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A general practitioner's approach to myxomatous mitral valve disease
Veterinarians can do a lot to treat this cardiac condition in their clinics by following the most updated clinical evidence.
Myxomatous mitral valve disease (MMVD) is the most common heart disease in dogs. The good news for pet owners and veterinarians is that this is a slowly progressive degenerative disease. But "if we don't catch this or get these dogs on the right medications for the stage they're in, it can be devastating,” said Natalie Marks DVM, CVJ, while presenting a session about practical approach to management of MMVD for general practitioners at the 2023 Fetch dvm360 conference in Charlotte, North Carolina.1
Communicating with clients
Communicating the underlying disease process to clients can be challenging. "Many of our pet parents think of heart disease like in humans," said Marks. In truth, humans most often get coronary artery disease leading to heart attacks. Many clients have either personally experienced this disease or know someone who has, which can influence their response to finding out their pet has heart disease. Marks encouraged veterinarians to help clients distinguish canine heart disease as a different disease process so that clients can come into the conversation about diagnostics and management with an open mind.1
Additionally, Marks recommended providing clients with information in multiple ways as they sometimes forget a large amount of the information provided during their appointment. Providing handouts, links to educational videos, and written medication instructions can improve client understanding and compliance.1
The 2019 ACVIM guidelines2 presented an updated staging system for MMVD:
- Stage A: Patients at higher risk for MMVD, such as Cavalier King Charles spaniels, but that have not yet developed clinical signs of disease.
- Stage B1: Patients with a heart murmur who are asymptomatic and do not have significant heart enlargement.
- Stage B2: Patients with a heart murmur >Grade III/IV who do not have clinical signs of heart failure. They have significant cardiac enlargement as determined by echocardiogram or a radiographic vertebral heart score (VHS) of >10.5 with echocardiogram or >11.5 without echocardiogram.
- Stage C: Patients with current heart failure or a history of heart failure.
- Stage D: Patients with refractory heart failure.
"In an ideal world, all mitral valve disease patients would be staged," shared Marks. However, she reminded veterinarians to remain cognizant of client finances. When money is tight, diagnostics that are the most likely to change the treatment course should be prioritized. Although echocardiogram is the gold standard diagnostic test to distinguish between stages B1 and B2, the staging can also be done based on radiographs. Staging is important to guide treatment and monitoring.1
The GP approach to MMVD
Marks suggested the acronym HEART to guide GPs in the diagnosis and treatment of MMVD.1
Marks noted that a good history is essential to raising the clinicians index of suspicion for heart failure. MMVD patients "don't all come in coughing or with auscultation changes," she said. Unexplained weight loss, decreased appetite or changes in eating patterns, behavior changes, exercise intolerance, and change in breathing can all be signs of MMVD. A thorough dietary history should also be collected.
A thorough physical examination is also essential. Listen carefully to the heart for murmurs and arrhythmias. Palpate the femoral pulses during auscultation to evaluate for pulse deficits. Watch the respiratory pattern and auscultate the lungs carefully. Distinguishing between respiratory and cardiac disease is important though it can be tricky at times. Body condition score (BCS) and heart rate are 2 findings that can be helpful in distinguishing between respiratory and cardiac disease. BCS tends to be normal to decreased in heart disease due to cardiac cachexia but normal to increased with respiratory disease, Marks noted. Heart rates tend to be increased in the presence of heart disease and normal to decreased with pulmonary disease.
A: Analyze BW/BP/ECG
Diagnostic testing helps to rule out extracardiac disease. A complete blood count, chemistry panel with electrolytes, heartworm test, and blood pressure should be performed. "Electrocardiograms (ECG) are not necessarily essential in a patient without an arrhythmia," said Marks. However, for patients with tachycardia, bradycardia, arrhythmias, pulse deficits, or a history of syncope, ECGs should be a priority.
Thoracic imaging is a powerful tool that helps the general practitioner in determining the diagnosis and treatment of MMVD. Cardiac enlargement, measured by a VHS, is a key component of radiographic evaluation. Additional key findings include size of pulmonary vasculature and the caudal vena cava and signs of congestive heart failure, Additionally, radiographs help to exclude concurrent respiratory disease.
The disease stage guides treatment choices2:
Patients in stage A and B1 should have close monitoring but do not require dietary changes or pharmacologic therapy.
Patients in stage B2 should be started on pimobendan, which can delay the onset of heart failure based on results of the EPIC study.3 A salt restricted diet can be considered.
Patients in stages C and D should be treated with quadruple therapy, which includes furosemide, an ACE-inhibitor, pimobendan, and spironolactone. A salt restricted diet is recommended.
Understanding quadruple therapy
Historically, heart failure has been treated with a combination of furosemide, an ACE-inhibitor, and pimobendan. However, loop diuretics like furosemide activate the renin-angiotensin-aldosterone system (RAAS). In the short term, RAAS activation is beneficial to the body, but chronic activation and high levels of aldosterone lead to numerous detrimental sequalae, including excess sodium retention, decreased heart rate variability, decreased baroreceptor sensitivity, arrhythmias, and vascular inflammation.4 RAAS activation can be blocked with a combination of benazepril and spironolactone.5
Marks noted that the BESST study5 showed there was a real-world difference seen in going from triple to quadruple therapy. The BESST study is one of the largest and longest canine cardiac studies to date. Dogs receiving the spironolactone and benazepril combination had a longer time to reach their cardiac endpoint, which was defined as death, worsening pulmonary edema, or development of ascites. “For clients, any time that is quality time is important,” Marks noted. The addition of spironolactone increases both quality and quantity of life in patients with heart failure due to MMVD.
Poor adherence is “the No. 1 reason our patients don’t do well in many disease,” said Marks. Common barriers to medication adherence include palatability and frequency of administration. Asking clients to give 4 daily medications to their dog for months or even years of therapy is a lot to ask. Marks recommends prescribing Cardalis, a once daily, highly palatable chew that contains 2 of the 4 medications of quadruple therapy: benazepril and spironolactone.1
Take home points
With a careful history, physical examination, and in-house diagnostics such as radiographs, general practitioners can successfully stage and manage myxomatous mitral valve disease. Medical management should be started in stage B2 with pimobendan. Once patients reach heart failure, quadruple therapy should be instituted to provide the best possible patient outcomes.
- Marks N. Practical canine cardiology—let’s get to the heart of the matter. Presented at: Fetch dvm360 Conference; Charlotte, NC. March 25, 2023.
- 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(3):1127-1140. https://doi.org/10.1111/jvim.15488
- Boswood A, Haggstrom J, Gordon SG, et al. Effect of pimobendan in dogs with preclinical myxomatous mitral valve disease and cardiomegaly: The EPIC study—A randomized clinical trial. J Vet Intern Med 2016;30(6):1765-1779. https://doi.org/10.1111/jvim.14586
- Ames MK, Atkins CE, Pitt B. The renin-angiotensin-aldosterone system and its suppression. J Vet Intern Med 2019;33(2):363-382. https://doi.org/10.1111/jvim.15454
- Coffman M, Guillot E, Blondel T, et al. Clinical efficacy of a benazepril and spironolactone combination in dogs with congestive heart failure due to myxomatous mitral valve disease: The BEnazepril Spironolactone STudy (BESST). J Vet Intern Med 2021;35(4):1673-1687. https://doi.org/10.1111/jvim.16155