Fetal Circulation😊

Umbilical Cord Contents

• Contains: 1 vein & 2 arteries (70%)

Constituents	Function
2 umbilical arteries	Carry deoxygenated blood from fetus.
1 umbilical vein	Carries oxygenated blood to fetus. (SpO2 -80%)
Wharton's jelly	Gelatinous substance
Allantois	Early urine formation → becomes urachus
Vitello-intestinal duct	between yolk sac and midgut

• Single umbilical artery
• 5-10/1000 live births
• A/w ↑↑ risk of a renal anomaly in the baby

Order of Decreasing Saturation of O2

• Umbilical vein: 80%

• Inferior vena cava (IVC): 70%

• LV: 65% > RV: 55-60%

• Superior vena cava

Where would you place the pulse oximeter to measure preductal oxygen saturation in an infant who was born 3 minutes ago?

1. Lungs become the source of O2 instead of the placenta

2. Pulmonary vascular resistance decreases:
1. Blood flow to the lung increases
2. produces systolic murmur

3. Systemic vascular resistance ↑↑↑

4. Foramen ovale closes

Additional Notes on Remnants

• Septum primum → Fossa ovalis.

• Septum secundum → Limbus fossa ovalis.

Closure of Structures

• Anatomical: Order V (Veno) Are (Art) Onnikkunnu (Ovale)

• Anatomical Closure time
• Vein → close fast → 1 week
• Artery → 3 week
• Heart → 3 months

• Pathways coming after Placenta closes functionally immediately after its removal
• Like Foramen ovale and Ductus venosus

• Foramen ovale closure Process:
• Blood goes to lungs via pulmonary vein.
• LA pressure ↑↑ and RA pressure ↓↓
• Fusion of septum primum and secundum.
• Closure of foramen ovale.

Applied Anatomy

• Patent ductus arteriosus (PDA):
• Causes acyanotic heart disease.

• Probe patency of foramen ovale:
• Gap between septum primum and septum secundum (seen in 20% cases).
• Not a functional defect.

• Umbilical arteries → 2
• Obliterate before birth.
• Remnant:
• Proximal part → Superior vesical artery.
• Distal part → Obliterated umbilical artery → Medial umbilical ligament
• NOTE
• Lateral umbilical ligament
• Remnant of Inferior Epigastric vessels

• Umbilical vein (left) → 1
• Obliterates after closure of umbilical artery.
• Remnant: Ligamentum teres hepatis.

Bulbus cordis

• Part of conus of Heart Tube or Conus arteriosus
• Proximal 1/3rd → Rough inflowing/trabeculated Part of RV
• Middle 1/3rd → Smooth Outflowing/Infundibulum part of RV
• Distal 1/3rd → Spiral septum/Bulbar septum → Interventricular Septum

• Smooth outflowing part aka Infundibulum of Both Ventricles
• leading to Pulmonary trunk
• From conus > middle 1/3rd of bulbus cordis
• (bulbus is a part of conus of Heart Tube or Conus arteriosus)

• NOTE: Smooth parts of
• RA → Body, Right horn of sinus venosus (septum spurium)
• LA → Primitive Pulmonary Vein

• Left horn of sinus venosus → Coronary sinus

• Common cardinal vein → SVC

Bulbus cordis

• Part of conus of Heart Tube or Conus arteriosus
• Proximal 1/3rd → Rough inflowing/trabeculated Part of RV
• Middle 1/3rd → Smooth Outflowing/Infundibulum part of RV
• Distal 1/3rd → Spiral septum/Bulbar septum → Interventricular Septum

• Spiral septum never formed

• Sitting duck appearance

• Associated with maternal diabetes DM

• Parallel Circulation

• The cardiac silhouette shows
• “Egg on the side”
• Egg on string appearance.

• Important
• Septum dependent heart ds
• Keep PDA Open
• ↑ pulmonary blood flow
• Narrow Pedicle

• Not compatible with life unless a/w ASD + PDA
• Keep PDA open up to surgery
• IV Prostaglandin E1
• To make ASD
• Atrial Septoplasty
• Rashkind's Balloon Atrial Septostomy immediately

• Definitive surgery - Jatene's arterial switch operation by two weeks of age

• Mnemonic: Thenga → TGA → Emergency Rush (Rashkind) to surgery, Jiitne keliye (Jatene)

• Most common congenital cyanotic heart disease in children

• The most common congenital cyanotic heart disease beyond infancy

• 4 Components of TOF
1. Large non-restrictive VSD
2. Pulmonary infundibular stenosis
3. Overriding of aorta
4. Right ventricular hypertrophy

• NOTE:
• ASD is a component of the
• trilogy and pentalogy of Fallot
• Pentalogy = TOF + ASD
• NOT tetralogy of Fallot

Pathophysiology and Clinical Features

• Pulmonary artery stenosis
• ↓↓ blood pumped to the lungs

Clinical Features

• Cyanosis (central) due to hypoxia: spo2=75-85%

• Clubbing

• Polycythemia

• Cyanotic spells
• Small → knee chest position
• Older → squatting position

• Heart failure is NOT SEEN unless
• Anemia
• Infective endocarditis
• Myocarditis
• Systemic hypertension

• Shunt is Right-to-Left shunt through VSD

• Reversal of shunt is NEVER SEEN in TOF
• NO Eisenmenger syndrome
• Reason
• TOF = congenital right-to-left shunt from the beginning.
• Due to Right Ventricular Outflow Tract Obstruction (RVOTO) → ↑ Right Ventricular pressure > Left ventricle

• Auscultatory Findings
• Ejection systolic murmur in the pulmonary area
• Single S2 (P2 is soft and inaudible)

Severity of TOF

• Lesser blood goes across pulmonary valve

• Murmur is shorter and softer

• More severe cyanosis

Investigations

• Chest X-ray:
• Boot-Shaped Heart (or) 'Cor En Sabot' Appearance
• D/t RVH
• + Pulmonary Oligemia

Treatment

• Moist O2 inhalation (to reduce hypoxia)

• Inj. Sodium Bicarbonate (to neutralize acidosis)

• Morphine

• Ketamine (increases systemic vascular resistance)

• Alpha agonists (phenylephrine)

• Beta — blockers (Propranolol): decreases pulmonary infundibular spasm

• Cyanotic spells
• Squatting or knee-chest position

• PRBCs transfusion

Definitive (corrective) Sx

• VSD closure +

• Repair of pulmonary stenosis

Shunt (palliative) Sx