Long-term stroke risk is lower for postop AFib than for primary AFib

By Wayne Kuznar, for MDLinx
Published April 18, 2018

Key Takeaways

Patients who developed new-onset postoperative atrial fibrillation (POAF) following coronary artery bypass graft (CABG) surgery had lower long-term thromboembolic risk than patients who had nonsurgical nonvalvular atrial fibrillation (NVAF), according to findings from a retrospective study published online in JAMA Cardiology.

The study generated three major findings, according to the authors, led by Jawad H. Butt, MD, Copenhagen University Hospital, Denmark. The first is that 30.9% of patients who had CABG surgery developed new-onset POAF during hospitalization, and 8.4% of these patients began oral anticoagulant (OAC) therapy within 30 days of discharge. The second is that POAF was associated with a significantly lower risk of thromboembolism compared with NVAF. Finally, POAF was associated with a significantly lower risk of all-cause mortality and recurrent AF hospitalization than 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,” the researchers concluded.

Prior to this study, the incidence of POAF following CABG surgery was reported to be 11% to 40%. But there’s been no clear consensus on stroke prevention in patients with new-onset AF following CABG.

To address these issues, the researchers used a Danish clinical cardiac surgery database and nationwide registries to compare the initiation of OAC therapy and rates of thromboembolism in patients with new-onset POAF and those with NVAF.

They identified 7,524 patients who had undergone first-time isolated CABG surgery from January 1, 2000, through June 30, 2015. In this group, 2,324 patients developed new-onset POAF, and of these, 2,108 patients met inclusion criteria.

The POAF cohort was compared with 8,432 matched patients with nonsurgical NVAF who had been diagnosed during hospitalization or in an outpatient clinic. Patients were matched for age, sex, and CHA2DS2-VASc score. The mean CHA2DS2-VASc score was 3.1 on a scale of 0 to 9. The median age for all patients was 69.2 years, and 82.3% were men.

The median follow-up time from the index date until occurrence of a thromboembolic event, death, emigration, or end of the study was 5.1 years for patients with POAF and 3.5 years for patients with NVAF.

The crude rates of thromboembolism were found to be 18.3 per 1,000 person-years in the POAF cohort vs 29.7 events per 1,000 person-years for the NVAF group, indicating a significantly lower risk of thromboembolism in the POAF group compared with the NVAF group (adjusted hazard ratio [HR] 0.67, P < 0.001).

Within 30 days after discharge, 175 patients (8.4%) in the POAF cohort and 3,549 (42.9%) in the NVAF cohort began OAC therapy. Anticoagulation therapy during follow-up was associated with a lower risk of thromboembolic events in both POAF (adjusted HR 0.55, P=0.03) and NVAF (adjusted HR 0.59, P < 0.001) patients compared with patients who did not receive OAC therapy.

The rates of all-cause mortality and recurrent hospitalization were also lower in the POAF cohort. For all-cause mortality, crude incidence rates were 46.9 per 1,000 person-years in the POAF cohort vs 88.0 per 1,000 person-years in the NVAF cohort. For recurrent hospitalization for AF, the crude incidence rates were 19.9 vs 96.3 per 1,000 person-years in the two groups, respectively.

Existing guidelines from major societies are unclear whether POAF should be given the same consideration as NVAF in the decision to institute prophylaxis for subsequent stroke and thromboembolism, the authors noted.

“Although it may seem reasonable to initiate OAC therapy if the risk of thromboembolism outweighs the risk of bleeding in this setting, 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,” they wrote.

In an invited commentary, Jeff S. Healey, MD, MSc, and colleagues from McMaster University’s Population Health Research Institute, Hamilton, Ontario, Canada, wrote, “The results of this well-done study are complementary to prior work, conveying the same message that AF following cardiac surgery may pose a lower long-term risk of stroke than traditional clinical AF.”

Given these findings, what should clinicians do about anticoagulant therapy for patients with POAF?

There’s no definitive answer for that just yet, Dr. Healey and colleagues conceded. “A large clinical trial would be invaluable to help resolve this uncertainty,” they wrote. “Until such time, clinicians must use their best judgement regarding the need for long-term anticoagulation therapy.”

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