Most breakthrough ischaemic stroke/TIA events on oral anticoagulation were either associated with anticoagulant under-exposure or a competing mechanism rather than anticoagulant failure.
The majority of breakthrough IS/TIA events in AF patients on oral anticoagulation were adjudicated as cardioembolic in mechanism.
Cardioembolic aetiology was associated with lower rates of good anticoagulant control compared to non-cardioembolic events.
Peri-event missed or under-dosing was significantly more common in cardioembolic than non-cardioembolic events.
Cardioembolic events were associated with younger patients compared to non-cardioembolic events.
The study design involved cross-sectional analysis with standardised adjudication of IS/TIA mechanism in a community-based stroke cohort.
This research examined why some people with atrial fibrillation (an irregular heart rhythm that increases stroke risk) still have strokes or mini-strokes (TIAs) even when they are taking blood-thinning medications (anticoagulants). The study looked at 179 patients in Auckland, New Zealand, who had a stroke or TIA while supposedly on anticoagulation therapy. It found that in 77% of cases, the stroke was caused by a blood clot originating from the heart (cardioembolic), while the remaining 23% had other underlying causes unrelated to AF. Importantly, the research found that most of the cardioembolic strokes were linked to patients not taking their medication consistently or missing doses around the time of the event — rather than the medication simply failing to work when taken correctly. Patients with cardioembolic strokes were more likely to have poor medication adherence (63% had good control vs. 83% in the non-cardioembolic group) and were more likely to have missed or under-dosed their anticoagulant in the days around the stroke (65% vs. 44%). When patients had good medication control, they were nearly four times more likely to have a non-cardioembolic (non-AF-related) cause for their stroke. This research suggests that when a person on anticoagulation has a stroke, clinicians should carefully investigate whether the medication was being taken as prescribed before assuming the drug has failed. Many so-called 'breakthrough' strokes may actually reflect gaps in medication adherence rather than true treatment failure. This distinction matters because the appropriate strategy to prevent future strokes differs depending on the underlying cause — reinforcing medication adherence may be more important than simply switching or intensifying anticoagulant therapy in many patients.
Mahawish K, Feigin V, Krishnamurthi R, White H. (2026). Mechanisms of ischaemic strokes and transient ischaemic attacks despite oral anticoagulation in patients with atrial fibrillation.. The New Zealand medical journal. https://doi.org/10.26635/6965.7380