Electromechanical wave imaging and electromechanical wave velocity estimation in a large animal model of myocardial infarction

Abstract

Background Echocardiography is often used in the clinic for detection and characterization of myocardial infarction. Electromechanical wave imaging (EWI) is a non-invasive ultrasound-based imaging technique based on time-domain incremental motion and strain estimation that can evaluate changes in contractility in the heart. In this study, electromechanical activation is assessed in infarcted heart to determine whether EWI is capable of detecting and monitoring infarct formation. Additionally, methods for estimating electromechanical wave (EW) velocity are presented, and changes in the EW propagation velocity after infarct formation are studied. Methods and Results Five (n=5) adult mongrels were used in this study. Successful infarct formation was achieved in three animals by ligation of the left anterior descending (LAD) coronary artery. Dogs were survived for a few days after LAD ligation and monitored daily with EWI. At the end of the survival period, dogs were sacrificed and TTC (Tetrazolium chloride) staining confirmed the formation and location of the infarct. In all three dogs, as soon as day 1 EWI was capable of detecting late-activated and non-activated regions, which grew over the next few days. On final day images, the extent of these regions corresponded to the location of infarct as confirmed by staining. EW velocities in border zones of infarct were significantly lower post-infarct formation when compared to baseline, whereas velocities in healthy tissues were not. Conclusions These results indicate that EWI and EW velocity might help with the detection of infarcts and their border zones, which may be useful for characterizing arrhythmogenic substrate.

Local two-dimensional distribution of propagation speed of myocardial contraction for ultrasonic visualization of contraction propagation

“…where T T x x = ¶ ¶ / and T T y. y = ¶ ¶ / 33,46) Because the local and two-dimensional propagation speed of myocardial contraction was estimated although only the average speeds were estimated in our previous study, 23,31,32) the estimation of spatial distribution of the propagation speed vectors became possible.…”

“…Displacement waveforms obtained by integrating the velocity waveforms are also shown. Although several studies have reported the detection of myocardial contraction using displacement waveforms, 7,8,19,27,28,30,[44][45][46] it is possible to measure not only the visible contraction but also minute vibrations caused by contraction using velocity waveforms. The contraction response at the time of the electrocardiographic QR interval representing the onset of ventricular contraction can be identified as the bimodal movements of myocardium toward the LV, i.e., the bimodal positive waveform in velocity waveforms, although the displacement waveforms were almost smooth.…”