AbstractsComputer Science

A study of internal defibrillation efficacy using finite element analysis: a 3D isotropic finite element model of the myocardium electric fields

by Maryam Golshayan

Institution: McGill University
Department: Department of Electrical and Computer Engineering
Degree: M. Eng.
Year: 2008
Keywords: Engineering - Electronics and Electrical
Record ID: 1828221
Full text PDF: http://digitool.library.mcgill.ca/thesisfile18790.pdf


Ventricle fibrillation (VF) is a condition in which the heart's lower chambers show an unsynchronized and chaotic motion which prevents the heart from pumping blood and oxygen to the body. VF is considered a sudden cardiac arrest and it is responsible for 300,000 sudden deaths in the USA yearly. The most effective way of reversing this life threatening condition is to apply an electrical shock directly to the heart using an Implantable Cardioverter-Defibrillator (ICD). The main issue in using ICDs is the placement of the defibrillating electrodes so that the current can be optimally channeled through the cardiac muscle, particularly in the left ventricular myocardium. According to the critical mass hypothesis, defibrillation will be successful when 75% of the myocardium tissue is halted by the defibrillation shock. The defibrillation threshold (DFT) or the minimum effective voltage required for successful results is suggested to be related to the myocardial voltage gradient (VG) distribution, but it has not been quantified. Moreover, the goal is to keep the DFT as low as possible to try to maximize the success of defibrillation, minimize the chance of myocardium damage and cardiac arrhythmias caused by high-intensity shocks, and also potentially reduce the battery size and as well as prolong the device's useful lifespan. Various numerical techniques have been used to model the heart to solve the governing equations required to obtain the myocardium VG distribution during electrical defibrillation. The Finite Element Method (FEM) has been of particular interest since it can handle the irregular domains, material inhomogeneities, and complex boundary conditions of problems in bioelectricity. In this thesis, a finite element model of the heart tissue is constructed in order to study and optimize the defibrillation mechanism. The modelling process starts with a surface reconstruction based on radial basis function interpolation to generate the triangular surface me La fibrillation ventriculaire (FV) est un état dans lequel la cavité inférieure du coeur montre une motion asynchrone et chaotique, empêchant le coeur de pomper le sang et l'oxygène au corps. La FV est considérée comme un arrêt cardiaque soudain, responsable de la mort subite de 300,000 personnes chaque année aux Etats-Unis. Afin d'inverser cette condition mortelle, le recours le plus efficace est la délivrance d'un choc électrique directement au niveau du coeur à l'aide d'un Défibrillateur Cardioverteur Implantable (DCI). Le principal problème de l'utilisation des DCIs est le placement des électrodes défibrillateurs pour permettre au courant d'être conduit optimalment à travers du muscle cardiaque, en particulier, le myocarde ventriculaire gauche. Selon l'hypothèse de la masse critique, la défibrillation sera réussi quand 75% du tissu de myocarde est inactivé par le choc de défibrillation. Le seuil de défibrillation ou la tension efficace minimale exigée pour donner des résultats réussis est suggéré d'être liés à la distribution du gradient de la tension…