The presentation of EVEREST registry clinical results of the MitraClip (Evalve) therapy for patients with mitral regurgitation took place at the 21st annual Transcatheter Cardiovascular Therapeutics (TCT) scientific symposium in San Francisco, US. Mitral regurgitation is the most common type of heart valve insufficiency in Europe and the US, and affects millions of people worldwide.
Abbott’s recent acquisition of Evalve, a leader in the development of devices for minimally invasive repair of cardiac mitral valves, provides Abbott with a presence in the growing area of non-surgical treatment for structural heart disease.
On 22 September, at the TCT symposium, Renu Virmani, Cardiovascular Pathology Institute, Gaithersburg, US, reported the long-term histologic response following MitraClip implantation. The healing response following MitraClip device implantation has not been characterised in humans, Virmani said. The MitraClip device has been explanted for clinical reasons providing a unique opportunity to study the healing process, she explained. The study examined the histopathology and mechanical integrity of 16 clips explanted after 300 days. During explant surgery, 13 clips required sharp dissection to expose the unlocking mechanism resulting in surgical artifacts, while the remaining three clips were explanted with minimal tissue disturbance. Prior to processing of the clips, X-rays and digital photos were taken to record gross pathology and to assess mechanical integrity of clip components. The clip with adjacent tissue was dehydrated in a series of alcohol and embedded in methyl methacrylate. After polymerisation, the clip was sectioned in half, cut, polished and stained with toluidine blue-basic fuchsin. Sections were examined by light microscopy for healing and implant integrity.
Virmani went on to report that the results showed the healing response observed from 301 days to 1,878 days demonstrated a collagen-rich matrix incorporating the clip components and complete encapsulation of the clip with organised, fibrous endocardial growth. In the three intact clips, a fibrous tissue bridge was observed over and between the clip arms resulting in tissue continuity between the two valve leaflets. Tissue growth over the clip arms had a mean thickness 0.29±0.40mm. There was no, or minimal, inflammation and no evidence of infection. None of the 16 long-term clips demonstrated any evidence of wear, component fracture or corrosion for up to five years.
In conclusion, Virmani told delegates, MitraClip device mechanical integrity was maintained up to five years. No significant stenosis or inflammation was observed beyond 300 days. Fibrous encapsulation of the clip and adjacent leaflets demonstrated complete healing and incorporation of the implant within the native mitral valve.