Tetralogy of Fallot

Tetralogy of Fallot
Other names	Fallot’s syndrome, Fallot’s tetrad, Steno–Fallot tetralogy[1]
Diagram of a healthy heart and one with tetralogy of Fallot
Specialty	Cardiac surgery, pediatrics
Symptoms	Episodes of bluish color to the skin, difficulty breathing, heart murmur, finger clubbing[2]
Complications	Irregular heart rate, pulmonary regurgitation[3]
Usual onset	From birth[4]
Causes	Unknown[5]
Risk factors	Alcohol, diabetes, >40, rubella during pregnancy[5]
Diagnostic method	Based on symptoms, echocardiogram[6]
Differential diagnosis	Transposition of the great arteries, Eisenmenger syndrome, Ebstein anomaly[7]
Treatment	Open heart surgery[8]
Frequency	1 in 2,000 babies[4]

Tetralogy of Fallot (TOF), formerly known as Steno-Fallot tetralogy,^[9] is a congenital heart defect characterized by four specific cardiac defects.^[4] Classically, the four defects are:^[4]

• pulmonary stenosis, which is narrowing of the exit from the right ventricle;
• a ventricular septal defect, which is a hole allowing blood to flow between the two ventricles;
• right ventricular hypertrophy, which is thickening of the right ventricular muscle; and
• an overriding aorta, which is where the aorta expands to allow blood from both ventricles to enter.

At birth, children may be asymptomatic or present with many severe symptoms.^[10] Later in infancy, there are typically episodes of bluish colour to the skin due to a lack of sufficient oxygenation, known as cyanosis.^[2] When affected babies cry or have a bowel movement, they may undergo a "tet spell" where they turn cyanotic, have difficulty breathing, become limp, and occasionally lose consciousness.^[2] Other symptoms may include a heart murmur, finger clubbing, and easy tiring upon breastfeeding.^[2]

The cause of tetralogy of Fallot is typically not known.^[5] Risk factors include a mother who uses alcohol, has diabetes, is over the age of 40, or gets rubella during pregnancy.^[5]: 62 It may also be associated with Down syndrome and other chromosomal defects that cause congenital heart defects.^[11]

TOF is typically treated by open heart surgery in the first year of life.^[8] The timing of surgery depends on the baby's symptoms and size.^[8] The procedure involves increasing the size of the pulmonary valve and pulmonary arteries and repairing the ventricular septal defect.^[8] In babies who are too small, a temporary surgery may be done with plans for a second surgery when the baby is bigger.^[8] With proper care, most people who are affected live to be adults.^[4] Long-term problems may include an irregular heart rate and pulmonary regurgitation.^[3]

The prevalence of TOF is estimated to be anywhere from 0.02 to 0.04%.^[4] Though males and females were initially thought to be affected equally, more recent studies have found males to be affected more than females.^[4][12] It is the most common complex congenital heart defect, accounting for about 10 percent of cases.^[13][14] It was initially described in 1671 by Niels Steensen.^[1][15] A further description was published in 1888 by the French physician Étienne-Louis Arthur Fallot, after whom it is named.^[1][16] The first total surgical repair was carried out in 1954.^[3]