Cardiology · Congenital Heart Disease
The facts most likely to be tested
The four anatomical defects of Tetralogy of Fallot are pulmonary stenosis, ventricular septal defect (VSD), overriding aorta, and right ventricular hypertrophy.
The classic chest X-ray finding is a boot-shaped heart caused by right ventricular hypertrophy and a small pulmonary artery segment.
Patients often experience Tet spells, which are hypercyanotic episodes triggered by crying, feeding, or agitation that decrease systemic vascular resistance.
The immediate maneuver to improve a Tet spell is knee-to-chest positioning, which increases systemic vascular resistance and reduces the right-to-left shunt.
The physical exam typically reveals a harsh, systolic ejection murmur at the left mid-to-upper sternal border due to pulmonary stenosis.
Tetralogy of Fallot is the most common cyanotic congenital heart disease presenting in childhood.
Definitive treatment for Tetralogy of Fallot is surgical repair of the VSD and relief of the right ventricular outflow tract obstruction.
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A 4-month-old infant is brought to the emergency department after a sudden episode of blue discoloration of the lips and skin while crying. On physical examination, the infant is tachypneic and cyanotic. A harsh, systolic ejection murmur is heard at the left mid-sternal border. A chest X-ray reveals a boot-shaped heart with decreased pulmonary vascular markings. The infant's oxygen saturation is 72% on room air.
What is the most appropriate initial intervention to improve this patient's condition?
Knee-to-chest positioning
The patient is experiencing a Tet spell; knee-to-chest positioning increases systemic vascular resistance, which decreases the right-to-left shunt across the VSD and improves pulmonary blood flow.
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Etiology / Epidemiology
Most common cyanotic congenital heart disease in infants; associated with DiGeorge syndrome (22q11 deletion).
Clinical Manifestations
Presents with Tet spells (hypercyanotic episodes) and a harsh systolic ejection murmur at the left sternal border.
Diagnosis
Echocardiography is the gold standard; chest X-ray classically shows a boot-shaped heart.
Treatment
Manage Tet spells with knee-to-chest positioning and oxygen; definitive treatment is surgical repair.
Prognosis
Excellent post-repair survival, but patients are at risk for arrhythmias and pulmonary regurgitation.
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Epidemiology & Etiology
This is the most frequent cause of cyanotic congenital heart disease in children. It is strongly linked to chromosomal abnormalities, specifically 22q11.2 deletion syndrome. Maternal factors like phenylketonuria and retinoic acid exposure increase risk.
Pertinent Anatomy
The defect consists of four components: pulmonary stenosis, ventricular septal defect (VSD), overriding aorta, and right ventricular hypertrophy. The degree of right ventricular outflow tract obstruction dictates the severity of cyanosis.
Pathophysiology
The VSD allows for right-to-left shunting of deoxygenated blood into the systemic circulation. During periods of increased oxygen demand or decreased systemic vascular resistance, the shunt worsens, leading to Tet spells. Chronic hypoxemia triggers polycythemia as a compensatory mechanism.
Clinical Manifestations
Infants present with cyanosis that worsens during crying or feeding, known as Tet spells. Physical exam reveals a harsh systolic ejection murmur at the left mid-to-upper sternal border due to pulmonary stenosis. Sudden loss of murmur during a spell indicates severe obstruction and is a medical emergency.
Diagnosis
Echocardiography is the diagnostic test of choice to visualize all four defects. Chest X-ray classically demonstrates a boot-shaped heart due to right ventricular hypertrophy and a small pulmonary artery segment. Pulse oximetry will show persistent hypoxemia.
Treatment
For acute Tet spells, use knee-to-chest positioning to increase systemic vascular resistance and oxygen to decrease pulmonary vascular resistance. Morphine may be used to calm the infant. Avoid beta-blockers unless specifically indicated for infundibular spasm. Definitive treatment is surgical repair (VSD closure and relief of pulmonary stenosis) usually performed in the first year of life.
Prognosis
Long-term survival is high following surgical repair. Patients require lifelong monitoring for ventricular arrhythmias and pulmonary regurgitation. Late-onset sudden cardiac death remains a rare but significant risk.
Differential Diagnosis
Transposition of the Great Arteries: presents with cyanosis but no murmur
Tricuspid Atresia: shows left axis deviation on ECG
Truncus Arteriosus: presents with a single S2 heart sound
Total Anomalous Pulmonary Venous Return: shows 'snowman' sign on X-ray
Pulmonary Atresia: presents with severe cyanosis and absent pulmonary valve flow