Limitations
The intent of this series is to illustrate the potential importance of alternative stimulation sites when assessing VT inducibility. It is unclear how often VT is only inducible from sites other than the RVA or RVOT. This is a retrospective case series without randomization of alternate stimulation sites or control for other factors which are inevitably changing during the course of the ablation procedure including the sympathetic tone, filling conditions, level of sedation, and absorption of local anesthetic, that can affect VT inducibility. The programmed stimulation was done as the procedure dictated. Hence it is difficult to provide guidance as to a specific approach to the problem.
The use of some alternate pacing sites may increase procedural risk. For example, most epicardial pacing sites require pericardial access. LV endocardial stimulation requires retrograde aortic or transseptal access to the LV, with the risks that this entails. In most cases, it seems likely that the additional risk is not warranted.
Clinical Implications: The site of PES has a marked effect on inducibility of VT in some patients. In some patients, PES from the RV apex and outflow regions will fail to expose clinically relevant VTs. The frequency with which this occurs is not certain. Stimulation from alternative sites is a reasonable consideration in selected patients. Our observations suggest that this may be especially useful when performing ablation in patients whose VT is not inducible despite previously documented clinical VTs. A PES site anatomically closer to the suspected reentry circuit is reasonable. Further studies are warranted to clarify the utility and selection of alternate pacing sites.