Medical School · Year 1 · Cardiovascular · includes a quiz and discussion video

Lecture 14: Congenital Heart Disease

Unit 1.7: Cardiovascular System

Learning Objectives

By the end of this lecture, students will be able to:

1. Describe the embryology relevant to congenital heart defects
2. Classify congenital heart disease by cyanotic vs acyanotic
3. Explain the pathophysiology of common left-to-right shunts
4. Describe cyanotic heart defects and their presentations
5. Explain Eisenmenger syndrome and its consequences
6. Describe the principles of management of congenital heart disease

Overview and Classification

Congenital heart disease encompasses structural cardiac abnormalities present at birth, occurring in approximately 8-10 per 1,000 live births. Advances in surgical and catheter-based interventions have dramatically improved survival, creating a growing population of adults with congenital heart disease who require lifelong specialized care.

The most common individual defects are ventricular septal defect (most frequent overall), atrial septal defect, and patent ductus arteriosus. The fundamental classification divides lesions into acyanotic and cyanotic categories based on whether deoxygenated blood reaches the systemic circulation.

Acyanotic defects do not produce systemic cyanosis because oxygenated blood from the left side of the heart shunts to the right side (left-to-right shunt). The higher pressures on the left side drive blood across septal defects or abnormal connections. These shunts increase pulmonary blood flow without introducing deoxygenated blood into the systemic circulation. However, chronically increased pulmonary blood flow can eventually cause pulmonary vascular disease and reverse the shunt.

Cyanotic defects introduce deoxygenated blood into the systemic circulation, causing visible cyanosis when significant. This occurs either because of a right-to-left shunt (blood bypasses the lungs) or because the great arteries are abnormally connected.

Risk factors for congenital heart disease include both genetic and environmental factors. Chromosomal abnormalities are strongly associated: Down syndrome (trisomy 21) frequently causes atrioventricular septal defects, DiGeorge syndrome (22q11 deletion) causes conotruncal abnormalities (tetralogy of Fallot, truncus arteriosus), Turner syndrome causes coarctation of the aorta, and Noonan syndrome causes pulmonary stenosis and hypertrophic cardiomyopathy. Environmental factors include maternal rubella infection (associated with patent ductus arteriosus), maternal diabetes, alcohol exposure, and certain medications (lithium, phenytoin).

<image>Panel A: Division of congenital heart disease into acyanotic and cyanotic categories, with acyanotic lesions subdivided into left-to-right shunts including VSD, ASD, and PDA shown with shunt direction arrows. Panel B: Acyanotic obstructive lesions including coarctation of the aorta, aortic stenosis, and pulmonary stenosis shown as simplified heart diagrams. Panel C: Cyanotic lesions including tetralogy of Fallot, transposition of the great arteries, and other cyanotic defects with anatomic abnormalities highlighted. Panel D: Genetic associations table showing Down syndrome with AVSD, DiGeorge syndrome with conotruncal defects, Turner syndrome with coarctation, and Noonan syndrome with pulmonary stenosis and HCM.</image>

Fetal Circulation and Transition

Understanding fetal circulation is essential for comprehending why certain defects are well-tolerated in utero but become life-threatening after birth.

In the fetus, gas exchange occurs at the placenta rather than the lungs. Oxygenated blood returns from the placenta through the umbilical vein, partially bypasses the liver through the ductus venosus, and enters the inferior vena cava. This relatively oxygenated blood preferentially streams across the foramen ovale—a one-way valve allowing right-to-left shunting at the atrial level—into the left atrium, then to the left ventricle and out the aorta to supply the brain and upper body with the best-oxygenated blood.

Blood returning from the superior vena cava (relatively deoxygenated) preferentially enters the right ventricle and is ejected into the pulmonary artery. However, because fetal pulmonary vascular resistance is very high (the fluid-filled lungs provide no gas exchange function), most of this blood bypasses the lungs by flowing through the ductus arteriosus—a connection between the pulmonary artery and the descending aorta. This blood then returns to the placenta through the umbilical arteries for oxygenation.

At birth, dramatic circulatory changes occur within minutes. The first breath expands the lungs and dramatically reduces pulmonary vascular resistance as the pulmonary arterioles dilate. Pulmonary blood flow increases tenfold. Clamping the umbilical cord removes the low-resistance placental circulation and increases systemic vascular resistance. As left atrial pressure rises above right atrial pressure, the foramen ovale closes functionally. The increased oxygen tension triggers constriction and eventual closure of the ductus arteriosus, typically within 24-48 hours.

