What are cardiac enzymes?

From the Guidelines

Cardiac troponin is the preferred marker for diagnosing myocardial infarction due to its high sensitivity and specificity, and it should be measured at presentation and then serially over time to detect characteristic rise and fall patterns. The use of high-sensitivity cardiac troponin assays is recommended over less sensitive ones, as they allow for earlier detection of cardiomyocyte injury and improve diagnostic accuracy for myocardial infarction 1. When evaluating potential cardiac events, it is essential to consider the timing of enzyme elevation, as troponin typically rises within 1 hour after symptom onset and remains elevated for several days, while creatine kinase-MB (CK-MB) rises within 4-6 hours after heart damage and returns to normal within 2-3 days.

Some key points to consider when using cardiac enzymes for diagnosis include:

• Troponin I and T are highly specific to cardiac tissue and are the gold standard for detecting heart damage
• CK-MB is another enzyme that can be used to diagnose myocardial infarction, but it is less sensitive and specific than troponin
• Myoglobin is not specific to the heart, but it can be useful for early detection of cardiac injury
• The diagnostic cut-off for myocardial infarction is defined as a cardiac troponin measurement exceeding the 99th percentile of a normal reference population using an assay with an imprecision of ≤10% at the upper reference limit 1
• Other life-threatening conditions, such as aortic dissection and pulmonary embolism, may also result in elevated troponin levels and should be considered as differential diagnoses 1

In clinical practice, the measurement of cardiac troponin should be combined with clinical assessment and 12-lead ECG to diagnose and risk-stratify patients with suspected non-ST-elevation acute coronary syndromes (NSTE-ACS) 1. The use of high-sensitivity cardiac troponin assays can help to rapidly "rule-in" or "rule-out" myocardial infarction, especially in patients presenting early after chest pain onset. Overall, the choice of cardiac enzyme and the timing of measurement should be guided by the clinical context and the availability of high-sensitivity assays.

From the Research

Cardiac Enzymes and Markers

• Cardiac enzymes, such as troponin T or I, are used as markers of myocardial necrosis in the diagnosis of acute myocardial infarction (MI) 2
• Elevation of these markers, along with ischemic symptoms and/or ischemic ECG changes, is mandatory for the diagnosis of acute MI 2
• Troponin T or I is the preferred marker of myocardial necrosis, and the diagnostic process should start as soon as possible 2

Role of Cardiac Enzymes in Risk Assessment

• Repeated measurements of markers of myocardial damage, such as troponin, can help identify patients at low or high risk of future cardiac events 2
• Patients identified as low risk may be discharged early, while those at high risk may require more intense treatment 2
• An elevated troponin concentration can identify patients who may benefit from antithrombotic therapy and invasive procedures 2

Management of Acute Coronary Syndrome

• Aspirin is recommended for all patients with suspected acute coronary syndrome (ACS) unless contraindicated, and a second antiplatelet agent may also be recommended 3
• Parenteral anticoagulation, statins, angiotensin-converting enzyme inhibitors, beta blockers, nitroglycerin, and oxygen may also be used in the management of ACS 3
• Percutaneous coronary intervention (PCI) with stent placement is recommended for patients with ST-segment elevation myocardial infarction, and fibrinolytic therapy may be used if PCI is delayed 3

Antiplatelet Therapy

• Antiplatelet medications, such as aspirin, clopidogrel, ticagrelor, and prasugrel, inhibit platelet activation and aggregation, and are used in the management of acute coronary syndrome 4
• The addition of clopidogrel to aspirin and fibrinolytic therapy has been shown to improve outcomes in patients with ST-segment elevation myocardial infarction 5
• Tirofiban, a nonpeptide glycoprotein IIb/IIIa inhibitor, may also be used in combination with clopidogrel and aspirin to decrease adverse cardiovascular events after percutaneous coronary intervention for ST-elevation myocardial infarction 6