Myocardial Infarction: Mechanism and Classification.

Myocardial Infarction: Mechanism and Classification.

Image showing Atherosclerosis


It is commonly known as "Heart Attack" and is a very serious complication of Ischemic Heart Disease.
It is an irreversible death or necrosis of cardiac muscles due to ischemia, mostly due to atherosclerosis (thrombotic occlusion of coronary arteries).
It is one of the most common life threatening conditions, due to blockage of one or more coronary artery. Common symptoms are chest pain, dyspnoea, sweating, faintness etc.

Risk Factors:

  1. Age- Elderly
  2. Hereditary- Family history may be there.
  3. Hypertension
  4. Smoking
  5. Diabetes mellitus
  6. Lack of exercise
  7. Hyperlipidemia
  8. Alcoholic
  9. Obesity
  10. Stress (Emotional)

Etiopathogenesis-

It is a coronary artery disease, and is due to complete blockage of one or more coronary vessels (arteries). The blockage may be due to-
  • Atherosclerosis
  • Thrombosis
  • Spasm of coronary artery due to stress, cold etc.
  • Embolism

Mechanism-

Atherosclerotic plaque is formed in coronary artery, which ruptures and formed a clot which completely blocks the artery leading to lack of blood supply and oxygen to the area of myocardium which it supplies. This ischemia causes tissue death (necrosis) which is irreversible and is called as Infarction. A collagen scar is formed in this place.
The size, extent and location of infarct depend on the artery affected. The degree of blockage , duration collateral circulation and oxygen deprivation decides the severity of condition.
Necrosis and Apoptosis damages the heart muscles permanently. Death of myocardial tissue and scarring alters the condition pathway and weakens the area, leading to abnormal cardiac rhythms i.e., arrhythmias, and may result in formation of ventricular aneurysm, which can rupture. Ventricular fibrillation can cause sudden cardiac death, shock etc.

Signs and Symptoms-

1. Chest Pain-
  • The commonest presenting symptoms of MI is acute, severe pain in chest on left side.
  • Pain may be in the form of feeling of tightness, pressure or squeezing.
  • Thew pain may radiate to left arm, shoulder, neck and lower jaw.
  • Sometimes pain even may radiate to left arm, back and upper abdomen.
  • Patient may can localize the pain by clenching his fist over is sternum. (Levine’s sign).
  • Chest pain sometimes may get confused with or interpreted as heart burn.
  • Pain is severe and may last for more than 20 minutes.
2. Shortness of Breath (Dysnoea)- 
It is usually always associated with chest pain
3. Excessive sweating
4. Nausea and vomiting
5. Weakness
6. Anxiety
7. Palpitation
8. Atypical or silent infarction can occur in elderly or diabetics.
9. Atypical symptoms are present in women. Dyspnoea fatigue and weakness are present while chest pain is not significant, pain in back or jaw can be felt during attack.

Classification:

MI is classified as 2 main types- based on ECG finding :-
1. ST elevation MI (STEMI)
2. Non-ST elevation MI (NSTEMI)




Complications:

  • Heart failure
  • Arrhythmias
  • Shock
  • Cardiac arrest
  • Death

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