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Updated: Feb 1 2019

Tetralogy of Fallot

  • Snapshot
    • A 7-month infant presents with his mother for episodes of turning blue. The mother reports that his lips turn blue when he is crying or when he has fevers. The baby was born via a spontaneous vaginal delivery without any complications. His mother did not undergo routine prenatal care while pregnant with him. On physical exam, the infant is underweight. Cardiac exam reveals a harsh systolic ejection murmur. He starts crying in the middle of the exam and becomes cyanotic. The physician puts him in a knee-chest position, and the cyanosis resolves.
  • Introduction
    • Clinical definition
      • a congenital cardiac defect caused by anterosuperior displacement of the infundibular septum, characterized by PROV
        • Pulmonary infundibular stenosis
          • important prognostic factor
        • 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 failure of neural crest cells to migrate
    • Pathogenesis
      • pulmonary stenosis causes right ventricular outflow obstruction and 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 systemic vascular resistance, alleviating the right-to-left shunting caused by right ventricular outflow obstruction, and thus relieves the cyanosis
    • Associated conditions
      • thymic aplasia (DiGeorge syndrome)
      • Down syndrome
    • Prognosis
      • severity of symptoms depends on the severity of right ventricular outflow obstruction
      • long-term survival is good with surgical repair
  • 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, dyspnea, 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 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
    • Operative
      • surgical repair
        • indication
          • definitive treatment
        • surgeries
          • closure of VSD
          • removal of pulmonary outflow obstruction
  • Complications
    • Thrombosis
    • Infective endocarditis
    • Heart failure
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