What does concealed entrainment imply during ischemic VT pacing?

• A. Pacing yields a QRS morphology identical to the VT.
• B. Pacing leads to a QRS morphology different from the VT.
• C. There is no pacing capture.
• D. The timing of QRS is earlier than VT onset.

Answer: (D)

Concealed entrainment happens when pacing during a ventricular tachycardia drives the reentrant circuit but does not change what the QRS looks like on the surface ECG. The key clue is not a different QRS morphology, but the timing: the QRS that follows the pacing stimulus appears earlier than the VT would have started, meaning the pacing impulse has entered the circuit and preempted the next VT beat without altering the overall QRS appearance. This demonstrates that the pacing site is within the VT circuit and is resetting it, even though you don’t see a fusion or a morphology change. If you did see a different QRS (fusion) during pacing, that would be manifest entrainment; lack of capture would show no QRS at all.