Cardiac Electrodynamics

Overview
An understanding of the propagation of electrical activity through ventricular myocardium requires knowledge of both the electrical behavior of an individual cardiac cell, and the role of the cardiac syncytium. The electrical properties of cardiac tissue are the utmost importance in the generation and termination of cardiac arrhythmias, including fibrillation. Our group has developed a high-speed imaging technique that allows visualization of the electrical activity of the isolated rabbit heart during normal and abnormal cardiac rhythms. We are presently developing a panoramic imaging system that is allowing us to visualize and quantify the non-linear dynamics of the transmembrane potential over the entire epicardial surface of an isolated rabbit heart during tachycardia and fibrillation.

We utilize electric, magnetic, and optical mapping of cardiac activation in the isolated rabbit heart and numerical simulations with the bidomain model to link ion channel kinetics to macroscopic electrical behavior. In the bidomain model, cardiac tissue is a 3-dimensional electrical cable with anisotropic intra- and extracellular spaces that are separated by a non-linear cell membrane. Recent experiments confirm the validity of this model with unequal intra- and extracellular anisotropies, and demonstrate the important role of virtual cathodes and anodes in the cardiac response to electrical stimulation. We are exploring a few poorly understood phenomena in cardiac electrophysiology that may be the result of unequal anisotropies, and are applying the resulting knowledge to problems in cardiac stimulation and defibrillation. For example, there is not yet an explanation of the mechanism of electrical defibrillation! To answer this and other questions, we are determining how electrical anisotropies and tissue macrostructure affect the propagation of depolarization, the spread of repolarization, and the response to external electrical stimuli. We are examining the interaction between pharmacological agents and cardiac propagation, particularly during fibrillation.