SSCTS

(Sean Bello¹)

Choice of conduit (graft) is of paramount importance in coronary artery Bypass Surgery (CABG). Since the first coronary artery bypass operation was carried out about 50 years ago, a number of conduits have been employed and some extensively studied in an attempt to identify the conduit most capable of providing long-term patency. The various grafts employed to date can be broadly grouped as autologous, non-autologous or synthetic conduits (Table 1).

Table 1: Conduits for CABG ^[1]

In clinical practice it is the long saphenous vein and the internal mammary and radial arteries that are in widespread use today. Most of the other conduits listed in table 1 are now obsolete as conduits.

Long Saphenous Vein Graft

The LSV is traditionally the most frequently used conduit for coronary artery bypass surgery. It is harvested from the leg and thigh via an ‘open’, ‘bridging’, or endoscopic technique. The superficial location of the vein and long length are largely responsible for its frequent use despite limited long-term patency. On average 50%  of LSV grafts are partially or completely occluded by 10-15 years. ^{[2], [3]} They have a higher susceptibility to atherosclerosis due to their wall structure, endothelium, intraluminal anatomy, response to arterial hypertension and flow dynamics secondary to the presence of reversed valve segments.

The Short Saphenous Vein can also be used but it is harder to harvest, less consistent in its anatomy, and obviously much shorter.

Internal Mammary Artery

Overwhelming clinical and radiological evidence over the last 3-4 decades has placed the internal mammary artery (IMA) as the conduit of choice for coronary revascularisation. Several good scale studies suggest an estimated patency rate of 85-92% at 15 years for Left IMA (LIMA) grafts^[4]. The IMA can be harvested as a pedicled graft or by skeletonization. Skeletonization involves harvesting of the IMA without any surrounding rim of tissue. The impressive patency rates noted for IMA grafts are not replicated by any other arterial or venous.

Radial Artery (RA)

The RA is gradually returning into favour as a viable conduit. Initial excellent patency rates of about 90% at 10 months reported by Carpentier in 1973 generated much enthusiasm due to its several advantages: arterial wall structure, easy to harvest, ideal length, comparable calibre, superior healing of forearm wounds compared to leg wounds, easy to handle and readily available in most patients. Subsequent reports of poor patency and biological predisposition to spasm due to its thick media however led to widespread abandonment.^[5] Following the work of Acar and colleagues there has been resurgence in its use.^[6]

Discussion

The supremacy of the IMA means standard practice is now to graft the left IMA to the artery supplying the largest myocardial territory, usually the left anterior descending artery (LAD). Debate remains as to what should be the graft of second choice after the left IMA (to supply the next most important recipient artery).

Studies have demonstrated that the use of bilateral IMA grafts improves survival and clinical outcome compared with use of single IMA.^[7] Bilateral internal mammary artery (BIMA) grafting however has its potential disadvantages. There are issues around its short length limiting its use as an insitu graft, increased operative time required, and poor sternal wound healing particularly in diabetics.^[8]

References