Wave Emission From Heterogeneities For Low-Energy Termination Of Cardiac Arrhythmias

Cardiac fibrillation is a leading cause of death in the modern world. Its treatment has so far been limited to painful and damaging defibrillation shocks. In this thesis, we experimentally investigate the possibility of using low-energy electric pulses to terminate fibrillation. We built two high-resolution fluorescence optical mapping systems to investigate the phenomenon of wave emission from heterogeneities in in vitro canine cardiac tissue preparations and whole rabbit hearts. The activation sequence from single pulses of varying amplitude was captured and quantified. The global activation time is found to obey a power-law with exponent -0.5 in rabbits and -0.15 in canines. We also present a novel model of tissue activation based on the density of wave sources within the tissue, valid for both 2d and 3d. Using data from CT scans of our tissue preparations, we found that the size distribution of the cardiovasculature also follow a power-law distribution over an order of magnitude, with scaling exponents -1.8 in canines and -2.13 in rabbits. Our model of activation time links the activation time with the size distribution via their scaling exponents. Finally, we tested the hypothesis that anti-fibrillation pacing (AFP) can terminate ventricular fibrillation with lower pulse energy than conventional defibrillation. We found an 81 % reduction in pulse energy in canine experiments. We saw no such reduc- tion in rabbit hearts, suggesting additional interactions between the fibrillatory activity and the far-field induced wave emission. Our results are presented as a contribution to our understanding of excitable systems and to the development of new treatment approaches in clinical cardiology

Phase-resolved analysis of the susceptibility of pinned spiral waves to far-field pacing in a two-dimensional model of excitable media

Life-threatening cardiac arrhythmias are associated with the existence of stable and unstable spiral waves. Termination of such complex spatio-temporal patterns by local control is substantially limited by anchoring of spiral waves at natural heterogeneities. Far-field pacing (FFP) is a new local control strategy that has been shown to be capable of unpinning waves from obstacles. In this article, we investigate in detail the FFP unpinning mechanism for a single rotating wave pinned to a heterogeneity. We identify qualitatively different phase regimes of the rotating wave showing that the concept of vulnerability is important but not sufficient to explain the failure of unpinning in all cases. Specifically, we find that a reduced excitation threshold can lead to the failure of unpinning, even inside the vulnerable window. The critical value of the excitation threshold (below which no unpinning is possible) decreases for higher electric field strengths and larger obstacles. In contrast, for a high excitation threshold, the success of unpinning is determined solely by vulnerability, allowing for a convenient estimation of the unpinning success rate. In some cases, we also observe phase resetting in discontinuous phase intervals of the spiral wave. This effect is important for the application of multiple stimuli in experiments

Low-energy control of electrical turbulence in the heart

abstract: ©2011 Macmillan Publishers Limited. All rights reserve