Abstract:

BACKGROUND: This article presents a study, which examines the effects of biphasic electrical shocks on human ventricular tissue. The effects of this type of shock are not yet fully understood. Animal experiments showed the superiority of biphasic shocks over monophasic ones in defibrillation. A mathematical computer simulation can increase the knowledge of human heart behavior. METHODS: The research presented in this article was done with different models representing a three-dimensional wedge of ventricular myocardium. The electrophysiology was described with Priebe-Beuckelmann model. The realistic fiber twist, which is specific to human myocardium was included. Planar electrodes were placed at the ends of the longest side of the virtual cardiac wedge, in a bath medium. They were sources of electrical shocks, which varied in magnitude from 0.1 to 5 V. In a second arrangement ring electrodes were placed directly on myocardium for getting a better view on secondary electrical sources. The electrical reaction of the tissue was generated with a bidomain model. RESULTS: The reaction of the tissue to the electrical shock was specific to the initial imposed characteristics. Depolarization appeared in the first 5 ms in different locations. A further study of the cardiac tissue behavior revealed, which features influence the response of the considered muscle. It was shown that the time needed by the tissue to be totally depolarized is much shorter when a biphasic shock is applied. Each simulation ended only after complete repolarization was achieved. This created the possibility of gathering information from all states corresponding to one cycle of the cardiac rhythm. CONCLUSIONS: The differences between the reaction of the homogeneous tissue and a tissue, which contains cleavage planes, reveals important aspects of superiority of biphasic pulses.

Abstract:

Defibrillation of the heart is used widely to resuscitate pa tients with fibrillating heart, being the most effective ther apy for this otherwise lethal disturbance of cardiac rhythm. The basic electrophysilogical mechanisms of this proce dure are not well understood. The aim of this work is to in vestigate the conditions that influence the so called virtual electrodes that appear in human ventricular myocardium and also their effects. A two-dimensional and a three dimensional computer model of cardiac tissue is used. For this the temporal evolution of the transmembrane voltage is studied until the entire tissue is repolarized, the needed time interval being around 400 ms.

Abstract:

Defibrillation is the most important measure of resuscitation aiming at restoration of the physiological heart rhythm. A complete understanding of the defibrillation mechanism has not been achieved yet. The research presented in this article gives a mathematical computer simulation of the defibrillation of chaotically fibrillating human ventricular myocardium. The study was done with a model representing a three-dimensional wedge of human ventricular myocardial tissue. The cellular electrophysiology was described with the Priebe-Beuckelmann model. The electrical activity of the cardiac tissue was calculated with a bidomain model. A spiral wave was induced in the myocardium with standard S1-S2 protocols. The myocardium was brought into a chaotically fibrillating state by breaking the spiral wave. Few hundred milliseconds after the chaotically fibrillation started, monophasic electrical defibrillating shocks were applied through planar electrodes. The defibrillation shocks were applied at different moments. At each chosen moment we studied both cases of electrical polarity. The reaction of myocardium was studied during the following 400 ms. The results are indicating important information related to the factors, which are influencing the defibrillation success.

Abstract:

The purpose of this study is to develop a computer model-based planning environment for therapeutically cardiac interventions, i.e. surgical or catheter ablation procedures in atrial cases and placing pacemaker electrodes in biventricular pacing. Existing mathematical models are used to simulate the electrophysiology on an anatomical pig model during a heart cycle. The results of these models were validated in multiple domestic pig animal experiments. We found that the models created enable us to simulate the electrical behaviour of the heart nearly in real time and that it reproduces the properties of the heart in atrial flutter and in ventricular pacing with different pacing locations. The results of computer-based simulations may lead to a better understanding of cardiac rhythm disorders and the development of new, less invasive operative techniques.

Abstract:

Cardiac electro-mechanical models are valuable tools to gain insights in physiology and pathophysiology of the heart. Progressive models can be created by fusion of various basic models. In this work biventricular models of cardiac electro-mechanics were developed by fusion of anatomical, electrical, and mechanical models. The importance of anatomical modeling was researched by inclusion of two different anatomical models, i.e. an analytical and a magnetic resonance diffusion tensor imaging based model. The fused models were applied in simulations of physiological behavior and results of these were analyzed. Significant difference of deformation were found, which can be attributed to the anatomical models. The analysis emphasized the importance of appropriate anatomical modeling for simulations of cardiac mechanics.

Abstract:

Atrial fibrillation (AF) is a critical pathology due to the risk of secondary diseases like thromboemboli and ventricular arrhythmia. A recent study identified a familial type of AF based on a mutation influencing the cardiac IKs channel. The mutant channel is characterized by a gain-of-function and a nearly linear current-voltage relationship. The kinetics and density of IKs in a model of atrial myocytes was adjusted to the measured characteristic to describe the mechanisms and effects of the mutation. A schematic anatomical model of the right atrium was designed to simulate the excitation propagation. The action potential duration of the mutant cell was reduced to 105 ms and the effective refractory period to 148 ms. Both factors lead to a reduction in wavelength and thus the risk of an initiation and perpetuation of AF rises. The results support the understanding of the complex behavior of cardiac cells. The described model will be used to investigate AF and potential treatments.