Congenital Heart Disease — Tricuspid Atresia

• Embryologic developmental failure: Failure of endocardial cushion and bulbus cordis development results in absence of tricuspid valve tissue and hypoplasia or complete aplasia of the right ventricle. The embryologic defect occurs between weeks 4-7 of gestation, involving abnormal neural crest cell migration and endocardial cushion formation. This developmental failure may be associated with chromosomal abnormalities (chromosome 22q11 deletion in DiGeorge syndrome) or teratogenic exposures (maternal lithium, retinoic acid).

• Obligatory right-to-left shunting: With no tricuspid valve, systemic venous return cannot enter the right ventricle. Blood must shunt right-to-left across an ASD/PFO to reach the left atrium, then through the left ventricle to the systemic circulation. This mandatory right-to-left shunt results in cyanosis (deoxygenated systemic venous blood mixing with oxygenated pulmonary venous blood) and reduced systemic oxygen delivery. The degree of cyanosis depends on the magnitude of right-to-left shunt and the adequacy of pulmonary blood flow.

• Pulmonary circulation dependency on ductal patency: In TA, the pulmonary circulation relies entirely on one of three sources: (1) PDA, (2) aortopulmonary collaterals, or (3) an RVOT (present in some cases with hypoplastic RV). The right ventricle is severely hypoplastic or absent, making it incapable of generating pulmonary blood flow independently. Ductal closure in the neonatal period causes acute reduction in pulmonary blood flow, leading to severe cyanosis, metabolic acidosis, and cardiogenic shock—a medical emergency. Prostaglandin E1 (PGE1) maintains ductal patency by preventing smooth muscle contraction in the ductal tissue.

• Secondary hemodynamic consequences: Right atrial pressure elevation occurs due to obstruction to systemic venous return, potentially predisposing to atrial arrhythmias and hepatic congestion. The left ventricle becomes hypertrophied as it handles both pulmonary and systemic circulation, eventually leading to systemic ventricular dysfunction. Reduced pulmonary blood flow results in underdevelopment of pulmonary vascular beds, which may limit the feasibility of later surgical repair.

• Chromosomal abnormalities: Chromosome 22q11 deletion (DiGeorge/velocardiofacial syndrome) is the most common genetic association with TA, present in 25-30% of cases; trisomy 13, 18, and 21 also carry increased risk. Heterozygous GATA4 and NKX2-5 mutations have been identified in familial cases.

• Maternal teratogenic exposures: Maternal lithium use in first trimester (50-100 fold increased risk), maternal retinoic acid exposure, maternal diabetes, maternal phenytoin use, and maternal rubella infection during pregnancy are established risk factors.

• Sporadic developmental abnormalities: The majority of TA cases (approximately 70-80%) occur sporadically without identified genetic or environmental etiology, suggesting multifactorial inheritance or de novo mutations affecting cardiac development pathways.

Cardinal symptoms

• Severe cyanosis appearing within hours to days of life (typically by day 1-3 as PDA closes); "blue baby" presentation
• Dyspnea and respiratory distress resulting from hypoxemia and metabolic acidosis
• Poor feeding and failure to thrive due to cyanosis and increased metabolic demands
• Sudden deterioration or "cyanotic spell" with acute increase in cyanosis and loss of consciousness if ductal closure occurs

Physical examination findings

• Single loud S2 (only aortic component audible; pulmonary valve inaudible or soft) due to pulmonary artery hypoplasia
• Absence of systolic murmur from tricuspid regurgitation (no tricuspid valve present); murmur may be heard from PDA (continuous "machinery" murmur) or ASD (usually silent)
• Cyanosis with clubbing (in untreated older infants/children); may demonstrate hypercyanotic spells (sudden worsening of cyanosis with hyperpnea, syncope, possible seizure or death)
• Hepatomegaly due to elevated right atrial pressure and hepatic congestion
• Diminished femoral pulses if severe left ventricular dysfunction develops
• Prominent right ventricular heave may be absent (hypoplastic RV), but left ventricular impulse may be hyperdynamic

