Utility of baseline inducibility and activation mapping during VT
ablation
VT in the setting of SHD is usually associated with the presence of scar
and the principal eletrophysiological mechanism involved in the genesis
and manteinance of the tachycardias is re-entry. Traditional VT ablation
strategies involved baseline induction of the tachycardia and activation
mapping when possible trying to depict the tachycardia circuit in order
to guide the ablation strategy. During the last years substrate mapping
and ablation without baseline VT induction or activation mapping has
proved to be an effective and safe strategy9-13. The
rationale for this new approach is that complete elimination of the
abnormal substrate/signals is associated with better acute success in
terms of non-inducibility of any VT (either clinical or not) at the end
of the procedure when compared with ablation of the clinical VT only,
and has clearly been related with a significant reduction of VT
recurrences during follow-up. On the other hand, concerns regarding the
developement of hemodynamic decompensation during or after VT ablation
procedures have also favored the avoidance of baseline VT induction and
activation mapping15-16. However, one of the downsides
of stand-alone substrate ablation is that it may lead to an extensive
ablation that may not be always necessary and could be avoided by a more
physiologic approach identifying and ablating only the critical parts of
the substrate that are responsible of VT generation and maintenance.
Moreover, although re-entry is the principal mechanism of scar-related
VT, other less frequent VT mechanisms can be present in patients with
SHD and would not be identified unless VT induction is attempted thus
hindering the procedure success probabilities17-18.
Current existing literature in this regard is
controversial11-13. Two previous meta-analyses have
evaluated the influence of VT ablation strategy on outcome. Briceño et
al. included 396 patients from 6 different studies (5 observational
cohort studies and 1 randomized prospective study) comparing complete
substrate ablation vs. standard ablation of stable
VTs12. Substrate ablation was found to be associated
with a decrease in the composite end point of ventricular arrhythmias
recurrence/all-cause mortality when compared with the standard approach
(RR 0.57, 95% CI 0.40–0.81). Kumar et al. included 403 patients from 6
studies and found no differences in the VT recurrence rate between
substrate based VT ablation vs. standard VT ablation using activation
mapping/entrainment with a mean follow-up of 18 months (0.72, 95%
confidence interval [CI] 0.44-1.18, p=0.2)13.
Our study shows that baseline VT inducibility adds significantly
important prognostic information in patients with SHD undergoing VT
ablation. Following this strategy, patients with baseline inducibility
of >1VT morphology are clearly identified at a very high
risk of VT recurrences (42% over median follow-up of 38.5 months) while
patients with no baseline inducibility or with only 1 VT morphology
induced have very low VT recurrences rates (6.6% and 15.1% after the
first procedure). It is remarkable that PVS at the end of the procedure
did not have this prognostic value in our series. Group 2 patients with
acute success at the end of the procedure (determined by non
inducibility with PVS) had significantly higher VT recurrence free
survival when compared with group 3 patients with acute success (85.4%
vs. 63.6%, Log-rank p=0.005)(Supplementary data).
Moreover, activation mapping during VT seems to add additional value and
was also associated with lower VT recurrence rates in our study although
did not reach statistical significance in multivariate analysis. The
utility of VT activation mapping has been recently
described19-20. Hadjis et. al.19showed that VT recurrence was significantly lower among those patients
with complete delineation of the diastolic pathway (12%) during VT when
compared with partial or no recording of the diastolic pathway (50% and
45%, respectively, p=0.02).
Of interest, hemodynamic decompensation during or after the procedure
occurred only in 9 patients (5.6%) in our series. This is a low
percentage considering the presence of baseline VT inducibility in up to
89% of the patients and complete VT activation mapping in 35%.
Santangeli et al. reported 11% incidence of acute hemodynamic
decompensation among 193 patients with scar-related VT undergoing VT
ablation15. Unfortunately, no information about the
incidence of acute hemodynamic decompensation depending on the ablation
strategy has been yet published.