Browsing by Subject "Annulus tension"
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Item Annulus tension in the tricuspid valve: The effects of annulus dilation and papilliary muscle movement(2012-08) Smith, Dylan; He, Zhaoming; Idesman, Alexander V.Tricuspid valve (TV) annular dilatation compromises TV coaptation and may lead to regurgitation. Annular mechanics involves interaction between the TV leaflets and right ventricle myocardium and plays a role in annular dilatation. Annulus tension (AT) is a leaflet force on the annulus and contributes to understanding of annular dilatation. The objective for this study was to determine the effect of PM position and annulus dilation on AT. Force transducers were attached to the porcine TV annulus using a TV closure test rig. The test rig allowed us to apply 40 mmHg of pressure on the TV and adjust the size of the annulus to the normal and dilatated size, which were 9.0 cm2 and 50% increase in area. Papillary muscles were secured and adjusted to simulate papillary muscle displacement, which are 5 mm apical displacement, 5mm lateral displacement, and 5 mm both apical and lateral displacement of the anterior papillary muscle. AT was measured in a normal and 3 pathological papillary muscle positions for a normal and a dilatated annuli. Eight TVs were tested. AT peaked at the commissures for both normal and dilatated annuli. The average AT in the normal TV was approximately 8.9 N/m with the highest AT along the posterior segment of the annulus. The average AT for the dilatated annulus was 16.3 N/m which was almost a 90% increase. The greatest average increase was found along the septal and anterior commissures and the smallest increase along the posterior commissure. As compared with average AT in the normal annulus, the average AT increased by 18.0%, 7.9%, and 30.3% for a 5mm apical, 5mm lateral, and both 5mm apical and lateral PM displacements, respectively. The similar AT distribution was found for both annuli. The apical anterior papillary muscle displacement increased AT evenly throughout the entire annulus. The lateral anterior papillary muscle displacement lowered AT in the anterior commissure and increased AT in other segments. Both apical and lateral anterior papillary muscle displacement caused no change of AT in the anterior commissure for the normal annulus, lowered AT in the anterior commissure for the dilated annulus, and increased AT in all other segments. In the normal annulus, the average AT is significantly increased(p<.05) for the apical and both apical and lateral anterior papillary muscle displacement, with no significant change for lateral anterior papillary muscle displacement. In the dilated annulus, the average AT is significantly increased only for the both apical and lateral anterior papillary muscle displacement, and not changed for the other two anterior PM conditions. TV AT is smaller in the TV than that in the mitral valve, which indicates the TV interacts with right ventricle wall in a weak manner. The increase in AT due to annulus dilatation and papillary muscle displacement helps to counteract TV annular dilatation.Item Mitral Valve annulus tension : an in vitro study(2011-05) Bhattacharya, Shamik; He, Zhaoming; Hashemi, Javad; Boros, Rhonda L.; Ma, Yanzhang; Parameswaran, SivaThe mitral valve is an important valve inside the heart controlling the flow of oxygenated blood from lungs to heart. It has a complex cardiac structure comprising the annulus, the leaflets, chordae tendinae and papillary muscles. There are two leaflets; anterior and posterior which are attached with the annulus. The leaflets are anchored to the inner wall of left ventricle at the papillary muscles through the chordae tendinae. During mitral valve closure, the leaflets are pulled towards the center which in turn pulls the mitral annulus. The mitral annulus is attached to the myocardium or the muscle of the heart. When the valve closes during systole, the leaflets coaptate and tries pull the mitral annulus towards center. The myocardium resists this pulling. So there is a balance of force in the annulus which is important for the valve closure. There is an alteration of this force balance if there is any change in the geometry and shape of the annulus. Mitral valve annulus dilation is a structural change where the annulus gets enlarged, prevents the valve closure and abets mitral regurgitation. This thesis summarizes the in vitro measurement of the annulus tension (AT) in the mitral valve annulus when the valve is fully closed and the transmitral pressure is highest i.e. at peak systole. AT is the force which is transmitted to annulus from the leaflet force and balances the myocardium force. The knowledge of AT can help to understand the normal mitral valve mechanics and can give new insights into annulus dilation which is one of the common pathology of the mitral valve. In addition this knowledge of AT can also help in designing annuloplasty rings. The overall hypothesis was the establishment of the concept of AT as a parameter and the important role it plays in normal mitral valve mechanics and annulus dilation. The concept of AT can also be used to evaluate repair techniques like edge-to-edge-repair where there is a tendency of annulus dilation after the repair. In order to prove the hypothesis in vitro experiments were done with porcine mitral valve in a static set up under a transmitral pressure of 120 mm Hg. The static set up was designed to get a direct measurement of AT. The AT was measured in normal annulus, dilated annulus and annulus repaired with edge-to-edge-repair technique after prolapse. The results showed the AT was highest in the anterior region of the mitral vlave annulus followed by posterior region of the mitral valve. The AT was lowest in the commissural region. The AT increased in dilated annulus .The papillary muscle (PM) position influenced the AT. A slack PM position representing prolapse have less AT and the AT was high with a taut PM position representing myocardial infarction. The edge-to-edge-repair techniques conditions have less AT than the normal valve. From this result we can conclude that AT is an important parameter that plays in the normal mitral valve mechanics. It shows that the force acting along the annulus is not uniform. Since the force is less in the commissural region there are more chances of prolapse in the commissural region. The AT is highest in the anterior and the posterior region which probably is the reason for D shape of the annulus. The annulus tension is not affected by the saddle shape of the annulus. Annulus dilation is a consequence of imbalance between the annulus tension and myocardium force.