Hand-held, dynamic indentation system for measuring myocardial transverse stiffness

Primary muscle abnormalities and/or alterations in regional loading may be critical in myocardial infarct expansion and remodeling, cardiomyopathy progression, and arrhythmia generation. To differentiate muscle abnormalities from loading abnormalities, an estimation of regional wall stress is needed. Researchers have previously relied on geometric models and finite element analysis to estimate wall stress, but these estimations have not been validated. It has been shown that the transverse stiffness (the ratio of indentation stress to indentation strain during transverse indentations) of a cardiac muscle can be used to estimate the myocardial wall stress. The authors designed and tested a hand-held dynamic indentation system that can determine the regional transverse stiffness of an intact heart in as little as 15 milliseconds, allowing multiple estimations of wall stress over a single contraction cycle. The sensor was validated with a finite-element analysis of the indentation process, as well as with direct measurements on isolated heart muscle, and on soft, nonbiologic materials. The validations confirmed that the dynamic indentation system does accurately estimate myocardial wall stress. This regional-wall-stress sensor could help to enhance the understanding of cardiac pathophysiology, guide therapy, and assist surgeons in planning cardiac surgeries.