CARDIAC SURGERY
FOCUS: Coronary Artery Imaging
EPICARDIAL COLOR-DOPPLER SCANNING IN CORONARY ARTERY BY-PASS SURGERY
Rune Haaverstad, MD, PhD, Nicola Vitale MD, PhD
Department of Cardiothoracic Surgery, University Hospital of Trondheim,
Trondheim, Norway
Epicardial color-Doppler ultrasound scanning with a new phased array
10 MHz transducer allows easy approach to the
external surface of the heart and satisfactory
imaging of coronary stenoses and graft anastomoses.
Epicardial color-Doppler ultrasound should become
a further advancement to transit-time flowmetry
during coronary surgery.
(Heart Views. 2001;2(3)112-115) ©
2001 Hamad Medical Corporation
Key Words:
Epicardial colour-Doppler ultrasound
Intraoperative echocardiography
Coronary Artery Bypass Surgery
Coronary angiography is the standard
method of evaluating coronary artery
disease before coronary artery bypass grafting (CABG) but, in some instances, it is difficult to apply the information gathered from angiography to the operation site.
During operation the surgeon can palpate the coronary arteries, which can provide some indication of the localisation of a stenosis, but not of the degree of stenosis.
However, this maneuver may prove difficult if the target vessels lie intramyocardially, are deeply buried in fat, or are covered by adhesions.
Intraoperative assessment of distal graft anastomoses in coronary artery bypass surgery (CABG) is of paramount importance. This is true particularly for off-pump CABG grafting, where technical abnormalities requiring revision of the distal anastomoses have been reported to occur in up to 9.9 % of operations (1).
Ideally, this assessment should be carried out by means of a simple and reliable device so that whenever a technical problem is identified, the anastomosis can be revised immediately.
In the past, several devices for intraoperative ultrasound assessment of coronary arteries and graft anastomoses have been tested in laboratory experiments as well as clinical studies (2-7).
Unfortunately, none of these devices have gained wide acceptance due mainly to their many technical limitations. The only widely recognized method of assessing graft patency intraoperatively is transit-time flowmetry (1,8,9), but this is of limited value because coronary resistance and morphology of the anastomosis is not visualized by this method.
Several devices for intraoperative echocardiographic visualisation of coronary arteries and graft anastomoses have been tested in animal experiments as well as clinical studies over the last 15 years (2-7).
Recently, a new linear phased array 10 MHz GE Vingmed transducer specially designed for epicardial vascular ultrasound scanning during coronary surgery has become available.
The transducer is connected to a GE Vingmed System FiVe echocardiography unit (GE Vingmed, Horten, Norway).
In this review we summarise our initial experience in assessing coronary grafts with epicardial color Doppler imaging (10, 11).
Epicardial imaging of coronary artery stenoses
Figure 1. The GE Vingmed ultrasound transducer specially
designed for epicardial imaging of coronary
arteries and anastomoses. This 10 MHz hand-held
transducer has a contact area of 27.3 by
9.6 mm.
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and graft anastomoses was performed in 25 patients undergoing CABG on cardiopulmonary bypass as well as during CABG on beating heart.
Intraoperatively, epicardial color-Doppler ultrasound of distal graft anastomoses was routinely compared with transit-time flowmetry (Medi-Stim Flowmeter, Oslo, Norway).
Surgical approach was through median sternotomy in all cases.
A new linear phased array 10 MHz transducer specially designed for epicardial
vascular ultrasound during CABG has become available.
The transducer design allows epicardial scanning
of native coronary arteries for most of their
course. At the beginning of our experience the
left anterior descending artery (LAD) was the
main target vessel for the assessment of stenoses
and distal graft anastomoses. The transducer with
sterile gel as conduction medium was applied directly
onto the epicardium.
Images of the coronary arteries and grafts anastomoses
were obtained through longitudinal and transverse
planes.
Color-Doppler imaging through a longitudinal plane
showed increased blood flow velocity and turbulence
occurring at the stenotic site.
The transducer was applied onto distal graft anatomoses
for the detection of technical inadequacies.
In most of the cases, we obtained very satisfactory
images of LAD stenoses on both view planes.
Figure 2. The 10 MHz hand-held epicardial
transducer is kept inside a sterile
sleeve onto a LIMA anastomosis to
the LAD in a patient operated with
the use of cardiopulmonary bypass.
