Redefining myocardial infarction: detecting the role of cardiac troponin

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Recently, the European Society of Cardiology (ESC), the American College of Cardiology (ACC) and the American Heart Association (AHA) published a consensus document to recommend the application of biochemical markers for the detection of MI. The criteria for redefining the classification of patients with acute coronary syndrome (ASC) with ischemic symptoms (such as acute, progressive, or recent myocardial infarction) are based on serum (plasma) cardiac troponin (I or T) The concentration depends on the increase. In the treatment of unstable angina pectoris and MI patients with ST segment elevation, the new ACC / AHA guideline believes that in patients with ischemic ASC, elevated cardiac troponin value can establish ST segment elevation. Diagnosis of myocardial infarction, and normal cardiac troponin value can establish a diagnosis of unstable angina.
The new guidelines emphasize the following clinical issues: First, elevated cardiac troponin indicates the presence of myocardial injury, but it can be asymptomatic MI or ischemic injury without obvious symptoms. If there is no ischemic injury, you should consider looking for other causes of myocardial damage. Second, the increase in cardiac troponin indicates that the myocardial damage is irreversible, of course, this issue remains to be discussed. Third, the degree of cardiac troponin elevation in patients with myocardial ischemic injury is related to the prognosis. Fourth, patients may have elevated cardiac troponin after percutaneous transluminal coronary angioplasty (PTCA) or cardiac surgery. In patients undergoing cardiac surgery, there is currently no biochemical marker that can distinguish whether the injury is caused by MI caused by surgical trauma. Either way, an increase in cardiac troponin after coronary angioplasty or Stent fixation membrane surgery predicts ischemic cell death and can be considered MI.
The guidelines also emphasize the following detection (analysis) issues: First, there are differences in the results of various detection methods for cardiac troponin (especially cardiac troponin I), which has caused confusion to clinicians and testers . Standardization will help solve some of these problems. You should decide to use a certain troponin detection method after carefully reading the relevant literature. Second, after reading the literature on clinical research, you should know about the imprecision (CV) of the measurement method, the reference range, possible analytical interference, and the type of specimens that can be used. It is recommended that the acceptable imprecision of the upper limit of the reference range of the 99th percentile be CV ≤ 10%, which requires that all manufacturers related to cardiac troponin testing have the responsibility to adjust their respective testing methods to the most good. Although few manufacturers are currently able to meet this recommendation, if a company can do it, the Cardiology Committee requires other manufacturers to meet this requirement because the diagnosis and treatment decisions are based on cardiac troponin The lower limit of the critical value. In order to reduce the cycle of testing and reporting the results, heparin anticoagulated plasma specimens were initially advocated rather than serum specimens. However, recent studies have shown that heparin anticoagulated plasma and serum specimens were detected using several different methods of cardiac troponin detection. The results of heparin anticoagulated plasma specimens are more variable and lower than those of serum specimens. Therefore, each test method must be effective on serum and plasma specimens. Third, at least 6-9 hours after the onset of symptoms, blood samples should be taken to determine cardiac troponin to confirm or exclude MI. Fourth, if the cardiac troponin test cannot be performed, it is best to choose the CK-MB quality test. Early increased biochemical markers, such as myoglobin or CK-MB subtypes, can be used for early classification of patients' severity, but they cannot be used to confirm the diagnosis of MI. We fully agree with the new cardiology guidelines and agree with the evidence from the literature that cardiac troponin can be used as a definite marker for the diagnosis of MI, the classification of the degree of risk, and to help clinicians adjust the treatment plan .
From a clinical point of view, any detectable cardiac troponin is obviously related to the degree of risk of clinical prognosis. FRISC II research on cTnT proves that the critical concentration at the 99th percentile can be used to classify the degree of risk (cTnT <0.01μg / L 12-month mortality or AMI incidence rate is 8.5%, compared to Below cTnT ≥ 0.01μg / L, the 12-month mortality rate or AMI incidence rate was 18.0%, P <0.001. Studies of cTnI have similar results. CTnI uses 0.1μg Chen / L at the 97.5th percentile Critical values, respectively measured by Immuno I (Bayer), ACS: 180 (Bayer) and Dimension RxL (Dade Behring) analyzers are respectively effective difference ratio 2.2 (confidence interval 1.3 ~ 3.6), 2.8 (1.5 ~ 5.1 ) And 3.0 (1.5 to 5.7). For each method, the measured values ​​at the 97.5th and 99th percentiles are similar. As mentioned above, preliminary tests have shown that cardiac troponin The value of the lower limit of detection for the classification of the degree of risk, but most manufacturers cannot meet the requirement of imprecision (CV) ≤ 10% at the 99th percentile. Therefore, we believe that in clinical medical diagnosis and treatment , Before the 99th percentile CV ≤ 10% target is reached, choose one for each method to satisfy CV ≤ The slightly higher threshold of 10% concentration is used clinically. The importance of medical problems caused by misclassification of patients due to imprecision is currently unknown, and may be known in the future. In any case, the new guidelines Emphasize that clinical evaluation of patients is part of the medical decision process.
