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; see Overview for the list)
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.
As 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 laboured 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 dental 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).
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. Send us materials by uploading them to DogHeirs or by sending them directly to us at Team@DogHeirs.com
Copyright 2013 DogHeirs. All Rights Reserved.