How to Calculate Your Chance of Stoke If You’ve Been Diagnosed With Afib?

Atrial fibrillation (afib) is among the most common heart rhythm irregularities. During a bout of afib, the usually rhythmic contractions of the heart muscle’s upper chambers (the atria) are replaced by an ineffectual quiver that does not completely move blood out of the heart chamber. As a result, blood can stagnate and form clots. These clots can then travel to the brain and cause an ischemic stroke.

More than one in six ischemic strokes can be traced to atrial fibrillation. In people ages 80 and older, the proportion jumps to one in three. What’s more, strokes that stem from afib-related clots carry a higher risk of permanent brain damage or death than other ischemic strokes do, says Dr. Robert Giugliano, associate professor of medicine at Harvard-affiliated Brigham and Women’s Hospital.

Calculating stroke risk
Because many strokes could be averted by detecting and treating afib, doctors have refined their efforts to forecast who should get anticoagulants to lower stroke risk. For people who’ve had at least one episode of afib, doctors have long used a tool known as the CHADS2 score. But a new, expanded system includes additional factors that affect a person’s risk, called the CHA2DS2-VASc score (the name is an acronym for all the factors; see table at right). The additions include vascular disease (the presence of narrowed arteries anywhere in the body), a new age category, and sex.

Anticlotting drugs
Drugs that help prevent blood clots—known as anticoagulants or blood thinners—include warfarin (Coumadin) and several newer medications, including apixaban (Eliquis), dabigatran (Pradaxa), edoxaban (Savaysa), and rivaroxaban (Xarelto). Warfarin requires frequent blood tests and possible dose adjustments, and it also interacts with certain foods and drugs. The newer drugs don’t have those same downsides. And while all anti-clotting drugs increase the risk of serious internal bleeding, the newer drugs are less likely than warfarin to cause the most serious type (brain bleeding).

Preventing stroke
With the new system, the scores can range from 0 to 9. Doctors typically treat people who have a CHA2DS2-VASc score of 2 or higher. “However, studies show that only about half the people who should take anticoagulants receive them,” says Dr. Giugliano. There’s also an ongoing debate about treating people who have a score of 1, he notes. In this situation, current guidelines from the American College of Cardiology, the American Heart Association, and the Heart Rhythm Society leave it to the doctor to choose between aspirin, an anticoagulant drug, or no medication at all. But the European guidelines recommend anticoagulants for these people. In the last year, a flurry of new reports found that people in this seemingly low-risk category actually have a higher rate of strokes than previously thought—and fare better if they take anti-clotting medicines.

If you’ve ever had an episode of afib, talk to your doctor about monitoring and treatment options, advises Dr. Guigliano. Many times, afib occurs without symptoms, so you could be having repeated periods of heartbeat irregularity without knowing it. Your doctor may suggest that you use a portable heart rate monitor for a period of time to help detect silent afib. “Now that we have anticoagulants that are safer, easier to use, and more effective, we’re in a better position to provide a proven therapy to more people who are at risk for stroke,” concludes Dr. Giugliano.

Evaluating stroke risk if you have afib: The CHA2DS2-VASc score

Congestive heart failure: Signs and symptoms of heart failure + 1 point
Hypertension: Resting blood pressure over 140/90 mm Hg on at least two occasions or currently taking blood pressure + 1 point
Age: 75 years or older + 2 points
Diabetes: Fasting glucose over 125 mg/dL or taking medication
for diabetes
+ 1 point
Stroke, ministroke, or a blood clot in the lung, leg, or elsewhere in
the body; includes any history of lack of blood flow to the brain
+ 2 points
Age: 64 to 74 years + 1 point
Sex category: Females face a higher risk than males + 1 point
Source: Chest, February 2010, pp. 263–72.