Anticoagulation at a CHA2DS2-VASc score of 1 in men or 2 in women has been a class IIa recommendation resting on observational data. SINGLE-AF tested it. This multicentre, open-label, adjudicator-masked trial in South Korea randomised 1,803 patients with atrial fibrillation at exactly that intermediate risk to a direct oral anticoagulant or to no anticoagulation. Mean age was 60.4 years and 23.7% were women — a young cohort, as the entry criteria require.
At 24 months the composite of stroke, systemic embolism, major bleeding or cardiovascular death occurred in 4 patients on a DOAC (cumulative incidence 0.5%) and 13 on no anticoagulation (1.5%), a difference of -1.0 percentage points (95% CI -2.0 to -0.1, p=0.03; hazard ratio 0.31, 95% CI 0.10 to 0.94). Stroke drove the difference: 3 events versus 10. Major bleeding and systemic embolism were similar between groups, and there were no cardiovascular deaths in either arm. Serious adverse events were 8.9% versus 9.3%.
The practical reading is that the guideline recommendation now has a trial behind it, and the trial found what the guideline assumed: a small absolute benefit, achieved without a bleeding penalty. The counting matters, though — 17 primary events in total across 1,803 patients. This is a low-event trial and the confidence interval reflects that.
What it does not license is anticoagulating everyone with a score of 1. It licenses the conversation. A patient with one risk factor and a low bleeding risk now has randomised evidence to weigh, rather than extrapolation from higher-risk cohorts. A patient with poor anticoagulation access or a high fall risk still has the same reasons not to.
- Offer a DOAC to patients with atrial fibrillation and a CHA2DS2-VASc of 1 in men or 2 in women, discussing an absolute benefit of about 1 percentage point over two years
- Reassure on bleeding: major bleeding rates were similar in both arms over 24 months
- Note the cohort was young (mean 60 years) and Korean; extrapolate to older or frailer patients with care
- Recount the score properly before deciding — female sex alone is the second point in women and does not itself trigger treatment
- Do not treat a single low-event trial as a reason to override an individual high bleeding risk
The statistics, in plain English
The hazard ratio of 0.31 sounds dramatic, and the confidence interval — 0.10 to 0.94 — shows why it should not be read as a precise estimate. Its upper limit sits just under 1.0, meaning the true effect could be anywhere from a 90% reduction to almost none. That width comes from having only 17 events in total. The absolute figures are the ones to quote to a patient: 1.5% down to 0.5% over two years. A trial this small can establish that a benefit exists; it cannot pin down its size.
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