title: Pathological healing response of explanted MitraClip devices.
abstract: BACKGROUND
  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.
  
  
  RESULTS
  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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Medical Director/President, CVPath Institute, Inc, 19 Firstfield Rd, Gaithersburg, MD 20878, USA. rvirmani@cvpath.org
authors.forename: Elena
authors.initials: E
authors.lastname: Ladich
authors.forename: Mary Beth
authors.initials: MB
authors.lastname: Michaels
authors.forename: Russell M
authors.initials: RM
authors.lastname: Jones
authors.forename: Elizabeth
authors.initials: E
authors.lastname: McDermott
authors.forename: Leslie
authors.initials: L
authors.lastname: Coleman
authors.forename: Jan
authors.initials: J
authors.lastname: Komtebedde
authors.forename: Donald
authors.initials: D
authors.lastname: Glower
authors.forename: Michael
authors.initials: M
authors.lastname: Argenziano
authors.forename: Ted
authors.initials: T
authors.lastname: Feldman
authors.forename: Masataka
authors.initials: M
authors.lastname: Nakano
authors.forename: Renu
authors.initials: R
authors.lastname: Virmani
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D019918:Heart Valve Prosthesis Implantation / Q000295:instrumentation* / Q000592:standards; D006801:Humans; D008297:Male; D008875:Middle Aged; D008943:Mitral Valve / Q000473:pathology* / Q000601:surgery*; D008944:Mitral Valve Insufficiency / Q000473:pathology / Q000601:surgery; D013525:Surgical Instruments / Q000592:standards; D014945:Wound Healing / Q000502:physiology*