Patients with atrial fibrillation who have experienced a stroke would benefit greatly from earlier treatment than is currently recommended in current UK guidelines, finds a new study led by UCL (University College London) researchers.
The results of the CATALYST study, published in The Lancet, included data from four randomised trials with a total of 5,441 patients across the UK, Switzerland, Sweden and the United States, who had all experienced a recent stroke (between 2017-2024) due to a blocked artery and atrial fibrillation (irregular heartbeat).
Patients had either started medication early (within four days of their stroke) or later (after five days or more).
The researchers found that starting direct oral anticoagulants (DOACs, which thin the blood to prevent it from clotting as quickly) within four days of having a stroke was safe, with no increase in bleeding into the brain. Additionally, early initiation of treatment significantly reduced the risk of another stroke due to bleeding or artery blockage by 30% compared to those who started treatment later.
Atrial fibrillation is a heart rhythm disturbance that affects many people as they get older. It results in an irregular heartbeat, which can lead to a clot forming inside the heart. This clot can travel to the brain, blocking its blood supply and causing a stroke.
More than 1.6 million people in the UK have been diagnosed with atrial fibrillation – and they are five times more likely to have a stroke than people without atrial fibrillation. People with atrial fibrillation who have had a stroke have an increased risk of having another stroke, but this risk can be reduced by taking anticoagulants.
However, anticoagulants come with the rare but dangerous side effect of bleeding into the brain, and there is a lack of evidence about when is best to start taking them after a stroke. Current UK guidelines are varied, suggesting that those who have had a moderate or severe stroke should wait at least five days before starting blood thinning treatments.
To tackle this question, the researchers investigated the impact of early compared to delayed anticoagulant treatment.
Chief Investigator, Professor David Werring (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."
The researchers now hope that their findings will influence clinical guidelines and improve outcomes for stroke patients worldwide.
First author and main statistician, Dr Hakim-Moulay Dehbi (UCL 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."
The CATALYST study builds on findings from the British Heart Foundation funded OPTIMAS study – where the UCL-led research team analysed 3,621 patients with atrial fibrillation who had had a stroke between 2019 and 2024, across 100 UK hospitals.
Half of the participants began anticoagulant treatment within four days of their stroke (early), and the other half started treatment seven to 14 days after having a stroke (delayed). Patients were followed up after 90 days to assess several outcomes including whether they went on to have another stroke and whether they experienced bleeding in the brain.
Both the early and late groups experienced a similar number of recurrent strokes. Early treatment was found to be effective and did not increase the risk of a bleed into the brain.
Professor Nick Freemantle, Senior Investigator and Director of the UCL Comprehensive Clinical Trials Unit (CCTU) that co-ordinated the OPTIMAS trial, said: "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 is funded by the British Heart Foundation and by a Swiss National Science Foundation grant. It is supported by the National Institute for Health and Care Research UCLH Biomedical Research Centre.
Professor Bryan Williams OBE, chief scientific and medical officer at the British Heart Foundation, commented: "Doctors must strike a delicate balance between acting fast and avoiding potentially harmful side effects when treating people with atrial fibrillation who have had a stroke and require anticoagulants – blood-thinning medications.
"This study, including data from more than 5,000 patients across four randomised trials, provides further evidence that taking these blood-thinning medications within the first few days of a stroke does not carry an increased risk of bleeding into the brain.
"This kind of evidence is really important and could be transformative, as it should allow people to have treatment earlier, to prevent people with atrial fibrillation having another stroke."
Study limitations
The timing for starting blood-thinning medication was based on previous trial designs (such as OPTIMAS), which may not cover all possible scenarios.
Additionally, not all participants were randomised to the same timing groups, so some data was excluded.
Lastly, the study didn't include many patients with very severe strokes, so the findings might not apply to those cases.