Failure of these normal transitions produces congenital heart defects. A persistently patent foramen ovale is common (present in 25% of adults) and usually hemodynamically insignificant but can serve as a conduit for paradoxical embolism. A persistently patent ductus arteriosus is a common defect, particularly in premature infants. Persistent pulmonary hypertension of the newborn occurs when pulmonary vascular resistance fails to decrease normally.

<image>Panel A: Fetal circulation showing placenta providing oxygenated blood through the umbilical vein, ductus venosus bypassing the liver, and inferior vena cava delivering blood to the right atrium. Panel B: Fetal shunts showing foramen ovale allowing right-to-left atrial shunting and ductus arteriosus connecting pulmonary artery to aorta bypassing high-resistance lungs, with oxygen saturations color-coded. Panel C: Postnatal transitional events including first breath expanding lungs and dropping pulmonary vascular resistance, and cord clamping raising systemic vascular resistance. Panel D: Neonatal circulation after transition showing foramen ovale closure as left atrial pressure exceeds right, ductus arteriosus constriction in response to oxygen, and normal postnatal blood flow without shunts.</image>

Atrial Septal Defect

Atrial septal defect is an abnormal opening in the interatrial septum that allows communication between the atria. Several types exist based on location. Secundum ASD, the most common type (75% of cases), occurs in the region of the fossa ovalis (the former foramen ovale). Primum ASD (15-20%) occurs in the lower atrial septum adjacent to the atrioventricular valves and is often associated with cleft mitral valve (as part of the atrioventricular septal defect spectrum). Sinus venosus ASD (5-10%) occurs near the junction of the superior or inferior vena cava with the right atrium and is frequently associated with partial anomalous pulmonary venous return. Coronary sinus defect (unroofed coronary sinus) is rare.

The pathophysiology involves left-to-right shunting driven by the pressure difference between atria and, more importantly, by the greater compliance (distensibility) of the right heart. Blood flows preferentially from the left atrium to the right atrium, causing right atrial and right ventricular volume overload. The increased pulmonary blood flow produces a relative pulmonary stenosis (increased flow across a normal-sized pulmonary valve), generating a systolic ejection murmur at the left upper sternal border.

The characteristic physical finding is a fixed split S2. Normally, the second heart sound splits during inspiration because increased venous return to the right heart delays pulmonic valve closure. In ASD, the right heart is chronically volume-overloaded regardless of respiratory phase, so the split is fixed (does not vary with respiration).

Many patients with ASD remain asymptomatic through childhood and early adulthood. Symptoms typically develop in the fourth or fifth decade and include dyspnea, fatigue, exercise intolerance, and atrial arrhythmias (atrial fibrillation is common due to right atrial dilation). Late development of pulmonary hypertension can occur.

ECG findings differ by type. Secundum ASD shows right axis deviation and incomplete right bundle branch block (reflecting right ventricular volume overload). Primum ASD shows left axis deviation due to abnormal conduction system development.

Treatment is indicated for significant shunts (Qp:Qs ratio greater than 1.5:1) or symptoms. Secundum ASDs are typically closed percutaneously using a septal occluder device delivered via catheter. Primum and sinus venosus ASDs require surgical patch repair.

<image>Panel A: Four ASD types in cross-sectional heart views: secundum ASD in the fossa ovalis region, primum ASD adjacent to AV valves with cleft mitral valve, sinus venosus ASD near the SVC junction with anomalous pulmonary venous drainage, and coronary sinus defect. Panel B: Pathophysiology showing left-to-right shunting causing right atrial and right ventricular volume overload, increased pulmonary blood flow, and potential pulmonary hypertension. Panel C: Physical findings including systolic flow murmur at the pulmonary area and fixed split S2 with constant A2-P2 interval regardless of respiration. Panel D: ECG patterns showing rSR-prime in V1 with right axis deviation for secundum ASD and left axis deviation for primum ASD.</image>

Ventricular Septal Defect

Ventricular septal defect is the most common congenital heart defect overall. The interventricular septum has multiple components, and defects are classified by location. Perimembranous (membranous) VSDs occur in the thin membranous septum beneath the aortic valve and account for approximately 80% of cases. Muscular VSDs occur within the trabecular muscular septum and may be multiple ("Swiss cheese" septum). Inlet VSDs occur in the portion of the septum adjacent to the atrioventricular valves and are seen in atrioventricular septal defects. Outlet (supracristal, subarterial) VSDs occur beneath the semilunar valves and can cause aortic regurgitation due to lack of support for the aortic cusp.

