According to studies, myxomatous mitral valve disease (MMVD) is the most commonly diagnosed congenital heart disease in dogs. Additionally, it is the top cause of heart failure in canines. The disease is more prevalent among older dogs, but it can occur in younger animals.
Cocker Spaniel, Cavalier King Charles Spaniel, Chihuahua, and Maltese are the breeds mostly affected by MMVD. Vets diagnose the disease by listening to abnormal heart sounds. They can also use a veterinary MRI, echocardiography, and thoracic radiographs to confirm the condition.
What Is Myxomatous Mitral Valve Disease?
MMVD is an acquired heart disease that typically affects dogs over six years. It results from malformation of the mitral valve, which controls the blood flow between two chambers on the heart’s left side.
Affected dogs have a floppy, enlarged mitral valve that allows leakage of blood back into an empty chamber or ventricle during the diastole (relaxation) phase when the ventricle should fill with blood. Depending on how much leakage is there and how well the affected dog tolerates it, this condition can be mild, moderate, or severe.
Over time, pressure in the left atrium increases to compensate for this problem (increased preload), eventually leading to fluid accumulation in tissues and fluid buildup in the lungs (pulmonary edema). Dogs also tend to swallow more often and salivate excessively due to increased pressure on nerves.
It’s essential to choose a reputable vet hospital, such as Veterinary Medical and Surgical Group, that can advise you on doing the necessary tests and procedures. They will also be in a better position to help you out in the long run.
Symptoms of MMDV
The severity of the signs in dogs with MMVD depends on the extent and rapidity of left ventricular (LV) dilation, which is different from dog to dog. Initial symptoms include increased respiratory rate due to pulmonary edema or fluid accumulation in tissues. Other signs include:
- Exercise intolerance
- Increased heart rate
- Swelling of the belly due to liver enlargement secondary to high blood volume
- Reduced blood pressure resulting in low systemic vascular resistance (SVR)
- Weak pulses due to reduced cardiac output originating from the affected side of the heart
- Difficulty breathing during exertion or while lying down secondary to shortness of breath caused by pulmonary edema.
- As the disease progresses, it might lead to hepatomegaly (enlarged liver), ascites, pleural effusion, and/or right-sided congestive heart failure.
How MMDV Progresses
Patients with mild MMVD might live for several years without any evident symptoms, while those with the moderate or severe disease usually develop signs related to heart failure within a few months. Typically, these dogs experience shortness of breath and rapid breathing after little physical activity. They pant excessively and consume enormous amounts of water because fluid accumulates in their lungs and intestines.
Since both left ventricle chambers operate as a “one-way” valve during the systole (contraction) phase, blood must flow forward to reach the body instead of flowing backward into the heart. In the presence of MMVD, blood leakage from the left ventricle into the atrium might cause enough pressure to reverse this flow and lead to backward pumping of blood into the lungs. This is known as pulmonary venous hypertension. It worsens with time because more blood returns to the lungs instead of being pumped forward through a narrowing aorta, resulting in elevated preload.
Patients with severe MMVD have very high lung pressures but little circulation to deliver oxygenated blood to tissues throughout the body. Heart failure becomes evident as arteries supplying the kidneys begin to fail, leading to reduced urine production and retention of excess fluids that can accumulate in various organs or around joints. Dogs also tend to become lethargic as they develop anemia from blood loss, and they might lose their appetite and develop muscle wasting and weakness.
If untreated, these problems lead to fatigue and shortness of breath even when the dog is at rest. Eventually, weak pulses in the legs can be felt while feeling for a pulse on the chest wall above the heart. When the cardiac pressure is high enough, fluid will leak into spaces around joints such as at elbows or knees (pericardial effusion). Patients with severe MMVD develop congestive heart failure within three to six months after diagnosis.
Is Surgery an Option?
In very few cases, surgery can be used to correct MMVD, but its success is highly dependent on the patient’s general health. Since multiple organ systems are affected by this disease, it might not be possible to perform surgery safely in all patients.
If you believe your dog may have MMVD but is not showing any symptoms yet, taking them to the vet for an early examination can be beneficial. Click here to know more about open-heart surgeries.
How Long Can Dogs with MMVD Last?
Because the rate of progression and severity of heart problems varies, there is no set time frame for how long an individual dog might survive once diagnosed with this condition. For breeds that are more likely to be affected by MMVD than other breeds, such as Cavalier King Charles Spaniel and Cocker Spaniel, early diagnosis and treatment may help improve chances of survival.
Dogs diagnosed at a younger age tend to have milder forms of MMVD compared with those who developed symptoms later in life. Even though some dogs live longer than others, most people expect their pet’s lifespan to be shortened by 1-2 years after their vets notify them about this problem. However, heart failure can develop rapidly in some patients, especially if they are not weighed regularly or become dehydrated.