Regional Remodeling as the Cause of Late Stent Malapposition

BACKGROUND: Late stent malapposition (LSM) is only detected if intravascular ultrasound (IVUS) is performed at implantation and follow-up. We used a novel "regional" IVUS analysis to assess the mechanism of LSM. METHODS AND RESULTS: Corresponding image slices on postimplantation and follow-up IVUS studies of 11 malapposed stents were identified and electronically rotated until they were aligned. The geometric center of the stent was identified, and the angle of late malapposition measured. Radii were drawn from this center through the transition points between complete apposition and LSM. These two circumferences were divided into equal arcs, and radii were drawn to the external elastic membrane (EEM). Measurements included EEM radius and circumference, plaque and media (P P=0.0004). DeltaEEM for each malapposed radius was greater than for each apposed radius (P<0.05 for all comparisons). Stent-intima separation correlated with EEM radius increase within the malapposed circumference (r=0.83, P=0.0013). At follow-up, the mean P P<0.0001). However, the decrease in P P=0.05), the result of positive remodeling. CONCLUSIONS: The main cause of LSM is a regional increase in EEM (regional positive remodeling).