Download Grade 0/6 denotes no murmur. Grade 1/6 and 2/6 murmurs are

Grade 0/6 denotes no murmur.
Grade 1/6 and 2/6 murmurs are generally considered to be "mild".
Dogs with Grade 1/6 and 2/6 murmurs are very unlikely to develop any symptoms as a result of their
aortic stenosis and should lead perfectly "normal" lives.
Grade 3/6 and 4/6 murmurs are generally considered to be "moderate".
The majority of dogs with Grade 3/6 and 4/6 murmurs are also unlikely to develop any symptoms, but
a small number will go on to become symptomatic.
Grade 5/6 and 6/6 murmurs are generally considered to be "severe".
Dogs with Grade 5/6 and 6/6 murmurs are most at risk of developing symptoms - (see below).
X-ray looks at the shape and size of the heart and can identify abnormal enlargement of the heart
chambers e.g. left ventricle in severe AS.
Electrocardiography measures the electrical impulses of the heart and can identify any abnormal
heart rhythms e.g. VPCs (ventricular premature contractions) in severe AS.
Ultrasound with Doppler studies:
Ultrasound enables the vet to measure all the internal dimensions of the heart, in particular the
thickness of the left ventricular wall with regard to aortic stenosis.
Doppler studies allow the vet to measure the speed of blood flow through the heart valves i.e. from
one chamber to another or, in the case of aortic stenosis, specifically from the left ventricle to the aorta
via the aortic valve; this is the aortic outflow velocity.
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DISEASE PROGRESSION
In the majority of cases, development of the defect does not usually progress beyond puppyhood i.e.
the grading of the heart murmur would be unchanged from the age of 1 to 2 years throughout the rest
of the dog's life. However, in a small number of dogs (estimated to be about 10% of those affected)
the defect appears to get progressively worse over the years. This certainly gives weight to the
argument that annual auscultation should be considered in those breeds known to be affected by AS.
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SYMPTOMS
This hereditary heart defect may be mild and not affect the quality or longevity of the dog's life, or it
may be severe and result in symptoms, such as exercise intolerance and syncope (fainting). It is also
one of the causes of sudden death.
Symptoms can occur [a] as a direct result of the defect or [b] secondary to left ventricular
hypertrophy.
[a] A severe defect can significantly compromise the outflow of oxygenated blood from the heart to the
brain and other vital organs.
[b] Over time, the walls of the left ventricle may become "hypertrophied" (thickened). This is the left
ventricle "compensating" for its increased workload. If there is excessive hypertrophy, dogs can then
develop abnormal heart rhythms; these VPCs (ventricular premature contractions) can compromise the
delivery of oxygenated blood from the left ventricle through the aortic valve and into the aorta.
Syncope (fainting) occurs when there is a lack of oxygen to the brain.
If the stenosis (narrowing) is severe, this can result in significantly restricted outflow of oxygenated
blood from the heart and, therefore, decreased oxygen supply to the brain.
VPCs are abnormal heart rhythms, which can be initiated by stress or exertion, whereby the left
ventricle contracts too early i.e. before it has filled properly. This can also result in restricted outflow
and decreased oxygen supply to the brain.
Sudden death can occur after a "run" of VPCs, which then cause the heart to go into a state of
ventricular tachycardia. Instead of pumping normally, the left ventricle pumps too quickly and is
therefore unable to effectively deliver oxygenated blood into the aorta, and to the brain and other vital
organs, resulting in collapse and death.
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TREATMENT OPTIONS
General veterinary advice to the owners of dogs with AS
~ Avoid strenuous exercise for the dog, especially in hot weather.
~ Do not allow the dog to become overweight.
These are sensible precautions, which avoid putting excessive strain on the dog’s heart.
Medication
Beta-blockers may be prescribed for the following:
~ Dogs with severe aortic stenosis.
~ Dogs with evidence of left ventricular hypertrophy.
~ Dogs with evidence of VPCs.
Beta-blockers help to improve exercise tolerance, reduce cardiac (heart) workload and prevent
abnormal heart rhythms.