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Journal ArticleDOI

Regional wall mechanics in the ischemic left ventricle: numerical modeling and dog experiments

01 Jan 1996-American Journal of Physiology-heart and Circulatory Physiology (American Physiological Society)-Vol. 270, Iss: 1

TL;DR: The mechanics of the ischemic left ventricle during a complete cardiac cycle were simulated using a finite-element model accounting for the thick-walled ventricular geometry, the fibrous nature of the myocardial tissue, and the dependency of active muscle fiber stress on time, strain, and strain rate.

AbstractThe mechanics of the ischemic left ventricle during a complete cardiac cycle were simulated using a finite-element model accounting for the thick-walled ventricular geometry, the fibrous nature of the myocardial tissue, and the dependency of active muscle fiber stress on time, strain, and strain rate. Ischemia was modeled by disabling the generation of active stress in a region comprising approximately 12% of total wall volume. In the model simulations, the approximately 12% reduction in the amount of normally contracting tissue resulted in an approximately 25% reduction in stroke work compared with the normal situation. The more-than-proportional loss of stroke work may partly be attributed to storage of elastic energy in the bulging ischemic region. Furthermore the mechanical performance in the nonischemic border zone deteriorated because of reduced systolic fiber stress (if fibers were in series with those in the ischemic region) or reduced fiber shortening (if fibers were parallel). The deformation pattern of the ventricle was asymmetric with respect to the ischemic region because of the anisotropy of the myocardial tissue. Epicardial fiber shortening in and around the ischemic region, as predicted from the model simulations, was in qualitative agreement with shortening, as measured in four dogs in which ischemia was induced by occlusion of the distal part of the left anterior interventricular coronary artery.

Topics: Ischemia (53%), Ventricle (51%)

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Patent
25 Apr 2002
Abstract: A method for direct therapeutic treatment of myocardial tissue in a localized region of a heart having a pathological condition. The method includes identifying a target region of the myocardium and applying material directly and substantially only to at least a portion of the myocardial tissue of the target region. The material applied results in a physically modification the mechanical properties, including stiffness, of said tissue. Various devices and modes of practicing the method are disclosed for stiffening, restraining and constraining myocardial tissue for the treatment of conditions including myocardial infarction or mitral valve regurgitation.

759 citations


Journal ArticleDOI
TL;DR: It is hypothesized that normal passive material properties dominate the mechanics during acute ischemia, edema during the subsequent necrotic phase, large collagen fiber structure during the fibroticphase, and cross-linking of collagen during the long-term remodeling phase.
Abstract: Therapies for myocardial infarction have historically been developed by trial and error, rather than from an understanding of the structure and function of the healing infarct. With exciting new bioengineering therapies for myocardial infarction on the horizon, we have reviewed the time course of structural and mechanical changes in the healing infarct in an attempt to identify key structural determinants of mechanics at several stages of healing. Based on temporal correlation, we hypothesize that normal passive material properties dominate the mechanics during acute ischemia, edema during the subsequent necrotic phase, large collagen fiber structure during the fibrotic phase, and cross-linking of collagen during the long-term remodeling phase. We hope these hypotheses will stimulate further research on infarct mechanics, particularly studies that integrate material testing, in vivo mechanics, and quantitative structural analysis.

335 citations


Journal ArticleDOI
Thor Edvardsen1, Helge Skulstad1, Svend Aakhus1, Stig Urheim1, Halfdan Ihlen1 
TL;DR: The new SDE approach might be a more accurate marker than TDE for detecting systolic regional myocardial dysfunction induced by LAD occlusion and reduced velocities in all septal segments during angioplasty.
Abstract: OBJECTIVES We sought to evaluate if echocardiographic strain measurements could detect acute myocardial ischemia, and to compare this new method with myocardial velocity measurements and wall motion score index. BACKGROUND Tissue Doppler echocardiography (TDE) is a promising method for assessing regional myocardial function. However, myocardial velocities measured by tissue Doppler echocardiography (TDE) vary throughout the left ventricle (LV) because of tethering effects from adjacent tissue. Strain Doppler echocardiography (SDE) is a new tool for measuring regional myocardial deformation excluding the effect of adjacent myocardial tissue. METHODS Seventeen patients undergoing angioplasty of the left anterior descending coronary artery (LAD) were studied. Left ventricular longitudinal wall motion was assessed by TDE and SDE from the apical four-chamber view before, during and after angioplasty from multiple myocardial segments simultaneously. RESULTS Systolic strain values were uniformly distributed in the different nonischemic LV segments, whereas systolic velocities decreased from basis to apex. During LAD occlusion, strain measurement showed expansion in the apical septal segment in 16 of 17 patients (7.5 ± 6.5% vs. −17.7 ± 7.2%, p CONCLUSIONS The new SDE approach might be a more accurate marker than TDE for detecting systolic regional myocardial dysfunction induced by LAD occlusion.

251 citations


Journal ArticleDOI
TL;DR: A novel, robust method to couple finite element models of cardiac mechanics to systems models of the circulation, independent of cardiac phase is presented, encompassing levels from cell to system.
Abstract: In this study we present a novel, robust method to couple finite element (FE) models of cardiac mechanics to systems models of the circulation (CIRC), independent of cardiac phase. For each time step through a cardiac cycle, left and right ventricular pressures were calculated using ventricular compliances from the FE and CIRC models. These pressures served as boundary conditions in the FE and CIRC models. In succeeding steps, pressures were updated to minimize cavity volume error (FE minus CIRC volume) using Newton iterations. Coupling was achieved when a predefined criterion for the volume error was satisfied. Initial conditions for the multi-scale model were obtained by replacing the FE model with a varying elastance model, which takes into account direct ventricular interactions. Applying the coupling, a novel multi-scale model of the canine cardiovascular system was developed. Global hemodynamics and regional mechanics were calculated for multiple beats in two separate simulations with a left ventricular ischemic region and pulmonary artery constriction, respectively. After the interventions, global hemodynamics changed due to direct and indirect ventricular interactions, in agreement with previously published experimental results. The coupling method allows for simulations of multiple cardiac cycles for normal and pathophysiology, encompassing levels from cell to system.

236 citations


Journal ArticleDOI
TL;DR: Systolic material parameters were determined that enabled FE models to reproduce midwall, systolic myocardial strains from tagged MRI, and contrary to previous hypotheses but consistent with biaxial stretching experiments, active cross-fiber stress development is an integral part of LV systole.
Abstract: Tagged MRI and finite-element (FE) analysis are valuable tools in analyzing cardiac mechanics. To determine systolic material parameters in three-dimensional stress-strain relationships, we used ta...

180 citations


Cites background or methods from "Regional wall mechanics in the isch..."

  • ...Analytical equations have been developed to estimate LV wall stress (19), but more versatile approaches use the finite-element (FE) method, which can incorporate asymmetric geometry, tissue anisotropy (6, 14), and varying material properties (5, 15)....

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  • ...These biomechanical findings represent a fundamental change in modeling active myocardial contraction; before these studies were performed, myocyte contraction was modeled only in the direction of the muscle fiber (5)....

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  • ...Previous FE studies of the LV have validated stress calculations by showing good agreement with myocardial deformations (strains) measured with implanted markers (5, 14, 29, 38, 39)....

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