Learning Notes on Troponin cTnI and cTnT Explained Simply

🥼 Practice and Clinical
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What is Necrosis? What is Infarction?

Necrosis: Death of local tissue cells in vivo characterized by enzymatic digestion changes.
Infarction: Death of an organ or local tissue caused by vascular occlusion and cessation of blood flow leading to hypoxia.
The scope of necrosis is larger than infarction.

Acute myocardial infarction: myocardial death caused by sustained acute ischemia

  • STEMI: ECG with ST-segment elevation + symptoms or myocardial biochemical markers
  • NSTE-ACS: no ST-segment elevation on ECG + evidence of acute ischemia (common scenario for troponin)
    • New onset myocardial ischemic symptoms
    • New ECG changes: ST-segment changes, LBBB, pathological Q waves
    • New imaging changes (UCG, nuclear, MRI, CTA)
    • CAG revealing coronary thrombus

Overview of Troponin

Divided into three subunits: cTnT, cTnI, TnC
cTnT and cTnI have higher specificity; TnC has poor specificity (present in both cardiac and skeletal muscle)

After myocardial injury, troponin quickly enters the bloodstream and can be used for early diagnosis. It can also remain elevated for a relatively long time (1–2 weeks) and can be used for later diagnosis.

Clinical Significance

According to the 2015 Guidelines for Diagnosis and Treatment of Acute ST-Segment Elevation Myocardial Infarction, troponin is the most specific and sensitive preferred biomarker for diagnosing myocardial necrosis.

Troponin has an excellent negative predictive value and average positive predictive value:

  • Good negative predictive value: chest pain > 3 hours, if negative, almost 100% exclusion of myocardial infarction.
  • Average positive predictive value: elevated troponin does not necessarily mean myocardial infarction because free troponin can be present in the blood, and troponin is released in myocardial injury regardless of ischemia (heart failure, myocarditis, etc.)

How to diagnose myocardial infarction using troponin? :right_arrow: 2018 Universal Definition of Myocardial Infarction, “1+1” model

  • First 1: troponin elevation (excluding other causes such as heart failure, myocarditis)
  • Second 1: evidence of acute myocardial ischemia
    • New symptoms
    • New ECG changes: new ST-segment changes, pathological Q waves, LBBB
    • New imaging: UCG, nuclear, MRI, CTA

How to diagnose myocardial infarction using high-sensitivity troponin? :right_arrow: 2020 ESC NSTE-ACS Guidelines, 0/1h rule

Factors Affecting Troponin

Various factors causing myocardial injury will lead to elevated troponin

graph TD;
    Myocardial_Injury --> Acute;
    Myocardial_Injury --> Chronic;
    Acute --> Ischemic;
    Acute --> Nonischemic_such_as_heart_failure_myocarditis;
    Chronic --> Chronic_myocardial_injury;
    Ischemic --> Acute_ischemic_myocardial_injury;
    Acute_ischemic_myocardial_injury --> Type_1_myocardial_infarction;
    Acute_ischemic_myocardial_injury --> Type_2_myocardial_infarction;
  • Heart failure:
    • Mild elevation, generally not exceeding 10 times the normal upper limit
    • In heart failure patients (n=84872, excluding renal dysfunction)
      • 6.2% cTnI > 1.0 μg/L or cTnT > 1 μg/L
      • 75% cTnI > 0.4 μg/L or cTnT > 0.1 μg/L
  • Renal failure: affects troponin excretion and often coexists with heart failure
  • Severe infection: Meta-analysis (1998–2008) showed up to 62% of patients with severe infection had elevated troponin without ACS

Summary

  1. Main use: diagnosis of acute myocardial infarction, not for diagnosing chronic coronary artery disease
  2. Troponin rises quickly (1–3 hours) after myocardial infarction, with good sensitivity
  3. Negative troponin (0/1/3h) nearly 100% excludes myocardial infarction
  4. Positive troponin indicates myocardial injury; further differential diagnosis is needed to determine if it is myocardial infarction (dynamic changes + combining other factors: symptoms, ECG, imaging)

References

心肌损伤相关指标课程——BNP、心肌酶谱、肌钙蛋白
心损心梗检验指标（心肌酶谱
心肌损伤相关指标课程——BNP、心肌酶谱、肌钙蛋白