Summary of Tetralogy of Fallot
Pulmonary infundibular stenosis (most important determinant for prognosis)
Right ventricular hypertrophy (RVH)— boot‑shaped heart on chest X-ray
Ventricular septal defect (VSD)
The pulmonary stenosis forces a right-to-left flow across the VSD, and eventual RVH. "Tet spells" can occur with crying, fever, and exercise due to exacerbation of RV outflow obstruction. Squatting decreases cyanosis by increasing the systemic vascular resistance and thus decreasing the right-to-left shunt. Surgical correction is the only definitive treatment option.
Transcript for Tetralogy of Fallot
Content Reviewers:Rishi Desai, MD, MPH, Jahnavi Narayanan, Tanner Marshall, MS, Vincent Waldman, PhD
Tetralogy of Fallot
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.