Abstract Wed177: Evaluating Ultrasonic Backscatter Variation To Determine Cardiac Structure During Contraction And Relaxation

Background: The non-invasive assessment of cardiac muscle changes is crucial for understanding myocardial function, mechanics, and the structural determinants of human cardiomyopathies. We have previously determined that collagen crosslinking reduces anisotropy of ultrasonic backscatter in isolated, passive hearts. Cyclic variation of ultrasonic backscatter is a clinical index, but how contraction alters this anisotropy, a measure of myofiber alignment, is not yet known. Goal: This study investigates physiologic modulation of ultrasonic backscatter in contracted and relaxed hearts, ex vivo. Methods: Isolated Langendorff perfused hearts were obtained from rats. Short-axis ultrasound was obtained at the mid-papillary level. The heart was alternately passively relaxed using a low calcium and potassium solution with 2,3-Butanedione monoxime (BDM) and contracted with a high calcium and potassium solution. Flow rate and perfusion pressure were measured. Backscatter was quantified from four cardinal positions in the short axis (anterior, lateral, posterior, septal walls) utilizing a custom Matlab program, and wall thickness was approximated using endocardial and epicardial ellipsoids. Results: Initial Linear Mixed Model analysis suggests interactions between contraction condition, position in the heart, and wall thickness. Interactions between contraction and position support that contraction alters anisotropy, and wall thickness suggests cell or extracellular matrix spacing contribute to the change(s). Preliminary studies in core samples support that changes in matrix spacing (versus cellular components) are a key modifier. Discussion: Positional differences and wall thickness might inform more precise ultrasound based diagnostic techniques and improve the ability to use backscatter to quantitatively characterize myocardial structural and functional changes. Future experiments to isolate and quantify the role of extracellular matrix spacing in ultrasonic backscatter changes that occur in pathological conditions may further define the relationship between backscatter and cardiac structure.