Abstract 2296: Propagation of Electric Excitation in Human Heart is Visualized by Transthoracic Echocardiography
Background: Though ECG is an invaluable clinical tool for diagnosis of the heart, regional properties cannot be directly evaluated. This study visualizes the propagation of vibration caused by electric excitation just before R-wave of ECG using ultrasound.
Methods: We have shown that the pulsive vibration is caused on the myocardium 15 ms after the electrical stimulation to an isolated heart ( Acoust Sci Tech 2003;24:17). By the ultrasonic measurement ( Ultrasound Med Biol 2001;27:481), we measured the vibration almost simultaneously at about 1,000 points set in the heart wall at a high frame rate ( IEEE Trans UFFC 2005;51:1931). The consecutive spatial distributions of the interpolated phase of the waves reveal wave propagation along the wall. The propagation time is several ms, which is too short to be detected by conventional methods.
In Vivo Experiments: The method was applied to 10 healthy subjects and 5 patients with OMI. The propagation of spontaneously driven pulsive wave was clearly visible in all normal regions but it was not detected for the diseased area. Just after the Q-wave of ECG, the propagation started from the apex (terminal of Purkinje fiber) to the base side. Its speed was slow (1–2 m/s) without dispersion, which shows to the propagation of electrical excitation. Then, after R-wave of ECG, another pulsive wave started to propagate reversely from base to apex. Since its speed was about 3 m/s for 50 Hz but there was large dispersion, this is the shear wave caused by the mitral-valve closure.
Conclusion: The method noninvasively reveals the propagation of electrical conduction wave by measuring myocardial response, which will be close relationship with regional cell damage.