Impaired myocardial energy metabolism plays an important role in the development of myocardial ischemia, so myocardial ischemic lesions caused by coronary atherosclerosis can also be considered as a “metabolic disease” [1]. L-carnitine (L-CN) is an essential cofactor of fatty acid metabolism in humans, which can accelerate β-oxidation of fat, increase ATP levels, improve abnormal metabolic conditions in myocardial ischemia, and increase the oxidative utilization of glucose [2]. We selected 120 patients who underwent non-ex vivo coronary artery bypass grafting at our institution for a randomized case-control study to observe the clinical efficacy of levocarnitine use in the perioperative period. 1. Subjects and methods One hundred and sixty patients, 93 men and 67 women, aged 54-74 years, with a mean of (63.12±7.23) years, were selected for the perioperative period of non-ex vivo coronary artery bypass grafting performed in the cardiac surgery department of our hospital from January 2004 to August 2008. The patients were randomly divided into control and L-CN groups, with 80 cases in each group. The diagnosis was determined based on the coronary angiography results. General anesthesia was applied to all 160 patients, and the procedure was performed by non-ex vivo coronary artery bypass grafting, with the left internal mammary artery used for the anterior descending branch and the rest of the vascular grafts being the autologous saphenous vein. The target vessel was anastomosed with an elastic suture temporarily blocking both ends of the anastomosis. Patients in both groups were routinely treated with nitrates, ß-blockers, calcium antagonists, aspirin and statin lipid-lowering drugs postoperatively. patients in the L-CN group were given levocaine 3.0 g in 250 ml of saline once daily from 3 days before surgery until 3 d postoperatively, which was changed to L-CN orally at 3 g per day in 3 divided doses for 30 d as a course of treatment. The improvement of the main symptoms of coronary heart disease such as chest tightness, shortness of breath and palpitations were observed within 7 days after surgery; the changes of ST segment in ECG immediately after surgery, ECG after 12h and ECG after 24h (elevation of 2mV was regarded as a change); the occurrence of new atrial fibrillation after surgery; the changes of EF values (2D method) at 3 and 6 months after surgery. The data were processed by SPSS16.0 statistical package, and the incidence was applied to the Χ2 test and the others to the t-test. 2. Results All 160 patients survived the perioperative period, and the time to block the elastic suture at the distal anastomosis of each vessel was 7.21±2.11 in the control group and 7.16±2.47 in the L-CN group, with no statistical difference between the two groups (P>0.05). Compared with the control group, the incidence of perioperative chest tightness and palpitations were significantly reduced, and the incidence of shortness of breath did not change significantly (see Table 2); the ECG did not change significantly in the immediate postoperative period, and the ECG improved significantly at 12h and 24h after surgery; the EF values did not differ significantly before and 6 months after surgery, and the EF values increased significantly at 3 months after surgery. 3.Discussion 60%~80% of the energy required for myocardial metabolism comes from fat metabolism, and L-CN is a carrier factor for transporting long-chain amino acids into mitochondria for β-oxidation, which is essential for maintaining normal cellular function. In myocardial ischemia and heart failure, intracellular carnitine deficiency and impaired fatty acid β-oxidation in the myocardium result in impaired energy production, increased free fatty acids, and accumulation of fatty acid metabolites, leading to cardiac dysfunction [3]. In coronary artery disease, cardiac muscle alkaline levels are significantly reduced [4]. Adequate L-CN restores ischemic myocardial energy metabolism, reduces the accumulation of fatty metabolites in cardiomyocytes, and results in less myocardial damage [5]. The incidence of postoperative chest tightness and palpitations was significantly reduced in the L-CN group in this study, which is consistent with the results of a multicenter double-blind controlled trial reported by Cherchi et al [6]. However, there was no significant change in the incidence of postoperative shortness of breath in the two groups, which may be related to open-heart surgical injury, masking some of the changes in the condition. Regarding ECG changes, there was no significant difference between the immediate postoperative ECG and the control group in the L-CN group, but ST-T changes were better than those in the control group at 12h and 24h postoperatively, and the rate of new postoperative atrial fibrillation was significantly less than that in the control group. The relevant literature also suggests that the application of L-CN has an ameliorative effect on ST-T changes and arrhythmia treatment [7, 8]. Animal experiments have confirmed that intravenous L-CN increases the concentration of ATP in cardiac tissues and that it reduces myocardial injury. The administration of L-CN also reduced the incidence of ventricular fibrillation, which has been reported in the literature to decrease from 26% to 4% before administration. Follow-up results showed that EF values were significantly better in the L-CN group than in the control group at 3 months postoperatively, which is consistent with the results of the large-scale CEMID clinical trial. However, there was no significant difference in EF values between the two groups at 6 months postoperatively at follow-up, which may be related to the recovery of cardiac function after OPCAB, and may also be related to the fact that the application of L-CN was shorter than that of the CEMID clinical trial, so there was a gap between the results and the CEMID clinical trial. Studies by Japanese scholars have demonstrated that L-CN can dilate blood vessels and improve myocardial contractility, and there should be some auxiliary effect on the improvement of cardiac function. We have recently conducted a follow-up of patients taking L-CN for a long time, and the results need to be further analyzed and summarized. In conclusion, the use of L-CN can reduce the discomfort of patients in the perioperative period of nonstop coronary artery bypass grafting, protect the myocardium to a certain extent and promote the recovery of cardiac function after surgery, and is a good choice of adjuvant therapy in the perioperative period of nonstop coronary artery bypass grafting.