Congenital Heart Defect (Atrial Septal Defect) in Dogs

An atrial septal defect (ASD) is a hole in the septum between the two atrial chambers at the top of the heart. The right atrial chamber collects blood from the body before transferring it to the right ventricle which pumps the blood to the lungs. The left atrium collects the oxygen rich blood as it returns from the lungs and transfers it to the left ventricle to be pumped throughout the body. With an ASD, a hole connects the two chambers creating an abnormal blood flow between them. Typical pressure in the heart causes a left to right shunt, so some oxygen rich blood will be pumped back to the lungs instead of out to the rest of the body. If the hole is very small, dogs are often asymptomatic. Large holes disrupt the blood flow more and the dog’s heart will have to work harder to maintain a normal level of oxygen. If the hole is especially large, or if the right side of the heart is starting to fail, blood may be shunted right to left as well. This will mean that some oxygen depleted blood gets pumped back into the body instead of to the lungs, which can cause even more of a problem for your dog. ASD is a congenital condition present from birth. Dogs with a severe defect will start to show symptoms under three years of age. Affected dogs will have difficulty breathing and sustaining exercise. Congestive heart failure can develop as the heart gets weaker.

 

A hole in the septum between the two atrial chambers of the heart causes a shunt, an abnormal pattern of blood flow. This is called an atrial septal defect. It is rare in dogs, accounting for less than 4% of all congenital heart defects. Some dogs may have few or no symptoms, while others will develop congestive heart failure.

Take your dog to see a veterinarian if you notice any of the following symptoms.

• Heart murmur or abnormal rhythm
• Tires easily
• Generalized weakness
• Stunted size and failure to grow in puppies
• Respiratory difficulties
• Intermittent cough
• Bluish tinge to gums and other mucus membranes
• Fainting
• Abdominal swelling

Types

There are three different types of ASD depending on where the defect is located.

• Ostium secundum – the hole occurs in the central part of the atrial septum; his is the most common type in dogs and humans
• Sinus venomous defect – the defect occurs in the top part of the atrial septum
• Ostium primum (sometimes called a partial atrioventricular septal defect) – the defect occurs at the bottom of the atrial septum close to the ventricle chambers

ASD can also occur in combination with other heart defects.

ASD is an inherited condition that is thought to be the result of multiple genetic factors.

• ASD is more common in Boxers and Samoyeds
• Canine parents with ASD often pass it on to their children

Asymptomatic dogs may still have a heart murmur. Veterinarians sometimes diagnose this while listening to a puppy’s heart during a routine vaccination. Many heart murmurs are non-specific, but those located over the left-heart base tend to be associated with ASD. Further testing will usually be done if the veterinarian hears a significant murmur through a stethoscope.

Many dogs show symptoms of respiratory difficulty and lack of stamina with exercise. Puppies with a severe defect often fail to grow at a normal rate. When these symptoms are combined with a heart murmur, they tend to suggest ASD. The veterinarian will examine the dog or puppy completely and take bloodwork and urine tests to evaluate overall health and look for other diseases that could be causing the problem.

If the veterinarian suspects ASD, an echocardiogram will be ordered. Large holes can be diagnosed on a two dimensional echocardiogram, while Doppler echocardiography will identify the abnormal pattern of blood flow. X-rays and ultrasound will also show the severity of the problem. In cases that are symptomatic, the right side of the heart and the pulmonary arteries may be enlarged. If the dog is developing congestive heart failure, fluid will often be visible in the abdomen and the lungs. Your dog’s age, breed, and family history can help to diagnose the problem. Any other known medical conditions are also relevant.

Veterinarians don’t usually recommend treatment for dogs that aren’t showing symptoms. Although surgery is routine in humans with ASD, in dogs it is more risky and rarely done with conditions that aren’t life threatening. The veterinarian may suggest frequent check-ups to evaluate if the problem is getting worse.

Dogs with mild symptoms will be given medication to support heart function and reduce congestive heart failure. A sodium restricted diet can help to reduce fluid build up and limited exercise may also be recommended.

Surgery is an option for severe life-threatening conditions. It is more effective in dogs that haven’t developed congestive heart failure yet. Your dog will likely be referred to a specialist. Successful surgery has been performed for all types of ASD in dogs, but there is a risk of fatal complications. The specialist will discuss the chances of success before surgery. An extensive recovery period will be necessary after the operation.

The prognosis for dogs with ASD is much better than with other heart defects. Many dogs with only a small defect live normal lives. Dogs with mild symptoms may be treated medically for a number of years. Surgery might be effective in young, otherwise healthy dogs with a life-threatening defect, but this will depend on the recommendation of a veterinarian.

Dogs with ASD should not be bred in order to avoid passing the condition on to the next generation. Siblings should also be evaluated to determine if they have a similar problem. Careful attention to breeding can help to reduce instances.