Heart Anatomy and Pericarditis Overview

Pericardial Fluid

• Lubricating fluid between the two layers of the serous pericardium
• Reduces friction between layers as the heart beats
• About 30 ml of fluid

Pericarditis

• Inflammation of the pericardium
• Causes can be viral, bacterial, or due to radiation
• Symptoms include chest pain that extends to the left shoulder and down the left arm
• Can be mistaken for a heart attack as there is often ST elevation across all leads on an ECG
• A pericardial friction rub, a creaking sound, can be heard through a stethoscope in 40% of patients.

Heart Layers

• Epicardium:
  • External layer of the heart
  • Visceral layer of the serous pericardium
  • Contains adipose tissue
  • Contains blood vessels that supply the myocardium
• Myocardium:
  • Cardiac striated muscle tissue
  • Responsible for the heart's contractions
• Endocardium:
  • Endothelium over connective tissue
  • Smooth lining for the heart chambers

Heart Chambers

• Four chambers:
  • Atria (auricles): Superior chambers
  • Ventricles: Inferior chambers
• Sulci: Grooves on the surface of the heart
  • Coronary Sulcus: Encircles the heart and divides the atria from the ventricles
  • Interventricular Sulci: Anterior and posterior grooves that divide the ventricles

Right Atrium

• Pectinate Muscles: Muscular ridges on the anterior wall
• Interatrial Septum: Thin wall that separates the right and left atria
• Receives blood from:
  • Inferior Vena Cava
  • Superior Vena Cava
  • Coronary Sinus
• Fossa Ovalis: Remnant of the foramen ovale, a hole present in the fetal heart

Right Ventricle

• Trabeculae Carneae: Raised bundles of cardiac muscle fibres
• Chordae Tendineae: Tendons connected to the leaflets of the tricuspid valve
• Papillary Muscles: Connected to chordae tendineae
• Interventricular Septum: Divides the two ventricles
• Blood exits the heart through the pulmonary valve into the pulmonary trunk

Left Atrium

• Receives blood from the four pulmonary veins
• Blood passes from the atrium to the ventricle through the bicuspid (mitral) valve

Left Ventricle

• Similar to the right ventricle, it contains:
  • Trabeculae Carneae
  • Chordae Tendineae that anchor the cusps of the mitral valve to papillary muscles
• Blood leaves the ventricle via the aortic valve into the ascending aorta

Myocardial Thickness

• The thickness of the myocardium in the four chambers varies, depending on the pressure it needs to generate.
• Atria: 2-3 mm thick; they only need to push blood to the ventricles.
• Ventricles: Thicker, they need to pump blood further with higher pressure.
  • Right Ventricle: 4-5 mm thick (shorter distance to the lungs)
  • Left Ventricle: 10-15 mm thick (longer distance to the body)

Fibrous Skeleton

• Dense connective tissue that provides structural support to the heart.
• Provides points of insertion for muscle bundles.
• Acts as an electrical insulator between the atria and ventricles.

Anatomical Location of the Heart

• Approximately the size of a closed fist: 12 cm long, 9 cm wide, 6 cm thick, and weighs around 250g.
• Located in the mediastinum, the space between the sternum and the vertebral column, the first rib, and between the lungs.
• Two-thirds of the mass lies to the left of the midline

Heart Surface Anatomical Landmarks

• Anterior (Sternocostal) Surface: Right atrium and right ventricle
• Inferior (Diaphragmatic) Surface: Right and left ventricles
• Posterior Surface: Mainly the left atrium.

Heart Borders

• Inferior Border: Right ventricle
• Left Border: Left ventricle + some left atrium
• Right Border: Right atrium

Heart Apex

• The tip of the left ventricle, which rests on the diaphragm.

Heart Base

• Formed by the atria.

Pericardium

• Membrane that surrounds the heart.
• Keeps the heart in place while allowing for vigorous contractions.
• Consists of two parts:
  • Fibrous Pericardium: Tough and inelastic connective tissue; fused to the connective tissue of the heart and blood vessels; anchors the heart to the mediastinum and prevents overstretching.
  • Serous Pericardium: Thinner layer, double-layered:
    • Parietal Layer: Fused to the fibrous pericardium.
    • Visceral Layer: Known as the epicardium.

Atrioventricular Valves

• Tricuspid and Mitral Valves
• Mechanism of Operation:
  • Valve Opens: When blood flows from the atrium into the ventricle during atrial contraction, the pressure causes the valve to open. The cusps project into the ventricle.
  • Valve Closes: As the ventricle contracts, pressure pulls the cusps upward, causing them to close. The papillary muscles contract, pulling the chordae tendineae to ensure the cusps don’t bulge back into the atrium.

Semilunar Valves

• Aortic and Pulmonary Valves
• Mechanism of Operation:
  • Valve Opens: When the ventricles contract, the pressure is higher than in the arteries. This causes the semilunar valve to open, and the cusps project into the artery lumen.
  • Valve Closes: When the ventricle relaxes, blood starts to flow back, filling the cusps, which then close tightly.

Main Great Vessels

• Superior and Inferior Vena Cava: Carry deoxygenated blood from the body to the right atrium.
• Pulmonary Artery: Carries deoxygenated blood from the right ventricle to the lungs for oxygenation.
• Pulmonary Veins: Carry oxygenated blood from the lungs to the left atrium
• Aorta: Carries oxygenated blood from the left ventricle into systemic circulation.