Acute Management of Atrial Fibrillation: Part I. Rate and Rhythm Control

American Family Physician,  July 15, 2002  by Dana E. King,  Lori M. Dickerson,  Jonathan L. Sack

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Atrial fibrillation is the arrhythmia most commonly encountered in family practice. Serious complications can include congestive heart failure, myocardial infarction, and thromboembolism. Initial treatment is directed at controlling the ventricular rate, most often with a calcium channel blocker, a beta blocker, or digoxin. Medical or electrical cardioversion to restore sinus rhythm is the next step in patients who remain in atrial fibrillation. Heparin should be administered to hospitalized patients undergoing medical or electrical cardioversion. Anticoagulation with warfarin should be used for three weeks before elective cardioversion and continued for four weeks after cardioversion. The recommendations provided in this two-part article are consistent with guidelines published by the American Heart Association and the Agency for Healthcare Research and Quality. (Am Fam Physician 2002;66:249-56. Copyright[C] 2002 American Academy of Family Physicians.)

In recent years, management strategies for atrial fibrillation have expanded significantly, and new drugs for ventricular rate control and rhythm conversion have been introduced.(1-3) Family physicians have the challenge of keeping current with recommendations on heart rate control, antiarrhythmic drug therapy, cardioversion, and antithrombotic therapy.

Atrial fibrillation is the most common sustained arrhythmia encountered in the primary care setting. Approximately 4 percent of persons in the general U.S. population have permanent or intermittent atrial fibrillation, and the prevalence of the arrhythmia increases to 9 percent in persons older than 60 years.(2) Atrial fibrillation can result in serious complications, including congestive heart failure, myocardial infarction, and thromboembolism. Recognition and acute management of atrial fibrillation in the physician's office or emergency department are important in preventing adverse consequences.

Diagnosis

The diagnosis of atrial fibrillation should be considered in elderly patients who present with complaints of shortness of breath, dizziness, or palpitations. The arrhythmia should also be suspected in patients with acute fatigue or exacerbation of congestive heart failure.(3) In some patients, atrial fibrillation may be identified on the basis of an irregularly irregular pulse or an electrocardiogram (ECG) obtained for the evaluation of another condition.

Cardiac conditions commonly associated with the development of atrial fibrillation include rheumatic mitral valve disease, coronary artery disease, congestive heart failure, and hypertension. Noncardiac conditions that can predispose patients to develop atrial fibrillation include hyperthyroidism, hypoxia, alcohol intoxication, and surgery.(4)

The ECG is the mainstay for diagnosis of atrial fibrillation (Figure 1). An irregularly irregular rhythm, inconsistent R-R interval, and absence of P waves are usually noted on the cardiac monitor or ECG. Atrial fibrillation waves (f waves), which are small, irregular waves seen as a rapid-cycle baseline fluctuation, indicate rapid atrial activity (usually between 150 and 300 beats per minute) and are the hallmark of the arrhythmia.

When the fibrillation waves reach 300 beats per minute, they may be difficult to see (fine versus coarse fibrillation).(5) These waves may be even harder to detect on a cardiac monitor in a busy emergency department because of interference from other electrical equipment. The f waves may be easier to identify on a printed rhythm strip. In addition, when the ventricular response to atrial fibrillation is very rapid (more than 200 beats per minute), variability of the R-R interval can frequently be seen more easily using calipers on a paper tracing.

Atrial flutter is included in the spectrum of supraventricular arrhythmia. This rhythm disturbance is usually distinguishable by its more prominent saw-tooth wave configuration and slower atrial rates (Figure 2). Atrial fibrillation should also be distinguished from atrial tachycardia with variable atrioventricular block, which usually presents with an atrial rate of approximately 150 beats per minute. In this condition, the atrial rate is regular (unlike the irregular disorganized f waves of atrial fibrillation), but conduction to the ventricles is not regular. The resultant irregularly irregular rhythm may be difficult to differentiate from atrial fibrillation.(3)

Initial Management

Recent advances in treatment and the introduction of new drugs have not changed initial management goals in patients with atrial fibrillation. These goals are hemodynamic stabilization, ventricular rate control, and prevention of embolic complications.(4,6-8) When atrial fibrillation does not terminate spontaneously, the ventricular rate should be treated to slow ventricular response and, if appropriate, efforts should be made to terminate atrial fibrillation and restore sinus rhythm(4,7,9) (Figure 3).(8)

VENTRICULAR RATE CONTROL

Ventricular rate control to achieve a rate of less than 100 beats per minute is generally the first step in managing atrial fibrillation. Beta blockers, calcium channel blockers, and digoxin (Lanoxin) are the drugs most commonly used for rate control(3,4,7) (Table 1).(3) These agents do not have proven efficacy in converting atrial fibrillation to sinus rhythm and should not be used for that purpose.(4,7,10,11)