Tetralogy of fallot overview

# Overview
Tetralogy of Fallot was first discovered by  Etienne Fallot, a French ohysician in 1888. 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). It is understood that tetralogy of fallot is the result of improper positioning of the outlet septum. In the normal heart, the outlet septum is an indistinguishable component of the crista supraventricularis that communicates with the septomarginal trabeculae to divide the right and left ventricular cavities. In Tetralogy of Fallot, proper ventricular septation is perturbed by anterocephalad displacement of the outlet septum relative to the septomarginal trabecula. These features include a ventricular septal defect, overriding aorta, pulmonary stenosis, and right ventricular hypertrophy. 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. Common causes of tetralogy of Fallot may include: Alcoholism in the mother, diabetes, pregnancy after the age of 40, rubella or other viral illnesses during pregnancy, phenylketonuria (PKU) in the mother, fetal hydantoin syndrome, and fetal carbamazepine syndrome. On the basis cyanosis, tetralogy of Fallot must be differentiated from total anomalous pulmonary venous connection, tricuspid atresia, transposition of the great vessels, and truncus arteriosus. Tetralogy of Fallot occurs in approximately 30 to 60 per 100,000 births. Tetralogy of Fallot represents 5-7% of congenital heart defects. The majority of cases are thought to be sporadic and are not familial. Tetralogy of Fallot occurs slightly more often in males than in females. Common risk factors in the development of tetralogy of Fallot include: Alcoholism in the mother, diabetes, and pregnancy after the age of 40. According to the Canadian Cardiovascular Society/Canadian Pediatric Cardiology Association, screening for tetralogy of Fallot by pulse oxymetry is recommended for all newborns. 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. Echocardiography is the gold standard test for the diagnosis of tetralogy of fallot. 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. Echocardiography may be helpful in the diagnosis of tetralogy of fallot. Findings on an echocardiography diagnostic of tetralogy of fallot include ventricular septal defect, right ventricular outflow tract obstruction, and overriding aorta. Repair of tetralogy of Fallot reduces mortality.  we can either perform palliative surgery which involves forming an anastomosis between the subclavian artery and the pulmonary artery. This redirected a large portion of the partially oxygenated blood leaving the heart for the body into the lungs, increasing flow through the pulmonary circuit, and greatly relieving symptoms in patients or total surgical repair which involves making incisions into the heart muscle, relieving the right ventricular outflow tract stenosis by careful resection of muscle, repairing the VSD using a Gore-Tex or Dacron patch or a homograft. Additional reparative or reconstructive work may be done on patients as required by their particular anatomy.The repair could be done by either of the approaches i.e.transatrial or transpulmonary.

# Historical Perspective
Tetralogy of Fallot was first discovered by  Etienne Fallot, a French ohysician in 1888.

# Classification
There is no established system for the classification of tetralogy of Fallot.

# Pathophysiology
Tetralogy of Fallot is a congenital heart lesion characterized by a constellation of four morphologic abnormalities present in the newborn heart. It is understood that tetralogy of fallot is the result of improper positioning of the outlet septum. In the normal heart, the outlet septum is an indistinguishable component of the crista supraventricularis that communicates with the septomarginal trabeculae to divide the right and left ventricular cavities. In Tetralogy of Fallot, proper ventricular septation is perturbed by anterocephalad displacement of the outlet septum relative to the septomarginal trabecula. These features include a ventricular septal defect, overriding aorta, pulmonary stenosis, and right ventricular hypertrophy. 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
Common causes of tetralogy of Fallot may include: Alcoholism in the mother, diabetes, pregnancy after the age of 40, rubella or other viral illnesses during pregnancy, phenylketonuria (PKU) in the mother, fetal hydantoin syndrome, and fetal carbamazepine syndrome.

# Differentiating Tetralogy of Fallot from other Diseases
On the basis cyanosis, tetralogy of Fallot must be differentiated from total anomalous pulmonary venous connection, tricuspid atresia, transposition of the great vessels, and truncus arteriosus.

# Epidemiology and Demographics
Tetralogy of Fallot occurs in approximately 30 to 60 per 100,000 births. Tetralogy of Fallot represents 5-7% of congenital heart defects. The majority of cases are thought to be sporadic and are not familial. Tetralogy of Fallot occurs slightly more often in males than in females.

# Risk factors
Common risk factors in the development of tetralogy of Fallot include: Alcoholism in the mother, diabetes, and pregnancy after the age of 40.

# Screening
According to the Canadian Cardiovascular Society/Canadian Pediatric Cardiology Association, screening for tetralogy of Fallot by pulse oxymetry is recommended for all newborns.

# 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

## Diagnostic Study of Choice
Echocardiography is the gold standard test for the diagnosis of tetralogy of fallot.

## History and Symptoms
Patients with tetralogy of Fallot may have a positive history of alcoholism, diabetes, Poor nutrition in mother in mother. Common symptoms of tetralogy of Fallot include sudden, marked bluish skin (tet spell), dyspnea on exertion, difficulty in feeding, failure to gain weight, failure to thrive, retarded growth and physical development, and hemoptysis.

## Physical Examination
Patients with tetralogy of Fallot usually appear small due to a failure to thrive. Physical examination of patients with tetralogy of Fallot is usually remarkable for cyanosis, systolic thrill, systolic ejection murmur, and Clubbing.

## Laboratory Findings
Laboratory findings consistent with the diagnosis of tetralogy of fallot include diminished oxygen saturation, hematocrit between 65% to 70%, and  low platelet count and coagulation factors.

## Electrocardiogram
An ECG may be helpful in the diagnosis of tetralogy of Fallot. Findings on an ECG suggestive of tetralogy of Fallot include  right axis deviation, right ventricular hypertrophy, wide QRS, and right bundle branch block.

## X Ray
An x-ray may be helpful in the diagnosis of tetralogy of fallot. Findings on an x-ray diagnostic of tetralogy of fallot include normal or decreased pulmonary vascularity, concave pulmonary artery segment,  "boot-like" heart, and  right sided aortic arch.

## 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. Echocardiography may be helpful in the diagnosis of tetralogy of fallot. Findings on an echocardiography diagnostic of tetralogy of fallot include ventricular septal defect, right ventricular outflow tract obstruction, and overriding aorta.

## 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.

## Other Imaging Findings
There are no other imaging findings associated with tetralogy of fallot.

## Other Diagnostic Studies
There are no other diagnostic studies associated with tetralogy of fallot.

# Treatment

## Medical Therapy
Although operative repair of tetralogy of Fallot is definitive, medical therapy can be used to manage hypoxic or tet spells. Tet spells cause acute hypoxia and may be treated with beta blockers, morphine, phenylephrine, and oxygen.

## Surgery
Repair of tetralogy of Fallot reduces mortality.  we can either perform palliative surgery which involves forming an anastomosis between the subclavian artery and the pulmonary artery. This redirected a large portion of the partially oxygenated blood leaving the heart for the body into the lungs, increasing flow through the pulmonary circuit, and greatly relieving symptoms in patients or total surgical repair which involves making incisions into the heart muscle, relieving the right ventricular outflow tract stenosis by careful resection of muscle, repairing the VSD using a Gore-Tex or Dacron patch or a homograft. Additional reparative or reconstructive work may be done on patients as required by their particular anatomy.The repair could be done by either of the approaches i.e.transatrial or transpulmonary.

## Primary Prevention
There are no established measures for the primary prevention of Tetralogy of Fallot.

## Secondary Prevention
According to the Canadian Cardiovascular Society/Canadian Pediatric Cardiology Association, screening for tetralogy of Fallot by pulse oxymetry is recommended for all newborns.