The Tell-Tale Heart: Failures of Control and Descent into Cardiac Chaos*

Proper contraction of cardiac muscle relies on the coordinated propagation of transmembrane voltage. Disturbances of this propagation can result in deadly cardiac arrhythmias such as fibrillation, the manifestation of chaos in the heart. Even in healthy tissue, high heart rates can drive the system to a dynamical instability known as alternans, a period doubling bifurcation in action potential duration (APD) which is strongly correlated with the onset of fibrillation and sudden cardiac death. Much theoretical effort based on the relationship between the APD and preceding diastolic interval (DI) has aimed to suppress the onset of alternans. Results from simulation and theory claim the suppression of alternans under stimulation at a constant DI; however, few experiments have addressed these predictions. In this talk, I will discuss comparative cardiac dynamics in the hearts of species including rabbit, dog, cat, pig, frog, zebrafish, snake, lizard, and alligator through the use of microelectrode recordings and high spatiotemporal resolution optical mapping of fluorescent voltage and calcium signals across the surfaces of hearts. Furthermore, I will discuss my closed-loop control system for performing constant DI stimulation and the highly unexpected results.