From the Guidelines
Cardiac enzymes, including troponin, creatine kinase (CK), and myoglobin, are crucial biomarkers for diagnosing heart conditions, with troponin being the most specific and sensitive indicator of heart damage. These enzymes are released into the bloodstream when heart muscle cells are damaged, serving as important indicators of myocardial necrosis 1. The diagnosis of acute, evolving, or recent myocardial infarction (MI) requires findings of a typical rise and/or fall of a biomarker of necrosis, in conjunction with clinical evidence that the cause of myocardial damage is ischemia 1.
Key Cardiac Enzymes
- Troponin (I and T): most specific and sensitive indicator of heart damage, typically rising within 3-4 hours after a heart attack and remaining elevated for up to two weeks 1
- Creatine kinase (CK), particularly the MB isoenzyme (CK-MB): rises within 4-6 hours and returns to normal within 2-3 days, but has lower specificity than troponin 1
- Myoglobin: increases the earliest (1-3 hours) but lacks specificity 1
Measurement and Interpretation
Blood samples for the measurement of troponin should be drawn on first assessment and 6–9 hours later, with an occasional patient requiring an additional sample between 12 and 24 hours if the earlier measurements were not elevated and the clinical suspicion of myocardial infarction is high 1. The demonstration of a rising and/or falling pattern is needed to distinguish background elevated troponin levels from elevations indicative of myocardial infarction 1. If troponin assays are not available, the best alternative is CK-MB (measured by mass assay) 1.
Clinical Application
These enzymes are measured through blood tests ordered when patients present with chest pain or other symptoms suggesting heart problems. Multiple measurements are often taken over time to track changes in enzyme levels, which helps determine if heart damage is ongoing or resolving. The pattern and timing of enzyme elevation help clinicians distinguish between different cardiac conditions, guiding appropriate treatment decisions 1.
From the Research
Definition of Cardiac Enzymes
- Cardiac enzymes, also known as cardiac biomarkers, are proteins that are released into the bloodstream when the heart is damaged, such as during a heart attack 2.
- These enzymes are used as diagnostic tools to assist cardiologists in the diagnosis and management of patients with cardiovascular diseases 2.
Types of Cardiac Enzymes
- Traditional cardiac enzymes include aspartate aminotransferase, lactate dehydrogenase, and creatine kinase 2.
- Isoenzymes such as CK-MB and LD-1 provide more specific organ specificity 2.
- Modern cardiac markers include protein markers such as cardiac troponin T (cTnT) and I (cTnI), which are more sensitive and specific than isoenzyme markers 2.
Clinical Use of Cardiac Enzymes
- Cardiac enzymes are used to diagnose acute myocardial infarction (AMI) and to risk stratify patients with unstable angina 2.
- Elevated levels of cardiac troponin are associated with a higher risk of AMI and cardiac death within the immediate future (4 to 6 weeks) 2.
- The use of cardiac enzymes has evolved over time, with a shift from traditional enzyme markers to more sensitive and specific protein markers 2.