The ablation target for AVRT involving an accessory pathway is most appropriately described as which of the following?

• A. Site of earliest atrial activation
• B. Site of earliest ventricular activation
• C. Site of earliest fusion
• D. Site near the AV node

Answer: (C)

The key idea is that in AVRT using an accessory pathway, the critical target is the insertion point of that pathway on the AV annulus. At the true insertion site, the activation fronts coming from the atrium and from the ventricle meet and blend, producing the earliest fusion of atrial and ventricular signals in the local electrogram. Ablation at this site disrupts the pathway’s ability to conduct between the chambers, effectively erasing the reentrant circuit.

Relying on the site of the earliest atrial activation alone can be misleading, because that signal might reflect retrograde activation patterns or nearby conducting tissue rather than the actual insertion point. Similarly, the earliest ventricular activation could be influenced by other conduction pathways. Targeting the fusion site directly focuses on where the accessory pathway physically connects atrial and ventricular tissue, which is the most reliable location to stop conduction through the pathway. Avoiding areas near the AV node helps prevent iatrogenic AV block.