Myocardial infarction (MI), commonly called a heart attack, happens when blood flow to a part of the heart suddenly stops. Without blood and oxygen, the heart muscle begins to die. Most heart attacks happen because a coronary artery gets blocked by a blood clot on top of a fatty plaque.
If blood flow is not restored within 20–40 minutes, the damage becomes permanent, and the dead muscle is replaced by scar tissue.
Definition
MI is the irreversible death of heart muscle due to prolonged lack of oxygen. It is usually caused by complete blockage of a coronary artery by a clot or severely narrowed artery due to atherosclerosis.
Causes & Risk Factors
- Smoking and alcohol use
- High blood pressure
- Diabetes
- High cholesterol / high triglycerides
- Obesity and sedentary lifestyle
- Drug abuse (cocaine, methamphetamine)
- Stress and emotional shock
- Older age, male gender
- Family history of heart disease
- Chronic kidney disease
How MI happens (simple pathophysiology)
MI usually starts with a plaque (fat buildup) in a coronary artery. When the plaque ruptures, blood platelets clump together and form a clot. This clot blocks the blood vessel and stops oxygen supply to the heart muscle.
Other contributing factors
- Sudden increase in heart workload (exercise, emotional stress)
- Coronary artery spasm
- Thromboembolism
- Trauma or inflammation of coronary arteries
Symptoms
Patients may notice symptoms days or weeks before the attack (fatigue, chest discomfort). During the attack:
- Severe chest pain lasting > 30 minutes
- Pain spreading to left arm, jaw, neck or back
- Feeling of pressure, tightness or burning in the chest
- Shortness of breath
- Heavy sweating
- Nausea or vomiting
- Anxiety or fear of death
- Fast or irregular heartbeat
- Indigestion-like discomfort
- Dizziness or fainting
Diagnosis
- Symptoms and clinical examination
- Blood markers: Troponins, CK-MB, LDH
- ECG: ST elevation, T-wave inversion, Q-waves
- MRI, PET scan, angiography: identify damaged areas
- Chest X-ray: evaluates heart size and lung congestion
Treatment Overview
The goals of treatment are to restore blood flow quickly, reduce heart damage, control pain, prevent complications, and improve long-term survival.
Non-pharmacological measures
- Quit smoking and limit alcohol
- Eat a heart-healthy diet (low fat, more fruits and vegetables)
- Control BP, blood sugar, and cholesterol
- Exercise regularly as advised
- Maintain healthy weight (BMI 18.5–24.9)
- Manage stress and treat depression
Pharmacological Therapy
1. Antiplatelet & Antithrombotic Drugs
- Aspirin: prevents platelets from forming new clots.
- Clopidogrel / Ticlopidine / Ticagrelor: additional platelet inhibition.
- Heparin (UFH, LMWH): prevents further clot growth.
- GPIIb/IIIa inhibitors (e.g., Tirofiban, Abciximab): block final step of platelet aggregation.
2. Fibrinolytics (clot-dissolving drugs)
- Streptokinase
- Alteplase
- Reteplase
- Tenecteplase
These dissolve the clot and restore blood flow if given within hours of symptom onset.
3. Analgesics
- Morphine: relieves severe chest pain and reduces stress on the heart.
- Nitroglycerin: widens coronary vessels and relieves pain.
4. Beta Blockers
- Propranolol
- Metoprolol
- Atenolol
Reduce heart workload, slow heart rate, and improve survival.
5. Other supportive drugs
- ACE inhibitors (reduce heart strain and improve long-term outcome)
- Calcium channel blockers (for some patients)
- Antiarrhythmics like amiodarone or lidocaine (manage dangerous rhythms)
Emergency Treatments
- Angioplasty (PCI): Balloon opens the blocked artery. A stent is usually placed.
- Bypass surgery: Creates a new route for blood around blocked arteries.
- PCI timeline: Best within 90 minutes of hospital arrival.
Detailed Notes:
For PDF style full-color notes, open the complete study material below: