Characterizing Chaotic Cardiac Voltage Dynamics across Space, Time, and Species

Cardiac arrhythmias present a persistent challenge for medical intervention due to the complex spatiotemporal voltage patterns disrupting normal rhythmic contractions that can lead to cardiac arrest and death. At high stimulation frequencies, many cellular cardiac voltage models exhibit chaotic behavior, suggesting that arrhythmic dynamics in living tissue may fundamentally arise from chaos. In this study, we characterize and quantify chaotic behavior in the ventricles across species of varying heart sizes, including humans. Using single-cell microelectrode recordings and multicellular optical mapping, we reveal a spectrum of nonlinear voltage dynamics, including period-doubling bifurcation cascades leading beyond alternans, periodic orbit shadowing, transitions between higher-order periodicities, and multiple forms of nonlinear intermittency. We further observe discordant alternans embedded within spatiotemporal cardiac chaos—from amphibian hearts to, for the first time to our knowledge, human hearts. To quantify this complexity, we estimate leading Lyapunov exponents from action potential duration (APD) sequences and map their spatial variation across tissue. Finally, we demonstrate control of chaotic behavior through biphasic perturbations to the pacing frequency. Our findings highlight the rich, chaotic voltage dynamics inherent to cardiac tissue and open new directions for their targeted control and medical treatment.