Definition and Efficacy
Cardiac markers are used in the diagnosis and risk stratification of patients with chest pain and suspected acute coronary syndrome (ACS). The cardiac troponins, in particular, have become the cardiac markers of choice for patients with ACS. Indeed, cardiac troponin is central to the definition of acute myocardial infarction (MI) in the consensus guidelines from the European Society of Cardiology (ESC) and the American College of Cardiology (ACC): These guidelines recommend that cardiac biomarkers should be measured at presentation in patients with suspected MI, and that the only biomarker that is recommended to be used for the diagnosis of acute MI at this time is cardiac troponin due to its superior sensitivity and accuracy. [1, 2, 3, 4]
For example, patients with elevated troponin levels but negative creatine kinase-MB (CK-MB) values who were formerly diagnosed with unstable angina or minor myocardial injury are now reclassified as non–ST-segment elevation MI (NSTEMI), even in the absence of diagnostic electrocardiogram (ECG) changes.
Similarly, only 1 elevated troponin level above the established cutoff is required to establish the diagnosis of acute MI, according to the ACC guidelines for NSTEMI. [4,5, 6]
These changes were instituted following the introduction of increasingly sensitive and precise troponin assays. Up to 80% of patients with acute MI will have an elevated troponin level within 2-3 hours of emergency department (ED) arrival, versus 6-9 hours or more with CK-MB and other cardiac markers.
Accordingly, some have advocated relying solely on troponin and discontinuing the use of CK-MB and other markers. [7, 8, 9, 10, 11] Nevertheless, CK-MB and other markers continue to be used in some hospitals to rule out MI and to monitor for additional cardiac muscle injury over time.
Note that cardiac markers are not necessary for the diagnosis of patients who present with ischemic chest pain and diagnostic ECGs with ST-segment elevation. These patients may be candidates for thrombolytic therapy or primary angioplasty. Treatment should not be delayed to wait for cardiac marker results, especially since the sensitivity is low in the first 6 hours after symptom onset. ACC/American Heart Association (AHA) guidelines recommend immediate reperfusion therapy for qualifying patients with ST-segment elevation MI (STEMI), without waiting for cardiac marker results.