Day 1 — Developmental Anatomy of the Heart + Cardiac Physiology

(PM 01, first block — basic embryology through MD-level integration)

I. CARDIAC EMBRYOLOGY

1. Timeline (know these day-numbers — MD vivas love them)

2. Septation (the exam favourite — build the "why defects happen" logic here)

• Atrial septum: septum primum grows down from the roof of the common atrium toward the endocardial cushions, leaving the ostium primum, which closes as the cushions fuse — but before it fully closes, perforations form the ostium secundum. Then septum secundum grows to the right of septum primum, leaving the foramen ovale, covered on the left by the flap-like septum primum. This valve-like arrangement is why blood can flow right-to-left in fetal life but not left-to-right.
  • Clinical link: failure of septum primum/secundum fusion after birth → patent foramen ovale (present in ~25% of adults, usually asymptomatic); excessive resorption of septum primum or maldevelopment of septum secundum → ostium secundum ASD (commonest ASD).
• Endocardial cushions (AV canal): fuse to divide the single AV canal into right and left AV orifices, contribute to the membranous interventricular septum, and close the ostium primum. Failure of fusion → ostium primum ASD / persistent AV canal (common in Down syndrome).
• Interventricular septum: muscular part grows up from the floor of the ventricle; the gap left above it (interventricular foramen) is closed by tissue derived from the endocardial cushions and the conal (truncoconal) ridges → membranous septum. This is the last part to close and the commonest site of VSD.
• Truncus arteriosus/conus septation: truncal and conal ridges spiral and fuse to form the aorticopulmonary septum, dividing the outflow into aorta and pulmonary trunk in a spiral fashion (this is why the great vessels normally twist around each other). Faulty spiraling/unequal division underlies Tetralogy of Fallot (unequal division shifting the aorta anteriorly/rightward over a VSD, with resultant pulmonary stenosis and RV hypertrophy) and transposition of the great arteries (straight, non-spiral septation).
• Semilunar valves: form from 3 swellings around the truncal orifice. AV valves (mitral, tricuspid): form from tissue around the AV canal, undermined and thinned to form leaflets and chordae tendineae, remaining tethered to papillary muscles.

3. Conducting system development

• SA node: from the right horn of the sinus venosus, ends up near the SVC-RA junction.
• AV node and bundle of His: from cells around the AV canal / left horn of the sinus venosus region.
• Purkinje network differentiates later from ordinary myocardium under the influence of endocardial signalling (endothelin pathway).

4. Fetal circulation and the changes at birth (always asked)

1. Ductus venosus: umbilical vein → IVC, bypassing the liver sinusoids.
2. Foramen ovale: IVC stream (highly oxygenated, from placenta) preferentially directed across into the LA → LV → head/upper body (streaming effect, "crista dividens").
3. Ductus arteriosus: pulmonary trunk → descending aorta, bypassing the high-resistance fetal lungs; kept open in utero by prostaglandin E2/I2 and low fetal PaO2.

• First breath → lungs expand → pulmonary vascular resistance falls sharply → pulmonary blood flow increases.
• Placental circulation is cut off → systemic vascular resistance rises.
• LA pressure rises above RA pressure → foramen ovale flap closes functionally within minutes-hours, anatomically over weeks-months → becomes fossa ovalis.
• Rising PaO2 and falling prostaglandins → ductus arteriosus constricts and closes functionally within 10-15 hours, fibroses over weeks → becomes ligamentum arteriosum.
• Ductus venosus closes → ligamentum venosum; umbilical vein → ligamentum teres (round ligament of liver); umbilical arteries → medial umbilical ligaments.

II. GROSS / CLINICALLY-APPLIED ANATOMY

• Chambers: RA (smooth sinus venosus part + rough pectinate-muscle atrium proper, separated by the crista terminalis), RV (trabeculated, moderator band, conus/infundibulum leading to pulmonary valve), LA (smooth walled mostly, pectinate muscles confined to the auricle), LV (thicker wall, two papillary muscles, fine trabeculae carneae).
• Valves: Tricuspid (RA-RV, 3 cusps), Mitral (LA-LV, 2 cusps — anterior/aortic and posterior/mural), Pulmonary and Aortic (semilunar, 3 cusps each — aortic has coronary ostia in the right and left cusps).
• Fibrous skeleton of the heart: anchors the 4 valve rings, gives electrical insulation between atria and ventricles except through the AV node/bundle — clinically relevant for accessory pathway syndromes (e.g. WPW bypasses this insulation).
• Coronary circulation:
  • Right coronary artery (RCA): SA node artery (~60%), AV node artery (~80-90%, "right dominant" pattern), posterior descending artery (PDA) in right-dominant circulation, supplies RV, inferior LV, posterior 1/3 septum.
  • Left coronary artery → LAD (anterior 2/3 septum, anterior LV, apex) and LCx (lateral/posterior LV, may supply SA node in ~40%).
  • Venous drainage mainly via the coronary sinus (in the AV groove, receives great/middle/small cardiac veins) into the RA; small anterior cardiac veins drain directly into RA.
• Pericardium: fibrous pericardium (protective, limits acute distension) + serous pericardium (parietal + visceral/epicardial layers, pericardial cavity between them, ~30-50 mL fluid normally).

