New-onset atrial fibrillation after coronary artery bypass grafting (CABG) surgery was associated with a lower, long-term thromboembolic risk than seen with nonsurgical, nonvalvular AF (NVAF), an observational study found.
The risk of thromboembolism — ischemic stroke, transient cerebral ischemia, and thrombosis or embolism in peripheral arteries — was lower in the postoperative AF (POAF) group than in the NVAF group (18.3 versus 29.7 events per 1,000 person-years; adjusted HR 0.67, 95% CI 0.55-0.81, P<0.001), Jawad Butts, MD, of Rigshospitalet Copenhagen University Hospital, and colleagues reported online March 28 in JAMA Cardiology.
This lower risk was despite substantially lower initiation of oral anticoagulation therapy within 30 days post-discharge in POAF (8.4%) compared with NVAF (42.9%).
In fact, patients who developed POAF following CABG had a statistically similar risk for vessel obstruction due to blood clots as patients who remained in sinus rhythm (adjusted HR 1.11, 95% CI 0.94-1.32, P<0.24).
The study is among the first to examining the long-term risk of thromboembolism associated with POAF following CABG, which occurs in 11% to 40% of patients, according to the researchers.
“Our data do not support the notion that new-onset POAFs should be regarded as similar to primary NVAF in terms of long-term thromboembolic risk,” wrote
The researchers noted that while oral anticoagulation clearly reduces stroke and systemic embolism risk in patients with NVAF, “data on stroke prophylaxis in new-onset POAF after CABG are lacking, and international guidelines on the management of patients with AF do not provide clear recommendations on this issue.”
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=0.03) and NVAF (adjusted HR, 0.59, 95% CI, 0.51-0.68; P<0.001) compared with patients who did not receive any anticoagulation therapy.
However, “no causal inferences can be made from the analysis on the effectiveness of oral anticoagulation (OAC) therapy for the prevention of thromboembolism in the two cohorts, although these data suggest that therapy is associated with a similar lower thromboembolic risk among groups,” the researchers cautioned.
Butts and colleagues used data from a clinical cardiac surgery database and nationwide patient registries in Denmark to identify patients undergoing first-time CABG surgery who developed new-onset POAF during a 15-year period beginning in 2000.
Each of those patients was matched by age, sex, CHA2DS2-VASc score and year of diagnosis to four patients with nonsurgical NVAF. In all, 2,108 post CABG patients who developed POAF were matched with 8,432 patients with NVAF.
Study limitations included the possibility of residual confounding associated with the observational design.
The study is not the first to suggest that new-onset AF following cardiac surgery poses a lower risk for stroke than traditional AF. Separate research published in 2014 by Whitlock et al. and Gialdini et al. also showed a lower risk for blood clots and stroke in patients who developed POAF.
The findings “have important implications for how clinicians should treat patients with this common problem,” Jeff Healey, MD, of McMaster University, Ontario, Canada, and colleagues, wrote in an invited commentary published with the study.
“It is likely that some AF following cardiac surgery is indeed transient and caused by inflammation, while in other cases, it is typical clinical AF in an at-risk individual that happens to receive a diagnosis for the first time in the postoperative setting,” they wrote, adding that it is not yet possible to distinguish between the two groups.
They concluded that given the observed lower risk for stroke associated with POAF in the three cohort studies and the low rate of oral anticoagulant use in the post-CABG AF setting, “there is clinical equipoise regarding the need for long-term oral anticoagulation therapy in this setting.”
“A large clinical trial would be invaluable to help resolve this uncertainty. Until such time, clinicians must use their best judgment regarding the need for long-term anticoagulation therapy,” they wrote.
The researchers reported no funding source nor disclosures of conflict of interest within the scope of this study.
Healey disclosed research grants from Bristol-Myers Squibb and Pfizer.
F. Perry Wilson, MD, MSCE Assistant Professor, Section of Nephrology, Yale School of Medicine and Dorothy Caputo, MA, BSN, RN, Nurse Planner