Mitral Valve Dysplasia (MVD) is also known as Mitral Valve Disease, Mitral Valve Disorder, Mitral Valve Malformation, Mitral Dysplasia, Mitral Systolic Murmur, Cardiac Valve Disease (CVD), Endocardiosis, Atrioventricular Valve Endocardiosis, Chronic Degenerative Valvular Disease, Chronic Valvular Disease, Chronic Mitral Valve Insufficiency, Myxomatous Atrioventricular Degeneration, Chronic Valvular Fibrosis, Acquired Mitral Regurgitation or Insufficiency, and Mitral Valve Defect.
Mitral Valve Dysplasia is a condition in which a defect in the mitral valve (the left atrioventricular valve) causes backflow of blood into the left atrium, or mitral regurgitation. Chronic mitral regurgitation leads to volume overload of the left heart, which results in dilatation of the left ventricle and atrium.
When mitral regurgitation is severe, cardiac output decreases, which results in signs of cardiac failure. Severe mitral regurgitation can also result in pulmonary venous congestion and left-sided congestive heart failure (CHF). Dilatation of the left-sided chambers predisposes affected animals to arrhythmias. In some cases, malformation of the mitral valve complex causes a degree of valvular stenosis as well as insufficiency.
Mitral valve insufficiency is age- and breed-related, with older, small-breed dogs demonstrating a higher incidence. There is also a slight predisposition among male dogs. This disease is the most common acquired cardiac disease in older dogs, affecting over one third of dogs greater than 10 years of age. In some breeds however, mitral insufficiency develops at a much younger age, due to an inherited predisposition for this disorder. In fact, in some breeds, abnormal development (dysplasia) of the valve has been identified in embryos.
Mitral valve murmurs are graded from the mildest and least audible to the loudest and most turbulent. The loudness of the murmur usually indicates the severity of the disease.
Grade 1: Murmur can be heard with a stethoscope in a quiet room.
Grade 2: Can be consistently heard with the stethoscope.
Grade 3: Murmurs are louder and are heard as soon as the stethoscope is applied.
Grade 4: Quite loud, and the vibration can be felt with fingertips without a stethoscope.
Grade 5: Murmur is louder, with a precordial “trill”.
Grade 6: So loud it can be heard with the stethoscope removed from the chest, or even without using the stethoscope.
Age at onset: Abnormal heart morphologies have been seen observed during embryonic stages, however this disease is more commonly seen in dogs over the age of 10 years.
Breeds Affected: Mitral valve disease is the most common heart disorder in older dogs of all breeds. In general, small breeds are most often affected and some studies show a greater incidence in males than in females, but any breed can be affected. MVD is more common in the following breeds:
Cavalier King Charles Spaniel
Symptoms: Dogs have a an increasingly loud heart murmur, abnormal heart rhythm, reduced tolerance for exercise, difficulties in breathing, or a cough at night or at rest. They may faint, show weakness, or collapse.
Genetics of Mitral Valve Dysplasia: The genetics of mitral valve dysplasia are not well understood yet, however research studies indicate it is an inherited trait.
Mitral Valve Dysplasia in Humans: Mitral valve disease is a genetic disorder in humans that is highly similar to the disease in dogs. In addition, Ebstein’s anomaly in humans is thought to be share similarities to tricuspid valve dysplasia.
Below is a video produced by the American College of Veterinary Internal Medicine featuring Teresa DeFrancesco, DVM, DACVIM (Cardiology), DACVECC, speaking with Steve Dale on the topic of Mitral Valve Disease in dogs.
The symptoms of Mitral Valve Dysplasia (MVD) vary depending on the stage of the disease.
Four stages of MVD have been described:
Stage A identifies patients at high risk for developing heart disease but that currently have no identifiable structural disorder of the heart (e.g. breeds that are genetically predisposed to MVD)
Stage B identifies patients with structural heart disease (e.g., the typical murmur of mitral valve regurgitation is present), but that have never developed clinical signs caused by heart failure. Because of important clinical implications for prognosis and treatment, Stage B is further subdivided into Stage B1 and B2.
