What is the purpose of pace-mapping during VT or focal atrial tachycardia ablation?

• A. To identify the likely origin by matching paced QRS morphology to the clinical tachycardia
• B. To terminate tachycardia by pacing
• C. To test AV conduction
• D. To measure cycle length

Answer: (A)

Pace-mapping aims to locate the source of the tachycardia by testing pacing from different sites and seeing which site can recreate the same QRS pattern as the clinical tachycardia. When pacing from a particular spot produces a QRS morphology that closely matches the tachycardia across multiple leads, that site is likely near the origin or exit of the arrhythmia circuit. This lets the operator target ablation precisely at the origin rather than applying a blind lesion.

The technique is diagnostic, not primarily about stopping the tachycardia with pacing. While pacing over time can sometimes entrain or alter a tachycardia, the main purpose is to identify the origin by the QRS match. It isn’t used to assess AV conduction or to measure the tachycardia cycle length, which are different assessments or measurements in electrophysiology studies.