While MI often is difficult to diagnose, researchers from the European Society of Cardiology (ESC) said that elevated levels of cardiac troponin, when there is a lack of clinical evidence of ischemia, can be an important biomarker for MI. Additionally, the ESC slightly revised the definition of an MI, suggesting it be adopted, according to new guidelines published Aug. 3 in the European Heart Journal.
“The preferred biomarker for myocardial necrosis is cardiac troponin (I or T), which has nearly absolute myocardial tissue specificity as well as high clinical sensitivity, thereby reflecting even microscopic zones of myocardial necrosis,” the guidelines stated. “An increased value for cardiac troponin is defined as a measurement exceeding the 99th percentile of a normal reference population (URL = upper reference limit). Detection of a rise and/or fall of the measurements is essential to the diagnosis of acute myocardial infarction.”
While optimal precision for the assay should be greater or equal to 10 percent, the researchers cautioned against using assays that do not hold validation of this optimal precision.
They recommended that blood samples be taken on first assessment and six to nine hours later in patients to measure troponin. The guidelines suggested that an elevated value of troponin above the decision level is required for the diagnosis of MI.
However, the authors noted that a release of troponin could also be caused by other etiologies of myocardial necrosis including myocarditis, aortic dissection, pulmonary embolism, congestive heart failure and renal failure, among others.
While the researchers pinpointed troponin as being the best measurement for MI, if the assays are unavailable, creatine kinase-MB (CK-MB) is the “best alternative” for diagnosing an MI. While the guidelines noted that CK-MB has been used previously to detect reinfarction, a total CK measurement is not recommended for use to diagnose infarction due to the enzyme's “lack of specificity” and large skeletal muscle distribution.
For cases of recurrent MI, the guidelines stated that clinicians should take immediate measures of the employed cardiac marker, either CK-MB or troponin. Recurrent infarction is present when a patient has a 20 percent or less increase in values of the second sample that should be obtained three to six hours later after the initial sample is drawn.
In the guidelines, the researchers also suggest that use of ECGs alone are “insufficient to diagnose acute MI or infarction since ST deviation may be observed in other conditions such as acute pericarditis, left ventricular hypertrophy, left bundle branch block, Brugada syndrome and early repolarization patterns.”
However, the guidelines stated that abnormalities of myocardial ischemia within an ECG could evolve into MI.
Additionally, the authors concluded that “a universal definition for myocardial infarction would be of great benefit to future clinical studies in this area since it will allow for trial-to-trial comparisons as well as accurate meta-analyses involving multiple investigations.”
The task force recommended that clinical researchers employ the definition mentioned in the guidelines during a trial: “A rise and/or fall of cardiac biomarkers (preferably troponin) with at least one value above the 99th percentile of the URL together with evidence of MI.” Additionally, there should be at least one of the following present: ischemia symptoms; ECG changes indicative of new ischemia; development of pathological Q waves in the ECG; or imaging evidence of new loss of viable myocardium or wall motion abnormalities.
The task force concluded that increasing diagnostic sensitivity for MI can help to identify more cases, prevent serious adverse events and lead to better treatment for the condition.
“Professional societies should take steps to facilitate the rapid dissemination of the revised definition to physicians, other healthcare professionals, administrators and the general public,” the authors stated.
"It should be appreciated that the agreed modification of the definition of MI may be associated with consequences for the patients and their families with respect to psychological status, life insurance, professional career, as well as driving and pilot licenses. Also the diagnosis is associated with societal implications as to diagnosis-related coding, hospital reimbursement, mortality statistics, sick leave and disability