This thesis evaluates the impact of transcatheter aortic valve implantation (TAVI) in nonagenarian patients with severe aortic stenosis, a population often underrepresented in clinical research despite high disease prevalence and mortality. Using data from a single-center Geneva TAVI cohort, outcomes were analyzed with a focus on mortality, procedural complications, frailty, and quality of life. Among 710 consecutive patients undergoing TAVI between 2008 and 2023, nonagenarians were compared with younger counterparts, with frailty assessed using a modified Essential Frailty Toolset. Results demonstrate that while advanced age is associated with increased baseline vulnerability, selected nonagenarians derive meaningful survival and quality-of-life benefits following TAVI. Importantly, frailty emerged as a stronger predictor of adverse outcomes than chronological age alone. These findings support a comprehensive, multidisciplinary evaluation integrating geriatric parameters to optimize patient selection and avoid undertreatment, as well as futile interventions in this growing population.