III. THE CONDUCTING SYSTEM

IV. CARDIAC PHYSIOLOGY — THE CARDIAC CYCLE

1. Definition and phases (HR 75/min → cycle length ≈ 0.8 s)

1. Atrial systole (~0.1 s) — atrial contraction tops up ventricular filling (the "atrial kick," contributes ~15-25% of ventricular filling at rest, much more with exercise or in a stiff/non-compliant ventricle).
2. Isovolumetric ventricular contraction — mitral/tricuspid valves close (→ S1), ventricular pressure rises steeply, all valves shut, volume constant.
3. Rapid ejection — aortic/pulmonary valves open once ventricular pressure exceeds aortic/pulmonary diastolic pressure; most stroke volume ejected here.
4. Reduced ejection — ejection continues but slower as ventricular pressure starts to fall.
5. Isovolumetric relaxation — semilunar valves close (→ S2), ventricular pressure falls rapidly, volume constant (all four valves shut).
6. Rapid filling — AV valves open once atrial pressure exceeds ventricular pressure; most of ventricular filling happens here.
7. Diastasis (reduced/slow filling) — flow slows as pressures nearly equalize; shortest with tachycardia (why fast heart rates compromise filling and coronary perfusion).

• LV pressure, aortic pressure, LA pressure, LV volume, ECG, and heart sounds are all plotted against the same time axis.
• Aortic valve opens when LV pressure > aortic diastolic pressure; closes at the dicrotic notch (a small pressure blip from valve closure and elastic recoil of the aorta).
• Mitral valve opens when LA pressure > LV pressure (early diastole).

2. Heart sounds

• S1 — closure of mitral + tricuspid valves, start of systole.
• S2 — closure of aortic + pulmonary valves, start of diastole; normal physiological splitting widens on inspiration (increased venous return delays pulmonary closure).
• S3 — rapid ventricular filling sound; normal in children/young adults, pathological in adults = volume overload (heart failure, mitral regurgitation).
• S4 — atrial contraction against a stiff/non-compliant ventricle; always pathological in adults (LVH, hypertension, ischemia, HFpEF).

3. Preload, afterload, contractility

4. Stroke volume, cardiac output, ejection fraction

• Stroke volume (SV) = EDV - ESV (normal ~70 mL)
• Cardiac output (CO) = SV × HR (normal ~5 L/min at rest)
• Ejection fraction (EF) = SV/EDV × 100 (normal ≥55%) — the key number distinguishing HFrEF from HFpEF later in the course.
• Cardiac index = CO/body surface area (normal ~2.6-4.2 L/min/m²), used clinically to normalize for body size.

5. Fetal vs adult cardiac cycle — the key differences

• Fetal circulation is a parallel circuit (both ventricles pump into the systemic circulation via the shunts) vs the adult series (in-line, lung-dependent) circuit.
• Fetal RV output actually exceeds LV output (RV is the dominant ventricle in utero, ejecting mostly across the ductus arteriosus into the descending aorta), because pulmonary vascular resistance is very high (lungs are fluid-filled/unexpanded) — this reverses completely at birth once the lungs expand and PVR falls.
• Fetal heart rate is higher (~110-160 bpm) and relies more on rate than stroke volume/contractility for changes in output, because immature myocardium has less compliant, less organized sarcomeres.

6. Basic blood pressure regulation (brief foundation — expanded on hypertension day)

• Short-term: baroreceptor reflex (carotid sinus/aortic arch → NTS → autonomic outflow), seconds-to-minutes.
• Intermediate: capillary fluid shift, stress-relaxation of vessel walls, renin-angiotensin activation.
• Long-term: renal pressure-natriuresis and the renin-angiotensin-aldosterone system — the dominant long-term controller of arterial pressure.

