Aortic Stenosis in Dogs

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Aortic (subaortic) stenosis is a congenital heart disease that can affect dog.

Aortic (subaortic) stenosis is a narrowing of the pathway for blood leaving the heart. The narrowing is usually beneath the aortic valve of the left ventricle; the condition is then called subvalvular aortic stenosis or SAS for short. SAS is a genetically predetermined disease that affects dogs. The condition is rare in cats. The mode of inheritance, or the genetic cause, is not simple and healthy carriers of the disease genes are common.

Several dog breeds are predisposed to aortic stenosis including golden retrievers, Newfoundlands, boxers, German shepherds, Rottweilers, shar-peis, bull terriers, English bulldogs and Bouvier de Flanders.

Mild cases of SAS have little impact on the dog other than causing a heart murmur and rendering the dog unsuitable for breeding. Moderate to severe cases are at risk for exercise intolerance, fainting, heart failure, irregular heart rhythms, infections on the heart valve and sudden death.

What to Watch For

  • The presence of a murmur in a puppy, especially in breeds at risk
  • Poor exercise capacity
  • Cough
  • Difficult breathing
  • Collapsing
  • Fainting
  • Illness with fever


  • Diagnosis

    Diagnostic tests are needed to recognize SAS and exclude other diseases. Tests may include:

  • Complete medical history and physical examination, including examination with a stethoscope (cardiac auscultation)

  • There is no blood test for diagnosis of aortic stenosis.

  • An echocardiogram (ultrasound of the heart) with Doppler is needed to make a definitive diagnosis. If possible, see a veterinary cardiologist for this examination.

  • A chest X-ray may be recommended, especially if there are signs of heart failure.

  • An electrocardiogram (EKG) or a 24-hour electrocardiogram (Holter EKG) may be recommended to identify abnormal heart rhythms.

    Treatment

    For mild cases, there is no treatment. For more serious cases, treatments for SAS may include one or more of the following:

  • Surgery and cardiac catheterization procedures have been used to dilate or cut out the affected area; however, these procedures do not significantly increase long-term survival.

  • Drugs called beta-blockers, such as propranolol, atenolol and metoprolol, are often prescribed to protect the heart muscle and reduce irregular heartbeats.

  • Drugs for heart failure may be prescribed should an irregular heartbeat develop.

    Home Care and Prevention

    If your dog has SAS, find out the degree of severity so you can modify your dog's activity. Mild cases of SAS pose no real activity/exercise limitations, but more advanced cases may require some exercise restriction or medical therapy.

    Learn to measure your dog's rectal temperature. If your dog is acting sick and has a fever (temperature greater than 103), call your veterinarian immediately.

    Schedule regular examinations (every 6 to 12 months) and possibly chest X-rays and/or an echocardiogram.

    Breeders should have their dogs screened for SAS. Never breed a dog with congenital heart disease.

  • Aortic (subaortic) stenosis (SAS) is a form of genetic heart disease in dogs that is very rare in cats. It is characterized by an obstructive band or ridge of tissue that prevents the normal ejection of blood from the left ventricle of the heart. The defect is located in the outlet of the left ventricle, immediately below the aortic valve, hence the name "subaortic" stenosis (or SAS). This genetic defect develops very early after birth, but the severity of blood flow obstruction may increase as the dog matures. Such progression can be particularly prominent in giant breeds such as the Newfoundland.

    The left ventricle reacts to a stenosis (narrowing) by increasing the pressure developed during pumping (systole) and generating a pressure difference that propels the blood out of the heart at a much faster rate. These changes cause disturbed blood flow that, in turn, creates a heart murmur, which can be detected by a noninvasive ultrasound diagnosis using Doppler echocardiography. The increased heart work in moderate to severe obstructions is associated with left ventricular hypertrophy or thickening, myocardial fibrosis (scarring), and coronary artery lesions. Coronary blood flow back to the heart is abnormal and poor blood supply to the heart muscle (ischemia) predisposes to irregular heart rhythms and sudden death.

    Clinical surveys have indicated that SAS is now the most common congenital heart disease in the dog in many areas. Commonly affected breeds include the golden retriever dog, Newfoundland, boxer, and German shepherd. Recent clinical and breeder surveys indicate the emergence of SAS in other breeds including the Rottweiler, shar-pei, bull terrier, English bulldog and Bouvier de Flanders. Breeding experiments have confirmed that SAS is inherited in these breeds, but the precise mode of transmission has not been proven. The disease does not appear to be transmitted by a gene or as a sex-linked trait. It is important to note that even mildly affected or clinically normal parents may transmit the defect to future generations.

