Which dysrhythmia does an impulse originate in the AV junction before the next expected sinus impulse?

• A. Atrial fibrillation
• B. Premature junctional complex
• C. Premature ventricular complex
• D. Junctional escape rhythm

Answer: (B)

An early beat coming from the AV junction is a premature junctional complex. This means an ectopic focus near the AV node fires before the next expected sinus impulse. Because the impulse starts in the AV region, ventricular depolarization usually occurs through the normal His-Purkinje system, so the QRS is narrow. The atrial activity can be altered by this retrograde focus: P waves may be hidden in the QRS, or if visible they’re often inverted and may appear before or after the QRS depending on the timing of atrial activation. This pattern distinguishes it from other rhythms: atrial fibrillation lacks discrete P waves and is irregular; a premature ventricular complex arises from the ventricles and has a wide, bizarre QRS; a junctional escape rhythm is a slow rhythm that emerges after a pause, not early.