Anticoagulation therapy has been shown to reduce the risk of stroke in patients with AF by about two-thirds.
17-19 An evidence-based guideline
17 developed by the American College of Cardiology, American Heart Association, and European Society of Cardiology recommends that treatment selection be made on the basis of stroke risk stratification and bleeding risk assessment.
Stratification of stroke risk uses scoring systems—including CHADS
2 (congestive heart failure, hypertension, age ≥75 years, diabetes mellitus, and stroke or transient ischemic attack [2 points]) or CHA
2DS
2-VASc (addition of vascular disease, age 65 to 74 years, sex category)—and is an important first step in guiding selection of anticoagulation therapy (
Table 1 and
Table 2). These scores estimate risk by allocating points to patients on the basis of their past and current medical conditions. For example, CHADS
2 records factors such as history of prior stroke or transient ischemic attack, patient age, and presence of hypertension and diabetes mellitus. Risk is then categorized as low, moderate, or high.
20 The CHA
2DS
2-VASc score complements the CHADS
2 score by adding other “stroke risk modifier” factors: lower age bracket (65-74 years), female sex, and vascular disease. In addition, the CHA
2DS
2-VASc assigns an extra point if a patient is aged 75 years or older.
21
In November 2010, a scoring system to assess the risk of developing bleeding complications while receiving anticoagulation therapy was validated.
22 This system, called HAS-BLED (hypertension, abnormal renal/liver function, stroke, bleeding history or predisposition, labile international normalized ratio [INR], elderly [age >65 years], and drugs or alcohol), assigns 1 point to each component (
Table 3). Higher scores indicate a greater risk for a bleeding event while receiving anticoagulant therapy. An important issue to consider with HAS-BLED is the overlap of risk factors for both stroke and bleeding, wherein excessive focus on bleeding avoidance will result in failing to reduce stroke for patients at higher risk.
Historically, aspirin or vitamin K antagonists (eg, warfarin) have been the primary therapeutic options for the prevention of thromboembolism.
17 Aspirin, although modestly effective in reducing the risk of stroke for patients with AF, is inferior to warfarin and is reserved for patients at low risk for stroke.
17 Warfarin is highly effective, reducing the stroke risk for patients with AF by about two-thirds.
18,23 Yet, despite the well-established benefits of warfarin treatment, anticoagulant therapy is underused and is inconsistently prescribed for patients with AF, even if those patients are at highest risk for stroke.
24-28 In a systematic review,
28 25 of the 29 studies reported undertreatment (defined as treatment in less than 70% of high-risk patients) of AF patients with a history of stroke or TIA who were deemed eligible for oral anticoagulation therapy according to published guidelines. Even patients with a CHADS
2 score of 2 or higher were suboptimally treated.
A meta-analysis
29 of 8 studies assessed warfarin control among patients with AF and found that patients spent an average of only 55% of their time within the therapeutic INR range. However, when the data were stratified by treatment setting, the authors found that patients with AF receiving care in a community-based physician practice spent 11% less time within target INR range (ie, a lower limit INR between 1.8 and 2.0 and an upper limit INR between 3.0 and 3.5) compared with patients treated in a specialized anticoagulation clinic. Thus, fewer than half of patients with AF receiving warfarin are achieving and maintaining their target blood levels.