Electrocardiography (ECG)

• Left-axis deviation (QRS axis -30 to -90 degrees, highly characteristic) due to hypoplastic RV and left ventricular dominance; this is the most specific ECG finding for TA
• Right atrial enlargement (peaked P waves, P wave amplitude >2.5 mm)
• Left ventricular hypertrophy (tall, broad QRS complexes in lateral leads)
• Absence of right ventricular forces (no R waves in leads V1-V3); rS pattern in precordial leads
• First-degree AV block may be present

Chest X-ray (CXR)

• Decreased pulmonary vascular markings ("oligemic" lung fields) due to reduced pulmonary blood flow
• Boot-shaped or egg-on-string heart silhouette (cardiac enlargement with elevated apex, reflecting left ventricular enlargement)
• Right atrial enlargement (prominent right heart border)
• Concave pulmonary artery segment (pulmonary artery hypoplasia)

Echocardiography (two-dimensional and Doppler)

• Absent or severely hypoplastic tricuspid valve with no flow across the tricuspid region on color Doppler
• Hypoplastic or absent right ventricle; RV cavity is diminutive or not visualized
• Enlarged right atrium with prominent eustachian valve or Chiari network
• ASD or PFO with right-to-left shunt evident on color Doppler (bubble study positive)
• PDA with left-to-right shunt (or bidirectional flow) visualized in parasternal short-axis view; continuous wave Doppler shows continuous flow
• Normally formed mitral valve and left ventricle (often hypertrophied and hyperdynamic)
• Normal aorta arising from left ventricle; pulmonary artery small and arises from RV (if present) or receives flow from aorta via PDA
• Secundum ASD most common; ostium primum ASD or unroofed coronary sinus may be present in 30% of cases

• Demonstrates inability to catheterize right ventricle from right atrium (tricuspid atresia)
• Confirms right-to-left shunt at atrial level (blood oxygen saturation identical in RA and LA)
• Documents elevated right atrial pressure (mean RA pressure typically 8-12 mmHg, elevated)
• Assesses coronary anatomy preoperatively (anomalous coronary origin from opposite sinus may be present in 3-5%, affecting surgical planning)
• Allows balloon atrial septostomy (Rashkind procedure) to enlarge PFO/ASD and improve right-to-left shunting

• Atretic tricuspid valve with no communication between RA and RV
• Obligatory ASD (PFO) or PDA for survival
• Hypoplastic or absent RV
• Left-axis deviation on ECG

• Prostaglandin E1 (PGE1) infusion (0.05-0.1 μg/kg/min IV) immediately upon diagnosis or suspicion to maintain patency of the ductus arteriosus; this is the single most critical intervention for survival in the immediate neonatal period. PGE1 works by inhibiting smooth muscle contraction in ductal tissue and must be continued until definitive surgical intervention. Side effects include apnea (requiring intubation in 10-60% of cases), fever, hypotension, and fluid retention.
• Supplemental oxygen carefully titrated (target SpO2 75-85%); excessive oxygen causes pulmonary vasodilation and worsens right-to-left shunting by decreasing the pressure gradient driving shunt flow across the ASD
• Avoid alkalosis: Metabolic or respiratory alkalosis increases hemoglobin-oxygen affinity and worsens cyanosis; mild hypercarbia is tolerated (target pCO2 45-55 mmHg) to maintain pulmonary vascular tone and ductal patency
• Maintain systemic-pulmonary collateral flow: Avoid excessive PEEP or hyperventilation; permissive hypercapnia is acceptable
• Fluid resuscitation and correction of metabolic acidosis with sodium bicarbonate (indicating inadequate systemic perfusion and mixed venous oxygen desaturation)
• Prostaglandin E1 continuation throughout initial hospitalization and until surgical intervention

First-line definitive surgical intervention

• Balloon atrial septostomy (Rashkind procedure) as temporizing measure in the cardiac catheterization laboratory; creates larger ASD to optimize right-to-left shunting and improve systemic oxygen delivery. This provides temporary bridge (days to weeks) to definitive surgical repair and is less invasive than immediate surgical septostomy.
• Stage I Norwood procedure or Blalock-Taussig (BT) shunt (modified BT shunt most commonly used) as initial surgical intervention in first weeks of life. The BT shunt creates an artificial communication between the systemic circulation (subclavian or innominate artery) and the pulmonary artery, providing pulmonary blood flow independent of the PDA. The hypoplastic RV is left in place.

