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Dog: Congenital Heart Defects

General information

Other common/scientific names: aortic stenosis, pulmonary stenosis, patent ductus arteriosus, atrial septal defect, ventral septal defect, tetralogy of Fallot

Congenital heart defects are malformations of the heart, heart muscle or large blood vessels that are present at birth. Many of these abnormalities are thought to be genetically transmitted from parents to offspring. Many times, pups will be born with more than one congenital defect.

The heart is a muscular organ responsible for pumping oxygenated blood to the body and receiving unoxygenated blood back from the body. It is divided into two halves-the left side and the right side. The left side of the heart is the larger, more muscular side receiving oxygen rich blood from the lungs and pumping it throughout the body. The right side of the heart is smaller and receives oxygen depleted blood from the body delivering it to the lungs where the carbon dioxide is exchanged for oxygen.

Both sides of the heart have two chambers - the upper atrium and the lower ventricle. One-way valves between the atrium and ventricle regulate the flow of blood. Blood is received into the right atrium from the body and flows through the tricuspid valve into the right ventricle. The valve prevents backflow into the atrium. From the right ventricle, blood enters the pulmonary artery through the pulmonary valve and travels to the lungs. The left atrium receives the oxygenated blood from the lungs which flows through the mitral valve into the left ventricle. The left ventricle then pumps the blood through the aortic valve into the aorta which carries it to the body.

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Abb. H2IOLYL8: Schematic illustration of the four chambers of the heart and bloodflow pattern.

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Abb. GGUI1XLJ: Schematic illustration of the heart, pulmonary and systemic circulation.

Congenital Heart Diseases

Aortic Stenosis

Aortic stenosis is one of the most common congenital heart defects seen in dogs. With aortic stenosis, the opening between the left ventricle and the aorta is narrowed and blood flow out of the heart is restricted. This is caused by a band or ridge of tissue. Because of this, the left ventricle has to work harder to pump blood to the body. Mild cases of aortic stenosis may have little impact on the dog other than causing a heart murmur. Moderate to severe narrowing can result in left-sided heart failure, abnormal heart rhythms and sudden death. Various surgeries have been attempted to dilate the narrowed area with limited success. Medical therapy is indicated in cases of heart failure.

  • Breeds Affected: Golden Retriever, Newfoundland, German Shepherd, Boxer and Rottweiler.

Pulmonary Stenosis

With pulmonary stenosis, there is a narrowing or obstruction in or around the pulmonary valve where the blood exits the right ventricle to enter the lungs. This forces the right ventricle to work harder to pump bloods to the lungs. Mild cases of pulmonary stenosis may go undetected while severe cases can result in signs of right-sided heart failure which can worsen with age. Various surgeries have been attempted to dilate the narrowed area with limited success. Medical therapy is indicated in cases of heart failure.

  • Breeds Affected: English bulldog, Beagle, Wire-Haired Fox terrier, Chihuahua and West Highland terrier.

Patent Ductus Arteriosus (PDA)

In the unborn fetus, oxygenated blood is received from the mother via the umbilicus. Therefore, fetal blood bypasses fetal lungs. The ductus arteriosus is a blood vessel present in the unborn fetus which acts as the bypass, carrying blood from the pulmonary artery to the aorta. At birth, this blood vessel should close as the pup begins to breathe. Patent ductus arteriosus is a common congenital heart defect in dogs and occurs when the ductus remains open. Because pressure is higher in the aorta after birth, blood usually flows from the aorta through the open ductus and into the pulmonary artery. Over time, this can result in fluid build-up in the lungs and left-sided heart failure. Surgery is recommended for dogs less than 2 years of age to tie off or close the open ductus. The prognosis is good if surgery is performed early before heart damage occurs.

  • Breeds Affected: Maltese, Pomeranian, Shetland sheepdog, Miniature poodle and German Shepherd. Females are more commonly affected than males.

Septal Defects

Septal defects are holes in the muscular wall of the heart which separates the right and left side of the heart. These defects are most commonly seen between the ventricles (VSD). Septal defects in the atria (ASD) are rare in dogs. Many dogs have small defects which may close spontaneously. These dogs have few clinical signs. With larger ventricular defects, the blood will flow from the left ventricle to the right ventricle causing the left ventricle to work harder and fluid build-up in the lungs. With an atrial defect, blood will also flow from the left to right but result in the right side of the heart being overworked. Dogs with septal defects can be treated with medications. Large defects can be surgically repaired but open heart surgery is expensive and associated with a high risk of surgical complications.

