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Cardiovascular Disorders
Abdominal Aneurysm
Aortic Insufficiency
Aortic Stenosis
Arterial Occlusive
Atrial Septal Defect
Buerger's Disease
Cardiac Arrhythmias
Cardiac Tamponade
Cardiogenic Shock
Coarctation of the Aorta
Coronary Artery Disease
Dilated Cardiomyopathy
Femoral And Popliteal Aneurysms
Heart Failure
Hypertrophic Cardiomyopathy
Hypovolemic Shock
Mitral Insufficiency
Mitral Stenosis
Myocardial Infarction
Patent Ductus Arteriosus
Pulmonic Insufficiency
Pulmonic Stenosis
Raynaud's Disease
Rheumatic Heart Disease
Septic Shock
Tetralogy of Fallot
Thoracic Aortic Aneurysm
Transposition of The Great Arteries
Tricuspid Insufficiency
Tricuspid Stenosis
Varicose Veins
Ventricular Aneurysm
Ventricular Septal Defect (VSD)

Tetralogy of Fallot

What is Tetralogy of Fallot?

This cardiac defect is really four defects that occur together: a ventricular septal defect, infundibular stenosis (possibly with pulmonic valve stenosis), right venuicular hypertrophy, and dextroposition of the aorta,which overrides the ventricular septal defect.

The degree of pulmonic stenosis and the size and location of the ventricular septal defect determine the clinical and hemodynamic effects of this complex anomaly. Blood may shunt left to right or right to left, depending on the defect's configuration.

Usually, the ventricular septal defect lies in the outflow tract of the right ventricle and is large enough to equalize right and left ventricular pressures. However, the ratio of systemic vascular resistance to pulmonic stenosis affects how much blood flows across the defect and the direction in which it flows.

When blood shunts right to left through the ventrucular septal defect, unoxygenated blood mixes with oxygenated blood, which leads to cyanosis.

When right ventricular outflow is severely obstructed, blood flows right to left, which decreases aterial oxygen saturation (Sao2) and leads to cyanosis, reduced pulmonary blood flow, and hypoplasia of all the pulmonary vessels. Increased right ventricular pressure causes right ventricular hypertrophy.

Milder forms of pulmonic stenosis result in a left-to­right shunt or no shunt at all.

About 15% of infants born with a congenital heart defect have tetralogy of Fallot. It's equally common in males and females. Sometimes it coexists with other congenital heart defects, such as patent ductus arteriosus or an atrial septal defect. Before surgical techniques were available to correct this defect, about one-third of affected children died in infancy.

Causes of Tetralogy of Fallot

Tetralogy of Fallot stems from embryonic hypoplasia of the right ventricle's outflow tract. No one knows what causes that hypoplasia. However, the defect has been associated with fetal alcohol syndrome and maternal ingestion of thalidomide during pregnancy.

Signs & Symptoms of Tetralogy of Fallot

Signs and symptoms of tetralogy of Fallot vary, depending on the extent of obstruction of blood flow out of the right ventricle and into the lungs. Typical signs and symptoms may include:

  • A bluish coloration of the skin caused by blood low in oxygen (cyanosis)
  • Shortness of breath and rapid breathing
  • Loss of consciousness (fainting)
  • Failure to gain weight
  • Clubbing of fingers and toes (an abnormal, rounded shape of the nail bed)
  • Lack of appetite
  • Poor development
  • Tiring easily during play
  • Irritability
  • Sudden death

Diagnostic Tests

Chest X-rays - X-rays produce pictures by passing an X-ray beam through a patient. The beam is absorbed in different amounts by body structures. A typical sign of tetralogy of Fallot on X-ray film is a "boot-shaped" heart, because the right ventricle is enlarged.

Electrocardiography shows right ventricular hypertrophy with upright T waves in the right chest leads. These results are commonly associated with peaked P waves, right axis deviation and, possibly, right atrial hypertrophy.

Echocardiography identifies a septal override of the aorta, the ventricular septal defect, and infundibular pulmonic stenosis. It also reveals the right ventricle's hypertrophied walls.

Laboratory tests reveal diminished Sao2 and polycythemia (hematocrit may be more than 60%) if the cyanosis is severe and long-standing. This condition predisposes the patient to thrombosis.

Cardiac catheterization can be used to confirm the diagnosis by displaying pulmonic stenosis, the ventricular septal defect, and the overriding aorta. It also can be used to rule out other cyanotic heart defects and to measure the degree of oxygen saturation in aortic blood.


During cyanotic spells, oxygenation improves if the patient assumes the knee-chest position and receives oxygen and morphine. Propranolol may prevent cyanotic episodes. Surgery that joins the subclavian artery to the pulmonary artery (Blalock-Thussig operation) may enhance blood flow to the lungs, reducing hypoxia.

Supportive measures include antibiotics administered before, during, and after dental treatments or surgery. Phlebotomy may also be needed in children with polycythemia.

Surgery to relieve pulmonic stenosis and close the ventricular septal defect requires cardiopulmonary bypass with hypothermia (to decrease oxygen utilization during surgery, especially in young children). Surgery is necessary when progressive hypoxia and polycythemia impair the patient's quality of life, usually before age 2.

Prevention Tips

There is no known prevention.


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