Elyse Foster, MD, FACC,
[Journal of the American Society of Echocardiography]=Through technical
advances in ultrasound imaging, direct visualization of the arteries and
measurement of coronary artery flow is now possible in the majority of
patients.
Although coronary angiography remains the reference standard for
measuring the anatomic severity of a stenotic lesion, analysis of coronary
artery flow signals and measurement of coronary flow reserve(CFR) provide
physiologic correlates of disease severity. Direct invasive measurements using
Doppler flow wires and catheters have provided a wealth of information on the
pathophysiology of coronary flow dynamics. In clinical practice, these invasive
techniques are rarely applied because of the time and expense required. Thus,
treatment is primarily on the basis of anatomic measures of severity. A reliable
noninvasive method such as those described below could change the
standard on which treatment of coronary disease is based.
Direct echocardiographic assessment of coronary artery disease was first
described 15 years ago but only in the past few years has there been rapid
progress in the field. In 1987, Fusejima succeeded in measuring coronary
artery flow using Doppler transthoracic echocardiography(TTE) with a 3.75-㎒
transducer. However, clinical application was limited by low success rate;
adequate signals were available in only 35% of control subjects and 50% of
patients with cardiac disease. Subsequent publications by Ross et al, and
Kenny and Shapiro, demonstrated improved blood flow visualization rate using
higher-frequency transducers(≥5㎒).
With the recent technologic advances in digital imaging along with the
availability of high-frequency transducers and low Nyquist Doppler capability,
visualization of the coronary artery tree has improved. Currently, skilled
operators can be expected to achieve a 90% success rate in visualizing the
coronary arteries. More recently, identification of penetrating intramyocardial
coronary arteries and the internal mammary artery(IMA) flow signals using TTE
has been reported. Although a recent study reports visualization of the distal
right coronary artery(RCA), most of the literature to date has examined flow in
the mid and distal left anterior descending coronary artery(LAD).
TECHNICAL ASPECTS OF
IMAGE ACQUISITION
LAD
The proximal LAD is visualized in a modified parasternal short-axis view just
above the level of the aortic valve. A septal branch of LAD may also visualized
in the parasternal short-axis view at the midpapillary muscle level. To visualize
the distal LAD, the optimal acoustic window is found close to the midclavicular
line in the fourth or fifth intercostals space with the patient positioned in the
left lateral decubitus position. The distal LAD can best be identified in the long-
axis view with the ultrasound beam inclined laterally