Canine Cardiology - Myxomatous Mitral Valve Disease (MMVD)

Myxomatous Mitral Valve Disease (MMVD) in dogs, also known as just Mitral Valve Disease (MVD), is a prevalent cardiovascular disorder affecting a large portion of the canine population, particularly small breed dogs as they age. This disease is characterized by the degeneration of the mitral valve, which separates the left atrium from the left ventricle in the heart. The failure of this valve results in the backflow of blood (mitral regurgitation) from the left ventricle to the left atrium, which can eventually lead to congestive heart failure (CHF).

CAUSE AND PREVALENCE
The exact etiology of MMVD remains unclear, although it is particularly common in older small breed dogs. The degeneration of the valve is a result of the accumulation of mucoid material, leading to the thickening and enlargement of the valve leaflets. Breeds predisposed to MMVD include Cavalier King Charles Spaniels, Dachshunds, and Poodles, among others.

SIGNS
Initially, MMVD is asymptomatic. However, as the disease progresses, dogs may exhibit a heart murmur, which is often the first detectable sign of this condition. Thoroughly ausculting (listening) to the heart is a part of every routine annual exam and exam at YVC and is critical in catching signs early.

Over time, as the regurgitation worsens, dogs may develop congestive heart failure. Signs associated with CHF include fatigue, increased sleeping respiratory rate (SRR), coughing (due to fluid in the lungs), difficulty breathing, and decreased exercise tolerance. The severity of clinical signs is often, but not always directly related to the amount of decreased blood flow occurring as a result of mitral regurgitation.

DIAGNOSIS
At YVC, diagnosis of MMVD starts with a thorough physical examination, including auscultation to detect a heart murmur.

Further diagnostic tests typically include chest radiographs to assess heart size and shape, and the presence of fluid in the lungs, blood and urine tests to evaluate overall health and organ function, an electrocardiogram (ECG) to measure the heart's electrical activity, and an echocardiogram (ultrasound of the heart) to evaluate the heart's contractions and measure the amount of blood pumped by the heart.

The amount of testing and the order is very case-dependent and your veterinarian here at YVC will coordinate with you on what the best course of action is for you and your pet.

TREATMENT AND MANAGEMENT
Treatment of MMVD aims at improving heart function and managing symptoms, particularly in the advanced stages associated with CHF.

Common medications may include diuretics like furosemide and spironolactone, which help remove excess fluid from the body, and drugs like Pimobendan that improve heart muscle strength.

Angiotensin-Converting Enzyme (ACE) inhibitors like enalapril and benazepril, and cardiac glycosides like digoxin, may also be used to manage symptoms and improve heart function.

Regular monitoring and follow-up are crucial for managing this condition long-term. Surgical replacement of the leaky mitral valve, a common practice in humans, is usually not feasible in dogs. Therefore, medical management remains the mainstay of treatment for canine MMVD.

LONG-TERM MANAGEMENT AND PROGNOSIS
The long-term outlook for dogs with MMVD varies greatly and is very case-dependent. With appropriate medical management, many dogs can live comfortably for some time.

The progression of MMVD can be slow, with months to years elapsing from the onset of a heart murmur to the development of CHF. Annual (or sometimes even more frequent) check-ups are critical, and prescribed medications can significantly contribute to a dog's quality of life and potentially slow the progression of MMVD and CHF.

MONITORING
An essential aspect of managing MMVD is regular monitoring of the dog's condition. Here at YVC, we believe Sleeping or Resting Respiratory Rate (SRR or RRR) is one of the single most powerful tools that we have, and it can be done by pet owners at home. Please see our article regarding this test specifically. Changes in this rate can indicate a worsening or improvement of their condition. We will typically also recommend routine follow-up examinations and diagnostic tests to assess the progression of the disease and the effectiveness of the treatment plan.


MMVD is a common yet serious condition in aging small breed dogs. Early diagnosis, regular monitoring, and appropriate medical management are crucial for prolonging a good quality of life for affected dogs. This is one of many reasons why we at YVC encourage our clients to maintain regular veterinary check-ups, especially as their dogs age, to catch and address any potential heart issues early.