Role of Transthoracic Echocardiography in Visualization of the Coronary Arteries and Assessment of Coronary Flow Reserve

Abstract

Visualization of the epicardial coronary arteries by echocardiography is technically challenging. The physical nature of ultrasound waves prevents them from delineating the coronary tree because of multiple factors. The resolution of tansthoracic echo using a 2.53.5MHz probe is only 2mm while the diameter of the epicardial coronary arteries ranges from 1.5 to 4mm. The epicardial coronaries are relatively superficial in the chest, so the lie in near field of the ultrasound waves. The translational and rotational motion of the coronary arteries in the AV grooves poses a challenge in obtaining stable Doppler signals. The relatively low velocity of coronary flow compared to the flow velocity in the ventricles makes color signals hard to discern. Finally, the tomographic nature of the echocardiographic study makes differentiation between adjacent vessels e.g. the LAD and the diagonal branches extremely difficult. Despite these difficulties, the need for a noninvasive bedside tool that could allow inference of the coronary arteries pushed towards more efforts in using echo for that aspect. Using dedicated high-frequency probes made assessment of the left main coronary, the LAD and even the posterior descending branch of the RCA feasible in a large proportion of patients (Hozumi et al., 1998). Transthoracic and transesophageal echo can provide data regarding coronary patency, the presence of coronary stenosis or coronary ectasia (Iliceto S, et al., 1991, Kozakova M, et al., 1997, Lambertz et al., 2000).