BACKGROUND: Valve-in-valve (ViV) transcatheter aortic valve replacement (TAVR) is an established therapy for failed bioprosthetic valves but carries risks for coronary obstruction and subclinical leaflet thrombosis, characterized by hypoattenuated leaflet thickening (HALT) on multidetector computed tomography. Intentional leaflet modification techniques, such as BASILICA (bioprosthetic or native aortic scallop intentional laceration to prevent iatrogenic coronary artery obstruction), have been developed to prevent coronary obstruction, but their impact on leaflet thrombosis remains unclear. OBJECTIVES: The aim of this study was to evaluate the association of intentional leaflet modification with the incidence of HALT in patients undergoing ViV TAVR. METHODS: In a retrospective analysis of 141 patients undergoing ViV TAVR with postprocedural multidetector computed tomography, 61 patients received leaflet modification, and 80 underwent standard ViV TAVR without leaflet modification. Baseline characteristics, post-TAVR computed tomographic findings including HALT, and other procedural outcomes were compared. A sensitivity analysis stratified outcome by transcatheter heart valve type. Predictors of HALT were assessed using multivariable logistic regression with clinically relevant covariates. RESULTS: Leaflet modification was more frequently performed in female patients (62.3% vs 45%; P = 0.04) and those with small (≤21 mm) prosthetic valves (50% vs 22.5%; P < 0.001). Patients undergoing leaflet modification had significantly lower postprocedural mean transvalvular gradients (13 ± 6 mm Hg vs 18 ± 9 mm Hg; P < 0.001) and a reduced incidence of HALT (19.7% vs 40%; P < 0.01) compared with those without leaflet modification. These findings persisted after the analysis was restricted to self-expanding transcatheter heart valves. HALT involving multiple leaflets was numerically less common with leaflet modification (33.3% vs 65.6%; P = 0.054), and thrombosis predominantly affected nonlacerated cusps (66.6% vs 33.3%). No cases of HALT were observed in patients undergoing dual-leaflet modification. Reduced leaflet motion was identified in one-third of patients with HALT, with no significant difference between groups. CONCLUSIONS: In patients undergoing ViV TAVR, intentional leaflet modification is associated with a significantly reduced incidence of HALT, suggesting a protective association with subclinical leaflet thrombosis. These results support a potentially hemodynamic benefit of leaflet modification beyond coronary obstruction prevention.