Tetralogy of fallot overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editors-In-Chief: Priyamvada Singh, M.B.B.S. [2], Assistant Editor-In-Chief: Kristin Feeney, B.S. [3]
Overview
Tetralogy of Fallot is a congenital heart defect which classically has four anatomical components: obstruction to right ventricular outflow, right ventricular hypertrophy, ventricular septal defect, and overriding of aorta. It accounts for approximately 10% of all forms of congenital heart disease. It is the most common cause of cyanosis in children over one year of age (blue baby syndrome). In comparison to a normal heart, Tetralogy of Fallot has many key deviations including: increased outflow in the aorta, partial obstruction of the right ventricular outflow and pulmonary valve, a thickened right ventricle, and a ventricular septal defect.
Historical Perspective
The condition was described in 1672 by Niels Stensen and in 1888 by the French physician Etienne Fallot, for whom it was named.
Anatomy
Tetralogy of Fallot has four characteristic components i.e. pulmonic stenosis, right ventricular hypertrophy, ventricular septal defect and over-riding of the aorta
Pathophysiology
The obstruction of right ventricular outflow in tetralogy of Fallot causes blood to shunt or flow from the right to left side of heart through the ventricular septal defect. This causes right ventricular hypertrophy and eventual right sided heart failure. There is flow of deoxygenated venous blood from the right side of the heart to the systemic circulation resulting in cyanosis.
Causes
Both environmental and genetic factors appear to be involved in the development of tetralogy of Fallot.
Differentiating Tetralogy of Fallot from other Diseases
Tetralogy of Fallot is the most common form of cyanotic heart disease, and must be distinguished from other forms of cyanotic heart disease.
Epidemiology and Demographics
Tetralogy of Fallot represents 5-7% of congenital heart defects. Tetralogy of Fallot is the most common cause of cyanotic heart disease and accounts for one third of all cases of cyanotic heart disease.
Natural History, Complications and Prognosis
The prognosis of patients with repaired tetralogy of Fallot has improved over the years and these patients now have the potential to lead normal lives. As these patients grow, there may be leakage of the repaired pulmonic valve. There may be a persistent risk of sudden cardiac death.
Diagnosis
History and Symptoms
Tetralogy of Fallot causes cyanosis, dyspnea, failure to thrive and potentially fatal tet spells.
Physical Examination
Tetralogy of Fallot is associated with cyanosis, clubbing, a thrill and a harsh systolic ejection murmur over the left sternal border.
Laboratory Findings
Polycythemia and oxygen desaturation may be present in the patient with tetralogy of Fallot. Thrombocytopenia and deficiencies in coagulation factors may also be present.
CT
Computed tomography can be helpful as a diagnostic tool in conditions where the echocardiographic findings are inconclusive.
MRI
Magnetic resonance imaging can be helpful as a diagnostic tool in patients in whom the echocardiographic findings are inconclusive.
Echocardiography
Echocardiography establishes the initial diagnosis of tetralogy of Fallot, and is useful in evaluating the hemodynamic abnormalities that are present. Right-to-left shunting through the VSD can be visualized by color doppler imaging, and the severity of right ventricular outflow tract obstruction can be determined by spectral doppler measurements.
Cardiac Catheterization
Cardiac catheterization can be performed if the anatomy cannot be evaluated on echocardiography. Although echocardiography is the imaging modality of choice, cardiac catheterization allows confirms the diagnosis and permits collection of additional anatomical and hemodynamic data, including the location and magnitude of right-to-left shunting, the level and severity of right ventricular outflow obstruction, the anatomical features of the right ventricular outflow tract as well as the main pulmonary artery and its branches. Repair of residual defects following a repair of tetralogy (leaking VSD, or residual pulmonic narrowing) can also be undertaken percutaneously in experienced centers.
Treatment
Medical Therapy
Although operative repair of tetralogy of Fallot is definitive, medical therapy can be used to manage hypoxic or tet spells.
Surgery
Repair of tetralogy of Fallot reduces mortality. With the development of modern surgical techniques, there was a 40% reduction in mortality attributed to tetralogy of Fallot between 1979 to 2005.