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A primary goal in the management of patients with atrial fibrillation is the prevention of stroke. Patients with atrial fibrillation are about 5 times more likely to have a stroke than patients without atrial fibrillation. Approximately 60,000 cases of stroke attributed to atrial fibrillation occur in the United States each year. A major risk factor of stroke associated with atrial fibrillation is advancing age. The estimated risk of stroke in patients with atrial fibrillation in relation to age is as follows:

• 50-59 age group = 1.5%
• 60-69 age group = 2.8%
• 70-79 age group = 9.9%
• 80-89 age group = 23.5%

In addition to advancing age, doctors have identified other significant risk factors for stroke associated with atrial fibrillation and have developed a stroke risk stratification system. This stroke risk stratification system groups patients into the following three risk categories:

• High stroke risk
• Intermediate stroke risk
• Low stroke risk

High Stroke Risk

Patients with atrial fibrillation are assigned to the high risk stroke category if they have one or more of the following risk factors:

• Rheumatic heart disease
• High blood pressure
• Diabetes
• Are 75 years of age or older
• Have a prior history of stroke or transient ischemic attacks (TIAs)
• Have moderate to severe left ventricular dysfunction (left ventricular ejection fraction of less than 25%).

Intermediate Stroke Risk

Patients with atrial fibrillation are assigned to the intermediate risk stroke category if they are between the ages of 65 and 75 but do not have any of the high risk stroke factors outlined above.

Low Stroke Risk

Patients with atrial fibrillation are assigned to the low risk stroke category if they are younger than 65 years in age and do not have any of the high risk stroke factors outlined above.

Anticoagulation

Numerous studies have established that anticoagulation therapy reduces the risk of stroke in patients with atrial fibrillation. Anticoagulants are "blood thinning" medications that are used to prevent the formation of blood clots that can cause a stroke. Anticoagulation is an important tool in stroke prevention in atrial fibrillation and may be accomplished with either daily aspirin therapy or warfarin (Coumadin). An analysis of data pooled from 5 randomized clinical trials found a relative risk reduction for stroke of almost 70% among patients with atrial fibrillation who were treated with warfarin.

The choice of which anticoagulant to use for stroke prevention in atrial fibrillation depends on the patient's stroke risk profile and can be summarized as follows:

• Patients with AF in the "High Stroke Risk" category - anticoagulation with warfarin

• Patients with AF in the "Intermediate Stroke Risk" category - anticoagulation with warfarin or aspirin

• Patients with AF in the "Low Stroke Risk" category - anticoagulation with aspirin

Aspirin is less effective than warfarin and, therefore, is used for persons who are at very low risk of stroke, or who are not able to take warfarin because of the increased risk of bleeding, risk of falls, or the inability to take the medication reliably.

Warfarin must be taken daily with strict adherence to the prescribed dosage orders. Adjustments to the dose are based on the prothrombin time (PT) and International Normalized Ratio (INR) results. These levels will be done frequently (perhaps even daily initially) until the INR is consistently between 2 and 3. At that time, the frequency is usually decreased to monthly.