Temporal correlation of the degree of decrement during functional extra-stimulus substrate mapping to regions within the critical VT isthmus

Background Functional extra-stimulus (ES) substrate mapping using decremental evoked potential (DeEP) mapping improves ventricular tachycardia (VT) ablation success rates (1). Electrograms manifesting decrement highlight regions of conduction velocity slowing and co-localise to the critical VT isthmus. However, the degree of decrement observed may highlight different components of the critical isthmus. Aim The aim of this study is to determine the temporal relationship between the degree of decrement within corresponding regions of the VT isthmus. Methods Patients undergoing DeEP-guided VT ablation with VT local activation timing (LAT) maps were included. DeEP mapping from the right ventricular apex was performed as previously described using a S1 600 ms drive train followed by an S2 delivered at the clinical VT cycle length. The VT LAT map defined the critical diastolic isthmus. Offline analysis of all S1/S2 EGMs to calculate the degree of EGM duration-based decrement was manually performed at all locations where diastolic isthmus potentials were identified in the corresponding VT LAT map. VT LAT map defined diastolic intervals were normalised to percentage diastolic interval (DI) (0% = entrance; 100% = exit). Results Baseline characteristics of the 15 included patients are shown in table 1. A total of 820 DeEP points were analysed with an average 54.1 ± 55.0 per VT isthmus. Graphical representation of individual DeEP values at corresponding VT isthmus DI locations for all patients are shown in the scatter plot figure 1. DeEPs with larger decrement co-localize to entrance sites and DeEPs with smaller decrement co-localise to exit sites. A mixed-effects model with both a random intercept and a random slope for each patient demonstrated for every 1% increase in DI, decrement decreases by 0.23 ms with a statistically significant (negative slope) inverse relationship (95% CI [-0.454,-0.014]; p-value = 0.037). In 4 patients, where a positive decrement slope was observed, pre-ablation amiodarone was used in all cases compared to 27% of patients with a negative decrement slope (p=0.026). Additionally, 131 DI sites manifested negative S1/S2 decrement during functional ES mapping: S1 EGM duration > S2 EGM duration thus defined as a Blocked Evoked Potential (BeEP). BeEPs were observed in 5 patients across entrance, mid and exit DI sites with a greater degree of negative S1/S2 decrement observed at entrance sites compared to exit sites. For every 1% increase in DI, there was a 0.33 ms reduction in negative decrement (95% CI [0.072, 0.596], p = 0.013). Conclusion Positive (DeEP) and negative (BeEP) decremental electrogram responses during functional ES substrate mapping are observed throughout the entire VT isthmus region, however more pronounced at VT entrance sites. Prospective VT ablation studies targeting different degrees of decrement are ongoing to determine long-term clinical impact.