Atrial Septal Defect is Added to Tetralogy of Fallot to Make it a Pentalogy
The correct answer is A) ASD (Atrial Septal Defect). When an atrial septal defect is added to the four cardiac anomalies that comprise Tetralogy of Fallot, it becomes Pentalogy of Fallot 1.
Understanding Tetralogy of Fallot (TOF)
Tetralogy of Fallot is defined by the American College of Cardiology/American Heart Association as a group of congenital cardiac malformations with biventricular atrioventricular alignments characterized by four key components 2:
- Ventricular septal defect (VSD) of the malalignment type
- Narrowing or atresia of the pulmonary outflow (pulmonary stenosis)
- Aortic override (biventricular origin of the aorta)
- Right ventricular hypertrophy
These four components are the result of anterosuperior deviation of the conal or outlet septum or its fibrous remnant 2.
Pentalogy of Fallot
Pentalogy of Fallot occurs when an atrial septal defect (ASD) is present in addition to the four classic components of Tetralogy of Fallot 1, 3. The ASD creates an additional shunt at the atrial level, allowing communication between the right and left atria.
According to research evidence, Pentalogy of Fallot is characterized by 3:
- The four components of Tetralogy of Fallot
- PLUS an atrial septal defect (ASD)
Clinical Implications
Pentalogy of Fallot represents a more complex form of congenital heart disease than Tetralogy of Fallot alone. The additional ASD can:
- Increase right-to-left shunting
- Exacerbate cyanosis
- Contribute to decreased pulmonary blood flow
- Potentially lead to more severe clinical manifestations
In patients with Pentalogy of Fallot, the ASD typically allows right-to-left shunting of blood at the atrial level, which further contributes to the cyanosis already present due to the right ventricular outflow tract obstruction and VSD 3, 4.
Differential Diagnosis
It's important to distinguish Pentalogy of Fallot from other variants of Tetralogy of Fallot, such as:
- Tetralogy of Fallot with pulmonary atresia
- Tetralogy of Fallot with absent pulmonary valve syndrome
- Tetralogy of Fallot with major aortopulmonary collateral arteries (MAPCAs)
None of the other options listed in the question (VSD, right ventricular hypertrophy, or pulmonary stenosis) would create a pentalogy when added to Tetralogy of Fallot, as they are already components of the tetralogy itself.