DEGENERATIVE MITRAL VALVE DISEASE

Degenerative mitral valve disease is an acquired condition that primarily affects the heart valves, and it accounts for approximately 80% of all diagnosed canine heart conditions. This prevalent disease impacts a significant population, with up to seven million dogs in the United States alone experiencing its effects.

Degenerative mitral valve disease affects the mitral valve, a flap that is located on the left side of the heart, between the atrium and the ventricle.  The valves tissue tends to degenerate over time, gradually thickens, losing its elasticity and is no longer able to function properly.  This lack of a proper closure leads to abnormal reversal of blood flow inside the heart, known as mitral regurgitation.

The disease is typically first detected by a veterinarian during a routine checkup. They will usually detect what’s called a heart murmur while listening to your dog’s heart on a stethoscope. A heart murmur is caused by the turbulent blood flow in the heart that creates extra noise, also known as heart sound. As the heart disease worsens, the chordea tendineae (cords) connecting the valve to the left ventricle may rupture.  This complication can lead to pulmonary edema (a buildup of fluid in the lungs making it difficult to breathe). The mitral valve leaflets are now prolapsed which cause the leaflets to flail back into the left atrium when the ventricle contracts after each heartbeat.

Degenerative mitral valve disease may appear as early as 1-5 years of age although commonly detected around 10-11. More than 80% of small dogs under 15 pounds or under are diagnosed as having mitral valve disease.  The disease is most common In the King Charles Cavalier and the Dachshund breeds. Other breeds we see commonly affected are, Miniature poodles, Shih Tzu, Maltese, Chihuahua, Cocker Spaniels, Miniature Schnauzers, Whippets, and Pomeranians.

This disease can also be seen in some larger breeds and mixed breed dogs, although it is less common and most are typically less ill than small dogs. Some medium and large breeds are predisposed to heart disease, although not by an anomaly of the mitral valve, usually to cardiac muscle disease known as cardiomyopathy.  This accounts for 15-20% of medium and large breed dog’s heart disease.

MVD is a very common genetic disease.  It is also commonly observed that males are more frequently and more severely affected than females. The disease is progressive, gradually worsening over time, more or less rapidly depending on the individual.  The tricuspid valve is also affected in ⅓ of cases.  Medications are typically prescribed to relieve the work of the heart and to help resolve pulmonary edema. They are usually prescribed as early as possible in order to prolong your dog’s life to the maximum.  This treatment is often adjusted on a case-by-case basis through clinical, blood, ultrasound and echocardiograms checks by a board certified veterinary cardiologist.

At the onset of the disease, the heart performs physiological adaptation work called the compensatory phase, the disease at this stage is considered “dormant”.  When the adaptive capacities of the heart are exceeded, symptoms such as fatigue, cough, and fainting, (syncope) may begin to develop.  When these symptoms are present, the disease is now in its “decompensated phase”. Medicines are essential at this point and typically prescribed for life, unless mitral valve repair surgery is decided. Eighty five percent of dogs that had repair surgery have come off most if not all medications for extended periods of time or life. As this is a continuing progressive disease, the disease continues to advance even after surgery. Every progression is different with each case. Surgery has given a beautiful gift of time for all effected by this terrible disease.

Photo courtesy of The Pet Authority

American College of Veterinary Internal Medicine (ACVIM) Disease Staging System

Typically, the first sign of mitral degeneration is detected as a low grade heart murmur that increases over time based on many factors including heart muscle strength, age, chord rupture, or other complicating factors. Radiological examinations, echocardiograms, doppler ultrasounds, electrocardiographic, and blood tests (NT -proBNP and Troponin I) will allow a complete cardiac assessment to be carried out in order to classify the insufficiency in the heart.

Below are the ACVIM disease stages:

  • This staging system for MMVD describes 4 basic stages of heart disease and heart failure:

    • Stage A identifies dogs at high risk for developing heart disease but that currently have no identifiable structural disorder of the heart (eg, every Cavalier King Charles Spaniel or other predisposed breed without a heart murmur).

    • Stage B identifies dogs with structural heart disease (eg, the typical murmur of mitral valve regurgitation, accompanied by some typical valve pathology, is present), but that have never developed clinical signs caused by heart failure. In a change from the 2009 recommendations, strong evidence now supports initiating treatment to delay the onset of clinical signs of heart failure in a subset of stage B patients with more advanced cardiac morphologic changes (outlined below).

      • Stage B1 describes asymptomatic dogs that have no radiographic or echocardiographic evidence of cardiac remodeling in response to their MMVD, as well as those in which remodeling changes are present, but not severe enough to meet current clinical trial criteria that have been used to determine that initiating treatment is warranted (see specific criteria below).

      • Stage B2 refers to asymptomatic dogs that have more advanced mitral valve regurgitation that is hemodynamically severe and long-standing enough to have caused radiographic and echocardiographic findings of left atrial and ventricular enlargement that meet clinical trial criteria used to identify dogs that clearly should benefit from initiating pharmacologic treatment to delay the onset of heart failure (specific criteria detailed below).

    • Stage C denotes dogs with either current or past clinical signs of heart failure caused by MMVD. Because of important treatment differences between dogs with acute heart failure requiring hospital care and those in which heart failure can be treated on an outpatient basis, these issues have been addressed separately by the panel. It is important to note that some dogs presented with heart failure for the first time may have severe clinical signs requiring aggressive treatment (eg, with additional afterload reducers or temporary ventilatory assistance) that more typically would be reserved for those patients refractory to standard treatment (see Stage D below).

    • Stage D refers to dogs with end-stage MMVD, in which clinical signs of heart failure are refractory to standard treatment (defined later in this consensus statement). Such patients require advanced or specialized treatment strategies to remain clinically comfortable with their disease, and at some point, treatment efforts become futile without surgical repair of the valve. As with Stage C, the panel has distinguished between dogs in Stage D that require acute, hospital-based treatment and those that can be managed as outpatients.

Dogs diagnosed with MVD require a lifetime of medical follow-up with an update of the medical treatment plan as the disease progresses, each dog is usually treated on a case-by-case basis.  Dogs that have heart failure may suffer from fatigue, coughing, fainting, labored breathing, anorexia, and unfortunately eventual death from refractory pulmonary edema and/or cardiac arrest.

Mitral Valve Repair Surgery Example

Here is a surgery video of our founder Nate Estes’s dog Zoey Marie Estes in Japan undergoing her mitral valve repair surgery.