CABG patients with complex coronary lesions and surgical trauma, intraoperative extracorporeal circulation and surgical operations can cause myocardial ischemia or injury, therefore, perioperative monitoring of myocardial ischemia or injury is very important and affects the success or failure of surgery and the long-term prognosis of patients. In the past, CK and CK-MB were often used as indicators for monitoring myocardial injury in perioperative cardiac surgery [1], but their sensitivity or specificity is low, and their practical application is not very satisfactory. In recent years, cTnT has been widely used in cardiology as an index of myocardial ischemia and injury specificity. In this paper, we observed the dynamic changes of CK, CK-MB and cTnT in the perioperative period of CABG patients, and initially explored the application value of cTnT in determining myocardial injury.
Clinical data and methods
1. Materials There were 22 elective surgery patients in this group, 18 males and 4 females, aged 45-72 years. All patients had a history of recurrent angina pectoris, 14 of them had a history of myocardial infarction, and the infarction was 2 months-8 years from the time of surgery. One case had a history of cerebral thrombosis. There were 16 cases of hypertension, 4 cases of diabetes mellitus, 8 cases of hyperlipidemia, 3 cases of 2-branch lesions, 20 cases of 3-branch lesions, and 1 case of combined ventricular wall tumor. All patients had grade 2-3 cardiac function. The average left ventricular ejection fraction was 0.68.
All patients stopped taking aspirin 1 week before surgery, and cardiovascular drugs were used until the day of surgery. 0.1-0.2mg/kg of oral valium was given in the morning, and 0.3mg of scopolamine and 10mg of morphine were injected intramuscularly. 0.05-0.1mg/kg of imipramine or 0.2-0.3mg/kg of etomidate was used for induction, followed by 0.2-0.3mg/kg of vecuronium bromide and 10-10mg of fentanyl. /kg, fentanyl 10-15mg/kg intravenously and intubated through the oral plain view trachea. During the important steps of the operation, such as before skin incision, before sawing the sternum and before CPB, a total of 10-20mg/kg of fentanyl was added immediately, while isoflurane was inhaled to maintain anesthesia. Blood pressure was monitored dynamically throughout the procedure, and a 6-lumen Swan-Ganz catheter was used to monitor central venous pressure, pulmonary artery pressure, pulmonary capillary pressure and continuous cardiac output.
3.Extracorporeal circulation and myocardial protection Sarns extracorporeal circulation machine with membrane oxygenator (D703) was used. 500-1500ml of hemidine, 500ml of Ringer’s solution, 250ml of 20% mannitol and 2 million IU of peptidase were used for pre-charging, totaling 1800-2800ml. 3 million IU of peptidase was used before and during the transfer. aortic clamp was followed by transcatheter aortic root machine infusion of cold blood (15℃) high potassium stop solution (blood: stop solution 4:1)
10-20 ml/kg at a rate of 200-300 ml/min. The infusion of low-potassium cold blood stop solution was repeated after 15-20 min. The extracorporeal circulation was naturally cooled by prefilled fluid perfusion tube, nasopharyngeal temperature 36.2-32.2°C, anal temperature 36.6-33.2°C, rewarming rate 0.2°C/min. CPB time 131.78±23.48 min, aortic block time 84.45±23.84 min. arterial flow 40-70ml/kg/min, transmedial arterial pressure 40- 104mmHg.
CK and CK-MB were measured by Beckman biochemistry, and the standard values were 40-200 IU/L and 0-10 IU/L, respectively. cTnT was measured by German Boehringer
The Es33 fully automated enzyme immunoassay system and kit provided by Mannheim, Germany was used to determine cTnT values by double antibody sandwich enzyme immunoassay, and the standard in our laboratory was <0.2ng/kg.
Results
Twenty-two patients in this group completed the surgery successfully, and the patients recovered well after surgery. The average number of bypasses was 3.27 per case.
The median CK, CK-MB and cTnT were all within the normal range before CPB, and all three values were significantly increased immediately after CPB and at 24 hours, with CK being the most significant at 24 hours postoperatively and the remaining two values being the most significant immediately after surgery.
