Multifocal Atrial Tachycardia

Multifocal atrial tachycardia is one of the main differential diagnoses for an irregularly irregular narrow complex tachycardia (the main other 2 being atrial fibrillation and atrial flutter with variable block). The patients that develop this are traditionally elderly patients with respiratory failure (usually COPD, though patients with severe multisystem disease may also display this). The respiratory failure causes increased pulmonary artery pressures, leading to increased RV pressures and, ultimately, RA size; additionally, the acute illness increases the stress response and the adrenergic substances increase automaticity. Although the rhythm itself is rarely dangerous, it is indicative of a worsened prognosis with high 1-year mortality rates. The treatment for this arrhythmia is primarily to treat the underlying disease, though beta blockers can be used for acute rhythm control if needed.

The definition is a tachycardia with at least 3 different P wave morphologies as there are multiple ectopic atrial pacemaker sites (number of sites equal to number of different P wave morphologies). It is commonly considered a transitional rhythm between frequent PAC's and atrial fibrillation (where there are numerous ectopic pacemaker sites). Because of these multiple pacemaker sites with variable P wave morphologies, there is also variable PP, PR, and RR intervals (there are different lengths from pacemaker site to AV node). When there are multiple P wave morphologies but the rate is <100bpm, it is called a wandering atrial pacemaker. Patients with an ectopic atrial pacemaker have a dominant single P wave morphology that is not of sinus origin. Patient's with frequent PAC's will have sinus node morphology P waves with intermittent different P wave morphology with the PAC's. Atrial flutter has a dominant single P wave morphology not of the sinus origin. MAT is most commonly mistaken for atrial fibrillation. This is differentiated from atrial fibrillation given the consistent P waves (may have course but inconsistent P waves in atrial fibrillation). Because of the irregularly irregular supraventricular tachycardia produces variable PP intervals, patients with MAT may also display the Ashman phenomenon (explained in atrial fibrillation).

A wandering atrial pacemaker is when multiple atrial ectopic sites are the origin of the impulse. It is essentially like MAT, though the patient does not have tachycardia. However, it also does not require 3 different P wave morphologies (just various P wave morphologies as the origin of the impulse varies). The cause is not always clear, but is commonly seen in the young and otherwise healthy (similar to sinus arrhythmia); it does not require any specific intervention.

Examples:

Further Reading:

https://litfl.com/multifocal-atrial-tachycardia-mat-ecg-library/

http://hqmeded-ecg.blogspot.com/search/label/Multifocal%20Atrial%20Tachycardia%20%28MAT%29

http://hqmeded-ecg.blogspot.com/search/label/wandering%20atrial%20pacemaker