Myxomatous Mitral Valve Degeneration (MMVD, Endocardiosis) in Dogs (NAVLE Notes)
Myxomatous mitral valve degeneration (MMVD), also known as endocardiosis, is a common degenerative heart disease in dogs, particularly small breeds. It leads to mitral valve insufficiency and can progress to congestive heart failure (CHF).
Classic Case
- Breeds: Cavalier King Charles Spaniel, Dachshund, Yorkshire Terrier, Chihuahua, Shih Tzu.
- Age: Middle-aged or older.
- Signs:
- Often asymptomatic initially.
- Exercise intolerance, cough.
- Left-sided apical murmur.
- +/- Palpable thrill in advanced cases.
Diagnosis
- Thoracic Radiography:
- May appear normal in early stages.
- Left atrial dilation and increased vertebral heart score.
- +/- Pulmonary vein dilation.
- +/- Left mainstem bronchus compression (may contribute to coughing).
- Echocardiography:
- Mitral Valve Regurgitation: Thickening of mitral valve leaflets.
- Varying degrees of secondary left ventricular dilation.
- +/- Left atrial dilation.
- Increased left atrial-to-aortic ratio in short-axis view may indicate significant left-sided enlargement.
Treatment
- Before CHF Onset:
- Pimobendan: Positive effects in dogs with moderate to severe left heart dilation, delaying progression to CHF.
- ACE Inhibitors: Benefit is debated, but often included in treatment.
- After CHF Onset:
- Diuretics: Furosemide, with or without spironolactone.
- ACE Inhibitors: Commonly used to decrease afterload.
- Pimobendan: Continued to support heart function.
- Exercise Restriction: To limit cardiac workload.
- Weight Loss: Advised if the dog is overweight to reduce cardiovascular strain.
Key Points
- Prognosis:
- Before CHF onset, prognosis ranges from guarded to good.
- After CHF onset, average life expectancy is approximately one year.
- New studies indicate that starting pimobendan when left atrial dilation is moderate to severe may delay CHF onset.
NAVLE-Style Practice Questions on Myxomatous Mitral Valve Degeneration
Question 1
A 9-year-old Cavalier King Charles Spaniel presents with a cough and exercise intolerance. On auscultation, a left-sided apical murmur is noted. Radiographs show mild left atrial dilation and a slightly elevated vertebral heart score. What is the most likely diagnosis?
- A) Dilated cardiomyopathy
- B) Myxomatous mitral valve degeneration
- C) Pulmonary hypertension
- D) Tricuspid valve disease
Correct Answer: B
Explanation: The breed, age, clinical signs, and findings of left atrial dilation and a left-sided murmur are classic for myxomatous mitral valve degeneration, especially common in small breeds.
Question 2
A dog with moderate left atrial dilation due to myxomatous mitral valve degeneration but no signs of CHF is presented for treatment. Which medication would be beneficial to delay CHF onset?
- A) Furosemide
- B) Pimobendan
- C) Atenolol
- D) Prednisone
Correct Answer: B
Explanation: Pimobendan has been shown to delay the onset of CHF in dogs with moderate to severe left heart dilation due to MMVD. Furosemide is typically reserved for CHF, and atenolol and prednisone are not indicated in this condition.
Question 3
A 10-year-old Dachshund with myxomatous mitral valve degeneration has developed CHF. What is an essential part of chronic management?
- A) High-sodium diet
- B) Daily corticosteroids
- C) ACE inhibitors and diuretics
- D) Increased exercise
Correct Answer: C
Explanation: Chronic CHF management in MMVD includes ACE inhibitors and diuretics to reduce fluid overload and cardiac workload. Sodium restriction and exercise limitation are also recommended.
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