Further, we counted the number of cases in which each parameter was above the upper limit of normal before and after CPB and found that the percentage of elevated CK and cTnT was very high, with no significant difference between them, while the rate of positive CK-MB was lower, with a significant difference compared with the remaining two groups, P<0.01.
Since WHO listed dynamic elevation of cardiac enzymes CK , CK-MB as one of the three major diagnostic indicators of acute myocardial infarction in the 1960s, cardiac enzymes have played an important role in the diagnosis of myocardial injury, and their increased degree can reflect the extent of myocardial injury more accurately [1]. However, cardiac enzymes such as CK and CK-MB are not unique to the heart, but also exist in the cytoplasm of skeletal muscle, gastrointestinal smooth muscle and other tissues, so when extracardiac tissues are injured, the blood concentrations of these cardiac enzymes may also increase to varying degrees, making them less specific for the diagnosis of myocardial injury.
The determination of peripheral blood myocardial cTnT concentration for the diagnosis of acute myocardial infarction was first reported by Cummins [2] and others in the UK in 1987, which attracted widespread attention from scholars at home and abroad. Recent studies have confirmed that cTnT has myocardial specificity, is not affected by trauma, and is one of the most specific and sensitive markers for the diagnosis of myocardial injury, with a specificity of 100% and a sensitivity of over 90% [3].
CK, CK-MB and cTnT were mostly within the normal range before CPB in our patients, probably due to adequate preoperative preparation, stable control of the disease, adequate preoperative drug application, safe and perfect induction and maintenance of anesthesia. cK increased significantly immediately after CPB and at 24 hours, and although the sensitivity is high, it has been clinically demonstrated that CK values can increase significantly in all non-cardiac major surgeries [2], so the specificity is poor. Therefore, the specificity is poor. median CK-MB, although increased after CPB, did not reach the diagnostic criteria of 10 IU/L in most cases, indicating that it does not reflect myocardial injury sensitively in a relatively short time after trauma.
The cTnT increased significantly in the immediate and 24 hours after CPB, with median values of 0, 53 ng/ml and 0, 45 ng/ml, respectively, which may be related to intraoperative aortic block, myocardial ischemia, myocardial reperfusion injury after aortic opening, and direct myocardial surgical operation. cTnT values did not decrease significantly after 24 hours, and monitoring should continue to be strengthened.
The literature reports that cTnT begins to rise 4-6 hours after acute myocardial infarction [3]. Our clinical observations showed that cTnT was significantly elevated immediately after the end of CPB (i.e., 2 hours after the start of CPB), which on the one hand indicates that cTnT appears earlier in the blood compared with CK-MB; on the other hand, it may be related to the “wash-out effect” after aortic opening [4].
TnT anchors the whole troponin to prothymocyte, TnC is negatively charged and binds calcium ions, TnI transmits the information about the binding of TnC to prothymocyte, causing a conformational change in the latter. The amino acid sequence of TnC is very similar in cardiac and skeletal muscles, however, the N-terminal amino acid sequences of TnT and TnI are different in both, according to which monoclonal antibodies specific for cTnT and cTnI were prepared [3] for the determination of cardiac cTnT and cTnI.
In two patients, CK values were abnormally increased at 24 hours, in patients who underwent open-heart hemostasis 8 h after surgery and in patients in whom sternal fractures were found 24 hours later, so we appreciate that CK, although not a specific indicator of perioperative myocardial injury, may be used as a monitoring indicator of the degree of perioperative trauma.
cTnT is a sensitive index for diagnosing perioperative myocardial injury in CABG, appears early in blood, and is specific for myocardium. cTnT can also be used in the study of CABG in myocardial protection, which has promotion value.
With the development of detection technology, cTnT bedside detection devices have been used in clinical applications with simple, rapid and practical features [5], and in combination with enzyme-linked immunoassay, it has the potential to be used in the future for dynamic monitoring of intraoperative myocardial injury and determination of patient prognosis.