Stage B1 refers to asymptomatic patients that have no radiographic or echocardiographic evidence of cardiac remodeling in response to CVHD.
Stage B2 refers to asymptomatic patients that have hemodynamically significant valve regurgitation, as evidenced by radiographic or echocardiographic findings of left-sided heart enlargement.
Stage C denotes patients with past or current clinical signs of heart failure associated with structural heart disease. Because of important treatment differences between dogs with acute heart failure requiring hospital care and those with heart failure that can be treated on an outpatient basis, these issues have been addressed separately. Some animals presenting with heart failure for the first time may have severe clinical signs requiring aggressive therapy (eg, with additional afterload reducers or temporary ventilatory assistance) that more typically would be reserved for those with refractory disease (Stage D).
Stage D refers to patients with end-stage disease with clinical signs of heart failure caused by CVHD that are refractory to standard therapy. Such patients require advanced or specialized treatment strategies in order to remain clinically comfortable with their disease. As with Stage C, there is a distinction between animals in Stage D that require acute, hospital-based therapy and those that can be managed as outpatients.
Symptoms of MVD
In the early stages of the disease, there are no clinical signs, although a systolic murmur of low intensity (grade I-II/VI) can be heard with maximum intensity at the left apex. If fact, there is a possibility that a dog will develop Congestive Heart Failure (CHF) without displaying any symptoms at all. With continued progression, the murmur intensity generally increases (up to a grade VI/VI systolic murmur); however, the intensity does not always coincide with disease severity.
Mitral Valve DiseaseAs the disease progresses, exercise intolerance, increased respiratory rate and effort (breathlessness), and cough develop. Watch for excessive panting when exercising, a distended abdomen, weight loss, and fainting (syncope). Fainting may occur secondary to either compromised cardiac output or, more likely, a transient cardiac arrhythmia.
In addition to a dry, hacking cough and breathlessness, MVD may even cause the trachea to collapse as the heart enlarges and fills voids in the chest cavity. Moreover, when a critical pressure is reached, pulmonary edema (flooding of the lungs) can occur.
Due to increasingly poor blood circulation, non-essential blood vessels begin to shut down to conserve blood flow for vital organs. While the brain and heart are given priority, blood flow to the skin and the kidneys decrease. This causes the skin to pale and the kidneys to retain fluids in circulation. The excess fluid retention results in further stretching of the heart and greater mitral valve leakage. If the tricuspid valve is also affected, the retained fluid, called ascites, is squeezed into other body tissues, the liver, chest, and peritoneal cavity of the abdomen.
Dogs with murmurs of between Grade 3 and Grade 6 may display episodic weakness of the hindquarters, ataxia, or collapse, which is called presyncope. When these symptoms occur in combination with loss of consciousness, the dogs faint due to a sudden decline in blood flow to the brain.
Symptoms of advanced MVD include a loss of appetite, severe weight loss (called cardiac cachexia), and a loss of muscle mass. Ultimately, MVD leads to heart failure. Once dogs develop severe congestive heart failure (CHF), the median survival period is approximately seven months, with 75% of patients dead within one year. For dogs with less severe CHF, the median survival period is one year, with 75% dead within 21 months.
Sudden death is rare, but may occur secondary to left atrial rupture caused by severe and chronic mitral regurgitation. Physical examination findings in patients that have developed left-sided CHF include respiratory crackles and wheezes and dyspnea. If tricuspid valve degeneration is significant, signs of right-sided CHF may be noted (eg, ascites, jugular pulses).
The following is a list of reported symptoms of Mitral Valve Dysplasia (MVD):
- systolic murmur that increases in intensity
- exercise intolerance
- increased respiratory rate and effort
- breathlessness and labored breathing
- dry, hacking cough
- excessive panting when exercising
- distended abdomen
- pale skin
- gums turn from pinkish to bluish (cyanosis)
- weight loss
- loss of muscle mass
- congestive heart failure
- episodic weakness of the hindquarters
The following are videos of dogs affected with heart disease. The first below is of Chowmein, the Chinese Crested Powderpuff displaying the coughing symptom that is characteristic of this disease. In fact, Chowmein was diagnosed with a grade III/VI murmur that progressed over time and was believed to be associated with her severe case of periodontal disease. We gratefully acknowledge The Fairy Dawgmother for providing this video.
