Heart Anatomy and Physiology

Heart Wall Layers

  • Endocardium:

    • The innermost layer faces the heart cavity.
    • It is in contact with the blood within the heart.

  • Myocardium:

    • The thickest layer composed of cardiac muscle.
    • Responsible for the heart's contraction (the "workhorse" of the heart).

  • Epicardium:

    • The outermost layer of the heart.
    • Contains the coronary blood vessels that supply blood to the heart.

Coronary Blood Vessels

  • Located in the epicardium.
  • Send branches into the myocardium.
  • The endocardium is the last portion of the heart wall to receive blood.
  • Sequence of blood supply:
    • Epicardium (coronary vessels)
    • Myocardium
    • Endocardium

STEMI and NSTEMI

  • STEMI (ST-Elevation Myocardial Infarction):

    • Occurs when a major coronary blood vessel is completely blocked.
    • Results in no blood flow to the myocardium and endocardium.
    • All three layers of the heart undergo infarction (tissue death).
    • Referred to as a transmural infarct.

  • NSTEMI (Non-ST-Elevation Myocardial Infarction):

    • Occurs when there is an obstruction, but the patient receives timely intervention to reverse it.
    • Only a small portion of the endocardium and myocardium may die.
    • Infarct is subendocardial.

Chambers of the Heart

  • Atria:

    • The two upper chambers.
    • Receiving chambers that receive blood.

  • Ventricles:

    • The two lower chambers, larger than the atria.
    • Discharging chambers that pump blood out of the heart.

  • Interventricular Septum:

    • The wall that divides the two ventricles.

  • Interatrial Septum:

    • The wall that divides the two atria.

Blood Vessels of the Heart

  • Superior Vena Cava (SVC) & Inferior Vena Cava (IVC):

    • Bring blood to the right atrium.

  • Coronary Sinus:

    • Also drains blood into the right atrium.

  • Pulmonary Trunk:

    • Takes blood away from the right ventricle to the lungs.

  • Pulmonary Veins:

    • Bring blood back to the left side of the heart from the lungs.

  • Aorta:

    • Arises from the left ventricle and distributes blood to the body.

  • Right and Left Coronary Arteries:

    • Originate from the aorta, posterior to the aortic valve.

  • Auricles:

    • Ear-like appendages of the atria.

Valves of the Heart

  • Right and Left AV (Atrioventricular) Valves:

    • Tricuspid valve (right side).
    • Mitral (Bicuspid) valve (left side).
    • Anchored to papillary muscles on the ventricles by chordae tendineae.

  • Pulmonary and Aortic Semilunar Valves

Chordae Tendineae

  • Thread-like structures that anchor the AV valve leaflets to the papillary muscles.
  • Prevent the AV valves from everting (prolapsing) into the atria during ventricular contraction.
  • All valves have three leaflets, except for the bicuspid (mitral) valve.

Fibrous Skeleton

  • A connective tissue structure that helps:
    • Insertion of cardiac muscle.
    • Support the valves.
    • Prevent stretching of the valves.
    • Provide electrical insulation.

Heart Sounds

  • S1:

    • The first heart sound.
    • Caused by the closing of the mitral and tricuspid (AV) valves.

  • S2:

    • The second heart sound.
    • Caused by the closing of the aortic and pulmonary (semilunar) valves.

Heart Murmurs

  • Abnormal sounds caused by abnormal blood flow through the valves.
  • Occur when a valve does not open completely or close properly.

Valvular Issues

  • Valvular Insufficiency (Regurgitation):

    • Valves do not close completely, causing blood to leak backward.
    • During ventricular contraction, blood can flow back into the atria.

  • Valvular Stenosis:

    • Valves do not open completely, restricting blood flow.
    • When blood flows into the ventricles, it creates an abnormal sound.

Aortic Valve Replacement

  • Surgical procedure to replace a stenotic aortic valve with a prosthetic valve.
  • Cardioplegia (icing the heart) is used to slow down the heart during surgery.

Heart Size and Ventricular Thickness

  • The left ventricle is thicker than the right ventricle.
  • This is because the left ventricle needs more muscle to pump blood to the entire body.
  • The right ventricle only pumps blood to the lungs.

Blood Vessels of the Heart

  • The heart muscle needs blood flow for oxygen and nutrients.

  • Two coronary arteries originate posterior to the aortic valve.

  • Right Coronary Artery (RCA):

    • Branches include the posterior interventricular artery and the right marginal artery.
    • Supplies the right ventricle.

  • Left Coronary Artery (LCA):

    • Branches into the circumflex artery and the anterior interventricular artery (also known as the left anterior descending or LAD).
    • The LAD supplies the majority of the left ventricle.
    • Blockage of the LAD can cause significant damage or death.
    • AKA "Widow Maker."

Cardiac Veins

  • Great Cardiac Vein:

    • Drains into the coronary sinus.

  • Middle and Small Cardiac Veins:

    • Take blood from the right ventricle and drain into the coronary sinus.

  • Coronary Sinus:

    • Drains into the right atrium.

Blood Vessels Draining into Right Atrium

  • Superior Vena Cava
  • Inferior Vena Cava
  • Coronary Sinus

Coronary Artery Disease (CAD)

  • The narrowing of blood vessels due to plaque buildup.
  • This obstruction decreases blood flow, potentially damaging the heart.

Angina Pectoris (Chest Pain)

  • Typically caused by reduced blood flow to the heart muscle.

  • Stable Angina:

    • Predictable pattern of chest pain with exercise.
    • Relieved by rest.

  • Unstable Angina:

    • Chest pain that does not go away with rest.
    • May lead to myocardial infarction.

  • Variant or Prinzmetal Angina:

    • Can happen at rest due to vasospasm.
    • Relieved by drugs like nitroglycerin.