Coronary artery bypass graft
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 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 distal coronary artery beyond the obstructive lesion. Right coronary grafts are usually anastamosed to right coronary artery or posterior descending artery. Left coronary grafts are usually anastomosed to left anterior descending (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 anastamosis, however, continuous contrast column in graft, can be taken as patent graft. Most grafts are directly sutures to aorta, however, recently aortovenous connector devices have also come, which appear differently 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. It is seen on imaging, as proximal end from normal anatomical origin (left subclavian artery), and distal end usually anastamosed to LAD. The right ITA graft can also be used in similar fashion.
In two-vessel disease, LITA is connected to the LAD, and RITA 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 forearm
- gastroepiploic artery: used by extended sternotomy and is dissected from the greater curvature of stomach and anastomosed to the target vessel (difficult and rare surgery)
Radiographic work up
Pre CABG evaluation
Re-operative cardiothoracic surgery
Important aspects of assessment includes 6
- relationship of cardiovascular structures to sternum
- relationship of coronary bypass grafts to sternum
- atherosclerotic calcification in the ascending aorta
- anatomy of subclavian and axillary arteries and the arch
- thrombosis: most common in early post-operative 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 early post-operative period. In case of graft spasm, proximal graft appears narrower than distal graft (c.f. graft stenosis, where 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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