Imaging of Coronary Artery Bypass Grafts by Computed Tomography Coronary Angiography
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Imaging of Coronary ArComputed Tomography
Fotios Laspas, MD, MSc,1 Arkadios RoussChristos Mourmouris, MD, Roxan
IntroductionCoronary artery bypass graft (CABG) surgery hasbecome an established treatment of advanced coro-nary artery disease. As late survival after CABG
on a dual-source (2 64 slices) CT scanner (CARE Dose 4D, an automatic exposure controlsystem which adapts tube current to patient size)Curr Probl Diagn Radiol, November/December 2013and a 100 kV tube voltage for patients with bodyweight 100 kg and a tube potential of 120 kV forpatients with body weight 4100 kg. Other parame-ters are 64 0.6-mm detectors, gantry rotation time330 ms, and pitch of 0.2-0.5 automatically adapted tothe heart rate.Electrocardiograph pulsing of tube current for
radiation dose reduction is used in all patients. The
Curr Probl Diagn Radiol 2013;42:241248.& 2013 Mosby, Inc. All rights reserved.0363-0188/$36.00 + 0http://dx.doi.org/10.1067/j.cpradiol.2013.05.004
1Home address: Thisseos 29, 15234, Halandri, Athens, Greece.From the CT and MRI Department, Hygeia Hospital, Athens, Greece.nReprint requests: Fotios Laspas, MD, MSc, Hygeia Hospital, 4,Erythrou Stavrou St and Kisias Ave 151 23 Marousi, Athens, Greece.E-mail: email@example.com
241of patients who have undergone CABG surgerywere recorded. All examinations were performed
formed with a tube current-time product of 320 mAsurgery is largely dependent on graft patency, follow-up examinations are inevitable. Technical advances inmultidetector computed tomography (CT) haveallowed the development of a reliable noninvasivemethod for determining patency or occlusion ofbypass grafts.1,2
We searched our database for CT coronary arteryexaminations performed at our institution, and dataIn recent years, computed tomography coronary angiog-raphy is commonly performed as a follow-up examinationafter coronary artery bypass graft surgery. Coronarygrafts owing to their minimal motion are well visualizedby computed tomography coronary angiography, allowingradiologists to assess their patency noninvasively with veryhigh diagnostic accuracy. The purpose of this pictorialessay is to provide an excellent overview of the anatomyand ndings concerning coronary artery bypass grafts.tery Bypass Grafts byCoronary Angiography
akis, MD, PhD, Nikolaos Kritikos, MD,i Efthimiadou, MD, PhD, and, MD, PhD
(Somatom Denition, Siemens Medical Solutions,Germany).
ProtocolThere are a variety of protocols for image acquisitionin the evaluation of patients after CABG surgery. Atour institute, the patients are placed in the gantry insupine position and the electrocardiographic leadsare placed on the anterior chest wall for electro-cardiograph recording. Intravenous administration of-adrenergic blocking agent is performed to patientswith a heart rate exceeding 70 beats/min (bpm),unless underlying contraindications such as asthmaare present. Scanning is performed in a caudocranialdirection from cardiac base to the subclavian arteries.A bolus of 120 mL of a nonionic, iodinated, low-osmolar contrast agent is injected into an antecubitalvein via an 18-gauge catheter with a ow rate of5 mL/s followed by 100 mL of normal saline sol-ution using a dual-head injector. Contrast agentapplication is controlled by bolus tracking. Theregion of interest is placed into descending aorta,and image acquisition starts 6 seconds after thesignal attenuation reaches the predened thresholdof 150 Hounseld units. Data acquisition is per-
FIG 2. VRT image from post-CABG CT coronary angiography in a 66-pulsing window (in percentage of the RR interval)is adjusted to the individual heart rate of thepatient. For mean heart rates less than 70 bpm, fulltube current is applied from 70%-70% and at heartrates more than 70 bpm from 30%-70% of RRinterval. The normal tube current is reduced out-side the adjusted windows to 4% of full tubecurrent. Data sets of CT coronary angiographyare reconstructed with a slice thickness of0.75 mm and an increment of 0.5 mm duringmid-diastole at 70% of the RR interval. If neces-sary (when cardiac motion artifacts are present inthe predened reconstruction), additional recon-structions are performed within the full tubecurrent window.
year-old man with left dominant circulation (the PDA arises from the CXartery) depicts a SVG to the PDA. CX, circumex artery; PDA, posteriordescending artery; VRT, volume rendering technique. (Color version ofgure is available online.)
