Myocardial deformation

Waldman, L.K., Fung, Y.C., and Coveil, J.W., Transmural myocardial deformation in the canine left ventricle normal in vivo three-dimensional finite strains, Circ. Res., 57,152-163,1985. 

Cine MRI is an excellent imaging modality for dyssynchrony that provides reproducible, high-resolution three-dimensional assessment of global and regional myocardial function (48). MRI tagging measures myocardial deformation during systole and early diastole and gives quantitative analysis of... 

The mechanical properties of fibrin are essential for its functions in hemostasis and wound healing, since the clot must stop bleeding and yet allow the penetration of cells. The mechanical properties of a thrombus will determine how it responds to flowing blood, including elastic or plastic deformation and embolization. Epidemiological studies have revealed a relationship between myocardial infarction and clot stiffness (Fatah et al., 1996 Scrutton et al., 1994). 

Scrutton, M. C., Ross-Murphy, S. B., Bennett, G. M., Stirling, Y., and Meade, T. W. (1994). Changes in clot deformability - a possible explanation for the epidemiological association between plasma fibrinogen concentration and myocardial infarction. Bbod Coagul. Fibrinolysis 5, 719-723. 

The past two decades have seen a proliferation of mathematical models which have been developed for the purpose of assessing myocardial function. Most of these models have focused on the quantitation of ventricular wall stresses and deformations which take place during diastole. 

Whether or not the in vitro test results of the myocardial properties are applicable for the in vivo cardiac analyses remains as a heated debate topic. As has already been discussed earlier, the finite element models enable te myocardial passive and active characteristics to be estimated in vivo. It is an inverse problem of knowing the loading and the consequent deformation and of continuously guessing the material properties until the simulated and measured deformations are approximately matched. 

A short chronological review of the diverse available mechanical models of the LV precedes a critical reassessment of the various main factors involved in a finite element analysis of the ventricle. These factors constitute the three-dimensional geometry of the LV and its kinematical boundary conditions the extent of the deformation the ventricle undergoes the pressure distribution on the endocardium the myocardial constitutive law as well as its anisotropy, and the activation mechanism of the muscle. A rationale for developing an improved finite element model, gradually incorporating these factors, concludes the presentation. 

Several basic factors are involved in the process of modelling the mechanical behaviour of the LV by the FE method. These factors are the geometry of the ventricle including its kinematic boundary conditions, the extent of the deformation that the LV undergoes, the pressure distribution on the endocardium, the myocardial constitutive law as well as its anisotropy and the activation mechanism of the muscle, mainly manifested in the systolic phase. Furthermore, computer resources such as storage and computation time requirements should also be considered. 

During the diastolic phase of the cardiac cycle the ventricle is usually considered to be a passive material deforming under the increasing blood pressure pumped into it. Contrary to this, during the systolic phase the myocardium actively contracts. The active properties of the muscle fibers have been implemented only in one model of the LV (Chen et al, 1980). It would therefore be important in future FE simulations of the LV to incorporate the active characteristics of the myocardial fibers. 

Nonlinear Geometric Effects. J Biomechanics 7 509-516 Mirsky I (1969) Left ventricular stresses in the intact human heart. Biophys J 9 189-208 Neckyfarow CW, Perlman AB (1976) Deformation of the human left ventricle material and geometric effects. Proc 4th New-England Bioeng Conf, 169-172 Panda SC, Natarajan R (1977) Finite-element method of stress analysis in the human left ventricular layered wall structure. Med Biol Eng Comp 15 67-71 Pao YC, Ritman EL, Wood EH (1974) Finite-element analysis of left ventricular myocardial stresses. J Biomechanics 7 469-477... 

Accurate quantitation of the shape and dimensions of all cardiac chambers and myocardium is possible with the Dynamic Spatial Reconstructor (DSR). Generally a single bolus injection of approximately 2ml/kg roentgen contrast agent in the right atrium will provide information of the chamber volumes and myocardial mass within 5% of the actual value. The detailed shape of the chambers and myocardium facilitates evaluation of heart deformed by complex congenital heart disease or myocardial infarction (aneurysm). 

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