| dc.description | Ventricular tachycardia and fibrillation are potentially lethal heart rhythms that can cause sudden cardiac death. The spatial and temporal electrical dynamics and stability of these complex rhythms are not well understood. We employed computer simulation to study the mechanisms of VT and VF in reaction-diffusion media, and to examine correlates in the electrocardiograms. A simple coupled map lattice model of cardiac tissue was developed to explore spatiotemporal complexity, by quantifying entropy and Lyapunov exponents during phase transitions to deterministic chaos. This model allowed basic features of electrocardiograms to be derived from their dipole source maps. A new mathematical model based on the Luo-Rudy formulation was then developed to simulate dynamics of sodium, calcium, and potassium ionic currents (INa, ICa, I K, IK1, Ito) in human ventricular action potentials. This theoretical model was simplified to contain only the minimal number of currents necessary to capture the essential behaviour of endocardial, epicardial, and M cells, while retaining sufficient simplicity to permit large-scale computation in a whole heart. Propagation and stability of electrical waves was explored in one-, two-, and three-dimensional monodomain cellular arrays, and in an anisotropic biventricular heart. Reentrant circuits were induced in normal tissue, and evolved into two-dimensional spiral waves and three-dimensional scroll waves. Stability was altered by varying the action potential restitution curves to achieve solitary fixed or meandering spiral waves, which fractionated into more complex fibrillation. Several subtypes of VF and their simulated electrocardiograms were characterized. The nature of successful and unsuccessful defibrillation shocks were then examined. This work represents application of a multiple-component ionic model of human ventricular cells to VT and VF in a whole heart model, a theoretical study of body surface electrocardiograms during reentrant VT and VF, and an attempt to develop a thermodynamic theory of fibrillation based on statistical mechanics. | en_US |
