MMVD, the ACVIM Guidelines, and You: What Clinicians Need to Know

As a veterinary professional, canine heart disease is a problem that you will observe commonly in general practice. Myxomatous mitral valve disease is the most prevalent type of heart disease identified in dogs worldwide, representing three-quarters of all cases of heart disease. But many clinicians aren’t confident with MMVD, even despite the ACVIM guidelines. From predispositions to causes, ACVIM staging, to recommendations regarding treatment, read below to help your clients help their dogs.

What is MMVD?

Myxomatous mitral valve disease occurs when degenerative changes to the left atrioventricular valve (mitral valve) accumulate and affect the normal function of the valve. These changes in both collagen content and intercellular arrangement can be observed in all parts of the valve, including the leaflets and chordae tendineae. Extracellular matrix dysregulation seems to be the driving force behind the changes, leading to degradation of collagen and elastin that outpaces the body’s ability to replace it. Over time, the deformation of the valve components leads to valve leakage (regurgitation), increased work for the heart, and eventually, to heart failure. Most dogs demonstrate signs of valve leakage in the form of a heart murmur for several years before heart failure occurs. In many dogs, there is likely a genetic component, although the exact cause has not been determined. Male dogs are 1.5 times more likely to develop MMVD with smaller dogs (<20kg) being predominantly affected. Certain breeds, such as Cavalier King Charles Spaniels, are genetically predisposed to development of MMVD at an early age but generally do not progress to heart failure more quickly than other breeds.

What Does the ACVIM Consensus Statement Have to do with General Practitioners?

With our patients living longer lives, it is likely we will continue to see increasing numbers of dogs with MMVD in our practices. Many clients cannot or will not seek specialty care for their pets when heart disease becomes apparent. As the family veterinary clinic, it is often up to you to treat heart disease in the absence of specialty input. To assist with this crucial responsibility, the ACVIM released a consensus statement detailing the clinically relevant stages of heart disease in dogs in 2009 , with an updated online statement in 2019 . This is known as the ‘ACVIM guidelines’. Based on recent studies , many veterinarians either do not know the stages, or even when aware, do not use the advice in the ACVIM guidelines. With potentially years between the first incidence of heart murmur and the onset of heart failure, understanding of the ACVIM stages of heart disease and the current treatment recommendations for each stage offers primary care veterinarians an opportunity to recognize which dogs are at higher risk for developing heart failure. Staging heart disease, and familiarity with the ACVIM recommendations also provides information regarding interventions that, when implemented at the appropriate stage, can potentially reduce the morbidity associated with this very common form of heart disease.

The Clinical Relevance of ACVIM Cardiac Staging in General Practice

Let’s take a look at the ACVIM guidelines and the stages of MMVD they describe:

Stage A:

Stage A is a patient who is known to have a genetic predisposition or is at higher risk for MMVD, but does not have either a heart murmur or any clinical signs. A general yearly check up, with routine auscultation by a veterinarian, may be all that is needed. No medical or dietary alterations are needed at this stage. New murmurs automatically place the dog in Stage B, with additional testing recommended, while clinical signs of heart failure place the pet in a later stage.

Stage B:

Stage B is identified as a patient who has a typical MMVD heart murmur, but no clinical signs of heart failure, either now or in the past. Dogs in Stage B require some additional considerations as well as diagnostics beyond auscultation to fully assign a sub-stage. Radiography is readily available in many general veterinary clinics and the value of a baseline record of the appearance of the thorax and cardiac silhouette when the dog is asymptomatic is indispensable; often these pets will have tracheal or other lung pathology as they age, and having a reference from before clinical signs of heart failure can help differentiate from many other respiratory conditions in the future. Echocardiography, ideally from an experienced echocardiographer, can refine the diagnosis further, definitively identify the cause of the murmur, as well as inspect for any other pathology that may be of concern now or in the future. Echocardiography is the preferred, gold-standard diagnostic test to differentiate the subtypes of Stage B in dogs.

