Funding Acknowledgements Type of funding sources: None. Introduction Patients with ischemic cardiomyopathy (ICM) and monomorphic, sustained ventricular tachycardia (VT) are considered to be at risk for arrhythmia-related sudden cardiac death (SCD). Prior studies have suggested that patients with well-tolerated VTs and preserved or moderately reduced left ventricular ejection fraction (LVEF) and successful VT ablation may not benefit from cardioverter defibrillator implantation (ICD Current guidelines indicate that in selected patients catheter ablation should be considered instead of ICD, but supporting evidence is limited. Aim This study aims to analyze arrhythmia outcomes of ICM patients referred for VT ablation without prior ICD implantation according to LVEF, hemodynamical stability during VT and ablation outcome. Methods ICM patients without prior ICD implantation undergoing VT ablation in a tertiary center between 2009 and 2022 were included. Patients who presented with a first episode of tolerated VT and w a LVEF≥35% were offered catheter ablation (CA) as first-line therapy. Patients were categorized according to (1) LVEF, (2) clinical presentation (hemodynamically tolerated/non-tolerated VT) and (3) acute ablation outcome. According to the institutional protocol, ICD was offered to all patients after ablation, but was subject to shared decision making, explaining the available evidence supporting ICDs for the different categories. Results Eighty-six ICM patients without ICD underwent ablation for VT. Mean age was 69±9 years and 72 (84%) were men, mean LVEF was 41±9% and 34 patients (28%) were using anti-arrhythmic drugs (AAD). The median VT cycle length (VTCL) at presentation was 323ms [300 – 375] and VT was tolerated in 58 (67%) patients (median tolerated VTCL 325ms [300 – 371]). In 66 (77%) patients, the LVEF was ≥35% of which 51 had well-tolerated VT. Of these 51 patients, 37 (73%) were rendered non-inducible after ablation and in 14 patients non-clinical VTs remained inducible (median remaining VTCL 238ms [203-288]). In 5/37 non-inducible and in 11/14 inducible patients, an ICD was implanted. Of the 35 patients who had LVEF<35% and/or non-tolerated VTs, 7 refused ICD implantation. (Figure 1) During a median follow-up of 35 [22 – 53] months, 10 patients (12%) had VT-recurrence and one patient with an ICD had SCD. Mortality was 22%. In the 37 patients with LVEF≥35%, tolerated VT and non-inducibility post procedure, no SCD or VT-recurrence was observed. Also, in this group no patient was using AAD for VT at last follow-up. In the 14 remaining patients with LVEF≥35% and tolerated VT who were still inducible after ablation, no SCD occurred but VT recurred in 29% (median VTCL 303ms [200-374]) with AAD-use for VT in 29%. Conclusion This study supports that ICM patients without prior ICD and LVEF≥35% who present with hemodynamically well-tolerated VT and are non-inducible after ablation have an excellent prognosis. Successful CA without ICD implantation seems to be safe in these selected patients.

Funding Acknowledgements Type of funding sources: None. Background Conducting systematic annotation and ablation of evoked delayed potentials (EDP) in response to short coupled right ventricular extra-stimuli (RV-ES) has improved ablation outcome of post myocardial infarction (MI) ventricular tachycardia (VT). The reported short radiofrequency catheter ablation (RFCA) times suggests the presence of predilection areas for these functional substrates. Purpose To evaluate the electroanatomical characteristics and distribution of EDPs in post-MI patients referred for RFCA of VT. Methods Electroanatomical mapping (EAM) data of 48 post-MI patients (69 ± 9 years, 39 male, LV ejection fraction 36 ± 10%, anterior MI 20 [42%], inferior MI 28 [58%]), who underwent functional substrate mapping and ablation were analyzed. Pre-procedural cardiac CTs of 16 patients (8 anterior, 8 inferior MI) were integrated with EAM data. Infarct extension (defined as bipolar voltage [BV] <3.0mV, dense scar <0.5mV and scar borderzone [BZ] 0.5-3mV) and EDP location were determined based on the AHA 17-segment model of the left ventricle. Results RV-ES was performed during mapping at 2180 LV sites (median 46 per patient, range 8-81) and EDPs were observed at 631 (29%) sites. Patients had a median of 11 (range 1-37) EDP sites. Compared to no-EDP sites, EDP sites had lower BV (median 0.57 mV vs. 0.77 mV, P <0.001), longer duration (median 79 ms vs. 66 ms, P <0.001), and larger number of positive sharp deflections (median 6 vs. 5, P <0.001) during sinus rhythm. Of all EDP sites, 278 (44%), 286 (45%), 64 (10%), and 3 (1%) had BV of <0.5mV, ≥ 0.5mV and <1.5 mV, a BV of ≥1.5 mV and <3.0 mV, and a BV of >3.0 mV, respectively. In the 16 patients with CT image integration, a total of 124/272 segments showed EA scar with a median (IQR, range) of 8 (6-9, 4-12) segments per patient. Any EDP was identified in 71/124 (57%) of segments with EA scar. Of note, 73% of all EDPs in inferior MIs and 64% of all EDPs in anterior MI were located in 4 AHA segments, namely 3,4, 9,10 and 7,8,13,14, respectively, close to the inferior or anterior RV insertion. Such a cluster of EDP sites around the RV insertion was found in 6 (75%) patients with inferior MI and in 7 (88%) patients with anterior MI. Conclusion About 10% of EDPs are identified at sites with BV of ≥1.5mV and <3.0mV during sinus rhythm supporting the recently proposed BV threshold <3.0mV for post-MI scars. EDPs are frequently located near the RV insertion in both inferior MI and anterior MI suggesting a role of the RV insertion in the functional substrate of post-MI VT.