tetralogy of Fallot

Tetralogy of Fallot is not one defect but a package of four that tend to occur together, the most common cause of blue (cyanotic) congenital heart disease beyond infancy. The Greek-derived name simply means a set of four. The combination arises from a single developmental misstep that shifts a wall inside the heart, throwing off several connections at once.

The four features are: a hole between the ventricles (ventricular septal defect); a narrowed path out of the right ventricle to the lungs (pulmonary outflow obstruction); an aorta that sits shifted to straddle the hole (overriding aorta); and a thickened right ventricle that has had to push against the obstruction (right ventricular hypertrophy). Because the lung pathway is blocked, oxygen-poor blood is diverted through the hole into the body, lowering oxygen levels.

Affected infants may have spells of deepening blueness, classically relieved by squatting, which raises body resistance and redirects more blood to the lungs. Surgical repair, usually in the first year of life, patches the hole and relieves the obstruction, allowing most patients to thrive into adulthood, though many need ongoing follow-up for valve problems.