Acute Coronary Syndrome Quiz

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Questions and Answers

Which of the following is NOT a risk factor for Acute Coronary Syndrome (ACS) or Myocardial Infarction (MI)?

Regular Exercise (correct)

Age greater than 65

Body Mass Index (BMI) greater than 30

Low-density lipoprotein (LDL) cholesterol levels

What is the most common cause of ACS/MI?

Tobacco Smoking

Diabetes

Atherosclerosis (correct)

Hypertension

Which type of angina is characterized by chest pain at rest?

Stable Angina

Myocardial Infarction

Silent Ischemia

Unstable Angina (correct)

Which of the following describes the difference between NSTEMI and STEMI?

NSTEMI is a partial blockage of the coronary artery, while STEMI is a complete blockage. Signup and view all the answers

What is the significance of ST elevation on an electrocardiogram (ECG)?

It indicates a heart attack. Signup and view all the answers

Which of the following is NOT a cardiac biomarker?

Prothrombin Time (PT) Signup and view all the answers

What is the primary function of cardiac biomarkers in the diagnosis and management of heart disease?

All of the above. Signup and view all the answers

Which of the following is a reason for monitoring cardiac biomarkers over time?

All of the above. Signup and view all the answers

What is the purpose of cardiac biomarkers?

To detect and monitor myocardial damage Signup and view all the answers

Which characteristic is not essential for an effective cardiac biomarker?

Low sensitivity Signup and view all the answers

When is cardiac marker testing particularly necessary?

When myocardial infarction is suspected Signup and view all the answers

What is the primary isoenzyme of creatine kinase that indicates heart damage?

CK-MB Signup and view all the answers

Which cardiac biomarker is essential for early detection of myocardial infarction?

Creatine Kinase Signup and view all the answers

What effect does a pseudomembranous colitis have on cardiac markers?

It can falsely elevate troponin levels Signup and view all the answers

How long after a myocardial infarction do creatine kinase levels typically peak?

12-24 hours Signup and view all the answers

What can be inferred from the area under the peak slope of creatine kinase elevation?

The severity of the infarct Signup and view all the answers

Study Notes

Cardiac Biomarkers

Cardiac biomarkers are substances released from heart muscle when stressed or damaged, often as a result of myocardial infarction.
A biomarker is a substance used as an indicator of a biological state.

Aim

To relate the measurement of cardiac biomarkers in bodily fluids to the diagnosis, treatment, and monitoring of cardiac diseases.

Learning Objectives

Discuss the biochemical principles underlying cardiac diseases.
Relate biochemical markers of cardiac disease to the disease pathophysiology.
Develop knowledge of biochemical methods used in the investigation, treatment, and monitoring of cardiac disease.
Interpret laboratory results of cardiac markers in relation to other diseases.

ACS/MI: Causes and Pathophysiology

Atherosclerosis is the most common cause of acute coronary syndrome (ACS) and myocardial infarction (MI).
Risk factors include: BMI > 30, age > 65, diabetes (↑LDL and ↓HDL), hypertension, alcohol consumption, relatives' history (genetics), and tobacco smoking.
Stable angina: stable plaques, chest pain on exertion, ischemia.
Unstable angina: unstable plaques, chest pain at rest, ischemia.
Myocardial infarction: subendocardial infarct (NSTEMI), transmural infarct (STEMI), myocardial infarction: total occlusion, cell death.
Unstable angina + NSTEMI + STEMI = ACS.

The Electrocardiogram (ECG)

ST elevation: ST segment is above the PR interval.

Cardiac Biomarkers: Test Selection Criteria

Short turnover time.
High sensitivity.
High specificity.
Not influenced by sample preparation.
Not influenced by sample storage.

Why Cardiac Biomarkers?

Detecting acute coronary syndrome (ACS): early detection of myocardial ischemia, monitoring disease progression, and predicting the risk of cardiac dysfunction.
Diagnosing congestive cardiac failure due to ventricular dysfunction.

Conditions that necessitate Cardiac Marker Testing

Triaging chest pain: highly variable and subjective pain, "silent infarct" or painless infarcts.
Differentials for ACS: suspicious ECG changes, suspected myocardial infarction, patient history including patients with hypotension, dyspnea and surgical coronary revascularization.

Common Cardiac Biomarkers

Enzyme markers: Creatine kinase (CK), aspartate aminotransferase (AST), lactate dehydrogenase (LDH), gamma glutamyl transferase.
Non-enzyme markers: Troponin, myoglobin, brain natriuretic peptide (BNP).

Creatine Kinase (CK)

Catalyzes the conversion of creatine in creatine phosphate.
Increases in myocardial infarction.
Onset: 3-6 hours.
Peaks: 18-24 hours.
Duration of elevation: 36-72 hours.
Essential for early detection.
Helps detect and monitor subsequent ischemic episodes.
Severity of infarct equivalent to the area under the peak and slope of the first rise.

Iso-enzymes of Creatine Kinase (CK)

Three iso-enzymes: CK-MM, CK-BB, CK-MB.
CK-MB: predominantly in heart (40% of CK activity in cardiac muscle), <2% in other skeletal muscle.
High specificity for cardiac tissue (CK-MB).
Begins to rise 4-6 hours after onset of infarction.
Peaks at about 12 hours.
Not timely enough for thrombolytic intervention.
Returns to baseline at 24-36 hours.
Can detect re-infarcts.

Limitations of CK

Less specific relative to troponin.
Present in both skeletal and heart muscle.
Trauma or post-surgery may trigger plasma levels.
Less relevant in the confirmation of MI when the patient presents late: plasma levels normalize in <3 days.

