Extra-stimulus pacing from the HRA catheter will allow you to determine which electrophysiological properties?

• A. AERP and AVNERP
• B. PR interval and QRS duration
• C. QT interval and heart rate
• D. AV nodal conduction time only

Answer: (A)

Extra-stimulus pacing from the high right atrial catheter is used to probe refractoriness in both the atrial myocardium and the AV node. By delivering a train of paced beats (S1) and then a premature stimulus (S2) at progressively shorter coupling intervals, you identify the atrial effective refractory period as the shortest S1–S2 interval that still elicits atrial capture. For the AV node, you look at whether the premature impulse conducts to the ventricles; the shortest S1–S2 interval that still results in ventricular activation defines the AV nodal effective refractory period. So this technique directly measures AERP and AVNERP. Baseline conduction times (PR interval, QRS duration) or other measures like QT interval or heart rate are not the primary targets of extrastimulus pacing from the HRA in this context.