Congenital Heart Defects: Cyanotic and Acyanotic

ACYANOTIC CONGENITAL HEART DEFECTS

Common congenital left-to-right shunts - (A) ASD, (B) VSD, (C) PDA. Arrows show direction of abnormal blood flow. (Robbins & Kumar Basic Pathology)

Key mechanism: Prolonged left-to-right shunting raises pulmonary vascular resistance, causing pulmonary hypertension that eventually reverses the shunt direction -- this is Eisenmenger syndrome, at which point cyanosis appears and defects become irreversible.

1. Atrial Septal Defect (ASD)

• Defect: Fixed opening in the atrial septum allowing left-to-right shunt (LA pressure > RA pressure)
• Types:
  • Ostium secundum (90%): Near foramen ovale; most common. Usually isolated.
  • Ostium primum (5%): Lowest part of septum; may be associated with mitral/tricuspid valve abnormalities and AV canal defects
  • Sinus venosus (5%): High in atrial septum; often with anomalous pulmonary venous drainage
• Hemodynamics: Right atrial and ventricular dilation, RV hypertrophy, dilated pulmonary artery
• Note: Distinguish from PFO - a patent foramen ovale is a flap valve, not a true fixed defect; it can allow paradoxical embolism but usually is clinically silent
• Clinical features:
  • Usually asymptomatic until adulthood (most common CHD presenting in adults)
  • Fixed, widely split S2 is the hallmark auscultatory finding
  • Chest X-ray: cardiomegaly, increased pulmonary vascular markings
  • ECG: RVH, right axis deviation (RAD), incomplete RBBB
• Treatment: Surgical or transcatheter closure to prevent CHF, paradoxical embolism, irreversible pulmonary vascular disease. Mortality is low.

2. Ventricular Septal Defect (VSD)

• Most common CHD diagnosed at birth (~42% of all CHDs)
• Defect: Opening in ventricular septum; ~90% in the membranous (basal) portion
• Hemodynamics: Left-to-right shunt → RV hypertrophy, increased pulmonary blood flow and pressure, LV volume overload
• Clinical features:
  • Small VSDs: asymptomatic; harsh pansystolic murmur at lower left sternal border (LLSB). About 50% close spontaneously in childhood
  • Large VSDs: CHF, failure to thrive, recurrent pulmonary infections, risk of Eisenmenger syndrome earlier than ASD
  • ECG: LVH or biventricular hypertrophy
• Treatment: Small defects observed. Larger defects: surgical patch closure. VSD may be isolated or part of Tetralogy of Fallot, trisomy 21, etc.

3. Patent Ductus Arteriosus (PDA)

• Defect: Failure of the ductus arteriosus to close after birth (normally closes within 1-2 days in response to increased O2, decreased PGE2)
• Shunt: Aorta (higher pressure) → left pulmonary artery → pulmonary circulation (left-to-right)
• Murmur: Classic "machinery-like" continuous murmur, best heard at upper left sternal border
• Clinical features:
  • Small PDA: asymptomatic
  • Large PDA: pulmonary hypertension, LV dilation, risk of infective endocarditis, eventual Eisenmenger syndrome
  • Associated with prematurity, maternal rubella, Down syndrome
• Treatment: Indomethacin (inhibits prostaglandins, stimulates closure) in premature infants; surgical or catheter-based closure in term infants and adults

4. Aortic Coarctation

• Defect: Narrowing of the aorta, classically at or near the ductus arteriosus (juxtaductal). Males > females (2:1); females with Turner syndrome frequently have coarctation
• Two presentations:
  • Infantile type (preductal): Severe obstruction; presents with heart failure in neonate; requires urgent intervention
  • Adult type (postductal): Collateral circulation develops; presents with upper extremity hypertension, differential arm-leg blood pressure, weak/delayed femoral pulses
• Examination finding: Radio-femoral pulse delay; rib notching on CXR (from collateral intercostal arteries)
• Associations: Bicuspid aortic valve (in 50%), berry aneurysms, Turner syndrome
• Treatment: Surgical resection and anastomosis, or balloon angioplasty with stenting

5. Pulmonary Stenosis

• Defect: Obstruction at the level of the pulmonary valve
• Clinical: Systolic ejection murmur at upper left sternal border; right ventricular hypertrophy; usually well tolerated
• Treatment: Balloon pulmonary valvuloplasty for moderate-to-severe stenosis

