(Chest. 2005;127:1371-1377.)
© 2005
American College of Chest Physicians
A Pictorial Review of Coronary Artery Bypass Grafts at Multidetector Row CT*
Riccardo Marano, MD;
Maria Luigia Storto, MD;
Biagio Merlino, MD;
Nicola Maddestra, MD;
Gabriele Di Giammarco, MD and
Lorenzo Bonomo, MD
* From the Department of Clinical Sciences and Bioimaging (Drs. Marano, Storto, and Maddestra), Institute of Radiology, University "G. d’Annunzio," Chieti; Department of Bioimaging and Radiological Science (Drs. Merlino and Bonomo), Institute of Radiology, Catholic University, Rome; and Department of Cardiology and Cardiac Surgery (Dr. Di Giammarco), University "G. d’Annunzio," Chieti, Italy.
Correspondence to: Riccardo Marano, MD, Department of Clinical Sciences and Bioimaging, Institute of Radiology, University "G. d’Annunzio," Osp. "SS. Annunziata," Via dei Vestini, 66100 Chieti, Italy; e-mail: r.marano{at}rad.unich.it
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Abstract
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Multidetector row CT scanners with submillimeter spatial resolution and high temporal resolution are now available and are increasingly used for noninvasive assessment of vascular disease including coronary arteries and grafts. The entire heart and graft course can be scanned within a single breath-hold, and contrast-enhanced images are reconstructed through retrospective ECG gating. In this pictorial review, we describe the CT findings of the most commonly used coronary artery bypass grafts on both axial images and two-dimensional and three-dimensional images providing a correlation with conventional coronary angiography.
Key Words: coronary artery bypass graft • coronary artery disease • multidetector row CT
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Introduction
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Graft disease after coronary artery bypass graft (CABG) surgery is an important issue in cardiology, as reflected by the large number of patients with recurrent chest pain after myocardial surgery revascularization. As a matter of fact, late survival after CABG surgery is largely dependent on graft patency and the progression of coronary artery disease.1234 Although conventional coronary angiography still represents the imaging procedure of choice for assessment of CABGs and the status of recipient vessels, IV angiography using multidetector row CT (MDCT) with retrospective ECG gating is emerging as a new noninvasive technique in the field of cardiac imaging.56 Since coronary arteries and coronary grafts are small vessels, 2 to 4 mm in diameter, and are characterized by both complex anatomy and continuous movements, high spatial and temporal resolutions are mandatory to visualize these vessels at CT. MDCT scanners characterized by submillimeter spatial resolution and a temporal resolution of 94 to 200 ms are now available and are increasingly used for cardiac imaging with promising results.78
Knowledge of CABG anatomy and configuration as seen on MDCT is important for the radiologist in order to correctly assess graft patency and/or the presence of significant stenosis. This pictorial review illustrates CT findings of the most frequently used grafts together with a brief description of scanning protocols for noninvasive evaluation of CABGs using 4-row and 16-row MDCT scanners. A correlation with conventional coronary angiography will also be provided.
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Imaging Technique
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Scanning is performed with the patient in the supine position, during breath-hold. After placement of the leads for ECG recording on the chest wall and a check of the heart rate, a noncontrast CT scan image is acquired through the entire thorax in order to define the volume of the subsequent CT angiography and to detect associated or unsuspected findings. Hence, MDCT angiography is performed during ECG recording, from the subclavian arteries to the cardiac base; in patients with venous grafts, a smaller scanning volume starting from the lower third of the ascending aorta is usually sufficient. On the contrary, when a right gastroepiploic artery (RGEA) has been used, the scanning volume should include the upper abdomen. Working with a 4-row MDCT scanner, we usually select a collimation of 2.5 mm in order to cover the entire acquisition volume in a reasonable scanning time of approximately 25 to 28 s; thinner collimations in the order of 0.5 to 1.5 mm can be used with 16-row MDCT scanners. Low heart rates (< 65 beats/min) are recommended to obtain high-quality CT scans, and in the absence of contraindications (heart failure, systolic BP < 100 mm Hg, atrioventricular blockade greater than grade I, and referred adverse reaction), ß-blockers can be administered before CT acquisition.
