Stable vs unstable angina
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"stable angina" OR "unstable angina" AND "acute coronary syndrome"
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Stable vs. Unstable Angina
Overview
Angina pectoris is intermittent chest discomfort caused by transient, reversible myocardial ischemia - insufficient to cause myocyte necrosis. It results from ischemia-induced release of adenosine, bradykinin, and other molecules that stimulate autonomic afferent nerves. Three variants are recognized: stable, unstable, and Prinzmetal (variant) angina.
The key clinical distinction is that unstable angina is part of the acute coronary syndrome (ACS) spectrum and carries a much higher short-term risk of MI and death, requiring urgent evaluation and management.
Pathophysiology
| Stable Angina | Unstable Angina | |
|---|---|---|
| Mechanism | Fixed atherosclerotic stenosis causing supply-demand mismatch | Plaque rupture/erosion → platelet aggregation → partial (subtotal) thrombus → subtotal occlusion |
| Plaque status | Stable plaque, no disruption | Disrupted/eroded plaque with superimposed thrombus, distal embolization, and/or vasospasm |
| Oxygen supply-demand | Demand exceeds supply (exertion raises demand beyond fixed supply) | Supply suddenly reduced by thrombus at rest |
| Myocyte necrosis | None | No biomarker elevation (if elevated troponin → NSTEMI) |
| Thrombus | Absent or stable | Present - partial/dynamic occlusion |
The precipitating event in nearly all unstable angina cases is coronary arterial plaque rupture or erosion with subsequent platelet aggregation and thrombus formation, leading to subtotal occlusion. Importantly, the majority of unstable angina cases now show evidence of myocyte injury on sensitive assays.
- Robbins & Kumar Basic Pathology, p. 462
- Goldman-Cecil Medicine, Chapter 57
Clinical Features
Stable Angina
- Trigger: Physical exertion, emotional stress, cold, meals, tachycardia - any increase in myocardial O₂ demand
- Pattern: Predictable, reproducible episodes; same triggers, same duration
- Duration: Typically 2-5 minutes
- Character: Heaviness, pressure, squeezing, smothering, or choking substernal sensation ("Levine's sign" - patient places clenched fist over sternum)
- Radiation: Left shoulder, both arms (ulnar aspects), back, interscapular region, jaw, teeth, epigastrium
- Relief: Rest (reduces demand) or sublingual nitroglycerin within minutes
- NOT typical: Pain below the umbilicus, above the mandible, or radiating to trapezius (latter suggests pericarditis)
Males make up ~70% of all angina patients, and an even greater proportion under age 50. Women may present with atypical features - jaw, neck, throat pain, dyspnea, and fatigue - though there is substantial symptom overlap between sexes.
- Harrison's 22E (2025)
Unstable Angina
Any one of the following defines unstable angina:
- New-onset angina - CCS class III or IV severity on first presentation
- Crescendo (accelerating) angina - previously stable angina that is now more frequent, more severe, longer-lasting, or provoked by less exertion
- Rest angina - chest discomfort occurring at rest, especially lasting >20 minutes
- Sudden dyspnea equivalent to ischemia at rest
Per Goldman-Cecil Medicine: "The patient with unstable angina has cardiac chest pain that is new, worsening (more severe, prolonged, or frequent), or occurring at rest, without serologic evidence of myocyte necrosis - no elevation of serum troponin."
Low-risk unstable angina features (can be managed more conservatively): age <70 years, exertional pain lasting <20 minutes, pain not rapidly accelerating, normal or unchanged ECG, no elevation of cardiac biomarkers.
- Fuster and Hurst's The Heart, 15th Ed.
