Controlled 2D cardiac elasticity imaging on an isolated perfused rabbit heart

Ultrasound strain and strain rate imaging have been proposed to detect myocardial muscle viability and contractility change. However, it's not easy to control experimental parameters and acquire high SNR data during in-vivo animal experiments. To address this, we performed 2D cardiac elasticity imaging on a well-controlled isolated retroperfused rabbit heart paced through the apex. The excitation-contraction decoupler, 2,3-butanedione monoxime (BDM) was used to optimize the maximum strain given frame acquisition rate, reducing the decorrelation due to excessive frame-to-frame strain. Under a local animal protocol, a heart was harvested from an anesthetized New Zealand White rabbit and prepared using a Langendorff preparation. Modified Oxygenated (95% O2 5% CO2) Krebs-Henseleit (K-H) buffer (PH 7.4, 37°C) solution was retroperfused through the aorta. The heart was paced through the apex with electrodes at 3Hz. The internal left ventricle (LV) pressure was recorded using a pressure meter connected to a water-filled latex balloon placed in the LV. The ECG signal was simultaneously recorded. Two linear array connected to a commercial US scanner (Sonix RP, Ultrasonix, Richmond, BC, Canada) were used to acquire RF data. The pacing signal, US RF, ECG and LV pressure data capturing were all synchronized using an field programmable gate array (FPGA) chip (ezFPGA-C6-6, Dallas Logic, Plano, TX, USA). All these data were acquired before administering, during perfusion and after flushing BDM without/with the ligation of left anterior decending (LAD) artery At each data acquisition point, US RF data were acquired over two heart cycles (41 frames/cycle). 2D speckle tracking was applied to estimate displacement and strain. In this experiment, principal stretches were also derived using tracking results from two probes with resolution about 1.25mm along its own axial direction. The principal stretches were compared for the normal heart and heart with ischemia or MI produced by LAD ligation. The isolated rabbit heart combined with BDM (2mM) provided a well-controlled experimental environment for cardiac strain imaging with a virtually high frame acquisition rate. By comparing the synchronized pacing signal, LV pressure, ECG signal, and principal stretch, we were able to monitor and verify the local cardiac contractility referenced to the electrical stimulation.