Cardiac Enzymes in Myocardial Infarction

Introduction

When a person has a heart attack (myocardial infarction, or MI), heart muscle cells become damaged and release certain proteins into the bloodstream. These proteins, known as cardiac biomarkers or cardiac enzymes, help doctors diagnose and assess the severity of the heart attack.

Key Cardiac Enzymes

1. Troponin (Troponin T and Troponin I)

  • The most specific and reliable marker for heart muscle damage.
  • Begins to rise 2-4 hours after myocardial injury.
  • Peaks at 12-24 hours and remains elevated for up to 10-14 days.
  • A high-sensitivity troponin test (hs-Tn) allows for earlier detection.

2. Creatine Kinase-MB (CK-MB)

  • Less specific than troponin but still useful.
  • Starts to rise 3-6 hours after MI onset.
  • Peaks at 12-24 hours and normalizes within 2-3 days.
  • Used when troponin testing is unavailable or to detect reinfarction.

3. Myoglobin

  • A very early marker, rising within 1-2 hours.
  • Peaks at 6-8 hours and quickly normalizes.
  • Not highly specific to the heart, as it can come from other muscles.

Role of Cardiac Enzymes in Diagnosis

  • Repeated blood tests are done over several hours to track trends.
  • Electrocardiogram (ECG) is combined with cardiac enzymes to confirm MI.
  • Other conditions such as myocarditis or pulmonary embolism can also raise cardiac enzymes.

Additional Considerations

  • Chronic kidney disease (CKD) can cause chronically elevated troponins.
  • Pulmonary embolism & heart failure can also lead to higher troponin levels.
  • Lab variability must be considered, and results should always be interpreted along with clinical symptoms.

Conclusion

Understanding cardiac enzymes is essential for diagnosing heart attacks promptly. Troponin is the gold standard, but CK-MB and myoglobin may provide additional information in certain cases. Always correlate enzyme levels with symptoms and ECG findings.

Source recommendations

1. American Heart Association Guidelines for the Management of Patients with Acute Coronary Syndromes

  1. https://www.ahajournals.org/doi/10.1161/cir.0000000000000134
  2. https://pubmed.ncbi.nlm.nih.gov/25260718/
  3. https://www.ahajournals.org/doi/10.1161/CIR.0000000000001309
  4. https://professional.heart.org/en/science-news/2025-guideline-for-the-management-of-patients-with-acute-coronary-syndromes
  5. https://newsroom.heart.org/news/acc-aha-issue-new-acute-coronary-syndromes-guideline

2. European Society of Cardiology Guidelines for the Management of Acute Coronary Syndromes

  1. https://www.escardio.org/Guidelines/Clinical-Practice-Guidelines/Acute-Coronary-Syndromes-ACS-Guidelines
  2. https://academic.oup.com/eurheartj/article/44/38/3720/7243210
  3. https://pubmed.ncbi.nlm.nih.gov/37622654/
  4. https://academic.oup.com/eurheartj/article/42/14/1289/5898842
  5. https://pubmed.ncbi.nlm.nih.gov/21873419/

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