In which dysrhythmia does the P wave disappear or occur just before or after the QRS complex?

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

Answer: (A)

This pattern reflects a junctional rhythm, where the impulse originates in or around the AV node. When the pacemaker is in this region, atrial depolarization can occur at the same time as, after, or even be hidden within the ventricular depolarization. As a result, the P wave may be absent, or it may appear just before or after the QRS, and it is often inverted if seen—because the atrial activation is retrograde relative to the ventricles. The QRS is typically narrow, since conduction through the His-Purkinje system is intact.

In contrast, a normal sinus rhythm shows P waves clearly before each QRS with a consistent PR interval; atrial fibrillation lacks discrete P waves altogether; and ventricular tachycardia usually has wide QRS complexes with possible AV dissociation.