Canis ISSN: 2398-2942

Heart: mitral valve degenerative disease

Synonym(s): Degenerative mitral valve disease (DMVD), mitral valve disease, endocardiosis, chronic valvular disease, myxomatous mitral valve degeneration (MMVD)

Contributor(s): Serena Brownlie, Mark Rishniw, Ruth Willis, Mark Oyama, Pedro Oliveira, Amara Estrada

Introduction

  • Myxomatous mitral valve degeneration (MMVD) is the most common acquired disease in dogs.
  • MMVD causes mitral regurgitation, heart enlargement, and can lead to left-sided congestive heart failure (CHF).
  • Cause: inherited predisposition in some breeds, ie Cavalier King Charles Spaniel, and Dachshunds. Toy and miniature Poodles, miniature Schnauzers, Pomeranians, Chihuahuas, Cocker Spaniels, Pekingese, Fox Terriers, Maltese and Boston Terriers are predisposed to MMVD. Cavalier King Charles Spaniels (CKCS) have the highest reported incidence of DVD with 56% over 4 years of age and 100% over 10 years of age affected in a US study.
  • Signs: left apical systolic murmur.
  • Diagnosis: presumptive: detection of the characteristic murmur in an adult small-breed dog; definitive: echocardiograph.
  • Treatment: for dogs who meet EPIC Stage B2 criteria (pimobendan) and Stage C or D (CHF).
  • Prognosis: the median time to development of CHF once a MMVD dog progresses to a Stage B2 is 1228 days (95% CI: 856-NA because stopped early). Patients typically remain asymptomatic during this time period. The median time from the first CHF episode to the first intensification of CHF treatment is 98 days (range 3-885 days). Median survival time after diagnosis of CHF is 281 days (range 3-885 days). Survival times tend to be shorter in large breed dogs and dogs with myocardial failure.
    Print off the owner factsheet on Mitral valve disease in dogs Mitral valve disease in dogs to give to your client.

Pathogenesis

Etiology

  • MMVD has been studied for a long time and while the underlying cause of it remains unknown, the pathology of the disease has been well described. Histologic changes in this disease show accumulation of the mucopolysaccharides hyaluronic acid and chondroitin sulfate.
  • Fibroblastic proliferation results in swirls and nodules in the expanded mucopolysaccharide matrix. The fibrosa layer degenerates with swelling, hyalinizination, and disintegration of the collagen bundles.
  • Gross lesions become more severe with time. The lesions begin as small discrete nodules at the margins of the valve leaflets. At this stage, the valve is typically competent. When the nodules enlarge they also start to coalesce, forming irregular opacities at the tips of the leaflets. These lesions enlarge further and tend to bulge up on the atrial surface. Calcification and hemorrhage can be seen in the body of the valve.
  • With these changes, the valve becomes grossly distorted by coalescing grayish-white nodules and plaques and becomes incompetent and leaks across the incompetent valve start to occur. The valve edges are contracted and appear rolled up.
  • Chordae tendineae also become thickened, irregular, and may be ruptured. As these changes continue to progress, so does the functional incompetence of the valve. Other structures comprising the mitral valve apparatus are primarily or secondarily affected.
    • The valve annulus becomes dilated secondary to atrial and ventricular dilation.
    • The left atrium becomes dilated due to an increase in left atrial pressure.
    • Jet lesions of the atrial endocardium occur due to the turbulent jet of MR disrupting the endothelium and leading to fibrosis.
    • The left ventricle becomes eccentrically hypertrophied due to volume overload.

