Abstract Introduction Current recommendations support short-term dual antiplatelet therapy (DAPT) for patients undergoing transcatheter aortic valve replacement (TAVR) despite no relevant study exploring the extent of platelet inhibition by clopidogrel. Purpose To assess whether P2Y12 inhibition by clopidogrel as evaluated by vasodilator-stimulated phosphoprotein flow cytometry test (VASP-FCT) impacts 1-year clinical outcomes in patients undergoing TAVR. Methods Patients were included in a prospective registry between February 2010 and May 2019. VASP-FCT was assessed 24h after the procedure. Responder to clopidogrel was defined by a platelet reactivity index ≤50%. Results Of 640 patients who underwent TAVR with preprocedural clopidogrel therapy, we enrolled 491 patients for whom VASP data were available. Responders were identified in 22% (n=110) of patients and low responders were 78% (n=381) of patients. Low body mass index, active cancer, and clopidogrel on admission were found to be independent predictors of responder. Mean transaortic pressure gradient was lower in the responder group at 1-month post-TAVR (9.9±4.4 mmHg vs. 11.2±5.8 mmHg, p=0.03) but was similar at 1-year (11.5±6.2 mmHg vs. 11.9±7.4 mmHg, p=0.74). By multivariate Cox regression analysis, patients responding to clopidogrel (hazard ratio [HR]: 2.19; 95% confidence interval [CI]: 1.04 to 3.64; p=0.04), prior PCI (HR: 2.12; 95% CI: 1.07 to 4.37; p=0.03), and mean transaortic pressure gradient at baseline (HR: 0.07; 95% CI: 0.01 to 0.70; p=0.02) were identified as independent predictors of 1-year adverse clinical outcomes, including all-cause death, myocardial infarction, stroke, and heart failure hospitalization. Conclusions Appropriate P2Y12 inhibition by clopidogrel is a major determinant of adverse clinical events after TAVR. In sum, the present data challenges the need of DAPT as a standard therapy during TAVR. Figure 1 Funding Acknowledgement Type of funding source: None