FIG 1. CT coronary angiography in a 74-year-old male patient afterCABG surgery. Curved multiplanar reformatted (MPR) image (A) andvolume rendering technique (VRT) image (B) show a patent SVG to theRCA. A LIMA graft and an occluded SVG graft are also present on VRTimage (B). RCA, right coronary artery. (Color version of gure isavailable online.)
FIG 3. VRT image from post-CABG CT coronary angiography in a 73-year-old man shows a SVG to the LAD. VRT, volume renderingtechnique. (Color version of gure is available online.)
Curr Probl Diagn Radiol, November/December 2013242
FIG 5. CT coronary angiography with curved MPR reformatted imagefrom a 68-year-old man with CABG surgery displays a SVG (pre-viously treated with stenting) to the CX. Note that the origin of the graftis slightly narrower than the rest body owing to a small soft plaque. TheTypes of Grafts Used and Graft AnatomySaphenous Vein Grafts (SVG)Segments of the saphenous vein are the earliest
grafts used for CABG and are still the most widelyused grafts in coronary bypass surgeries.1,3 Saphenousvein conduits are harvested from legs and grafted fromascending aorta (usually anterior aspect) to distalcoronary artery beyond the obstructive lesion. AnSVG to the right side is usually anastomosed to thedistal right coronary artery (Fig 1) or posteriordescending artery (Fig 2). An SVG to the left side istypically connected distally to the left anteriordescending artery (LAD) (Fig 3), diagonal branch(Diag) (Fig 4), left circumex artery (Fig 5) or theobtuse marginal artery (Fig 6). On occasion, the distalSVG is anastomosed sequentially to 2 coronary
vessels (Fig 7). On CT coronary angiography,SVGs tend to appear as large contrast-lled vessels(Fig 4B).
FIG 4. CT coronary angiography in a 75-year-old man 5 years afterCABG surgery. (A) Curved MPR image shows the entire length of aSVG from its proximal aortic origin to its distal anastomosis with theDiag. (B) VRT image of the same patient. A LIMA graft is also present.Note the larger caliber of the SVG compared with LIMA graft. MPR,multiplanar reformatted; VRT, volume rendering technique. (Colorversion of gure is available online.)
patency of the stent is well demonstrated. CX, circumex artery.
Curr Probl Diagn Radiol, November/December 2013FIG 6. VRT image from post-CABG CT coronary angiography in a 72-year-old woman shows a SVG to the OM. A LIMA graft is also present.OM, obtuse marginal artery; VRT, volume rendering technique. (Colorversion of gure is available online.)
Internal Mammary Artery (IMA) GraftsCompared with SVGs, IMA conduits are charac-
terized by resistance to atherosclerosis and high long-term patency rates.3,4
Owing to its location near the LAD artery andfavorable patency rates, the left IMA (LIMA) ismost commonly used as an in situ arterial graft (itsorigin at the subclavian artery remains intact) to
FIG 7. CT coronary angiography with maximum intensity projection (MIP) (A) and VRT (B) reformatted images from a 70-year-old CABG patient displaysequential anastomoses of a SVG to the distal RCA and distal CX. CX, circumex artery; RCA, right coronary artery; VRT, volume rendering technique.FIG 8. CT coronary angiography with MIP (A), curved MPR (B) and VRT (Cto LAD. The patency of the conduit, its origin, its distal anastomosis, and thintensity projection; MPR, multiplanar reformatted; VRT, volume rendering
244) reformatted images from a 75-year-old man show a patent LIMA grafte LAD segment distal to the anastomosis are well seen. MIP, maximumtechnique. (Color version of gure is available online.)
Curr Probl Diagn Radiol, November/December 2013
revascularize the LAD (Fig 8) to supply the greatestterritory of the heart. Sometimes LIMA grafts showa single distal anastomosis with Diag or multiplesequential anastomoses to both LAD and Diag areperformed.The right IMA is used less frequently than the
LIMA. The right IMA can be placed as an in situ graftto revascularize the right coronary artery or vessels to
the left side; however, it is more commonly used as afree or composite graft.
Other Arterial GraftsThe radial artery (RA) is used as a free or
composite graft (often it supplies the left cardiacwall) after harvesting from the nondominant forearm.
ltiveict tIP, mureFIG 9. CT coronary angiography in a 72-year-old male patient with muthe other to Diag), a RA graft to OM and LIMA to LAD. MIP images depthe larger caliber of the SVG compared with the LIMA and RA graft. Mmarginal artery; VRT, volume rendering technique. (Color version of g
Curr Probl Diagn Radiol, November/December 2013ssel bypass grafting. VRT images (A-C) show 2 SVGs (1 to the RCA andhe proximal (D) and distal (E) part of the grafts to Diag and OM. Noteaximum intensity projection; RCA, right coronary artery; OM, obtuseis available online.)
