Ultrasonically Measured Propagation Speed of Myocardial Contraction Rapidly Decreased in Swine Heart Just after Avascularisation of Coronary Artery

Fatal necrosis of the myocardium can be avoided by prompt re-perfusion at the onset of myocardial ischemia. Therefore, rapid identification of the ischemic region is essential for diagnosis and subsequent correct treatment in the early stage of ischemic heart disease. In the present study, in order to establish an ultrasonic-based method of identification of the ischemic region, the change of the myocardial contraction response from a normal to ischemic state was elucidated by ultrasonic measurement. Ultrasonic measurement was applied to the interventricular septum (IVS)of open-chest hearts of 5 swine under normal conditions. Ischemia in the IVS was then induced by avascularizing the left anterior descending (LAD)coronary artery, and ultrasonic measurement of the ischemic IVS was applied within several seconds. The number of the scanning ultrasonic beams was restricted to 13 in order to keep the high pulse repetition interval. By applying the phased-tracking method to the signals acquired under each condition, velocity waveforms with minute vibration were simultaneously obtained at about 3,000 points in the IVS. The propagation of the myocardial contraction was evaluated as spatial transition of the delay time by a cross-correlation method. In the IVS, the myocardial contraction response propagated from the basal to apical sides. The propagation velocity was almost constant at 2.7 ± 0.5 m/s under normal conditions. On the other hand, an approximately 31% decrease in the propagation velocity to 1.9 ± 0.5 m/s was observed about 5 s after LAD avascularization. Furthermore, about 7 s after LAD avascularization, an approximately 49% decrease in the propagation velocity to 1.4 ± 0.3 m/s was observed. These results suggest that the myocardial ischemic regions can be identified noninvasively by ultrasonic measurement.