Determinants of Sapheous Vein Graft Patency

Graft patency is dependent on a number of factors, including the type of graft used (internal thoracic artery, radial artery, or great saphenous vein), the size or the coronary artery that the graft is anastomosed with, and, of course, the skill of the surgeon(s) performing the procedure. Arterial grafts (e.g. left internal mammary (LIMA), radial) are far more sensitive to rough handling than the saphenous veins and may go into spasm if handled improperly.

Systemic or Patient-Based Risk Factors for SVG Failure
Diabetes,hyperlipidemia,smoking, and to variable degrees hypertension are all risk facotrs for SVG failure. There is some data to suggest that lipoprotein subfractions may be associated with SVG failure such as HDL cholesterol and plasma LDL apoprotein B.

In-situ vs Free Grafts
Generally the best patency rates are achieved with the in-situ (the proximal end is left connected to the subclavian artery) left internal thoracic artery (a LIMA) with the distal end being anastomosed with the coronary artery (typically the left anterior descending artery or a diagonal branch artery). Lesser patency rates can be expected with radial artery grafts and "free" internal thoracic artery grafts (where the proximal end of the thoracic artery is excised from its origin from the subclavian artery and re-anastomosed with the ascending aorta).

Venous vs Arterial Conduits
Saphenous vein grafts have poorer patency rates than arterial grafts, but are more available, as the patients can have multiple segments of the saphenous vein used to bypass different arteries.

LITA grafts are longer-lasting than vein grafts, both because the artery is more robust than a vein and because, being already connected to the arterial tree, the LITA need only be grafted at one end. The LITA is usually grafted to the left anterior descending coronary artery (LAD) because of its superior long-term patency when compared to saphenous vein grafts.

Impact of Harvesting Method on Saphenous Vein Graft Patency
The method of harvesting vein grafts may be associated with late vein graft patency at 12-18 months. In a non-randomized subgroup analysis from the PREVENT IV study, harvesting of vein-grafts with the use of endoscopy (endoscopic harvesting) was associated with a higher rate of saphenous vein graft failure compared with open harvesting of the veins under direct visualization (46.7% vs. 38.0%, P<0.001 at 12-18 months). Likewise, clinical outcomes were worse at 3 years: use of endoscopy was associated with higher rates of death, myocardial infarction, or repeat revascularization (20.2% vs. 17.4%; p=0.04), death or myocardial infarction (9.3% vs. 7.6%; p=0.01), and death (7.4% vs. 5.8%; adjusted hazard ratio, 1.52; 95% CI, 1.13 to 2.04; p=0.005). Although these observational data are provocative, further randomized clinical trials would be needed to compare the safety and effectiveness of the two harvesting technique.

Pharmacotherapy
In a relatively modest sized study, there was a significant improvement in SVG patency to 91.6% (219/239) among patients treated  with both aspirin and clopidogrel versus 85.7% (198/231) in those  patients treated with aspirin alone (relative risk: 1.707; 95%  confidence interval: 1.010 to 2.886; multivariat p = 0.043)  These results are in contrast to those of CASCADE. CASCADE was a double-blind phase II trial of 113 patients undergoing coronary artery bypass grafting. Patients were randomized to treatment with either aspirin 162 mg plus clopidogrel 75 mg daily versus aspirin 162 mg daily for one year. The primary endpoint of SVG intimal area at 1 year did not differ between the 2 comparators (p=0.44). SVG patency at one year was 95.2% among patients treated with aspirin plus clopidogrel versus 95.5% among patients treated with aspirin alone (P=0.90). There was no difference at one year in freedom from major adverse cardiovascular events (MACE) at 1 year was 92.9% among patients treated with aspirin-clopidogrel and 91.1% among patients in the aspirin-placebo group (p=0.76).

Impact of Initial CABG Results and Runoff
Greater runoff, and higher mean graft flow have been associated with improved SVG patency, whereas the pulsatile index has been associated with worse patency.

Potential for Pre-Operative SVG Failure
It should be noted that studies of SVGs that are not implanted show that about 1% of veins are already stenosed by > 50% before implantation.