Changes in the Structure and Overall Thickness of the Anterior and Posterior Mitral Valve Leaflets after Undersizing Mitral Annuloplasty to Repair Ischemic Mitral Regurgitation
Alicja K. Sielicka, Muralidhar Padala.
Emory University, Atlanta, GA, USA.
OBJECTIVE: Undersizing ring annuloplasty (URA) is a frequently used repair technique to correct ischemic mitral regurgitation (IMR). Though IMR is repaired, the leaflet biomechanics is highly abnormal, with extended anterior and posterior leaflets (Fig. A). Thus failure of URA and recurrence of IMR are as high as 58% at 2 years. We hypothesized that abnormal leaflet mechanics after URA renders them fibrotic, inducing thickening and stiffening leading to repair failure. A repair that better restores leaflet kinematics (papillary muscle approximation - PMA) can inhibit this leaflet fibrotic remodeling.
METHODS: 30 Yorkshire pigs were induced with an inferior myocardial infarction (Fig. B) and allowed 2.5 months to develop moderate IMR (Fig. C1). Pigs were randomized to four groups: (G1, n=5) sham/no repair; (G2, n=7) URA (Fig. C2); (G3, n=6) PMA (Fig. C3); (G4, n=12) URA+PMA. Leaflet kinematics were measured pre-op, post- op and at 3 months post-repair. Mitral valve tissue was collected for histology staining.
RESULTS: Hyperextension of the anterior leaflet and immobility of the posterior leaflet were observed in URA and URA+PMA, but not in sham or PMA. Anterior leaflet was thicker in all the repair groups, but not the sham group, whereas the posterior leaflet was thicker only in the URA and URA+PMA groups (Fig D). Pro-fibrotic TGF-beta expression was higher in the URA and URA+PMA leaflets, indicating a mechanosensitive fibrotic response (Fig E). The trilayered structure of the leaflet was damaged in URA and URA+PMA, but not in the PMA or sham groups (Fig. F). CONCLUSIONS: URA was associated with pro-fibrotic remodeling of mitral leaflets, potentially from abnormal leaflet mechanics. Adding PMA to URA could not sufficiently restore leaflet mechanics. Elevated leaflet stretch in tandem with TGFβ may enhance leaflet fibrosis and potentially cause repair failure.
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