Abstract
Purpose: For myocardial ischemic regions, when medical diagnosis and treatment are applied in the early stage of ischemic heart disease, fatal necrosis of the myocardium can be avoided by prompt reperfusion. Therefore, appropriate and rapid identification of ischemic regions is essential. In the present study, to noninvasively elucidate the propagation characteristics of the myocardial response to electrical excitation in the heart, the propagation of myocardial contraction was visualized by applying ultrasonic measurement of a minute vibration velocity waveform to each point in both the interventricular septum (IVS) and left ventricular posterior wall (LVPW) of the human heart. Methods: By simultaneously applying the phased-tracking method with a high frame rate of over 400 Hz to the IVS and the LVPW, vibration velocity waveforms in the myocardium were obtained at about 3,000 points in both walls. In addition, using a cross-correlation between the resultant vibration velocity waveform at each measurement point and that at the reference point, the delay time of the contraction response at each point from that at the reference point was determined so that the propagation of myocardial contraction could be visualized. Results: In the IVS, the myocardial contraction response propagated at 1.9-3.8 m/s from the basal to the apical side. In the LVPW, on the other hand, the response propagated at 2.0-3.2 m/s from the apical to the basal side. Since the above measurement was simultaneously applied to both walls, it was confirmed that the myocardial contraction propagated from the basal to the apical side in the IVS, and then from the apical to the basal side in the LVPW. These results correspond to the route of the Purkinje fibers. Conclusion: Using the proposed measurement and analysis method, it was shown that propagation of myocardial contraction in the IVS and the LVPW could be visualized by ultrasound.
