Non-invasive localization and quantification of graded ischemia using Electromechanical Wave Imaging in vivo

Electromechanical Wave Imaging (EWI) has recently been introduced as a non-invasive, ultrasound-based imaging modality, which could map the electrical activation of the heart in various echocardiographic planes in mice, dogs and humans in vivo. By acquiring radio-frequency (RF) frames at very high frame rates (390-520Hz), the onset of small, localized, transient deformations resulting from the electrical activation of the heart, i.e., generating the electromechanical wave (EMW), can be mapped. The correlation between the EMW and the electrical activation speed and pacing scheme has previously been reported. In this study, we pursue the development of EWI and analysis of the EMW properties in dogs in vivo for early detection of ischemia. EWI was performed in normal and ischemic open-chested dogs during sinus rhythm. Ischemia of increasing severity was obtained by gradually occluding the left-anterior descending (LAD) coronary artery. EWI was shown to be sensitive to the presence of intermediate ischemia. EWI localized the ischemic region when the LAD was occluded at 60% and beyond and was capable of mapping the increase of the ischemic region size as the LAD occlusion level increased. Those results indicate that EWI could be used to assess electrical conduction properties of the myocardium, and detect ischemic onset and disease progression entirely non-invasively.