In multi-focal atrial tachycardia, the QRS complex is typically?

• A. Prolonged
• B. Normal
• C. Absent
• D. Irregular

Answer: (B)

In multi-focal atrial tachycardia (MAT), the QRS complex is typically observed to be normal. This is because MAT is characterized by the presence of multiple ectopic atrial foci that produce different P-wave morphologies, but the conduction through the ventricles remains intact, leading to a QRS complex that appears normal in shape and duration.

The normal QRS complex indicates that there is no underlying bundle branch block or ventricular conduction disturbance, which allows the normal timing of ventricular contraction. In cases of MAT, it is primarily the atrial activity that is varied, which does not affect the QRS unless there is a coexisting ventricular condition.

In contrast to other conditions where QRS duration might be affected, such as in bundle branch blocks or certain tachycardias with aberrant conduction, MAT maintains the normal appearance of the QRS unless there is an additional complication. Hence, a normal QRS complex is a characteristic feature of multi-focal atrial tachycardia, further highlighting the distinction from other arrhythmias that may exhibit prolonged or absent QRS complexes.