What is the difference between unstable angina and stable angina?

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Last updated: January 12, 2026 • View editorial policy

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Stable vs. Unstable Angina: Key Differences

Stable angina is predictable chest pain that occurs with exertion and has been present for ≥4 weeks, while unstable angina is unpredictable chest pain occurring at rest or with minimal exertion that has been present for <2 weeks—representing an acute coronary syndrome requiring urgent evaluation. 1

Stable Angina Characteristics

Stable angina is defined by the following features:

  • Predictable pattern: Occurs with increasing amounts of stress or physical activity 1
  • Duration: Present for at least 4 weeks without recent change in frequency or pattern 1, 2
  • Relief: Resolves with cessation of activity and/or sublingual nitroglycerin 2
  • Exertional trigger: Symptoms are consistently related to level of physical exertion 1

The pain is typically aggravated by exertion or emotional stress and follows a reproducible pattern that patients can anticipate. 1

Unstable Angina Characteristics

Unstable angina represents an acute coronary syndrome with three principal presentations:

Three Clinical Patterns

  • Rest angina: Prolonged anginal pain (typically ≥20 minutes) occurring at rest without provocation 3, 2
  • New-onset severe angina: Recent development (within 2 months) of angina with at least Canadian Cardiovascular Society Class III severity, causing marked limitation of ordinary physical activity 3
  • Crescendo angina: Previously stable angina that becomes distinctly more frequent, longer in duration, or occurs with lower threshold (increased by ≥1 CCS class to at least CCS Class III) 3

Temporal Definition

  • Duration: Present for less than 2 weeks 1
  • Pattern: Occurs without stress or activity, or with decreasing stress/activity compared to previous stable pattern 1

Critical Distinguishing Features

Pathophysiology

  • Stable angina: Fixed coronary stenosis causing supply-demand mismatch during exertion 1
  • Unstable angina: Acute coronary plaque rupture, erosion, or thrombosis with variable degrees of superimposed thrombosis and distal embolization 3

Biomarkers: The Defining Difference from NSTEMI

The only difference between unstable angina and NSTEMI is the presence or absence of detectable myocardial necrosis. 3

  • Unstable angina: Troponin levels remain below the 99th percentile upper reference limit on at least 2 samples collected ≥6 hours apart 3
  • NSTEMI: Elevated troponin indicating myocardial necrosis 3

ECG Findings

Unstable angina may show:

  • ST-segment depression ≥0.5 mm in two or more contiguous leads 3
  • T-wave inversion ≥1 mm in leads with predominant R waves 3
  • Transient ST-segment elevation between 0.6-1 mm 3
  • Important caveat: Approximately 5% of patients have completely normal ECG even during symptoms 3, 2

Stable angina typically shows:

  • Normal ECG at rest or chronic changes from prior events 1
  • Reversible ST-segment changes only during exercise testing 1

Risk Stratification

Stable Angina Risk

Patients with stable angina have predictable symptoms and lower short-term risk when the pattern remains unchanged. 1

Unstable Angina Risk

Unstable angina represents a critical phase of coronary disease with variable but significant short-term risk. 3, 2

High-risk features include:

  • Acceleration of ischemic symptoms 2
  • Prolonged rest pain 2
  • Pulmonary edema 2
  • New mitral regurgitation murmur 2
  • Significant electrocardiographic changes 2

Compared to NSTEMI patients, those with unstable angina have substantially lower risk of death, less benefit from intensified antiplatelet therapy, and less benefit from early invasive strategy—but still require urgent evaluation. 3

Common Pitfalls

  • Serial troponin measurements are mandatory: A single negative troponin is insufficient; obtain at least 2 samples ≥6 hours apart to definitively exclude NSTEMI 3
  • Atypical presentations are common: Elderly patients, diabetics, and those with chronic kidney disease may present with atypical symptoms such as dyspnea, epigastric pain, or recent-onset indigestion 3
  • Patients can progress: Unstable angina can evolve into NSTEMI during the acute presentation, requiring repeat biomarker assessment 3
  • High-sensitivity troponin impact: Modern high-sensitivity troponin assays have resulted in a 20% relative increase in MI detection, with many patients previously classified as unstable angina now diagnosed with NSTEMI 3

References

1
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

2
Guideline

Unstable Angina Characteristics and Diagnosis

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2025

3
Guideline

Unstable Angina 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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