The hemodynamic significance depends on defect size. Small (restrictive) VSDs produce a high-velocity jet that limits shunting; paradoxically, these produce the loudest murmurs ("maladie de Roger" for small VSDs). Cardiac chambers remain normal in size, and patients are asymptomatic. Moderate VSDs produce significant left-to-right shunting and left ventricular volume overload but not enough to cause heart failure in infancy. Large (nonrestrictive) VSDs allow equalization of ventricular pressures and massive pulmonary blood flow; infants present with heart failure, failure to thrive, tachypnea, and recurrent respiratory infections.

Physical examination reveals a holosystolic (pansystolic) murmur at the left lower sternal border, often with a palpable thrill. The murmur is louder with smaller defects that generate higher-velocity jets. With large VSDs, signs of heart failure (tachypnea, hepatomegaly, failure to thrive) predominate, and the murmur may be less impressive.

Natural history varies by defect type and size. Small muscular VSDs frequently close spontaneously during childhood (30-50% closure rate). Perimembranous VSDs can also close spontaneously but less frequently. Large VSDs, if left untreated, lead to pulmonary vascular disease and eventual Eisenmenger syndrome. Outlet VSDs are associated with progressive aortic regurgitation due to aortic cusp prolapse into the defect.

Treatment is surgical repair for large VSDs causing symptoms or hemodynamic significance (Qp:Qs greater than 2:1). Small asymptomatic VSDs are observed, with endocarditis prophylaxis recommended for the first six months after surgical repair or if residual defects exist near prosthetic material.

<image>Panel A: Interventricular septum divided into regions with four VSD types: perimembranous in the membranous septum as the most common, muscular in the trabecular septum which may be multiple, inlet near the AV valves, and outlet beneath the semilunar valves. Panel B: Hemodynamic comparison by size showing small VSD with loud murmur but no chamber enlargement, moderate VSD with significant shunt and LV volume overload, and large VSD with massive shunt and heart failure risk. Panel C: Holosystolic murmur at the left lower sternal border with thrill, and chest X-ray showing cardiomegaly and increased pulmonary vascular markings in large VSD. Panel D: Natural history timeline showing spontaneous closure rates for muscular VSDs and risk of Eisenmenger syndrome in unoperated large VSDs.</image>

Patent Ductus Arteriosus

Patent ductus arteriosus occurs when the ductus arteriosus fails to close after birth, maintaining a connection between the pulmonary artery and the descending aorta. PDA is particularly common in premature infants due to immature ductal tissue that is less responsive to oxygen-induced closure.

The pathophysiology involves left-to-right shunting from the aorta to the pulmonary artery, driven by the pressure difference between systemic and pulmonary circulations. Blood flows from the aorta into the pulmonary artery during both systole and diastole, producing a continuous murmur. The left ventricle faces volume overload from the excessive pulmonary venous return. The diastolic runoff from the aorta into the pulmonary artery produces wide pulse pressure with bounding peripheral pulses.

The classic physical finding is a continuous "machinery" murmur heard best at the left infraclavicular area or upper left sternal border. The murmur peaks around S2 (when the aorto-pulmonary gradient is greatest) and continues into diastole. Bounding pulses and an active precordium reflect the volume overload state.

In premature infants, PDA can cause significant hemodynamic problems including heart failure, pulmonary hemorrhage, necrotizing enterocolitis, and difficulty weaning from mechanical ventilation. In term infants and children, small PDAs may be asymptomatic and detected only by the characteristic murmur.

Treatment in premature infants typically begins with pharmacologic closure using indomethacin or ibuprofen, which inhibit prostaglandin synthesis and promote ductal constriction. Surgical ligation is performed if pharmacologic closure fails. In term infants, children, and adults, closure is performed either percutaneously (coil or device occlusion) or surgically (ligation). Small, asymptomatic PDAs detected only by echocardiography (silent PDA) may be observed without intervention.

