Postoperative A-fib Not as Bad as Nonsurgical A-fib for Thromboembolism

Patients who develop postoperative A-fib (POAF) after CABG have a lower long-term thromboembolic risk than do patients with nonvalvular A-fib that is not related to recent surgery, a retrospective cohort study shows. The findings have important implications for the medical management of patients when POAF occurs, researchers say.

The combined rate of ischemic stroke, transient cerebral ischemia, and thrombosis or embolism in peripheral arteries through several years of follow-up was a relative 33% lower in patients with POAF (18.3 vs 29.7 events per 1,000 person-years; adjusted HR 0.67; 95% CI 0.55-0.81), according to researchers led by Jawad Butt, MD (Rigshospitalet, Copenhagen University Hospital, Denmark).

Risks of all-cause mortality and recurrent hospitalization for A-fib also were lower in patients whose A-fib developed after surgery, they report in a study published online March 28, 2018, ahead of print in JAMA Cardiology.

“Our study suggests that POAF should not be regarded as equivalent to primary [nonvalvular A-fib] in terms of long-term thromboembolic risk,” Butt told TCTMD in an email, noting, too, that the results show that long-term risk is not higher in patients who do versus do not develop A-fib after CABG.

“The main clinical implication of our study is that long-term [oral anticoagulation] therapy may not necessarily be warranted in all patients developing POAF in the setting of cardiac surgery,” he said.

Commenting for TCTMD, Atul Verma, MD (Southlake Regional Health Center, Newmarket, Canada), said the study fills a gap in that it is one of the first—if not the first—to examine the effect of oral anticoagulation in this setting.

Although anticoagulation was associated with lower event rates both in patients with POAF and in those with nonsurgical A-fib, whether patients with POAF should be anticoagulated remains an open question, Verma added. He pointed out that the impact of such therapy is less in patients with POAF because of the lower event rates and that there was no difference in thromboembolic risk between patients who did develop A-fib after surgery and those who did not in this study.

“It suggests that oral anticoagulation may provide some benefit, but the magnitude of that benefit is still unclear from this paper,” Verma said, noting that bleeding is always a concern with oral anticoagulation. “This study, while adding to our information, is far from definitive and lays the groundwork for a properly designed randomized trial.”

A Common Problem

POAF is a frequent complication of CABG—occurring in 11% to 40% of cases—that has recently been associated with heightened risks of stroke and mortality and prolonged hospital stays. There is not much information available regarding long-term thromboembolic outcomes in these patients, however, and the studies that have been done have not taken into account use of oral anticoagulation during follow-up.

For their study, Butt et al looked at data from the clinical cardiac surgery database at their center and from Danish nationwide registries. The analysis included 2,108 patients who underwent first-time, isolated CABG between January 2000 and June 2015 and developed new-onset A-fib after surgery. They were matched in a 1:4 ratio by age, sex, CHA2DS2-VASc score, and year of diagnosis to 8,432 patients with nonsurgical A-fib.

Despite the fact that predicted stroke risk was similar in both groups (mean CHA2DS2-VASc score 3.1) and that patients with postoperative versus nonsurgical A-fib were less likely to initiate oral anticoagulation within 30 days (8.4% vs 42.9%), rates of adverse outcomes were lower over the long term in patients with POAF. Those findings were consistent in various sensitivity analyses.

Use of oral anticoagulation during follow-up was associated with a lower risk of thromboembolic events both in patients with POAF (adjusted HR 0.55; 95% CI 0.32-0.95) and in those with nonsurgical A-fib (adjusted HR 0.59; 95% CI 0.51-0.68), but it was only tied to a lower mortality risk in the latter group.

In the analysis confined to patients who underwent CABG, those who did versus did not develop POAF lacked a higher risk of thromboembolism but did carry greater risks of all-cause mortality and rehospitalization for A-fib.

Should You Anticoagulate?

US and European guidelines don’t provide firm guidance on how best to manage patients who develop POAF after cardiac surgery, but they state that it’s reasonable to give antithrombotic medications in this setting.

Though oral anticoagulation may make sense for these patients if the risk of thromboembolism outweighs the risk of bleeding according to established risk assessment tools, Butt et al write, “it is important to keep in mind that this recommendation is based on low-quality evidence and also that these risk stratification scores have not been validated in surgical patients.”

More studies, ideally randomized, are needed to evaluate the potential role of oral anticoagulation for POAF, they add.

In an accompanying commentary, Jeff Healey, MD (Population Health Research Institute, McMaster University, Hamilton, Canada), and colleagues point out that prior studies agree with this one in showing that POAF carries a lower long-term risk of stroke compared with clinical A-fib. This, they say, has implications for treatment.

“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. Identifying this latter group who may be at higher risk of AF recurrence and stroke is not yet possible and should be a priority,” they write.

The editorialists say that there is clinical equipoise regarding the question of whether patients with POAF should be started on oral anticoagulation. “A large clinical trial would be invaluable to help resolve this uncertainty,” they say. “Until such time, clinicians must use their best judgment regarding the need for long-term anticoagulation therapy.”