What is a limitation of pace-mapping when identifying VT origin?

• A. Pace-mapping may be affected by catheter position and activation sequence, so morphological match may be imperfect
• B. Pace-mapping always yields an exact match
• C. It cannot be used in the ventricle
• D. It is unreliable for AF ablations

Answer: (A)

Pace-mapping relies on the idea that pacing from a site near the VT focus will produce a QRS that matches the VT morphology. But a key limitation is that the activation pattern from a paced beat can differ from the spontaneous VT activation. The impulse travels outward from the pacing site, and the exact QRS looks depend on how the catheter is positioned, how well tissue is captured, and the local conduction properties. If the catheter isn’t at the VT exit or contact/orientation isn’t ideal, the paced QRS morphology may resemble VT without being an exact replica. This makes the morphologic match imperfect and means pace-mapping alone isn’t foolproof for pinpointing VT origin.