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Atrial Arrhythmias ECG 5
1. Multifocal atrial tachycardia
2. Old inferior myocardial infarction
3. Premature supraventricular beat with aberrancy (left bundle branch block pattern).
Multifocal atrial tachycardia (MAT) occurs when multiple areas (ectopic foci) within the atrium generate consecutive action potentials that are all conducted to the ventricles. Thus, each QRS complex will be preceded by a P wave, however each P wave will have a different morphology since it is originating from a different area. By definition, multifocal atrial tachycardia has to have at least 3 distinctly different P wave morphologies and a ventricular rate of greater than 100 beats per minute. Ectopic P waves originating from an area outsude the sinus node will not have the typical upright appearance in lead II as seen below. Also note the differential diagnosis of an irregularly irregular rhythm includes atrial fibrillation, atrial flutter with variable conduction and multifocal atrial tachycardia or wandering atrial pacemaker.
Also note the premature supraventricular beat that conducted with a left bundle branch block pattern. There is a clear P wave prior to the aberrant QRS complex. This occurs since the conduction to the ventricles occured before the left bundle could recover from it's refractory period. This more commonly occurs with a right bundle branch pattern and in this scenario is referred to as an "Ashman beat" as seen below:
