In AVNRT and AVRT, what pacing response should be observed following right ventricular pacing?

• A. A pacing sequence that starts with a ventricular beat and ends with a ventricular beat separated by atrial activation and no change in rhythm
• B. A pattern described as a ventricular-atrial-ventricular sequence
• C. A pacing sequence consisting of ventricular beats with no accompanying atrial activation
• D. A ventricular pacing pattern with two consecutive ventricular activations

Answer: (B)

Pacing the right ventricle during AVNRT or AVRT tests the retrograde limb of the reentrant circuit. If retrograde conduction exists, the paced ventricular impulse travels back to the atrium, producing an atrial activation after the paced ventricle, and that atrial activation then conducts back to the ventricles to produce the next ventricular beat. This creates a ventricular-atrial-ventricular sequence, which is the typical pacing response in these tachycardias because it shows a functioning ventricle-to-atrium retrograde pathway (via the AV node in AVNRT or via the accessory pathway in AVRT). Patterns lacking retrograde atrial activation or showing only ventricular activations do not reflect the reentrant conduction that sustains AVNRT or AVRT, so the V-A-V sequence best represents the expected response.