Traction mechanical characterization of porcine mitral valve annulus.

The Mitral Annulus (MA) is an anisotropic, fibrous, flexible and dynamical structure. While MA dynamics are well documented, its passive mechanical properties remain poorly investigated to complete the design of adequate prostheses. Mechanical properties in traction on four sections of the MA (aortic, left, posterior and right segments) were assessed using a traction test system with a 30 N load cell and pulling jaws for sample fixation. Samples were submitted to a 1.5 N pre-load, 10 pre-conditioning cycles. Three strain rates were tested (5 %/min, 7 %/min and 13 %/min), the first two up to 10 % strain and the last until rupture. High-resolution diffusion-MRI provided microstructural mapping of fractional anisotropy and mean diffusion within muscle and collagen fibres. Ten MA from porcine hearts were excised resulting in 40 tested samples, out of which 28 were frozen prior to testing. Freezing samples significantly increased Young Moduli for all strain rates. No significant differences were found between Young Moduli at different strain rates (fresh samples 2.4 ± 1.1 MPa, 3.8 ± 2.2 MPa and 3.1 ± 1.8 MPa for increasing strain rates in fresh samples), while significant differences were found when comparing aortic with posterior and posterior with lateral (p < 0.012). Aortic segments deformed the most (24.1 ± 9.4 %) while lateral segments endured the highest stress (>0.3 MPa), corresponding to higher collagen fraction (0.46) and fractional anisotropy. Passive machinal properties differed between aortic and lateral segments of the MA. The process of freezing samples altered their mechanical properties. Underlying microstructural differences could be linked to changes in strain response.

[Pulmonary stenosis and atresia with intact ventricular septum]. / Sténose pulmonaire et atrésie pulmonaire à septum interventriculaire intact.

Pulmonary atresia and critical pulmonary stenosis with intact ventricular septum includes a wide spectrum of cardiopathies with great morphological heterogeneity. The pulmonary valve may be completely atretic or may contain a puncture hole if stenosis is present. The obstruction may be membranous and/or muscular. All components of the right ventricle can be affected, even the coronary circulation with ventriculocoronary connections and stenosis or atresia of the pulmonary arteries. Prenatal diagnosis is made when the right ventricle is hypoplastic and hypertrophic. The pulmonary valve is thickened and the pulmonary artery is perfused retrogradely through the ductus arteriosus. Right ventriculocoronary connections may sometimes be seen with fetal echocardiography. Postnatal survival depends on the patency of the ductus arteriosus, requiring prostaglandin E1 infusion. When hypoplastic right ventricle and/or ventricle-dependent coronary circulation exists, biventricular circulation is not possible. In these cases, surgical treatment is palliative. In cases with well-developed right ventricle, transcatheter therapy is usually provided with perforation and balloon dilation of the pulmonary valve. In cases of muscular obstruction of the right ventricle outflow tract, surgery may be considered as first-line therapy. In case of prenatal diagnosis, the medical termination of pregnancy is possible when severe right ventricular hypoplasia exists, precluding biventricular circulation. Postnatally, the prognosis of the patients is highly variable, mainly related to the size of the right cavities and the presence of coronary anomalies.