Tetralogy of Fallot

Rebecca E. Gompf, DVM, MS, DACVIM (Cardiology)

BASIC INFORMATION capabilities usually confirms the diagnosis and the severity of the Description problem. Because many veterinarians do not have the Doppler Tetralogy of Fallot is a congenital heart defect that is present at equipment, your pet may be referred to a veterinary specialist for birth. It arises from three primary, spontaneous defects and a fourth the procedure. Laboratory tests may be recommended to evaluate defect that results from the other three. The three main defects are the body’s response to the decreased oxygen levels. pulmonic stenosis, which is a narrowing of the pulmonary artery, which travels from the right side of the heart to the lungs; an over- TREATMENT AND FOLLOW-UP riding aorta, in which the aorta is too large and drains blood from both the right and left sides of the heart; and a ventricular sep- Treatment Options tal defect, which is a hole between the two large chambers of the Animals with tetralogy of Fallot are treated medically. Children heart. The fourth defect is thickening of the right ventricle, which with this condition undergo complete repair via open heart sur- arises from the need to generate more energy to push blood into gery, but dogs and cats do not tolerate being on a heart bypass the aorta through the narrowed pulmonary artery. machine long enough to do a total repair of their defects. Some CAUSE surgeries have been tried to shunt extra blood through the lungs, Tetralogy of Fallot is inherited in some breeds, but the inheritance but these are not routinely done in animals. In some cases, the pattern is not well understood. Exposure of a pregnant animal to pulmonic stenosis may be treated by balloon dilation, to increase certain toxins, infections, or drugs can theoretically affect heart the amount of blood going to the lungs and thereby reduce the ani- development and allow a tetralogy of Fallot to occur. mal’s symptoms. Tetralogy of Fallot occurs because the two main vessels leav- Two types of medical treatment may be used. When the body ing the heart, the aorta and the pulmonary artery, do not divide senses that less oxygen is being delivered to the tissues, it starts equally during the heart’s development. As a result, the aorta is too making more red blood cells. If too many red blood cells circulate large and the pulmonary artery is too small. Since the aorta is too in the bloodstream, the blood thickens like sludge, and seizures big, it has an opening into both of the ventricles (larger chambers) can arise from blood clots and strokes. In these patients, blood is of the heart, and unoxygenated blood from the right heart mixes periodically removed (phlebotomy) to lower the number of red with oxygenated blood from the left heart. This mixing of blood blood cells. Some animals may also be given a drug (hydroxyurea) causes the gums to be blue, hence the term “blue baby.” Because that decreases the amount of red blood cells produced. the pulmonary artery is narrow, less blood reaches the lungs to be oxygenated, which also contributes to the lack of oxygen enter- Follow-up Care ing the body. The severity of the pulmonic stenosis determines the Animals with tetralogy of Fallot are monitored frequently to make degree to which an animal is clinically affected. sure their red blood cell count does not become too high. The older the animal, the more frequently it must be checked. Clinical Signs Prognosis Animals with tetralogy of Fallot are smaller than their littermates, Animals with a sedentary lifestyle may tolerate this problem and and some remain stunted. They also cannot keep up with their lit- live for 5 years or longer. However, most animals develop serious termates when they play and run. Eventually the animal may have signs at 1-2 years and die suddenly between 1 and 5 years of age fainting episodes and rapid breathing from the lack of oxygen. On from blood clots, sludging of the blood, abnormal heart rhythms, physical examination, a heart murmur may be heard, and the mem- or chronic lack of oxygen in the body. branes in the mouth and around the eyes appear bluish. Because this congenital heart defect may be inherited, these animals should not be bred. Females with tetralogy of Fallot are Diagnostic Tests likely to die during the last trimester of pregnancy because of Chest x-rays are commonly performed if a heart murmur is the increased demands put on their hearts from the developing detected. An echocardiogram (heart ultrasound) with Doppler fetuses.