Indexing Left Atrial Volumes: Alternative Indexing Methods Better Predict Outcomes in Overweight and Obese Populations.

BACKGROUND

Left atrial volume (LAV) is often adjusted for body surface area (BSA). In overweight individuals this may result in underestimation of left atrial (LA) dilation. The authors investigated whether alternative indexing techniques better predict mortality and cardiovascular (CV) events.

OBJECTIVES

The purpose of this study was to evaluate the efficacy of different methods of indexing LAV in predicting mortality and CV events across a range of body sizes.

METHODS

LAV was adjusted for BSA, idealized BSA (iBSA), height, and height-squared (H2) in patients aged over 50 years who underwent outpatient echocardiography and longitudinal follow-up at our institution. LA dilation was categorized using published criteria. Mortality and CV events were assessed via medical records.

RESULTS

LAVs were calculated in 17,454 individuals. In this study, 71.2% were overweight or obese. Indexing using iBSA, height, and H2 resulted in reclassification of LA size in up to 28.4% (P < 0.001) compared with indexing using BSA. In severely obese individuals (body mass index [BMI] ≥40 kg/m2), LA dilation indexed for BSA no longer predicted mortality (P = 0.70). Other indexing methods remained predictive of mortality. Height, H2, and iBSA all had greater performance, compared with BSA, for prediction of mortality and CV events in all overweight patients with H2 showing the best overall performance (P < 0.001). Net reclassification index for mortality was significant for all alternative indexing techniques (P < 0.001) and patients whose LA was reclassified from normal to dilated had increased risk of mortality (P < 0.001) and CV events (P < 0.001) across all BMI categories.

CONCLUSIONS

LA dilation based on standard indexing using BSA is nondiscriminatory for prediction of mortality in the severely obese. Indexing using height, H2, or iBSA to diagnose LA dilation better predicts mortality in this population and has better overall predictive performance across all overweight and obese populations. Using BSA indexing may lead to underappreciation of LA dilation and underestimation of patients at increased risk.