A coronary artery bypass graft (CABG or CAG) is placed during a surgical procedure to increase blood flow to the myocardium due to coronary stenoses, usually caused by coronary artery disease. Arteries or veins can be grafted during this procedure.
Long term outcome of coronary artery bypass grafting depends on graft patency. Angiography was done for routine assessment of CABG, especially when the patient presented with recurrent angina. However, in the era of cardiac multidetector CT imaging, screening of grafts for patency is quite useful in the early (<1 month) as well as late (>1 month) post-operative period. Thus, it is important to know the appearances of various bypass grafts.
Types of coronary artery bypass grafts
Saphenous vein grafts
Saphenous grafts are the earliest grafts used for CABG, which are still the most widely used in coronary bypass surgeries. Saphenous vein conduits are harvested from legs and grafted from ascending aorta (usually anterior aspect) to the coronary artery beyond the obstructive lesion. Right coronary grafts are usually anastomosed to the right coronary artery (RCA) or posterior descending artery (PDA). Left coronary grafts are usually anastomosed to left anterior descending artery (LAD), left circumflex, obtuse marginal or diagonal branches. Saphenous grafts are most convenient, however most prone to occlusion. In CT imaging, it may not be possible to see the distal anastomosis, however, continuous contrast column in the graft can be taken as the graft is patent. Most grafts are directly sutured to the aorta, however, recently aortovenous connector devices are being utilized more and more which appear different in imaging.
Internal thoracic artery grafts
Left internal thoracic (or mammary) artery (ITA) grafts have emerged as the preferred bypass graft due to its excellent graft patency and close proximity to the LAD. They are often referred to as LIMA grafts (left internal mammary artery grafts). The graft is directly seen on cross-sectional imaging or appears alongside a row of mediastinal surgical clips. It's proximal end from arises from the normal anatomical origin (first part of the left subclavian artery for the LIMA), and its distal end is usually anastomosed to the LAD. The right ITA (RIMA) graft can also be used in a similar fashion.
In two-vessel disease, the LIMA is usually connected to the LAD, and RIMA is attached proximally to LITA and distally to the second target vessel. In this case, both arterial grafts have better patency rates than venous grafts.
Other arterial grafts
- radial artery: used after harvesting from the forearm
- gastroepiploic artery: used by extended sternotomy and is dissected from the greater curvature of the stomach and anastomosed to the target vessel (difficult and rare surgery)
Radiographic work up
Re-operative cardiothoracic surgery
Important aspects of assessment include 6:
- relationship of cardiovascular structures to the sternum
- relationship of coronary bypass grafts to the sternum
- atherosclerotic calcification in the ascending aorta
- anatomy of subclavian and axillary arteries and the aortic arch
- thrombosis: most common in the early postoperative period, due to improper anti-coagulation or endothelial damage during surgery
- graft malposition or kinking
- graft kinking can cause graft occlusion.
- it is especially common in longer grafts and graft with connector devices
- graft spasm
- this is common in radial artery grafts
- it is seen in the early postoperative period. In the case of graft spasm, proximal graft appears narrower than distal graft (c.f. graft stenosis, where the distal graft is narrower)
- iatrogenic complications
- graft damage during surgery
- retained clips
- aneurysmal dilatation of graft >2 cm is considered significant and will require surgery
- pseudoaneurysms may arise at the proximal or distal ends of grafts
Non-graft related surgical complications
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