Echocardiographic Measurements of Left Heart Chamber Size in a Large Cohort of Subjects: Comparison of Body Surface Area and Height Indexing to Account for Effects of Obesity

Abstract

Background: The assessment of cardiac chamber size in the obese population is a challenging subject. Values usually indexed to body surface area (BSA) are smaller in obese subjects and prone to overcorrection. The aims of this study were to find reference thresholds to account for the effects of obesity among a large cohort of patients and to evaluate indexing to height as an alternative to BSA.

Methods: The past 10 years of records from a single echocardiography unit were retrospectively analyzed, and 14,007 subjects without known cardiac disease were included (mean age, 45 ± 15 years; 54% women; 20% obese). Measurements included left atrial diameter, area, and volume, left ventricular (LV) end-diastolic and end-systolic diameters, aortic root diameter, and LV mass. Absolute, BSA-indexed, and height-indexed maximum thresholds (mean + 1.96 SDs) were calculated. Allometric indexing of the form variable/height^β was tested. Correlation coefficients between indexed and absolute values were calculated to evaluate their proportional association (ideally r = 1). Correlations between indexed values and body size represented residual associations to be minimized (ideally r = 0).

Results: The strongest association of echocardiographic measurements with body size was observed for BSA (r = 0.36-0.63), whereas the isometric and allometric height models showed lower comparable values (r = 0.28-0.48). Positive correlations with body mass index were mostly observed for left atrial size (r ≈ 0.36) and LV mass (r ≈ 0.36) measurements. Values of the scaling exponent β for allometric height indexing were 1.72 for left atrial volume and 2.33 for LV mass. Correlations between indexed and absolute values were higher for height than BSA (0.80-0.98 vs 0.44-0.92). Correlations between indexed values and height were closer to 0 than for BSA, particularly using the allometric model. The overcorrection observed with increasing obesity class after BSA indexing was avoided after height indexing.

Conclusions: Unlike BSA, height indexing provided adequate body size scaling of left heart chamber size, avoiding overcorrection using allometric models in particular.

Keywords: Body size; Echocardiography; Left heart; Obesity.