A trial of 1,803 atrial fibrillation patients found that a common class of blood thinner cut serious complications by 69% compared with no treatment at all, results Yonsei University cardiologist Boyoung Joung presented to the European Society of Cardiology’s 2026 congress. The SINGLE-AF trial targeted a group doctors have long argued over: people with AFib whose stroke risk sits in the middle, too elevated to ignore but historically judged too low to justify committing them to lifelong anticoagulation.
Patients randomized to a direct oral anticoagulant, either apixaban twice daily or rivaroxaban once daily, saw a composite of stroke, systemic embolism, major bleeding or cardiovascular death in just 0.5% of cases over 24 months, against 1.5% for patients who received no blood thinner at all. Joung’s team ran the study across 18 South Korean medical centers, enrolling adults with a CHA2DS2-VASc score of 1 in men or 2 in women — the formal cutoff separating intermediate stroke risk from the higher-risk patients guidelines already tell doctors to anticoagulate.
Why a CHA2DS2-VASc score of 1 or 2 has divided cardiologists
Current guidance is unambiguous for AFib patients with high CHA2DS2-VASc scores: anticoagulate. It goes quiet for the tier just below that, where a single risk factor such as age, diabetes or vascular disease pushes a patient’s score to 1 or 2 without triggering the same automatic recommendation. Existing guidelines rate anticoagulation for that group only a “class IIa” recommendation, according to the trial’s own published protocol, meaning doctors are told treatment is reasonable rather than required. That soft wording has produced years of inconsistent practice: some cardiologists prescribe DOACs preemptively at the first single risk factor, others wait for a second one to appear before committing a patient to years of blood thinners, and the resulting variation across clinics is exactly what an investigator-initiated trial with blinded outcome assessment, run across 18 centers, was designed to settle.
Joung’s trial is the first randomized evidence built specifically for that gap. In the European Society of Cardiology’s release on the results, he said the trial now provides randomized evidence that patients with AFib at intermediate stroke risk benefit from DOAC therapy without an accompanying rise in major bleeding, framing the finding as filling a hole in the guidelines rather than overturning existing high-risk recommendations.
Ischemic stroke fell to 0.1%, and bleeding did not rise to match it
The stroke-specific numbers were the sharpest split in the data: ischemic stroke occurred in just 0.1% of patients on DOAC therapy compared with 1.1% of those receiving no anticoagulant, according to the trial results reported by ScienceDaily. In absolute terms, the American College of Cardiology’s own summary of the ESC Hot Line session put that at three stroke cases in the treatment arm against ten in the untreated arm.
What makes that gap meaningful rather than merely dramatic is what happened to bleeding, the standard tradeoff clinicians weigh before prescribing a blood thinner to anyone. Major bleeding occurred in 0.3% of DOAC patients versus 0.5% of those without anticoagulation — numerically higher in the untreated group, not the treated one. Stopping strokes at that rate without a matching rise in bleeding complications is the exact profile a trial needs to shift a cautious prescribing habit.
A caution built into the same data that produced the 69% figure
The 69% relative risk reduction translates to a hazard ratio of 0.31, calculated from a 95% confidence interval running from 0.10 to 0.94 — a wide range for a headline number, and one the trial’s own investigators flagged. Results, they said, should be interpreted with caution given a lower-than-expected number of endpoint events and a total patient count smaller than some earlier AFib anticoagulation trials.
ESC discussant Paulus Kirchhof captured the mixed verdict cardiologists are likely to reach from the data. Anticoagulation in patients with AFib and a single stroke risk factor “may be encouraged” by the findings, he said, while adding that in patients with a low AFib burden, no therapy may still be preferred, and that future treatment options could change the calculation further.
South Korea’s Ministry of Health and Welfare funded the trial alongside drugmakers Samjin Pharmaceutical and Hanmi Pharmaceutical. It also ran the same day in the New England Journal of Medicine.
What happens next for intermediate-risk guidelines
Joung’s team has been explicit that the goal is guideline change, not just publication. The European Society of Cardiology’s release states the findings “may be used to inform future guideline recommendations and reimbursement policies” for exactly the patient tier SINGLE-AF studied — those sitting just above the threshold where doctors currently feel free to wait.
No society has yet revised its formal guidance in response, and Kirchhof’s caveat about a still-developing treatment landscape suggests any change will not be automatic. For now, the trial leaves cardiologists with a specific number to weigh against a specific gap in the rules: a 69% drop in serious events, measured in patients guidelines have not yet told anyone what to do with.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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