How can you distinguish between supraventricular tachycardia and multifocal atrial tachycardia?

EKG: Usually, an expert will be able to tell the difference in these two arrhythmias with a 12-lead EKG. Specifically, the shape of the "p-waves" will vary in multifocal atrial tachycardia (MAT), whereas most other SVT's will have only one shape. MAT characteristically occurs in the setting of hypoxia (i.e. low oxygen availability), which is another clue. An invasive EP study is rarely needed.

Tachycardia: Multifocal atrial tachycardia is a form of SVT. ECG and Holters should help. Sometimes you need electrophysiology study.