The effect of mitral annuloplasty shape in ischemic mitral regurgitation: a finite element simulation

Abstract

Background: Undersized mitral annuloplasty (MA) is the preferred surgical treatment for chronic ischemic mitral regurgitation. However, the preferred shape of undersized MA is unclear.

Methods: A previously described finite element model of the left ventricle with mitral valve based on magnetic resonance images of a sheep with chronic ischemic mitral regurgitation after posterolateral myocardial infarction was used. Saddle-shape (Edwards Physio II) and asymmetric (IMR ETlogix) MA rings were digitized and meshed. Virtual annuloplasty was performed using virtual sutures to attach the MA ring. Left ventricular diastole and systole were performed before and after virtual MA of each type.

Results: Both types of MA reduced the septolateral dimension of the mitral annulus and abolished mitral regurgitation. The asymmetric MA was associated with lower virtual suture force in the P2 region but higher force in P1 and P3 regions. Although both types of MA reduced fiber stress at the left ventricular base, fiber stress reduction after asymmetric MA was slightly greater. Neither type of MA affected fiber stress at the left ventricular equator or apex. Although both types of MA increased leaflet curvature and reduced leaflet stress, stress reduction with saddle-shape MA was slightly greater. Both MA types reduced stress on the mitral chordae.

Conclusions: The effects of saddle-shape and asymmetric MA rings are similar. Finite element simulations are a powerful tool that may reduce the need for animal and clinical trials.

Figure 1

Positioning of the Physio II annular configuration (black) and sutures (cyan). A. Virtual sutures are about to `attach' a Physio II ring. B. Expanded view of region in A. AL =Anterior leaflet, PL = Posterior leaflet, MA = Mitral annuloplasty, VS = virtual suture. C. At end-systole after virtual Physio II attachment. The white shade indicates the cut-plane for creating the leaflet coaptation profiles shown in Figure 6.

Figure 2

Shape of the two mitral annuloplasty rings. A. Top view (left) and front view (right) of Physio II ring; B. Top view (left) and front view (right) of IMR ETLogix ring.

Figure 3

Virtual suture force. As discussed in the text only force on the posterior annulus is reported.

Figure 4

Fiber stress by longitudinal region for the A. End-diastole, B End-systole.

Figure 5

End-systolic fiber strain.

Figure 6

Septal-lateral leaflet coaptation profiles at the A2-P2 (A) and A3-P3 (B) regions for control (blue), Physio II (red), and IMR ETlogix (green) ring groups.

Figure 7

Effective stress at end-systole in the anterior and posterior mitral leaflets. A. Anterior and posterior leaflets, B. Broken down by leaflet scallop. A = anterior, P = posterior, 1 = left scallop, 2 = middle scallop, and 3 = right scallop.