AssessmentsTetralogy of Fallot
USMLE® Step 1 style questions USMLE
USMLE® Step 2 style questions USMLE
A 7-year-old boy comes to the emergency department because of worsening shortness of breath for the past 3 months. He has a history of recurrent viral and fungal infections. In the morning, his mother noticed that his lips were bluish in color. He is currently seated leaning forward with his neck extended and has perioral cyanosis and acrocyanosis. His pulse is 120/min, respirations are 44/min, and a blood pressure is 110/80 mm Hg. Cardiac examination shows a 2/6 systolic murmur that worsens with inspiration. Chest radiograph shows an absent thymic shadow, elongated cardiac silhouette, and decreased pulmonary vascular markings. Which of the following diagnoses best describes the mechanism responsible for the patient’s shortness of breath and pulmonary findings?
If you’ve ever played Tetris, you probably know that you use pieces made of groups of four squares. Tetralogy of Fallot, or TOF, is a congenital heart condition where patients have four heart abnormalities.
Here’s a look at the normal heart: the upper chambers, or the left and the right atria; the lower chambers, or the left and the right ventricles; the aorta; and the pulmonary artery.
Instead of using this anatomical heart, let’s look at a simplified version.
Let’s go through four abnormal findings of TOF, one at a time. The first abnormality is stenosis, or narrowing of the right ventricular outflow tract into the pulmonary artery. This could either be narrowing of the valve itself, or narrowing of the infundibulum, which is the area right below the valve. Either way, this makes it harder for deoxygenated blood to get to the pulmonary circulation.
In response, the myocardium of the right ventricle hypertrophies, or gets thicker, in order to contract harder and push blood past the stenosis. This is the second feature of TOF.
This causes their heart to look “boot-shaped” on an x-ray.
The third feature is that patients have a large ventricular septal defect, which is a gap between the ventricles that allows blood to shunt between them.
Now, in a patient with an isolated ventricular septal defect, which is when the patient doesn’t have TOF, oxygenated blood is shunted from the left side to the right side because the pressure on the left is higher than the pressure on the right. For patients with TOF, however, the right ventricular outflow obstruction might block the normal blood flow so much that the pressure in the right ventricle has to be really high to get past it. Well, the high right-sided pressure causes the left side of the heart to become the path of least resistance, and deoxygenated blood shunts from the right side to the left side.