Multifocal atrial tachycardia: Mechanisms, clinical correlates, and treatment

Abstract

MAT is an uncommon arrhythmia most often seen in elderly patients with chronic pulmonary disease who are critically ill due to acute respiratory or cardiac decompensation. Its importance lies in the fact that it is commonly mistaken for AF, since both disorders are characterized by narrow ventricular complexes, irregular rates, and (depending on the ECG lead observed in MAT) by an apparent lack of P wave activity. This may lead to treatment with digoxin, a drug known to be ineffective in the therapy of MAT, with the potential for producing toxicity in patients who are predisposed. The incidence of MAT in hospitalized patients in various studies ranges from 0.13% to 0.40%. The mechanism of the arrhythmia is thought to be triggered activity arising from increased intracellular calcium stores that may be produced by hypokalemia, hypoxia, acidemia, and increased catecholamines, characteristics commonly found in patients with MAT. COPD, coronary artery disease, CHF, and infection (both pulmonary and nonpulmonary) are the most common clinical settings of MAT. Mortality is very high in all patients studied, ranging from 38% to 62%, and is due to their underlying disease processes and not to the arrhythmia. The need for intubation and mechanically assisted ventilation portends a particularly poor prognosis for survival. Treatment should initially consist of correction of the precipitating causes, as it is common for patients to convert to sinus rhythm both spontaneously and after these measures are taken. If specific antiarrhythmic therapy is desired at this point in order to obtain a rapid decline in heart rate, verapamil and metoprolol have been used successfully (both theoretically reducing the substrate for triggered activity), with metoprolol proven more effective in a double-blind placebo-controlled study. However, the high rate of conversion to sinus rhythm spontaneously and in response to general supportive measures, coupled with the potential for adverse reactions to these drugs, should have the clinician carefully select patients for these therapeutic options.