What are cardiac enzymes?

From the Guidelines

Cardiac enzymes, particularly troponin I and T, are the most reliable biomarkers for diagnosing myocardial infarction and should be measured in a series at presentation, 3-6 hours later, and sometimes at 12 hours, as recommended in the management of acute coronary syndromes 1. When evaluating potential cardiac events, it is crucial to focus on troponin levels, with elevated levels indicating myocardial damage. The timing of elevation is important, as troponins begin rising 3-4 hours after injury, peak at 24-48 hours, and may remain elevated for 7-14 days. Some key points to consider when interpreting cardiac enzymes include:

• Troponin I and T are highly specific to cardiac tissue and are the preferred biomarkers for diagnosing myocardial infarction 1.
• Creatine kinase (CK) and its cardiac-specific isoenzyme CK-MB are also measured but have been largely replaced by troponins due to their superior specificity.
• Myoglobin rises quickly after cardiac damage but lacks specificity.
• Serial measurements showing a rise and fall pattern are more diagnostic than a single elevated value, as chronic conditions like renal failure can cause persistent troponin elevation without acute cardiac injury. In the context of acute coronary syndromes, the use of cardiac enzymes, particularly troponin, is essential for risk stratification and guiding treatment decisions, as outlined in the recommended strategy for managing acute coronary syndromes without persistent ST-segment elevation 1.

From the Research

Cardiac Enzymes and Myocardial Infarction

• Cardiac enzymes, such as CK and LD, play a crucial role in diagnosing acute myocardial infarction (AMI) 2
• Changes in serum-enzyme levels are important findings when diagnosing AMI, and blood sampling frequency and which enzymes to measure are crucial for obtaining maximum information 2
• Myoglobin is a good early parameter for diagnosing AMI, but its efficiency is only 66% and specificity is low 2

Medication and Myocardial Infarction

• Aspirin, beta-blockers, ACE inhibitors, and statins are commonly used medications for secondary prevention of AMI 3, 4, 5
• These medications have been shown to reduce 1-year mortality in patients after AMI 3 and decrease the risk of presenting with ST-segment elevation MI (STEMI) 4
• However, patients with end-stage renal disease (ESRD) are less likely to receive these medications, which may contribute to increased 30-day mortality 5

Renal Function and Medication Use

• Renal function, as measured by estimated glomerular filtration rate (eGFR), does not appear to be a significant factor in the use of beta-blockers and aspirin after AMI 6
• Admission to the coronary care unit (CCU) is a stronger predictor of beta-blocker and aspirin use than renal function 6