The Effect of Ventricular Myofibre Orientation on Atrial Dynamics

Abstract

Cardiac output is dependent on the tight coupling between atrial and ventricular function. The study of such interaction mechanisms is hindered by their complexity, and therefore requires a systematic approach. We have developed a four-chamber closed-loop cardiac electromechanics model which, through the coupling of the chambers with a closed-loop cardiovascular system model and the effect of the pericardium, is able to capture atrioventricular interaction. Our model simulates electrical activation and contraction of the atria and the ventricles coupled with a closed-loop model based on the CircAdapt framework. We include the effect of the pericardium on the heart using normal springs, scaling the local spring stiffness based on image-derived motion. The coupled model was used to study the impact of ventricular myofibre orientation on atrial dynamics by varying ventricular fibre orientation from –40∘ /+40∘ to –70∘ /+70∘. We found that steeper fibres increase atrioventricular valve plane motion from 1.0 mm to 14.0 mm, leading to a lower minimum left atrial (LA) pressure (–0.4 mmHg vs –1.1 mmHg) and greater venous return (LA maximum volume: 168 mL vs 182 mL), and that fibres angles –50∘ /+50∘ were consistent with a physiological atrial contraction and filling pattern. Our framework is capable of capturing complex interaction dynamics between the atria, the ventricles and the circulatory system accounting for the effect of the pericardium. Such simulation platform represents a useful tool to study both systolic and filling phases of all cardiac chambers, and how these get altered in diseased states and in response to treatment.