Risk and Subtypes of Stroke Following New‐Onset Postoperative Atrial Fibrillation in Coronary Bypass Surgery: A Population‐Based Cohort Study

BACKGROUND: New‐onset postoperative atrial fibrillation (POAF) develops in approximately one‐third of patients undergoing cardiac surgery and is associated with a higher incidence of ischemic stroke and increased mortality. However, it remains unknown to what extent ischemic stroke events in patients with POAF are cardioembolic and whether anticoagulant therapy is indicated. We investigated the long‐term risk and pathogenesis of postoperative stroke in patients undergoing coronary artery bypass grafting experiencing POAF. METHODS AND RESULTS: This was a register‐based cohort study. Data from the WDHR (Western Denmark Heart Registry) were linked with the DNPR (Danish National Patient Register), the Danish National Prescription Register, and the Cause of Death Register. All stroke diagnoses were verified, and ischemic stroke cases were subclassified according to pathogenesis. Furthermore, investigations of all‐cause mortality and the use of anticoagulation medicine for the individual patient were performed. A total of 7813 patients without a preoperative history of atrial fibrillation underwent isolated coronary artery bypass grafting between January 1, 2010, and December 31, 2018, in Western Denmark. POAF was registered in 2049 (26.2%) patients, and a postoperative ischemic stroke was registered in 195 (2.5%) of the patients. After adjustment, there was no difference in the risk of ischemic stroke (hazard ratio [HR], 1.08 [95% CI, 0.74–1.56]) or all‐cause mortality (HR, 1.09 [95% CI, 0.98–1.23]) between patients who developed POAF and non‐POAF patients. Although not statistically significant, patients with POAF had a higher incidence rate (IR; per 1000 patient‐years) of cardioembolic stroke (IR, 1 [95% CI, 0.6–1.6] versus IR, 0.5 [95% CI, 0.3–0.8]), whereas non‐POAF patients had a higher incidence rate of large‐artery occlusion stroke (IR, 1.1 [95% CI, 0.8–1.5] versus IR, 0.7 [95% CI, 0.4–1.4]). Early initiation of anticoagulation medicine was not associated with a lower risk of ischemic stroke. However, patients with POAF were more likely to die of cardiovascular causes than non‐POAF patients (P<0.001). CONCLUSIONS: We found no difference in the adjusted risk of postoperative stroke or all‐cause mortality in POAF versus non‐POAF patients. Patients with POAF after coronary artery bypass grafting presented with a higher, although not significant, proportion of ischemic strokes of the cardioembolic type.