From the Guidelines
The fourth characteristic of Tetralogy of Fallot, in addition to right ventricular outflow tract obstruction, ventricular septal defect (VSD), and aortic override, is right ventricular hypertrophy. This is based on the most recent and highest quality evidence available, including a 2022 study published in Circulation 1, which describes the main pathologic basis of Tetralogy of Fallot as antero-cephalad deviation of the developing conal septum, resulting in a malalignment type ventricular septal defect, an “overriding aorta”, right ventricular outflow tract obstruction, and ultimately leading to right ventricular hypertrophy.
The right ventricle must work harder to pump blood through the narrowed outflow tract, causing the ventricular muscle to thicken over time. This hypertrophy is a direct physiological consequence of the obstruction and is visible on echocardiography, cardiac MRI, or during surgical repair. The degree of hypertrophy often correlates with the severity of the outflow tract obstruction and contributes to the overall hemodynamic compromise seen in these patients. Understanding this fourth component is essential for complete characterization of the condition and helps explain the progressive nature of cardiac dysfunction in untreated Tetralogy of Fallot, as also supported by the 2021 ACC/AHA key data elements and definitions for heart failure 1.
Key characteristics of Tetralogy of Fallot include:
- Right ventricular outflow tract obstruction
- Ventricular septal defect (VSD)
- Aortic override
- Right ventricular hypertrophy These characteristics are crucial for the diagnosis and management of Tetralogy of Fallot, and are supported by the latest evidence from reputable sources, such as the American College of Cardiology and the American Heart Association 1.
From the Research
Tetralogy of Fallot Characteristics
The characteristics of Tetralogy of Fallot include:
- Right ventricular outflow tract obstruction
- Ventricular septal defect (VSD)
- Aortic override
- Right ventricular hypertrophy
Evidence from Studies
Studies have consistently shown that the fourth characteristic of Tetralogy of Fallot is right ventricular hypertrophy 2, 3, 4.
- A study published in the Orphanet journal of rare diseases in 2009 described Tetralogy of Fallot as a congenital cardiac malformation that consists of an interventricular communication, also known as a ventricular septal defect, obstruction of the right ventricular outflow tract, override of the ventricular septum by the aortic root, and right ventricular hypertrophy 2.
- Another study published in the World journal of surgery in 2010 described Tetralogy of Fallot as a cyanotic congenital cardiac defect that consists of pulmonary outflow tract obstruction, ventricular septal defect (VSD), overriding aortic root, and right ventricular hypertrophy 3.
- A study published in Advances in experimental medicine and biology in 2024 also described Tetralogy of Fallot as consisting of a large malalignment ventricular septal defect, an obstruction of the right ventricular outflow tract, an aorta that "overrides" the ventricular septal defect, and right ventricular hypertrophy 4.
Answer to Question 5
Based on the evidence from the studies, the correct answer to Question 5 is: c) Right ventricular hypertrophy