FAST FACTS: Cardiac Biomarkers in Acute Coronary Syndrome (ACS)
By Dr Devina Govender
What Are Cardiac Biomarkers?
Cardiac biomarkers are substances released into the bloodstream when the heart is under stress or damaged — such as during ischaemia or infarction. They help with:
-Diagnosis
-Risk stratification
-Management of chest pain or ACS symptoms
ACS Includes:
- Unstable Angina (UA)
- Non-ST Elevation MI (NSTEMI)
- ST Elevation MI (STEMI)
Early diagnosis and treatment significantly reduce morbidity and mortality.
Biomarker Timeline After Cardiac Injury
Cardiac Troponins (cTn)
Preferred biomarker for myocardial injury (per 2012 universal MI definition).
Endorsed by ACC, ESC, AHA, and World Heart Federation.
High-Sensitivity Troponins (hs-cTn):
- Detect MI earlier
- Make older markers (Myoglobin, CK-MB) obsolete
- Should be standard for chest pain triage
Must be interpreted with:
- Clinical exam
- Risk assessment
- ECG findings
-In MI (NSTEMI/STEMI), cTn > 99th percentile of healthy individuals.
-Detection limits vary: 1–5 ng/L
-99th percentile: 10–20 ng/L
cTn identifies high-risk patients needing:
- Glycoprotein IIb/IIIa antagonists
- Urgent invasive evaluation
ESC 2023 Guidelines recommend:
- 0/1-hour protocol (preferred)
- 0/2-hour and, 0/3-hour protocols (alternatives)
More sensitive and faster than 0/3-hour protocol
Not applicable to patients with known coronary artery disease
Myoglobin
Early marker but not cardiac-specific
Can be elevated due to skeletal muscle damage
May confound ACS diagnosis
CK-MB
CK-MB is an isoform of Creatine Kinase (CK), released from damaged heart, muscle, or brain cells.
Common Causes of Elevated CK-MB:
- Non-cardiac surgeries
- Trauma
- Exercise
- Skeletal muscle disease
- Renal failure
CK-MB sensitivity is reduced when total CK is high.
Ratio of CK-MB to total CK improves specificity but reduces sensitivity.
Spurious increases seen with:
- Haemolysis
- Hyperbilirubinaemia
- Macrokinases
2014 AHA/ACC Guidelines
CK-MB is not useful for ACS diagnosis due to:
- Lower sensitivity than cTn
- Delayed serum appearance
- No added value in risk stratification
- Poor reinfarction detection
- Unnecessary cost
CK-MB Index (CK-MB/CK)
Useful In:
1️.Renal Failure (eGFR < 15 ml/min)
- cTn elevated due to reduced clearance
- hs-Troponin I preferred over T
- CK-MB still elevated in 30–50% of cases
2️.Recent ACS (within 2 weeks)
- cTn stays elevated for 5–14 days
- CK-MB’s shorter lifespan may indicate new event
- Delta change in cTn helps detect reinfarction
3️.Estimating MI Size
- Peak hs-cTn correlates equally with infarct size as CK-MB
4️. Post-PCI MI Detection
- cTn may rise slightly post-procedure
- CK-MB use may underestimate necrosis
- Baseline cTn sample before PCI helps interpret post-PCI rise
- Universal Definition of MI requires baseline cTn before procedures