For anyone living with atrial fibrillation — or caring for someone who does — stroke is the fear that sits quietly in the background. AF is the most common heart rhythm disorder in the UK, affecting around 1.5 million people according to the British Heart Foundation, and the Stroke Association says it is linked to around one in five strokes in this country.
Now a new randomised trial has produced the first evidence of its kind that a group of AF patients whose treatment guidance has been less clear-cut could benefit from taking modern blood thinners.
What the trial found
The SINGLE-AF trial, presented at the European Society of Cardiology (ESC) Congress 2026 in Munich and published simultaneously in the New England Journal of Medicine, looked at people with AF classed as being at "intermediate" risk of stroke. Doctors estimate stroke risk using a checklist called the CHA2DS2-VASc score, which adds points for factors such as age, high blood pressure, diabetes and existing heart problems. In this trial, intermediate risk meant a score of 1 for men or 2 for women.
People at high risk are already strongly recommended blood thinners. For those at intermediate risk, ESC guidelines say anticoagulants "should be considered" — a softer recommendation, because earlier observational studies produced mixed results.
Researchers at 18 medical centres in South Korea, led by Professor Boyoung Joung of Yonsei University in Seoul, randomly assigned 1,803 people either to take a modern blood thinner — apixaban or rivaroxaban, known as direct oral anticoagulants or DOACs — or to take no anticoagulant at all.
After two years, serious events — a combined measure of stroke, dangerous clots elsewhere in the body, major bleeding and death from heart-related causes — had occurred in 1.5% of patients who weren't on blood thinners, compared with 0.5% of those who were. That's where the "69% reduction" comes from: it is a relative comparison between two small numbers (a hazard ratio of 0.31), not a claim that seven in ten patients avoided a stroke.
Put simply: for every 1,000 patients in the trial, roughly 15 in the untreated group had a serious event over two years, compared with about 5 in the treated group — a difference of around 10 people per 1,000.
Because the number of events was small, that estimate carries a wide margin of uncertainty. The statistical range around the headline figure runs from roughly a 6% reduction to a 90% reduction, so the true size of the benefit could be smaller — or larger — than 69%.
The benefit was driven mainly by fewer strokes caused by blood clots. Ischaemic stroke occurred in 0.1% of patients taking blood thinners, against 1.1% of those who weren't.
The bleeding question
Blood thinners always involve a trade-off: they reduce clotting, but that can also raise the risk of bleeding. That is exactly why treating intermediate-risk patients has been debated for years.
Encouragingly, the trial found no increase in major bleeding: 0.3% of patients on blood thinners had a major bleed, compared with 0.5% of those who weren't. That is reassuring, though the numbers are small and the trial followed people for two years, not a lifetime.
What this means for guidelines — and for patients
Professor Joung said: "We now have evidence from a randomised trial that patients with AF at intermediate stroke risk benefit from DOAC therapy, without an increase in major bleeding. Data from the SINGLE-AF trial may be used to inform future guideline recommendations and reimbursement policies."
Guidelines haven't changed yet, and there are good reasons for caution before they do. Every participant was treated in South Korea, and patients' underlying risks of stroke and bleeding — as well as how they are cared for — can vary between countries and populations, so the results may not translate exactly to the UK. The trial was also "open-label", meaning patients and doctors knew who was taking a blood thinner, and it was relatively modest in size. Further studies in other populations will help show how widely the findings apply.
If you or someone you care for has AF, this is genuinely encouraging news — but it isn't a signal to change medication on your own. Whether a blood thinner is right for you depends on your individual stroke risk, bleeding risk and other health conditions. Anyone with questions about their treatment, or wondering whether they should be on one, should talk to their GP or cardiologist.
