Macroreentrant atrial tachycardia is due to a large reentry circuit, often associated with areas of scar in the atria. Common or typical right atrial flutter is due to a circuit that revolves around the tricuspid valve annulus, bounded anteriorly by the annulus and posteriorly by functional conduction block in the crista terminalis. The wavefront passes between the inferior vena cava and the tricuspid valve annulus, known as the sub-Eustachian or cavotricuspid isthmus, where it is susceptible to interruption by catheter ablation. Thus, common atrial flutter is also known as cavotricuspid isthmus-dependent atrial flutter. This circuit most commonly revolves in a counterclockwise direction (as viewed looking toward the tricuspid annulus from the ventricular apex), which produces the characteristic negative sawtooth flutter waves in leads II, III, and aVF and positive P waves in lead V1 (Fig. 245-1). When the direction is reversed, clockwise rotation produces the opposite P-wave vector in those leads. The atrial rate is typically 240–300 beats/min but may be slower in the presence of atrial disease or antiarrhythmic drugs. It often conducts to the ventricles with 2:1 AV block, creating a regular tachycardia at 150 beats/min, with p waves that may be difficult to discern. Maneuvers that increase AV nodal block will typically expose flutter waves, allowing diagnosis.
A. Common right atrial flutter, also known as cavotricuspid isthmus flutter, showing positive P waves in lead V1 and negative “sawtooth” pattern in lead II typical of counterclockwise rotation relative to the tricuspid valve annulus. (Adapted from F Marchlinski: The tachyarrhythmias. in DL Longo et al [eds]: Harrison’s Principles of Internal Medicine, 18th ed. New York, McGraw-Hill, 2012, pp 1878–1900.) B. A right atrial map of common counterclockwise flutter is shown. Colors indicate activation time, progressing from red to yellow to green, blue, and purple. The reentry path parallels the tricuspid annulus.
Common right atrial flutter usually occurs in association with atrial fibrillation and often with atrial scar from senescence or prior cardiac surgery. Some patients with atrial fibrillation treated with an antiarrhythmic drug, particularly flecainide, propafenone, or amiodarone, will present with atrial flutter rather than fibrillation, since these agents slow atrial conduction velocity and can promote reentry.
Macroreentrant ATs that are not dependent on conduction through the cavotricuspid isthmus are referred to as atypical atrial flutters. They can occur in either atrium and are almost universally associated with areas of atrial scar. Left atrial flutter and perimitral left atrial flutter are commonly seen after extensive left atrial ablation for atrial fibrillation or atrial surgery. The clinical presentation is similar to common atrial flutter, but with different P-wave morphologies (Fig 245-2). They can be difficult to distinguish from focal AT, and in most cases, the mechanism can only be confirmed by an electrophysiology study.