Optimized systolic material properties
The systolic material parameter, Tmax, was determined to be 199.56 kPa in the remote myocardium and 62.85 kPa in the infarct borderzone.
Effect on annular geometry
The pre-operative (baseline) commissure-commissure (CC) distance is 31.5 mm and septo-lateral (SL) distance is 22.6 mm.
Although both rings are listed as 24 mm by Edwards, as seen in , ring dimensions are slightly different. The CC dimension of the Physio II and IMR ETLogix ring were similar at 24.3 and 23.5 mm respectively. The percent reduction in CC distance was therefore similar with Physio II and IMR ETLogix ring reductions of 22.9 and 25.4% respectively. The bigger difference is in the SL dimension where the Physio II is 14.4% larger than the IMR ETlogix ring. Reduction in the SL diameter was therefore more pronounced in the IMR ETlogix ring with Physio II and IMR ETLogix ring reductions of 18.0 and 26.0% respectively.
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.
Force on virtual sutures
Force on the virtual sutures attached to the posterior side of the rings is shown in . The IMR ETlogix ring was associated with lower virtual suture force in the P2 region but higher force in P1 and P3 regions.
Virtual suture force. As discussed in the text only force on the posterior annulus is reported.
LV fiber stress reduction
As shown in , mitral annuloplasty reduced fiber stress at both ED and ES only at the base of the LV. However, fiber stress reduction occurred in the remote, borderzone and infarct zones. Specifically, Physio II and IMR ETlogix rings reduced fiber stress at ES by 2.9 kPa and 3.3 kPa in the remote zone, 2.2 and 3.1 kPa in the borderzone, and 1.6 kPa and 1.9 kPa in the infarct respectively.
Fiber stress by longitudinal region for the A. End-diastole, B End-systole.
LV fiber strain
Similar to fiber stress, mitral annuloplasty reduced fiber strain only at the base of the LV (). In the basal region, the Physio II ring led to a larger fiber strain reduction than the IMR ETlogix ring (Physio II: −0.104; IMR ETlogix: −0.107; Control: −0.12).
In our previous model, ischemic MR was identified as a gap between the leaflets at end-systole. shows the coaptation profiles of the leaflets at ES for control Physio II and IMR ETlogix simulations. Note that both annuloplasty simulations demonstrated complete closure of the regurgitant gap.
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.
The SL leaflet dimension/ width was reduced after both types of annuloplasty. For instance, the SL width of the anterior leaflet at baseline and with Physio II and IMR ETlogix rings was 14.3, 13.3 and 12.9 mm respectively. As a consequence, annuloplasty was associated with an increase in leaflet curvature. The simulation also suggests that coaptation between the posterior and anterior leaflets occurs higher on the anterior leaflet after annuloplasty with the IMR ETlogix ring.
Leaflet stress reduction
Both rings significantly reduced average effective (von Mises) stress on the anterior and posterior leaflets, as shown in . The Physio II and IMR ETlogix rings respectively reduced stress in the anterior leaflet by 13.2 kPa and 7.1 kPa respectively, and in the posterior leaflet by 15.1 kPa and 10.7 kPa.
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.
shows stress reduction in the six leaflet regions (namely A1–A3, P1–P3). Stress reduction was observed in all regions. Between the Physio II and IMR ETlogix rings, the difference in stress reduction in P2 and P2 regions was minimal. The Physio II ring lowered stress more than the IMR ETlogix ring by 9.2 kPa in the P3 region.
Chordal Stress Reduction
Both rings reduce the chordal stress at end systole. The average chordal stress was 18.4 kPa before annuloplasty ring. The stress was reduced to 13.4 kPa and 9.1 kPa by the Physio II and IMR ETlogix rings, respectively.