Tetralogy of fallot

Tetralogy of Fallot, which is one of the most common congenital heart disorders, comprises right ventricular (RV) outflow tract obstruction (RVOTO) (infundibular stenosis), ventricular septal defect (VSD), aorta dextroposition, and RV hypertrophy (see the image below). The mortality rate in untreated patients reaches 50% by age 6 years, but in the present era of cardiac surgery, children with simple forms of tetralogy of Fallot enjoy good long-term survival with an excellent quality of life.

Anatomic findings in tetralogy of Fallot.

Signs and symptoms

The clinical features of tetralogy of Fallot are directly related to the severity of the anatomic defects. Infants often display the following:

• Difficulty with feeding
• Failure to thrive
• Episodes of bluish pale skin during crying or feeding (ie, "Tet" spells)
• Exertional dyspnea, usually worsening with age

Physical findings include the following:

• Most infants are smaller than expected for age
• Cyanosis of the lips and nail bed is usually pronounced at birth
• After age 3-6 months, the fingers and toes show clubbing
• A systolic thrill is usually present anteriorly along the left sternal border
• A harsh systolic ejection murmur (SEM) is heard over the pulmonic area and left sternal border
• During cyanotic episodes, murmurs may disappear
• In individuals with aortopulmonary collaterals, continuous murmurs may be auscultated

The following may also be noted:

• RV predominance on palpation
• A bulging left hemithorax
• Aortic ejection click
• Squatting position (compensatory mechanism)
• Scoliosis (common)
• Retinal engorgement
• Hemoptysis

See Clinical Presentation for more detail.

Diagnosis

Hemoglobin and hematocrit values are usually elevated in proportion to the degree of cyanosis. Patients with significant cyanosis have the following, in association with a tendency to bleed:

• Decreased clotting factors
• Low platelet count
• Diminished coagulation factors
• Diminished total fibrinogen
• Prolonged prothrombin and coagulation times

Arterial blood gas (ABG) results are as follows:

• Oxygen saturation varies
• pH and partial pressure of carbon dioxide (pCO2) are normal unless the patient is in extremis

Imaging studies include the following:

• Echocardiography
• Chest radiographs
• Magnetic resonance imaging (MRI)

Echocardiography has the following attributes:

• Color-flow Doppler echocardiography accurately diagnoses ductus arteriosus, muscular VSD, or atrial septal defect
• The coronary anatomy can be revealed with some degree of accuracy
• Valvar alterations can be detected with ease
• In many institutions, echocardiography is the only diagnostic study used before surgery

Chest radiographs have the following attributes:

• Often normal initially
• Diminished vascularity in the lungs and diminished prominence of the pulmonary arteries gradually become apparent
• The classic boot-shaped heart ( coeur en sabot) is the hallmark of the disorder

MRI has the following attributes:

• Provides good delineation of the aorta, RVOT, VSDs, RV hypertrophy, and the pulmonary artery and its branches ^[1]
• Can also be used to measure intracardiac pressures, gradients, and blood flows

Cardiac catheterization is extremely useful in any of the following instances:

• The anatomy cannot be completely defined by echocardiography
• Disease in the pulmonary arteries is a concern
• Pulmonary vascular hypertension is possible

Cardiac catheterization findings include the following:

• Assessment of the pulmonary annulus size and pulmonary arteries
• Assessment of the severity of RVOTO
• Location of the position and size of the VSD
• Ruling out possible coronary artery anomalies

See Workup for more detail.

Management

Acute treatment for hypercyanosis is as follows:

• Place the baby on the mother's shoulder with the infant's knees tucked up underneath; this provides a calming effect, reduces systemic venous return, and increases systemic vascular resistance (SVR)
• Oxygen is of limited value, as the primary abnormality is reduced pulmonary blood flow
• Morphine sulfate, 0.1-0.2 mg/kg intramuscularly (IM) or subcutaneously (SC), may reduce the ventilatory drive and decrease systemic venous return
• Phenylephrine, 0.02 mg/kg IV, is used to increase SVR
• Dexmedetomidine infusion has been used, but requires caution and careful titration ^[2]
• General anesthesia is a last resort

Most infants with tetralogy of Fallot require some type of surgical procedure. Surgery is preferably done at or about 12 months of age. Primary correction is the ideal operation and is usually performed under cardiopulmonary bypass. Palliative procedures (eg, placement of the modified Blalock-Taussig shunt) may be necessary in patients with contraindications to primary repair, which include the following:

• The presence of an anomalous coronary artery
• Very low birth weight
• Small pulmonary arteries
• Multiple VSDs
• Multiple coexisting intracardiac malformations                                                                                           

  Corrective Surgery

  Primary correction is the ideal operation for treatment of tetralogy of Fallot (TOF) and is usually performed under cardiopulmonary bypass (CPB). The aims of the surgery are to close the ventricular septal defect (VSD), resect the area of infundibular stenosis, and relieve the right ventricular (RV) outflow tract obstruction (RVOTO).

  Before cardiopulmonary bypass is initiated, previously placed systemic-to-pulmonary artery shunts are isolated and taken down. Patients then undergo cardiopulmonary bypass. Associated anomalies, such as atrial septal defect (ASD) or patent foramen ovale, are closed.