ESSENTIALS OF DIAGNOSIS
Characterized by bursts of rapid, regular tachycardia.
Multifocal atrial tachycardia commonly seen with severe COPD and presents with three or more distinct P wave morphologies on ECG, often confused for atrial fibrillation. Treatment of the underlying lung disease is most effective therapy.
Atrial tachycardia is an uncommon form of SVT characterized by paroxysms or bursts of rapid, regular arrhythmia due to focal atrial impulses originating outside of the normal sinus node. Common sites include the tricuspid annulus, the crista terminalis of the right atrium and the coronary sinus. Multifocal atrial tachycardia is a particular subtype seen in patients with severe COPD and characterized by varying P wave morphology (by definition, three or more foci) and markedly irregular PP intervals (eFigure 10–83). The rate is usually between 100 beats/min and 140 beats/min, and it is often confused for atrial fibrillation. Solitary atrial premature beats are benign and generally not associated with underlying cardiac disease. They occur when an ectopic focus in the atria fires before the next sinus node impulse (see eFigure 10–55). The contour of the P wave usually differs from the patient’s normal complex, unless the ectopic focus is near the sinus node. Acceleration of the heart rate by any means usually abolishes most premature beats. Early atrial premature beats may cause aberrant QRS complexes (left or right bundle branch block [eFigure 10–84]) or may not be conducted to the ventricles because the AV node or ventricles are still refractory. Making the distinction between aberrantly conducted supraventricular beats and ventricular beats can be very difficult in patients with a wide QRS complex; it is important because of the differing prognostic and therapeutic implications of each type (see Ventricular Tachycardia section). Findings favoring a ventricular origin include (1) AV dissociation; (2) a QRS duration exceeding 0.14 second; (3) capture or fusion beats (infrequent); (4) left axis deviation with right bundle branch block morphology; (5) monophasic (R) or biphasic (qR, QR, or RS) complexes in V1; and (6) a qR or QS complex in V6. Supraventricular origin is favored by (1) a triphasic QRS complex, especially with initial negativity in leads I and V6; (2) ventricular rates exceeding 170 beats/min; (3) QRS duration longer than 0.12 second but not longer than 0.14 second; and (4) the presence of preexcitation syndrome (eFigure 10–85) (eFigure 10–86). The relationship of the P waves to the tachycardia complex is helpful. A 1:1 relationship usually means a supraventricular origin, except in the case of ventricular tachycardia with retrograde atrial activation.
Multifocal atrial tachycardia. The ventricular rhythm is irregular. Each QRS is preceded by a P wave, but P wave contours and PR intervals vary. (Reproduced, with permission, from Goldschlager N, Goldman MJ. Principles of Clinical Electrocardiography 13th ed. Originally published by Appleton & Lange. Copyright © 1989 by The McGraw-Hill Companies, Inc.)