Pathophysiology

  • During the initial stages of MMVD, although there is gross thickening of the mitral valve, the valve is competent and there are no hemodynamic changes. The leaflets may begin to prolapse, or bow backward, into the left atrium in systole; however, they remain competent.
  • As the degeneration progresses, the mitral valve and chordae tendineae continue to thicken, so that the leaflets no longer coapt properly. This leads to insufficiency across the valve, most commonly called mitral regurgitation (MR) when some of the blood from the left ventricle is pumped backwards into the left atrium instead of into the aorta in systole.
  • As MMVD progresses, the MR will progress and so the compensatory cardiac changes will attempt to maintain normal cardiac output. There will be progressive left atrial dilation and eccentric hypertrophy of the left ventricle and as long as the metabolic demands of the body are met, there will be no signs of heart failure.
  • Over time, while the cardiac compensation may maintain cardiac output at rest, it may be unable to do so with activity or stress. There will be inadequate perfusion to meet the increased metabolic demands of the body and the systemic compensatory mechanisms will become activated to maintain blood pressure. This likely begins to occur when the MR has become moderate to severe. The sympathetic nervous system and the renin-angiotensin-aldosterone system (RAAS) will be activated and lead to increases in preload and afterload.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Boswood A, Haggstrom J, Gordon S et al (2016) Effect of Pimobendan in Dogs with Preclinical Myxomatous Mitral Valve Disease and Cardiomegaly: The EPIC Study-A Randomized Clinical Trial.​ JVIM 30, 1765-1779 PubMed.
  • Ebisawa T, Ohta Y, Funayama M, Yamano S, Mizuno M, Mizuno T, Kasuya A, Sawada T, Lee J, Mizukoshi T, Uechi M (2013) Plasma atrial natriuretic peptide is an early diagnosis and disease severity marker of myxomatous mitral valve disease in dogs. Res Vet Sci 94 (3), 717-721 PubMed.
  • Mattin M, Boswood A, Church D, Brodbelt D (2013) Mitral valve disease study. Vet Rec 173 (21), 531-532 PubMed.
  • Atkins C E, Häggström J (2012) Pharmacologic management of myxomatous mitral valve disease in dogs. J Vet Cardiol 14 (1), 165-84 PubMed.
  • Borgarelli M, Buchanan J W (2012) Historical review, epidemiology and natural history of degenerative mitral valve disease. J Vet Cardiol 14 (1), 93-101 PubMed.
  • Borgarelli M, Crosara S, Lamb K, Savarino P, La Rosa G, Tarducci A, Haggstrom J (2012) Survival characteristics and prognostic variables of dogs with preclinical chronic degenerative mitral valve disease attributable to myxomatous degeneration. J Vet Intern Med 26 (1), 69-75 PubMed.
  • Chetboul V, Tissier R (2012) Echocardiographic assessment of canine degenerative mitral valve disease. J Vet Cardiol 14 (1), 127-48 PubMed.
  • Dillon A R, Dell'Italia L J, Tillson M, Killingsworth C, Denney T, Hathcock J, Botzman L (2012) Left ventricular remodeling in preclinical experimental mitral regurgitation of dogs. J Vet Cardiol 14 (1), 73-92 PubMed.
  • Fox P R (2012) Pathology of myxomatous mitral valve disease in the dog. J Vet Cardiol 14 (1), 103-26 PubMed.
  • Hezzell M J, Boswood A, Moonarmart W, Elliott J (2012) Selected echocardiographic variables change more rapidly in dogs that die from myxomatous mitral valve disease. J Vet Cardiol 14 (1), 269-279 PubMed.
  • Kellihan H B, Stepien R L (2012) Pulmonary hypertension in canine degenerative mitral valve disease. J Vet Cardiol 14 (1),149-64 PubMed.
  • Oyama M A (2012) Re: Radiographic heart size and its rate of increase as tests for the onset of congestive heart failure in Cavalier King Charles Spaniels with mitral valve regurgitation. J Vet Intern Med 26 (2), 227 PubMed.
