Study limitations
This is a retrospective observational study, and therefore, has inherent limitations of the retrospective design. There are a few other important limitations. First, the study is subjected to differences over time in individual surgical techniques and operative management. Second, preoperative AF type (paroxysmal or persistent) was not classified, however even patients with paroxysmal AF undergoing surgical AVR appear to be at higher risk of developing persistent AF and death at 12 months follow-up compared with patients with preoperative sinus rhythm. Third, patients with postoperative new-onset AF had either spontaneous recovery of sinus rhythm or successful cardioversion before hospital discharge, or, less frequently, were discharged on anticoagulation therapy if remained in AF. This is unlikely to affect the results as the study focuses on the preoperative rhythm state. Fourth, data on long-term anticoagulation for AF thromboprophylaxis were not available. This is potentially an important confounder, as appropriate provision of anticoagulation to mitigate thromboembolic events in those with atrial arrhythmias has been demonstrated to reduce mortality Fifth, whilst our long-term analysis reports all-cause mortality, and thus deaths unrelated to preoperative AF might have been included, all-cause mortality is considered an appropriate endpoint to follow in the long-term as it accounts for both cardiac and systemic diseases and is unaffected by any reporting or misclassification bias.