Which rhythm often presents with P waves that are hidden, absent, or occur near the QRS and is associated with AV nodal pacing?

• A. Sinus tachycardia
• B. Atrial fibrillation
• C. Junctional escape rhythm
• D. Ventricular tachycardia

Answer: (C)

P waves that are hidden, absent, or occur right around the QRS indicate the impulse is firing from the AV node or below it, not from the atria. This is a junctional rhythm, reflecting AV nodal pacing. Because the impulse originates near the AV node, atrial depolarization may occur retrograde (producing an inverted P wave in some leads) or be concealed within the QRS, so you don’t see a normal P wave preceding every beat. The QRS is typically narrow because ventricular conduction uses the normal His-Purkinje system, even though the atria aren’t driving the rhythm.

This pattern helps distinguish it from sinus tachycardia, which has normal P waves before each normal-sized QRS; atrial fibrillation, which has no distinct P waves and an irregular rhythm; and ventricular tachycardia, which usually shows wide QRS complexes and no reliable relation to P waves. The key idea is that AV nodal pacing produces P waves that are hidden or displaced near the QRS, with a slower rate characteristic of a junctional escape rhythm.