Cardiac non-linear dynamics and chaos control in the cardiac electrical activity with practical applications

Abstract

Disruption of the normal heart rhythm can lead to a chaotic cardiac dynamic driven by the multiple scroll waves. If ventricular fibrillation (VF) develops, the cardiac intrinsic control system is unable to terminate it, and without any external control, death is imminent. In a phase space, the cardiac dynamic during normal heart rhythm is represented as a set of overlapping closed orbits that are destabilized during cardiac arrhythmias, mostly notably during VF. From the perspective of chaos theory and control theory of chaotic dynamics, parallels can be made with cardiac chaotic behavior and control methods can be devised. Two external continuous feedback control methods are presented in this thesis. In both control methods stabilization is achieved by forcing the dynamical system back to “maintain” the correct orbit by administering a defibrillation shock in a form of a feedback signal. First the continuous feedback control method stabilizes the period of the chaotic orbit during VF, while the second terminates VF by forcing the system back into phase space orbits during sinus rhythm. To apply the control methods, it was necessary to develop instrumentation including an arbitrary-waveform voltage-to-current converter with a 1 KHz bandwidth and a feedback controller that records in real time an optical electrocardiogram and provides a feedback signal to the voltage-to-current converter. The experimental results showed that our proposed continuous feedback control methods can control VF, converting it into monomorphic tachycardia and sinus rhythm by administering low energy shocks.