2.2 Congenital Heart Defects

Congenital Heart Defects

Quick Answer: Sort NICU congenital heart disease by oxygenation, pulse and blood-pressure symmetry, and whether the ductus is feeding the body or the lungs. Cyanotic and mixing lesions—TGA, HLHS, TOF, TAPVR, truncus, tricuspid atresia, critical pulmonary stenosis or atresia—present with hypoxemia that oxygen cannot fully fix. Acyanotic volume or obstruction lesions—VSD, ASD, AVSD, coarctation, interrupted arch, critical aortic stenosis—may stay pink until the duct closes or until PVR falls enough to flood the lungs. PGE1 is the emergency infusion when the duct is the only pathway for systemic or pulmonary flow. The hyperoxia test, right-hand/foot pulse oximetry, and the difference between differential and reverse-differential cyanosis tell you whether you are looking at lung disease, PPHN, or a structural lesion.

This OpenExamPrep section is independent teaching on congenital heart defects as they present in the NICU. Pediatric CCRN pages at /study-guides/ccrn-pediatric emphasize older children; here the first week of life, the closing duct, and mixing are the problems that generate hours at the crib.

Sort the infant before you sort the eponym

A 2.9 kg infant who is 70% on 100% oxygen with a single S2 is not “a murmur workup.” A 3.8 kg infant who was feeding well at 12 hours and is now gray with absent femorals at 40 hours is not “rule out sepsis only.” Both may need blood culture and antibiotics, but the circulation question is: Is oxygenated blood reaching the body? Is enough blood reaching the lungs? Is the only remaining pathway a closing duct?

Work the physical in a fixed order so you do not miss a closing arch:

1. Pre- and post-ductal saturations (right hand and a foot) and four-limb blood pressures or at least right-arm versus leg pulses.
2. Perfusion and liver size. Closing-duct systemic lesions look like shock: mottling, delayed capillary refill, oliguria, rising lactate, metabolic acidosis. Pulmonary-flow lesions look like progressive cyanosis without that full shock picture until hypoxia is extreme.
3. Chest radiograph and blood gas. Oligemic lungs plus deep cyanosis point toward right-heart obstruction. Flooded lungs plus mild cyanosis point toward mixing or left-to-right volume. A narrow mediastinum (“egg on a string”) supports transposition. A large heart with pulmonary edema in the first hours supports obstructed pulmonary veins or severe left-heart obstruction.
4. Hyperoxia test when the diagnosis is still lung-versus-heart and an arterial gas can be obtained safely.
5. PGE1 as soon as a ductal-dependent lesion is the leading diagnosis—do not wait for a perfect echocardiogram if the infant is crashing.

Normal neonatal heart rate remains about 120–160 beats/min in a quiet term infant (higher when distressed). Mean blood pressure on day 1 still roughly tracks gestational age in weeks for preterms; a term infant’s mean is often 40–50 mm Hg. Those numbers do not diagnose CHD, but a term infant with a mean of 28 mm Hg and no femorals is a closing-duct emergency until proven otherwise.

Cyanotic, acyanotic, and mixing — useful labels, not a religion

Cyanotic lesions produce visible hypoxemia because deoxygenated blood reaches the aorta or because pulmonary blood flow is too low. The classic teaching cluster includes transposition of the great arteries (TGA), tetralogy of Fallot (TOF), truncus arteriosus, total anomalous pulmonary venous return (TAPVR), and tricuspid atresia. Hypoplastic left heart syndrome (HLHS) may look gray more than blue because cardiac output is low, but it is a mixing, single-ventricle circulation.

Acyanotic lesions send oxygenated blood back to the lungs (VSD, ASD, PDA, AVSD) or obstruct the left heart without obligatory right-to-left shunt until the duct closes (coarctation, interrupted aortic arch, critical aortic stenosis). A “pink” infant can still die of closing-duct shock.

Mixing lesions have a common chamber or obligatory communication (truncus, TAPVR, complete AVSD, unobstructed mixing in TGA). Saturations often sit in a middle band—sometimes 80–90%—because pulmonary and systemic venous blood share an outlet. Chasing 100% with free oxygen can drop PVR, raise pulmonary blood flow, and steal from the systemic and coronary beds.

Ductal-dependent systemic versus pulmonary blood flow

Ductal-dependent systemic blood flow means the body (and often the coronaries) is perfused through the PDA. When the duct constricts—classically day 2 to day 7 as PGE2 falls—the lower body, or the entire systemic bed in HLHS, loses flow. Think HLHS, critical coarctation, interrupted aortic arch, critical aortic stenosis. The crib picture is shock, weak femorals, differential pulses, rising lactate, and a liver that enlarges as the left heart fails or the ductal runoff vanishes.

