Cardiovascular System

Heart Development - Embryo's Beat Box

• Week 3-4: Heart tube forms, D-looping (cardiac looping).
• Septation: Atrial (primum, secundum, foramen ovale), Ventricular (muscular, membranous). Truncus arteriosus (→ aorta, pulmonary trunk) & aortic arches develop.
• Fetal Shunts: Ductus venosus (liver bypass), foramen ovale (RA→LA), ductus arteriosus (PA→aorta).
• Postnatal: Shunt closures → ligamentum venosum, fossa ovalis, ligamentum arteriosum.

⭐ Most common site of Atrial Septal Defect (ASD) is ostium secundum.

Chambers & Valves - Heart's Inner Workings

• External: Sternocostal & diaphragmatic surfaces; right, left, inferior borders; coronary & interventricular grooves. Apex (LV), Base (LA).
• Chambers:
  • RA: Crista terminalis, pectinate muscles (anterior), sinus venarum (posterior), fossa ovalis. Openings: SVC, IVC (Eustachian valve), coronary sinus (Thebesian valve).
  • RV: Trabeculae carneae, moderator band (septomarginal trabecula), conus arteriosus (infundibulum).
  • LA: Smooth walls, receives 4 pulmonary veins, LA appendage.
  • LV: Thickest wall, aortic vestibule.
• Valves:
  • AV: Tricuspid (3 cusps), Mitral (bicuspid, 2 cusps). Chordae tendineae, papillary muscles.
  • SL: Aortic, Pulmonary (each 3 semilunar cusps). Sinuses of Valsalva (aortic).

⭐ Moderator band (septomarginal trabecula) is a distinctive feature of the Right Ventricle.

Coronary Circulation & Nerves - Lifelines & Controls

Coronary Arteries & Cardiac Dominance

Cardiac Veins

• Coronary Sinus: Drains Great, Middle, Small cardiac vv.
• Anterior Cardiac vv.: Drain directly to RA.
• Venae Cordis Minimae (Thebesian vv.): Drain to all chambers.

Nerve Supply

• Cardiac Plexus:
  • Sympathetic (T1-T5 spinal nerves): ↑Heart Rate, ↑Contractility.
  • Parasympathetic (Vagus nerve, CN X): ↓Heart Rate, ↓Contractility.

Referred Pain

• Ischemic pain referred to T1-T5 dermatomes (e.g., inner arm, chest, jaw).

⭐ The Posterior Interventricular Artery (PDA), crucial for supplying the inferior wall and posterior third of the septum, most commonly arises from the Right Coronary Artery (RCA), defining right cardiac dominance (seen in ~85% of individuals).

Conduction & Pericardium - Rhythm & Protective Sac

• Conduction System:
  • SA node: Pacemaker; crista terminalis (SVC-RA).
  • AV node: Koch's triangle; AV delay.
  • Bundle of His: IV septum; R & L bundle branches.
  • Purkinje fibers: Ventricular myocardium.
  • Blood Supply: SA/AV nodes (RCA ~60%), Bundle branches (LAD).
• Pericardium:
  • Fibrous: Outer; attachments (great vessels, diaphragm).
  • Serous: Parietal & Visceral (epicardium).
  • Cavity: Potential space; ~15-50 mL fluid.
  • Sinuses: Transverse (arterial/venous separation), Oblique (post. to LA).

⭐ Transverse pericardial sinus: anterior to SVC, posterior to ascending aorta & pulmonary trunk; used for surgical clamping of great arteries.

Great Vessels - Body's Main Pipes

• Aorta: Main systemic artery.
  • Ascending: From LV.
  • Aortic Arch: Branches 📌 ABC'S: Brachiocephalic Tr., Left Common Carotid A., Left Subclavian A.

    Branch	Order
    Brachiocephalic Tr.	1st
    L. Common Carotid A.	2nd
    L. Subclavian A.	3rd

  • Descending: Thoracic & Abdominal parts; key branches.
• Pulmonary Artery: RV to lungs (deoxygenated blood). Trunk → R & L Pulmonary Arteries.
• Vena Cavae:
  • Superior Vena Cava (SVC): Drains upper body; from R/L brachiocephalic veins.
  • Inferior Vena Cava (IVC): Drains lower body; from common iliac veins.
• Ligamentum Arteriosum: Ductus arteriosus remnant.
• Portal Circulation: GI/spleen blood → liver (portal vein).

⭐ The left recurrent laryngeal nerve hooks around the arch of the aorta (ligamentum arteriosum).

High‑Yield Points - ⚡ Biggest Takeaways

• RCA dominance (~60%) supplies SA & AV nodes; PDA from RCA.
• Ventricular fibrillation is the most common cause of sudden death post-MI.
• S3 gallop signifies volume overload (e.g., heart failure, MR); S4 gallop signifies stiff ventricle (e.g., LVH).
• Ductus arteriosus (fetal) shunts blood from pulmonary artery to aorta.
• Beck's triad (hypotension, JVD, muffled heart sounds) indicates cardiac tamponade.
• Inferior MI: ST elevation in leads II, III, aVF. Anterior MI: V1-V4.