Study of Sivelestat Sodium in OPCABG

The goal of this clinical trial is to learn if drug Sivelestat Sodium works to improve the prognosis of off-pump coronary artery bypass grafting (OPCABG) in adults. It will also learn about the safety of drug Sivelestat Sodium. The main questions it aims to answer are: * Does drug Sivelestat Sodium have a protective effect on myocardial injury after OPCABG? * Does Sivelestat Sodium exert a protective effect on myocardial inflammatory stress after OPCABG? Researchers will compare drug Sivelestat Sodium to a placebo (a look-alike substance that contains no drug) to see if drug Sivelestat Sodium works to protect myocardium following OPCABG. Participants will: * Accept drug Sivelestat Sodium injection or a placebo 2 h after OPCABG for 72 h. * Undergo a series of blood tests and echocardiography examinations after the OPCABG.