A myocardial infarction (MI), often known as a heart attack, happens when blood supply to a portion of the heart is reduced or stops, harming the heart muscle. The most typical symptom is soreness or tightness in the chest, which may extend throughout back, neck, arm, shoulder, or jaw. Myocardial infarction is a disease characterised by decreased blood flow in a coronary artery brought on by atherosclerosis and arterial obstruction by an embolus or thrombus. Thus, myocardial tissue suffers irreparable damage from prolonged hypoxia and ischaemia, which is known as a MI or heart attack.

Ischaemic heart disease

It is the acute or chronic form of cardiac disability caused by the imbalance between the myocardial supply and the demand for oxygenated blood. Myocardial infarction, also known as ischemic necrosis, is the result of a coronary artery blockage and persistent myocardial ischemia. This condition is also known as the coronary artery disease.

Etiology of IHD

Etiology of IHD can be studied under three topics,

  • Coronary atherosclerosis
  • Transmural vs Subendocardial infarcts
  • Non-atherosclerotic causes
  • Myocardial ischemia
  • Role of platelets
  • Acute plaque rupture

Coronary atherosclerosis

IHD is generally caused by a condition that affects the coronary arteries, with atherosclerosis accounting for more than 90% of cases and other causes accounting for less than 10%.

Transmural vs Subendocardial infarcts

Partially or completely blocked coronaries frequently serve as an initiating factor in transmural acute myocardial infarction. Surface ulceration of fixed chronic atheromatous plaque leads to the beginning of thrombus, which ultimately results in total luminal blockage. Particularly, the lipid core of plaque is very thrombogenic. Then, little pieces of thrombotic material are released, embolize to terminal coronary branches, and result in myocardial microinfarcts.

Non atherosclerotic causes

One of the major coronary artery trunks that might result in myocardial infarction or angina in persons without severe atherosclerotic coronary stenosis is vasospasm. Narrowing of the arteries caused by repeated vasoconstriction (contraction of the blood vessels) is known as vasospasm.

Myocardial ischaemia

One or more of the following mechanisms causes myocardial ischaemia:

  • Reduced coronary blood flow, such as in shock or coronary artery disease.
  • Myocardial demand, such as during exercise or emotions, increases.
  • Heart hypertrophy without a corresponding rise in coronary blood flow, as in hypertension and valvular heart disease.

Role of platelets

When an atherosclerotic plaque ruptures, platelets are exposed to the sub-endothelial collagen and undergo reaction of aggregation, activation, and release. These occurrences help the mass of platelets that can form emboli or start thrombosis to accumulate.

Pathogenesis of Myocardial infarction

The pathogenesis of MI can be illustrated by the following flow chart

Pathogenesis of Myocardial infarction

Clinical manifestations of myocardial infarction

The clinical manifestations of myocardial infarction is given by,

  • Chest pain
  • Fatigue
  • Increased sweating
  • Weakness
  • Nausea
  • Palpitations
  • Light headedness
  • Anxiety
  • Hypertension/hypotension

Complications of myocardial infarction

When this condition is left untreated, it may lead to complications like,

  • Arrhythmias.
  • Congestive heart failure.
  • Cardiogenic shock.
  • Mural thrombosis and thromboembolism.
  • Rupture.
  • Cardiac aneurysm
  • Pericarditis.
  • Post-myocardial infarction syndrome.

Diagnosis

There are several ways through which the disease can be diagnosed. While the basic technique of it being analysing the symptoms, the other methods are given as follows.

ECG changes

Changes that are seen in the affected person’s ECG is given by,

  • ST segment elevation
  • Appearance of deep Q waves
  • T wave inversion

Serum cardiac markers

Some proteins and enzymes are released into the blood from the heart that has MI. The important myocardial markers that are being used in the diagnosis are given by,

  • CK and CK – MB enzymes (Elevation of this isoenzyme is specific for myocardial damage
  • Lactic dehydrogenase (LDH) (LDH – 1 is specific for myocardial damage)
  •  Myoglobin (1st cardiac biomarker that gets elevated after the incidence of MI)
  • Cardiac troponins (They remain higher for a longer duration)

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