Association between Isometric and Allometric Height-Indexed Left Atrial Size and Atrial Fibrillation

Height-based indexations for the evaluation of left atrial (LA) volumes have been proposed as an alternative method to account for body stature when body composition is abnormal. The aim of this study was to derive reference values for these indexation methods and to examine their association with atrial fibrillation (AF).

A healthy population was randomly split into derivation and validation cohorts (n = 493 each). The derivation cohort was used to derive reference values for iso- and allometric height-indexed LA volumes. Echocardiography included measurement of maximal LA volume (LAV_max) and minimal LA volume (LAV_min). Associations between these measures and AF were investigated in the validation cohort. Cox proportional-hazards regression was performed, adjusting for CHARGE-AF (Cohorts for Heart and Aging Research in Genomic Epidemiology Atrial Fibrillation) risk score.

From 986 healthy subjects, allometric height-indexed exponents were determined to 1.72 and 1.56 for LAV_max and LAV_min, respectively. Upper reference values were determined to be LAV_max > 22.1 mL/m^1.72 and LAV_min > 12.7 mL/m^1.56. In the validation cohort, 41 patients (8%) developed AF during follow-up (median, 14.7 years). In unadjusted analyses, both isometric and allometric indexed LAV_max were associated with AF (hazard ratio, 1.07 [95% CI, 1.03-1.11; P < .001] and 1.11 [95% CI, 1.05-1.18; P < .001] per 1 mL/m and 1 mL/m^1.72 increase, respectively) with equal C statistics of 0.63. Height-indexed LAV_min was also associated with AF, with higher C statistics than for LAV_max. All findings were consistent after multivariable adjustment. LAV_max > 22.1 mL/m^1.72 posed an increased risk for AF (hazard ratio, 4.65; 95% CI, 1.83-11.86), but LAV_min > 12.7 mL/m^1.56 carried a higher risk (hazard ratio, 6.33; 95% CI, 2.66-15.07).

Both isometric and allometric height-indexed LA volumes are associated with AF in the general population. LAV_min is more strongly associated with AF than LAV_max regardless of indexation.