Optimizing current delivery in defibrillation: Finite element models and experimental validation

This dissertation describes a method for constructing and solving detailed patient-specific three-dimensional finite element models of the human thorax for use in defibrillation studies. The method utilizes the patient's own X-ray CT scan and a simplified meshing scheme to quickly and efficiently generate a model typically composed of approximately 400,000 elements. A parameter sensitivity study on one human thorax model to examine the effects of variation in assigned tissue resistivity values, the level of anatomical detail included in the model, and the number of CT slices used to produce the model is presented. Of the seven tissues types examined, the average left ventricular (LV) myocardial voltage gradient was most sensitive to the values of myocardial and blood resistivity. Incorrectly simplifying the model, for example, modeling the heart as a homogeneous structure by ignoring the blood in the chambers, caused the average LV myocardial voltage gradient to increase by 12%. The sensitivity of the model to variations in electrode size and position was also examined. Small changes ({dollar}<{dollar}2.0 cm) in electrode position caused average LV myocardial voltage gradient values to increase by up to 12%.; In order to assess quantitatively the validity of the 3-D thoracic finite element models, we directly compared predicted voltages to those obtained experimentally. We constructed detailed 3-D subject-specific thorax models of six pigs based on their individual CT images. The models were correlated with the results of experiments conducted on the animals to measure the voltage distribution in the thorax at 52 locations during synchronized high energy shocks. One transthoracic and two transvenous electrode configurations were used in the study. The measured voltage values were compared to the model predictions resulting in a correlation coefficient of 0.927 {dollar}pm{dollar} 0.036 (average {dollar}pm{dollar} standard deviation) and a relative rms error of 28.50 {dollar}pm{dollar} 8.959%. After compensating the finite element models for the large voltage drop seen experimentally at the electrode-tissue interface, the rms error was reduced by 22% to 22.13 {dollar}pm{dollar} 5.99. In addition, by examining the computed myocardial voltage gradient distributions, differences in the efficacy of the various electrode configuration in the individual animals was revealed. This variability reinforces the potential benefit of patient-specific modeling.; In vivo tissue resistivity measurements under conditions simulating defibrillation were done in eight pigs with a tetrapolar electrode system. The tissues were exposed to voltage gradients in the range of 0.5 to 28 V/cm. The tissue resistivity values varied significantly among the animals. (Abstract shortened by UMI.)...