CTA Assessment of Saphenous Vein Grafts and Internal Thoracic (Mammary) Arteries






  • Key Points



  • Coronary artery bypass grafts are amenable to cardiac CT angiography assessment because they are larger in size than native arteries and are subject to little motion artifact and little calcification, factors that otherwise present major limitations to CCT.



  • The abundance of surgical clips on internal thoracic and mammary grafts is an impediment to adequate CCT angiography.



  • Unfortunately, the need to assess native coronary artery disease, which is always advanced in patients who have had a prior bypass, renders coronary graft assessment only a portion of the necessary evaluation.



  • However, CCT coronary graft angiography may be useful in well-chosen cases, such as mapping graft course in cases where reoperation is anticipated.




Coronary Bypass Graft Assessment


Coronary bypass grafts, both venous and arterial, are more readily evaluated by CT angiography (CTA) than are coronary arteries, because of:




  • Their large diameter (more so for venous than arterial conduits)



  • Their minimal motion, when compared with coronary arteries, because they are largely extracardiac



  • Their general lack of calcification, versus the common and often extensive calcification of native coronary arteries



  • Simpler courses (but not always) with little overlap. Some exceptions:




    • Posterior transverse sinus course of a venous graft or right internal mammary artery (RIMA) graft to the circumflex



    • Twisted course of vein grafts if multiple and adjacent



    • The presence of jump-grafts (sequential graft insertions; usually saphenous)



    • Internal thoracic artery positioned tightly against the chest wall, in which case the use of bone extraction software when post-processing may eliminate depiction of the internal mammary artery (IMA) graft




Potential Uses of Coronary CTA in Patients with Coronary Artery Bypass Grafts





  • Nonvisualization of a coronary artery bypass graft (CABG) at the time of catheter angiography



  • Chest pain in a patient with CABG



  • Prior to repeat open heart surgery (CABG or valve surgery), to localize the bypass grafts relative to the sternum and intended sternotomy



Problems with Bypass Graft Assessment





  • The large field of view. This is especially true if there is an internal thoracic artery to be imaged, because the field of view will extend from above the subclavian artery down to the diaphragm. This requires:




    • Longer breath-hold and greater chance for motion artifact



    • Greater radiation exposure




  • Surgical clips abound around mammary arteries and may present a challenge and sometimes a problem when the adjacent lumen is being imaged.



  • Sternal wires also may cause artifacts, as may ECG electrodes, which can confound assessment of anterior bypass grafts.



  • The direction of flow within a graft cannot be established by its opacification. It is tempting to view opacification as indicative of anterograde flow. This becomes a problem, however, when there is a proximal severe-appearing lesion: assumption of anterograde filling implies nonocclusion, whereas retrograde filling of a proximally occluded graft may have been the case.



  • If a left internal thoracic artery graft is present, the contrast will have to be injected via the right arm to avoid high-attenuation artifacts in the left subclavian artery; such artifacts may confound imaging of the ostium of the internal thoracic artery.



  • If both the left and right internal thoracic arteries are used as conduits, then the ostium of one of the two will be obscured by subclavian vein overattenuation artifacts.



  • Often a larger concentration of metallic clips is seen at the graft-native vessel anastomosis, resulting in a beam-hardening artifact and obscuring the depiction of the anastomosis.



  • Cardiac CT (CCT) is better at assessing bypass grafts than native vessels, which are, of course, always diseased in the scenario of bypass grafting, often extensively, and may be calcified. Adequate and complete visualization of the native vessels distal to the bypass graft anastomosis may be (often is) problematic, because the native coronary arteries at this level tend to be smaller.



  • Stenting within bypass grafts is still a challenge; however, stents within grafts often are better assessed than native stented vessels due to the larger size of the grafts and less cardiac motion.



  • Interobserver agreement of quantification of lesions is poor: less than 50%.



  • For more information, see Tables 8-1 and 8-2 .



    TABLE 8-1

    Cardiac CT Assessment of Coronary Artery Bypass Grafts























































































































































































































































































































































































































    AUTHOR JOURNAL YEAR CT NO. PTS/NO. GRAFTS NONASSESS. (%) GRAFT TYPES (SVG:IMA) LESION SENSITIVITY (%) SPECIFICITY (%) PPV (%) NPV (%)
    Achenbach et al. Am J Cardiol 1997 EBCT 25 4 55:1 Occlusion 100 100
    16 Stenosis 100 97
    Chiurlia et al. Am J Cardiol 2005 16-CT 52 99 117:47 Occlusion 100 100
    Stenosis 96 100
    Martuscelli et al. Circulation 2004 16-CT 96 166:85 Occlusion 100 100
    Stenosis 90 100
    84 Anastomosis 97 100
    Nieman et al. Radiology 2003 4-CT 109 16 93 42 70 81
    Ropers et al. Am J Cardiol 2001 MSCT 65 0 162:20 Occlusion 97 98 97 98
    38 Stenosis 75 92 71 93
    Schlosser et al. JACC 2004 16-CT 51 0 91:40 96 95 81 99
    Anders et al. Eur J Radiol 2006 16-CT 32 18 74:19 Occlusion 100 98
    Stenosis 81 87
    Salm et al. Am Heart J 2005 16-CT 25 8 53:14 Occlusion 100 100 100 100
    8 53:14 Stenosis 100 94 50 100
    Moore et al. Clin Radiol 2005 50 0% Occlusion 100 100
    0% Stenosis 100 99
    Burgstahler et al. Int J Cardiol 2006 16-CT 0 43 g Occlusion 100 100 100
    5 Stenosis 100 93 100
    Schuijf et al. Am J Cardiol 2004 16-CT 1 43 g Occlusion 96 100 99
    15 Stenosis 100 96 100
    Pache et al. Eur Heart J 2006 64-CT 0 93 g Occlusion 100 100 100
    6 Stenosis 100 100 100
    Stauder et al. Eur Radiol 2006 16-CT 20
    22.5 80 art Stenosis 96 97 96 97
    7.3 180 svg Stenosis 99 94 92 99
    31 Native Stenosis 92 77 88 85
    Malagutti et al. 52/109 Grafts 99 96
    Native 89 93 50
    Ropers et al. Graft occlusion
    Graft stenosis
    Native arteries
    0

    0
    9
    100

    100
    86
    100

    94
    76
    100

    92
    44
    100

    100
    96

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Apr 10, 2019 | Posted by in COMPUTERIZED TOMOGRAPHY | Comments Off on CTA Assessment of Saphenous Vein Grafts and Internal Thoracic (Mammary) Arteries
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