Ductal-dependent pulmonary blood flow means the lungs are perfused through the PDA. When the duct closes, cyanosis deepens and pulmonary markings become oligemic. Think pulmonary atresia, critical pulmonary stenosis, and some TOF or tricuspid atresia with severe right ventricular outflow obstruction.

PGE1 is the shared emergency. Starting dose is commonly 0.05–0.1 mcg/kg/min with readiness for apnea. You are buying ductal patency, not fixing the anatomy. Side effects (apnea, fever, vasodilation) are expected costs, not reasons to withhold the drug from a crashing neonate.

Obstructed TAPVR is the famous exception. Pulmonary venous blood cannot get out of the lung. Opening the duct does not unobstruct the veins and can increase pulmonary blood flow into a blocked exit, worsening edema. The treatment is urgent surgical repair, not a longer PGE1 wean.

Hyperoxia test and the CCHD pulse-oximetry screen

The hyperoxia test places the infant in 100% oxygen for about 10 minutes, then samples an arterial PaO2—ideally pre-ductal if you can get a right-radial gas.

• A robust rise, often PaO2 >150 mm Hg, favors lung disease that can still oxygenate blood once alveolar oxygen is high.
• A PaO2 that remains below about 100 mm Hg, and especially below 50–60 mm Hg, favors fixed mixing or parallel circulations (TGA, other cyanotic CHD).
• Intermediate values overlap with PPHN. The test is a sorter, not a standalone diagnosis. Never let the test delay PGE1 in a shocked or deeply cyanotic neonate.

The critical congenital heart disease (CCHD) screen is a pulse-oximetry algorithm, usually after 24 hours of life so transitional PVR has had time to fall:

• Sites: right hand (pre-ductal) and either foot (post-ductal).
• Pass: both readings ≥95% and the difference ≤3%.
• Fail: either reading <90%.
• Repeat zone: 90–94% or a difference >3%—repeat the screen per protocol (commonly two more times, an hour apart) before you call a fail.

A passed screen does not exclude all CHD (coarctation can still present later). A failed screen is a prompt for urgent clinical review and echocardiography, not a label you argue with because the infant “looks fine.”

Differential cyanosis and reverse differential cyanosis

Differential cyanosis means the right hand is pinker than the foot (pre-ductal saturation higher than post-ductal). Deoxygenated blood is entering the descending aorta through a right-to-left PDA. The two NICU explanations you must hold together are PPHN (high PVR) and coarctation or interrupted arch with right-to-left ductal flow around an obstructed arch. Pulses and four-limb blood pressures separate those stories: PPHN has palpable femorals; critical coarctation does not.

Reverse differential cyanosis means the foot is pinker than the right hand. That pattern is uncommon and highly localizing. In TGA, the aorta arises from the RV, so the right hand receives the most desaturated blood. If a PDA also supplies the descending aorta with relatively oxygenated pulmonary-artery blood—because PVR is high (TGA plus PPHN) or because an arch obstruction forces that pathway (TGA plus coarctation)—the lower body can look pinker than the right hand. Reverse differential cyanosis is therefore TGA plus PPHN or TGA plus coarctation/interrupted arch until echocardiography says otherwise.

Mixing and balloon atrial septostomy

Parallel circulations (TGA) need a communication: ASD/PFO, VSD, or PDA. If the atrial septum is restrictive, the infant stays profoundly cyanotic even on PGE1 because the two circuits barely mix. Balloon atrial septostomy (Rashkind) is a catheter procedure that tears or enlarges the atrial communication so oxygenated and deoxygenated blood can mix. You will see it discussed as a bridge to arterial switch, not as a destination. Nursing around septostomy is about line security, rhythm, recurrent cyanosis if the hole is still inadequate, and the same PGE1/apnea watch if the duct is still required.

Lesion-by-lesion bedside clues

Transposition of the great arteries (TGA). Aorta from RV, PA from LV. Two parallel circuits. Profound cyanosis in a term infant with little respiratory distress is the classic delivery-room surprise. Single S2. Egg-on-a-string silhouette on some films. Mixing is life. PGE1 plus assessment of the atrial communication; septostomy if mixing is inadequate.

