Vascular Tissue Reaction to Acute Malapposition in Human Coronary Arteries

BACKGROUND: The vascular tissue reaction to acute incomplete stent apposition (ISA) is not well known. The aim of this study was to characterize the vascular response to acute ISA in vivo and to look for predictors of incomplete healing. METHODS AND RESULTS: Optical coherence tomography studies of 66 stents of different designs, implanted in 43 patients enrolled in 3 randomized trials, were analyzed sequentially after implantation and at 6 to 13 months. Seventy-eight segments with acute ISA were identified in 36 of the patients and matched with the follow-up study by use of fiduciary landmarks. The morphological pattern of healing in the ISA segments was categorized as homogeneous, layered, crenellated, bridged, partially bridged, or bare, depending on the persistence of ISA and on the coverage. After 6 months, acute ISA volume decreased significantly, and 71.5% of the ISA segments were completely integrated into the vessel wall. Segments with acute ISA had higher risk of delayed coverage than well-apposed segments (relative risk 2.37, 95% confidence interval 2.01-2.78). Acute ISA size (estimated as ISA volume or maximum ISA distance per strut) was an independent predictor of ISA persistence and of delayed healing at follow-up. CONCLUSIONS: Neointimal healing tends to reduce ISA, with the malapposed stent struts often integrated completely into the vessel wall, resulting in characteristic morphological patterns. Coverage of ISA segments is delayed with respect to well-apposed segments. The larger the acute ISA, the greater the likelihood of persistent malapposition at follow-up and delayed healing.