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 the early (<1 month) as well as late (>1 month) postoperative period. Thus, it is important to know the appearances of various bypass grafts.

Procedure

In most cases, CABG is performed through a midline sternotomy. Graft anastomoses can be made with the heart still or beating:

• off pump: no cardioplegia and cardiopulmonary bypass

• on pump: cardioplegia and cardiopulmonary bypass

Types of coronary artery bypass grafts

Saphenous vein grafts

Saphenous vein grafts were the earliest grafts used for CABG procedures, and are still the most widely used in coronary bypass surgeries. Saphenous vein conduits are harvested from legs and grafted from the 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, a continuous contrast column in the graft can be read as the graft being patent. Most grafts are directly sutured to the aorta, however, recently aortovenous connector devices are being increasingly used which have a different imaging appearance.

Internal thoracic artery grafts

Left internal thoracic (or mammary) artery (ITA) grafts have emerged as the preferred bypass graft due to their excellent graft patency and close proximity to the left anterior descending artery (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. Its proximal end 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 may be used in a similar way.

In two-vessel disease, a LIMA is usually connected to the LAD, and a RIMA is attached proximally to a 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

Pre-CABG evaluation

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

Complications

• thrombosis: most common in the early postoperative period, due to improper anticoagulation 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 (cf. graft stenosis, where the distal graft is narrower)

• iatrogenic complications

  • graft damage during surgery

  • retained clips

• graft aneurysms

  • 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

• pleural or pericardial effusion

• sternal, mediastinal or donor-site infection

• sternal non-union ^8,9

• pulmonary embolism

• mediastinal hematoma