  • Reynolds C A, Brown D C, Rush J E, Fox P R, Nguyenba T P, Lehmkuhl L B, Gordon S G, Kellihan H B, Stepien R L, Lefbom B K, Meier C K, Oyama M A (2012) Prediction of first onset of congestive heart failure in dogs with degenerative mitral valve disease: the PREDICT cohort study. J Vet Cardiol 14 (1), 193-202 PubMed.
  • Singh M K, Johnson L R, Kittleson M D, Pollard R E (2012) Bronchomalacia in dogs with myxomatous mitral valve degeneration. J Vet Intern Med 26 (2), 312-319 PubMed.
  • Uechi M, Mizukoshi T, Mizuno T, Mizuno M, Harada K, Ebisawa T, Takeuchi J, Sawada T, Uchida S, Shinoda A, Kasuya A, Endo M, Nishida M, Kono S, Fujiwara M, Nakamura T (2012) Mitral valve repair under cardiopulmonary bypass in small-breed dogs: 48 cases (2006-2009). J Am Vet Med Assoc 240 (10), 1194-201 PubMed.
  • Uechi M (2012) Mitral valve repair in dogs. J Vet Cardiol 14 (1), 185-192 PubMed.
  • Wolf J, Gerlach N, Weber K, Klima A, Wess G (2012) Lowered N-terminal pro-B-type natriuretic peptide levels in response to treatment predict survival in dogs with symptomatic mitral valve disease. J Vet Cardiol 14 (3), 399-408 PubMed.
  • Boswood A, Smith S, Patteson M (2011) Evaluation of pimobendan in dogs with cardiomegaly caused by preclinical mitral valve disease. Vet Rec 168 (8), 222 PubMed.
  • Lord P F, Hansson K, Carnabuci C, Kvart C, Häggström J (2011) Radiographic heart size and its rate of increase as tests for onset of congestive heart failure in Cavalier King Charles Spaniels with mitral valve regurgitation. J Vet Intern Med 25 (6), 1312-9 PubMed.
  • Bernay F, Bland J M, Häggström J, Baduel L, Combes B, Lopez A, Kaltsatos V (2010) Efficacy of spironolactone on survival in dogs with naturally occurring mitral regurgitation caused by myxomatous mitral valve disease. J Vet Intern Med 24 (2), 331-341 PubMed.
  • Borgarelli M, Haggstrom J (2010) Canine degenerative myxomatous mitral valve disease: natural history, clinical presentation and therapy. Vet Clin North Am Small Anim Pract 40 (4), 651-663 PubMed.
  • Boswood A (2010) Current use of pimobendan in canine patients with heart disease. Vet Clin North Am Small Anim Pract 40 (4), 571-580 PubMed.
  • Lord P, Hansson K, Kvart C, Häggström J (2010) Rate of change of heart size before congestive heart failure in dogs with mitral regurgitation. J Small Anim Pract 51 (4), 210-218 PubMed.
  • Moonarmart W, Boswood A, Luis Fuentes V, Brodbelt D, Souttar K, Elliott J (2010) N-terminal pro B-type natriuretic peptide and left ventricular diameter independently predict mortality in dogs with mitral valve disease. J Small Anim Pract 51 (2), 84-96 PubMed.
  • Häggström J et al (2008) Effect of pimobendan or benazepril hydrochloride​ on survival times in dogs with congestive heart failure caused by naturally occurring myxomatous mitral valve disease: the QUEST study. JVIM 22, 1124-1135 PubMed
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  • Kvart C et al (2002) Efficacy of enalapril for prevention of congestive heart failure in dogs with myxomatous valve disease and asymptomatic mitral regurgitation. JVIM 16 (1), 80-88 PubMed.
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  • The COVE Study Group (1995) Controlled clinical evaluation of enalapril in dogs with heart failure - results of the cooperative veterinary enalapril study group. JVIM 9 (4), 243-252 PubMed.
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Other sources of information

  • Smith P J, French A et al (2002) Long term efficacy and safety of pimobendan in slight-to-moderate heart failure caused by myxomatous mitral valve disease in dogsVCS Proceedings, November 2002. Loughborough.
  • Kittleson M & Kienle R (1998 ) Myxomatous atrioventricular valve degeneration. In: Small Animal Cardiovascular Medicine. 1st edition. Eds: M Kittleson and R Kienle. Mosby, St Louis pp 297-318.


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