M-mode ARFI imaging demonstrates the effect of coronary perfusion on cardiac stiffness

Myocardial stiffness is an important clinical indicator of cardiac function. One of the contributors to stiffness in the heart is coronary perfusion. The interaction between cardiac tissue and coronary vasculature has been studied for several decades using pressure-volume loop measurements. Recently, developments in elastography methods have enabled researchers to study the mechanical properties of tissues from a distance. Among them, Acoustic Radiation Force Impulse (ARFI) Imaging utilizes an acoustic pulse to push the tissue and ultrasound tracking to measure the resulting displacement. M-mode ARFI was used in this work to investigate the effect of coronary perfusion on cardiac stiffness. In six isolated Langendorff perfused rabbit hearts, we investigated the effect on myocardial stiffness of a perfusion pressure reduction from normal to half-normal. The acute decrease in coronary perfusion decreases the stiffness of the heart in systole and diastole (Gregg and garden-hose effects respectively). As the coronary perfusion was reduced from normal to half-normal, the average M-mode ARFI displacements for all the subjects increased from 5.1 ± 2.2 μm (mean ± standard deviation) to 9.7 ± 3.7 μm in systole and 24.5 ± 8.9 μm to 35.2 ± 9.1 μm in diastole (p <; 0.05). These results are consistent with the Gregg and garden-hose effects reported by researchers using other measurement methods. Despite complicated issues regarding attenuation, anisotropy, and viscoelasticity, ARFI can be used to study relative or acute changes in cardiac function and myocardial stiffness.