Importantly, in certain cyanotic congenital heart defects (such as severe pulmonary stenosis, pulmonary atresia, or transposition of the great arteries), the ductus arteriosus provides the only route for pulmonary or systemic blood flow. In these duct-dependent lesions, prostaglandin E1 infusion is used to maintain ductal patency as a bridge to definitive surgical intervention.

<image>Panel A: Anatomic connection of the PDA between the aortic isthmus and the main pulmonary artery, with left-to-right shunting during both systole and diastole. Panel B: Continuous machinery murmur pattern peaking around S2 when the aorto-pulmonary pressure gradient is maximal, heard at the left infraclavicular area. Panel C: Treatment options showing indomethacin or ibuprofen for pharmacologic closure in premature infants, with surgical ligation or percutaneous device occlusion for older patients. Panel D: Duct-dependent circulation in cyanotic heart defects where prostaglandin E1 is infused to maintain ductal patency as a bridge to surgical intervention.</image>

Coarctation of the Aorta

Coarctation of the aorta is a discrete narrowing of the aorta, typically occurring at the aortic isthmus just distal to the left subclavian artery, near the insertion of the ductus arteriosus (or ligamentum arteriosum). This location results from ductal tissue extending into the aortic wall and constricting as the ductus closes.

The hemodynamic consequence is mechanical obstruction to blood flow. Blood pressure is elevated in the aorta and its branches proximal to the coarctation (arms, head) and reduced distally (legs). Over time, collateral circulation develops through the internal mammary, intercostal, and scapular arteries, providing alternative routes for blood to reach the lower body.

Coarctation is strongly associated with bicuspid aortic valve (present in 50-85% of patients), which may itself cause aortic stenosis or regurgitation. Turner syndrome is associated with coarctation. Other associated defects include VSD, mitral valve abnormalities, and intracranial berry aneurysms (which increase stroke risk).

Clinical presentation depends on severity. Severe coarctation presents in infancy when the ductus closes, with shock and heart failure as blood flow to the lower body suddenly decreases; these infants require urgent prostaglandin infusion to reopen the ductus and surgical repair. Less severe coarctation may not present until later childhood or adulthood, often detected during evaluation for hypertension.

Physical findings are characteristic. Blood pressure is elevated in the arms and reduced in the legs, with a gradient greater than 20 mmHg indicating significant coarctation. Radial-femoral pulse delay occurs as blood reaches the femoral arteries through collateral vessels rather than the direct aortic route. A systolic murmur is heard over the back between the scapulae. Continuous murmurs may be heard from collateral vessels.

Chest X-ray may show rib notching on the inferior surfaces of the posterior ribs (from dilated, pulsatile intercostal arteries eroding the bone) and the "3 sign" or reverse "E" sign (indentation of the aorta at the coarctation with pre- and post-stenotic dilation).

Treatment is intervention for significant coarctation. Options include surgical repair (resection with end-to-end anastomosis, or patch aortoplasty) and balloon angioplasty with or without stent placement. Patients require lifelong follow-up for re-coarctation, associated aortic valve disease, and hypertension (which often persists even after successful repair).

<image>Panel A: Anatomy showing discrete narrowing of the aorta at the isthmus just distal to the left subclavian artery, with elevated blood pressure in the arms and low pressure in the legs. Panel B: Collateral circulation through dilated tortuous internal mammary and intercostal arteries bypassing the obstruction to supply the lower body. Panel C: Physical examination findings including blood pressure gradient between arms and legs and radial-femoral pulse delay. Panel D: Imaging findings showing rib notching on chest X-ray from dilated intercostal arteries, the 3-sign on the aortic contour, and CT or MR angiogram showing the coarctation site with collaterals.</image>

Tetralogy of Fallot

Tetralogy of Fallot is the most common cyanotic congenital heart defect beyond infancy. The four classic components result from a single embryologic abnormality: anterior and superior deviation of the outlet (infundibular) septum. This deviation creates (1) a large ventricular septal defect from malalignment of the septum, (2) overriding of the aorta, which straddles the VSD and receives blood from both ventricles, (3) right ventricular outflow tract obstruction from narrowing at the infundibulum (subpulmonic stenosis) often with valvular pulmonary stenosis, and (4) right ventricular hypertrophy secondary to the obstruction.