Below is a video of Bing the Boxer showing symptoms of Congestive Heart Failure. We are grateful to Ger for providing this video.
MVD is diagnosed through several means. Veterinarians may detect a heart murmur using a stethoscope before any signs are displayed. Further investigation by radiographs and electrocardiogram may reveal some of the changes that occur in the heart over time, as it works harder to compensate for the insufficiency of the mitral valve. These changes may include enlargement of the left side of the heart, enlargement of blood vessels in the lungs, and cardiac arrhythmias.
- Murmur: soft to loud, harsh, regurgitant, holosystolic – loudest at left apex (5th to 6th intercostal space) over the mitral valve area.
- Electrocardiogram: commonly see left atrial enlargement pattern (increased P wave duration) with or without left ventricular enlargement (depends on severity). Atrial arrhythmias, especially atrial fibrillation, are common.
- Radiographs: moderate to marked left atrial enlargement with or without left ventricular enlargement. Pulmonary veins are often enlarged.
- Echocardiography: may see abnormal location, shape, motion or attachment of the valve apparatus. Doppler assessment will show an abnormal flow (regurgitant jet or valvular stenosis or both).
Dogs affected with Mitral Valve Dysplasia (MVD) may opt for expensive and risky heart surgery. It is possible to replace the defective mitral valve; surgical replacement of heart valves is both costly and requires that the dog’s renal system and other vital organs be in ideal condition. For those that do opt for open heart surgery, if the dog survives surgery, they may be essentially cured of the disease or enjoy an arrest of the disease, where MVD no longer progresses and can be treated and stabilized with medications. A normal healthy young dog could likely undergo and recover from cardiac surgery without complication. One that is older, with cardiac disease or other organ involvement, presents a much more difficult challenge.
More commonly, MVD is treated by managing heart failure, with the goals to improve the dog’s quality of life and to increase the length of its life. Therapies include a special sodium-restricted diet, exercise restriction, diuretics, and medication to support the failing heart. The medical therapies utilized vary according to the stage of the disease, that is, early-stage MVD is not treated in the same way as advanced-stage MVD (review the stages above).
MVD stage-associated treatments:
For asymptomatic dogs diagnosed with Stage A to Stage B1 MVD, no medical treatment is required. These patients are considered to be in the pre-clinical stage of MVD by cardiologists, but heart size should be monitored by x-rays every 6 to 12 months. Some veterinary cardiologists prescribe the medications carvedilol (Coreg) and Bisoprolol. These drugs are non-selective alpha and beta blockers with anti-oxidant effects, which slow heart rate, relax arteries, reduce heart work load and decrease blood pressure.
- overweight dogs should be put on a weight-reducing diet
- low salt diets have been suggested to help reduce water retention
- dogs should avoid extreme exertion
- the following have also been suggested: Vitamin C (300 to 400 mg. daily), Vitamin E Tocopherol (100 I.U. daily), CoQ10 (30 mg. daily), Fish oils high in Omegas 3 and 6 (e.g. wild salmon oil; ~ 400 mg. daily)
For dogs diagnosed with Stage B2 MVD, medical treatment is necessary. Reducing exercise is advised to reduce the heart’s workload and counteract fluid and salt retention.
- Diuretics, including furosemide (Lasix, Diuride, Frudix, Frusemide) and hydrochlorothiazide (Dyazide), are drugs that cause the kidneys to excrete more fluid than normal and may be used to remove fluid from the lungs. Risks: side effects include increased thirst and urination. Furosemide can severely affect the kidney by activating the renin-angiotensin aldosterone system (RAAS), as well as the liver and other bodily functions, so the kidneys and liver should be evaluated before starting furosemide and should be monitored every three months thereafter. Furthermore, veterinary cardiologists do not recommend chronic use of furosemide in the absence of concurrent therapy to blunt RAAS activity, such as ACEI, aldosterone receptor blockers, or angiotensin II type I receptor blockers. Furosemide should be used only combined with ACE inhibitors (see below) to reduce the dosage of furosemide needed and avoid thmost negative of its side effects. Extensive use of diuretics alone may contribute to renal dysfunction by activating the renin-angiotensin aldosterone system (RAAS), as well as dehydration, azotemia, and hypokalemia.
