ObjectiveTo investigate the prognostic value of left atrial volume index (LAVI) in patients with moderate to severe aortic regurgitation (AR) and bicuspid aortic valve (BAV).Methods554 individuals (45 (IQR 33–57) years, 80% male) with BAV and moderate or severe AR were selected from an international, multicentre registry. The association between LAVI and the combined endpoint of all-cause mortality or aortic valve surgery was investigated with Cox proportional hazard regression analyses.ResultsDilated LAVI was observed in 181 (32.7%) patients. The mean indexed aortic annulus, sinus of Valsalva, sinotubular junction and ascending aorta diameters were 13.0±2.0 mm/m², 19.4±3.7 mm/m², 16.5±3.8 mm/m² and 20.4±4.5 mm/m², respectively. After a median follow-up of 23 (4–82) months, 272 patients underwent aortic valve surgery (89%) or died (11%). When compared with patients with normal LAVI (<35 mL/m²), those with a dilated LAVI (≥35 mL/m²) had significantly higher rates of aortic valve surgery or mortality (43% and 60% vs 23% and 36%, at 1 and 5 years of follow-up, respectively, p<0.001). Dilated LAVI was independently associated with reduced event-free survival (HR=1.450, 95% CI 1.085 to 1.938, p=0.012) after adjustment for LV ejection fraction, aortic root diameter, LV end-diastolic diameter and LV end-systolic diameter.ConclusionsIn this large, multicentre registry of patients with BAV and moderate to severe AR, left atrial dilation was independently associated with reduced event-free survival. The role of this parameter for the risk stratification of individuals with significant AR merits further investigation.