Tetralogy of Fallot: Pathophysiology Explained

Introduction

Tetralogy of Fallot (TOF) is a congenital heart defect that consists of four key anatomical abnormalities. These defects lead to oxygen-poor blood being circulated throughout the body, causing cyanosis (bluish skin coloration).

The Four Components of TOF

1. Pulmonary Stenosis: A narrowing of the pulmonary valve or artery reduces blood flow to the lungs for oxygenation.
2. Right Ventricular Hypertrophy: The right ventricle thickens due to increased workload caused by the obstructed outflow.
3. Overriding Aorta: The aorta is positioned over both ventricles instead of only the left, allowing mixed oxygenated and deoxygenated blood to enter circulation.
4. Ventricular Septal Defect (VSD): A hole between the ventricles allows oxygen-poor blood to mix with oxygenated blood from the left ventricle, worsening systemic oxygen delivery.

Pathophysiology

• Decreased Pulmonary Blood Flow: Due to pulmonary stenosis, less blood reaches the lungs for oxygenation.
• Right-to-Left Shunting: The VSD allows deoxygenated blood to bypass the lungs and enter systemic circulation.
• Hypoxia and Cyanosis: This results in lower arterial oxygen content, leading to cyanosis.
• Compensatory Mechanisms: To counteract chronic hypoxia, the body may increase red blood cell production (polycythemia), which can lead to increased blood viscosity and further complications.

Clinical Manifestations

• Cyanosis, especially during exertion.
• Tet spells (acute episodes of hypoxia).
• Squatting behavior (in older children) to increase systemic vascular resistance and reduce right-to-left shunting.
• Heart murmur due to turbulent blood flow.

Conclusion

Tetralogy of Fallot is a serious congenital condition requiring early detection and surgical correction. Understanding its pathophysiology helps guide treatment and long-term management.

Source recommendations

1. American Heart Association Guidelines

1. https://professional.heart.org/en/guidelines-and-statements
2. https://www.heart.org/
3. https://professional.heart.org/en/guidelines-statements
4. https://www.heart.org/en/healthy-living/fitness/fitness-basics/aha-recs-for-physical-activity-in-adults
5. https://cpr.heart.org/en/resuscitation-science/cpr-and-ecc-guidelines

2. European Society of Cardiology Guidelines

1. https://www.escardio.org/Guidelines/Clinical-Practice-Guidelines
2. https://academic.oup.com/eurheartj/article/42/34/3227/6358713
3. https://www.escardio.org/Guidelines
4. https://academic.oup.com/eurheartj/article/44/39/4043/7238227
5. https://www.escardio.org/