Radiological methods
This was performed using a Somatom Flash dual-source CT scanner (Siemens, Erlangen, Germany). All subjects received 0.25 mg of Nitroglycerin sublingually. Those with a heart frequency >70 beats/minute and no contraindications were also given up to 10 mg of Metoprolol intravenously before the examination. Contrast media (60-70 ml Iomeron 400 mg/ml, Bracco, Milan, Italy) was administered with a pressure injector at a flow rate of 6 ml/second, followed by a bolus of 60 ml saline. Scanning started at the left subclavian artery and ended at the base of the heart. The images were reviewed at a Siemens SyngoVia workstation. All images were independently reviewed by two thoracic radiologists who were blinded to group assignment. Disagreements were resolved by consensus. A graft was judged as occluded when the graft was not opacified by contrast media. A graft stenosis was judged as significant when the narrowing of the lumen diameter was > 50% relative to the adjacent parts of the vessel.