• Stage I (neonatal): BT shunt or Norwood procedure (as above)
• Stage II (Glenn procedure, at 4-6 months of age): Superior vena cava is anastomosed directly to the pulmonary artery (cavopulmonary connection), eliminating the need for RV-mediated pulmonary blood flow and reducing cyanosis. The inferior vena cava still drains to the hypoplastic RV.
• Stage III (Fontan procedure, at 2-4 years of age): Inferior vena cava is also connected to the pulmonary artery via a conduit (total cavopulmonary connection), completing separation of systemic and pulmonary circulation without using the ventricle as a pump. This achieves near-complete resolution of cyanosis and represents definitive correction (not true "repair" as tricuspid atresia is not reversed).

Non-pharmacological measures

• Prophylactic antibiotics (ampicillin + gentamicin or cefotaxime) for bacterial endocarditis prevention in all patients until surgical repair (cephalosporins preferred post-operatively)
• Infective endocarditis (IE) prophylaxis: Dental, GI, and GU procedures require antibiotic coverage (though routine prophylaxis not recommended for all cyanotic lesions by current guidelines)
• Avoid dehydration: Polycythemia from chronic cyanosis increases blood viscosity; dehydration worsens viscosity and increases stroke risk; adequate hydration and iron supplementation are critical
• Activity restriction during infancy and early childhood; older children may tolerate increasing activity as surgical staging progresses
• Genetic counseling for families (recurrence risk approximately 2% for siblings)

Monitoring and surveillance

• Regular echocardiographic assessment before and after each surgical stage to assess RV function, shunt patency, and valve function
• Cardiac catheterization prior to each surgical stage to assess hemodynamics and coronary anatomy
• Serial chest X-rays and ECGs to monitor for progression of ventricular hypertrophy
• Growth parameters and neurodevelopmental assessment (catch-up growth expected post-operatively)

• Ductal closure (can occur within hours to days) leading to acute cyanosis, metabolic acidosis, shock, and death if not anticipated and PGE1 rapidly initiated
• Hypercyanotic ("Tet") spells: Acute worsening of cyanosis with hyperpnea, syncope, seizure, or sudden cardiac death from increased right-to-left shunting; managed acutely with knee-chest position (increases systemic vascular resistance), oxygen, morphine, propranolol (decreases RV contractility and RVOT obstruction, though not applicable to pure TA), and sodium bicarbonate for acidosis
• Arrhythmias: Atrial fibrillation and atrial flutter from chronic right atrial enlargement, particularly in older infants and children; may compromise cardiac output
• Thromboembolic complications: Right-to-left shunting allows paradoxical embolism (blood clots, air bubbles, bacterial vegetations); stroke risk is increased in cyanotic patients with polycythemia
• Bacterial endocarditis: Elevated risk due to turbulent flow across shunts and ASD

