Recognition and treatment of multifocal atrial tachycardia: a critical review.

Multifocal atrial tachycardia (MAT) is an uncommon but clinically important tachydysrhythmia that is usually seen in the setting of severe cardiopulmonary illness. Diagnostic criteria include the presence of at least three different, nonsinus P waves in the same lead; an atrial rate greater than 100 beats per minute; and an isoelectric baseline between P waves. MAT is often difficult to differentiate from atrial fibrillation. The pathogenesis of MAT is unknown; however, it is probably incited by "triggered" electrical activity, a form of abnormal automaticity. This electrophysiologic model has led to several small, uncontrolled clinical trials using calcium channel and beta-adrenergic blocking agents, specifically verapamil and metropolol. None of these trials meets rigorous methodologic standards, and all exclude unstable patients who are at greatest risk for hemodynamic compromise from the tachycardia. Treatment of MAT should first be directed at potential predisposing factors, such as hypoxia, congestive heart failure, and theophylline toxicity. Pharmacologic treatment includes intravenous metoprolol or verapamil; in published reports both agents have been well tolerated and have controlled the heart rate in a majority of patients.