Epicardial surface dynamics in the closed-chest normal canine.

Past studies of the changing three-dimensional shape of the heart in the closed chest during the cardiac cycle have been restricted to the measurement of local deformations at a relatively few specific locations, and often have required surgical procedures that alter the measurements obtained. In the study reported here, high precision displacement and velocity measurements were obtained at the epicardial interface using a Compton backscatter imaging technique that does not require a surgical intervention or contrast injections. Displacement and velocity measurements were obtained at more than 200 locations at the epicardial interface at 13 ms intervals throughout the cardiac cycle. Measurements of the changing shape of the heart during the cardiac cycle with this technique are precise to 0.1 mm (S.D.). Displacement and velocity patterns recorded in this study confirm and integrate the studies of many others and also add new information. An unexpected vigorous inward motion of both the LV (39 mm s-1) and RV (26 mm s-1) surfaces during isovolumic relaxation and early rapid refill is demonstrated. Velocities during this period equal or exceed those that occur during ejection. During ejection, inward LV motion at the base of the heart precedes that at the apex by 80-90 ms. Posterior LV displacements and velocities during ejection are 4-6 times greater than those at the anterior and apex. The Compton backscatter imaging technique for obtaining undisturbed measurements of cardiac dynamics in the closed chest has potential as a non-invasive clinical tool for serial studies of cardiac surface motion abnormalities. The data presented can also be used to set surface boundary conditions for biomechanical models of heart deformation.