Ultrasonic visualization of propagation of myocardial vibration driven by electrical excitation of myocardium of rat in ex vivo experiment

For the realization of noninvasive and regional myocardial tissue characterization, in the present study, we attempted to elucidate the characteristics of the myocardial response to electrical excitation and its propagation by an ex vivo experiment using a rat left ventricular wall. To visualize such a propagation phenomenon, whose speed is up to several m/s, high-frame-rate ultrasound was used to measure the myocardial vibrations driven by electrical excitation at 72 points along the heart wall with 200 µm intervals at a frame rate of 3472 Hz. The propagation of myocardial vibration was visualized by estimating the delay time between vibration waveforms measured in the reference ultrasonic beam and each ultrasonic beam using the cross-correlation function between the vibration waveforms. From the estimated delay time, we visualized the propagation of myocardial vibration caused by electrical excitation. The propagation speed was estimated to be 2.5 m/s in the entire excised myocardium. It was also estimated to be 1.8 m/s in the middle of the heart wall and 2.2 m/s at the internal and external surfaces of the left-ventricular wall. The results showed that the myocardial vibration driven by electrical excitation could be measured with high-frame-rate ultrasound.