A bolus of 100 to 120 mL nonionic contrast material (high iodine concentration is recommended) is IV administered using an automatic injector at a flow rate of 3 to 4 mL/s. Since the left internal mammary artery (LIMA) is the most frequently used graft to the anterior cardiac wall, a right arm venous access is preferable in order to avoid streak artifacts from the left subclavian vein that may hamper a complete evaluation of LIMA course and takeoff.
Axial images are reconstructed in the mid-to-late diastolic phase, using a fraction (percentage; relative delay) of the R-R interval of the cardiac cycle. Depending on the scanning protocol used, 3-mm or 0.5- to 1-mm-thick images are reconstructed with 4-row and 16-row MDCT scanners, respectively. Multiplanar, maximum intensity projection, and volume-rendered images can be obtained to better understand and delineate CABG anatomy and course. Images included in this pictorial were obtained with a 4-row MDCT (Volume Zoom; Siemens; Forchheim, Germany) and a CT off-line workstation for image reconstruction (Leonardo; Siemens) or a 16-row MDCT (Lightspeed 16pro; General Electric; Milwaukee, WI) and a dedicated CT workstation (Advantage 4.1; General Electric).
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Internal Mammary Arteries
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Internal mammary arteries (IMAs) are characterized by unique resistance to atherosclerosis and extremely high long-term patency rates. These vessels do not have vasa vasorum, and the presence of a nonfenestrated internal elastica lamina inhibits cellular migration and intimal hyperplasia. Moreover, the medial layer of the IMA is thin and poor of muscle cells, with poor vasoreactivity, and the endothelium is characterized by high production of vasodilator (nitric oxide) and platelets inhibitor (prostacyclin). Lipid and glycosaminoglycan composition of IMAs are less atherogenetic in comparison with saphenous veins.
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LIMA
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The LIMA is frequently used as an in situ arterial graft to supply the anterior cardiac wall. On axial images, the LIMA is no longer visible in its usual site, on the left side of the sternum, but courses in the anterior mediastinum along the right ventricle outflow tract (RVOT) [Fig 1
]. Although in most cases LIMA grafts show a single distal anastomosis to the left anterior descending artery (LAD) [Fig 2
] or a diagonal branch, multiple sequential anastomoses to both the LAD and diagonal branches are sometimes performed (Fig 3
). Surgery revascularization with an LIMA requires a longitudinal median sternotomy; in some centers, however, the LIMA is distally anastomosed by a left minithoracotomy at the level of the fourth anterior rib space and mobilization of the distal portion of the artery (Fig 4
).49101112 Surgical clips are routinely used to occlude collaterals and to avoid arterial bleeding and can be seen either adjacent to the graft or at the original site of the LIMA (Figs 1 234).
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Figure 1.. Axial CT image in a patient with an in situ LIMA bypass. The normal course of the RIMA (arrow) is close to the sternum (St), while on the left side the IMA is dislocated posterior in the mediastinum fat along the RVOT and is surrounded by surgical clips (arrowhead). Ao = aorta; SVC = superior vena cava; LA = left atrium; Laa = left atrial appendage.
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Figure 2.. Three-dimensional volume-rendering CT images (left, A, and top right, C) and corresponding conventional angiogram (center, B) in a patient with an in situ LIMA bypass to the LAD. MDCT images show a patent LIMA, with surgical clips adjacent to the graft (arrowheads in left, A) and the distal anastomosis to the LAD. Retrograde filling of the mid-LAD (asterisks in left, A, and center, B) with visualization of the first diagonal branch (d1) is also present. Incidentally, a small saccular aneurysm of the proximal RCA was detected with MDCT (arrows in left, A, and top right, C). MDCT findings are confirmed by the conventional selective angiography (center, B, and bottom right, D; the arrow in bottom right, D, indicates an RCA aneurysm).
