Corazon espinado: microelectrode closed-loop control in cardiac tissue

Proper contraction of cardiac muscle relies on the coordinated propagation of transmembrane voltage, and disturbances of this propagation can result in deadly cardiac arrhythmias. One such disturbance strongly associated with the onset of fibrillation is a dynamical instability known as alternans, a beat-to-beat alternation in action potential duration (APD) arising from a period-doubling bifurcation. The restitution hypothesis claims that a return map in APD can describe and predict alternans, and decades of work have shown it can successfully reproduce many experimental observations. The restitution hypothesis likewise predicts a method for suppressing the onset of alternans which has been confirmed by some computational simulations; however, few experiments have addressed these predictions due to its difficult implementation. In this talk, I will discuss our development of a closed-loop control scheme to experimentally address predictions made by the restitution hypothesis via high resolution microelectrode recordings of transmembrane voltages in zebrafish, frog, and rabbit hearts. I will present our results which conclusively show the appearance of alternans in opposition to predictions made by theoretical models and provide an improved model that describes the dynamics.