    The presence of a heart murmur in a puppy, especially in breeds at risk should be investigated; SAS is only one cause of a murmur. In diagnosed cases, any of the following symptoms should prompt a visit to your veterinarian:

  • Poor exercise capacity
  • Cough
  • Difficult breathing
  • Collapsing or fainting
  • Illness with fever

    Advanced cases of SAS can lead to complications including heart failure, heart arrhythmia (irregular heart beating), fainting (syncope) or sudden death. Also, heart valve infections can occur in this condition leading to fever, illness and joint ache.

    Other heart problems can appear similar to aortic stenosis. These are differentiated based on the history, physical examination, and the echocardiogram. These diseases include:

  • Patent ductus arteriosus
  • Pulmonic stenosis
  • Ventricular septal defect
  • Mitral valve and tricuspid valve malformation
  • Complex congenital (birth defect) heart disease

    SAS can occur concurrently with other heart defects.

  • Veterinary care should include diagnostic tests and subsequent treatment recommendations.

    Diagnosis In-depth

    Diagnostic tests are needed to recognize aortic (subaortic) stenosis, and exclude other diseases. Tests may include:

  • Complete medical history and physical examination

  • Currently, no blood test is available to detect the genetic markers of SAS in dogs.

  • Dogs without heart murmurs are unlikely to have SAS, and routine use of costly Doppler studies is not justified for screening purposes.

    Breeders like to speak of the "grade of SAS," which usually refers to the grade or intensity of the heart murmur. The intensity or grade of the heart murmur depends on the "tightness" of the stenosis and other factors as well. It is generally true that a soft murmur (grade I or II out of a possible VI) is typically a "mild" defect while a grade V or VI murmur is usually related to a more severe defect.

    Murmurs can be variable and a soft murmur may first be obvious in a mature dog of breeding age. For practical purposes, most dogs can be screened at one year of age for "final" heart clearance if the dog is intended for breeding. It is also crucial to understand that this clearance represents a clinical description and does not tell us the dog is free from the genetic liability for aortic stenosis.

  • Referral to a specialist. If a heart murmur is detected in a puppy, the possibility of an innocent heart murmur or congenital heart defect must be considered. This distinction can be difficult and may require examination by a veterinary cardiologist. In general, innocent murmurs are very soft, are detected best over the left side of the chest, become softer with growth and are absent by the time of the first rabies vaccination at four to six months.

    If your veterinarian suspects congenital heart disease, referral to a cardiologist is usually the best course, unless your veterinarian is particularly experienced in congenital heart defects. Commonly recommended tests are echocardiography (ultrasound of the heart) with Doppler studies (blood flow studies using the Doppler ultrasound method), and often chest X-rays and an electrocardiogram. The last two tests are useful only in moderate to severe disease.

  • Doppler echocardiography is the diagnostic test of choice and usually requires a referral to a specialist. Doppler echocardiography (DE) is the method most often used today for evaluating dogs with systolic murmurs. This test is a sophisticated examination, but like any laboratory test, there is some overlap between normal and abnormal. This is just one of the reasons why cardiologists don't recommend the Doppler as a routine screening test. The severity of the disease, the size of the heart, the function of the heart chambers, and the tightness of the obstruction can be determined by this test.

  • Specialists rarely suggest cardiac catheterization.

  • A 24-hour electrocardiogram (EKG) may be recommended in some cases.

    Treatment In-depth

    Therapy of moderate to severe SAS has generally been disappointing. While technical success can be achieved surgically, long-term survival has not been satisfactory. Specialists can dilate the area with a balloon catheter, but the long-term benefits of this have proved no better than surgery. Chronic management of aortic (subaortic) stenosis may include:

  • Drug therapy. The use of drugs called beta-blockers has been advocated to reduce myocardial oxygen demand and prevent irregular heart rhythms.

  • Medical therapy is indicated in cases of heart failure. Common treatments include administering digoxin, enalapril or benazepril, and/or furosemide. These medications can stabilize the dog, but the long-term prognosis is poor once congestive heart failure has developed.

  • Exercise should be restricted.

    The prognosis for dogs with SAS varies with lesion severity. Mild lesions may not compromise quality of life or longevity, but moderate to severe lesions often lead to fainting (syncope), weakness with exercise, congestive heart failure (fluid or edema in the lungs) or sudden death. Infection of the heart valve (endocarditis) occurs in a very small percent of dogs with this condition. A fever is the telltale sign and requires urgent care.

    Optimal treatment for the dog with moderate to severe SAS requires a combination of home and professional veterinary care. Follow-up can be critical.

    Administer any prescribed medication as directed by your veterinarian. Be certain to alert your veterinarian if you are experiencing problems while treating your dog, especially collapsing with exercise, difficulty in breathing, coughing or signs of illness with fever.

    Schedule regular examinations every 6 to 12 months, including perhaps chest X-rays and/or an echocardiogram.

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