Which technique is used to map reentrant circuits in tachyarrhythmias?

• A. Entrainment mapping
• B. Foci mapping
• C. Voltage mapping
• D. Pace mapping

Answer: (A)

Entrainment mapping is used to map reentrant circuits because it actively perturbs a tachycardia that relies on a loop, allowing us to pinpoint where the circuit lies. By pacing during the tachycardia from a site within the circuit, you can temporarily control the rhythm (entrain it) and then observe how the tachycardia responds when pacing stops. If you’re within the circuit, the post-pacing interval closely matches the tachycardia cycle length, and the time from the pacing stimulus to the QRS (the stimulus-to-TQ interval) reflects the conduction time around the circuit to the exit site. The QRS morphology during entrainment remains the same as during tachycardia, confirming a reentrant mechanism and revealing critical parts of the loop, such as the slow-conduction isthmus that is a prime ablation target.

Foci mapping targets single, focal sources of automatic or triggered activity rather than a surrounding loop. Voltage mapping shows substrate by highlighting scar or low-voltage areas but doesn’t specifically trace a circuit. Pace mapping attempts to reproduce the tachycardia morphology at a site to locate an exit, but it doesn’t delineate the entire reentrant pathway or its timing characteristics.