Vet column: Valve disease common cause of canine heart murmurs
Heart disease affects about 10 percent of dogs. Insufficiency of the mitral valve is the most common cause, accounting for 75-80 percent of heart disease cases. Mitral valve disease is more common in small dogs such as the Cavalier King Charles Spaniel, Toy Poodles and Pomeranians.
A degenerative process affecting the mitral valve is thought to be genetic. The first sign of mitral valve disease is a murmur that begins between 6-10 years of age. When the murmur is low grade, there may not be any other signs. However, as the murmur (insufficiency) progresses, signs can include coughing, increased breathing rates or effort, exercise intolerance and even fainting.
The mitral valve is located in the left side of the heart between the left ventricle and left atrium. It provides a vital function by preventing blood from moving backward during heart contraction. Insufficiency means that the valve is not functioning properly allowing blood to leak backward past the valve when the heart contracts.
Understanding how mitral insufficiency affects the body requires further discussion about heart anatomy and function.
The heart is divided into two sides. Each side has two chambers — the atrium and the ventricle. The right side of the heart pumps blood to the lungs so that carbon dioxide (CO2) can be released and oxygen (O2) picked up for delivery to the body. Blood with oxygen returning from the lungs to the left side of the heart is pumped to the rest of the body.
When degeneration affects the mitral valve, the edges of the valves become rough and no longer completely close. This allows blood to move backward with each heart contraction. This leaked blood must be pumped again by the heart, resulting in increasing work and inefficiency.
The increased volume of blood in the heart chamber, also results in increased stretching of the heart muscle. This stretching can reduce the efficiency of the heart muscle contractions. When enough blood has leaked backward, it can start backing up into the blood veins leading from the lungs to the heart, causing problems with blood circulation in the lungs.
Mitral insufficiency can be detected by hearing a murmur over the mitral valve. However, it is important to have a full work-up completed to determine how severe the problem is. Tests often include chest X-rays to determine the heart size and changes in lung blood vessels, ECG to determine the presence of abnormal heart rhythms, blood pressure, and liver and kidney test values. Echocardiogram (ultrasound) of the heart provides an assessment of heart structure and function; however, it is not generally needed for mild mitral insufficiency.
Treatment and supportive care depend on the severity of the heart condition. Generally, medications that improve heart contraction, reduce blood pressure and remove excess fluid are used to manage the effects of mitral insufficiency. Reduced sodium diets are considered to be important. Fish oil, vitamins E, C, and B complex, L-carnitine and trace minerals may be of benefit. Herbs such as hawthorn berry (Crataegus oxyacantha) have a wide range of benefits, including safety, improved blood flow to the heart muscle, enhanced strength of the heart contraction,and removal of excess fluid.
When considering supportive care for dogs with mitral insufficiency, it is important to recognize that other parts of the body are indirectly affected. For example, many dogs with heart problems are in a chronic stress mode as the body tries to cope. This ongoing stress can lead to reduced adrenal function. The kidneys can also be affected and may need supportive care.
If you have questions about mitral insufficiency in your dog, contact your veterinarian.
Ron Carsten was one of the first veterinarians in Colorado to use the integrative approach, has lectured widely to veterinarians and has been a pioneer in the therapeutic use of food concentrates to manage clinical problems. In addition to his doctor of veterinary medicine, he holds a Ph.D. in cell and molecular biology and is a Certified Veterinary Acupuncturist and Certified Canine Rehabilitation Therapist. He practices integrative veterinary medicine in Glenwood Springs.