Indeterminacy of Spatiotemporal Cardiac Alternans

TL;DR

This paper reveals that calcium-driven cardiac alternans can exhibit multiple coexisting spatiotemporal patterns depending on pacing history, challenging the assumption of a unique pattern determined solely by pacing period.

Contribution

It demonstrates the coexistence of multiple alternans solutions in homogeneous cardiac tissue due to calcium cycling and electrotonic interactions, introducing a new perspective on arrhythmia mechanisms.

Findings

Multiple alternans patterns coexist for a given pacing period.

Pattern unpredictability arises from calcium-electrotonic interactions.

Numerical and theoretical analysis support the coexistence phenomenon.

Abstract

Cardiac alternans, a beat-to-beat alternation in action potential duration (at the cellular level) or in ECG morphology (at the whole heart level), is a marker of ventricular fibrillation, a fatal heart rhythm that kills hundreds of thousands of people in the US each year. Investigating cardiac alternans may lead to a better understanding of the mechanisms of cardiac arrhythmias and eventually better algorithms for the prediction and prevention of such dreadful diseases. In paced cardiac tissue, alternans develops under increasingly shorter pacing period. Existing experimental and theoretical studies adopt the assumption that alternans in homogeneous cardiac tissue is exclusively determined by the pacing period. In contrast, we find that, when calcium-driven alternans develops in cardiac fibers, it may take different spatiotemporal patterns depending on the pacing history. Because there coexist multiple alternans solutions for a given pacing period, the alternans pattern on a fiber becomes unpredictable. Using numerical simulation and theoretical analysis, we show that the coexistence of multiple alternans patterns is induced by the interaction between electrotonic coupling and an instability in calcium cycling.