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When approaching the LAD stenoses by a transverse plane we were able to visualise the shape of the atheroma (oval, round, complex) and its localization within the original lumen (eccentric versus concentric).
Unfortunately, coronary angiography is not able to distinguish the localisation of the atheroma.
Thus, epicardial imaging provides information details that angiography cannot.
Real-time ultrasound images and storage of data on VHS videotape or digitally on a diskette were obtained approximately within ten minutes in each patient.
There were some limits to the echo power of the transducer.
Very proximal location of the stenosis or a deep intramyocardial position of the artery were the most important obstacles against
Figure 3
detection of LAD stenoses. Therefore, we were not able to confirm previous studies supporting the use of epicardial ultrasound for locating intramural coronary arteries (2-7). Furthermore, tortuous and heavily calcified LAD caused limited echo visibility due to acoustic shadowing.
The shape of coronary lesions and their location within the coronary lumen as seen by epicardial scanning are valuable information for the cardiac surgeon when he decides to perform coronary arteriotomy. Images of coronary arteries and a stenosis are presented in Figs. 3,4.
In previous reports we demonstrated that coronary artery bypass graft anastomoses could be easily evaluated intraoperatively with this small phased array transducer specially designed for coronary surgery (10, 11).
The anastomotic site was shown very clearly in most of the cases, so that
Figure 5
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Figure 5. Epicardial color-Doppler scan of a LIMA-LAD anastomosis: longitudinal view. The inflow vessel (LIMA), the anastomosis and the run-off vessel (LAD) are all clearly visualised.
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Figure 6
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Figure 6. In the off-pump patients a sterile 10 MHz hand-held transducer is applied in between the feet of the stabilizer and directly onto a LIMA-LAD anastomosis.
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both the toe and heel of the anastomosis as well as the run-off vessel could be visualised (Figs. 5, 6).
When assessing a distal graft anastomosis with epicardial imaging, special attention has to be paid to the toe, because this is the most critical site.
Whenever a technical abnormality occurs at this point, flow disturbances develop that are clearly demonstrated by epicardial color-Doppler imaging.
These flow disturbances maybe clues to early graft occlusion.
Our findings support previous experimental and clinical studies showing that the assessment of the technical adequacy of bypass grafts may be enhanced by the use of epicardial echocardiography (6).
We assessed the grafts with transit-time flowmetry before chest closure because this technique is the only method widely accepted and validated for intraoperative assessment of graft patency.
Several institutions have reported on the usefulness and specificity of epicardial scanning, but encouraging initial results were not followed by a wide application in clinical practice.
The main technical reason for this was the large size of the ultrasonic probe, which allowed only the visualisation of LAD, diagonals and proximal right coronary artery (2-7).
The introduction of this new transducer for epicardial imaging of very small dimensions with color-Doppler features will enhance the widespread use of epicardial scanning in coronary artery surgery.
In the later and still ongoing part of our experience, we tested the Vingmed transducer during off-pump CABG. When performing off-pump CABG the heart is exposed with pericardial stitches and modern stabilizers in a way that allow easy epicardial scanning of all areas of the heart (Fig. 6).
The probe could be easily placed over most areas of the heart with very satisfactory images of coronary anatomy and their anastomoses. Thus, this technique is an excellent device for the evaluation of distal graft anastomoses in off-pump coronary surgery.
Indications for intraoperative color-Doppler ultrasound scanning in coronary artery surgery are:
Localization of coronary arteries
Localization of coronary stenoses and occlusions
Measurement of vessels and stenoses
Imaging of bypass grafts
Imaging of distal graft anastomoses
Our preliminary experience shows that epicardial ultrasound scanning with the new phased array 10 MHz Vingmed transducer allowed satisfactory imaging of coronary stenoses and distal graft anastomoses.
Proximal lesions, deep intramyocardial vessels, vessel tortuosity and extensive calcifications may limit the quality of imaging.
Real-time visualisation of distal graft anastomoses is a further advancement to graft assessment in off-pump CABG.
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Correspondence to: Rune Haaverstad MD, PhD,
St. Elisabeth Cardiac Centre
University Hospital of Trondheim, N-7018 Norway
Fax: (+47) 73867029 E-mail:rhaavers@online.no
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