Instability and Variability in the Heart

Daisuke Sato^1*

¹Pharmacology, UC Davis, Davis, CA, USA

* Presenter:Daisuke Sato, email:dsato@ucdavis.edu

Variability in the QT interval—a key marker on electrocardiograms (ECGs)—is closely linked to the risk of life-threatening cardiac arrhythmias and sudden cardiac death. Although random fluctuations from ion channel activity contribute to electrical variability, their effects should, in theory, cancel out due to the vast number of channels in the heart. Our study reveals that electrical instabilities within cardiac cells can amplify these small fluctuations, creating significant beat-to-beat variability. Using a theoretical model, we show that voltage instability, quantified by the steepness of the action potential duration (APD) restitution curve, correlates strongly with QT variability. This variability peaks at the onset of alternans—a condition where alternating patterns emerge in heartbeats, often signaling increased arrhythmogenic risk. These findings suggest that QT variability may serve as early markers of dynamical instability, providing new avenues for predicting and managing arrhythmogenic risk. This study highlights how dynamical instabilities in biological systems can amplify small-scale randomness into large-scale physiological effects, underscoring a new perspective on the origins of variability in the heart.

Keywords: Cardiac dynamics, Nonlinear dynamics, Action potential dynamics