What conditions fall under Acute Coronary Syndrome (ACS)?

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Last updated: September 13, 2025 • View editorial policy

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What Conditions Fall Under Acute Coronary Syndrome (ACS)

Acute Coronary Syndrome (ACS) includes three distinct clinical conditions: unstable angina (UA), non-ST-segment elevation myocardial infarction (NSTEMI), and ST-segment elevation myocardial infarction (STEMI). 1, 2

Classification of ACS Conditions

1. Unstable Angina (UA)

  • Characterized by myocardial ischemia without detectable myocardial necrosis (normal cardiac biomarkers)
  • Clinical features:
    • Rest angina (chest pain occurring at rest)
    • New-onset severe angina
    • Increasing pattern of previously stable angina
    • ECG may show transient ST-segment depression or T-wave changes
    • Duration often >20 minutes
  • Pathophysiology: Plaque disruption with non-occlusive thrombus

2. Non-ST-Segment Elevation Myocardial Infarction (NSTEMI)

  • Characterized by myocardial ischemia with evidence of myocardial necrosis
  • Clinical features:
    • Prolonged chest pain/discomfort
    • ECG shows ST-segment depression, T-wave inversion, or may be normal
    • Elevated cardiac biomarkers (troponin)
    • Duration typically >20 minutes
  • Pathophysiology: Partial coronary artery occlusion leading to subendocardial ischemia and infarction

3. ST-Segment Elevation Myocardial Infarction (STEMI)

  • Characterized by myocardial ischemia with evidence of myocardial necrosis
  • Clinical features:
    • Prolonged chest pain/discomfort
    • ECG shows persistent ST-segment elevation or new left bundle branch block
    • Elevated cardiac biomarkers (troponin)
    • Duration typically >20 minutes
  • Pathophysiology: Complete coronary artery occlusion leading to transmural myocardial ischemia and infarction

Distinguishing Features Between ACS Types

Feature Unstable Angina NSTEMI STEMI
ECG Changes Transient ST depression or T-wave changes ST depression, T-wave inversion ST-segment elevation
Cardiac Biomarkers Normal Elevated Elevated
Coronary Occlusion Non-occlusive thrombus Partially occlusive thrombus Completely occlusive thrombus
Myocardial Damage No myonecrosis Subendocardial necrosis Transmural necrosis
Mortality Risk Lower Intermediate Higher

Pathophysiology Common to All ACS

All three conditions share a common pathophysiological substrate 1, 2:

  • Atherosclerotic plaque rupture or erosion
  • Exposure of plaque contents to circulation
  • Activation of coagulation cascade
  • Thrombus formation
  • Compromised coronary blood flow
  • Myocardial ischemia

Less Common Causes of ACS

While atherosclerotic plaque disruption is the most common cause, other less common causes of myocardial ischemia that may present as ACS include 1, 2:

  • Coronary artery spasm (Prinzmetal's angina)
  • Coronary embolism
  • Coronary artery dissection
  • Myocardial oxygen supply-demand mismatch (Type 2 MI)
  • Stress (Takotsubo) cardiomyopathy

Clinical Importance

Understanding the spectrum of ACS is critical for proper risk stratification and management decisions. The distinction between these conditions guides:

  • Need for immediate reperfusion therapy
  • Selection of antiplatelet and anticoagulant regimens
  • Timing of invasive coronary angiography
  • Long-term secondary prevention strategies

Common Pitfalls in ACS Classification

  • Biomarker interpretation: With increasingly sensitive troponin assays, unstable angina is becoming less common as more patients are classified as NSTEMI 1
  • Dynamic nature: The pathophysiology of ACS can be dynamic, and patients can rapidly progress from one clinical condition to another 1
  • ECG limitations: A normal ECG does not exclude ACS; serial ECGs and biomarker measurements are essential 2
  • Atypical presentations: Women, elderly patients, and those with diabetes may present with atypical symptoms, leading to delayed diagnosis 2

The classification of ACS into these three entities allows for appropriate risk stratification and guides evidence-based management strategies aimed at reducing morbidity and mortality.

References

1
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

2
Guideline

Acute Coronary Syndrome (ACS) Diagnosis and Management

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2025

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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