 1078 participants who voluntarily underwent extensive cardiovascular health check-ups, including laboratory tests and 2-dimensional speckle-tracking echocardiography to assess LVGLS and LA reservoir, conduit, and pump strain. SCH was defined as an elevated serum thyroid-stimulating hormone level with normal concentration of free thyroxine.

Mean age was 62 ± 12 years, and 56% were men. Seventy-eight (7.2%) participants exhibited SCH. Individuals with SCH had significantly reduced LA reservoir (37.1 ± 6.6% vs 39.1 ± 6.6%; P = 0.011) and conduit strain (17.3 ± 6.3% vs 19.3 ± 6.6%; P = 0.012) compared with those with euthyroidism, whereas there was no significant difference in left ventricular ejection fraction, LA volume index, LVGLS, and LA pump strain between the 2 groups. In multivariable analyses, SCH remained associated with impaired LA reservoir strain, independent of age, traditional cardiovascular risk factors, and pertinent laboratory and echocardiographic parameters. including LVGLS (standardized β -0.054; P = 0.032).

In an unselected community-based cohort, individuals with SCH had significantly impaired LA phasic function. This association may be involved in the higher incidence of HF in subjects with SCH.