Stroke patients with irregular heart rhythm could benefit from starting blood-thinning treatment within four days, rather than waiting as current UK guidelines often advise.
Researchers found that early use of direct oral anticoagulants (DOACs) – drugs that help prevent blood clots – reduced the risk of a second stroke due to bleeding or artery blockage by 30 per cent compared to starting after five days or more.
Crucially, early treatment was safe and showed no increase in bleeding into the brain.
The findings come from the CATALYST study, which analysed data from four randomised clinical trials involving 5,441 patients in the UK, Switzerland, Sweden and the US who experienced a recent stroke between 2017 and 2024.
All participants had atrial fibrillation and had suffered strokes caused by blocked arteries.
Professor David Werring, chief investigator from UCL Queen Square Institute of Neurology, said: “Our new study supports the early initiation of DOACs in clinical practice, offering better protection against further strokes for a wide range of patients.”
Atrial fibrillation is a common heart rhythm disorder that affects more than 1.6 million people in the UK.
It increases the risk of stroke fivefold by allowing clots to form in the heart, which can then travel to the brain and block blood flow.
While DOACs can reduce the risk of further strokes, they carry a rare risk of brain haemorrhage.
Current UK guidance often recommends waiting at least five days after a moderate or severe stroke before starting anticoagulant treatment.
The study, led by University College London (UCL), compared outcomes between patients who began DOACs within four days of stroke onset and those who started five days or later.
The findings build on the OPTIMAS trial, funded by the British Heart Foundation, which included 3,621 patients with atrial fibrillation who had strokes between 2019 and 2024 across 100 UK hospitals.
Half began anticoagulant treatment within four days, while the rest started between seven and 14 days.
Both early and delayed groups experienced a similar number of recurrent strokes. Early treatment was found to be effective and did not increase the risk of bleeding into the brain.
Dr Hakim-Moulay Dehbi, first author and main statistician at UCL’s Comprehensive Clinical Trials Unit, said: “By systematically combining the data from four clinical trials, we have identified with increased confidence, compared to the individual trials, that early DOAC initiation is effective.”
Professor Nick Freemantle, senior investigator and director of the UCL unit coordinating the OPTIMAS trial, added: “The benefits of early initiation of blood-thinning treatment are clear: patients receive the definitive and effective long-term stroke prevention therapy promptly, rather than waiting.
“This approach ensures that crucial treatments are not delayed or missed, particularly for patients who are discharged from the hospital.”
The CATALYST collaboration received funding from the British Heart Foundation and the Swiss National Science Foundation, with support from the National Institute for Health and Care Research UCLH Biomedical Research Centre.