Multifocal atrial tachycardia (MFAT) is defined as having at least 3 different foci that are all located above the AV node. On the EKG this will manifest as at least 3 unique P wave morphologies. Additionally, the PP, PR and RR distances will vary due to the fact that the initiating focus is constantly changing. In the strip above, there are 4 different P wave morphologies and 4 different PR and RR intervals that correspond to the 4 different foci of origin. One additional note is MFAT is commonly found in patients who have chronic lung disease such as COPD or asthma although it may be seen in other settings. It is believed that the chronic hypoxia of the atrial muscle mass leads to accelerated automaticity causing atrial cells not found in the SA node to depolarize and reach the depolarization threshold early causing ectopic atrial complexes to ensue.
See examples of MFAT