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Figure 3.. Three-dimensional volume-rendering CT images (left, A, and top center, B) and corresponding conventional angiograms (right, C, and bottom center, D) in a patient with arterial grafts. Sequential anastomoses of the LIMA to a diagonal branch (d1) and LAD are clearly shown (left, A, and right, C). The RGEA is used for the second graft course along the anterior hepatic surface (left, A) and the inferior cardiac surface (top center, B), where it is anastomosed to the PDA (top center, B; and bottom center, D). An in situ RIMA graft to the left cardiac wall was also present with surgical clips along its course (arrowheads in left, A). d2 = second diagonal branch of the LAD.
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Figure 4.. Three-dimensional volume-rendering CT image (left, A) and corresponding conventional angiogram (right, B) in a patient with a single LIMA graft to the LAD. Since a left minithoracotomy was performed, surgical clips are present only in the distal portion of the graft (arrowheads in left, A). St = sternum.
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Right IMA
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The right IMA (RIMA) is rarely used as an in situ graft for the right coronary artery (RCA); it is more commonly used as "free" graft from the ascending aorta to the RCA or from the LIMA to the left circumflex artery (LCx) or obtuse marginal branches (OMs) [Fig 5
]. As already described for LIMA grafts, surgical clips are used to occlude collaterals.
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Figure 5.. Curved MPRs (top left, A, and bottom left, B) and corresponding conventional angiogram (right, C) in a patient with a "Y" free grafted RIMA between the LIMA and the OM of the LCx. Both proximal (arrow in top left, A) and distal (arrowheads in top left, A, and bottom left, B) anastomoses of the free graft are shown on the CT images. The LIMA was used as an in situ graft to the LAD; however, the second portion of the LIMA, distal to the anastomosis with the RIMA, is not visualized because it is occluded.
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Radial Artery
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The first use of the radial artery (RA) as arterial conduit for coronary revascularization has been described by Carpentier et al13 in 1972. The RA is a muscular artery characterized by a pronounced medial layer and high vasoreactivity, with short to mid-term patency rates. Generally, the RA from the nondominant arm is used. The RA is occasionally used when a third arterial graft is necessary or to avoid a venous graft when an IMA cannot be used.1415 The RA is often grafted to supply the left cardiac wall (LCx, OM). Since the RA is a muscular artery, the number of surgical clips used to close collaterals along the graft is usually higher than with LIMAs or RIMAs. This may represent a limit for noninvasive assessment of RA grafts with MDCT because of artifacts from surgical clips hampering a complete visualization of the graft (Fig 6
).
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Figure 6.. Axial (left, A) and volume-rendering CT images (right, B) in a patient with the RA grafted to left cardiac wall. Numerous and quite big surgical clips are present along the arterial conduit and are responsible for streak artifacts that hamper a complete and satisfactory evaluation of the graft.
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RGEA
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The use of the RGEA was first described by Pym et al16 in 1984. Although it has been originally used in reoperation, in the absence of other suitable conduits, RGEA is now used as secondary, tertiary, or quaternary arterial conduit to provide all-arterial revascularization. The biological characteristics of RGEAs are similar to IMAs, but unclear benefits for third or fourth arterial grafts, the increment of surgery time, and the involvement of an additional body cavity are the main drawbacks limiting the widespread use of this conduit. The preoperative assessment of the RGEA is not well defined, but gastric surgery or mesenteric vascular insufficiency contraindicates the use of this vessel.
Occasionally, the RGEA is used to supply the inferior cardiac wall and is anastomosed as an in situ graft to the posterior descending artery (PDA) [Fig 3].1718 In these cases, the mobilized artery is seen coursing anterior to the liver and through the diaphragm to reach the site of anastomosis; small clips can be identified at the original site of the RGEA, near the small curvature of stomach.
