Myocardial infarction

Specialties > Emergency medicine and intensive care

Background knowledge 🧠

Definition

Myocardial infarction (MI) refers to the irreversible necrosis of heart muscle secondary to prolonged ischemia.
Commonly known as a heart attack.
Usually results from the rupture of an atherosclerotic plaque in a coronary artery.

Epidemiology

MI is a leading cause of death worldwide, particularly in developed countries.
In the UK, over 100,000 hospital admissions occur annually due to MI.
Incidence increases with age; higher in men compared to women.
Mortality rates have decreased due to improved treatments.

Aetiology and Pathophysiology

Most commonly caused by atherosclerosis of coronary arteries.
Rupture of plaque leads to thrombus formation, occluding the artery.
Can also be caused by coronary artery spasm or embolism.
Ischemia leads to myocardial cell death, triggering an inflammatory response.
Extent of damage depends on the duration and area of the occlusion.

Types

ST-segment Elevation Myocardial Infarction (STEMI): Complete occlusion of a coronary artery.
Non-ST-segment Elevation Myocardial Infarction (NSTEMI): Partial occlusion or distal embolization.
Type 1 MI: Spontaneous due to a primary coronary event.
Type 2 MI: Secondary to ischemic imbalance (e.g., due to increased demand or decreased supply).

Clinical Features 🌡️

Symptoms

Central chest pain, often described as a heavy, crushing, or tight sensation.
Pain radiating to the left arm, neck, jaw, or back.
Associated symptoms: sweating, nausea, vomiting, and shortness of breath.
May present atypically in diabetics, elderly, or women (e.g., epigastric pain, dyspnea).
Sudden cardiac death can be the first presentation in some cases.

Signs

Pallor and sweating.
Tachycardia or bradycardia.
Hypotension or hypertension.
S4 gallop due to stiff ventricles.
Signs of heart failure (e.g., raised JVP, lung crackles).
New heart murmurs (e.g., mitral regurgitation due to papillary muscle dysfunction).

Investigations 🧪

Tests

ECG: ST-segment elevation, T-wave inversion, or new LBBB in STEMI; ST-segment depression in NSTEMI.
Cardiac biomarkers: Troponin I/T (elevated in MI), CK-MB (less specific).
Chest X-ray: To rule out differential diagnoses like aortic dissection, pulmonary edema.
Echocardiography: Assess wall motion abnormalities, ejection fraction.
Coronary angiography: Gold standard for identifying and treating coronary occlusions.

Management 🥼

Acute Management

Immediate: MONA – Morphine, Oxygen (if hypoxic), Nitroglycerin, Aspirin.
Antiplatelet therapy: Dual antiplatelet therapy (Aspirin + P2Y12 inhibitor).
Anticoagulation: Unfractionated heparin or LMWH.
Reperfusion therapy: Primary PCI for STEMI within 120 minutes; fibrinolysis if PCI not available.
NSTEMI: Risk stratification to guide early invasive vs. conservative approach.

Long-term Management

Lifestyle modification: Smoking cessation, diet, exercise.
Pharmacotherapy: Beta-blockers, ACE inhibitors, statins, dual antiplatelet therapy (for 12 months).
Monitoring: Regular follow-ups, echocardiography to assess cardiac function.
Secondary prevention: Manage comorbidities (hypertension, diabetes).

Complications

Arrhythmias: Ventricular fibrillation, atrial fibrillation.
Heart failure: Due to extensive myocardial damage.
Cardiogenic shock: Severe LV dysfunction.
Mechanical complications: Papillary muscle rupture, ventricular septal defect.
Pericarditis: Early (within days) or Dressler’s syndrome (weeks later).

Prognosis

Depends on the extent of myocardial damage and promptness of treatment.
Mortality is highest within the first 30 days, particularly in STEMI.
Long-term outcomes improve with adherence to medical therapy and lifestyle changes.
Risk of recurrent MI or heart failure increases if risk factors are not controlled.

Key Points

Early recognition and treatment of MI are crucial for reducing mortality and morbidity.
STEMI requires urgent reperfusion therapy, ideally PCI.
NSTEMI management depends on risk stratification and may involve PCI or conservative treatment.
Secondary prevention and lifestyle modification are key to improving long-term outcomes.

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