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

Abstract

BACKGROUNDBody size indexation is a foundation of the diagnostic interpretation of cardiac size measures used in imaging assessment of cardiovascular health. Body surface area (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 (body mass index (BMI) <18·5 kg/m2 or ≥30 kg/m2, respectively). We hypothesized that mortality can be used to identify an optimal body size indexation metric for echocardiographic measures that would be a better predictor of survival than BSA regardless of BMI.METHODSIn this big data, cohort study, adult patients with no prior valve replacement were selected from the National Echo 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.FINDINGSIndexation of echocardiographic measures (left ventricular diameter [n=337,481] and mass [n=330,959], left atrial area [n=136,989], aortic sinus diameter [n=125,130], right atrial area [n=81,699], right ventricular diameter [n=3,575], right ventricular outflow tract diameter [n=2,841]) by BSA had better prognostic performance vs unindexed measures (healthy/overweight: C-statistic 0·656 vs 0·618, average change in Akaike Information Criteria (ΔAIC) 800; underweight: C-statistic 0·669 vs 0·654, ΔAIC 15; obese: C-statistic 0·630 vs 0·612, ΔAIC 113). Indexation by other body size metrics (lean body mass or height and/or weight raised to various powers) did not improve prognostic performance versus BSA by a clinically relevant magnitude (average C-statistic increase ≤0·01), with smaller differences in higher BMI subgroups. Similar results were obtained using sex-disaggregated analysis, for indexation of other aortic or cardiac dimension or volume measures, and for all-cause mortality.INTERPRETATIONIndexing 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.FUNDINGThis research was supported in part by grants (PI Ugander) from New South Wales Health, Heart Research Australia, and the University of Sydney.

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“…However, BMI and, particularly BSA, can influence the normal aortic sizes as reported in recent studies. [ 12 , 13 ] The aortic sizes with respect to the BMI or BSA were unable to be analyzed, as the BMI and BSA data were not available.…”