Anticoagulation Therapy

Therapy for the prevention of thromboembolic complications in patients with AF has been studied extensively over the last several years. In the late 1980s and early 1990s, five randomized clinical trials clearly established the efficacy of warfarin to reduce the risk of stroke in patients with AF (48) (Fig. 2). Although the majority of patients enrolled in these trials had chronic AF, patients with paroxysmal AF benefited as well. The relative merits of warfarin therapy vs aspirin were examined in these and later trials. A superior benefit of warfarin compared with aspirin was established in these trials, especially in patient populations with clinical risk factors for stroke, other than AF itself. These risk factors were determined by the trials in "post hoc" analyses.

These clinical trials prompted the publication of practice recommendations by the American College of Chest Physicians (ACCP) in 1996 and most recently in 2001 (49). Today, there is no controversy regarding whether the majority of patients with AF should be anticoagulated. Rather, debate persists on how to best identify the subset of patients in whom the risks, expense, and inconvenience of anticoagulation outweigh the benefits. The group at lowest risk for thromboembolic events are young (<60-65 yr old) patients without clinical and echocardiographic risk factors for thromboembo-lism, as determined by the pooled data from the prevention trials. Risk factors for stroke include prior stroke/transient ischemic attack (TIA), hypertension, diabetes, CHF, an enlarged left atrium, mitral stenosis, hyperthyroidism, and a depressed left ventricular systolic function. The patients who are younger than 65 yr of age and free of all of these risk factors usually fall into the category of "lone" AF. Their risk of stroke appears to be similar to the general population (approx 1%/yr or less).

The patients at high risk of stroke are the elderly (>75 yr old) and those who are 60-75 yr old, with one or more of the other clinical or echocardiography risk factors. Their risk of stroke is, on average, approx 5% per yr, but it has been shown to be as high as 12% per yr in those with a prior history of stroke or transient ischemic attack. Unless there are clear contraindications to anticoagulation, such as bleeding diathesis, active gastrointestinal bleeding, and a propensity to falls or trauma (such as seizures, or gait disturbance), these patients should be anticoagulated with warfarin.

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