A 4-month-old infant with Tetralogy of Fallot presents with fever and loose stools. Which of the following is compatible with the diagnosis of Tetralogy spells?
**Core Concept**
Tetralogy of Fallot is a congenital heart defect characterized by four components: ventricular septal defect, pulmonary stenosis, right ventricular hypertrophy, and an overriding aorta. Tetralogy spells, also known as cyanotic spells, occur due to a combination of factors including increased pulmonary vascular resistance, right-to-left shunting of blood, and decreased systemic vascular resistance.
**Why the Correct Answer is Right**
During a Tetralogy spell, the increased pulmonary vascular resistance and decreased systemic vascular resistance lead to a decrease in the oxygen saturation of the blood. This is due to the right-to-left shunting of blood through the ventricular septal defect, bypassing the lungs and resulting in a decrease in pulmonary blood flow. The increased resistance to blood flow in the pulmonary arteries contributes to the increased pressure in the right ventricle, leading to a decrease in the amount of blood being pumped to the body. This results in a characteristic blue discoloration of the skin and mucous membranes due to the increased amount of deoxygenated blood.
**Why Each Wrong Option is Incorrect**
**Option A:** Cyanosis is not the only symptom of Tetralogy spells, but it is a key feature. Other symptoms include syncope, seizures, and shortness of breath.
**Option B:** Diaphoresis is a symptom of Tetralogy spells, but it is not the most distinctive or characteristic symptom. Other symptoms such as cyanosis, shortness of breath, and syncope are more specific.
**Option C:** Apnea is a feature of Tetralogy spells, but it is not the most specific or distinctive symptom. Other symptoms such as cyanosis, shortness of breath, and syncope are more characteristic.
**Option D:** Bradycardia is not a typical feature of Tetralogy spells. In fact, tachycardia is often seen due to the increased sympathetic activity in response to the decreased oxygen saturation.
**Clinical Pearl / High-Yield Fact**
Remember the "5 C's" of Tetralogy spells: Cyanosis, Clubbing, Congestion, Cardiomegaly, and Cyanotic episodes. These features are often seen in infants with Tetralogy of Fallot and can help in making the diagnosis.
**Correct Answer:** C. Cyanosis.