Updated: Feb 17
A normal heart beat sounds like “lub-dub”, however a murmur has a “whooshing” sound. This “whoosh” is caused by abnormal turbulent blood flow within the heart, sometimes caused by abnormal “leaky” heart valves.
A heart murmur can be physiological, otherwise known as “innocent” or can be pathological which is caused by disease either within or external to the heart.
Heart murmurs are given a grade out of 6, 1 being a soft sound, 6 being the loudest and can often be felt as a “thrill” or vibration on the outside of the chest wall.
There are many types and causes of heart murmurs in dogs and cats, the details of which go beyond the scope of this article.
INNOCENT HEART MURMURS
Innocent or physiological heart murmurs do not cause any harm to your pet’s health.
It is not unusual for puppies to be diagnosed with an innocent murmur at their first vaccination. The murmur that is heard at this early age is usually a low grade i.e. a grade of 1 or 2 out of 6.
This murmur should disappear by the end of the puppy vaccination course at 14-16 weeks of age. If the murmur is a higher grade, or does not disappear, this warrants investigation.
Degenerative mitral valve disease (MVD) is the most common heart disease affecting dogs. It usually develops in middle-aged to older dogs.
The valve can become leaky, allowing blood to flow in the incorrect direction through the one-way valve. This can cause the heart to become larger, less efficient, creating fluid ‘back up’ in the lungs where your pet will have increased breathing effort and a faster breathing rate. These are signs of congestive heart failure and requires treatment.
Hypertrophic cardiomyopathy (HCM) is the most common heart disease in cats. HCM causes the heart walls to become thickened, so less blood can enter the heart chambers, therefore less blood is pumped out, potentially progressing to heart failure.
HEART MURMUR HOMEWORK
There are 3 things your Vet will ask you to monitor if your pet has a heart murmur:
1. Resting respiratory rate (RRR)
2. Exercise tolerance
RESTING RESPIRATORY RATE (RRR)
When your pet is resting and not exerting energy, count the number of breaths they take in 1 minute - 30 is the magic number.
One breath is counted as the rise and fall of the chest (i.e. in and out equals 1 breath).
Your dog’s RRR should be less than 30 breaths per minute. If your dog’s RRR is consistently more than 30, this indicates increased respiratory effort possibly due to worsening heart disease. If this is the case, please take your dog to the Vet for prompt evaluation.
There are some mobile phone apps which can help you record your dog’s RRR, including “Heart2Heart Canine RRR”.
A decrease in your dog’s activity level can be a sign of suboptimal heart function, but it can also be due to extra-cardiac reasons e.g. arthritis. A physical examination performed by your Vet can help distinguish the difference.
Coughing in a dog with a heart murmur can be due to multiple causes including pulmonary oedema (fluid on the lungs, can be heard as “crackles”), compression of the airway from an enlarged heart, or it may not be due to heart disease at all - it could be caused by respiratory disease.
The patient’s history, physical examination findings and thoracic (chest) radiographs can help diagnose the cause of the cough in order to select the most appropriate treatment.
Each heart murmur case is different, therefore each patient is diagnosed and treated individually.
Diagnostic tests may include a general blood test, NTpro-BNP blood test, thoracic (chest) x-rays, ECG (electrocardiogram) and echocardiogram (ultrasound of the heart).
Some tests can be performed in the clinic, however some tests may need to be performed by a Veterinary Specialist.
NTpro-BNP BLOOD TEST
N-terminal pro-B-type natriuretic peptide (NTpro-BNP) is a hormone which is released by heart muscles into the bloodstream in response to stretch and stress of the heart. The levels of NTpro-BNP will become elevated when the heart muscles undergo excessive stretching and stress due to various types of heart disease. The elevation of NTpro-BNP can be detected with a simple blood test, however other diagnostic tests may still be required to see the whole picture of the patient’s condition.
An echocardiogram, often referred to as an “echo”, is an ultrasound of the heart. It is an important, non-invasive test in patients with heart murmurs, as it enables the visualisation of the chambers and valves of the heart.
A Specialist Cardiologist will need to perform this advanced diagnostic test, so your pet will either be referred to a Specialist Veterinary hospital, or we can organise a mobile Specialist Veterinary Cardiologist to examine your pet in our own hospital.
Dr Geoff Nicolson is a Specialist Veterinary Cardiologist who frequently performs echocardiograms at the Albert Animal Hospital, and we can even arrange for you to be present with your pet to watch the whole process.
Thoracic radiographs are x-rays taken of the chest to examine the heart and lungs. The x-rays can show if the heart is enlarged, if there is fluid in the lungs or if there is another disease process causing a cough.
Treatment for a heart murmur really depends on the results of the diagnostic tests. Some animals may need medications, however some may just require regular monitoring and may not need any immediate treatment at all.
In general, patients with a heart murmur should avoid high intensity exercise and foods that are high in salt.
Knowledge is power. The more information gained by performing diagnostic tests on heart murmur patients allows you, together with your Veterinarian, to make better informed choices for your pet. Test results will let us know if we need to treat or just monitor, if your pet is a higher risk for a general anaesthetic procedure and generally where your pet is at.
If you have any concerns about your pet, please call us at the Albert Animal Hospital on 3208 9233 or book an appointment online.