Human heart under stress: its mysteries revealed by mechano-imaging modeling

Biological tissues remodeling is largely due to mechanical stresses withstood by the cells, with both anabolic and catabolic responses depending on loading type, magnitude, and duration. Thus in the last 16 years, my research program aimed at providing new imaging and modeling technologies for the robust in vivo mechanical stress evaluation within musculoskeletal or cardiac tissues, a cornerstone in understanding the fundamental mechanobiological processes in humans. It is well established that physical activity is beneficial for human health. Indeed, if more stress is withstood by the cells, more remodeling occurs. However, the thresholds beyond which exercise loading causes regenerative or degenerative remodeling still have to be defined. This issue confirmed my willingness to direct my research towards understanding and quantifying the cardiac behavior under stress conditions through new mechano-imaging modeling technologies. This presentation will introduce the mechanical characterization of human tissues, with an application to the differential impact of chemotherapy on cardiac wall structure. The limits of mechanical testing on biological tissues will be discussed to introduce multiparametric MRI, with an application as an indirect evaluation tool of the mechanical properties of ex-vivo cardiac tissues. Finite element models of the heart will then be summarized, followed by their use for the prediction of the mechanical properties of the myocardium from CMR in acute Lymphoblastic Leukemia survivors and for MRI-based analysis of the blood flow in the left ventricle. The limits of rest data on patients will be discussed to introduce a study on cardiac mechanical performance in childhood ALL survivors assessed by combined CMR and incremental exercise test. The development of a novel inotropic Exercise CMR Protocol for Cardiac Mechanics Characterization will conclude this presentation.