  • Breeds Affected with Ventricular Defects: English bulldog and Keeshond.
  • Breeds Affected with Atrial Defects: Boxer, Doberman Pinscher, Samoyed and Newfoundland.

Congenital Valve Disease

The atrioventricular (AV) valves ensure that blood flows from the atria to the ventricles when the heart beats. The valve leading from the right atrium to the right ventricle is called the tricuspid valve. The valve leading from the left atrium to the left ventricle is called the mitral valve. These valves can be damaged or narrowed at birth resulting in a leaky valve. This causes blood to backflow into the atria. Clinical signs will depend on the severity of the damage and which valve is impaired. Valvular disease is treated by medications to reduce the work load on the heart and prevent heart failure.

  • Breeds Affected with Tricuspid Valve Disease: Boxer, Great Dane, German Shepherd, Great Pyrenees and Irish Setter.
  • Breeds Affected with Mitral Valve Disease: Cavalier King Charles spaniel, Cairn terrier and Miniature poodle.

Vascular Ring Anomaly

Vascular ring anomalies describe several disorders that occur because of abnormal development in the fetus of blood vessels around the aorta. While these anomalies do not cause cardiovascular disease, they can form a ring which entraps the esophagus and sometimes the trachea. The most common form is called a persistent right aortic arch (PRAA) and can cause megaesophagus leading to regurgitation, lack of weight gain and aspiration pneumonia. Treatment is surgical removal to relieve the constriction. Prognosis is best if the surgery is performed early before permanent damage to the esophagus occurs.

  • Breeds Affected: Great Dane, German Shepherd, Irish Setter and Springer Spaniel

Tetralogy of Fallot

Tetralogy of Fallot is a serious combination of defects resulting from the abnormal development of the heart and major blood vessels. It consists of four defects: pulmonary stenosis, ventricular septal defect, malpositioned aorta and right ventricular hypertrophy (enlargement). As a result of these defects, poorly oxygenated blood is delivered to the body. Clinical signs include failure to grow, exercise intolerance, weakness and general cyanosis. Unfortunately, these dogs rarely live beyond one or two years of age. Medication can be used to allow more blood flow to the lungs. Surgery has a high mortality rate and is not considered a viable option.

  • Breeds Affected: Keeshond, Boxer and German Shepherd.

Cardinal symptom

Heart murmur

Symptoms

Clinical signs of a congenital heart defect will depend on the severity of the defect. A heart murmur is almost always present, however there are exceptions. Young pups may show no signs and the murmur may be detected on a routine examination for preventative vaccinations. Other dogs with more severe defects may develop signs of reduced activity, failure to grow, difficult breathing, coughing and a distended abdomen (ascites).

Diagnosis

A congenital heart defect can be diagnosed based on history, clinical signs and physical examination with careful auscultation (listening) of the heart and lungs with a stethoscope. Murmurs can be either left-sided or right-sided which helps determine the cause. Pulmonary edema or fluid can be heard as moist crackles. Other diagnostic tests include:

  • Bloodwork to assess blood parameters, inflammation and organ function is necessary for diagnosis, prognosis and treatment.
  • Radiography of the chest will help determine the size and shape of the heart. Radiographs will also reveal fluid in the lungs.
  • An electrocardiogram (ECG) is used to detect an arrhythmia (irregular heart rhythm) and identify heart enlargement.
  • Echocardiogram is an ultrasound of the heart used to assess chamber size, cardiac output, valve function, blood flow direction and blood flow velocity. An echocardiogram is usually performed by a veterinarian specializing in cardiology.

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Abb. GFP63L15: Echocardiogram.
This is a photograph of a dog undergoing an ultrasound examination of its heart.

Treatment

Treatment of congenital heart defects will depend on the severity and location of the abnormality, age of the dog and the financial resources of the owner. Some dogs will respond well to medical treatment and diet restrictions to improve heart function, prevent fluid accumulation and prevent further deterioration of the heart muscle. Other conditions will require surgical correction at a referral clinic or university by a veterinarian skilled in cardiac surgery.

Prognosis

The prognosis for dogs with a congenital heart defect will depend on the severity of the abnormality, their clinical signs and their response to treatment. Some dogs will respond well to medication and can live a symptom free life. However, heart failure is a common sequela requiring life-long medications. Life-threatening complications and sudden death are not uncommon.

Prevention

Since most of the congenital heart malformations are considered to be inherited, a dog diagnosed with one of these conditions should never be used for breeding.

Update version: 4/24/2014, © Copyright by www.enpevet.de
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