With the advent of these new guidelines, we believe that we will review the application guidelines for myocardial markers published by the American Society for Clinical Chemistry (NACB) and IFCC in 1999 and compare them with the guidelines of ACC / ESC / AHA Contrast is important and timely. First, both NACB and IFCC guidelines recommend the use of two markers (early markers and late markers). NACB recommends that blood samples be collected at the time of admission and between 2 ~ 4h, 6 ~ 9h and 12 ~ 24h after admission, while IFCC recommends at the time of admission, 4h, 8h and 12h (or the next morning) after admission Collect blood samples. The guidelines of ESC / ACC and ACC / AHA suggest that for early diagnosis of MI (within 6 hours of symptom onset), in addition to the later identified marker (troponin), early biochemical markers of myocardial damage should also be considered ( Such as myoglobin and CK-MB subtypes). The use of early markers means that the blood sample collection time should also be early, that is, the blood sample is collected at the time of admission and within 6 hours after admission. Therefore, there is consistency between the recommendations of the academic community and the cardiology academic community. And academic groups in both these areas are aware that if there is no other early classification scheme available, then cardiac troponin detection is necessary, and we agree with this. The American Academy of Emergency Physicians recommends a similar method. They recommend "repeatedly measuring CK-MB 2 to 3 hours after returning to the baseline value or re-determining myoglobin 1 to 2 hours after returning to the baseline value. MB and? Myoglobin ... ".
In the initial WHO diagnostic MI standard, a series of obvious changes in enzyme concentration were used as one of the three criteria for the diagnosis of MI. The other two were electrocardiographic changes and clinical symptoms such as chest pain. With the development of protein markers such as myoglobin and cardiac troponin, the committees of NACB and IFCC recommended that the diagnostic criteria for MI be extended from enzymes to proteins. However, NACB's recommendations did not significantly change the definition of MI, and redefining the diagnostic criteria of MI is the responsibility of cardiologists, not the responsibility of laboratory personnel. It is therefore logical that the relevant committees of ESC / ACC then jointly proposed to redefine MI.
Second, regarding the cut-off values ​​of myocardial markers, NACB and IFCC recommend the use of two cut-off values ​​for cardiac troponin. The low cut-off value (97.5th percentile) indicates the presence of myocardial damage, and the high cut-off value indicates that the damage has reached the degree of MI defined by the previous WHO (as determined by the ROC curve). At that time, the NACB committee considered the factors of "sociology, biopsychology, and socioeconomics", and believed that if the cut-off value is lowered and a small myocardial injury is diagnosed as MI, this will increase the incidence of MI. At the same time, the NACB committee believes that before WHO or other clinical academic organizations such as AHA or ACC redefine the diagnostic criteria for AMI, two thresholds are used for cardiac troponin. The ESC / ACC Committee pointed out that the development of biochemical marker analysis technology has made the diagnosis of MI more accurate, and the incidence of MI has increased year by year since the application of WHO diagnostic standards. With the advancement of medical technology, the detection of cardiac troponin has been introduced. We again agree with this progress. Once the MI guidelines redefined by ESC / ACC are widely accepted and fully implemented, there is no need to adopt NACB's recommendations for setting two threshold concentration levels.
Third, when establishing a low cut-off value, NACB and IFCC recommend the 97.5th percentile of the normal healthy population, which is consistent with other clinical testing methods. The false positive rate at this time is 2.5%. The ESC / ACC and AHA / ACC guidelines consider the 99th percentile as a single critical point, which is between the low and high critical values ​​recommended by NACB and IFCC. The theoretical basis for raising the low cut-off value from the 97.5th percentile to the 99th percentile is to reduce the false positive rate for diagnosing myocardial injury. Manufacturers of cardiac troponin testing must ensure that their products and methods achieve the necessary sensitivity and inaccuracy (CV ≤ 10%) to meet the new threshold requirements. Although the process of continuously improving the accuracy of the measurement cannot be achieved overnight, we still emphasize the importance of reducing the inaccuracy of the analysis at low detection limits. We expect that each method should achieve CV ≤ 10% at the 99th percentile. The critical point of the medical decision level will continue to decrease. In any case, with the improvement of cardiac troponin detection methods and determination precision, there will be more clinical trials to determine the optimal cut-off value.
Finally, NACB and IFCC suggest that cardiac troponin is a new biochemical marker for detecting myocardial injury. The NACB and IFCC committees believe that patients with unstable angina should be given immediate treatment even if there is only a slight increase in cardiac troponin, thereby minimizing the risk of causing myocardial damage. Other clinical academic groups unanimously agree with this recommendation. ACC / AHA uses cardiac troponin as a good indicator of early risk classification. The Braunwald classification III for unstable angina also includes cardiac troponin detection in the B classification criteria. Because patients with unstable angina have a recent risk of myocardial damage, the relevant regulations of the US Health Care Policy Research Agency will increase the serum TnI or TnT as a major criterion for including these patients in the high-risk group. Australia and New Zealand Cardiology Association also listed cardiac troponin as a marker for diagnosis of ACS. All clinical academic institutions and testing academic groups have come to the conclusion that cardiac troponin is the best marker for ACS diagnosis, risk classification and treatment guidance. We fully agree with the recommendation that only cardiac troponin meets the requirements. We also recommend that clinicians gradually change the preferred CK-MB approach when using myocardial markers.
In short, we believe that there are reasons to require all personnel engaged in health care, including clinicians, laboratory personnel, residents, medical students, hospital administrators, and reagent instrument manufacturers to read the ESC / ACC and ACC / AHA guidelines Because these documents will have a profound impact on medicine and society. We agree with all the conclusions of the new cardiology guidelines. This guideline completely contains the guideline content of the originally published academic community, which considers the cardiac troponin test to be a new test to confirm the diagnosis of MI.

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