Diagnosis

Most cases of CMVI present for some other reason and an incidental heart murmur typical of MR is detected on examination. Those dogs that present for congestive heart failure due to CMVI usually present with a complaint of a cough. Some dogs present with a complaint of syncope.

• In this aged cohort of patients, causes for cough include:
  • CMVI with congestive heart failure and pulmonary edema
  • Compression of the left mainstem bronchus due to left atrial enlargement from CMVI
  • Chronic small airway disease (including collapsing trachea) – potentially the most common cause of cough in this group of dogs
• Our job is to differentiate between these causes of cough

Physical Examination uncovers:

• A systolic murmur typical of MR (see above)
  • In the early stages of CMVI this is the only finding on physical exam.
• A systolic click may be present.
• An arrhythmia may be present.
• Pulmonary crackles (or snapping or popping sounds) on auscultation may be indicative of pulmonary edema or small airway disease.
• If heart failure is present, other signs may also be observed (see Clinical Evaluation of Heart Disease).

Radiology may uncover:

• Left atrial enlargement
• Left ventricular enlargement
• Splitting of the main bronchi on lateral view and compression of the left mainstem bronchus
• Peribronchial pattern – the finding of peribronchial changes may indicate either pulmonary interstitial edema or small airway disease. On the basis of the lung pattern alone one may not be able to distinguish between these disorders. If pulmonary venous distension is absent, the peribronchial changes likely reflect small airway disease
• Evidence of heart failure in the case of severe advanced disease
  • Pulmonary venous distension, pulmonary edema (peribronchial, interstitial, or alveolar changes, depending on severity) – See Thoracic Radiographic Tutorial
  • If acute chordal rupture has occurred, severe pulmonary edema may occur without substantive left atrial or left ventricular enlargement
• If pulmonary artery hypertension is present then pulmonary artery dilation may be observed along with right ventricular and right atrial enlargement.

Electrocardiography may uncover:

• Left atrial enlargement.
• Supraventricular arrhythmia.
• Atrial fibrillation.
• Left ventricular enlargement.
• May be normal. This is typical in the early stages of CMVI.

Blood work:

• Often normal.
• May see signs of reduced cardiac output if heart failure is present
  • Increased urea and/or creatinine (reduced renal perfusion)
  • Elevated lactate
  • Decreased venous oxygen tension (PvO2)
  • Reduced serum sodium
• Brain natriuretic peptide (NT-proBNP) levels increase with increasing severity of CMVI in dogs. NT-proBNP levels may also be predictive of prognosis in humans and dogs with mitral valve disease. See BNP as a Potentially Useful Test in the Clinical Evaluation of Heart Disease section.

Echocardiography:

• Thickened mitral valve leaflets often with prolapse and/or flail of a segment of leaflet. Ruptured chordae may be visualized.
• Doppler detects MR + TR.
• Left atrial enlargement.
• Left ventricular enlargement.
• In the presence of MR, the indices of contractility are falsely elevated. This renders these measures of limited value to assess reduced systolic function. There is evidence to suggest that systolic function is in fact reduced when congestive heart failure develops, though it is more problematic to quantify than in other disorders.
• Larger breed dogs with CMVI are more likely to demonstrate reduced contractility.
• Doppler echocardiography may detect pulmonary artery hypertension along with right atrial and ventricular enlargement.

Summary:

• Left atrial enlargement with compression of the left main bronchus is frequently responsible for cough.
• There is no evidence of heart failure in the early and mid stages of the disorder.
• This is, however, a progressive disorder, and eventually heart failure with pulmonary congestion may develop.
• Acute exacerbation can develop due to rupture of a chordae with severe acute pulmonary edema.
• Left atrial rupture with sudden death rarely occurs.
• Supraventricular arrhythmias may develop, especially atrial fibrillation.
• Ventricular arrhythmias may develop. This could lead to sudden death.
• Pulmonary hypertension can develop, usually in chronic cases.
• These geriatric dogs usually have some degree of chronic small airway disease.