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.