Non-MI Causes of CK Elevation

False positive (for MI): Significant skeletal muscle injury, significant CNS damage (stroke/trauma), occasionally from GI, renal, urologic disease.
Increased CK elevations following a flatter curve, rising and disappearing at a slower pace than a cardiac source.
Significant skeletal muscle injury.
Perioperative patients without cardiac injury.
Marathon runners.
Chronic renal failure.
Hypothyroidism.
Defibrillation.
Blunt chest trauma.
Sports injuries.
Cardiac and non-cardiac surgical procedures.
Cocaine abuse (vasospasm, tachycardia).

Laboratory Diagnosis of CK-MB

CK-MB enzyme activity (after CK-MM fraction inactivation).
Immunological method (antibody detection) – more sensitive.
Reference ranges vary by age.

Cardiac Troponins

Contractile proteins found within the muscle fibers.
Help regulate contractions.
Released into the bloodstream due to injury to heart muscles.
Essential for early detection of myocardial infarction and patient monitoring.
Levels of increase reflect clinical risk.
Troponin T and I: unique amino acid sequence at the N-terminus ensuring cardiac tissue specificity.

Troponin Isoforms

Troponin complex consists of 3 regulatory proteins exclusively present in striated muscle.
Troponin C: calcium-binding subunit.
Troponin I: actomyosin ATPase inhibitory subunit.
Troponin T: tropomyosin binding subunit.

Troponin I and T

Troponin I and T are released during infarction.
Increases in levels indicate damage to heart muscles and necrosis.
Cardiac Troponin I: specific to cardiac muscle (onset within 4 hours, peak 14-24 hours, returns to normal 5-7 days).
Cardiac Troponin T: specific to cardiac muscle (onset within 6 hours, peak 72 hours, normalisation 8-10 days), early marker.

Laboratory Diagnosis of Cardiac Troponin

Immunological method: radioimmunoassay (RIA), enzyme-linked immunosorbent assay (ELISA).
Cardiac troponin elevations at lower concentrations identify patients at risk of adverse cardiac events even without MI.

Troponin Upper Reference Limit

For specific makers like cTnl, only the upper reference limit (URL) for healthy individuals is reported.
Currently, URL quoted as the 99th percentile (as recommended by the European Society of Cardiology and the American College of Cardiology).
Standard Troponin T assay URL: 97.5th: 0.01 ng/mL URL 99th: 0.04 ng/mL.

Clinical Interpretation (Using Standard Assay)

Rule out MI (< 0.04 µg/L): cardiac muscle damage unlikely – ACS.
Prognostic (0.04 and 0.08 µg/L): aids in risk stratification of patients with unstable angina or non-ST segment elevation acute coronary syndromes, with respect to relative risk of mortality, myocardial infarction, or increased probability of ischemic events requiring urgent revascularization procedures.
Diagnostic (0.50 µg/L): to aid in the diagnosis and treatment of myocardial infarction and cardiac muscle damage.

Myoglobin

Oxygen-binding protein found in the cytoplasm of striated muscle cells.
Relevant in the diagnosis of myocardial infarction.
Not specific to cardiac muscle.
Onset: few hours (2-3 hours).
Earliest marker.
Peak: 4-6 hours.
Small molecular size: excreted by the kidneys.

Laboratory Diagnosis of Myoglobin

Radioimmunoassay.
Other time-efficient methods: Latex agglutination immunoassay or fluoroimmunoassay.

Heart-type Fatty Acid Binding Protein (H-FABP)

High concentrations in the heart, liver, and intestines (fat metabolism).
9 distinct types exist.
Cardiac myocytes have high concentrations of H-FABP isoform relative to myoglobin.
Lower concentrations in skeletal muscle, brain, distant tubules of kidneys, lactating mammary glands, and placenta.
Facilitates the transport of free fatty acids (FFA) to the mitochondrial membrane.
Onset: 1.5 hours after acute MI.
Peak: 4-6 hours.
Normalizes within 20 hours.
Rapid renal clearance (relatively small proteins 15kDa).
Sustained elevation may indicate reinfarction.

Lactate Dehydrogenase (LDH)

Function: converts pyruvate to lactate.
Onset: 6-12 hours.
Peak: 1-2 days.
Returns to baseline: 6-8 days.
Reference range: 100-200 U/L.
Concentrated in the RBC.
Elevation in total LDH seen in haemolytic anaemia, muscular dystrophy, leukaemia, and necrotic conditions.

Iso-enzymes of Lactate Dehydrogenase (LDH)

LDH-1, LDH-2, LDH-3, LDH-4, LDH-5.
LDH isoform changes: Myocardial infarction (↑total LDH, ↑H4 iso-enzyme 5-10x).
The tissues found: Heart Muscle, Red Blood Cells. Brain, Liver, Skeletal Muscle.

Aspartate Aminotransferase (AST)

High in the myocardium but not specific.
Rises in myocardial infarction, hepatic, and muscle diseases.
Onset: within 12 hours.
Peaks: 24 hours.
Normalizes: 3-5 days.
Serum enzyme levels correlate to disease prognosis.
Normal range: 4-17 IU/L.

Conclusion

The medical history, physical examination, ECG, and biochemical cardiac marker measurements can be integrated into an estimation of the risk of death and nonfatal cardiac ischemic events.

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Description

Test your knowledge on Acute Coronary Syndrome (ACS) and Myocardial Infarction (MI) with this quiz. Explore key concepts such as risk factors, types of angina, and the significance of cardiac biomarkers. Perfect for medical students and healthcare professionals looking to refresh their understanding of heart diseases.