Stage B1:

If no heart changes are noted on imaging, the patient is placed in Stage B1. Since there are no clinical signs and no conspicuous cardiac changes, it is difficult to assess success or failure of any treatment instigated at this stage; heart failure is not certain, and medication or dietary changes are not warranted.

Stage B2:

If radiographic changes are present, such as alterations in cardiac silhouette, or if any chamber enlargement is observed on echocardiography, the patient is placed in Stage B2. The ACVIM strongly recommends beginning medications at this stage to stabilize the patient hemodynamically, as well as making a general effort with diet to control excess sodium intake and maintain ideal body condition.

Stage C:

Once a dog has shown signs associated with heart failure, they are classified as Stage C, even if their signs have resolved with or without medical management. Dogs in Stage C have a heart murmur of at least grade 3/6, clinical signs associated with heart failure, including cough, exercise intolerance, or dyspnea, and often weight loss. Dogs at higher risk for MMVD are also at higher risk for other respiratory pathology, such as chronic tracheal collapse, chronic or allergic bronchitis, and cardiac tumor. Serial radiography, especially when previous baseline thoracic radiographs are available for comparison, can be useful in determining if heart disease is causing the clinical signs. However, echocardiography remains the gold standard to differentiate the cause of coughing in dogs. In general, dogs in Stage C are able to be managed long-term on an outpatient basis, even dogs who presented with acute heart failure that initially needed extensive and emergent care on an in-patient basis in order to control their disease. A minimum database evaluating CBC, renal and hepatic function, electrolytes, and urinalysis should be performed prior to initiating treatment; older dogs at risk for MMVD are also at risk for other diseases.

Stage D

Dogs with end-stage heart disease are placed in Stage D. These dogs are often refractory to standard care and often require advanced or specialty care to manage their disease. They may require increased doses of diuretics to control the clinical signs of heart failure, as well as antiarrhythmic medications, oxygen supplementation, cavitary centesis, and possibly increases in doses of other medications as well.

Treatment of Myxomatous Mitral Valve Disease

There exists myriad recommendations for treatment at various stages of heart disease in dogs, with even more guidelines for monitoring progression of disease and treatment success or failure. Each choice made by a clinician will depend on many parameters; pet temperament, response to previous therapies, owner wishes, owner finances, and availability of advanced care are just a few variables that must be taken into account when deciding on a course of treatment. A reliable rubric for medical management and therapeutic monitoring are outside of the scope of this article, but treatment recommendations are outlined in the ACVIM guidelines. Although this 2023 study reported a low utilization of the ACVIM consensus statment, it did suggest that this may be because clinicians needed further training. Many options for advanced cardiology training for general clinicians exist, including the highly regarded Improve Veterinary Education cardiology certificate , which can help all veterinary professionals feel more confident in their ability to make clinical decisions and help pet owners choose the best care for their pets.

Works Cited

Atkins, C., Bonagura, J., Ettinger, S., Fox, P., Gordon, S., Haggstrom, J., Hamlin, R., Keene, B., Luis-Fuentes, V. and Stepien, R. (2009), Guidelines for the Diagnosis and Treatment of Canine Chronic Valvular Heart Disease. Journal of Veterinary Internal Medicine, 23: 1142-1150. https://doi.org/10.1111/j.1939-1676.2009.0392.x Keene BW, Atkins CE, Bonagura JD, et al. ACVIM consensus guidelines for the diagnosis and treatment of myxomatous mitral valve disease in dogs. J Vet Intern Med . 2019; 33: 1127–1140. https://doi.org/10.1111/jvim.15488 van Staveren, M.D.B.; Muis, E.; Szatmári, V. Self-Reported Utilization of International Guidelines for Staging Dogs with Myxomatous Mitral Valve Degeneration: A Survey among Veterinary Practitioners. Vet. Sci. 2023, 10, 687. https://doi.org/10.3390/vetsci10120687

Author

The Improve Team