All forms of congenital heart disease occur in dogs. The most common defects are valve malformations (called dysplasias),valve narrowing (stenosis),abnormal openings between the heart chambers (septal defects), patent ductus arteriosus, and Tetralogy of Fallot.
Patent ductus arteriosusis a persistent arterial connection between the aorta and pulmonary artery that normally closes at birth or shortly thereafter. In the uterus, the ductus plays an important role in shunting blood away from the nonfunctioning lungs. Many large and small breeds are affected by patent ductus arteriosus. This murmur can often be felt through the body wall-it feels like a washing machine churning.
Tetralogy of Fallotis a congenital defect of the heart consisting of four abnormalities that result in insufficiently oxygenated blood pumped to the body.
Most dogs with severe congenital heart defects die within the first year of life. Dogs with moderate defects may survive but usually exhibit exercise intolerance, fainting episodes, and stunted growth. In these individuals, heart failure can occur suddenly and unexpectedly. Dogs with mild valvular disease or small septal defects are often asymptomatic; the only indication of a congenital heart defect is a heart murmur discovered on physical examination.
The diagnosis of congenital heart defect is based on ECG, chest X-rays and echocardiogram. An ultrasound study called Doppler echocardiography measures the velocity and direction of blood flow in the heart chambers. This information makes the diagnosis of congenital heart defects extremely accurate. You may need to be referred to a specialty clinic for this test.
Cardiac catheterization with angiocardiography was once the “gold standard” for diagnosing congenital heart defects, but it carries a small risk and is often available only at referral veterinary hospitals. Doppler echocardiography, being accurate and noninvasive, has largely replaced cardiac catheterization for routine diagnosis.
Treatment: Dogs with minor heart defects have a good prognosis and do not benefit from surgery. However, many dogs benefit from surgery to correct more severe defects. Many of these surgeries will require referral to a large veterinary center.
Patent ductus arteriosus is an example of a defect that does benefit from surgery. Without surgery, 60 percent of affected puppies die within the first year. With surgery, the death rate is less than 10 percent.
Moderate atrial and ventricular septal defects can be repaired surgically with varying degrees of success. This requires open-heart surgery and cardiopulmonary bypass.
Valve dysplasias and large septal defects have a poor prognosis, regardless of the method of treatment. Affected dogs are at risk of congestive heart failure and sudden death.
The treatment of congestive heart failure and cardiac arrhythmias is discussed later in this chapter.
Prevention: Most congenital heart defects have a hereditary basis. Breeds with a known predisposition for specific congenital heart defects are shown in the accompanying chart. This list is by no means comprehensive, and individuals of other breeds and mixed breeds may also show these defects.
Breed Predispositions for Congenital Heart Defects
Atrial septal defects
Ventricular septal defects
Aortic and subaortic stenosis
Newfoundland, Golden Retriever, German Shepherd, Rottweiler, Boxer, German Shorthaired Pointer, Samoyed
Labrador Retriever, Great Dane, Weimaraner, German Shepherd Dog
Great Dane, German Shepherd Dog, Bull Terrier
Patent ductus arteriosus
Poodle, Pomeranian, Collie, Shetland Sheepdog, German Shepherd Dog, Cocker Spaniel, English Springer Spaniel
Beagle, Labrador Retriever, Cocker Spaniel, Schnauzer, Newfoundland, Rottweiler
Tetralogy of Fallot
Keeshond, English Bulldog, Miniature Poodle, Miniature Schnauzer
It is important to identify affected individuals when treatment is most likely to be successful and before the dog is used for breeding. The best time to screen puppies for congenital heart defects is when they are 6 to 8 weeks of age, before being released to their new homes. Screening is done by carefully listening for murmurs with a stethoscope over the four valve areas. The examination is best performed by a veterinarian who is experienced in recognizing heart murmurs. Murmurs heard at this age may not be associated with disease; some will disappear as the pup matures. If the murmur is present at 16 weeks, however, the puppy should be screened using cardiac ultrasound.
OFA maintains a cardiac registry to gather data on congenital heart defects. Dogs are screened at 12 months of age or later by a board-certified veterinary cardiologist, and if they are found to be unaffected, they are issued a certificate and a registration number. For bloodlines with an increased incidence of congenital heart defects, it is highly desirable to seek OFA certification before selecting breeding animals.
This article is excerpted from “Cat Owner’s Home Veterinary Handbook” with permission from Wiley Publishing, Inc.