Could bilateral internal thoracic artery grafting increase surgical risk?

Yes: The use of bilateral internal mammary arteries can increase the risk for decreased blood flow to the sternum (breast bone) and increase the risk for wound infections and lack of healing or fusion of the sternum.

Not always : There is some evidence that in diabetic patients it can increase the risk of eternal wound infections. Not in non diabetics. This increase risk in diabetics has been debated and there is some recent data suggesting that it may not be true.