HEART ATTACK PATHOPHISIOLOGY

Overview of Heart Attacks

  • Definition of Heart Attack: A heart attack, clinically known as a myocardial infarct, occurs due to atherosclerotic plaque buildup in the coronary arteries, compromising blood flow to the heart muscle.

    • Myocardial: Refers to the heart muscle.

    • Infarct: Refers to tissue death due to lack of oxygen.

Mechanism of Heart Attack

Causes

  • Atherosclerotic Plaque Buildup: This buildup occurs in the coronary arteries, leading to diminished blood flow and oxygen delivery to the heart muscle, resulting in myocardial infarcts.

Events during a Heart Attack

  1. Initial Condition

    • Plaque accumulation in the coronary arteries that is not yet ruptured.

      • Causes obstruction of blood flow upstream but does not initially trigger symptoms.

  2. Triggering Events

    • Physical activity (e.g., running) increases heart rate, resulting in increased blood flow to the heart.

    • Rushing blood can apply pressure on the plaque, leading to its rupture.

  3. Formation of Thrombus

    • The rupture of plaque results in the formation of a thrombus, which blocks blood flow.

    • Reduced blood flow leads to oxygen starvation of cardiomyocytes (heart muscle cells).

  4. Symptoms Development

    • Oxygen-starved cardiomyocytes send pain signals to the brain, interpreted as discomfort often felt in the chest or similar to indigestion.

    • The pain may radiate to the left arm, due to shared nerve pathways (referred pain) and can even affect the jaw.

  5. Physiological Response

    • The body secretes adrenaline in response to stress and pain.

    • While this increases heart rate, it does not resolve the clot issue.

    • Cardiomyocytes become exhausted due to inadequate oxygen and begin to fail in contraction.

  6. Cellular Breakdown

    • Cardiomyocytes stop beating; compensatory mechanisms in the rest of the heart attempt to maintain function.

    • A lack of oxygen leads to cellular breakdown, with membranes rupturing and the release of proteins (e.g., troponins) into the bloodstream.

Symptoms of Heart Attack

  • Pain Symptoms

    • Location: Often below the heart, above the stomach, or referred pain in the left arm and jaw.

    • Severity: Increases as the thrombus grows and blood flow diminishes.

  • Other Symptoms

    • Dyspnea: Difficulty breathing due to fluid buildup in the lungs from backflow as the heart fails to pump efficiently.

    • Dizziness: Insufficient blood flow to the brain causes dizziness and disorientation.

Physiological Impact

  • Cardiac Damage

    • Approximately 500 cardiomyocytes die per second after the onset of heart attack symptoms without treatment.

    • Loss of cardiomyocytes leads to irreversible heart damage, as these cells cannot regenerate.

Classification of Myocardial Infarcts

  • Two Major Types

    1. Full Thickness Infarct (Transmural Infarct)

    • Involves the entire thickness of the heart muscle wall due to blockage in a major artery (e.g., left anterior descending artery).

    • Transmural: "Trans" means across; "mural" refers to the wall; thus, it crosses the entire wall.

    1. Partial Thickness Infarct (Subendocardial Infarct)

    • Occurs due to blockage in smaller arteries that penetrate the heart muscle, affecting only a limited region of the heart wall.

    • Subendocardial: Refers to the infarct being just beneath the inner layer of the heart muscle.

Conclusion

  • Understanding the physiological and pathological processes involved in a myocardial infarct is crucial for recognizing symptoms, seeking timely medical intervention, and effectively diagnosing heart attacks through biomarkers like troponins.