6. Aortic Stenosis (Congenital)

• Defect: Obstruction at the aortic valve level (commonly bicuspid valve), subvalvular, or supravalvular
• Clinical: Systolic ejection murmur at upper right sternal border; LV hypertrophy; risk of sudden cardiac death with severe stenosis

CYANOTIC CONGENITAL HEART DEFECTS

• Clubbing (hypertrophic osteoarthropathy)
• Polycythemia (erythropoietin-driven, due to hypoxia)
• Paradoxical embolization (venous clots enter systemic circulation)
• Infective endocarditis risk

1. Tetralogy of Fallot (TOF)

Classic Tetralogy of Fallot showing the four features. (Robbins & Kumar Basic Pathology)

1. Large VSD
2. Right ventricular outflow tract (RVOT) obstruction - subpulmonic/infundibular stenosis
3. Overriding aorta (aortic valve overlies the VSD)
4. Right ventricular hypertrophy

• Cyanosis at birth or developing within first year
• "Tet spells" (hypercyanotic spells): Episodes of severe cyanosis with tachypnea, loss of consciousness, worsening with crying/feeding - due to spasm of RVOT
• Squatting in older children (increases SVR, reduces right-to-left shunt, improves pulmonary blood flow)
• Chest X-ray: "Boot-shaped heart" (coeur en sabot) - RV hypertrophy elevates cardiac apex, hypoplastic pulmonary trunk
• ECG: Right axis deviation, RVH

2. Transposition of the Great Arteries (TGA/TGV)

• Defect: Aorta arises from the RV; pulmonary artery arises from the LV - completely reversed
• Result: Systemic and pulmonary circulations run in parallel rather than in series - incompatible with life without a mixing shunt
• Mixing occurs via PFO, PDA, or VSD (present in ~1/3 of cases)

• Severe cyanosis within 48 hours of birth
• Chest X-ray: "Egg on a string" appearance - narrow superior mediastinum (aorta directly anterior to PA) with cardiomegaly; increased pulmonary vascular markings
• ECG: RAD, RVH

• Prostaglandin E1 (alprostadil) IV - keeps PDA open to maintain mixing
• Balloon atrial septostomy (Rashkind procedure) - creates ASD for mixing
• Definitive treatment: Arterial switch operation (Jatene procedure) - performed within first few weeks of life; excellent long-term outcomes

3. Total Anomalous Pulmonary Venous Connection (TAPVC)

• Defect: Pulmonary veins drain into systemic venous system (SVC, RA, coronary sinus, IVC) instead of the left atrium. An ASD or PFO must be present for survival.
• Types:
  • Supracardiac (most common): drains into SVC
  • Cardiac: drains into coronary sinus or RA
  • Subdiaphragmatic (infradiaphragmatic): drains into IVC/portal vein - associated with obstruction
• Clinical: Moderate-to-mild cyanosis (mild if unobstructed), pulmonary congestion
• Chest X-ray: "Snowman" sign (figure-of-8) - only seen after age 4 months in supracardiac type

4. Tricuspid Atresia

• Defect: Absent tricuspid valve with hypoplastic RV; requires ASD + PDA or VSD to survive
• ECG hallmark: Superior QRS axis (left axis deviation) + LVH - distinguishes it from other cyanotic CHDs
• Treatment: Palliative staged procedures (Fontan circulation)

5. Truncus Arteriosus

• Single common arterial trunk arising from the heart, supplying systemic, pulmonary, and coronary circulations. Always associated with a large VSD.
• Associated with DiGeorge syndrome (22q11 deletion)

6. Ebstein Anomaly

• Defect: Downward displacement of a malformed tricuspid valve into the RV cavity, "atrialization" of the RV
• Variable severity; may present with cyanosis (right-to-left shunt through ASD/PFO), WPW syndrome (accessory pathway), arrhythmias
• Associated with maternal lithium use

Comparison Summary

Eisenmenger Syndrome

• Robbins & Kumar Basic Pathology, Chapter 9 (Cardiovascular)
• Gray's Anatomy for Students, Chapter 3
• Bailey and Love's Short Practice of Surgery, 28th Ed., Chapter 59
• Harriet Lane Handbook, 23rd Ed., Chapter 7 (Cardiology)
• Fuster and Hurst's The Heart, 15th Ed.