Real value of warfarin therapy

FIRENZE, ITALY. Several strictly controlled clinical trials have shown that anticoagulation (warfarin) therapy reduces the risk of cardioembolic stroke in atrial fibrillation (AF) patients with one or more risk factors for stroke. The relative importance of these risk factors has been classified in such stroke risk schemes as the CHADS2 and CHA2DS2-VASc scores.

CHADS2 Score
CHA2DS2-VASc Score
Age 75 years or older - 1 point Congestive heart failure - 1 point
Hypertension - 1 point Hypertension - 1 point
Diabetes - 1 point Age 75 years or older - 2 points
Congestive heart failure - 1 point Age between 65 and 74 years - 1 point
History of stroke or TIA - 2 points History of stroke or TIA - 2 points
- Vascular disease - 1 point
- Diabetes mellitus - 1 point
- Female gender - 1 point

According to the latest guidelines, warfarin therapy is generally recommended for a total risk score of 2 or higher, while aspirin or warfarin is recommended for a risk score of 1, and no antithrombotic therapy for a score of 0. Inasmuch as thrombi (blood clots) in AF-related cardioembolic stroke are fibrin-rich rather than platelet-rich, the value of aspirin in the protection against cardioembolic stroke is regularly being questioned. The authors of the present report call for a “paradigm shift” to better identify truly lower-risk patients who would not require any antithrombotic therapy, while all other patients would be prescribed an anticoagulant.

A group of Italian researchers now report the results of a study aimed at determining the value of stroke risk classification schemes in actually predicting stroke risk in already anticoagulated AF patients. Their study included 662 AF patients (64% male) with an average age of 74 years. The study participants had several stroke risk factors such as hypertension (64%), previous stroke/TIA (31%), and coronary artery disease or heart failure (45%).

During the follow-up period of 3.6 years, a total of 32 thromboembolic events occurred corresponding to an annual incidence rate of 1.3%. Neither the CHADS2 nor CHA2DS2-VASc scores were particularly effective in predicting stroke risk since the only risk factor that actually did confer an increased risk of stroke (5.6-fold) was a previous history of stroke, TIA or other systemic embolism. Age, hypertension, diabetes, heart failure, female gender, and low left ventricular ejection fraction did no increase the risk of stroke in this elderly, anticoagulated group of AF patients. The authors conclude that current stroke risk scores have modest ability to predict stroke risk in anticoagulated patients.

Poli, D, et al. Stroke risk stratification in a “real-world” elderly anticoagulated atrial fibrillation population. Journal of Cardiovascular Electrophysiology, Vol. 22, January 2011, pp. 25-30
Boriani, G, et al. The challenge of preventing stroke in elderly patients with atrial fibrillation. Journal of Cardiovascular Electrophysiology, Vol. 22, January 2011, pp. 31-33

Editor’s comment: First off, it should be kept in mind that cardioembolic strokes constitute only about 15% of all strokes, so protecting against this form of stroke by no means guarantees that one will not suffer an ischemic or hemorrhagic stroke. It would seem that warfarin therapy is not adequate to protect afibbers with a history of TIA, stroke or other embolic events against a repeat of these. On the other hand, having diabetes, heart failure, hypertension, or being over the age of 75 years do not increase stroke/TIA risk in anticoagulated AF patients.