Site-Specific Ventricular Tachycardia Inducibility.

Background: Programmed electrical stimulation (PES) is an essential part of ventricular tachycardia (VT) ablation procedures, but VT is not always inducible, usually for reasons that are not clear.

Objectives: This study sought to review pacing site-specific failure of PES to induce scar-related VT and to provide a potential mechanistic explanation of the phenomena using a computer simulation.

Methods: Six patients in whom aggressive PES from traditional RV pacing sites failed to induce VT, but VT was easily inducible from a nontraditional site, were reviewed. In computer simulations, initiation of re-entry by PES at sites distributed around the re-entry circuit was studied.

Results: We identified 6 patients who had no inducible sustained VT from the RV apex/outflow tract with at least 3 extrastimuli, but for whom VT was relatively easily induced from a site in the LV, basal RV, or epicardium. In 5 of the 6 patients, the site that induced VT was closer to the likely re-entry circuit region. In computer simulations, the spatial relation of the pacing site to the entrance and exits of a circuit isthmus influenced initiation of re-entry by an extrastimulus by determining the time available for recovery of excitability at the initial region of block.

Conclusions: The PES site can have a marked effect on inducibility of VT in some patients such that PES from the RV apex and outflow regions fails to induce clinically relevant VTs. The frequency with which this occurs is not certain. Stimulation from alternative sites is a reasonable consideration in selected patients.