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Saphenous Vein Graft
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The use of the saphenous vein graft (SVG) as a bypass graft has many advantages, including availability, accessibility, easy of harvest, resistance to spasm, and versatility. The main drawbacks are lower patency rates, varicosity, and sclerosis. The SVG has poor compliance after arterialization, with subsequent atherosclerosis.123 The great saphenous vein is the vein routinely used for CABG surgery; the proximal anastomosis of the venous graft with the ascending aorta is usually performed cranial to the origin of coronary arteries and as distal as the proximal portion of the aortic arch19 (Fig 7
). The distal anastomosis of the graft, particularly with the RCA or one of its branches, may lie on the phrenic wall of the heart. Venous grafts are larger than arterial grafts and are not accompanied by surgical clips along their course; sometimes a circumferential clip can be identified at the site of proximal anastomosis with the ascending aorta.20
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Figure 7.. MDCT images (top left, A; top right, B; bottom left, C) and conventional angiography (bottom right, D) in a patient with an SVG to the RCA, previously treated with stenting of the coronary artery (arrowhead in bottom left, C, and bottom right, D). On the axial CT image (top left, A), the SVG is seen at its proximal anastomosis along the anterior wall of the ascending aorta and coursing in the anterior mediastinum, lateral to the RVOT. Distal anastomosis to the RCA can be seen on both curved MPR (top right, B) and maximum intensity projection reconstructions (bottom left, C). A partial retrograde filling of the RCA is also shown on CT image (bottom left, C) and conventional angiogram (bottom right, D). See Figure 1 legend for expansion of abbreviations.
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SVGs may present a horizontal or slightly oblique course on axial images, especially when the distal anastomosis is placed on the LCx or a diagonal branch to supply the left cardiac wall. In these cases, the graft can be recognized in the fatty tissue of mediastinum, posterior to the sternum and anterior to the RVOT (Fig 8
).
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Figure 8.. MDCT images (top left, A; top right, C; center left, D; center middle, E; inset, F; bottom left, G) and corresponding conventional angiograms (top middle, B; bottom left, H) in a patient with two venous grafts (SVG) to the LAD and to the OM-PDA, respectively. MDCTs well shows the patency of both conduits and their distal anastomoses (top left, A; center middle, E; bottom left, G); in addition, MDCT shows a low-grade stenosis in the proximal portion of the upper graft (asterisks in top left, C, and center middle, E), as demonstrated by the axial image (inset, F) that displays a soft eccentric plaque (white arrowhead). This finding was confirmed at conventional angiography (asterisk in bottom left, H).
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Conclusions
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MDCT with retrospective ECG gating provides high-quality images and allows noninvasive assessment of CABGs.21 This tool could play an important role in patients with recurrence of chest pain or with unclear stress test results after myocardial surgery revascularization. Furthermore, the newest technological development of the CT scanner could strengthen the role of MDCT, allowing the consensual assessment of the native coronary arteries. Understanding of CABG anatomy as well as knowledge of the type and number of grafts used during surgery are fundamental for a correct interpretation of both axial and two-dimensional or three-dimensional images. Surgical clips, especially when big or numerous, may still represent a potential limit for MDCT assessment of graft patency or stenosis.
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Footnotes
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Abbreviations: CABG = coronary artery bypass graft; IMA = internal mammary artery; LAD = left anterior descending artery; LCx = left circumflex artery; LIMA = left internal mammary artery; MDCT = multidetector row spiral CT; MPR = multiplanar reconstruction; OM = obtuse marginal branch; PDA = posterior descending artery; RA = radial artery; RCA = right coronary artery; RGEA = right gastroepiploic artery; RIMA = right internal mammary artery; RVOT = right ventricle outflow tract; SVG = saphenous vein graft
Received for publication June 17, 2004.
Accepted for publication September 16, 2004.
