Mechanical analysis of congestive heart failure caused by bundle branch block based on an electromechanical canine heart model

Abstract

Asynchronous electrical activation, induced by bundle branch block (BBB), can cause reduced ventricular function. However, the effects of BBB on the mechanical function of heart are difficult to assess experimentally. Many heart models have been developed to investigate cardiac properties during BBB but have mainly focused on the electrophysiological properties. To date, the mechanical function of BBB has not been well investigated. Based on a three-dimensional electromechanical canine heart model, the mechanical properties of complete left and right bundle branch block (LBBB and RBBB) were simulated. The anatomical model as well as the fiber orientations of a dog heart was reconstructed from magnetic resonance imaging (MRI) and diffusion tensor MRI (DT-MRI). Using the solutions of reaction-diffusion equations and with a strategy of parallel computation, the asynchronous excitation propagation and intraventricular conduction in BBB was simulated. The mechanics of myocardial tissues were computed with time-, sarcomere length-dependent uniaxial active stress initiated at the time of depolarization. The quantification of mechanical intra- and interventricular asynchrony of BBB was then investigated using the finite-element method with an eight-node isoparametric element. The simulation results show that (1) there exists inter- and intraventricular systolic dyssynchrony during BBB; (2) RBBB may have more mechanical synchrony and better systolic function of the left ventricle (LV) than LBBB; (3) the ventricles always move toward the early-activated ventricle; and (4) the septum experiences higher stress than left and right ventricular free walls in BBB. The simulation results validate clinical and experimental recordings of heart deformation and provide regional quantitative estimates of ventricular wall strain and stress. The present work suggests that an electromechanical heart model, incorporating real geometry and fiber orientations, may be helpful for better understanding of the mechanical implications of congestive heart failure (CHF) caused by BBB.

A Study of Mechanical Optimization Strategy for Cardiac Resynchronization Therapy Based on an Electromechanical Model

“…Myocardial fiber orientations were obtained from diffusion tensor MR imaging (DT-MRI) in a 7.1 T MRI scanner (Figures 1(e), 1(f)) and different tissues were manually segmented into functional modules, including papillary muscles and Purkinje fiber networks (Figures 1(g), 1(h)). Full details of this model can be found in [20]. Note that papillary muscles are not used in the simulation.…”

“…The cell model with different ionic channel currents could be described by the following differential equations: $\begin{array}{c}\frac{d{V}_m}{dt}=-\frac{\mathrm{1}}{C_m}\left(false\sum I_{\text{ion}}+I_{\text{app}}\right),\\ I_{\text{ion}}=G_{\text{ion}}·\left(V_m-E_{\text{ion}}\right),\end{array}$ where V m is the transmembrane potential, C m is the membrane capacitance, I x is the current flow through the ion channel x ,   G x is the conductance of the channel, and E x is the reversal potential for the channel [20]. …”

“…As far as mechanical properties are concerned, the material was considered as transversely isotropic at any point in the myocardium. The in-vitro stiffness parameters and material constants were used as before [20]. …”

“…The aim of this study is to validate the feasibility of CRT optimization with mechanical predictors (CURE) and to make a contrast analysis of cardiac function improvement between mechanical (CURE) and electrical ( E RMS ) optimization strategy for CRT. The present study resolves this question through the simulation of the cardiac electrical activation spread and the mechanical strain maps based on our previous electromechanical canine model of HF combined with a complete LBBB (CLBBB) [20]. …”

A multiformalism and multiresolution modelling environment: application to the cardiovascular system and its regulation

“…For example, cell-to-organ representations of the electrical activity of the heart have been proposed by different authors (Noble 2004;Fenton et al 2005;Nickerson et al 2006). Certain works include, to some extent, both vertical and horizontal integration, such as the electromechanic models of the cardiac activity (Usyk & McCulloch 2003;Watanabe et al 2004;Kerckhoffs et al 2007;Dou et al 2009). These models have proven useful in a number of situations; however, their complexity and their significant computational costs make it difficult to perform essential tasks such as sensitivity analysis and parameter identification.…”