The degree of cyanosis depends on the severity of right ventricular outflow tract obstruction. Mild obstruction produces minimal right-to-left shunting and only slight cyanosis ("pink tet"). Severe obstruction produces pronounced right-to-left shunting through the VSD (blood preferentially ejected into the lower-resistance aorta rather than through the stenotic pulmonary outflow) and significant cyanosis.

Hypercyanotic episodes ("tet spells") are acute exacerbations of right-to-left shunting. They occur during crying, feeding, or other activities that increase oxygen consumption or decrease systemic vascular resistance. The spells are characterized by sudden onset of severe cyanosis, dyspnea, hyperpnea, and potentially syncope or seizures. Infants characteristically squat, which increases systemic vascular resistance and reduces right-to-left shunting.

Management of tet spells involves knee-chest positioning (to increase SVR), oxygen, morphine (to reduce hyperpnea), phenylephrine (to increase SVR pharmacologically), and beta-blockers (to relax the infundibular muscle). Severe or recurrent spells indicate the need for urgent surgical intervention.

Physical examination reveals cyanosis (variable degree), clubbing of fingers and toes if chronic cyanosis is present, and a systolic ejection murmur at the left upper sternal border from right ventricular outflow tract obstruction. Notably, the murmur is from the pulmonic stenosis, not the VSD (which is nonrestrictive, producing minimal turbulence). Chest X-ray shows the characteristic "boot-shaped" heart (coeur en sabot) from right ventricular hypertrophy and a concave pulmonary artery segment.

Definitive treatment is complete surgical repair: patch closure of the VSD, relief of right ventricular outflow tract obstruction (resection of infundibular muscle, pulmonary valvotomy, and often transannular patch), typically performed in infancy. Palliative shunts (such as a Blalock-Taussig shunt connecting the subclavian artery to the pulmonary artery) may be performed in severely cyanotic neonates to provide pulmonary blood flow as a bridge to complete repair. Long-term issues after repair include pulmonary regurgitation (often severe if a transannular patch was used), which may eventually require pulmonary valve replacement.

<image>Panel A: Four anatomic components of tetralogy of Fallot in heart cross-section: large VSD with malalignment, overriding aorta straddling the VSD, right ventricular outflow tract obstruction with infundibular narrowing and pulmonary valve stenosis, and right ventricular hypertrophy. Panel B: Hemodynamics of a tet spell showing decreased systemic vascular resistance allowing increased right-to-left shunting and worsening cyanosis, with treatment by knee-chest position and phenylephrine to increase SVR. Panel C: Clinical findings including cyanosis and digital clubbing from chronic hypoxemia, and the systolic murmur from right ventricular outflow tract obstruction. Panel D: Boot-shaped heart on chest X-ray with upturned apex from right ventricular hypertrophy and concave pulmonary artery segment.</image>

Transposition of the Great Arteries

Transposition of the great arteries (TGA) refers to abnormal ventriculoarterial connections. In dextro-TGA (D-TGA, complete transposition), the aorta arises from the right ventricle and the pulmonary artery from the left ventricle. This creates two parallel circulations: deoxygenated blood returning from the body enters the right heart and is pumped back to the body through the aorta, while oxygenated blood from the lungs enters the left heart and is pumped back to the lungs. Without mixing between these circuits, this condition is incompatible with life.

Survival depends on mixing between the two circulations, which occurs through naturally occurring defects (ASD, VSD) or a patent ductus arteriosus. Approximately 50% of infants with D-TGA have an intact ventricular septum, requiring mixing through an ASD and PDA. VSD is present in approximately 40%.

Infants with D-TGA present with profound cyanosis within hours of birth as the ductus arteriosus begins to close. The cyanosis does not respond to oxygen supplementation because the problem is inadequate mixing rather than inadequate ventilation. If inadequate mixing is present, acute deterioration with metabolic acidosis and death can occur rapidly.

Initial management involves prostaglandin E1 infusion to maintain ductal patency and ensure some mixing. If mixing remains inadequate, balloon atrial septostomy (Rashkind procedure) is performed urgently: a balloon catheter is passed through the foramen ovale and inflated, then withdrawn to enlarge the atrial communication and improve mixing.

