How does junctional tachycardia typically present on an ECG?

• A. Wide QRS with P waves preceding the QRS
• B. Narrow QRS with P waves inverted and retrograde or hidden in the QRS
• C. Narrow QRS with P waves clearly visible after the QRS
• D. Irregular rhythm with absent P waves

Answer: (B)

Junctional tachycardia arises from the AV junction, so the ventricles are activated through the normal His-Purkinje system, giving a narrow QRS complex. The atria, however, are depolarized in a retrograde fashion from the AV junction, which makes the P waves inverted in standard leads and often located just after the QRS or hidden within it. This combination—fast, regular rhythm with a narrow QRS and inverted, retrograde, or hidden P waves—is the typical ECG pattern for junctional tachycardia.