The authors provide a guide to a new approach for coronary circulation using transthoracic Doppler echocardiography (TTDE).
are Assistant Professors and Dr. Yoshikawa is a Professor and
Chairman of the Department of Internal Medicine and Cardiology,
Osaka City University Medical School, Osaka, Japan.
Coronary Artery Disease; Increasing Risk
Despite many efforts to prevent coronary artery disease, the
number of patients with coronary artery disease (CAD) is
increasing. According to the World Health Organization, there are
now 7.1 million deaths from coronary heart disease globally, and it
is predicted that this figure will have risen to 11.1 million by
Thus, continuous efforts to identify coronary narrowing and to
evaluate coronary circulation in patients without coronary
narrowing are a critical mission for us. In this article, we
provide a guide to a new approach for coronary circulation using
transthoracic Doppler echocardiography (TTDE) (Figure 1).
Echocardiographic Approach to CAD
Coronary flow velocity reserve (CFVR) has been accepted as one
of the most reliable indices in detecting functional coronary
stenosis. At the same time, it has been accepted as an index for
evaluating coronary circulation in patients without coronary
narrowing. However, this index has been measured by a Doppler guide
wire or Doppler catheter, which are invasive; or positron emission
tomography, which is expensive. Although these techniques
successfully introduced the utility of this index for assessment of
CAD or coronary risk factors in vivo, their use is limited in
patients with known CAD.
Recently, technologic advancements in echocardiography have
permitted us to evaluate coronary flow dynamics noninvasively,
using transthoracic Doppler echocardiography.
The success rate of CFVR measurement is > 90%, which is feasible
for daily clinical use. Thus, we can approach coronary flow not
only in the cath lab, but also in the echo lab, or even at the
How to Measure CFVR using TTDE
CFVR measurement by TTDE consists of three components: 1)
visualization of coronary flow by color flow mapping; 2) coronary
flow velocity recordings by pulsed Doppler method; and 3) off-line
measurement of coronary flow velocities and CFVR. CFVR is
calculated as a ratio of hyperemic to basal coronary flow
Step 1: Visualization of coronary flow by color flow
Echocardiographic images can be obtained from the acoustic
window around the apex; usually on midclavicular line in the fourth
and fifth intercostal spaces in the left lateral decubitus
position. After the lower portion of the interventricular sulcus is
located in the long-axis cross-section, the transducer should be
rotated in a clockwise manner to search flow signals on the left
anterior descending artery (LAD) under the guidance of color flow
mapping. The characteristic of coronary blood flow signals is
linear signals that persist during entire diastole (Figure 2).
Step 2: Coronary flow velocity recordings
Coronary blood flow velocity can be recorded by pulsed-wave
Doppler (3.5 MHz) using a sample volume (1.5 to 2.0 mm) placed on
the color signal in the mid to distal LAD. Adenosine is
administered by intravenous infusion (0.14 mg/kg per minute) for 2
minutes to record spectral Doppler signals during hyperemia.
Electrocardiogram, heart rates, and blood pressure should be
monitored continuously during examination in all patients. During
the recording, the examiner should try to hold the transducer on
the same position as much as possible.
Step 3: Measurement of coronary flow velocity and CFVR
Coronary blood flow velocity can be measured off-line by
contouring the spectral Doppler signals using the integrated
evaluation program in the ultrasound system (Figure 3). Both peak
and mean diastolic flow velocities at baseline and peak hyperemia
should be measured as parameters necessary for CFVR assessment.
CFVR is calculated as the ratio of hyperemic to basal peak (peak
CFR) and mean (mean CFR) flow velocity. Usually, diastolic flow
velocity is alternatively used. Normal CFR is defined as >2.0 on
the basis of the results of previous studies that had evaluated
flow velocities in the distal LAD.
Tips for Coronary Visualization
First, recognition of the anatomy is needed. A cross-section of
coronary imaging cannot be obtained in
standard two-dimensional images. Because the LAD exists in anterior
interventricular sulcus, the landmarks for coronary imaging are the
left ventricular wall, right ventricular wall, and interventricular
Next, specific machine settings for coronary flow are critical.
The most important setting is modification of velocity range in
color flow mapping. When using velocity range for routine color
flow mapping (approximately 60 cm/s), it is difficult to visualize
coronary flow, which is diminished by wall filtering in most cases.
Thus, velocity range should be set around 20 cm/s to visualize
A final important point is the use of the appropriate transducer
for coronary flow visualization. We recommend using a
high-frequency (5 MHz) transducer because the distal LAD is in the
near field for most patients. However, selection of the transducer
must be made in specific cases. When the distal LAD exists in the
far field, a lower frequency transducer may be better.
When flow visualization or velocity recordings are not
sufficient for analysis, a contrast agent is useful as a Doppler
Although the number of the patients who need a contrast agent
differs between study populations, the proper use of a contrast
agent increases the success rate of flow velocity recordings
Coronary flow assessment by TTDE, which is completely
noninvasive, opens a new window for physiological assessment of
coronary circulation. *