Junctional tachycardia originates from which cardiac structure?

• A. SA node
• B. Atrial myocardium
• C. Bundle of His
• D. AV node

Answer: (D)

Junctional tachycardia comes from tissue in or around the AV node, the AV junction. Because the impulse originates there, the ventricles are usually activated through the normal His-Purkinje system, producing a narrow QRS complex. P waves may not appear before each QRS and, if seen, are often inverted or occur after the QRS due to retrograde atrial activation.

This is different from sinus tachycardia, which starts in the SA node and has P waves before every QRS with a normal PR interval, and from atrial tachycardia, where the impulse originates in the atrial myocardium and P waves have the abnormal morphology and timing before the QRS.