By Dr. Becker
Seemingly healthy dogs can have heart murmurs indicative of cardiac disease. Owners don’t even realize there’s a problem until their veterinarian picks up the presence of a murmur during an exam.
While cats and puppies can have innocent murmurs, virtually all murmurs in adult dogs indicate structural heart disease.
Unfortunately, heart problems in dogs are relatively common.
A heart murmur can be caused by abnormal blood flow within the heart, usually involving the heart valves. Murmurs can also be caused by problems in communication between the left and right sides of the heart.
Murmurs can be present at birth (congenital). They can also be acquired due to disease or the aging process.
Normal Heart Sounds vs. Murmurs
When your veterinarian listens to your dog's heart, a technique called auscultation, she's checking for heart rate and rhythm, and heart sounds. In a normal, healthy heart, there are only two sounds heard – sort of a lub-dub – and they should be clearly audible, not muffled or difficult to pick up. The two sounds should have uniform loudness (the 'lub' isn't louder than the 'dub' or vice versa), and a regular rhythm.
Each heartbeat has an associated pulse in the blood vessels, which is felt easily in the femoral vein in the back leg.
The lub-dub sound is made by the heart valves closing as blood exits the heart chamber. If a valve doesn't close completely, it allows blood to flow backwards into the heart. A murmur is the sound of blood flowing in the wrong direction back into the heart.
There are six grades of heart murmur based on loudness. They are:
- Grade 1 = a very soft, localized murmur detected only after several minutes of listening
- Grade 2 = a soft murmur, heard immediately but localized to a small area
- Grade 3 = a moderately intense murmur, that is readily detected and detected over more than one location
- Grade 4 = a moderately intense or loud murmur, detected over several areas, usually both sides of the chest, however, a precordial thrill (vibration) is not detected in this case
- Grade 5 = a loud murmur accompanied by a precordial thrill over the point of maximal intensity
- Grade 6 = a very loud murmur accompanied by a precordial thrill and the murmur is detected when the stethoscope is pulled slightly off the chest wall
These grades or levels of murmurs don't necessarily distinguish a non-serious murmur from a dangerous one. For example, loud murmurs are heard in both mild and significant heart disease. And soft murmurs are typical in myocardial (heart muscle) failure, also called dilated cardiomyopathy (DCM).
Causes of Heart Murmurs
Murmurs on the right side of the heart can be caused by tricuspid regurgitation or ventricular septal defect (VSD).
Tricuspid regurgitation means the heart's tricuspid valve isn't closing correctly, allowing blood to flow backward into the heart. A ventricular septal defect (VSD) is a hole or holes in the wall separating the left and right ventricles of the heart.
Murmurs on the left side of the heart are most often caused by myxomatous mitral valve disease (MMVD), stenoses of aortic or pulmonary valves, or patent ductus arteriosus (PDA).
MMVD, also known as mitral valve prolapse, is a problem with the improper closure of the mitral valve separating the upper and lower chambers of the left side of the heart. This is the most common cause of acquired murmurs in adult dogs.
Stenosis of the aortic or pulmonary valves means the valves have narrowed, causing the heart to work harder to pump blood through the smaller openings. Patent ductus arteriosus (PDA) is a condition in which the ductus arteriosus blood vessel fails to close normally, interrupting the normal blood flow between the aorta and pulmonary arteries that carry blood from the heart.
Heart valve lesions cause murmurs. Congenital (from birth) lesions are much more common in young dogs, while acquired lesions are more often the case in adult dogs.
Diagnosing the Cause of a Murmur
When your vet has evidence of a heart murmur in your dog, he or she will discuss which of the following diagnostic tests are most appropriate.
- Blood tests. A CBC (complete blood count) and serum chemistries can aid in detecting problems with major organs like the kidneys and liver, which need to be healthy if heart medications are prescribed. There is also a blood test that measures the amount of stretching the heart muscle is undergoing, called a proBNP blood test
- Chest x-rays. X-rays of your dog’s chest can give important information about her heart and lungs. The heart’s size, shape and position can be visualized, as can blood vessels and lung patterns.
- ECG. An ECG (electrocardiogram) can aid in detection of heart rate and rhythm abnormalities, heart chamber size, and electrical activity in the heart.
- Cardiac Ultrasound. An ultrasound of the heart shows strength of contractions, the size of the chambers of the heart, thickness of heart muscle walls, and heart valve function. It can also detect heartworms and tumors.
Certain breeds of dogs are predisposed to specific types of heart conditions, so your vet will also use this information to aid in diagnosis.
|Cavalier King Charles Spaniel, Dachshund, Small breeds||Acquired mitral valve disease|
|Bull Terrier, Rottweiler||Congenital mitral valve disease|
|Boxer, Cocker Spaniel, Doberman Pinscher, Great Dane, Irish Wolfhound, Labrador Retriever||Myocardial failure|
|Cocker and English Springer Spaniels, German Shepherd, Maltese, Poodle||Patent ductus arteriosus|
|Boxer, Cocker Spaniel, English Bulldog, Mastiff, Miniature Schnauzer, Samoyed, West Highland White Terrier||Pulmonary stenosis|
|Boxer, German Shepherd, Golden Retriever, Newfoundland, Rottweiler||Subvalvular aortic stenosis|
|Labrador Retriever||Congenital tricuspid valve disease|
|English Springer Spaniel||Ventricular septal defect|
Treatment of a Heart Murmur
Actually, the murmur itself isn't treated.
The underlying cause of the murmur is treated or not, depending on a variety of factors including the severity of the problem, the age and health of your pet, cost of treatment, etc. A visit to a board-certified veterinary cardiologist can also provide more information about the severity of your pet's heart condition.
Your holistic vet should discuss all appropriate treatment options and partner with you to manage your dog's heart condition.
I recommend all animals suffering from any heart pathology increase their intake of ubiquinol, the reduced form of CoQ10, and Omega-3 essential fatty acids, specifically krill oil. Additionally, holistic vets may recommend Chinese herbs, homeopathic remedies, supplemental amino acids, such as Taurine, Arginine, and Acetyl-L-Carnitine, D-ribose and herbs, such as Hawthorne berry and Cayenne.
Symptoms of a Heart Condition
A few signs to watch for if you suspect or know your pet has a heart problem include:
- Bluish appearing tongue
- Loss of appetite
- Fatigue, weakness, loss of stamina, decreased exercise endurance
- Too fast or too slow heart beat; increased respiratory effort, including increased respiratory rate
Tips to Proactively Protect Your Dog's Heart Health
- Ask your veterinarian for the proBNP blood test. This test can give you peace of mind that your dog has no early signs of heart disease. It’s a simple blood test with a fast turn-around time that can provide the information you need to proactively manage your dog’s heart health.
- Help your dog maintain a good body weight through regular, aerobic exercise.
- Feed a high quality, species-appropriate diet, which meets your pet's nutritional requirements for optimal protein (and amino acid) levels, healthy fat and coenzyme Q10.
- Take excellent care of your dog's dental health (bacteria from dirty mouths have been linked to heart valve infections in dogs).