Abstract Body (Do not enter title and authors here): Background: Although there is an association between scar burden and an increased risk of recurrent arrhythmic events; but there is a limited data on the location of myocardial substrate and its association with the stage of non-ischemic cardiomyopathy (NICM) assessed by left ventricular ejection fraction (LVEF).

Hypothesis: Location and extent of arrhythmogenic scar burden in patients with NICM represent the progression of the disease.

Aim: To evaluate:
Association of location and extent of myocardial substrate (Isolated Septal vs. Septal and Non-Septal involvement) with LVEF.
Comparison of arrhythmic burden according to location of the myocardial substrate based on findings during VT ablation.

Methods: We performed retrospective data collection in patients with NICM who underwent VT ablation procedure and stratified them according to EF of < 35% vs. > 35%. For the initial analysis, we compared the location of myocardial substrate (Isolated septal vs. Septal + Non-Septal involvement) assessed with the use of Cardiac magnetic resonance imaging (cMRI) and electroanatomical mapping. We also compared the number of distinct mmVT morphologies induced during ablation according to the location of the myocardial substrate.

Results: We analyzed a total of 183 consecutive patients with NICM who underwent VT ablation during the time frame of 11/2016 to 11/2023 and had cMRI with mapping data available. The mean age of patients in our study cohort was 60.9 years (IQR 53-71) and 20.7% of population were females the mean LVEF in study was 39%. Isolated septal involvement was more common in patients with LVEF > 35% than the patients with LVEF < 35% (32.3% vs. 25.3%, p = 0.04). Despite isolated septal involvement, the total number of distinct mmVT induced during VT ablation were similar to the group with Septal + Non-septal involvement. (2.03 vs. 1.82, p = 0.22)

Conclusion: Our results suggest a temporal involvement in the extent of arrhythmogenic substrate as in; septal involvement might represent an earlier stage in NICM patients.
Despite the finding, isolated septal involvement seemed to have an equivalent risk as an arrhythmogenic VT substrate based on the findings of distinct morphologies of mmVT induced during ablation.