Tetralogy of Fallot

Tetralogy of Fallot (TOF) is the most common form of congenital cyanotic heart disease (~8-10%). Worldwide reported prevalence of TOF is 0.34 per 1,000 live births. TOF consists of a constellation of four findings, which include the following:

  • Pulmonary stenosis (PS)
    • The degree of pulmonary stenosis is variable.  Infundibular (subvalvar) stenosis is common and is often dynamic, but stenosis may also include hypoplasia and dysplasia of the pulmonary valve as well as main pulmonary artery hypoplasia (supravalvar).  Right ventricular outflow tract obstruction causes increased right ventricular pressure and can lead to right to left shunting across the VSD in addition to decreased pulmonary blood flow leading to cyanosis. In the setting of mild pulmonary stenosis, shunting across the VSD is predominantly left to right and patients are acyanotic. This is clinically referred to as a “pink Tet”. 
  • Ventricular septal defect (VSD)
    • The typical ventricular septal defect in TOF is a conoventricular septal defect with anterior malalignment, resulting in anterior, superior and leftward deviation of the conal septum causing narrowing of the right ventricular outflow tract. 
  • Right ventricular hypertrophy (RVH)
    • Right ventricular hypertrophy component is the consequence of right ventricular pressure rather than a primary morphologic feature but adds to the right ventricular outflow obstruction.
  • Overriding Aorta
    • The aorta overrides the VSD and native ventricular septum

Additional Findings

  • Right aortic arch is seen in about 25% of TOF
  • Clockwise rotation of the aortic root resultant same rotation of the origin of the coronary arteries is typical in TOF 
  • Coronary artery anomalies in ~ 5% of cases
    • Prominent conal branch from right coronary
    • Left anterior descending coronary artery from the right coronary artery

TOF Classifications/Subtypes

  1. TOF with varying degrees of pulmonary stenosis
  2. TOF with common atrioventricular septal defect (or atrioventricular canal defect) 
  3. TOF with absent pulmonary valve
    • Pulmonary valve hypoplasia with rudimentary valve leaflets
    • This subtype is usually associated with absent patent ductus arteriosus 
    • Branch pulmonary arteries are typically aneurysmally enlarged
 
References:
Image courtesy of CDC (http://www.cdc.gov/ncbddd/heartdefects/tetralogyoffallot.html)
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Delius RE, Kumar RV, Elliott MJ et al. Atriventricular septal defect and tetralogy of Fallot: a 15-year experience. Eur J Cardiothorac Surg 1977: 12: 171-176
Lakier JB, Stangr P, Heymann MA et al. Tetralogy of Fallot with absent pulmonary valve. Natural history and hemodynamic considerations. Circulation 1974; 50: 167-175
Craatz S, Kunzel E, Spanel-Borowski K. Right-sided aortic arch and tetralogy of Fallot in humans-a morphological study of 10 cases. Cardiovasc Pathol 2003; 12: 226-232
Need LR, Powell AJ, del Nido P, Geeva T. Coronary echocardiography in Tetralogy of Fallot: diagnostic accuracy, resource utilization and surgical implications over 13 years. J Am Coll Cardiol 2003; 36: 1371-1377