What are the differences between stable angina and unstable angina, including their pathophysiology and recommended management?

Stable vs. Unstable Angina: Key Differences

Unstable angina is a medical emergency occurring at rest or with minimal exertion and lasting >20 minutes, while stable angina is predictable chest discomfort triggered by exertion and relieved within minutes by rest or nitroglycerin.

Pathophysiology

Stable Angina

• Results from fixed atherosclerotic coronary stenosis causing supply-demand mismatch during increased myocardial oxygen consumption 1
• The underlying mechanism involves chronic, stable atherosclerotic plaques that limit coronary blood flow during exertion or stress 1
• Represents a chronic, predictable state where myocardial ischemia occurs only when oxygen demand exceeds supply 1

Unstable Angina

• Represents acute coronary syndrome with "clear evidence of important reversible myocardial ischemia" occurring without stimuli to increased oxygen consumption 2
• Involves acute plaque rupture, thrombosis, and dynamic coronary obstruction rather than fixed stenosis alone 3
• Lies on the spectrum between stable angina and acute myocardial infarction, representing a critical phase of coronary disease 2

Clinical Presentation Patterns

Stable Angina Characteristics

• Predictable pattern: Discomfort occurs with specific levels of exertion and resolves with rest 1
• Duration: Brief episodes lasting <10 minutes in most cases 1
• Location: Substernal chest pressure, tightness, or heaviness that may radiate to jaw, shoulder, back, or arms 1
• Relief: Rapidly relieved within minutes by rest or sublingual nitroglycerin 1
• Triggers: Consistently provoked by exertion, walking uphill, cold weather, heavy meals, or emotional stress 1

Unstable Angina Presentation (Three Distinct Patterns)

• Rest angina: Prolonged episodes lasting >20 minutes occurring without provocation, representing 80% of presentations 3
• Crescendo angina: Previously stable angina that progressively worsens in severity, frequency, and occurs at lower exertion thresholds over ≤4 weeks 3
• New-onset severe angina: Recent symptoms (within 2 months) causing marked limitation of ordinary physical activity, meeting Canadian Cardiovascular Society Class III criteria 3

Diagnostic Features

Stable Angina

• Physical examination typically normal between episodes 1
• ECG may show ST-segment changes during symptomatic episodes that resolve with rest 1
• Cardiac biomarkers (troponin) remain normal 1

Unstable Angina

• Physical examination most often completely normal, though pulmonary edema indicates high-risk disease 3
• ECG findings: ST-segment depression >1 mm in two or more contiguous leads during symptoms is the most reliable indicator 3
• Cardiac biomarkers: Troponin T or I are preferred markers and should be measured in all patients; elevated levels (>0.1 ng/mL) indicate minimal myocardial damage and unfavorable outcomes 3
• Approximately 5% may have completely normal ECG even during symptoms 2

Prognosis and Risk

Stable Angina

• Annual mortality rate ranges from 0.9-1.4% with non-fatal MI incidence of 0.5-2.6% 1
• Prognosis varies up to 10-fold depending on baseline clinical, functional, and anatomical factors 1
• Two-year incidence of non-fatal MI and coronary death: 14.3% and 5.5% in men, 6.2% and 3.8% in women 1

Unstable Angina

• Substantially higher short-term risk for acute coronary events compared to stable angina 1, 2
• TIMI risk score (0-7 points) predicts adverse outcomes ranging from 5% (score 0-1) to 41% (score 6-7) 3
• High-risk features include: accelerating symptoms in preceding 48 hours, prolonged rest pain >20 minutes, and elevated troponin levels 3
• Recent studies show acute infarction occurs in <15.5% and death in <2% with modern management 4

Management Approach

Stable Angina Management

• Lifestyle modifications: Smoking cessation, Mediterranean diet, weight reduction, regular physical activity within limitations 1
• Symptom relief: Sublingual nitroglycerin for acute episodes; prophylactic nitrate before predictable exertion 1
• First-line antianginals: Beta-blockers or calcium channel antagonists for symptom control 5
• Prognostic therapy: Low-dose aspirin and statins to prevent cardiovascular events 5
• Patients should seek medical attention if angina persists >10-20 minutes despite rest and nitroglycerin 1

Unstable Angina Management

• Immediate hospitalization with bed rest required due to high-risk nature 1, 4
• Antiplatelet therapy: Aspirin should be considered routine treatment 6
• Antianginal therapy: Beta-blockers, particularly in combination with calcium antagonists, have evidence for improving prognosis 6
• Anticoagulation: Heparin should be considered as routine treatment 6
• Risk stratification: TIMI score assessment and troponin measurement mandatory for all patients 3
• Goal is prevention of myocardial infarction and death, not just symptom relief 6

Critical Clinical Pitfalls

• Atypical presentations are common in younger patients (25-40 years), elderly (>75 years), diabetics, and women, who may present with epigastric pain, indigestion, or dyspnea rather than classic chest pain 3
• Patients with unstable angina may have non-obstructive coronary disease or normal angiography, particularly women 2
• Do not discharge patients with rest angina or crescendo pattern even if examination and initial ECG are normal—these require urgent evaluation and hospitalization 1, 3
• Stable angina patients should be warned about hypotension when first using sublingual nitroglycerin and advised to sit down 1