Where are EP catheters placed for EPS?

• A. High Right Atrium (HRA)
• B. HIS
• C. Coronary Sinus (CS)
• D. Right Ventricle (RV)

Answer: (B)

During an EPS, placing a catheter at the His bundle region is essential because it records the His-Purkinje conduction and lets you measure the HV interval. This interval, from the His bundle to the ventricles, tells you where conduction delay lies—within the AV node or below it in the His-Purkinje system. A normal HV interval suggests intact infra-nodal conduction, while a prolonged HV interval points to infra-nodal disease, guiding diagnosis and ablation strategy. Other catheters are also used—in the high right atrium to monitor atrial activity, in the coronary sinus to map left atrial activation, and in the right ventricle for ventricular pacing and recording—but the catheter at the His bundle region provides the crucial information about the conduction system itself, making it a central placement in EPS.