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References
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- Bourassa, MG, Fisher, LD, Campeau, L, et al (1985) Long-term fate of bypass grafts: the Coronary Artery Surgery Study (CASS) and Montreal Heart Institute experiences. Circulation 72,V71-V78
- Campeau, L, Enjalbert, M, Lesperance, J, et al Atherosclerosis and late closure of aortocoronary saphenous vein grafts: sequential angiographic studies at 2 weeks, 1 year, 5 to 7 years, and 10 to 12 years after surgery. Circulation 1983;68,II1-II7
- Motwani, JG, Topol, EJ Aortocoronary saphenous vein graft disease: pathogenesis, predisposition, and prevention. Circulation 1998;97,916-931[Abstract/Free Full Text]
- Cameron, A, Davis, KB, Green, G, et al Coronary bypass surgery with internal thoracic artery grafts: effects on survival over a 15-year period. N Engl J Med 1996;334,216-219[Abstract/Free Full Text]
- Achenbach, S, Ulzheimer, S, Baum, U, et al Noninvasive coronary angiography by retrospectively ECG-gated multislice spiral CT. Circulation 2000;102,2823-2828[Abstract/Free Full Text]
- Nieman, K, Oudkerk, M, Rensing, BJ, et al Coronary angiography with multi-slice computed tomography. Lancet 2001;357,599-603[CrossRef][ISI][Medline]
- Nieman, K, Cademartiri, F, Lemos, PA, et al Reliable noninvasive coronary angiography with fast submillimeter multislice spiral computed tomography. Circulation 2002;106,2051-2054[Abstract/Free Full Text]
- Ropers, D, Baum, U, Pohle, K, et al Detection of coronary artery stenoses with thin-slice multi-detector row spiral computed tomography and multiplanar reconstruction. Circulation 2003;107,664-666[Abstract/Free Full Text]
- Calafiore, AM, Di Giammarco, GD, Teodori, G, et al Left anterior descending coronary artery grafting via left anterior small thoracotomy without cardiopulmonary bypass. Ann Thorac Surg 1996;61,1658-1663[Abstract/Free Full Text]
- Calafiore, AM, Teodori, G, Di Giammarco, G, et al Minimally invasive coronary artery surgery: the last operation. Semin Thorac Cardiovasc Surg 1997;9,305-311[Medline]
- Diegeler, A Left internal mammary artery grafting to left anterior descending coronary artery by minimally invasive direct coronary artery bypass approach. Curr Cardiol Rep 1999;1,323-330[Medline]
- Weinschelbaum, E, Rodriguez, C, Cabello, ML, et al Left anterior descending coronary artery bypass grafting through minimal thoracotomy. Ann Thorac Surg 1998;66,1008-1011[Abstract/Free Full Text]
- Carpentier, A, Guermonprez, JL, Deloche, A, et al The aorta-to-coronary radial artery bypass graft: a technique avoiding pathological changes in grafts. Ann Thorac Surg 1973;16,111-121[Medline]
- Iaco, AL, Teodori, G, Di Giammarco, G, et al Radial artery for myocardial revascularization: long-term clinical and angiographic results. Ann Thorac Surg 2001;72,464-468[Abstract/Free Full Text]
- Calafiore, AM, Teodori, G, Di Giammarco, G, et al Coronary revascularization with the radial artery: new interest for an old conduit. J Card Surg 1995;10,140-146[ISI][Medline]
- Pym, J, Brown, PM, Charrette, EJ, et al Gastroeiploic-coronary anastomosis: a viable alternative bypass graft. J Thorac Cardiovasc Surg 1987;94,256-259[Abstract]
- Buche, M, Schoevaerdts, JC, Louagie, Y, et al Use of the inferior epigastric artery for coronary bypass. J Thorac Cardiovasc Surg 1992;103,665-670[Abstract]
- Buche, M, Schroeder, E, Gurne, O, et al Coronary artery bypass grafting with the inferior epigastric artery: midterm clinical and angiographic results. J Thorac Cardiovasc Surg 1995;109,553-559[Abstract/Free Full Text]
- Enzweiler, CN, Kivelitz, DE, Wiese, TH, et al Coronary artery bypass grafts: improved electron-beam tomography by prolonging breath holds with preoxygenation. Radiology 2000;217,278-283[Abstract/Free Full Text]
- Calafiore, AM, Bar-El, Y, Vitolla, G, et al Early clinical experience with a new sutureless anastomotic device for proximal anastomosis of the saphenous vein to the aorta. J Thorac Cardiovasc Surg 2001;121,854-858[Abstract/Free Full Text]
- Marano, R, Storto, ML, Maddestra, N, et al Non invasive assessment of coronary artery bypass graft with retrospectively ECG-gated four-row multidetector spiral computed tomography. Eur Radiol 2004;14,1353-1362[ISI][Medline]
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Abstract
Introduction
