Prognostic association supports indexing size measures in echocardiography by body surface area

BACKGROUND BSA is the most commonly used metric for body size indexation of echocardiographic measures, but its use in patients who are underweight or obese is questioned (BMI<18.5 kg/m 2 or ≥30 kg/m 2 , respectively). AIMS We aim to use survival analysis to identify an optimal body size indexation metric for echocardiographic measures that would be a better predictor of survival than body surface area (BSA) regardless of body mass index (BMI). METHODS Adult patients with no prior valve replacement were selected from the National Echocardiography Database Australia. Survival analysis was performed for echocardiographic measures both unindexed and indexed to different body size metrics, with 5-year cardiovascular mortality as the primary endpoint. RESULTS Indexation of echocardiographic measures (left ventricular end-diastolic diameter [n=230,109] and mass [n=224,244], left atrial area [n=90,596], aortic sinus diameter [n=90,805], right atrial area [n=59,516], right ventricular diameter [n=3,278], right ventricular outflow tract diameter [n=1,406]) by BSA had better prognostic performance vs unindexed measures (normal weight/overweight: average C-statistic 0.661 vs 0.620; underweight: C-statistic 0.650 vs 0.648; obese: C-statistic 0.627 vs 0.614). Indexation by other body size metrics (lean body mass, height, and/or weight raised to different powers) did not improve prognostic performance versus BSA by a clinically relevant magnitude (average C-statistic increase ≤0.02), with smaller differences in other BMI subgroups. CONCLUSIONS Indexing measures of cardiac and aortic size by BSA improves prognostic performance regardless of BMI, and no other body size metric has a clinically meaningful better performance.