Clinical implications of left atrial size adjustment: Impact of obesity

American and European societies recommend using left atrial (LA) volume adjusted to body surface area (BSA) as the means of indexing LA volume to the patient's body size irrespective of morphometric characteristics.

To evaluate the impact of obesity on LA volume indexation to BSA on the presence and degree of LA enlargement.

From our echocardiography database, we extracted all consecutive adults referred for a transthoracic echocardiography in 2019 (n=28,725; 64±17 years; 55% male; 31% obese [body mass index≥30kg/m²]). LA volume indexed to BSA was calculated using measured weight (LA_Meas) and ideal weight (LA_Ideal) calculated using the Devine Formula.

LA_Meas and LA_Ideal were 35±17mL/m² and 40±19mL/m², respectively (P<0.0001); 13% were classified as having a normal LA_Meas but LA_Ideal enlargement overall, 25% in obese patients and 7% in non-obese patients (P<0.0001). The percentages of patients with no, mild, moderate and severe LA dilatation were 57%, 19%, 9% and 16%, respectively, using LA_Meas, and 45%, 20%, 11% and 24%, respectively, using LA_Ideal (kappa=0.57). Degree of LA enlargement differed in 8194 patients (29%); 96% of the disagreement was related to underestimation of the degree of LA enlargement using LA_Meas. Agreement for the degree of LA enlargement was poor in obese and good in non-obese patients (kappa=0.28 and 0.71, respectively). As illustrative clinical implications, diastolic function grade was modified in 8.3% of patients with preserved ejection fraction and 10.8% of patients with reduced left ventricular ejection fraction/myocardial disease, and timing for intervention was potentially different in 12.9% of patients with primary mitral regurgitation.

Indexing LA volume to measured BSA versus ideal BSA markedly underestimates the presence and severity of LA enlargement, especially in obese patients, with potential important clinical implications.