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Updated: Dec 4 2021

Tetralogy of Fallot

  • Snapshot
    • A neonatal boy is found to be cyanotic a few hours after delivery. The mother noticed the neonate turning blue when crying and feeding. The boy was born via a spontaneous vaginal delivery without any complications and to a 30-year-old mother. The mother received inconsistent prenatal care throughout her pregnancy. Physical examination is significant for a harsh systolic ejection murmur. A chest radiograph is performed and demonstrates a "boot-shaped" heart.
  • Introduction
    • Clinical definition
      • a congenital cardiac defect caused by anterosuperior displacement of the infundibular septum characterized by PROV
        • Pulmonary infundibular stenosis
        • Right ventricular hypertrophy (RVH)
        • Overriding aorta
        • Ventricular septal defect (VSD)
  • Epidemiology
    • Demographics
      • neonates are affected
      • the most common cyanotic cardiac lesion
    • Risk factors
      • family history
      • maternal exposure to retinoic acid
  • Etiology
    • Conotruncal abnormality from the failure of neural crest cells to migrate
    • Pathogenesis
      • pulmonary stenosis causes right ventricular outflow obstruction and causes right-to-left shunting
        • in cases of severe lesions, neonates rely on a patent ductus arteriosus for survival
      • the right-to-left shunt across the VSD causes cyanosis
        • cyanosis causes marked clubbing and dyspnea on exertion if uncorrected
      • squatting or knee-chest position can increase preload and systemic vascular resistance, alleviating the right-to-left shunting caused by right ventricular outflow obstruction and relieving the cyanosis
    • Associated conditions
      • thymic aplasia (DiGeorge syndrome)
      • Down syndrome
  • Presentation
    • Symptoms
      • tet spells (hypercyanotic episodes)
        • patients often present with tet spells caused by crying, fever, or any physical exertion
        • acute onset of restlessness causes increased cyanosis, gasping, and occasionally syncope
        • tet spells often resolve with knee-chest position, oxygen, or morphine
        • usual onset is around 2-6 months of age
    • Physical exam
      • systolic thrill along the left sternal border
      • loud and harsh systolic ejection murmur on the upper sternal border
        • may or may not have a preceding click
      • single S2
      • clubbing (in older children with uncorrected defect)
  • Imaging
    • Radiography
      • indication
        • for all patients
      • views
        • chest
      • findings
        • boot-shaped heart
        • dark lung fields
    • Echocardiogram
      • indication
        • performed as the gold standard diagnostic test
        • most sensitive test
      • findings
        • features of tetralogy of Fallot
          • VSD
          • overriding aorta
  • Studies
    • Electrocardiogram
      • findings
        • right axis deviation
        • RVH
    • Making the diagnosis
      • based on clinical presentation and echocardiogram
      • in some cases, tetralogy of Fallot may be diagnosed prenatally with a fetal echocardiogram
  • Differential
    • Transposition of the great vessels
      • distinguishing factors
        • early cyanosis that does not correct with squatting or knee-chest position
        • egg-on-a-string appearance on chest radiography
    • Truncus arteriosus
      • distinguishing factors
        • electrocardiogram with left axis deviation and left ventricular hypertrophy
        • requires both atrial septal defect and ventricular septal defect
  • Treatment
    • Medical
      • prostaglandin E1
        • indication
          • for all patients who are cyanotic at birth
        • mechanism of action
          • maintains a patent ductus arteriosus for adequate lower extremity perfusion
      • β-blockers
        • indications
          • for patients prior to surgical repair
          • to decrease the risk of tet spells
          • mechanism of action is reduction of right ventricular infundibular spasm, increasing size of right ventricular outflow tract
    • Operative
      • surgical repair
        • indication
          • definitive treatment
        • surgeries
          • closure of VSD
          • removal of pulmonary outflow obstruction
  • Complications
    • Thrombosis
    • Infective endocarditis
    • Heart failure
  • Prognosis
    • Severity of symptoms depends on the severity of right ventricular outflow obstruction
    • Long-term survival is good with surgical repair
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