Nonlinear origin of heart's vulnerability

Elena Surovyatkina

Russian Academy of Sciences, Space Recearch Institute, Moscow, Russia

A clinically observed vulnerable window in an electrocardiogram (ECG) is a dangerous period of time between regular excitations of the heart within which delivering an electrical shock may in itself initiate a self-sustained heart rhythm disturbance that can cause life threatening arrhythmias and can even lead to sudden cardiac death (SCD). Despite recent advances in preventing SCD due to cardiac arrhythmia, the nature of the immediate precipitating event that triggers the fatal arrhythmia at a specific time in an otherwise stable patient remains a major and challenging question. The talk provides a new insight into the classical electrophysiological problem of complex dynamics of cellular electrical activity revealed by system analysis of nonlinear properties of the ionic-model of ventricular myocyte. The findings highlight the cellular origin of a sudden change of heart rhythm, which may cause lethal arrhythmias. It is discovered that i) the ionic-model of ventricular myocyte is multistable system; ii) basins of attraction (BA) of stable state of cell respond on external electrical stimulation suit with the vulnerable windows (VW) on the time-course curve of transmembrane potential of ventricular cell which are well known in cardiology. The delivery of single stimuli to the BA-VW causes a switch from one rhythm to another in multistable system. Boundaries and sizes of BA-WV depend on period stimulation, stimulus strength and restitution properties of a cell. Prediction of vulnerable windows on the curves of transmembrane potential could play a key role in the determination of vulnerable period in ECG records. The obtained results are significant for safety of defibrillation control and for improving antiarrhythmic drug screening.