Atrial Fibrillation

Abstract & Commentary

By John P. DiMarco, MD, PhD, Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville. Dr. DiMarco is a consultant for Novartis, and does research for Medtronic and Guidant.

Source: Fuster V, et al. ACC/AHA/ESC 2006 Guidelines for the Management of Patients With Atrial Fibrillation — Executive Summary: A Report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines and the European Society of Cardiology Committee For Practice Guidelines (Writing Committee to Revise the 2001 Guidelines for the Management of Patients with Atrial Fibrillation). J Am Coll Cardiol. 2006;48:854-906.

The 2006 guidelines for the management of patients with atrial fibrillation clarify previous recommendations for anticoagulation to prevent other thromboembolic events. The new guidelines focus on the number of risk factors that are present and the risk of bleeding in the individual. Estimates of stroke risk are based on the CHADS2 scoring system. This system gives one point each for the presence of cardiac failure, hypertension, age over 75, and diabetes, and 2 points for a history of stroke or transient ischemic attack (TIA). There is a graded increase in stroke risk as the CHADS2 score rises. Based on these data, the 2006 Guidelines recommend that patients should first be evaluated for risk factors.

They use the following definitions: High risk factors include previous stroke, TIA or embolism, mitral stenosis, or a prosthetic heart valve; Moderate risk factors include: age greater than or equal to 75 years, hypertension, heart failure, left ventricular ejection fraction 35% or less, and diabetes mellitus; Finally, they suggest that physicians should also consider the following less well-validated or weaker risk factors: female gender, age 65 to 74, coronary artery disease, and thyrotoxicosis. For patients who have no risk factors, the recommendation is aspirin in a dose range of 81 mg to 325 mg daily. For patients with one moderate risk factor, either aspirin 81 mg to 325 mg daily or warfarin (International Normalized Ratio [INR] 2.0-3.0, target 2.5) may be used, with a decision based on risk of bleeding and patient preference. Presumably, the additional presence of one of the weaker risk factors would influence this decision. Finally, any patient with a single high risk factor or more than one moderate risk factor should receive warfarin (INR 2.0-3.0; target 2.5). These anticoagulation recommendations hold whether or not the patient has paroxysmal or persistent atrial fibrillation, since the stroke risk appears to be similar in trials that have looked at both groups.

The revised guidelines also discuss anticoagulation around the time of elective pharmacologic or electrical cardioversion. Previous studies have shown a risk of stroke or systemic thromboembolism after cardioversion between 1% and 5%. The new guidelines continue to recommend anticoagulation with warfarin (INR, 2.0-3.0) for 3 to 4 weeks before, and for at least 4 weeks after, cardioversion. The new guidelines now recognize the validity of a trans-esophageal echocardiography-based approach. With the latter, the duration of pre-cardioversion anticoagulation may be shortened if a transesophageal echo shows no thrombus in the left atrial appendage. It is important with this approach, however, that anticoagulation be maintained from the time of the trans-esophageal echo until at least 4 weeks after the procedure. The duration of anticoagulation after cardioversion should be based on the likelihood that atrial fibrillation will recur in the individual patient and on the risk of thromboembolism in the presence of atrial fibrillation as estimated by a system such as the CHADS2 scoring system.

As in previous guidelines, anticoagulation is not thought to be necessary in patients with atrial fibrillation of less than 48 hours duration. Although Fuster and colleagues recognize that there are only limited data on patients with atrial flutter only, they suggest that the same anticoagulation guidelines for patients with atrial flutter should be followed.

Commentary

The new guidelines clarify some previous recommendations about anticoagulation for patients with atrial fibrillation. The new guidelines place a greater dependence on a risk scoring system, such as the CHADS2 scoring system. The major change in the guidelines relates to patients whose CHADS2 score places them at intermediate risk of thromboembolism (3%-5% per year). In these patients, anticoagulation warfarin is no longer mandated and aspirin is listed as an acceptable
alternative.

In any individual patient, the risk of stroke must be balanced against the risk of bleeding. Since the consequences of stroke are so high, I prefer to advise warfarin for patients at intermediate risk. I think one moderate risk factor plus a weaker risk factor should make one favor warfarin. Risk for bleeding should also be considered in these intermediate-risk patients. If patients are unwilling or unable to tolerate warfarin, then aspirin remains the alternate choice.