In people with AF, the atria's rapid, irregular beat moves blood inefficiently, and the blood inside the chambers tends to form clots. These clots can break loose and travel through the bloodstream to the brain, where they become lodged in an artery, causing a blocked-vessel (ischemic) stroke.
Illustration showing how atrial fibrillation can cause a blocked-vessel (ischemic) stroke. The blood clot travels from the heart to the brain where it blocks blood flow to part of the brain. Source: NHLBI
What impact does atrial fibrillation have on my stroke risk?
AF is responsible for 15% to 20% of all strokes. It increases the risk of a first stroke 3- to 4-fold,2, 4 and doubles the risk of a recurrent stroke.8 The stroke risk is the same whether the AF is persistent or paroxysmal (comes and goes).9
Several studies have found that AF is a more important stroke risk factor in women than in men.10, 11 In one observational study of 1581 patients (half were women) who had experienced a first stroke, women were almost twice as likely to have had AF that preceded the stroke (31% versus 19% of men).12
If you have AF, your personal stroke risk varies widely based on other conditions you may have: doctors use a formula called the CHADS2 score to determine your approximate risk. To find out your stroke risk, add up all your CHADS2 points in Table 1 below, and then look up your corresponding yearly stroke risk in Table 2.
|Table 1: CHADS2 Score13, 14|
For Predicting Stroke Risk in Patients with AF
|Systolic blood pressure higher than 160 mm Hg||+1|
|Being 75 years or older||+1|
|Previous Stroke or TIA||+2|
|Table 2: Your Stroke Risk|
|CHADS2 Score||Risk Level||Yearly Stroke Risk|
|1||Low to Moderate||1.5%|
|4, 5, or 6||Very High||More than 7%|
|*If you have had a stroke or TIA you are considered to be at high risk, even if you have no other risk factors|
In addition to increasing your chances of stroke, AF also tends to make strokes more severe: one study found that people with AF who had a stroke were more than twice as likely to be bedridden than those who had strokes from other causes.15