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Heart Disease in Dogs and the Benefit of Early Diagnosis
Heart disease affects up to 1 in 10 dogs over their lifetime, and 80% of these will be due to mitral valve disease.
Dogs over the age of 6 are at a greater risk, however they may show no clinical signs until the disease is quite advanced at which point we are limited in what we can achieve with treatment, compared to catching it early.
Stages of heart disease
There are 4 stages of mitral valve disease. The early stages (A and B) don’t display any visible signs of illness, however early signs can be detected in a routine clinical exam by listening to the heart and finding a murmur. Once the dog progresses to stages C & D there are visible indicators of disease as the heart fails to function properly (ranging from a cough to full blown collapse and congestive heart failure).
Previously there has been no evidence that early treatment before clinical signs are seen (stage B) has any benefit in the long term, however a new study has shown that there are significant benefits to early treatment which is great news!
The key findings of this large multinational study are:
- Early treatment can help slow the progression to a clinical stage (visible signs of illness) by up to 15 months.
- Can delay the development of clinical signs of congestive heart failure (CHF).
- 10% more life expectancy without signs that affect your dog’s quality of life.
All breeds can be affected however certain breeds are at higher risk. Mitral valve disease is more common in small breeds, particularly at risk breeds include Cavalier King Charles Spaniel, Dachshund, poodle, Schnauzer, Chihuahua, Fox terrier and Jack Russell Terrier.
If your pet has a heart murmur a few tests can allow an accurate diagnosis and determine the best treatment for the stage of heart disease present. This can range from herbal supplements to medications to help prolong the length and quality of life of your pet.
What is the mitral valve?
The heart has four chambers.
Each chamber of the heart has a one-way valve to keep blood from flowing backward. The valve between the left atrium and left ventricle is called the mitral valve. Oxygenated blood flows from the lungs into the left atrium before flowing into the left ventricle. From the left ventricle, oxygen-rich blood is pumped throughout the body.
What causes mitral valve disease?
Because of the high pressure created when the left ventricle contracts and pumps blood out to the body, the mitral valve may begin to ’wear out’ and leak over time. This is known as mitral valve insufficiency (MVI) or mitral regurgitation and is often associated with a heart murmur. Other causes of mitral valve insufficiency include ruptured chordae tendinae, a condition in which the fibrous cords that hold the valve leaflets in position break, and heart valve infections known as endocarditis. Endocarditis may result from blood-borne infections or, more commonly, may be secondary to chronic oral infections (periodontal disease).
What are the signs of mitral valve disease? What are the consequences of it?
The earliest sign of a leaking mitral valve is normally a heart murmur. This is produced by the turbulence created when some of the blood goes backward through the leaking mitral valve into the left atrium. Dogs may develop a murmur from a leaking mitral valve as early as four to six years of age.
Initially, MVI is asymptomatic (produces no obvious clinical signs). As time progresses, the regurgitation becomes more severe and as more blood flows back into the atrium, the heart’s efficiency is reduced. Eventually, congestive heart failure develops. From the time a murmur develops, it may be a few months to several years until heart failure occurs.
A heart murmur does not mean that heart failure is imminent, but eventually congestive heart failure will occur. Dogs with a heart murmur do have an increased risk of sudden death.
When I took my dog for his annual health examination, my veterinarian told me he had a mitral murmur but said he was not going to treat it at this stage. Is this correct?
Veterinary cardiologists differ in when they recommend medical intervention for asymptomatic heart murmurs. Research has now shown newer drugs may have cardio-protective benefits in dogs similar to those demonstrated in people. Your veterinarian will carefully evaluate your pet’s condition and lifestyle and make the best treatment recommendations to preserve health and vitality.
How will I know if my dog has heart failure?
When the left side of the heart is not properly pumping blood, the blood slowly backs up in the lungs. This results in small amounts of fluid leaking out of the capillaries into the air passageways. This fluid collection produces the earliest signs of heart failure that include gagging as if trying to clear the throat, a chronic, hacking cough, and lack of stamina (your dog will tire more easily on walks). Dogs with heart failure are usually sick whereas dogs with heart murmurs may have few, if any, clinical signs until heart failure develops.
The degree of clinical signs is directly related to the amount of decreased blood flow that is occurring. This is why early diagnosis and treatment is essential in slowing the progression of heart failure.
What happens in congestive heart failure?
Congestive heart failure begins when the heart is unable to provide the tissues with adequate oxygen and nutrients. Without adequate oxygen, the body’s cells become distressed and trigger a series of responses. Various hormones are released in an attempt to increase blood oxygen levels and blood circulation. These hormones conserve fluid in an effort to increase blood volume and the output of blood and oxygen by the heart. For several months, these compensatory responses help the situation and the dog has few observable clinical signs.
Eventually the increased fluid retention becomes a detriment as more and more fluid leaks out of capillaries and into the lungs, abdomen, and other body tissues. Fluid in the lungs is called pulmonary oedema, fluid below the skin is called peripheral or limb oedema, and fluid in the abdomen is called ascites. When these are present, congestive heart failure is present. Left-sided congestive heart failure (LS-CHF) is generally associated with MVI and most commonly results in pulmonary edema and coughing. However, within a short time, heart failure will continue to progress and bilateral heart failure will follow.
What tests are needed to diagnosis heart valve disease?
There are several tests that provide valuable information while looking at different aspects of heart function.
Physical examination will determine if there are other symptoms or underlying conditions that may complicate or be affected by heart disease.
Auscultation or listening to the heart and lungs with a stethoscope is the first step in diagnosing heart disease. Pulse quality and heart rate and rhythm are also assessed during auscultation. Fluid in the lungs (pulmonary edema) can often be detected with a stethoscope.
Chest radiographs (X-rays) are used to determine the size and shape of the heart and the presence of fluid in the lungs. Additionally, the lungs are examined for any abnormalities such as enlarged blood vessels (pulmonary hypertension).
Blood and urine tests are performed to give an indication of any other disorders in the body. Liver and kidney function are often decreased in dogs with heart disease.
An electrocardiogram (ECG) may be performed to measure the electrical activity of the heart and allow accurate determination of both heart rate and rhythm. Any abnormal rhythms (arrhythmias or dysrhythmias) can be detected and evaluated. The presence of abnormal heart rhythm helps your veterinarian determine the prognosis for your pet’s condition.
Ultrasound examination (echocardiogram) utilizes sound waves to evaluate the heart’s contractions and to measure the amount of blood pumped by the heart. This test is the most useful one to assess the heart’s function, and serial (repeated) examinations are recommended to chart the progress of disease and the response to treatment.
The combination of all of these tests gives the best evaluation of the dog and its heart function.
Is there treatment for a leaky mitral valve and heart failure?
A leaky heart valve can be replaced surgically in people. However, this is usually not feasible in dogs. However, there are several drugs and treatments that will improve heart function, your veterinarian will discuss which treatment will most benefit your pet in an individualised approach.