Multifocal atrial tachycardia is defined as three or more different types of P waves occurring at a rate more than 100 per minute. In the second rhythm strip there is a pause before the onset of sinus rhythm after the tachycardia terminates. This could be due to down regulation of the If current (funny current or pacemaker current) in the sinus node due to the tachycardia or due to a block atrial ectopic beat which is not very evident as it is superimposed on the T wave.
Sinus rhythm is seen in the middle portion of the ECG, while tachycardia is seen at both ends. Following the fourth beat in the rhythm strip, there is a pause due to a non conducted atrial ectopic beat (blocked atrial ectopic). The nearest differential diagnosis of a multifocal atrial tachycardia is atrial fibrillation (paroxysmal atrial fibrillation in this case). Multifocal atrial tachycardia (MAT) can occur in those with chronic obstructive lung disease .
Multifocal atrial tachycardia is sometimes called as chaotic atrial rhythm because of the variability in atrial activity. Ikaria study which evaluated the natural history of multifocal atrial rhythms in an elderly outpatient population showed that these rhythms are not associated with excess mortality in the elderly as in multifocal atrial tachycardias of hospitalised patients . The study also showed that multifocal atrial rhythms have a high prevalence in the elderly (6%), with much higher prevalence in those above ninety years (15%).
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Lazaros G, Chrysohoou C, Oikonomou E, Tsiachris D, Mazaris S, Venieri E, Zisimos K, Zaromytidou M, Kariori M, Kioufis S, Pitsavos C, Stefanadis C. The natural history of multifocal atrial rhythms in elderly outpatients: insights from the “Ikaria study”. Ann Noninvasive Electrocardiol. 2014 Sep;19(5):483-9.