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whole_GaleTimothyJohn1996_thesis.pdf (8.48 MB)

Modelling the electric field from implantable defibrillators

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posted on 2023-05-27, 00:25 authored by Gale, TJ
This thesis presents a mathematical model of the electric field from implantable defibrillators, together with the numerical implementation, validation and examples of application of the model. The model was based on Laplace's equation for potential and was implemented using the boundary element method with constant quadrilateral elements and realistic torso structures. An efficient out-of-core solver was developed, allowing any size problem to be solved, subject only to computer speed and time available. A method was also developed that allowed matrices calculated in one problem to be used in other, similar problems, often reducing calculation times by an order of magnitude. Model validation included comparison of myocardial potentials from the model to those from a finite element model (r.e..2.8%) and from measurements in a sheep (c.c.=0.464, r.e..23.6%). Validation was also done against resistance and voltage at defibrillation threshold from 29 patients implanted with a transvenous system and 8 patients with the transvenous system and an additional subcutaneous patch. Without the patch, the relative error between the average of the clinical results and the model result was 9.4% (voltage) and 0.8% (resistance). The average of the relative errors between each clinical result and the model result was 23.4% (voltage) and 11.6% (resistance). With the patch, the equivalent relative errors were 33.9%, 19.4%, 44.0% and 22.5%. Transvenous, epicardial and subcutaneous electrode configurations were modelled in a series of investigations. The best transvenous configuration was with a right ventricular cathode and an anode in the inferior vena cava, where defibrillation voltage and energy were reduced by 35% and 55%, respectively, compared to a standard configuration with the anode in the superior vena cava. Configurations with a right ventricular cathode and large epicardial patch performed best, though, and reduced voltage and energy by up to 59% and 79%, respectively. The optimal length of the right /ventricular transvenous electrode was approximately 60mm. An infarcted heart was also modelled. For future work, anisotropy may be added to the heart and skeletal muscle of the model. Anisotropic regions may be represented by many small boundary element regions or by finite elements. Automated construction of the torso mesh and an algorithm for automatically optimising electrode position may be developed. Individual patients may be modelled and predicted values of defibrillation voltage, energy and resistance compared to values measured at the time of implantation. In conclusion, the boundary element model was successful in modelling the electric field in the torso and in predicting implantable defibrillator performance. The model has potential to be used in research and development and in clinical settings.

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Copyright 1995 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s). Includes bibliographical references (leaves 158-169). Thesis (Ph.D.)--University of Tasmania, 1996

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