During entrainment, the ventricle is paced at 330 ms, 20 ms faster than the tachycardia cycle length. How would you ensure ventricular capture?

• A. Narrow QRS with elevated ventricular rate
• B. Wide QRS with elevated ventricular rate
• C. Fusion beats only
• D. No capture

Answer: (B)

When you’re trying to entrain a ventricular tachycardia by pacing the ventricle, the goal is to overdrive the tachycardia and actually capture the ventricular myocardium with the pacing stimulus. Capturing the ventricle is reflected by a QRS that is wide, because you’re directly depolarizing the ventricular muscle rather than using the normal His-Purkinje system. Pacing at a cycle length shorter than the tachycardia ensures you drive the ventricle on each beat, so you’ll see a consistently wide QRS at the faster rate. A narrow QRS would suggest involvement of the conduction system rather than direct ventricular capture, and fusion beats only would indicate partial capture rather than full entrainment. No capture would mean the tachycardia continues unabated. Thus, observing a wide QRS with an elevated ventricular rate confirms ventricular capture during entrainment.