ECG Case of the Month: IRREGULARLY IRREGULAR CARDIAC RHYTHM IN AN 87-YEAR-OLD WOMAN. MULTIFOCAL ATRIAL TACHYCARDIA; RIGHT BUNDLE BRANCH BLOCK.

Multifocal atrial tachycardia; right bundle branch block. The rhythm is totally irregular at a rate of 103 beats/min and originally was read as atrial fibrillation. Close examination, however, reveals a P wave before each QRS and ≥ 3 different P- wave morphologies with no dominant morphology. These are the criteria for multifocal atrial tachycardia MAT, also known as chaotic atrial rhythm,1 chaotic atrial tachycardia,2 and chaotic atrial mechanism.3 The wide QRS complexes ≥ 0.12 s with broad S waves in leads I, aVL, and the lateral precordial leads and broad R or R´ waves in leads aVR and V1 indicate right bundle branch block. MAT is frequently seen in patients with acute pulmonary or other non-cardiac disease and tends to resolve when the underlying disease is brought under control. Patients with MAT also tend to have bouts of other arrhythmias,2 and 3 months earlier this.