Hypoplastic left heart syndrome (HLHS). Mitral/aortic atresia or severe stenosis with a hypoplastic LV and arch. Systemic and coronary flow is retrograde through the PDA and aortic arch. As the duct closes, the infant becomes gray, acidotic, and anuric. Saturations are often targeted in the 75–85% band per unit protocol so Qp:Qs stays near 1:1. High FiO2 and aggressive alkalosis drop PVR, flood the lungs, and steal from coronaries. Avoid over-oxygenation as a reflex.

Tetralogy of Fallot (TOF). VSD, RV outflow obstruction, overriding aorta, RV hypertrophy. A “pink tet” has mild obstruction and may present later with a murmur. Severe obstruction is ductal-dependent pulmonary flow. Hypercyanotic spells in older neonates: infundibular spasm plus increased right-to-left VSD shunt. Nursing response is knees-to-chest, oxygen, calm, morphine as ordered, volume, and a vasoconstrictor such as phenylephrine if the spell is refractory—not a random bicarbonate-first approach.

Total anomalous pulmonary venous return (TAPVR). All pulmonary veins drain to a systemic venous structure. Unobstructed TAPVR is a mixing lesion with increased pulmonary flow. Obstructed TAPVR (often infracardiac, through the diaphragm) looks like intractable pulmonary edema and cyanosis in the first hours. The lung fields can be white. PGE1 does not open the venous confluence.

Coarctation and interrupted aortic arch. Pulse and blood-pressure gradient from right arm to legs. Shock when the duct closes. Interrupted arch is often associated with 22q11 deletion (DiGeorge): watch calcium and the airway. PGE1 restores lower-body flow through the duct.

Truncus arteriosus. A single arterial trunk gives aorta, PA branches, and coronaries, plus a VSD. Mixing is obligatory. Bounding pulses and early heart failure as PVR falls. Saturations often sit in the mid-80s to around 90%. Not classically ductal-dependent, but the infant can still crash from overcirculation.

Critical aortic stenosis and critical pulmonary stenosis. Critical AS behaves like other left-heart obstructive lesions: shock, poor pulses, PGE1 for systemic flow. Critical PS or pulmonary atresia behaves like other right-outflow lesions: cyanosis, PGE1 for pulmonary flow. Both can have a harsh murmur; the perfusion and saturation pattern tell you which side is starving.

VSD, ASD, and AVSD. A moderate or large VSD usually waits to declare itself until PVR falls—often 2–8 weeks in a term infant, sometimes earlier in a preterm infant whose PVR drops on a different clock. Then you see tachypnea, poor feeding, hepatomegaly, and a holosystolic murmur. ASD is often quieter in the NICU. Complete AVSD is strongly associated with trisomy 21; expect a mixing, common-valve picture and earlier heart failure than a small muscular VSD.

Tricuspid atresia. No direct RA-to-RV path. An ASD must exist for systemic venous blood to reach the left heart; pulmonary flow depends on a VSD and/or PDA. Cyanosis is expected. PGE1 if pulmonary flow is ductal-dependent. Left-axis deviation on ECG is a classic clue you may see mentioned on echocardiogram reports.

Nursing priorities while you wait for the cardiologist

Keep the duct open with PGE1 when the lesion is ductal-dependent. Watch for closing-duct shock: fading pulses, widening acidosis, falling urine output, a rising lactate (for example from 1.8 to 6 mmol/L over a few hours), and a sudden need for volume and inotropes. Do not treat that trajectory with a fluid bolus alone and a hope that the murmur is innocent.

Avoid over-oxygenation in HLHS and some mixing physiologies per unit protocol. Many single-ventricle pathways accept saturations in the mid-70s to mid-80s so pulmonary and systemic flows stay balanced. That is a written target, not a dare to withhold oxygen from a truly collapsing infant—if the infant is 50% and bradycardic, you resuscitate.

Neutral thermal environment still matters: cold stress raises PVR and can recreate fetal shunting. Keep glucose in a safe neonatal range (treat symptomatic hypoglycemia; many units intervene at <40–50 mg/dL in the first hours) because a shocked infant who is also hypoglycemic will not clear lactate. Lines (UVC/UAC or peripheral access that can run PGE1 without interruption) are part of the lesion, not extras.

Exam traps: calling every cyanotic infant PPHN; giving indomethacin to a shocked term neonate; assuming a passed CCHD screen excludes coarctation; treating obstructed TAPVR as a PGE1-responsive ductal lesion; and oxygenating an HLHS infant to 99% because “cyanosis is always bad.”

Independent practice items for this exam live at /practice/ccrn-neonatal.