Heart and Pericardium

Pericardium & Gross Anatomy - Heart's Protective Shell

• Pericardium: Double-walled sac protecting the heart.

  • Fibrous Pericardium: Tough, inelastic outer layer. Fuses with great vessels superiorly, central tendon of diaphragm inferiorly.
  • Serous Pericardium: Two layers:
    • Parietal layer: Lines inner surface of fibrous pericardium.
    • Visceral layer (Epicardium): Adheres to heart surface.
  • Pericardial Cavity: Potential space between parietal & visceral layers; contains 15-50 mL serous fluid (lubrication).
  • Innervation: Phrenic nerve (C3, C4, C5) - somatic sensation (pain referral to shoulder tip).
  • Blood Supply: Mainly Pericardiacophrenic artery (from Internal Thoracic artery).
  • Pericardial Sinuses: Transverse (posterior to aorta/pulmonary trunk), Oblique (posterior to LA, cul-de-sac).

• Heart - Gross Features:

  • Location: Middle mediastinum, 2/3rd to left of midline.
  • Apex: Formed by LV; directed downwards, forwards, to the left. Located in 5th left ICS, ~9 cm from midsternal line.
  • Base (Posterior aspect): Formed mainly by LA, part of RA.
  • Surfaces: Sternocostal (anterior - RV), Diaphragmatic (inferior - LV, RV), Left Pulmonary (LV).
  • Borders: Right (RA), Inferior (RV, LV apex), Left (LV, LA auricle), Superior (RA, LA, great vessels).

  ⭐ Beck's Triad for Cardiac Tamponade: Hypotension, Distended Neck Veins (JVD), Muffled Heart Sounds. (Rapid accumulation of ~200-300 mL fluid).

Chambers & Septa - Heart's Inner Workings

• Four Chambers:
  • Right Atrium (RA): Receives deoxygenated blood: SVC, IVC, Coronary Sinus.
    • Features: Crista terminalis, Pectinate muscles (ant.), Fossa ovalis (foramen ovale remnant), Tricuspid valve.
  • Right Ventricle (RV): Pumps deoxygenated blood to lungs via Pulmonary valve.
    • Features: Trabeculae carneae, Moderator band (RBB), Conus arteriosus, thinner wall.
  • Left Atrium (LA): Receives oxygenated blood from 4 pulmonary veins.
    • Features: Mostly smooth post. wall, auricle (pectinate), forms base, Mitral valve.
  • Left Ventricle (LV): Pumps oxygenated blood to systemic circulation via Aortic valve.
    • Features: Thickest myocardium (~3x RV), Trabeculae carneae, forms apex.
• Septa (Dividing Walls):
  • Interatrial Septum (IAS): Divides atria. Fossa ovalis (foramen ovale site).
  • Interventricular Septum (IVS): Separates ventricles. Two parts:
    • Muscular (bulk) & Membranous (superior, thin).

    ⭐ Perimembranous VSDs (membranous IVS) are most common congenital heart defects.

Vasculature & Valves - Plumbing & Gates

Coronary Arteries:

• RCA (Right Coronary Artery): Supplies RA, RV, SA node (60%), AV node (80%), post. 1/3 IV septum (PDA in Rt. dominant).
• LCA (Left Coronary Artery):
  • LAD (Left Anterior Descending): Ant. 2/3 IV septum, apex, ant. LV. "Widow-maker".
  • LCx (Left Circumflex): LA, lat. & post. LV, SA node 40%.
• Coronary Dominance: Determined by PDA origin. Right (~70%, from RCA), Left (~15%, from LCx).

Coronary Veins:

• Coronary Sinus: Main venous drain to RA. Trib: Gt, Mid, Small cardiac vv.
• Other veins: Ant. cardiac vv. (direct to RA); Thebesian vv. (Venae Cordis Minimae - to all chambers).

Heart Valves:

• AV (Atrioventricular) Valves: Tricuspid (Right), Mitral (Left); w/ chordae tendineae, papillary muscles.
• SL (Semilunar) Valves: Aortic, Pulmonary; 3 cusps each, no chordae.

  ⭐ Aortic valve: Right & Left cusps (coronary cusps) give rise to RCA & LCA respectively. Posterior cusp is non-coronary.

📌 Auscultation Areas (APTM): Aortic (R 2nd ICS), Pulmonic (L 2nd ICS), Tricuspid (L 4th ICS parasternal), Mitral (L 5th ICS MCL).

Conduction & Innervation - Heart's Electrical Symphony

• Pacemaker Hierarchy & Intrinsic Rates:
  • SA Node (Sinoatrial): 60-100 bpm (Primary pacemaker)
  • AV Node (Atrioventricular): 40-60 bpm
  • Bundle of His/Purkinje fibers: 20-40 bpm
• Conduction Pathway & ECG Correlation:

• Autonomic Innervation:
  • Sympathetic (T1-T5 spinal segments; Norepinephrine): ↑ HR (chronotropy), ↑ contractility (inotropy), ↑ conduction velocity (dromotropy) via β1 receptors.
  • Parasympathetic (Vagus nerve CN X; Acetylcholine): ↓ HR, ↓ AV nodal conduction via M2 receptors.
    • Right Vagus: Primarily SA node.
    • Left Vagus: Primarily AV node.

⭐ AV nodal delay (approx. 0.1 sec) is crucial; allows atrial contraction to complete before ventricular excitation, optimizing ventricular filling.

High‑Yield Points - ⚡ Biggest Takeaways

• Transverse sinus (posterior to aorta/pulmonary trunk, anterior to SVC) & Oblique sinus (posterior to left atrium).
• Right atrium: Receives SVC, IVC, coronary sinus; has crista terminalis, fossa ovalis.
• Moderator band (RV): Carries right bundle branch.
• Left ventricle: Thickest myocardium; two large papillary muscles.
• Right coronary dominance (85%): PDA from RCA; RCA supplies SA (60%) & AV (80%) nodes.
• LAD (LCA): Supplies anterior 2/3 IV septum, apex, AV bundle/branches.