- ACE inhibitors, including enalapril maleate (Enacard, Vasotec), benazepril (Lotensin, Fortekor), ramipril (Altace, Tritace, Vasotop) relax blood vessels, lower blood pressure and increase the supply of blood and oxygen to the heart by blocking the angiotensin converting enzyme that causes blood vessels to tighten. Ultimately, ACE inhibitors blunt the enlargement of the heart and slow the progression of heart failure. Risks: ACE inhibitors can cause severe renal insufficiency, so kidneys should be monitored carefully when using these drugs. In addition, the use of ACE inhibitors combined with extreme salt (sodium) restriction may contribute to renal dysfunction by activating the renin-angiotensin aldosterone system (RAAS). Therefore, some cardiologists recommend only moderate salt restricted diets when prescribing ACE inhibitors. Other side effects include the accumulation of toxins which can damage the liver, anorexia or loss of appetite, vomiting, azotemia, and the development of a dry cough due to the accumulation of bradykinin. It should be noted that a dry, hacking cough is a frequent symptom of progressing MVD, so this side effect of the drug could be confused with the worsening of the disease.
- A natural supplement that serves as an alternative to ACE inhibitors is active fish petides, including LKPNM, from the bonito fish (Sarda orientalis).
Dogs with severe MVD, diagnosed with Stage C MVD have difficulty breathing while at rest and may not be able to tolerate even minimal exercise. The following medications have been advised:
- Diuretics, Venodilators (which lower the pressure in the veins) and Arteriolardilators (hydrazaline (or Apresoline), pimobendan, sodium nitroprusside, which reduce pressure in the arteries) relieve presure in the left atrium, making it easier for the heart to pump. Diuretics should be given by injection in severe cases. ACE inhibitors also have venodilating effects.
- Digoxin (Lanoxin), a cardiac glycoside extracted from the foxglove plant (digitalis), may be used to improve heart muscle strength to facilitate heart contractions for advanced heart failure.
- Pimobendan (Vetmedin) reportedly eases the resistance in the circulatory system by dilating blood vessels, and improves the efficiency with which the heart can function as a pump, thereby both improving cardiovascular function and the blood flow to major organs.
- For dogs with congestive heart failure, Sildenafil (Viagra) and tadalafil (Cialis), which are phosphodiesterase (PDI) 5 inhibitors, respectively lower pulmonary hypertension and decrease systolic pulmonary arterial pressure significantly.
- D-Ribose, also known as alpha-D-ribofuranoside, serves as a natural supplement, which improves ventilatory efficiency and may help to strengthen and energize the heart of a dog with severe MVD and congestive heart failure (CHF).
Dogs in the late stage of MVD with Congestive Heart Failure (CHF), diagnosed with Stage D MVD suffer from a progressive deterioration of quality of life. Ultimately it becomes more and more difficult to comfortably keep the heart, lungs, and abdominal cavity free of fluid congestion. In addition, dogs in this stage suffer from enlarged heart chambers, lethargy, collapse, and deterioration of kidney and/or liver functions. Eventually diuretics, ACE inhibitors, pimobendan and other drugs are no longer able to remove enough of the fluids and to increase blood supplies and oxygen to the heart.
Nutrition is very important for dogs with Stage D MVD, as they may suffer severe weight loss, called progressive cardiac cachexia. Palliative food should be fed to maintain muscle mass.
- Mirtazapine (Remeron) or meclizine (Antivert, Bonine, Dramamine II, Driminate II) may be prescribed to stimulate appetite.
- N, N-Dimethylglycine (DMG) supports the immune system, promotes oxygen utilization, improves cardiovascular function, supports liver function, and supports ocular health.
- Aminophylline, oxtriphylline, or theophylline (Corvental), are a bronchial dialators, which relax and open air passages in the lungs, making breathing easier, and may be used to help dogs with severe flooding of the lungs.