V. ECG FOUNDATIONS (normal ECG only — arrhythmia recognition comes Day 3)

Today's Output Tasks (from your plan — do these before moving on)

1. Draw the heart + conducting system from memory (label SA node, AV node, bundle of His, bundle branches, Purkinje fibers, and blood supply to each).
2. Write a one-page cardiac-cycle flowchart with the Wiggers diagram correlation (pressure/volume/ECG/heart sounds together).
3. Calculate: if EDV = 120 mL, ESV = 50 mL, HR = 72/min — find SV, EF, and CO.

Checkpoint Questions (answer these and I'll correct/expand)

1. Why is the membranous interventricular septum the commonest site for a VSD?
2. Trace the direction of blood flow through all three fetal shunts, and state what closes each one and what it becomes anatomically after birth.
3. What causes S3 to be pathological in an adult but physiological in a child?
4. If sympathetic stimulation increases contractility, what happens to the Frank-Starling curve, and what happens to ESV at a fixed afterload?
5. Which coronary artery occlusion would most directly threaten the AV node, and what conduction abnormality would you expect on ECG?

1. Cardiac Looping (Day 21-23 embryo) — authentic embryology figure

2. Fetal Circulation — the three shunts

3. Heart Anatomy — chambers, valves, coronary arteries

4. Conduction System — the electrical pathway

5. Wiggers Diagram — the master diagram of the cardiac cycle

6. Normal ECG waveform

The actual concept: hierarchy of automaticity + anatomical pathway

Why tachycardia compromises both ventricular filling AND coronary perfusion

• Total time available for coronary flow per minute goes down, even though heart rate (and therefore total myocardial oxygen demand) goes up.
• You get a mismatch: increased O2 demand + decreased time for O2 supply - which is precisely why tachycardia provokes or worsens angina in someone with coronary artery disease, and why it's dangerous in critical aortic stenosis or severe LV hypertrophy (both already have compromised subendocardial perfusion at baseline).

• Beta-blockers are first-line anti-anginal therapy: slowing the heart rate lengthens diastole, giving more time for coronary filling, on top of reducing myocardial O2 demand.
• Tachycardia in a patient with critical coronary stenosis can itself precipitate ischemia even without any change in the stenosis - "supply-demand mismatch" purely from rate.

Day 2 — Cardinal Manifestations of CVS Disease + Complete Clinical Examination (In Depth)

I. CHEST PAIN

Mechanism

History framework (SOCRATES)

Differential diagnosis — organize by system, always in a viva

II. PALPITATIONS

Definition and mechanism

Differential diagnosis

III. DYSPNOEA (BREATHLESSNESS)

Mechanism

Key patterns to distinguish (high-yield)

• Exertional dyspnoea: earliest symptom of LV dysfunction, graded by NYHA Class I-IV (I = no limitation; II = slight limitation, dyspnoea on ordinary activity; III = marked limitation, dyspnoea on less-than-ordinary activity; IV = dyspnoea at rest).
• Orthopnoea: breathlessness lying flat, relieved by sitting/propping up with pillows (quantify as "2-pillow" or "3-pillow" orthopnoea). Mechanism: supine posture redistributes fluid from the legs/splanchnic bed back into central circulation, raising venous return and pulmonary capillary pressure in an already failing LV.
• Paroxysmal nocturnal dyspnoea (PND): sudden waking from sleep, gasping for air, relieved by sitting up/standing. Mechanism: same fluid redistribution plus blunted nocturnal respiratory centre responsiveness and reduced sympathetic tone supporting the LV overnight.
• Platypnoea: breathlessness on sitting up, relieved lying down (rare — think platypnoea-orthodeoxia syndrome, right-to-left shunting).

Differential diagnosis

IV. OEDEMA

Mechanism — Starling forces

Cardiac oedema characteristics

Differential diagnosis

V. CYANOSIS

Definition

VI. PRE-SYNCOPE AND SYNCOPE

Definition

Classification (this structure is exactly how it's tested)

• Vasovagal (emotional stress, prolonged standing, pain)
• Situational (cough, micturition, defecation)
• Carotid sinus syncope

• Volume depletion (dehydration, hemorrhage)
• Autonomic failure (diabetic autonomic neuropathy, Parkinson's, drugs)
• Drug-induced (antihypertensives, diuretics)

