Complex Structure and Dynamics of the Heart

The work presented in this thesis was driven by the conviction that viewing the heart as a complex system and understanding the interaction between its structural and dynamical complexities will help to identify the mechanisms underlying arrhythmia initiation and perpetuation, potentially opening the path towards innovative low-voltage defibrillation strategies.§In the European Union alone, an estimated 700,000 deaths per year are associated with ventricular fibrillation, a cardiac arrhythmia associated with spatially and temporally complex dynamics evolving in the inherently heterogeneous, excitable medium of the heart muscle. For want of a better method, high-voltage electrical shocks remain the only reliable way to stop life-threatening fibrillation, despite severe side effects including tissue damage and excruciating pain. Using theoretical tools from nonlinear dynamics, numerical simulations and experimental methods such as high-resolution fluorescence imaging, three main questions are addressed: What is the effect of substrate heterogeneity on the spatial-temporal dynamics of cardiac arrhythmias? What is the effect of an external electric field on heterogeneities in electrical conductance and to what extent does it depend on the surface geometry? How can weak pulsed electric fields be used to control spatial-temporal dynamics in a heterogeneous cardiac substrate?