Updated: 12/21/2019

Tetralogy of Fallot

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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
  • 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, 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
 

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