• Arrhythmic: bradyarrhythmias (complete heart block, sick sinus syndrome), tachyarrhythmias (VT, SVT with rapid rate)
• Structural/obstructive: severe aortic stenosis, HOCM, massive PE, cardiac tamponade, aortic dissection, atrial myxoma

Red flags suggesting cardiac syncope (must elicit in every history)

VII. COMPLETE CVS CLINICAL EXAMINATION

1. General inspection

2. Pulse examination

• Collapsing (water-hammer) pulse: rapid rise and fall — aortic regurgitation, PDA
• Anacrotic pulse: slow rising, notched upstroke — severe aortic stenosis
• Pulsus alternans: alternating strong/weak beats with regular rhythm — severe LV systolic failure
• Pulsus paradoxus: exaggerated fall (>10 mmHg) in systolic BP on inspiration — cardiac tamponade, severe asthma/COPD
• Pulsus bisferiens: double-peaked systolic pulse — combined AS + AR, or HOCM

3. Blood pressure

4. Jugular venous pressure (JVP) — one of the highest-yield bedside skills

• a wave: atrial contraction — absent in AF, large ("giant") a wave in tricuspid stenosis or pulmonary hypertension, cannon a waves (irregular, very tall) when atria contract against a closed tricuspid valve in complete heart block or AV dissociation.
• c wave: closure of tricuspid valve (small, often not visible clinically).
• x descent: atrial relaxation.
• v wave: passive atrial filling against closed tricuspid — large "v" wave in tricuspid regurgitation.
• y descent: tricuspid valve opening, rapid ventricular filling — sharp/deep in constrictive pericarditis (Friedreich's sign), slow in tricuspid stenosis.

5. Precordium

• Apex beat — location (normally 5th ICS, midclavicular line) and character:
  • Tapping — mitral stenosis (palpable S1)
  • Heaving/sustained (pressure overload) — aortic stenosis, hypertension, HOCM
  • Thrusting/hyperdynamic (volume overload) — mitral regurgitation, aortic regurgitation, VSD
  • Diffuse and displaced — dilated cardiomyopathy
  • Double apical impulse — HOCM
• Left parasternal heave — RV hypertrophy (pulmonary hypertension, mitral stenosis, ASD)
• Thrills — palpable murmurs (grade ≥4/6)

• S1/S2: intensity (loud S1 in MS/tachycardia; soft S1 in MR/long PR interval; loud P2 in pulmonary hypertension), splitting (physiological splitting of S2 widens on inspiration; fixed splitting in ASD; reversed/paradoxical splitting in LBBB or severe AS).
• Extra sounds: S3 (volume overload/systolic failure), S4 (pressure overload/stiff ventricle — see Day 1), opening snap (mitral stenosis, follows S2), ejection click (bicuspid aortic valve, pulmonary stenosis).
• Murmurs: timing (systolic vs diastolic), shape (crescendo-decrescendo = ejection systolic in AS; pansystolic = MR/VSD/TR; early diastolic decrescendo = AR/PR; mid-diastolic rumble = MS/TS), pitch, site of maximum intensity, radiation (AS radiates to carotids; MR radiates to axilla), grade (I-VI Levine scale).
• Dynamic maneuvers: squatting/handgrip increase MR and VSD murmur intensity (increase afterload); standing/Valsalva increase HOCM murmur (decrease preload) but decrease AS murmur — this maneuver differentiates HOCM from AS, a favorite viva discriminator.

6. Complete the examination

Output Tasks (per your plan)

1. Perform one complete CVS examination aloud, as if presenting a long case, in the correct sequence: general inspection → hands/pulse → face → JVP → precordium (inspection, palpation, auscultation) → back/lungs → abdomen → legs.
2. Build a checklist distinguishing normal vs abnormal findings at each step.
3. Write differential diagnosis lists for all six cardinal symptoms from memory, without looking back.

Checkpoint Questions

1. A patient has a raised JVP with a prominent "y descent" and Kussmaul's sign. What's your top diagnosis, and why does inspiration paradoxically raise JVP here?
2. Why does orthopnoea occur specifically on lying flat, and why is PND worse at night compared to daytime exertional dyspnoea?
3. Differentiate cardiac syncope from vasovagal syncope using three history features and explain the physiological reason cardiac syncope is more dangerous.
4. A patient has clubbing, central cyanosis, and pink upper limbs but blue lower limbs. What's the diagnosis and underlying shunt physiology?
5. On examination, standing up from squatting makes a systolic murmur louder. What valve lesion does this suggest, and why does the maneuver have this effect?