BACKGROUND: Extra-valvular cardiac damage (EVCD) and extracellular volume (ECV) are key determinants of poor outcomes in patients with severe aortic stenosis (AS) undergoing transcatheter aortic valve implantation (TAVI). We aimed to assess the association of ECV derived at cardiac computed tomography (CT) with EVCD pre and post-TAVI, its impact on left ventricular reverse remodeling and functional improvements at 3-month follow-up in patients with severe AS undergoing TAVI. METHODS: Prospective study of 73 consecutive patients undergoing TAVI, with CT-derived ECV assessment, baseline and follow-up echocardiographic evaluation of EVCD. After identifying the best ECV cut-off for predicting EVCD progression and advanced EVCD (Stages 3-4) at follow-up by Youden index, patients were divided into low (n=39) and high ECV (n=34) groups. Predictors of EVCD progression, advanced EVCD and functional improvements at follow-up were identified at logistic regression analysis. RESULTS: At 3-month follow-up, 34.2% of patients showed EVCD progression. ECV≥32% accurately predicted EVCD progression and Stages 3-4 (AUC=0.66, p<
0.002). At follow-up, patients with high ECV were more frequently in Stages 3-4 (p=0.011) and had a 50% progression rate (p=0.012). Conversely, patients with low ECV exhibited greater LV reverse remodeling (p=0.004) and improvement in NYHA Class at both 3-month (p=0.020) and 6-month follow-up (p=0.002) compared to high ECV ones. High ECV emerged as independent predictor of EVCD progression (OR=4.34, 95%CI 1.36-13.78, p=0.013), Stages 3-4 (OR=5.71, 95%CI 1.77-18.42, p=0.004) and lack of improvement in NYHA class (OR=3.22, 95%CI 1.14-9.09, p=0.027) at 3-month follow-up. CONCLUSIONS: Elevated CT-derived ECV was associated with EVCD progression and reduced functional improvement after TAVI.