Patency rates are now similar to those seen with IMA
FIG 10. MIP image from post-CABG CT coronary angiography in a74-year-old man shows small eccentric soft plaques in a SVG to RCA.MIP, maximum intensity projection; RCA, right coronary artery.grafts. The RA is occasionally used to avoid SVGwhen an IMA cannot be used or as a third arterialgraft when greater arterial revascularization is con-sidered to be preferable (Fig 9). On CT coronaryangiography, the caliber of the RA is small (similar tothe IMA).The right gastroepiploic artery has also been used
in CABG surgery. Owing to the technical difcultyof the surgical retrieval of the right gastroepiploicartery, its use in CABG procedures has beenlimited.
Obstructive Graft DiseasePatients with recurrent chest pain after CABGsurgery represent an important clinical problem incardiology. Recurrent symptoms may be caused byprogression of disease, either in the native coro-nary arteries or in the venous or, more rarely,arterial grafts.5 Many previous studies5-8 havedemonstrated that noninvasive CT coronary
246FIG 11. Curved MPR image from CT coronary angiography in a 78-year-old man after CABG surgery with recurrent chest pain showsscattered non calcied plaques on a SVG to OM with several sites ofsignicant narrowing. MPR, multiplanar reformatted; OM, obtusemarginal artery.angiography shows very high accuracy for thedetection of graft thrombosis and occlusion (Figs10-15). A condent diagnostic evaluation ofbypass graft requires careful assessment of thegraft body, proximal and distal anastomoses visu-alization (although the evaluation of the distalanastomosis can be limited by artifacts of surgicalclips [Fig 16]), and evaluation of the nativecoronary artery segment distal to the anastomosis.Of course, the evaluation of nongrafted coronaryarteries is mandatory.
ConclusionWith advancements in CT technology, multidetectorCT coronary angiography has emerged as a non-invasive technique for the follow-up after CABGsurgery, especially when recurrent chest pain mustbe investigated. Thus, it is crucial for radiologists tobe familiar with CABG anatomy and its congurationon CT coronary angiography.
Curr Probl Diagn Radiol, November/December 2013
FIG 13. CT coronary angiogram with MIP (A) and VRT (B) reformatted images from a 71-year-old man demonstrate a small outpouching from theascending aorta as only the most proximal part of an occluded aortocoronary graft is lled with contrast material. The rest part of the graft isoccluded and hence not visible. A LIMA graft and an SVG graft to the OM are also present on VRT image (B). MIP, maximum intensity projection;VRT, volume rendering technique. (Color version of gure is available online.)
FIG 14. CT coronary angiogram with MIP (A) and VRT (B) reformatted images from a 75-year-old man display multiple surgical clips in the courseof an occluded RA graft. The multiple surgical clips are used routinely to ligate branches of the arterial grafts. A LIMA graft is also present on VRTimage (B). MIP, maximum intensity projection; VRT, volume rendering technique. (Color version of gure is available online.)
FIG 12. CT coronary angiography with MIP (A) and VRT (B) reformatted images from a 76-year-old man shows contrast agent within only a shortproximal segment of an SVG (arrow). Hypodense material is seen on MIP image (A) in the course of the graft lumen due to thrombus formation. Thisappearance represents complete occlusion of the SVG. A LIMA graft and a SVG graft to the RCA are also present on VRT image (B). MIP, maximumintensity projection; RCA, right coronary artery; VRT, volume rendering technique. (Color version of gure is available online.)
Curr Probl Diagn Radiol, November/December 2013 247
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FIG 16. Curved MPR image from CT coronary angiography in a 69-year-old man shows a LIMA graft to LAD. The evaluation of the distalanastomosis is limited because of surgical clips in the region.However, opacication of the LAD distal to anastomosis with contrastsuggests the graft is patent. MPR, multiplanar reformatted.
FIG 15. MIP image from post-CABG CT coronary angiography in an80-year-old man shows multiple severe stenoses in the proximal half ofa SVG. Further down the graft is occluded. Note a previously placedstent in the occluded part of the graft. MIP, maximum intensityprojection.
248surgery using 64-slice spiral computed tomography with 330-ms gantry rotation. Circulation 2006;114:2334-41.
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