Stable Angina, Unstable Angina, and Myocardial Infarction

1. Overview

1. Unstable angina (UA)
2. Non-ST-elevation myocardial infarction (NSTEMI)
3. ST-elevation myocardial infarction (STEMI)

2. Stable Angina

Definition

Pathophysiology

• Caused mainly by a fixed, stable atherosclerotic narrowing of a coronary artery.
• During exertion, heart rate and oxygen demand rise.
• The narrowed artery cannot increase blood supply adequately, producing ischemia.
• The plaque is relatively less prone to rupture or fissure, hence symptoms are predictable. The Washington Manual of Medical Therapeutics, p. 115.

Clinical features

• Retrosternal pressure, heaviness, squeezing, or tightness
• May radiate to left arm, shoulder, neck, jaw, back, or epigastrium
• Triggered by exercise, climbing stairs, cold weather, heavy meals, or stress
• Lasts usually a few minutes
• Improves with rest or sublingual nitroglycerin
• Dyspnea, fatigue, nausea, or sweating may occur, especially in older adults, women, and people with diabetes

ECG and biomarkers

• ECG may be normal at rest.
• Exercise-induced ST-segment depression may occur.
• Troponin is normal, because there is no myocardial necrosis.

Management principles

• Lifestyle and risk-factor control: stop smoking, manage diabetes/hypertension, exercise and diet guidance.
• Antiplatelet and lipid-lowering treatment when indicated.
• Antianginal drugs: beta-blockers, calcium-channel blockers, nitrates, and sometimes ranolazine.
• Coronary angiography and revascularization with PCI or CABG may be required for persistent symptoms or high-risk coronary anatomy.

3. Unstable Angina

Definition

• New onset and severe
• Crescendo: increasingly frequent, severe, or prolonged
• Occurring at rest or with minimal activity

Pathophysiology

• Usually due to rupture or erosion of a vulnerable atherosclerotic plaque.
• Platelet activation and thrombus formation cause sudden reduction in coronary blood flow.
• The obstruction is often incomplete or intermittent.

Clinical features

• More severe, prolonged, or frequent than previous angina
• Occurs with less exertion than before or at rest
• Often lasts more than 20 minutes
• May not respond fully to rest or nitroglycerin
• It is an emergency because it may progress to MI.

ECG and biomarkers

• ECG may show ST depression, T-wave inversion, or may be normal.
• Troponin remains normal on serial testing.
• If troponin becomes elevated, the diagnosis changes from unstable angina to NSTEMI.

Management principles

• Immediate clinical assessment, serial ECGs, and serial high-sensitivity troponin.
• Antiplatelet therapy, anticoagulation, anti-ischemic treatment, and risk stratification.
• Early invasive coronary angiography/PCI for high-risk patients.
• Avoid thrombolytic therapy unless the patient has STEMI or another specific reperfusion indication.

4. Myocardial Infarction (MI)

Definition

Types of MI in ACS

A. NSTEMI

• Partial or transient coronary occlusion
• No persistent ST-segment elevation
• Troponin elevated
• ECG may show ST depression or T-wave inversion, but can occasionally be nondiagnostic.

B. STEMI

• Usually a sudden, complete and persistent coronary occlusion
• Persistent ST-segment elevation in relevant ECG leads, or a STEMI-equivalent pattern
• Troponin elevated
• Requires immediate reperfusion, preferably primary PCI.

Clinical features

• Severe, persistent central chest pressure or pain, usually lasting over 20 to 30 minutes
• Radiation to arm, jaw, neck, shoulder, back, or epigastrium
• Sweating, nausea, vomiting, dyspnea, palpitations, weakness, anxiety, or syncope
• Some patients, particularly older adults, women, and those with diabetes, can present atypically with breathlessness, fatigue, indigestion-like discomfort, or collapse.

Complications

• Arrhythmias, especially ventricular tachycardia/fibrillation
• Acute heart failure and pulmonary edema
• Cardiogenic shock
• Papillary muscle dysfunction or rupture causing acute mitral regurgitation
• Ventricular septal rupture
• Free-wall rupture and cardiac tamponade
• Pericarditis
• Ventricular aneurysm and mural thrombus

Management principles

• Emergency ECG and serial troponin testing.
• Aspirin plus an appropriate P2Y12 inhibitor and anticoagulation, selected by clinicians according to presentation and bleeding risk.
• High-intensity statin and secondary prevention measures.
• STEMI: immediate reperfusion, preferably primary PCI. Fibrinolysis may be considered if timely PCI is unavailable and there are no contraindications.
• NSTEMI: risk-stratified invasive evaluation rather than routine immediate fibrinolysis.
• Cardiac rehabilitation, smoking cessation, blood-pressure/lipid/diabetes control, and long-term evidence-based medicines after discharge.

5. Key Differences

6. Easy Memory Aid

• Stable angina: predictable pain with exertion, relieved by rest.
• Unstable angina: unexpected pain, worsening pain, or pain at rest, but troponin negative.
• NSTEMI: ischemic pain plus raised troponin, without ST elevation.
• STEMI: raised troponin with ST elevation, usually from complete coronary occlusion and requiring urgent reperfusion.

7. When to Seek Emergency Care