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.