Long-term Thromboembolic Risk in Patients With Postoperative Atrial Fibrillation After Coronary Artery Bypass Graft Surgery and Patients With Nonvalvular Atrial Fibrillation.

IMPORTANCE: New-onset postoperative atrial fibrillation (POAF) is a common complication of coronary artery bypass graft (CABG) surgery. However, the long-term risk of thromboembolism in patients who develop POAF after CABG surgery remains unknown. In addition, information on stroke prophylaxis in this setting is lacking.

OBJECTIVE: To examine stroke prophylaxis and the long-term risk of thromboembolism in patients with new-onset POAF after first-time isolated CABG surgery compared with patients with nonsurgical, nonvalvular atrial fibrillation (NVAF).

DESIGN, SETTING, AND PARTICIPANTS: This cohort study used data from a clinical cardiac surgery database and Danish nationwide registries to identify patients undergoing first-time isolated CABG surgery who developed new-onset POAF from January 1, 2000, through June 30, 2015. These patients were matched by age, sex, CHA2DS2-VASc score, and year of diagnosis to patients with nonsurgical NVAF in a 1 to 4 ratio. Data analysis was completed from February 2017 to January 2018.

MAIN OUTCOMES AND MEASURES: The proportion of patients initiating oral anticoagulation therapy within 30 days and the rates of thromboembolism.

RESULTS: A total of 2108 patients who developed POAF after CABG surgery were matched with 8432 patients with NVAF. In the full population of 10 540 patients, the median (interquartile range) age was 69.2 (63.7-74.7) years; 8675 patients (82.3%) were men. Oral anticoagulation therapy was initiated within 30 days postdischarge in 175 patients with POAF (8.4%) and 3549 patients with NVAF (42.9%). The risk of thromboembolism was lower in the POAF group than in the NVAF group (18.3 vs 29.7 events per 1000 person-years; adjusted hazard ratio [HR], 0.67; 95% CI, 0.55-0.81; P < .001). Anticoagulation therapy during follow-up was associated with a lower risk of thromboembolic events in both patients with POAF (adjusted HR, 0.55; 95% CI, 0.32-0.95; P = .03) and NVAF (adjusted HR, 0.59; 95% CI, 0.51-0.68; P < .001) compared with patients who did not receive any anticoagulation therapy. Further, the risk of thromboembolism was not significantly higher in patients with POAF compared with those who did not develop POAF after CABG surgery (adjusted HR, 1.11; 95% CI, 0.94-1.32; P < .24).

CONCLUSIONS AND RELEVANCE: New-onset POAF in patients who had undergone CABG surgery was associated with a lower long-term thromboembolic risk than that of patients who had NVAF. These data do not support the notion that new-onset POAF should be regarded as equivalent to primary NVAF in terms of long-term thromboembolic risk.