Tetralogy of Fallot
Patent ductus arteriosus, aortic stenosis, ventricular septal defect, pulmonic stenosis and tetralogy of Fallot are the most frequently reported cardiac anomalies of dogs.
Tetrology of Fallot is a complex combination of four congenital heart defects. The four heart defects are:
- Ventricular Septal Defect (VSD)
- Pulmonary Stenosis
- Right Ventricular Hypertrophy
- Overriding Aorta
The word Fallot is the name of the French physician Ettienne Louis Arthur Fallot who described the four heart defects.
Ventricular Septal Defect (VSD)
The heart has a wall that separates the chambers on its left side from those on its right side. This wall is called a septum. The septum prevents blood from mixing between the two sides of the heart.
A VSD is a hole in the part of the septum that separates the ventricles—the lower chambers of the heart. The hole allows oxygen-rich blood to flow from the left ventricle into the right ventricle instead of flowing into the aorta, the main artery leading out to the body.
Pulmonary Stenosis
This is a narrowing of the pulmonary valve and the passageway through which blood flows from the right ventricle to the pulmonary arteries. Normally, oxygen-poor blood from the right ventricle flows through the pulmonary valve into the pulmonary arteries and out to the lungs to pick up oxygen. In pulmonary stenosis, the heart has to work harder than normal to pump blood, and not enough blood can get to the lungs.
Right Ventricular Hypertrophy
This is when the right ventricle thickens because the heart has to pump harder than it should to move blood through the narrowed pulmonary valve.
Overriding Aorta
This is a defect in the location of the aorta. In a healthy heart, the aorta is attached to the left ventricle, allowing only oxygen-rich blood to go to the body. In tetralogy of Fallot, the aorta is between the left and right ventricles, directly over the VSD. As a result, oxygen-poor blood from the right ventricle can flow directly into the aorta instead of into the pulmonary artery to the lungs
The symptoms of tetralogy of Fallot vary in type and severity between individual dogs. Young animals may fail to grow normally if affected with the condition while dogs of all ages may exhibit weakness or may be unable to exercise normally. Affected animals are often short of breath and have a faster breathing rate; this is made worse by exercise and excitement. The low level of oxygen in the blood causes the blood to appear darker in colour than normal. This shows as a bluish-purple discoloration of the mucous membranes (e.g. the gums), particularly after exercise. In some affected animals the obstruction of the outlet results in a heart murmur. In extreme cases dogs with the condition may lose consciousness at times or suffer from seizures because of low blood oxygen levels. The disorder may also result in sudden death.
Diagnosis Diagnostic Tests and Procedures
The veterinarian will order several tests to diagnose tetralogy of Fallot. These tests will help determine the exact nature of the defects and how serious they are.
Echocardiogram is harmless and painless, uses sound waves to create a moving picture of the heart. During an echocardiogram, ultrasound waves bounce off the structures of the heart. A computer converts the sound waves into pictures on a video screen. The test allows the doctor to clearly see any problem with the way the heart is formed or the way it’s working. An echocardiogram is an important test for diagnosing tetralogy of Fallot because it shows the four problems with the heart’s structure and how the heart is reacting to these problems. This test helps the cardiologist decide the best time to repair these defects and what type of surgery is needed. Echocardiograms also are used to check a child’s condition over time, after the defect has been repaired.
Cardiac Catheterization During cardiac catheterization, a thin, flexible tube called a catheter is put into a vein in the arm, groin (upper thigh), or neck and threaded to the heart. A dye that can be seen on an x ray is injected through the catheter into a blood vessel or a chamber of the heart. This allows the veterinarian cardiologist to see the flow of blood through the heart and blood vessels on the x-ray image. Cardiac catheterization also can be used to measure the pressure inside the heart chambers and blood vessels. It can determine whether blood is mixing between the two sides of the heart.
Treatment The treatment is surgical. Surgery involves creating a shunt between the aorta and pulmonary artery so that sufficient blood can enter the lungs. Congestive heart failure and sudden cardiac death is a late complication of surgically-treated patients.
Go Pets America recommends seeking the advice of your local veterinarian for the most appropriate vaccination program and for the diagnosis and treatment of your pet's health problems. For vaccination requirements please contact your state and local licensing authorities.
|