Comparing left atrial volume indexation methods for predicting major adverse cardiovascular events and atrial fibrillation: Data from the Akershus Cardiac Examination 1950 Study

Background Left atrial volume measured by echocardiography has strong prognostic value, but needs to be adjusted to body size. It is recommended to index to body surface area (BSA), but this may over-adjust for the pathological remodelling driven by overweight. Therefore, indexation to height has been proposed. In addition, allometric indexation to height2 takes into account the non-linear relationship between left atrial volume and body size. Purpose To compare left atrial volume indexation methods for predicting major adverse cardiovascular events (MACE) and atrial fibrillation (AF). Methods In the population-based prospective cohort Akershus Cardiac Examination 1950 Study, all individuals born in 1950 and residing in Akershus County, Norway were invited. Baseline examinations were conducted during 2012-2015 and included transthoracic echocardiography. BSA was calculated using the Mosteller formula. Clinical outcomes were collected from national health registries until December 31st, 2022. MACE was defined as cardiovascular death, non-fatal stroke or non-fatal coronary ischemic events. The predictive ability of left atrial volumes on the occurrence of MACE and incident AF was assessed by Cox regression analyses and C-statistics. Results A total of 3706 individuals were included and 3489 (94.1%) had available left atrial volume measurements. Mean age was 63.9 years ± 0.6 and 1703 (48.8%) were female. There were 157 (4.5%) individuals with prevalent atrial fibrillation at baseline that were excluded from the prediction of atrial fibrillation analysis. MACE occurred in 275 (7.9%) individuals after a median follow-up of 8.1 years, whereas incident AF occurred in 168 (5.0%) individuals after a median follow-up of 8.3 years. Figure 1 shows Kaplan Meier plots for quartiles of left atrial volume indexed by different indexation methods and the two outcomes. Table 1 summarizes the predictive performance of left atrial volume indexed to BSA, height and height2. For incident AF, indexation to height had the highest hazard ratio and C-statistics were significantly better compared with BSA. For MACE, indexation to height had the highest hazard ratio and C-statistics for both height and height2 were significantly better compared with BSA. Conclusion In a population-based cohort of individuals in their mid-sixties, left atrial volume predicted both MACE and incident AF. Indexation to height or height2 had better predictive ability for both outcomes compared to BSA. This adds to the growing body of evidence suggesting that indexation to height instead of BSA should be considered.