Key Differentiating Features
| Feature | Stable Angina | Unstable Angina |
|---|---|---|
| Onset | Predictable, with exertion | New, worsening, or at rest |
| Trigger | Consistent threshold (e.g., climbing 2 flights) | Lower threshold than before, or no trigger |
| Duration | 2-5 min | Often >10-20 min |
| Relief | Rest or 1-2 NTG tablets | May not respond to rest or NTG |
| Biomarkers | Normal | Normal (if elevated → NSTEMI) |
| ECG | Normal or old changes at rest; ST depression/T-wave changes during episode | May show new ST depression, T-wave inversion at rest |
| Plaque | Stable | Ruptured/eroded |
| ACS | No | Yes (part of NSTE-ACS) |
| Hospitalization | Usually not required acutely | Required for monitoring and treatment |
ACS Spectrum
Unstable angina sits within the non-ST-elevation ACS (NSTE-ACS) continuum:
Unstable Angina ──► NSTEMI ──► STEMI
(no troponin rise) (troponin ↑, (troponin ↑,
no ST elev.) ST elevation)
The distinction between unstable angina and NSTEMI is made purely on troponin - the clinical presentation can be identical. Modern high-sensitivity troponin assays have nearly eliminated "troponin-negative ACS," meaning most previously-labeled unstable angina cases now qualify as NSTEMI.
- Goldman-Cecil Medicine, Chapter 57
Canadian Cardiovascular Society (CCS) Classification (Stable Angina)
| Class | Description |
|---|---|
| I | Angina only with strenuous/prolonged exertion; ordinary activity does not cause angina |
| II | Slight limitation of ordinary activity (e.g., angina on walking >2 blocks on level ground) |
| III | Marked limitation (angina on walking 1-2 blocks or climbing 1 flight) |
| IV | Inability to carry on any activity without discomfort; angina may be at rest |
CCS III-IV at first presentation = new-onset unstable angina by definition.
Management Principles
Stable Angina
- Risk factor modification: Hypertension, dyslipidemia, diabetes, smoking cessation, weight loss
- Anti-ischemic drugs:
- Beta-blockers (first-line: reduce HR and O₂ demand)
- Long-acting nitrates
- Calcium channel blockers
- Ranolazine (add-on)
- Antiplatelet: Aspirin 75-100 mg daily
- Statin: High-intensity statin for all patients with IHD
- Revascularization (PCI/CABG): For symptoms refractory to medical therapy or high-risk anatomy
- Cardiac rehabilitation: Exercise-based programs improve outcomes (Cochrane 2018, CD012786)
Unstable Angina (NSTE-ACS)
- Hospitalization - continuous ECG monitoring
- Antiplatelet: Dual antiplatelet therapy (aspirin + P2Y12 inhibitor - clopidogrel, ticagrelor, or prasugrel)
- Anticoagulation: Unfractionated heparin, LMWH (enoxaparin), fondaparinux, or bivalirudin
- Anti-ischemic: Beta-blockers, nitrates (IV if rest pain), CCBs
- Risk stratification (TIMI, GRACE score) to guide early invasive vs. conservative strategy
- Coronary angiography +/- PCI: Early invasive strategy for high-risk patients (recurrent ischemia, troponin rise, new ST changes, hemodynamic instability)
- Statin: High-intensity, initiated immediately
Prognosis
- Stable angina: risk of MI ~2-3%/year; mortality influenced heavily by LV function and extent of CAD
- Unstable angina: short-term MACE risk 10-15% at 30 days without treatment; prognosis determined by GRACE/TIMI risk score
- ~1/3 of ACS hospitalizations end in MI; the remainder are unstable angina/NSTEMI - Tintinalli's Emergency Medicine
Prinzmetal (Variant) Angina - for completeness
- Occurs at rest, caused by coronary artery spasm (not plaque rupture)
- Can affect angiographically normal vessels
- ECG shows transient ST elevation (not depression) during pain
- Responds promptly to vasodilators (nitroglycerin, calcium channel blockers)
- Robbins & Kumar Basic Pathology, p. 460
Sources: Harrison's Principles of Internal Medicine 22E (2025) | Goldman-Cecil Medicine | Robbins & Kumar Basic Pathology | Fuster and Hurst's The Heart 15th Ed.
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