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Fetal Circulation
Three structures bypass the lungs in fetal life — understanding them explains many congenital defects.
- Ductus Venosusbypasses liver
- Carries oxygenated blood from umbilical vein to inferior vena cava. Closes within days, becomes the ligamentum venosum. If stays open: rare; causes portal hypertension.
- Foramen Ovalebypasses lungs
- Opening between right and left atria — allows blood to bypass fetal lungs. Closed by increased left atrial pressure after first breath. If stays open: Atrial Septal Defect (ASD).
- Ductus Arteriosusbypasses lungs
- Connects pulmonary artery to aorta — shunts blood away from fetal lungs. Closes within 24–48 hours due to increased O2 and decreased prostaglandins. If stays open: Patent Ductus Arteriosus (PDA).
Exam Tip
Prostaglandin E1 is the drug used to KEEP the ductus arteriosus open when needed (e.g., in Transposition of the Great Vessels to allow mixing). Indomethacin (NSAID) is used to CLOSE a PDA. These are frequently tested drug questions.
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02
Classification: Acyanotic vs Cyanotic
The most important CHD distinction — determines oxygenation status and clinical picture.
- Acyanotic | Cyanotic
- Definition
- Oxygenation NOT affected. Blood flow abnormal but lungs still oxygenate blood adequately. | Oxygenation IS affected. Deoxygenated blood mixes with or bypasses the lungs.
- Skin color
- Normal — pink | Blue/dusky — cyanotic
- Blood flow
- Left-to-right shunt (oxygenated blood recirculates to lungs — extra, not dangerous initially) | Right-to-left shunt (deoxygenated blood enters systemic circulation)
- Examples
- ASD, VSD, PDA, coarctation of the aorta, pulmonary stenosis | Tetralogy of Fallot (TOF), Transposition of the Great Vessels (TGV), Tricuspid Atresia
Memory Trick
"Acyanotic = Adequate oxygenation" and "Left-to-right shunts are Less dangerous at first." Cyanotic defects cause blue babies — you can remember these are more urgent because blue = not enough oxygen.
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Acyanotic Defects
Baby is pink — but blood flow is abnormal. Left-to-right shunts overload the lungs.
Ventricular Septal Defect (VSD) — Most Common CHD
- Opening between the left and right ventricles
- Blood shunts left-to-right (oxygenated blood recirculates to lungs)
- Sign: loud harsh holosystolic murmur at left lower sternal border
- Symptoms: poor feeding, diaphoresis with feeding, failure to thrive, recurrent respiratory infections
- Small VSDs may close spontaneously. Large: surgical patch or catheter-based closure
Atrial Septal Defect (ASD)
- Opening between the left and right atria (foramen ovale never closed)
- Often asymptomatic in childhood — discovered on routine exam
- Sign: systolic murmur, fixed split S2
- Risk if untreated: pulmonary hypertension in adulthood, stroke risk (paradoxical embolism)
- Treatment: observation (small), catheter closure or surgery (large)
Patent Ductus Arteriosus (PDA)
- Ductus arteriosus (PA to aorta) fails to close after birth
- More common in premature infants
- Sign: continuous "machinery" murmur, bounding pulses, wide pulse pressure
- Treatment: Indomethacin IV (NSAID closes it). Surgery if medication fails.
- Do NOT give indomethacin if renal impairment or platelet issues
Coarctation of the Aorta
- Narrowing of the aorta — usually near ductus arteriosus
- Classic finding: high BP in arms, low BP in legs (weak/absent femoral pulses)
- May be detected at newborn screen or present in adolescence with HTN
- Treatment: balloon angioplasty or surgical resection
Failure to Thrive with Feeding
A key sign of acyanotic CHDs in infants is sweating and tiring during feeding — the infant's heart is working so hard that feeding becomes exhausting. Poor weight gain is the classic presentation. Always weigh infants at every visit and plot on a growth chart.
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Cyanotic Defects
Baby is blue — deoxygenated blood is entering systemic circulation.
Tetralogy of Fallot (TOF) — Most Common Cyanotic CHD
Four defects remembered by "PROVE":
- Pulmonary stenosis (obstruction to right ventricular outflow)
- Right ventricular hypertrophy
- Overiding aorta (sits over the VSD, receives blood from both ventricles)
- Ventricular septal defect (VSD)
- Excessive cyanosis (result of all four)
TOF Clinical Features
- Tet spells (hypercyanotic episodes): sudden severe cyanosis — child becomes blue, agitated, then limp
- Squatting position: child instinctively squats to increase systemic vascular resistance and push more blood to the lungs — this is PATHOGNOMONIC for TOF
- In infants: knee-chest position (equivalent of squatting)
- Boot-shaped heart on X-ray
- Clubbing of fingers/toes (chronic hypoxia)
Tet Spell Nursing Response
Place child in knee-chest position immediately. Give O2. Calm the child (crying worsens it). Notify provider. Morphine may be ordered to decrease infundibular spasm. Do NOT leave the child alone.
Transposition of the Great Vessels (TGV)
- Aorta and pulmonary artery are switched — two parallel, incompatible circuits
- Incompatible with life without mixing — survival depends on keeping ductus arteriosus open
- Emergency treatment: Prostaglandin E1 IV to maintain ductus arteriosus patency
- Definitive: arterial switch surgery within first week of life
- Baby: severely cyanotic at birth, not improved with O2
? What is the immediate nursing action during a tet spell?
