Transthoracic Echocardiography in the Assessment of Coronary Arteries

Quantitative coronary angiography remains the reference standard for assessing coronary anatomy, measuring anatomic severity of the stenotic lesion and assisting in the process of intracoronary interventions. Thus, treatment of coronary artery disease (CAD) is performed primarily on the basis of anatomic measurements of stenosis severity, although the disease severity correlates better with physiologic disturbances which can be revealed by the analysis of coronary artery flow and coronary flow reserve (CFR). Direct invasive measurements of coronary flow signal using Doppler flow wires and catheters provide a lot of information on the pathophysiology of coronary flow dynamics (Chamuleau et al, 2001; Bax et al, 2006; Braden, 2006; Werner et al., 2006; Kaul & Jayaweera, 2008; Courtis et al., 2009). But in clinical practice, these invasive techniques are rarely applied because of the time and expense required. Alternative methodology in detecting coronary flow and CFR is positron emission tomography which is feasible but expensive and scarcely available (West & Kramer, 2009). In fact, a large-scale assessment of such important functional parameters is hampered by the lack of a reliable, low-cost, noninvasive method that might be used for this purpose (Pellikka, 2004). Some years ago transesophageal echocardiography was proposed for evaluation of coronary flow and CFR in man. However, this method demonstrates some important limitations: it is semiinvasive, and has optimal feasibility in visualizing the flow in only very proximal part of the left anterior descending coronary artery (LAD) (ranging from 69% to 97%) and right coronary artery (RCA) (ranging from 66% to 83%) which allowes the assessment of transstenotic or prestenotic CFR but not poststenotic CFR (Vrublevsky et al., 2001, 2004). Until recently, transthoracic echocardiography (TTE) evaluation of the CAD was aimed at the assessment of regional and global left ventricular function (Youn & Foster, 2004). Direct transthoracic visualization of the coronary arteries was attempted in children and occasionally in adults with coronary artery anomalies, arteriovenous fistulas, and aneurysms (Harada et al., 1999; Hiraishi et al, 2000; P.C. Frommelt & M.A. Frommelt, 2004). However, with the advent of harmonic imaging, contrast agents and high-frequency transducers, direct transthoracic Doppler visualization of non-dilated arteries and measurement of coronary artery flow is now relevant in the majority of patients. The aims of this review are to outline the technical aspects of coronary artery visualization and flow measurements both at rest and with pharmacological stress, to demonstrate pathologic coronary artery flow patterns by TTE and to discuss clinical implications of TTE for patients with suspected or confirmed CAD.