• Shunt thrombosis (most common cause of sudden death post-BT shunt); presents with acute cyanosis, shock, and requires emergency re-operation or thrombolytic therapy
• Shunt obstruction or stenosis from intimal hyperplasia or scar tissue; may be gradual (progressive cyanosis) or acute
• Pulmonary artery hypoplasia from inadequate flow during initial stages; may limit final surgical outcome
• Ventricular arrhythmias: Right ventricular myocardium is scarred from surgical incisions; ventricular tachycardia or fibrillation may occur, particularly with activity or emotional stress (late complication)
• Protein-losing enteropathy (PLE): Occurs in 5-10% of Fontan patients from elevated systemic venous pressure; presents with diarrhea, hypoalbuminemia, edema, and increased infection risk; managed with dietary modifications (high protein, medium-chain triglycerides) and rarely immunosuppression
• Fontan-associated liver disease: Chronic hepatic venous congestion from elevated systemic venous pressure leads to hepatic fibrosis, cirrhosis, and hepatocellular carcinoma in 20-30% of long-term Fontan patients
• Atrial arrhythmias (late): Atrial fibrillation, flutter, or atrial ectopic tachycardia occurs in 15-20% of older Fontan patients; associated with risk of thromboembolic stroke
• Plastic bronchitis: Rare but serious complication causing fibrin casts in airways, acute respiratory failure

Long-term complications

• Progressive ventricular dysfunction: The single left ventricle must support both systemic and pulmonary circulation; dysfunction may develop over years; preserved ejection fraction does not guarantee adequate function
• Systemic atrioventricular valve regurgitation: The mitral valve (used as systemic AV valve) may develop progressive regurgitation from volume overload or annular dilatation; severe MR may necessitate valve repair or replacement
• Cyanosis and polycythemia-related complications (if residual cyanosis persists): Stroke, brain abscess, gout (uric

• Left axis deviation in a cyanotic newborn is tricuspid atresia until proven otherwise: the classic exam triad is left (superior) axis deviation + right atrial enlargement + left ventricular hypertrophy with absent right-sided forces. Mechanistically, absence of right ventricular forces plus an abnormally developed left-sided conduction system (hypoplastic left anterior fascicle) shifts the mean QRS vector superiorly and leftward — which is why other lesions with a dominant LV do not reliably show this axis.

• The ECG, not the chest film, is the discriminator: tetralogy of Fallot also causes cyanosis with decreased pulmonary vascular markings, but its hypertrophied RV produces right axis deviation. A stem giving "cyanosis + oligemic lungs + LAD" is steering you to tricuspid atresia.

• Single best next step in an unstable cyanotic neonate is prostaglandin E1, started before echo results return: ductal-dependent pulmonary blood flow means ductal closure equals death. Anticipate apnea and have airway support ready. The corollary distractor is any prostaglandin-synthesis inhibitor (indomethacin, ibuprofen) — these close the ductus and are contraindicated here.

• Failed hyperoxia test: on 100% FiO2, a preductal (right radial) PaO2 that fails to rise above roughly 100-150 mmHg indicates obligate intracardiac right-to-left mixing rather than primary lung disease. Transthoracic echocardiography is the confirmatory test of choice.

• A restrictive atrial septum is the emergency you can fix in the cath lab: systemic venous return has no other exit, so a small PFO produces systemic venous congestion and low output — treat with balloon atrial septostomy (Rashkind).

• Do not reflexively attach 22q11.2 deletion to this lesion: tricuspid atresia is usually sporadic and non-syndromic. 22q11.2 deletion (DiGeorge) is the association to reach for with conotruncal/neural-crest lesions — truncus arteriosus, tetralogy of Fallot, interrupted aortic arch type B, conoventricular VSD — where the stem adds hypocalcemic tetany, absent thymic shadow, and recurrent infections (use irradiated, CMV-safe blood products if transfusion is needed).

• Fontan physiology is preload-dependent and passive: pulmonary flow depends on systemic venous pressure, so dehydration, high PEEP, and elevated pulmonary vascular resistance all drop cardiac output. Chronic venous hypertension explains the late triad tested on Step 2 CK — protein-losing enteropathy, Fontan-associated liver disease, and atrial arrhythmias.

• Common distractor — beta blockade for a "tet spell": propranolol works in tetralogy by relaxing infundibular muscle, which pure tricuspid atresia does not have. Per AHA guidance on infective endocarditis, unrepaired cyanotic CHD and palliative shunts/conduits remain indications for dental-procedure prophylaxis.