P10: Branching Myofibrils Create Torsion During Contraction In Sheep Cardiomyocytes

Contraction of the heart, and the subsequent pumping of blood through the cardiovascular system, is driven by activation of muscle cell sarcomeres. Sarcomeres are contractile proteins which are organized within myofibrils that span the cell. Recent imaging has elucidated that myofibrils form a branching network throughout the cardiac muscle cell. This contrasts with the assumed strictly longitudinal and parallel organization that has been the basis of cardiac mechanobiology studies to date. A branching network organization could have biological implications on contraction dynamics in health, exercise, and pathology. We have developed a 3D anisotropic contraction model of a branched myofibril based on U-NET++ segmentation of electron microscopy images of sheep cardiomyocytes. We compare the stress distribution of a contracted myofibril in the idealised and branched cases. Our simulations indicate that branching myofibrils likely induce o-axial stress behaviour and transverse forces during contraction compared to the ideal structure. These findings may be critical for elucidating the structural di erences observed in mammalian muscle fibres and changes with disease.