Pentalogy of Fallot: The Added Cardiac Anomaly
The correct answer is A) ASD (Atrial Septal Defect). Pentalogy of Fallot occurs when an atrial septal defect is added to the four classic components of Tetralogy of Fallot. 1
Understanding Tetralogy of Fallot (TOF)
Tetralogy of Fallot consists of four key cardiac anomalies:
- Ventricular septal defect (VSD) of the malalignment type
- Pulmonary stenosis (narrowing or atresia of the pulmonary outflow)
- Overriding aorta (biventricular origin of the aorta)
- Right ventricular hypertrophy 1, 2
These four components result from anterosuperior deviation of the conal or outlet septum or its fibrous remnant, as defined by the American College of Cardiology/American Heart Association 1.
Pentalogy of Fallot: The Fifth Component
When an atrial septal defect (ASD) is present in addition to the four classic components of Tetralogy of Fallot, the condition is termed Pentalogy of Fallot 1, 2. This creates an additional shunt at the atrial level, allowing communication between the right and left atria.
Clinical Significance of the ASD in Pentalogy
The addition of an ASD to Tetralogy of Fallot has important clinical implications:
- Increases right-to-left shunting
- Exacerbates cyanosis
- Contributes to decreased pulmonary blood flow
- Can lead to more severe clinical manifestations 1
The ASD typically allows right-to-left shunting of blood at the atrial level, further contributing to the cyanosis already present due to the right ventricular outflow tract obstruction and VSD 1, 3.
Common Misconceptions
It's important to note that:
- Pulmonary stenosis (option D) is already one of the four components of Tetralogy of Fallot
- VSD (option B) is already one of the four components of Tetralogy of Fallot
- Right ventricular hypertrophy (option C) is already one of the four components of Tetralogy of Fallot
Therefore, none of these would be "added" to make a pentalogy, as they are already part of the tetralogy.
Clinical Recognition
When evaluating a patient with suspected congenital heart disease, the presence of all four components of Tetralogy of Fallot plus an ASD should prompt consideration of Pentalogy of Fallot. Echocardiography is the definitive diagnostic tool that can identify all five components 3.