Anticoagulation in atrial fibrillation at intermediate stroke risk

Design

Randomised, open-label, adjudicator-masked superiority trial

Population

1,803 Korean adults with AF and CHA2DS2-VASc 1 (men) or 2 (women)

Primary outcome

Stroke, systemic embolism, major bleeding or cardiovascular death at 24 months

Effect

0.5% vs 1.5%; HR 0.31 (95% CI 0.10–0.94)

SINGLE-AF, published in NEJM on 28 August, is the first randomised trial of anticoagulation in atrial fibrillation (AF) at intermediate risk — a CHA2DS2-VASc score of 1 in men or 2 in women. US and European guidelines give anticoagulation a class IIa recommendation here without trial evidence.

The open-label trial randomised 1,803 patients in South Korea, mean age 60, to a direct oral anticoagulant (DOAC) or no anticoagulation. Over 24 months the composite of stroke, systemic embolism, major bleeding or cardiovascular death occurred in 0.5% with a DOAC and 1.5% without — a hazard ratio of 0.31. Strokes numbered 3 against 10. Major bleeding appeared similar, and serious adverse events were 8.9% against 9.3%.

The direction supports the guideline's existing lean towards treatment. But the trial rests on 17 events, so the true effect is uncertain, and it enrolled a relatively young East Asian population with few women. The decision remains a shared one; this trial gives that conversation a randomised number.

• At CHA2DS2-VASc 1 (men) or 2 (women), a DOAC reduced the composite outcome from 1.5% to 0.5% over two years
• Major bleeding was not visibly higher with a DOAC in this trial
• Recalculate the score at each review; risk at this level rises with age
• Discuss the absolute numbers: about one event prevented per 100 patients treated for two years
• Guidelines already lean towards treatment here; this trial supports that, not a new rule

Why it matters

It turns a guideline recommendation built on observational data into one with a trial behind it.

Don't overread it

Only 17 primary events in total, so the size of the benefit is very uncertain.

The statistics, in plain English

A hazard ratio of 0.31 with a 95% CI of 0.10 to 0.94 is compatible with anything from a 90% reduction to almost none. The absolute difference of 1.0 point (CI 0.1 to 2.0) translates to treating about 100 people for two years to prevent one event.

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