Which feature defines Multifocal Atrial Tachycardia (MAT) on ECG?

• A. Irregular rhythm with at least three different P-wave morphologies and varying PP intervals
• B. Regular rhythm with identical P waves
• C. Absent P waves
• D. Peaked P waves with short PR interval

Answer: (A)

MAT is defined by an irregular rhythm with at least three different P-wave morphologies and varying PP intervals. This pattern happens because multiple atrial foci are driving the atria, so each beat can have a different P-wave shape. The timing between P waves changes from beat to beat, which makes the PP intervals irregular.

Because the atria are being paced by more than one site, you’ll see distinct P waves on consecutive beats rather than a single, uniform P-wave shape. The QRS complexes are usually narrow unless there’s an additional conduction issue. This combination—irregular rhythm plus several P-wave morphologies—is what sets MAT apart from other tachyarrhythmias.

If you see a regular rhythm with identical P waves, that points toward sinus rhythm or a single-focus atrial tachycardia rather than MAT. Absent P waves suggests atrial fibrillation (no discernible P waves and a constantly irregular rhythm). Peaked P waves with a short PR interval indicate another atrial abnormality, not MAT.