How do I differentiate between Stable Angina (SA), Unstable Angina (UA), ST-Elevation Myocardial Infarction (STEMI), and Non-ST-Elevation Myocardial Infarction (NSTEMI) based on onset, symptoms, and pathogenesis?

Differentiation Between Stable Angina, Unstable Angina, STEMI, and NSTEMI

The key differences between Stable Angina, Unstable Angina, STEMI, and NSTEMI lie in their onset patterns, symptom presentation, and underlying pathophysiological mechanisms, with STEMI representing the most severe form requiring immediate reperfusion therapy.

Pathogenesis

Stable Angina

• Mechanism: Fixed atherosclerotic narrowing of coronary arteries causing predictable ischemia with exertion
• Pathology: Stable plaque with >70% stenosis causing supply-demand mismatch only during increased demand
• No plaque disruption or acute thrombosis

Unstable Angina (UA)

• Mechanism: Disruption or erosion of atherosclerotic plaque with partial/transient thrombosis 1
• Pathology: Subtotally occlusive thrombus on pre-existing plaque or dynamic obstruction (coronary spasm) 1
• No myocardial necrosis: Biomarkers remain normal despite ischemia 2

NSTEMI

• Mechanism: Plaque rupture with subtotal occlusion or distal embolization 1
• Pathology: Partial/subtotal coronary occlusion with sufficient ischemia to cause myocardial necrosis 2
• Myocardial damage: Detectable cardiac biomarkers (troponin) indicating cell death 1

STEMI

• Mechanism: Complete thrombotic occlusion of a coronary artery 2
• Pathology: Total occlusion with minimal/no collateral circulation 2
• Extensive myocardial damage: Transmural infarction with ST-segment elevation on ECG 2

Onset Pattern

Stable Angina

• Predictable pattern: Occurs with specific level of exertion
• Consistent threshold: Similar activities consistently trigger symptoms
• Brief episodes: Typically resolves within 5 minutes with rest or nitroglycerin 1

Unstable Angina

• New onset: Severe angina of recent onset (≤2 months)
• Accelerating pattern: Previously diagnosed angina that has become more frequent, longer in duration, or occurs with less exertion
• Rest angina: Angina occurring at rest or with minimal exertion, usually lasting >20 minutes 1

NSTEMI

• Abrupt onset: Often occurs at rest or with minimal exertion
• Prolonged symptoms: Typically >20 minutes, not fully relieved by rest or nitroglycerin
• May have crescendo pattern: Worsening of previously stable symptoms 1

STEMI

• Sudden, severe onset: Typically dramatic presentation
• Persistent symptoms: Continuous chest pain not relieved by rest or nitroglycerin
• Duration >30 minutes: Often unremitting without intervention 2

Symptoms

Stable Angina

• Predictable chest discomfort: Deep, poorly localized chest or arm discomfort
• Triggered by: Physical exertion, emotional stress, cold weather, heavy meals
• Relief with rest: Symptoms resolve within 5 minutes of rest or nitroglycerin 1

Unstable Angina

• Similar to stable angina but more severe and prolonged
• May occur at rest: Not necessarily triggered by exertion
• Crescendo pattern: Increasing frequency, intensity, or duration 1
• No biomarker elevation: Distinguishes it from NSTEMI 2

NSTEMI

• Similar presentation to unstable angina:
  • Central/substernal compression or crushing chest pain
  • Pressure, tightness, heaviness, burning sensation
  • Radiation to neck, jaw, shoulders, back, or arms 1
• Associated symptoms: Dyspnea, diaphoresis, nausea/vomiting 1
• Atypical presentations more common in:
  • Women
  • Elderly patients
  • Diabetic patients (may have silent ischemia) 1

STEMI

• Intense, persistent chest pain: Often described as crushing or pressure-like
• Widespread radiation: Often radiates to jaw, neck, arms, back
• Associated symptoms: Prominent dyspnea, diaphoresis, nausea/vomiting, lightheadedness
• Cardiogenic shock symptoms: May include hypotension, pulmonary edema in extensive infarcts 2

Diagnostic Findings

Stable Angina

• ECG: Normal at rest or minor ST-T changes during pain
• Biomarkers: Normal troponin levels
• Stress testing: Positive for inducible ischemia

Unstable Angina

• ECG: May show transient ST depression, T-wave inversion, or be normal 2
• Biomarkers: Normal cardiac troponin (key distinguishing feature from NSTEMI) 1, 2
• Coronary angiography: Often shows significant stenosis or plaque disruption

NSTEMI

• ECG: ST depression, T-wave inversion, or may be normal initially 2
• No persistent ST elevation: Key distinguishing feature from STEMI
• Biomarkers: Elevated cardiac troponin (>99th percentile upper reference limit) 1
• Angiography: Usually subtotal occlusion or multiple severe stenoses

STEMI

• ECG: Persistent ST-segment elevation in anatomically contiguous leads 2
• Biomarkers: Elevated cardiac troponin (may not be elevated initially)
• Angiography: Complete occlusion of an epicardial coronary artery 2

Clinical Pearls and Pitfalls

Important Considerations

1. Biomarkers are critical: The distinction between UA and NSTEMI is based solely on cardiac biomarkers (troponin) 1

2. Atypical presentations are common in:

   • Women (more likely to present with atypical symptoms) 1
   • Elderly (may present with dyspnea, confusion, or fatigue) 1
   • Diabetics (may have silent ischemia due to autonomic neuropathy) 1

3. Delayed presentations: Patients with NSTEMI without chest pain delay seeking care longer (average 7.9 vs 5.3 hours) and have higher mortality (23.3% vs 9.3%) 1

4. Don't rely solely on ECG: Normal initial ECG doesn't exclude ACS; serial ECGs and biomarkers are essential 2

5. Symptoms that are NOT characteristic of cardiac ischemia:

   • Pleuritic pain (sharp pain with breathing)
   • Pain localized to a fingertip
   • Pain reproduced by movement or palpation
   • Very brief episodes lasting seconds
   • Pain radiating to lower extremities 1

Risk Stratification

• All patients with suspected ACS should have:

  • 12-lead ECG within 10 minutes of presentation
  • Initial and serial cardiac biomarkers (troponin)
  • Risk stratification using validated tools (TIMI, GRACE scores) 2

• High-risk features warranting urgent intervention:

  • Recurrent/ongoing chest pain
  • Dynamic ECG changes
  • Elevated troponin
  • Hemodynamic instability
  • Ventricular arrhythmias 1

Summary Table

Feature	Stable Angina	Unstable Angina	NSTEMI	STEMI
Onset	Predictable with exertion	New onset, accelerating, or at rest	Often sudden, at rest	Sudden, severe
Duration	<5 minutes	>20 minutes	>20 minutes	>30 minutes
Relief	Rest/NTG	Partial/delayed with rest/NTG	Limited relief with rest/NTG	No relief without intervention
ECG	Normal at rest	May show ischemic changes	ST depression/T-wave inversion	ST-segment elevation
Biomarkers	Normal	Normal	Elevated	Elevated
Pathology	Fixed stenosis	Plaque disruption with partial/transient thrombosis	Subtotal occlusion	Complete occlusion
Myocardial Necrosis	Absent	Absent	Present	Present (transmural)