Definitive surgical correction is the arterial switch operation, in which the great arteries are transected above the valves and reconnected to the appropriate ventricles (aorta to left ventricle, pulmonary artery to right ventricle). The coronary arteries must be reimplanted from the native aortic root to the neo-aorta. This procedure is performed in the first weeks of life, before the left ventricle loses its ability to pump against systemic pressures.

Levo-TGA (L-TGA, congenitally corrected TGA) involves double discordance: the atria connect to the wrong ventricles (atrioventricular discordance), and the ventricles connect to the wrong great arteries (ventriculoarterial discordance). The net result is that blood follows the correct physiologic pathway (systemic venous blood reaches the lungs, pulmonary venous blood reaches the body), but the morphologic right ventricle serves as the systemic ventricle. Patients may present later in life with systemic right ventricular failure or AV block.

<image>Panel A: D-TGA anatomy showing the aorta arising from the right ventricle and pulmonary artery from the left ventricle, creating two parallel circuits with deoxygenated blood cycling through the body and oxygenated blood cycling through the lungs without mixing. Panel B: Mixing sites required for survival including ASD, VSD, and PDA, with initial management using prostaglandin E1 to maintain ductal patency and balloon atrial septostomy to enlarge the ASD. Panel C: Arterial switch operation showing the great arteries transected and reconnected to the correct ventricles with coronary artery reimplantation. Panel D: L-TGA showing double discordance with blood following the correct physiologic path but the morphologic right ventricle supporting the systemic circulation.</image>

Eisenmenger Syndrome

Eisenmenger syndrome is the development of pulmonary vascular disease with reversal of a previously left-to-right shunt to become right-to-left. This represents the end stage of untreated large left-to-right shunts and is now less common due to early surgical repair of congenital heart defects.

The pathophysiology begins with a large left-to-right shunt (typically from a nonrestrictive VSD, large PDA, or atrioventricular septal defect) that exposes the pulmonary vasculature to increased flow and systemic pressures. The pulmonary arterioles respond with medial hypertrophy, intimal proliferation, and eventually fibrosis and obliterative changes. Pulmonary vascular resistance rises progressively. When pulmonary vascular resistance approaches or exceeds systemic vascular resistance, the shunt reverses, and deoxygenated blood enters the systemic circulation, producing cyanosis.

Clinical features reflect chronic hypoxemia and its complications. Cyanosis is progressive. Clubbing of the digits develops. Polycythemia is a compensatory response to hypoxemia but can cause hyperviscosity syndrome with headaches, visual disturbances, and thrombotic complications. Hemoptysis may occur from rupture of dilated bronchial vessels. Paradoxical embolism (venous thrombi crossing the right-to-left shunt and causing systemic arterial embolization) can cause stroke or other embolic events. Atrial and ventricular arrhythmias are common.

Critically, once Eisenmenger syndrome develops, surgical closure of the defect is contraindicated. Closing the shunt would eliminate the "pop-off valve" that allows the right ventricle to decompress into the systemic circulation, causing acute right ventricular failure.

Management is supportive. Pulmonary vasodilators (endothelin receptor antagonists, phosphodiesterase-5 inhibitors, prostacyclin analogues) may improve symptoms and exercise capacity but do not reverse the pulmonary vascular disease. Phlebotomy is performed for symptomatic hyperviscosity (not for a target hematocrit). Pregnancy is extremely high-risk (maternal mortality 30-50%) and should be avoided. Heart-lung transplantation (or lung transplantation with repair of the cardiac defect) is the only definitive treatment but is limited by organ availability.

<image>Panel A: Temporal progression from a large left-to-right shunt with increased pulmonary blood flow to pulmonary vascular remodeling with medial hypertrophy, intimal proliferation, and fibrosis of pulmonary arterioles. Panel B: Elevated pulmonary vascular resistance leading to shunt reversal with right-to-left flow and systemic cyanosis. Panel C: Clinical manifestations including progressive cyanosis, digital clubbing, polycythemia with hyperviscosity risk, hemoptysis, and paradoxical embolism causing stroke. Panel D: Management principles showing surgical closure is contraindicated, pulmonary vasodilators for symptom relief, phlebotomy for symptomatic hyperviscosity, pregnancy avoidance due to high mortality, and heart-lung transplantation as definitive therapy.</image>

Other Cyanotic Lesions

Several less common cyanotic lesions are important to recognize.

