What is it?
Canine myxomatous or degenerative
mitral valve disease (MVD) primarily affects older, small to medium size dogs, although any dog can be
affected. For example, virtually all Cavalier King Charles Spaniels and Dachshunds will develop DMVD during the course of their lifetimes.
Diagnosis of DMVD is one of the easiest clinical aspects of the disease. Most cases of DMVD are recognized by veterinarians who detect a heart murmur during an auscultation exam by listening to the heart with a stethoscope. This usually is followed by an echocardiogram to visualize early changes in the mitral valve, chest radiograph to determine whether the heart is becoming enlarged, and/or an electrocardiogram to pick up arrhythmias.
Unfortunately a cure does not exist for this condition. A combination of drugs is used to control signs of congestive heart failure and prolong life with the best quality of life possible.
Treatment might include a combination of:
- A diuretic (i.e. furosemide or torasemide) – to excrete the excess fluids in the body and treat congestive heart failure.
- ACE inhibitor (i.e. benazepril) – to counteract fluid retention by the kidneys and dilate the blood vessels and lessen the load on the heart
- Pimobendan – to improve heart muscle strength and dilate the blood vessels and lessen the load on the heart. This is started at stage B2 of the disease.
- Spironolactone – to further excrete fluids and counteract heart muscle fibrosis
- Digoxin and others…
Therapy is lifelong and drugs/dosages are adjusted over time according to disease progression and kidney function among other factors
An easy and reliable way to monitor for signs of heart failure (fluid in the lungs or chest) is to monitor the breathing rate at home during sleep. Count the number of breaths in 15 seconds and multiply by 4. Values above 30 suggest the presence of heart failure.
Once heart failure has been confirmed and medication has been started, a fair goal is a one year life expectancy. Escalating doses of furosemide will most likely be needed. About 50% of heart failure patients will have died within 6 months of diagnosis. About 80% will have died by 1.5-2 years.
Of course, dogs with murmurs and no heart failure commonly live normal life spans.
Stages of Degenerative Mitral Disease
Stage A: these dogs do not have evidence of heart disease, but are at risk from a genetic point of view; dogs that are predisposed to mitral valve disease are in stage A, for example any Cavalier King Charles Spaniel.
Stage B1: this refers to dogs that have heart disease (characterised by a typical mitral regurgitation murmur) but do not have an enlarged heart on radiography/echocardiography or clinical signs of the disease.
Stage B2: mitral valve disease patients should be considered at this stage when evidence of cardiac enlargement on echocardiography/radiography is present but still no clinical signs of the disease are apparent.
Stage C: this refers to the onset of heart failure and the development of clinical signs, such as rapid and/or laboured breathing, that characterises pulmonary oedema. The stage can be further subdivided as follows: 1. Acute (hospital based) therapy. In these life-threatening cases, a high dose bolus of furosemide (2-4mg/kg IV) is usually indicated initially, followed by 1-2mg/kg every hour (or 0.71mg/kg/hour as a constant rate infusion) until the respiratory rate and effort start to decrease.