ObjectivePostoperative atrial fibrillation (POAF) is a common complication after cardiac surgery associated with other adverse outcomes. Recent studies have shown that drainage of pericardial effusion by a posterior pericardial incision reduces the incidence of POAF. An alternative approach is a chest tube placed posteriorly in the pericardium. We evaluated if the use of a posterior pericardial drain was associated with reduced risk of POAF in patients undergoing coronary artery bypass graft (CABG) and/or aortic valve replacement (AVR). MethodsThis observational study included 2,535 patients who underwent CABG (n=1,997), AVR (n=293), or combined CABG and AVR (n=245) in Iceland from 2002-2020. From our study population, 553 (22%) received a 20Fr posterior pericardial chest tube in addition to standard mediastinal and left pleural drains. The incidence of POAF in patients with and without a posterior pericardial drain was compared before and after 1:1 propensity score matching. ResultsOf 2,535 patients, 1,100 were included in the matched cohort. The incidence of POAF was lower in patients receiving posterior pericardial chest tube drainage compared to the control group, both before (34% vs. 43%, p<0.001) and after (33% vs. 43%, p=0.002) matching. In a multivariable analysis, posterior pericardial chest tube drainage was independently associated with a reduced risk for POAF (adjusted odds ratio 0.67 [95%CI 0.52-0.88], p=0.003). ConclusionsThis observational study suggested that posterior pericardial chest tube drainage is associated with a significant reduction of POAF following routine CABG and/or AVR procedures. The results are hypothesis-generating and must be confirmed in prospective randomized trials.