Thesis

Study of Mechanical Properties of Left Ventricle using Finite Element

According to the CDC, 735,000 people in the United States experience a heart attack (myocardial infarction) every year. 30% of these have previously suffered a myocardial infarction (MI). With each successive event, mortality rates drastically increase. These episodes generate damaged tissue in the heart which adversely affect heart function and make diagnosis and treatment options difficult [6]. This study presents a finite element model of left ventricular function to gain insight into the mechanical changes that result from an infarct that may lead to increased risk of subsequent heart failure. This information would be a useful adjunct for physicians treating patients suffering from cardiovascular disease with a prior episode of infarct. Magnetic resonance imaging (MRI) was used to create a symmetric and geometrically realistic (natural) three-dimensional left ventricle (LV) computer model. Simulations were conducted using the finite element method to predict the mechanical behavior of the LV. Regions of simulated infarct damage were incorporated into the analyses by altering material properties for a specific region. Both symmetric and natural models were considered in the analysis. Infarct cases 1-6 corresponding to a infarct percent by volume of 8, 9, 4, 16, 25 and 51% had a reduction in end-diastolic volume of 5, 5, 3, 8, 11, 17 mL respectively. The pressure increase required to restore EDV for Infarct 1-6 were 3, 3, 1, 5, 9 and 12 mmHg. Three natural infarct cases denoted case A, B and C consisting of a 7%, 15% and 50% infarct region by volume respectively were evaluated. The decrease in EDV for cases A, B and C were 6, 9 and 17 mL requiring an increase in LV pressure (hypertension) of 2.5, 5 and 12 mm Hg to restore normal end-diastolic volume (EDV) [32]. The simulated decrease in EDV for the infarct cases was consistent with patient's experiencing decreased tissue compliance [21]. The higher LV pressure resulted in an increase in wall stress opposite the infarct for the symmetric and natural infarct cases. The stress distribution in the natural model had large spatial variation compared to the symmetric model, which has a smooth stress distribution from base to apex. The natural model was considered the most useful as LV geometry was found to greatly influence stress distribution and magnitude. The relative magnitude of the stress in the fiber and longitudinal direction was consistent with tensile testing of myocardial tissue [43]. The results are potentially useful in determining a relative severity in MI patients and identifying high stress locations in the LV.

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