A dynamic double helical band as a model for cardiac pumping

We address here, by means of finite-element computational modeling, two features of heart mechanics and, most importantly, their timing relationship: one of them is the ejected volume and the other is the twist of the heart. The corner stone of our approach is to take the double helical muscle fiber band as the dominant active macrostructure behind the pumping function. We show that this double helical model easily reproduces a physiological maximal ejection fraction of up to 60% without exceeding the limit on local muscle fiber contraction of 15%. Moreover, a physiological ejection fraction can be achieved independently of the excitation pattern. The left ventricular twist is also largely independent of the type of excitation. However, the physiological relationship between the ejection fraction and twist can only be reproduced with Purkinje-type excitation schemes. Our results indicate that the proper timing coordination between twist and ejection dynamics can be reproduced only if the excitation front originates in the septum region near the apex. This shows that the timing of the excitation is directly related to the productive pumping operation of the heart and illustrates the direction for possible bioinspired pump design.