Cardiac markers in acute coronary syndrome

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cardiac biomarkers acute coronary syndrome troponin CK-MB myoglobin

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BNP NT-proBNP natriuretic peptides acute coronary syndrome prognosis risk stratification

Here is a comprehensive overview of cardiac markers in acute coronary syndrome (ACS), synthesized from the ESC Guidelines on Management of ACS, Bailey & Love's Surgery, and established clinical knowledge.

Cardiac Markers in Acute Coronary Syndrome

Overview

Cardiac biomarkers serve three roles in ACS:

Diagnosis — confirm or exclude myocardial infarction
Risk stratification — estimate prognosis and guide therapy
Monitoring — assess infarct size and reperfusion

Key Cardiac Biomarkers

1. Cardiac Troponins (cTnI and cTnT) — Gold Standard

Troponins are structural proteins of the cardiac myofilament (part of the troponin-tropomyosin complex regulating actin-myosin interaction). They are highly cardiospecific.

Feature	Detail
Rise begins	2–4 hours after onset (1 hour with hs-cTn assays)
Peaks	12–24 hours
Returns to baseline	7–14 days (TnI), 10–14 days (TnT)
Diagnostic threshold	>99th percentile of healthy reference population
Preferred assay	High-sensitivity cardiac troponin (hs-cTn)

High-Sensitivity Troponin (hs-cTn): Per ESC ACS Guidelines, hs-cTn is recommended in all patients with suspected ACS (Management of Acute Coronary Syndromes, p. 20). It enables:

Detection within 1 hour of symptom onset
Significant rise and/or fall pattern distinguishes acute MI from chronic elevation
Negative predictive value >99% when used in rapid algorithms

Fourth Universal Definition of MI criteria: A rise and/or fall in cTn above the 99th percentile of a healthy reference population, in the context of clinical ischaemia.

2. CK-MB (Creatine Kinase Myocardial Band)

Feature	Detail
Rise begins	4–6 hours
Peaks	12–24 hours
Returns to baseline	48–72 hours
Key advantage	Returns to normal faster than troponin → useful for detecting reinfarction
Limitation	Less cardiospecific than troponin (also in skeletal muscle)

As noted in Bailey & Love's (p. 969), CK-MB remains a useful adjunct alongside troponin for both diagnosis and prognosis.

3. Myoglobin

Feature	Detail
Rise begins	1–3 hours (earliest marker)
Peaks	6–9 hours
Returns to baseline	24 hours
Advantage	Earliest to rise — useful for very early rule-out
Limitation	Very low specificity (also in skeletal muscle, renal failure)

Largely replaced by hs-cTn in modern practice.

4. BNP / NT-proBNP (Natriuretic Peptides)

Not diagnostic of MI but used for risk stratification in ACS:

Elevated levels indicate ventricular wall stress and dysfunction
Predict mortality, heart failure, and adverse outcomes post-MI
NT-proBNP elevation correlates with Killip class and infarct size

5. LDH (Lactate Dehydrogenase) — Historical

Rises at 24–48 hours, peaks at 3–6 days, normalizes at 8–14 days
Subtype LDH1 > LDH2 is cardiac-specific ("flipped LDH")
No longer routinely used; superseded by troponin

Temporal Profile of Biomarkers After AMI

Hours after symptom onset:
  0     2     4     6     12    24    48    72    7d    14d
  |     |     |     |     |     |     |     |     |     |
Myoglobin:   [rises]--[peaks]--[normal]
CK-MB:            [rises]--------[peaks]--[normal]
Troponin:       [rises]--------------------[peaks]----------[normal]

ESC Rapid Algorithms (0h/1h/2h)

The ESC recommends hs-cTn-based rapid rule-out/rule-in protocols (ACS Guidelines, p. 20):

0h/1h Algorithm (preferred)

Result	Interpretation	Action
hs-cTn very low at 0h	Rule-out	Discharge with outpatient follow-up
hs-cTn elevated + significant rise at 1h	Rule-in (MI)	Admit, treat as NSTEMI
Neither above	"Observe zone"	Repeat at 3h, clinical correlation

0h/2h Algorithm (alternative)

Absolute change in hs-cTn between 0h and 2h
Validated cutoffs differ by assay (Elecsys, ARCHITECT, Dimension, etc.)

0h/3h Algorithm (when hs-cTn unavailable)

Uses conventional troponin with sampling at 0h and 3h

Causes of Troponin Elevation Other Than Type 1 MI (Differential)

Elevated troponin is not synonymous with ACS. Other causes include:

Cardiac	Non-Cardiac
Heart failure (acute/decompensated)	Pulmonary embolism
Myocarditis	Sepsis / critical illness
Takotsubo cardiomyopathy	Renal failure
Arrhythmias (AF, SVT)	Stroke / subarachnoid hemorrhage
Cardiac contusion	Rhabdomyolysis
Post-cardioversion	Extreme exertion

This distinction is clinically critical — troponin must always be interpreted in context of symptoms, ECG, and clinical presentation.

Emerging / Investigational Markers

Marker	Role
hsCRP	Inflammation marker; predicts risk in stable CAD and ACS
Copeptin	Combines with hs-cTn for very early rule-out at 0h (NSTEMI)
Heart-type fatty acid binding protein (H-FABP)	Early rise similar to myoglobin, higher specificity
Myeloperoxidase (MPO)	Plaque instability marker

Summary Table

Marker	Rises	Peaks	Normalizes	Specificity	Main Use
Myoglobin	1–3h	6–9h	24h	Low	Early rule-out
CK-MB	4–6h	12–24h	48–72h	Moderate	Reinfarction
Troponin I/T	2–4h	12–24h	7–14d	High	Diagnosis/prognosis
hs-cTn	1h	12–24h	7–14d	Very high	Rapid algorithms
BNP/NT-proBNP	Hours	Variable	Variable	N/A	Risk stratification
LDH	24–48h	3–6d	8–14d	Low	Historical only

Key Clinical Takeaways:

hs-cTn is the biomarker of choice in all suspected ACS — use 0h/1h or 0h/2h algorithms
A rise and/or fall pattern is required to distinguish acute from chronic troponin elevation
CK-MB retains utility for suspected reinfarction (normalizes faster)
Troponin elevation must always be interpreted with clinical context and ECG findings
Negative troponin alone does not exclude unstable angina (no myocyte necrosis)

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