What are the definitions and management guidelines for stable versus unstable angina?

Definitions and Clinical Differentiation of Stable versus Unstable Angina

Stable angina is predictable chest discomfort triggered by exertion and relieved by rest within 10 minutes, while unstable angina presents as rest pain lasting >20 minutes, rapidly worsening symptoms over ≤4 weeks, or new severe angina causing marked activity limitation—the latter representing an acute coronary syndrome requiring immediate hospitalization. 1

Stable Angina: Definition and Characteristics

Stable angina is a clinical syndrome of substernal chest discomfort provoked by exertion or emotional stress and relieved by rest or nitroglycerin. 1

Clinical Features

• Substernal pressure, tightness, or heaviness that may radiate to the jaw, shoulder, back, or arms 1
• Duration typically <10 minutes, with most episodes even briefer 1
• Predictable triggers: walking uphill, climbing stairs rapidly, exertion after meals, cold weather, emotional stress, or first hours after awakening 1
• Rapid relief with rest or sublingual nitroglycerin 1

Classification of Chest Pain

Typical angina meets all three criteria: (1) substernal chest discomfort of characteristic quality and duration, (2) provoked by exertion or emotional stress, and (3) relieved by rest and/or nitroglycerin 1

Atypical angina meets only two of these characteristics, while non-cardiac chest pain meets one or none 1

Severity Grading (Canadian Cardiovascular Society)

• Class I: Ordinary activity does not cause angina; symptoms only with strenuous/prolonged exertion 1
• Class II: Slight limitation of ordinary activity; angina with rapid walking, climbing stairs, or exertion in cold/stress 1
• Class III: Marked limitation; angina walking 1-2 blocks on level ground or one flight of stairs at normal pace 1
• Class IV: Inability to perform any physical activity without discomfort; angina may occur at rest 1

Prognosis

Annual mortality ranges from 0.9-1.4% with non-fatal MI incidence of 0.5-2.6%, though individual prognosis varies up to 10-fold based on clinical and anatomical factors 1

Unstable Angina: Definition and Presentations

Unstable angina is associated with plaque rupture and carries significantly higher short-term risk of acute coronary events. 1 It presents in three distinct patterns:

Three Clinical Presentations

1. Rest angina (most common, ~80% of cases): Characteristic chest pain occurring at rest and lasting prolonged periods up to or exceeding 20 minutes 1

2. Crescendo angina: Previously stable angina that progressively increases in severity, frequency, and occurs at lower exertion thresholds over a short period of 4 weeks or less 1

3. New-onset severe angina: Recent onset (within 2 months) of severe angina causing marked limitation of ordinary activity (equivalent to CCS Class III) 1

Key Distinguishing Features from Stable Angina

Unstable angina represents reversible myocardial ischemia occurring without increased oxygen demand, unlike stable angina's supply-demand mismatch during exertion 2

• Pain duration >20 minutes at rest is characteristic 1
• Does not follow predictable patterns related to specific activity levels 2
• May not be fully relieved by rest or nitroglycerin 1
• Occupies the clinical spectrum between stable angina and acute myocardial infarction 2

Diagnostic Evaluation

Laboratory Testing

If clinical suspicion of instability exists, measure troponin or CK-MB to exclude myocardial injury. 1 Troponin elevations >0.1 ng/mL indicate minimal myocardial injury and predict worse outcomes in unstable angina. 2

Electrocardiographic Findings

• Stable angina: May show transient ST-segment changes during symptomatic periods that resolve with rest 2
• Unstable angina: ST-segment depression >1 mm in two or more contiguous leads during symptoms is the most reliable ECG indicator 2

Critical pitfall: Approximately 5% of unstable angina patients may have completely normal ECG even during symptomatic episodes 2

Physical Examination

• Stable angina: Usually normal between episodes 2
• Unstable angina: Often completely normal; presence of pulmonary edema signals high-risk presentation 2

Management Approach

Stable Angina Management

Medical therapy is the foundation, with revascularization reserved for inadequate symptom control or high-risk anatomy 1

• Sublingual nitroglycerin for acute episodes; patients should sit to avoid hypotension 1, 2
• Prophylactic nitrates before predictable exertion 1
• Seek medical attention if pain persists >10-20 minutes despite rest and nitroglycerin 1
• Aspirin 75 mg daily and statin therapy for all patients unless contraindicated 1
• Beta-blocker first-line for anti-anginal effect, or calcium channel blocker/long-acting nitrate as alternatives 1

Unstable Angina Management

Immediate hospitalization with bed rest and continuous ECG monitoring is mandatory due to high short-term risk of acute coronary events 1, 2

Unstable angina is managed according to acute coronary syndrome guidelines, not stable angina protocols 1

Critical Clinical Pitfalls

Never discharge patients presenting with rest angina or crescendo pattern even if initial examination and ECG are normal—these patients require hospitalization and ACS management 2

Atypical presentations are common in women, elderly, diabetics, and younger adults, who may present with epigastric pain, indigestion, or dyspnea rather than classic chest pain 2

Women with unstable angina may have non-obstructive coronary disease or normal angiography, complicating diagnosis 2

Non-anginal pain lacks characteristic qualities, may involve only small portion of left hemithorax, lasts hours to days, is not relieved by nitroglycerin (except esophageal spasm), and may be provoked by palpation 1