Heart Murmurs in Dogs
Normal hearts beat with a quiet flow of blood. A heart murmur occurs when blood flowing through the heart causes a sound that can be heard through a stethoscope and sometimes even felt by touch. The best way to describe this is like a wide, slow-moving river and suddenly a large obstruction such as a boulder rolls or falls into the river, causing the water to become turbulent as it flows around the stone, creating noise and sound. Keep reading to learn more about causes and what to do if your dog has been diagnosed with a heart murmur.
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Heart murmurs can be pathologic meaning the murmur is due to heart lesions that develop from the progression of heart disease and age. Heart murmurs can also be functional or physiologic and occur in young, growing dogs.
How are heart murmurs diagnosed in dogs?
A heart murmur is a clinical sign that can be present at birth (congenital) or may develop (acquired). Murmurs may be noticed during a routine physical exam in a dog that has no signs or symptoms of disease.
Sick dogs that have a heart murmur often need further diagnostic tests to determine if the murmur is associated with the illness. Dogs with symptoms of possible heart disease such as difficulty breathing, weakness, exercise intolerance, along with a heart murmur need further evaluation, including blood tests, x-rays, and echocardiogram (ultrasound of the heart).
If your dog has a heart murmur, your vet will discuss additional testing based on your dog’s physical exam findings, health status, history of illness, age, and risk.
Veterinarians often begin with x-rays of your dog’s chest to evaluate their heart and lungs. Echocardiography is the imaging test of choice to determine what is causing the heart murmur. Other tests, including a complete blood count, chemistry panel, and urinalysis will help determine a baseline and if your dog has any underlying issues or disorders that may be contributing to the murmur. NT-pro-BNP testing is a cardiac biomarker that is often used to determine the severity of a patient’s heart disease. This test is recommended in dogs with a murmur but no symptoms of heart disease.
Heart murmurs associated with congenital heart disease include:
- PDA (patent ductus arteriosis)
- Aortic stenosis
- Pulmonic stenosis
- Septal defects
- Atrioventricular valve dysplasia
- Tetralogy of Fallot
- Other less common lesions
Heart murmurs associated with acquired heart disease include:
- Mitral or tricuspid degenerative valvular heart disease
- Diastolic dysfunction syndromes
Describing Heart Murmurs in Dogs
Veterinarians describe heart murmurs by listening to the heart and lungs of a dog using a stethoscope and define them using the following terms:
- Grade from softest to strongest: Grade I-VI/VI (Grade 1-6/6)
- Location where the murmur is heard the loudest on the chest (left-sided, right-sided, high, low, etc.) and if it can be heard in other areas of the chest or neck.
- Murmurs are described by when they occur during the heart cycle (systole, diastole) or if they are continuously heard throughout the cycle.
Dog Breeds at Risk for Heart Murmurs
Different breeds of dogs are at risk for specific congenital heart malformations associated with heart murmurs. Some dog breeds are more likely to have physiologic murmurs, diseases of the heart, and the great vessels.
Small breed dogs such as Chihuahuas, Shih Tzus, and Toy Poodles are at risk for AVVI (atrioventricular valvular insufficiency), which is an acquired heart disease. Large breed dogs such as Great Danes, Doberman Pinschers, and Golden Retrievers can develop DCM (Dilated Cardiomyopathy).
Other Risk Factors
Heart murmurs can happen secondary to non-cardiac problems such as fever, infection, anemia, hyperthyroidism, extreme thinness, obesity, and pregnancy.
It is important to understand that some heart diseases may not have a murmur, meaning the absence of a heart murmur does not mean that a patient does not have heart disease.
Is treatment available for dogs with heart murmurs?
Treating a heart murmur begins with determining the cause of the murmur. There are different medications available, depending on the diagnosis. Not all murmurs need treatment. Your vet will use their assessment of the severity or intensity of the murmur along with x-rays evaluating the heart size to determine the seriousness and outcome of the heart disease and necessary or recommended treatment(s).
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