Intracardiac ARF-driven shear wave velocimetry to estimate regional myocardial stiffness and contractility in pigs with focal infarctions

Four pigs, three with focal infarctions in the apical intraventricular septum (IVS) and/or left ventricular free wall (LVFW), were imaged with an intracardiac echocardiography (ICE) transducer. Custom beam sequences were used to excite the myocardium with focused acoustic radiation force (ARF) impulses and image the subsequent tissue response. Tissue velocity in response to the ARF excitation was calculated with a phase-based estimator, and transverse wave velocity was estimated from a time-of-flight approach at each depth. The excitation sequence was repeated every 1/40 s for four seconds to generate 40 Hz M-Modes of induced Acoustic Radiation Force Impulse (ARFI) displacement magnitudes and Shear Wave Elasticity Imaging (SWEI) wave speeds. These images were taken from various views in the right and left ventricles, in and out of infarcted regions. Various views are presented and discussed. In all animals, ARFI and SWEI estimates indicated contraction and stiffness in non-infarcted tissues with high variance and no indications of remodeling in the diseased animals. Where available, views of infarcted tissue were compared to similar views from the control animal. In views of the LVFW, the infarcted tissue presented as stiff and non-contractile compared to the control. In a view of the IVS, no significant difference was seen between infarcted and healthy tissue. In another view, a heterogenous infarction was seen presenting itself as soft and noncontractile.