American College of Cardiology

FUSTER ET AL., ACC/AHA/ESC GUIDELINES FOR THE MANAGEMENT OF PATIENTS WITH ATRIAL FIBRILLATION
J Am Coll Cardiol 2001;38:1266i-1xx

ACC/AHA/ESC Guidelines for the Management of Patients with Atrial Fibrillation

II. Definition

A. Atrial Fibrillation

AF is a supraventricular tachyarrhythmia characterized by uncoordinated atrial activation with consequent deterioration of atrial mechanical function. On the electrocardiogram (ECG), AF is described by the replacement of consistent P waves by rapid oscillations or fibrillatory waves that vary in size, shape, and timing, associated with an irregular, frequently rapid ventricular response when atrioventricular (AV) conduction is intact ⁽¹⁾. The ventricular response to AF depends on electrophysiological properties of the AV node, the level of vagal and sympathetic tone, and the action of drugs ⁽²⁾ (Figure 1). Regular RR intervals are possible in the presence of AV block or interference due to ventricular or junctional tachycardia. In patients with electronic pacemakers, diagnosis of AF may require temporary inhibition of the pacemaker to expose atrial fibrillatory activity ⁽³⁾. A rapid, irregular, sustained, wide-QRS-complex tachycardia strongly suggests AF with conduction over an accessory pathway or AF with underlying bundle-branch block. Extremely rapid rates (over 200 bpm) suggest the presence of an accessory pathway.

B. Related Arrhythmias

AF may occur in isolation or in association with other arrhythmias, most commonly atrial flutter or atrial tachycardia. Atrial flutter may arise during treatment with antiarrhythmic agents prescribed to prevent recurrent AF. Atrial flutter is a more organized arrhythmia than AF and is characterized by a saw-tooth pattern of regular atrial activation called flutter (ƒ) waves on the ECG, particularly visible in leads II, III, and aVF, without an isoelectric baseline between deflections (Figure 2). In the untreated state, the atrial rate typically ranges from 240 to 320 beats per minute, with ƒ waves inverted in ECG leads II, III, and aVF and upright in lead V₁. The wave of activation in the right atrium (RA) may be reversed, resulting in ƒ waves that are upright in leads II, III, and aVF and inverted in lead V₁. Atrial flutter commonly occurs with 2:1 AV block, resulting in a ventricular rate of 120 to 160 beats per minute, most characteristically about 150 beats per minute. Several types of atrial flutter have been distinguished, but no consistent nomenclature has been widely accepted. Atrial flutter may degenerate into AF, AF may initiate atrial flutter, or the ECG pattern may alternate between atrial flutter and AF, reflecting changing activation of the atria.

Other atrial tachycardias, AV reentrant tachycardias, and AV nodal reentrant tachycardias may also trigger AF. In other atrial tachycardias, P waves are readily identified and separated by an isoelectric baseline in 1 or more ECG leads. The morphology of the P waves may help localize the origin of the tachycardias. A unique type of atrial tachycardia has recently been identified that commonly originates in the pulmonary veins but may arise elsewhere ⁽⁴⁾, is rapid (typically faster than 250 beats per minute), and often degenerates into AF. Electrophysiological studies with intracardiac mapping may help differentiate the various types of atrial arrhythmias and elucidate their mechanisms.

Copyright © 2001 by the American College of Cardiology, American Heart Association, Inc., and the European Society of Cardiolgy.
Published by Elsevier Science Inc.