In AVRT, which activation pattern characterizes right lateral pathways?

• A. CS distal early eccentric activation
• B. CS proximal late activation
• C. HRA earliest concentric activation
• D. HIS earliest concentric activation

Answer: (C)

Activation mapping during AVRT shows where the accessory pathway inserts by identifying where atrial activation begins during retrograde conduction. For a right lateral pathway, the impulse returning from the ventricle travels into the right atrium at the lateral wall, so the earliest atrial signal is recorded in the high right atrium and then spreads around the atrium in a relatively uniform, concentric pattern. That’s why the pattern is described as the high right atrium being the earliest site with concentric activation.

In contrast, patterns like distal coronary sinus activation point toward left-sided pathways (eccentric activation), while early activation at CS proximal or at the His bundle or His region points to septal or para-Hisian mechanisms. Thus, earliest activation in the high right atrium with a concentric spread best matches a right lateral pathway.