Summary X Implantable cardioverter-defibrillator (ICD) guidelines draw on trials with few older patients, yet ~50,000 ICDs are implanted annually in patients ≥65 years old. Half of older ICD recipients will either be dead or enrolled in hospice within 5 years of implantation, and little evidence supports critical long-term decisions including (1) whether to replace ICDs when the battery declines, or (2) timing of ICD deactivation to avoid painful shocks at the end of life. There is therefore a pressing need for longitudinal data on patient health status and clinical experiences in the years after ICD implantation to support patient-centered decisions. To extend our prior work and further improve the care of patients living and dying with ICDs, we now propose the Prospective Investigation of Palliative and End-of-Life ExpeRiences with ICDs (PIPER-ICD) Study, a rigorous, multi- center cohort with the goal of defining patient-centered experiences of older ICD patients >5 years post implantation. We will prospectively collect data on geriatric conditions and quality of life from 1200 patients at 5 sites, enriched with remote monitoring data on arrhythmias and physical activity, to evaluate clinical and functional trajectories (Aim 1). This cohort will support novel application of a semi-competing risks approach to personalizing individualized outcome profiles for death and ICD shocks (Aim 2). Lastly, we will apply mixed methods to the decedent cohort (N~200) to quantify ICD shocks at the end of life and identify potential targets for interventions to improve their care (Aim 3). This proposal is led by cardiac electrophysiologist with expertise in geriatrics, outcomes research, and bioethics, supported by an experienced research team with a strong record of collaboration. IMPACT: As the first comprehensive, prospective study of older ICD patients focused on long- term and end-of-life experiences, PIPER-ICD will generate patient-centered and personalized data essential for evidence-based guidance to serve a vulnerable population. PIPER-ICD will thus serve as a rich resource to support decision-making for millions of patients considering replacement or deactivation of their ICDs.