Research Of The Mechanical Characteristics Of Paced Myocardium Based On Ultrasound Doppler Tissue Imaging

Cardiovascular diseases have the highest death rate that is a ratio between mortality and population. One of the main reasons is that cardiac electronic activations and mechanical motions are under disorder. Mounting a pace-maker into a heart is a more effective method for treating such diseases. But many patients don't feel well after using them. In order to better understand the myocardial mechanical behavior under pacing, we launched out this study.We paced 5 canines at 3 different positions respectively because that we wanted to study the myocardial mechanical behavior more comprehensively. In our study, we saved sequential images of canine myocardial motions, together with the corresponding ECG based on an intracardial ultrasound Doppler tissue imaging system. We abstracted the quantitative velocities by analyzing those images. We study myocardial mechanical behaviors in time domain, frequency domain and the time-frequency domain.In time domain, we made a conclusion that the myocardial motive velocity increased from apex to base and E/A was more than one under HBP (his-bundle pacing), which accorded with other researchers' finding. We also found that the interval between the time myocardial beginning to depolarize and the time myocardial complete excitation increased gradually under RAAP (right atrium atria pacing), HBP and RVP (right ventricle pacing). Myocardial motions had an abnormal E peck of the time-velocity curve in RVP mode.In frequency domain, we obtained myocardial frequency characteristics by calculating its power spectrum density. We did these by estimating the maximal entropy of the power spectrum density with Burg's algorithm. We found that there were more high and convergent energy in 2Hz frequency and its frequency multiplication. Below 1Hz frequency, there were also more high and convergent energy. The energy in 2Hz frequency and its multiplication frequency were high due to the pacing frequency at 2Hz. And the energy was below 1Hz maybe because we didn't wipe off the effect of the myocardial average velocity and existing respiration components. In time-frequency domain, we got the duration of myocardial systole and diastole, which are 200ms and 300ms respectively. The myocardium we observed was located at his-bundle adjacent area and the top of the interventricular septum. We also obtained that some frequent characteristics of energy in 2Hz frequency and its frequency multiplication by the method of short time Fourier transform, which were similar with the characteristics we just obtained from frequency domain.In this paper, we found that we may study myocardial mechanical motions effectively by an intracardial ultrasound Doppler tissue imaging system together with an image analysis method. We verified that myocardial motions were more physiological if the propagation sequence of pacing electronic activation was from atrium to myocardium, as the sinoatrial node pacing does. At the mean time, the physiological characteristics of myocardial motions under RVP was worst in the 3 pacing modes of RAAP, HBP and PVP, because that the propagation sequence of pacing electronic activation was in reverse order comparision with nature sinoatrial node pacing.