Figure 21.

Example of concealed entrainment during ventricular tachycardia. This 12-lead ECG shows the last four beats of left ventricular pacing train at a paced cycle length (PCL) of 536 ms delivered during a slow ventricular tachycardia with a tachycardia cycle length (TCL) of 564 ms. Please note that sustained capture is demonstrated because the QRS are consistently activated at the PCL with identical stimulus (St) to QRS onset. Also note that stimulus to QRS onset is long (90 ms). But despite capture, the paced QRS morphology is identical in all 12 leads to the tachycardia QRS morphology. This tracing, by strict criteria, does not prove entrainment, because there is no proof of interaction between the paced wavefronts and the tachycardia, and, obviously none of the entrainment criteria are met.