Maple’s owners noticed a problem. Their nine-year-old Chihuahua started to have a dry, hacking cough three to four times a day, mainly in the morning. After coughing for 5 to 10 seconds, Maple would make a retching sound, lick her lips, and then return to normal.
Years earlier, Maple’s primary veterinarian had detected a heart murmur. But because Maple was asymptomatic and the murmur was quiet at that time, they had decided to monitor for changes rather than starting medications or performing other diagnostics.
Now the murmur could now be heard on both sides of the chest with a stethoscope. Maple had also developed a mild tracheal (windpipe) sensitivity, seen as a soft cough when her veterinarian touched her throat. The rest of her physical exam was within normal limits. Given Maple’s breed, age, and history of progressive heart murmur, her veterinarian suspected she had developed chronic valve disease and suggested that Maple see a veterinary cardiologist.
Dr. Todd Sumerfield, a veterinarian pursuing specialization in cardiology at the University of Illinois College of Veterinary Medicine, shares his experience caring for Maple so that other pet owners can learn the signs and treatments for heart murmurs and chronic valve disease in dogs.
What Are Heart Murmurs?
A heart murmur is a physical exam finding that indicates rapid or turbulent blood flow in the heart or nearby large blood vessels. Murmurs can vary in volume, sound, location, and phase of the cardiac cycle. Even low-grade murmurs can be detected by listening to the heart with a stethoscope.
Murmurs are graded on a scale of 1 to 6, commonly written in Roman numerals (I-VI) in the medical record, with grades given for each side of the chest. Murmurs receive a higher grade as they get louder. A grade V or VI murmur, which can feel like buzzing in a pet’s chest, can even be felt through the skin or heard without a stethoscope.
“While the grade of murmur is helpful to confirm suspicion of heart disease, the grade of murmur does not necessarily correspond with the severity of heart disease,” says Dr. Sumerfield. Additionally, a louder murmur does not always mean worse heart disease than a quiet murmur, and murmur grade cannot be used to monitor disease progression.
Sometimes murmurs are not a sign of disease. These so-called “innocent” heart murmurs are caused by normal blood flow through the heart and are usually harmless.
Pathologic murmurs can be from acquired or congenital disease. Congenital murmurs are present from birth. As in Maple’s case, a veterinarian may hear a heart murmur on physical exam and inform owners that their pet has an underlying heart disease before clinical signs, such as coughing or exercise intolerance, develop. Dr. Sumerfield says small-breed dogs, especially Cavalier King Charles spaniels and toy poodles, have a genetic predisposition to developing chronic valve disease when they are middle-aged or older.
What Is Chronic Valve Disease?
Chronic valve disease (also referred to as degenerative valve disease or myxomatous mitral valve disease) is the most common acquired heart disease in dogs. It typically affects the mitral valve that separates the left atrium and the left ventricle, although other valves may also be affected.
Myxomatous mitral valve disease describes a condition in which a scar-like substance builds up inside the mitral valve, causing it to lose function.
“Myxomatous changes cause the valve to become thickened and irregular, which allows blood to flow backwards across the valve when the heart contracts. This turbulent regurgitation of blood is what causes a heart murmur,” says Dr. Sumerfield.
Maple’s Visit with the Cardiologist
When Dr. Sumerfield examined Maple, he confirmed the presence of a heart murmur and performed an echocardiogram to identify the cause of the murmur. An echocardiogram is a non-invasive ultrasound exam of the heart. It involves shaving small patches of fur on the dog’s chest and may require mild sedation, depending on the temperament of the dog.
Maple’s echocardiogram showed thickened mitral valve leaflets with an enlarged left atrium and ventricle (Figure 1). The mitral valve leaflets are the flaps of tissue that open and close with each heartbeat to control blood flow between the left chambers of the heart.
A technique called color Doppler, which allows for the visualization of blood flow, revealed severe mitral regurgitation as the cause of Maple’s heart murmur (Figure 2).
The echocardiogram confirmed a diagnosis of chronic valve disease in Maple. As this disease progresses, the heart begins to enlarge, which puts the dog at risk of congestive heart failure. That means it is time to intervene medically.
Treatment of Heart Disease
“There are a variety of diseases that cause murmurs, and each is treated differently,” says Dr. Sumerfield. The treatment depends on the underlying cause of the murmur, so proper evaluation is very important. Referral to a veterinary cardiologist may be needed to guide appropriate therapies.
“Most heart diseases may be treated medically. Animals who require medical management will be on oral medications lifelong,” explains Dr. Sumerfield.
Some congenital heart diseases can be cured surgically. Puppies with loud heart murmurs should be evaluated at a young age to determine if they are a candidate for surgery.
In recent years, veterinarians have developed surgical treatment for some forms of acquired heart diseases such as chronic valve disease.
Managing Maple’s Heart Murmur
Maple was sent home on a medication called pimobendan that will help to delay the progression of her heart disease. Before she left, X-rays were taken of her chest (Figure 3) so that doctors can monitor the size of her heart and monitor for fluid accumulation in her lungs over time.
Dr. Sumerfield recommends new chest X-rays be performed every six months so her medication can be adjusted to delay congestive heart failure for as long as possible. He also told Maple’s owners that if she experiences difficulty breathing, she would need to see a veterinarian immediately as this may indicate the onset of congestive heart failure. The goal is to keep Maple as happy and healthy for as long as possible without experiencing clinical signs from her heart disease.
By Cassidy Kelly
Photo illustration at top from AdobeStock images
