In Atrial Tachy pacing following RV pacing, which sequence is observed?

• A. Ventricular-atrial-atrial-ventricular pattern (ventricular-atrial-atrial-ventricular)
• B. Ventricular-ventricular-ventricular activations
• C. A sequence of mixed ventricular and atrial activations
• D. Atrial-ventricular-ventricular pattern

Answer: (A)

When the ventricle is paced, the impulse can travel backward through the AV junction to the atria if retrograde conduction is present. That retrograde impulse causes an atrial depolarization after the ventricular beat. If atrial tachy pacing is then delivered, the atria depolarize again due to the paced beat, producing a second atrial activation before the next ventricular response. The sequence becomes ventricular activation, then an atrial activation from retrograde conduction, followed by another atrial activation from the paced atrial beat, and finally the next ventricular beat. This yields a ventricular-atrial-atrial-ventricular pattern, reflecting both retrograde atrial conduction and subsequent atrial pacing driving the next ventricular response. If retrograde conduction were blocked or the pacing timing differed, you’d see different sequences, but the described V-A-A-V pattern fits this interplay between RV pacing and atrial tachy pacing.