"Electro-Mechanical Coupling in the Cardiac Muscle"

Effective models of excitation-contraction coupling (ECC) for cardiac tissue involve many variables such as action potential, ionic conductance, intracellular calcium concentration, and contraction of muscle fibres due to the interaction of actin and myosin; a key issue is the coupling of a reaction-diffusion system, describing the diffusion of the action potential and the kinetics of ionic currents, with elastic models of the deformable tissue.

In the present work, we are interested in setting a macroscopic model of an excitable tissue based on the relevant characteristics of the tissue electrophysiology. Our original contribution consists in describing the excitable-contractile behaviour of the myocardium by considering active contractions (instead of active stresses); in particular, we describe muscular contraction as a variation of the rest length of muscle fibres, thus enriching standard elasticity with an additional kinematical descriptor, the field of active distortions.

A reaction-diffusion model, satisfying a two variable model, triggers the propagation of activation waves in the excitable medium; the activation potential is then coupled to muscular contraction via the intermediate of calcium ions kinetics. The microscopic ECC at the basis of the model is described by a relation, built from experimental data, between the rest length of the cardiac muscle fibres and the calcium concentration.