A better predictor of stroke risk in a-fib patients

Douglas Dawley, M.D.Douglas Dawley, M.D.
Cardiologist, Providence Heart and Vascular Institute

Published June 2011

As our population ages, the the prevalence of atrial fibrillation is expected to increase from 2.5 million to 12 million by 2050. While thromboembolism with a-fib accounts for only 15 to 20 percent of all strokes, the presence of paroxysmal or permanent a-fib increases the risk of a thromboembolic event five-fold.

Since a patient’s risk of a thromboembolism can vary depending on clinical factors, the challenge is to identify patients at sufficiently high risk to warrant the use of oral anticoagulants.

To date, we have used the CHADS2 score to risk stratify. A score of 0 defines low risk for a thromboembolic event; 2 or greater defines high risks, suggesting treatment with oral anticoagulants; and a score of 1 defines intermediate risk with no clear recommendations.

The Euro Heart Survey on Atrial Fibrillation refined CHADS2 by taking into account the additional risk in a-fib among women, patients with vascular disease and patients 75 or older.

This new predictor of a-fib risk – called CHA2DS2-VASc – was validated by a nine-year Danish nationwide registry study of more than 77,000 a-fib patients not on oral anticoagulants.

The study showed that CHA2DS2-VASc was a better predictor of a thromboembolic event than CHADS2 for all scores. CHA2DS2-VASc also found fewer patients – 8.7 percent – at very low risk than did CHADS2 (22.3 percent).

Compare the two scoring systems

Further, in patients with a risk score of 0, the rate of thromboembolic event-per-100-person-years was 1.67 with CHADS2 compared to 2.01 with CHA2DS2-VASc. In those with an intermediate risk score of 1, the thromboembolic event rate was 4.75 with CHADS2 and 2.01 with CHA2DS2-VASc.

These findings are clinically important because many patients at low to intermediate risk based on CHADS2 are not truly low risk, and treatment guidelines are not conclusive for those at intermediate risk.

In the CHA2DS2-VASc scoring system, being 75 or older, or having a prior stroke or TIA counts for 2 points, and automatically gives this patient a high score of 2.The chart therefore represents a somewhat simplified algorithm that may help a clinician decide whether to place a patient on oral anticoagulants.

Clinical articles by Douglas Dawley, M.D.