Congenital Heart Defects (CHD): Cyanotic and Acyanotic Lesions

Congenital heart defects (CHD) are among the most commonly tested pediatric cardiac topics on nursing exams. This note reviews their classification, the high-yield cyanotic and acyanotic lesions, key murmurs, and priority nursing interventions.

Definition

• Congenital heart defects (CHD) are structural abnormalities of the heart present at birth.
• They are the most common type of birth defect, affecting approximately 1 in 100 newborns.
• CHD results from abnormal development of the cardiovascular system during early embryogenesis; the heart is fully formed by approximately 16 weeks of gestation.

Classification

CHDs are broadly classified into cyanotic ("blue babies," low oxygen) and acyanotic ("pink babies," normal oxygen) defects.

• Cyanotic defects: right-to-left shunting or mixing of oxygenated and deoxygenated blood.
• Acyanotic defects: left-to-right shunting or obstructive lesions.

Cyanotic vs Acyanotic at a glance

The 5 T's of Cyanotic Heart Disease

A classic mnemonic for the major cyanotic lesions:

• Tetralogy of Fallot (TOF): Most common cyanotic defect. Includes pulmonary stenosis, VSD, overriding aorta, and right ventricular hypertrophy.
• Transposition of the Great Arteries (TGA): Aorta arises from the right ventricle and the pulmonary artery from the left ventricle, creating two parallel circuits. Ductal-dependent — survival requires a patent ductus arteriosus for mixing.
• Truncus Arteriosus: A single great vessel arises from both ventricles; pulmonary arteries branch off the truncus, causing mixing.
• Total Anomalous Pulmonary Venous Return (TAPVR): Pulmonary veins drain into the right atrium or systemic veins instead of the left atrium. An ASD is required for survival.
• Tricuspid Atresia: Absent tricuspid valve. Both an ASD and VSD are required for survival.

Cyanotic Defects

Tetralogy of Fallot (TOF)

• Components: pulmonary stenosis, VSD, overriding aorta, right ventricular hypertrophy.
• Pathophysiology: Pulmonary stenosis restricts pulmonary blood flow; blood shunts right-to-left through the VSD, causing cyanosis.
• Manifestations: cyanosis, clubbing, squatting (relieves dyspnea), systolic ejection murmur.
• Tet Spells: acute episodes of severe cyanosis and hypoxia within the first 2 years of life.
• Tet Spell management: knee-chest position, oxygen, IV morphine (~0.1 mg/kg). Correct acidosis only if confirmed by blood gas.

Transposition of the Great Arteries (TGA)

• Pathophysiology: Two parallel circuits; survival requires mixing through an ASD, VSD, or PDA (ductal-dependent).
• Manifestations: severe cyanosis in the first 24–48 hours of life.
• Management: Prostaglandin E1 to maintain PDA patency; arterial switch surgery in the first week of life.

Truncus Arteriosus

• Pathophysiology: Single great vessel from both ventricles; excessive pulmonary blood flow leads to heart failure.
• Manifestations: cyanosis, heart failure, systolic ejection murmur.
• Management: surgical repair in infancy.

Total Anomalous Pulmonary Venous Return (TAPVR)

• Pathophysiology: Pulmonary veins drain to the right atrium or systemic veins; mixing occurs through an ASD.
• Manifestations: cyanosis, tachypnea, failure to thrive.
• Management: surgical correction.

Tricuspid Atresia

• Pathophysiology: Absent tricuspid valve; ASD and VSD required for survival.
• Manifestations: cyanosis, clubbing, systolic murmur.
• Management: staged palliative surgeries, with the Fontan procedure as the final stage.

Acyanotic Defects

Ventricular Septal Defect (VSD)

• Pathophysiology: Left-to-right shunt increases pulmonary blood flow; may lead to pulmonary hypertension if untreated.
• Manifestations: holosystolic murmur at the LLSB, failure to thrive, tachypnea, frequent infections.
• Complications: Eisenmenger syndrome — reversal to right-to-left shunt causing cyanosis and clubbing.

Atrial Septal Defect (ASD)

• Pathophysiology: Left-to-right shunt increases pulmonary blood flow.
• Manifestations: often asymptomatic; classic findings are a fixed split S2 and systolic ejection murmur.
• Complications: Eisenmenger syndrome with large, untreated defects.

Patent Ductus Arteriosus (PDA)

• Pathophysiology: Left-to-right shunt from the aorta to the pulmonary artery.
• Manifestations: continuous "machine-like" murmur, bounding pulses, wide pulse pressure.
• Management: Indomethacin or ibuprofen to promote closure in preterm infants; surgical ligation if medical therapy fails.

Acyanotic defects summary

Exam Traps

• Do not confuse cyanotic (TOF, TGA, Truncus, TAPVR, Tricuspid Atresia) with acyanotic (ASD, VSD, PDA) defects.
• Remember the 5 T's of cyanotic heart disease.
• The knee-chest position is first-line for Tet spells.
• The PDA murmur is continuous ("machine-like"); the VSD murmur is holosystolic.
• Prostaglandin E1 maintains PDA patency in ductal-dependent lesions such as TGA.
• Indomethacin or ibuprofen closes a PDA in preterm infants.

Key takeaways

• CHDs are split into cyanotic (right-to-left shunt) and acyanotic (left-to-right shunt) categories — this is the highest-yield distinction.
• Memorize the 5 T's of cyanotic disease: Tetralogy of Fallot, TGA, Truncus, TAPVR, Tricuspid atresia.
• For Tet spells, place the child in the knee-chest position and give oxygen; morphine may be used.
• Ductal-dependent lesions (e.g., TGA) require Prostaglandin E1 to keep the PDA open until surgery.
• Know the classic murmurs: VSD = holosystolic at LLSB, ASD = fixed split S2, PDA = continuous machine-like.
• Untreated large left-to-right shunts can progress to Eisenmenger syndrome (shunt reversal with cyanosis).