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Canine Mitral Valve Degenerative Disease (Part 2)​

Canine Mitral Valve Degenerative Disease (Part 2)

01. Overview

This article focuses on the clinical examination methods for mitral valve diseases in dogs. While mitral regurgitation is common in canine mitral valve degenerative disease, mitral stenosis may also occur, either alone or concurrently. The key distinction between the two lies in the timing of occurrence: mitral regurgitation develops during ventricular systole, whereas mitral stenosis occurs during ventricular diastole.

02. Clinical Examination

1. Mitral Stenosis (MS)

  • Left Atrial Compensation Stage (Early Phase)
Dogs show no obvious clinical symptoms. Diagnosis of early-stage morphological changes of the mitral valve can be achieved via high-resolution echocardiography (recommended device: [PT60] ultrasound).
  • Left Atrial Decompensation Stage (Middle Phase)
Left atrial dilatation and elevated pressure lead to pulmonary congestion, manifesting as dyspnea and coughing in dogs. These signs can be further confirmed by combining echocardiographic measurements (e.g., left atrial dimension assessed via BPU100 ultrasound) with clinical observations.
Progressive Stage

Persistent pulmonary congestion (leading to pulmonary hypertension) progresses to right ventricular dilatation, accompanied by ascites and limb edema. At this stage, comprehensive assessment of cardiac chamber dimensions and hemodynamic parameters via BPU60C ultrasound is recommended for treatment planning.

  • Correlation with Staging
Clinical symptoms typically emerge starting from Stage B2: Initially, dogs present with nocturnal coughing, which gradually progresses to persistent coughing (day and night)—this is often misdiagnosed as respiratory tract infection. At this stage, atrial fibrillation may occur, increasing the risk of thrombosis; delayed treatment can result in sudden death of the dog. For timely staging evaluation, echocardiographic assessment (e.g., using [PT50] ultrasound) is recommended to monitor disease progression.
  • Echocardiographic Findings
Echocardiography is the gold standard for diagnosing mitral stenosis (recommended devices: PT60, BPU100 ultrasound).
Two-dimensional ultrasound: Valvular thickening with increased echo intensity, restricted valvular opening; in the left ventricular long-axis view, the anterior leaflet shows a domed morphology during diastole; in the left ventricular short-axis view (at the mitral valve level), the valvular orifice presents a “fish-mouth” shape during diastole.
Color Doppler: A narrow, high-velocity red vortex flow is visible on the left ventricular side of the mitral valve orifice during diastole (assessable via BPU60C ultrasound for flow velocity quantification).
  • Electrocardiographic Features

“Mitral P wave”: A P-wave duration > 0.05 seconds indicates left atrial enlargement.

QRS complex axis deviation to the right; the main waves in leads Ⅰ and Ⅱ show a “peak-to-peak” pattern, suggesting right ventricular enlargement.

Atrial fibrillation may occur in severe cases (to be confirmed by combined echocardiographic assessment with PT50 ultrasound).

Radiographic Findings
A “pear-shaped” cardiac silhouette, referred to as a “mitral valve-type heart”.

2. Mitral Regurgitation (MR)

Pathophysiological Process
Mitral regurgitation → left atrial and left ventricular hypertrophy → left heart failure → right heart failure.
Echocardiographic Findings
Recommended ultrasound devices: BPU60C, PT50.
Two-dimensional ultrasound: Mitral leaflet thickening, chordae tendineae thickening, no significant restriction of anterior mitral leaflet movement, increased echo intensity, and valvular prolapse; obvious regurgitation can be observed in some cases.
Color Doppler: The gold standard for detecting regurgitation; a multicolored (predominantly blue) regurgitant jet flows from the mitral valve defect into the left atrium during systole. The severity of regurgitation can be assessed by comparison with the left atrial size.
Electrocardiographic Features
Sinus P-wave widening with a biphasic pattern (P-wave duration > 0.05 seconds) indicates left atrial enlargement.
QRS complex axis deviation to the left; main waves in leads Ⅰ and Ⅱ show an “opposite-to-opposite” pattern, suggesting left ventricular enlargement.
Atrial fibrillation may occur in severe cases.
Radiographic Findings
“Spherical” heart.

3. Mitral Stenosis Combined with Regurgitation

Etiology
Infective endocarditis.
Congenital heart disease, etc.
Treatment Principles
Infective cases: Antibiotic therapy (e.g., ceftriaxone sodium, penicillin sodium) is recommended.
Congenital cases: Targeted medication is administered in the absence of surgical intervention (specific treatment methods will be introduced in subsequent articles).
Echocardiographic Findings
Combined manifestations of mitral regurgitation and mitral stenosis. For infective cases, common findings include leaflet, chordae tendineae, and papillary muscle deformation, as well as valvular vegetations (detectable via BPU50 ultrasound for precise lesion localization).

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