- Retained fluids (ascites) fill the peritoneal cavity of the abdomen due to tricuspid valve deterioration, and may be removed periodically by aspiration with a hypodermic needle (abdominocentesis).
- Some cardiologists recommend that dogs with advanced mitral valve disease not be vaccinated, including rabies, because of possible adverse reactions, which might accelerate damage to the dogs’ hearts.
At this stage, acute pulmonary edema is fatal without immediate recognition and therapy. In particular, oxygen treatment is essential. Delaying oxygen treatment can lead to oxygen deprivation damage to muscle, eyes, limbs, and kidneys, which may be already compromised by drugs. Additionally, the heart beats faster to deliver more blood, which requires more oxygen and leads to a negative feedback cycle. The signs of acute pulmonary edema include:
- Discomfort exhibited by restlessness or the inability to get comfortable
- Shallow and more rapid breathing (panting). Anything above 30-35 breaths per minutes is too rapid
- Visible heartbeat due to an enlarged heart
- A look of worry or panic (due to an inability to get enough oxygen either through restricted breathing or cardiac output)
- Labored, raspy, or “wet” breathing sounds
Dogs affected with Mitral Valve Dysplasia (MVD) require special care. Attention to dental care, diet and exercise that reduce strain on the hearts and vital organs of of MVD affected dogs have been highly recommended.
Studies have shown that the incidence of heart-valve pathology rises in dogs with concurrent dental disease. Bacteria residing in the mouth enter the bloodstream and settle on the heart valves, triggering endocardiosis. It is suspected, although not proven, that pre-existing valvular pathology attracts bacteria. Good dental hygiene should be maintained in all breeds prone to valvular heart disease. Read our articles on Dental Care: Brushing your dog’s teeth and Identifying Periodontal Disease in dogs.
Too much body fat increases the risk of heart disease because it increases how hard the heart has to work and increases the risk of high blood pressure, diabetes, and high cholesterol. A proper diet, combined with an exercise program, is key to maintaining a healthy weight.
In a study involving 29 dogs over four weeks, a special “Heart Diet” was developed and shown to reduce heart size in asymptomatic dogs. The heart diet is a moderately reduced sodium diet enriched with antioxidants, n-3 fatty acids, taurine, carnitine, and arginine.
The following are recommended heart-healthy supplements:
- Vitamin C
- Vitamin E
- fish oils
- Bio-Cardio, a Thorne Veterinary Products multi-vitamin, mineral, and herbal extract supplement (which includes Vitamin E, selenium, magnesium, potassium, L-Carnitine, L-Taurine, coenzyme Q-10, dimethylglycine [DMG], Hawthorne extract, desiccated bovine heart, and Siberian genseng extract)
- Canine Cardiac Support, and human-grade supplements, including Cardio-Plus, Cardiotrophin PMG, Cataplex E, and Vasculin, which are nutritional whole food supplements offered by Standard Process, Inc.
- Cardio-Support, a veterinary formula herbal supplement to aid heart function and blood circulation, offered by D’Arcy Naturals.
- Flavonex, a salvia and gingko extract herbal supplement made by Health Concern.
A diet that includes daily mashed bananas is recommended for dogs with CHF that are taking a diuretic. These dogs suffer from a decreased potassium and phosphorus levels, which can be partially restored with bananas.
While maintaining an exercise program to prevent obesity is essential, excessive exercise will tax the heart of a dog affected with MVD. Careful observation of breathlessness and excessive panting when exercised indicate exercise overload. In the case of exercise intolerance in dogs with MVD who are also overweight, a change in diet is critical.
Dogs with CHF suffer from fluid-filled abdomens, which are very uncomfortable to lie on. Making a regular bed pillow available will help to support the upper half of the body and relieve some of the pressure off the stomach.
The content is not intended to be a substitute for professional medical advice, diagnosis, or treatment by a veterinarian. Always seek the advice of your veternarian or other qualified health provider with any questions you may have regarding a medical condition.
Please contribute to this article! If you have a dog affected by MVD, please send us your photos, videos and feedback so we can include them in our article. Videos and photos are particularly useful for demonstrating symptoms to new owners who may have to face this disease. Here’s how to contact us.