Welcome to another edition of Medical Monday where we discuss veterinary medical issues experienced by pets and their families.
Today, I want to discuss heart murmurs. Heart murmurs can occur for a variety of reasons, in both dogs and cats, and can be a long term issue for your pet.
What is a Heart Mumur?
During my undergraduate degree, I was fortunate enough to take a physiology course. During that course, I learned that a heartbeat is actually the sound of two valves closing. When you hear a heartbeat, you may not actually distinguish that what you are hearing as one sound, is actually two different sounds occurring within milliseconds of each other. The heartbeat is a lub-dub, not just a dub.
Understanding that a heartbeat is a series of sounds rather than one, will really help you understand what a heart murmur is, and what exactly you are hearing. The two separate sounds are the result of multiple valves closing as blood flows through the heart.
The above picture provides a visual example of how blood flows through the heart.
Blood enters the heart through the right atrium, and passes through the right AV valve into the right ventricle, which will then pump blood through the pulmonary valve into the lungs where the blood will become oxygenated, and will then re-enter the heart through the left atrium, will flow through the mitral valve to reach the left ventricle, which then passes through the aortic valve to the rest of the body (Veterinary Partner).
These valves exist to keep blood flowing forward, and prevent it from flowing backward. When the valve is not opening or closing properly, this disturbs the blood flow and creates turbulence, which causes a murmur (Veterinary Partner). A heart murmur is an extra heart vibration that occurs when there is disturbance in the blood flow (PetMD).
It is imperative to understand that a murmur is not an arrhythmia. An arrhythmia is an erratic, irregular or disordered pulse (WebMD). Basically, if the flow of the blood is not disrupted, but the rhythm (lub-dub) sounds irregular, than you are dealing with an arrhythmia, not a murmur.
What causes a heart murmur?
According to PetMD, murmurs are caused by the following:
Disturbed blood flow caused by high blood flow through a normal or abnormal valve.
Flow disturbances identified by forward flow through abnormal valves.
Flow disturbances identified by regurgitant blood flow due to an abnormal valve.
According to Veterinary Partner, the most common murmurs in dogs are associated with leaky mitral valves. Sometimes, murmurs are caused by holes between two of the chambers in the heart, or narrowing of a chamber or vessel, or anemic blood.
What are the different kinds of murmurs?
There are benign (non-harmful) murmurs in which the cause of the murmur is not associated with an apparent heart disease, and is therefore, unexplained. These kinds of murmurs are not usually found in adult dogs, but can be found in puppies and cats of all ages. Characteristically, they have a soft sound and tend to be intermittent. Heart murmurs brought on by anemia or excitement often fall into this category (Veterinary Partner).
Congenital Murmurs are present from birth. The defect that is causing the murmur is always there, but may not be heard until later than life (Veterinary Partner).
Acquired Murmurs are brought on throughout the course of the pet’s life, but they are often associated with a heart or valve disease (Veterinary Partner).
If your pet’s murmur is associated with a structural heart diseases, they may display signs of congestive heart failure: coughing, exercise intolerance, or general weakness (PetMD).
Murmurs are classified on a grading scale. Grade of a murmur is determined by sound, configuration, and location (PetMD).
What do they sounds like?
A veterinarian that I worked for at Acorn Veterinary Clinic in Davis, California explained it to me the best. Dr. Jackman said that a heart murmur sounds like a washing machine as opposed to a lub-dub, this analogy would help me identify murmurs very well in the future.
The following videos are a series of audio clips, that show a view of the valves and how they are working with each type of murmur. Make sure to have your volume on, but I promise you this is very interesting. (I also want to thank Steven Farmer, DO for creating these videos).
First, this is the sound of a normal heart.
This second video is an Aortic Stenosis Murmur, which is defined but the AKC Canine Health Foundation as the narrowing of the aortic valve, or just above it. Listen for the “washing machine sound”.
This video is an Aortic Regurgitation Murmur, defined by Merck Manuals as back flow of blood from the aorta into the left ventricle.
This last video is a Mitral Regurgitation Murmur (the most common in dogs) , which can be defined by VCA Hospitals as back flow from the left ventricle to the left atrium.
If you were able to hear subtle differences between these videos, then you have a great ear for heart murmurs. These are very challenging to distinguish, but will give you an idea of what your veterinarian is listening for.
What should I do if my pet has a murmur?
The short answer is, work with your veterinarian. There are so many different classifications and underlying causes for murmurs, that your veterinarian will need to help you determine if treatment is necessary, and what you can do for your pet to help.
Our dog Maui (who lives with my mom and dad) has had a murmur since 2010, and is still doing well at the age of 14. Maui was not on medication until she was diagnosed with heart failure about 4 months ago, but has been doing well through these past few months.
Have you ever had a pet with a murmur?
To learn more about Heart Disease and heart murmurs, please visit GoodPetParent.com here.