Annular dilatation increases stress in the mitral valve and delays coaptation: a finite element computer model

The purpose of this study was to examine the effects of annular dilatation on coaptation, and leaflet and chordal stresses, using a three dimensional finite element computer model. To do this, the whole mitral valve was simulated using ANSYS 4.4A software. Normal model geometry, collagen fiber orientation, tissue thickness, and material properties were determined from fresh porcine valves. For annular dilatation, the annular circumference was increased by 18% versus normal. Isovolumic contraction and rapid ventricular ejection were simulated. Data showed that, in the annular dilatation model, the stress magnitudes increased more than two-fold compared with normal in both the anterior leaflet and posterior leaflet. Coaptation was greatly delayed in the dilatation model, and the leaflets never fully coapted. Chordal stresses were also greatly increased in the dilatation model. In conclusion, increased stress due to annular dilatation may lead to tissue disruption, further dilatation, delayed coaptation, and increased regurgitation, in a 'closed-loop' degenerative process.