Tetralogy of Fallot (TOF) is named for the "tetrad" of anomalies that it consists of: ventricular septal defects, right ventricular outflow blockage, right ventricular hypertrophy, and aortic overriding.
Epidemiology
Tetralogy of Fallot affects three out of every ten thousand live infants. It is the most common cause of cyanotic cardiac disease in patients over the age of one, accounting for up to a tenth of all congenital cardiac abnormalities.
A newborn with TOF will exhibit symptoms based on the degree of right ventricular tract obstruction, which results in decreased pulmonary blood flow and the presence of right-to-left shunting.
Pathophysiology
The fusing of the outer endocardial tubes into a single tubular structure, the cardiac tube, occurs around the 20th day of gestation. Following that, the heart tube folds and loops, resulting in the development of a cranial and dorsal atrium and a primitive ventricle that moves below, ventrally, and to the right. The right ventricle is the dominating chamber in the embryo and foetus, getting 65% of the venous return and contributing to the lower body, placenta, and lungs. The right ventricle is divided into three sections: the intake (which includes the tricuspid valve chordae tendineae and papillary muscles), the trabeculated apical myocardium, and the infundibulum or conus.
The ventricular septal abnormalities seen in patients with tetralogy of Fallot are typically perimembranous and can extend into the muscular septum. The pulmonary valve, which is usually bicuspid and stenotic, the hypoplastic pulmonary valve annulus, the deviation of the infundibular septum, which causes a subvalvular obstruction, and hypertrophy of the muscular bands in this region are all factors that can contribute to right ventricular outflow obstruction. The degree of the overriding aorta varies and receives blood flow from both ventricles. The physiological process underlying hypercyanotic episodes or "Tet spells" in tetralogy of Fallot consists of either a decrease in systemic vascular resistance or an increase in pulmonary resistance, both of which contribute to a right-to-left shunt across the ventricular septal defect, resulting in marked desaturation. The hypercyanotic spell is distinguished by a quick and dramatic drop in oxygen saturation caused by abrupt and complete, or almost complete, occlusion of the subpulmonary outflow tract. Hypercyanotic periods do not occur in every patient with tetralogy of Fallot. The periods usually begin at a couple of months of age, during times of stress or dehydration, both of which aggravate the dynamic infundibular blockage.
Elimination of hypoxemic conditions may also include the use of pharmacological drugs to increase systemic vascular resistance and decrease heart contractility. Surgical repairs are frequently completed within the first year.
Patients who have adequate forward flow through the subpulmonary outflow tract following ductal closure will be closely monitored until a complete repair is accomplished. Some hospitals will do full repairs on all neonates. Others will treat symptomatic newborns and conduct a full repair on all patients between the ages of 4 and 6 months.
Palliation, which does not always involve cardiopulmonary bypass, creates a safe source of blood flow to the lungs by inserting a prosthetic tube between a systemic and a pulmonary artery. The modified Blalock-Taussig shunt is the most prevalent type of aorto-pulmonary shunt. This is a connection between the subclavian and pulmonary arteries on the same side. A full repair, always performed while under cardiopulmonary bypass,
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