The relationship runs both ways; atrial fibrillation (AF) causes strokes, while strokes can trigger AF.
The relationship between AF and stroke runs both ways. On the one hand, AF markedly increases the risk of stroke and systemic embolism.6 For instance, AF increases stroke risk five-fold compared with people without the arrhythmia.2,6 The risk associated with AF is even higher in people with other stroke risk factors.20 Overall, AF may cause up to half of cardioembolic strokes and 10–30% of acute ischaemic strokes.4,11,19
On the other hand, strokes increase the likelihood of developing AF.21 In about a third of AF patients, the arrhythmia did not emerge until after the cerebrovascular event, despite being monitored for many months before the stroke.21 Indeed, 10% of patients with lacunar strokes have AF.21 Large-artery atherosclerosis is twice as common in AF patients as in people without the arrhythmia.21 This underscores the importance of routine long-term electrocardiogram (ECG) monitoring in all survivors of an ischaemic stroke without documented AF.5
Stroke risk does not seem to depend on AF severity: stroke risk with paroxysmal AF is the same as that with permanent or persistent AF.4 Even a brief episode of subclinical AF doubles the risk of stroke in older patients with vascular risk factors.21
Nevertheless, some patient groups seem to be especially vulnerable to developing AF-related strokes. For instance, stroke risk is 17 fold higher in AF patients with rheumatic mitral valve stenosis compared with people in sinus rhythm.4,11 Older people are at increased risk: 25% of all stroke in people older than 80 years occur in AF patients.2 Women are also at higher risk of experiencing a cardioembolic stroke from AF compared with men (Figure 4).6,22
The Copenhagen City Heart Study followed 29,310 subjects for a mean of 4.7 years. Of these, 110 women and 166 men had documented AF. After adjusting for age and co-morbidities, AF was 4.6 times more strongly associated with stroke in women (hazard ratio [HR] 7.8) compared with men (HR 1.7). Similarly, AF was 2.5 times more strongly associated with cardiovascular mortality in women (hazard ratio [HR] 4.4) compared with men (HR 2.2).22
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