Imaging of the Coronary Arteries
The ability to visualize the proximal segments of the left and right coronary arteries was initially demonstrated by Weyman et al. Subsequent studies established the ability of color and spectral Doppler examination to image and record the velocity of flow from TTE and TEE approaches, particularly with regard to the left anterior descending coronary artery.210 However, visualization of the coronary arteries by echocardiography has not achieved a significant role in clinical practice because the resolution of the technique is at the limit of vessel size and the vessels are circuitous and move vigorously, often coursing in and out of the beam path. Despite these limitations, transthoracic imaging has proven useful for the diagnosis and follow-up of patients with Kawasaki disease and coronary involvement337 (Fig. 15–140) and may also help distinguish normal from atherosclerotic coronary arteries.
The coronary arteries are routinely imaged with TEE, which can detect proximal stenoses, atherosclerosis, and congenital abnormalities of the coronaries more accurately than surface imaging. Doppler TEE analysis also has been used to determine coronary flow reserve.338 Visualization of mid- and distal coronary arteries is problematic with both TTE and TEE. Recent advances in technology and contrast agents, however, have significantly improved capabilities in this area. Figure 15–141A shows color flow within a septal coronary artery. Figure 15–141B shows a spectral Doppler recording of flow within the distal left anterior descending coronary artery (note the predominance of diastolic flow). These images were produced by an instrument utilizing a fundamental frequency range of 5 to 7 MHz, rather than the more commonly used range of 2.5 to 5.0 MHz. This area of echocardiography is expanding rapidly and clinical applications will grow in the future.
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