Clinical Effect of No-touch Harvesting Technique in OPCABG

Inclusion Criteria: * patients from northern China * first time isolated off-pump coronary artery bypass graft * echocardiogram show that ejection fraction is over 35% * the diameter of saphenous vein ≥ 2mm * the vein graft will be used in sequential anastomosis, and the anastomosis sites ≥2 * be able to sign informed consent form Exclusion Criteria: * patients who need to undergo urgent surgery * Severe renal insufficiency(creatinine \>200 umol/L) * allergic to radiocontrast agent * vein is used to isolated anastomosis * Combined with malignant tumor or other severe systemic conditions