Place the infant/child in knee-chest position (or squat for older children). This increases systemic vascular resistance, which forces more blood through the pulmonary artery to the lungs. Calm the child, give O2, and notify the provider.
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General Signs of CHD
These signs apply across all congenital heart defects — know them for select-all-that-apply questions.
- Poor feeding / failure to thrive#1 complaint
- Feeding requires cardiovascular effort. Infant fatigues quickly, stops feeding early, gains weight poorly.
- Diaphoresis with feedingred flag
- Sweating during feeding in a cool room = heart working too hard. Classic CHD red flag.
- Tachypnea / dyspnea
- Increased respiratory effort — lungs compensating for poor cardiac output.
- Cyanosis
- Cyanotic defects: central cyanosis (lips, tongue). Acyanotic: peripheral cyanosis only during exertion.
- Heart murmur
- Abnormal turbulent blood flow through defect. May be the only sign in mild defects.
- Clubbingchronic hypoxia
- Chronic hypoxia thickens fingertips/toes. Develops over months — not present at birth.
- Frequent respiratory infections
- Pulmonary congestion provides a breeding ground for infection.
- Squatting / knee-chest positionTOF classic
- Child adopts position to increase blood return to lungs. Classic for Tetralogy of Fallot.
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Nursing Care
Priority nursing interventions for children with congenital heart defects.
Priority Nursing Actions
- Monitor weight daily — single best indicator of fluid status and failure to thrive
- Small, frequent feedings — reduces cardiac workload. Use high-calorie formula if needed.
- Rest periods during and after feeding — allow 20–30 minutes max per feeding
- Gavage (NG) feeding may be needed if infant tires before adequate intake
- Monitor SpO2 continuously — report any drop
- Position: semi-Fowler's or infant seat to reduce cardiac workload
- Prevent infection — these children are immunocompromised and high-risk for endocarditis
Pre/Post-Op Cardiac Surgery
- Pre-op: NPO, consent, baseline VS, SpO2, weight
- Post-op: assess for bleeding, arrhythmias, respiratory distress, low urine output
- Chest tubes may be present — monitor drainage (should be minimal and serosanguineous)
- Monitor for cardiac tamponade: muffled heart sounds + hypotension + JVD
Exam Tip
If an exam question describes a baby who becomes sweaty and stops feeding after 5 minutes in a cool room — think congenital heart defect. The answer will involve calling the provider, weighing the infant, and monitoring feeding time. Never force a cardiac infant to finish a bottle.
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Frequently Asked Questions
Common student questions on this topic.
What is the difference between acyanotic and cyanotic heart defects?
Acyanotic defects involve left-to-right shunting — oxygenated blood mixes back into the right side. The child does NOT appear blue. Examples: ASD, VSD, PDA, coarctation of the aorta. Cyanotic defects involve right-to-left shunting — deoxygenated blood enters systemic circulation. Child appears blue. Examples: Tetralogy of Fallot, transposition of the great vessels, tricuspid atresia. Cyanotic defects are generally more serious and require earlier intervention.
What is a tet spell and how is it managed?
A "tet spell" is a sudden episode of hypercyanosis in Tetralogy of Fallot — typically after crying, feeding, or pooping. Triggers include any state that drops systemic vascular resistance. The child becomes very blue, irritable, and may lose consciousness. Immediate intervention: put the child in knee-chest position (or older child squats) — this increases systemic vascular resistance and forces blood through the lungs. Calm the child, oxygen, morphine if severe.
What are the four defects in Tetralogy of Fallot?
VSD (ventricular septal defect), pulmonary stenosis, overriding aorta, and right ventricular hypertrophy. Mnemonic: PROVe — Pulmonary stenosis, RVH, Overriding aorta, VSD. The combination causes deoxygenated blood to shunt right-to-left through the VSD, resulting in cyanosis. Surgical correction is typically performed in infancy.
What are the signs of heart failure in an infant?
Infants don't say "I'm short of breath" — watch for: poor feeding (gets tired during feeds), diaphoresis with feeds, tachypnea, tachycardia, poor weight gain (failure to thrive), respiratory distress (retractions, nasal flaring), hepatomegaly, periorbital edema. Pulmonary edema is less common than in adults. Suspect HF in any infant with feeding difficulties, especially with known congenital heart defect.
Why is endocarditis prevention important after CHD surgery?
Children with structural heart defects (especially after surgical repair with prosthetic material) are at higher risk for bacterial endocarditis. Antibiotic prophylaxis is recommended before dental procedures and certain surgeries — typically amoxicillin 30–60 minutes before the procedure. Strict dental hygiene is critical. Avoid body piercings. Wear medical alert ID. Watch for unexplained fever, fatigue, or new murmur after high-risk procedures.
How is a PDA treated in newborns?
A patent ductus arteriosus is normal in fetal circulation but should close within 24–48 hours of birth. Premature infants often have a persistent PDA. Treatment depends on size and symptoms: small/asymptomatic PDAs may close on their own. Indomethacin or ibuprofen (NSAIDs) can promote closure by inhibiting prostaglandins. Surgical or catheter-based closure is used for larger PDAs. Conversely, in some cyanotic defects, prostaglandin E1 is given to keep the PDA open until surgery.
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