Truncus arteriosus is a single arterial vessel arising from both ventricles, giving rise to the coronary, pulmonary, and systemic circulations. A VSD is always present, allowing mixing of blood. The common trunk receives mixed blood from both ventricles, causing cyanosis. Excessive pulmonary blood flow causes heart failure in infancy. Early surgical repair is required, creating a separate aorta and pulmonary artery with a conduit from the right ventricle to the pulmonary arteries.

Total anomalous pulmonary venous return (TAPVR) occurs when the pulmonary veins fail to connect normally to the left atrium and instead drain anomalously to the right atrium or its venous tributaries. Types include supracardiac (drainage to the SVC or innominate vein), cardiac (drainage to the coronary sinus or directly to the right atrium), infracardiac (drainage to the portal or hepatic veins), and mixed. All pulmonary venous return enters the right heart, and survival requires an ASD (or patent foramen ovale) for blood to reach the left heart and systemic circulation. Obstruction of pulmonary venous drainage (common in infradiaphragmatic type) causes severe pulmonary edema and cyanosis. Surgical repair reconnects the pulmonary venous confluence to the left atrium.

Tricuspid atresia is complete absence of the tricuspid valve, preventing blood from flowing from the right atrium to the right ventricle. The right ventricle is hypoplastic. Survival requires an ASD (for blood to reach the left heart) and either a VSD or PDA (for blood to reach the pulmonary circulation). Patients undergo staged palliation culminating in the Fontan operation, which directs systemic venous return directly to the pulmonary arteries without passing through a ventricular pump.

Hypoplastic left heart syndrome is severe underdevelopment of the left heart structures, including the mitral valve (atretic or severely stenotic), left ventricle (tiny), and aortic valve (atretic or severely stenotic). Systemic perfusion depends entirely on the right ventricle pumping blood through the ductus arteriosus to the systemic circulation. Treatment involves either staged surgical palliation (Norwood, Glenn, and Fontan operations) or heart transplantation.

<image>Panel A: Truncus arteriosus showing a single vessel arising from both ventricles with a truncal valve branching into coronary, pulmonary, and systemic circulations, with VSD beneath the truncal valve. Panel B: Total anomalous pulmonary venous return with three subtypes: supracardiac draining to the SVC, cardiac draining to the coronary sinus, and infracardiac draining below the diaphragm, all requiring an ASD for survival. Panel C: Tricuspid atresia showing absent tricuspid valve with hypoplastic right ventricle, ASD for blood to reach the left ventricle, and VSD or PDA for pulmonary blood flow. Panel D: Hypoplastic left heart syndrome showing tiny left ventricle with atretic mitral and aortic valves, and the right ventricle supporting both circulations through the ductus arteriosus, with surgical approaches including staged palliation or transplant.</image>

Summary

Congenital heart disease occurs in approximately 8-10 per 1,000 live births, with VSD being the most common defect. Classification distinguishes acyanotic lesions (left-to-right shunts including VSD, ASD, and PDA) from cyanotic lesions (right-to-left shunts including tetralogy of Fallot, transposition, and others).

Atrial septal defect causes right heart volume overload with the characteristic fixed split S2. Secundum ASDs are closed with percutaneous devices. Ventricular septal defect produces a holosystolic murmur at the left lower sternal border; many small VSDs close spontaneously. Patent ductus arteriosus produces a continuous machinery murmur and is closed pharmacologically in premature infants or with devices/surgery in older patients.

Coarctation of the aorta produces upper extremity hypertension and lower extremity hypoperfusion, with arm-leg blood pressure gradient and radial-femoral delay. It is strongly associated with bicuspid aortic valve.

Tetralogy of Fallot is the most common cyanotic heart disease, with VSD, overriding aorta, right ventricular outflow obstruction, and right ventricular hypertrophy. Tet spells are treated by increasing systemic vascular resistance. Complete surgical repair is definitive treatment.

Transposition of the great arteries creates parallel circulations requiring mixing for survival. Prostaglandin maintains the ductus; balloon septostomy increases mixing. Arterial switch operation is the definitive repair.

Eisenmenger syndrome represents irreversible pulmonary vascular disease with shunt reversal; surgical closure is contraindicated once established.

Key Terms

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