Pathological Healing Response of Explanted MitraClip Devices

The safety and effectiveness of the MitraClip device (Abbott Vascular, Menlo Park, CA) is being evaluated in the Endovascular Valve Edge-to-Edge Repair Study (EVEREST) clinical studies. The healing response after device implantation has not previously been characterized in humans.A total of 67 explanted devices (implantation duration, 1 to 1878 days) from 50 patients were submitted for histological evaluation. Explants were analyzed in 4 implantation intervals: acute (≤30 days; n=7), subacute (31 to 90 days; n=23), chronic (91 to 300 days; n=18), and long term (>300 days; n=19). The acute healing response consisted of platelet/fibrin deposition. The subacute response exhibited granulation tissue with early fibrous encapsulation (pannus). The chronic response was characterized by various degrees of tissue bridging between the device arms. The long-term healing response demonstrated collagen-rich matrix (by type I collagen), incorporating the device components with complete encapsulation by organized, fibrous growth. In long-term devices with minimal surgical disruption, a fibrous tissue bridge (mean area, 7.39±4.3 mm(2)) was observed over and between the device arms, resulting in atrial tissue continuity between the 2 valve leaflets. Devices demonstrated no evidence of endocarditis, mechanical wear, component fracture, or corrosion up to the time of explantation (median, 119 days; first and third quartiles, 42 and 365 days).In all patients, device mechanical integrity was maintained up to the time of explantation. Four phases of physiological healing were observed: platelet and fibrin deposition, inflammation, granulation tissue, and finally, fibrous encapsulation. Long-term device fibrous encapsulation with extension over adjacent mitral leaflets and tissue bridge formation adds structural stability. Clinical Trial Registration- URL: http://clinicaltrials.gov/show/NCT00209274. Unique identifiers: NCT00209339 and NCT00209274.