Generation and escape of local waves from the boundary of uncoupled cardiac tissue

TL;DR

This study investigates how abnormal cardiac waves originate and propagate from regions with reduced cell coupling, combining experiments and modeling to understand spiral wave formation and escape mechanisms in heterogeneous myocardial tissue.

Contribution

The paper introduces a combined experimental and numerical approach to analyze wave dynamics at coupling boundaries in cardiac tissue, revealing mechanisms of spiral wave formation and escape.

Findings

Heterogeneous substrate with coupling gradient promotes spiral wave formation.

Wavefronts can lock at interfaces due to source/load mismatch.

Wave escape depends on spatial distribution, automaticity, and coupling gradient speed.

Abstract

We aim to understand the formation of abnormal waves of activity from myocardial regions with diminished cell-to-cell coupling. In route to this goal, we studied the behavior of a heterogeneous myocyte network in which a sharp coupling gradient was placed under conditions of increasing network automaticity. Experiments were conducted in monolayers of neonatal rat cardiomyocytes using heptanol and isoproterenol as means of altering cell-to-cell coupling and automaticity respectively. Experimental findings were explained and expanded using a modified Beeler-Reuter numerical model. The data suggests that the combination of a heterogeneous substrate, a gradient of coupling and an increase in oscillatory activity of individual cells creates a rich set of behaviors associated with self-generated spiral waves and ectopic sources. Spiral waves feature a flattened shape and a pin-unpin drift type of tip motion. These intercellular waves are action-potential based and can be visualized with either voltage or calcium transient measurements. A source/load mismatch on the interface between the boundary and well-coupled layers can lock wavefronts emanating from both ectopic sources and rotating waves within the inner layers of the coupling gradient. A numerical approach allowed us to explore how: i) the spatial distribution of cells, ii) the amplitude and dispersion of cell automaticity, iii) and the speed at which the coupling gradient moves in space, affects wave behavior, including its escape into well-coupled tissue.