Postextrastimulus Termination of Ventricular Tachycardia: An Indicator of a Good Ablation Site?

Entrainment mapping, or continuous resetting of a re-entrant tachycardia, provides a powerful tool for distinguishing between focal and re-entrant ventricular tachycardias (VTs) and for identifying critical circuit components, such as the entrance, critical isthmus (CI), and exit sites. However, this technique is not always feasible and, in some cases, may itself terminate VT during the entrainment attempt. Whereas local capture of the CI without global ventricular capture (nonglobal capture [NGC]) can terminate VT by creating a bidirectional block (orthodromic or nonorthodromic capture) within the CI, the VT termination may also occur due to a rate-dependent block in the slow-conduction zone during pacing or as a result of spontaneous or mechanical trauma-related ventricular extrasystoles. Such NGC-related termination does not carry the same mechanistic implications as termination due to NGC. Although this termination is usually observed incidentally, it can also be demonstrated intentionally, eg, by delivering a single extrastimulus during tachycardia, as shown in the present case. Therefore, a careful analysis of the response to entrainment is essential.