New-onset atrial fibrillation after coronary surgery: epidemiology, risk factors and long-term prognosis

Abstract

Background and aim: New-onset postoperative atrial fibrillation (POAF) is common following coronary artery bypass grafting (CABG). Evidence on its prognostic implications, risk-stratification methods, and factors influencing prognosis is both limited and conflicting. This thesis aimed to explore POAF epidemiology, identify risk factors for its occurrence, investigate the long-term outcomes associated with POAF, and determine factors that influence prognosis.

Methods: This thesis comprises four registry-based observational studies on POAF after heart surgery. Study I investigated the epidemiology and long-term prognosis of POAF after CABG and potential associations between early-initiated oral anticoagulation (OAC) and outcome after POAF. Study II explored the association between cardiopulmonary bypass (CPB) management and the risk of developing POAF after CABG/valve surgery. Study III evaluated the CHA2DS2-VASc score in estimating the one-year ischemic stroke risk in patients with post-CABG POAF. Study IV explored ischemic stroke risk factors, evaluated non-surgical atrial fibrillation (AF) stroke risk stratification tools in POAF patients, and analyzed OAC prescription patterns in patients with POAF after CABG.

Results: Paper I: Patients with POAF (n=7 368/24 523, 30%), had a higher risk for ischemic stroke, thromboembolism, heart failure hospitalization, and AF recurrence, but not all-cause mortality compared to those without POAF. OAC at discharge was associated with a higher risk of major bleeding, but not with a reduced risk for ischemic stroke or thromboembolism. Paper II: There were 758/1999 patients with POAF (37.9%) after CABG and/or valve surgery 2016-2020. Longer CPB time and higher flow index were associated with increased risk for POAF whereas other CPB variables were not. Paper III: In 6 368 patients with POAF discharged without OAC, the one-year risk for ischemic stroke was 0.3%, 0.7%, and 1.5% in patients with CHA2DS2-VASc of 1, 2, and 3, respectively, and ≥2.3% in patients with a score 4. CHA2DS2-VASc had an area under the receiver operating characteristic curve of 0.67 (95% confidence interval: 0.64–0.69). Paper IV: Age, previous ischemic stroke, heart failure, and myocardial infarction were associated with an increased one-year ischemic stroke risk in patients with POAF after CABG. More than two-thirds of patients with POAF and an estimated high stroke risk were not dispensed OAC upon discharge.

Conclusions: POAF after CABG is common and linked to adverse prognostic outcomes. The risk for POAF seems not to be significantly affected by guideline-directed CPB management. Non-surgical AF stroke-risk stratification tools can be utilized in patients with POAF after CABG, albeit with higher threshold values compared to patients with non-surgical AF. The current OAC prescription pattern does not appear to reflect stroke risk. The risk-benefit of long-term OAC in patients with POAF following CABG remains to be established.