New-onset postoperative atrial fibrillation and nonvalvular atrial fibrillation have similar long-term thromboembolism risk for patients, according to research results published in JAMA Cardiology.

Researchers conducted an observational cohort study to assess the long-term risk for thromboembolism in patients who developed new-onset postoperative atrial fibrillation following isolated left-sided heart valve surgery compared with patients with nonsurgical, nonvalvular atrial fibrillation.

Patient data were pulled from a prospectively collected cardiac surgery database of patients who underwent cardiac surgery at Copenhagen University Hospital. All included patients were Danish residents 18 years or older who underwent first-time isolated left-sided heart valve surgery, either bioprosthetic aortic or mitral valve replacement and/or aortic mitral valve repair without concomitant cardiac surgical procedure, between January 2000 and June 2015. Included patients had no history of atrial fibrillation, developed postoperative atrial fibrillation, and had not redeemed an oral anticoagulant prescription in the 6 months prior to surgery.

In total, 1587 patients underwent first-time left-sided heart valve surgery during the study period. After applying exclusion criteria, 675 patients with postoperative atrial fibrillation were matched with 2025 patients with nonvalvular atrial fibrillation. Out of the total patients, there was 59.3% men (mean age 71; interquartile range [IQR], 65-77).


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In the postoperative atrial fibrillation group, 62.9% of patients initiated oral anticoagulation therapy (97.6% warfarin) within 30 days of the index date. In the nonvalvular atrial fibrillation group, 51.4% of patients initiated oral anticoagulation therapy within 30 days of the index date (73% warfarin).

During the study period, the investigators noted a steep increase in the crude proportion of patients receiving oral anticoagulation therapy after 2010 in the nonvalvular atrial fibrillation group; in the postoperative atrial fibrillation group, a decrease was noted.

In the postoperative group, 55% and 31.7% of patients who initiated oral anticoagulation therapy were in treatment at 3 and 6 months postdischarge, respectively; correspondingly, 81.5% and 81.8% of patients in the nonvalvular group were in treatment at 3 and 6 months postdischarge, respectively.

Investigators also measured thromboembolic events, recurrent atrial fibrillation, and all-cause mortality in both groups. The median follow-up time from the index date until the occurrence of a thromboembolic event, death, emigration, or the end of the study period was 4.2 years and 3.7 years in the postoperative and nonvalvular atrial fibrillation groups, respectively (IQR, 2-7.1 and 1.8-6.8). Crude incidence rates of thromboembolism were 21.9 and 17.7 events per 1000 person-years (95% CI, 17.4-27.6 and 15.2-20.6) in the postoperative and nonvalvular groups.

Crude incidence rates for recurrent atrial fibrillation were 118.9 and 358.3 events per 1000 person-years for both groups, respectively; a Cox regression analysis found that postoperative atrial fibrillation was associated with a “significantly lower risk” for recurrent atrial fibrillation compared with nonvalvular atrial fibrillation (hazard ratio, 0.62; 95% CI, 0.56-0.70).

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Similarly, crude incidence rates for all-cause mortality were higher in the nonvalvular atrial fibrillation group (68.9 per 1000 person-years) compared with postoperative atrial fibrillation (42.1 per 1000 person-years). A Cox regression analysis found that postoperative atrial fibrillation was also associated with a significantly lower risk for all-cause mortality.

Several sensitivity analyses yielded similar results to the main study findings.

Study limitations include the observational nature of the study, which precludes the assessment of cause-effect associations, as well as the possibility of residual confounding.

“The findings from these analyses do not necessarily indicate a clinical benefit of [oral anticoagulation] therapy in patients developing [postoperative atrial fibrillation],” the researchers concluded. “Rather, these findings underscore the need for future randomized clinical trials examining the effectiveness of [oral anticoagulation therapy] in [postoperative atrial fibrillation].”

Disclosure: Several study authors declared affiliations with the pharmaceutical industry. Please see the original reference for a full list of authors’ disclosures.

Reference

Butt JH, Olesen JB, Gundlund A, et al. Long-term thromboembolic risk in patients with postoperative atrial fibrillation after left-sided heart valve surgery [published online October 9, 2019]. JAMA Cardiol. doi:10.1001/jamacardio.2019.3649