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.