Introduction
- Tends to affects middle-aged and older dogs.
- Primarily occurs in the mitral valve.
- Results in slowly developing heart failure
- The valves become swollen and misshapen
- The heart cannot pump blood effectively to the circulation from the left ventricle.
- Blood passes back into the left atrium, compromising the filling from the pulmonary vein.
- Leads to back pressure on the pulmonary capillaries.
- Oedema forms in the lungs, and can be heard as moist sounds on auscultation.
- Reduces the oxygenation of blood leading to exercise intolerance.
- Leads to back pressure on the pulmonary capillaries.
- Failure of the left side eventually compromises the function of the right side.
- There is pooling of blood in the venous system i.e. in the liver.
- Blood passes back into the left atrium, compromising the filling from the pulmonary vein.
- The heart cannot pump blood effectively to the circulation from the left ventricle.
a.k.a. myxomatous mitral valve disease, mitral insufficiency, mitral regurgitation, chronic valvular disease
- Common lesion in heart valve (dog)
- Most often in the mitral valve
- Rare in cats
Signalment
- Age: Middle Age to Old dogs
- Sex: Males
- Genetics & Predisposed Breeds: Most common in smaller breeds (Chihuahua, Boston Terrier, Poodle, Pomeranian); Large Breeds (German Shepherd, Collies)
Description
Valvular insufficiency due to thickening and shortening of the valve leaflets. Consequently, during systole a small stream of blood passes back into the left atrium causing a white jet lesion where the blood contacts the atrial wall and atrial dilation. Advanced cases progress to left sided (congestive) heart failure and then to concurrent right sided heart failure.
Diagnosis
Clinical Signs
Signs depend on stage of disease:
-Coughing
-Syncope
-Weight loss
-Pale or cyanotic mucus membranes
-Prolonged capillary refill time
-Left-sided heart failure signs:
- exercise intolerance
- weakness
- dyspnoea
- inappetance
- lethargy
-Right-sided heart failure signs:
- hepatomegaly
- jugular pulses & distension
- pleural effusion
- ascites
- peripheral edema
Physical Exam
-Incidental finding: systolic click heard in asymptomatic animals
-Murmur over the left heart apex
-Snaps, crackles, pops heard if pulmonary edema is present
-Muffled heart sounds in the presence of pleural/pericardial fluid
Radiography
-Left sided heart enlargement
-(+/-) Left atrial enlargement (DV view appears at 2-3 o'clock position)
-(+/-) Left ventricular enlargement
-(+/-) Dorsal displacement of trachea
-(+/-) Bronchial compression
-Pulmonary venous congestion and/or edema
-(+/-) Right-sided signs (distended caudal vena cava, ascites, pleural effusion, heptaomegaly)
Electrocardiography (ECG)
-Left atrial enlargement pattern
-Left ventricular enlargement pattern
-Rhythm disturbances (supraventricular arrhythmias: atrial premature complexes, atrial tachycardia, and ventricular rhythm disturbances)
Echocardiography
-Irregularities of the valves affected (e.g. thickening, shortening, and/or prolapse of the valve leaflets)
-Abnormal valve movements & valve regurgitation
-Left atrial enlargement (wide P wave)
-Left ventricular dilation (tall R wave, wide QRS complex)
Early Stage of disease
- Normal to increased fractional shortening of the myocardium
Later Stage of disease
- Decreased fractional shortening of the myocardium
Treatment
- Left-sided heart failure treatment given at the onset of clinical signs.
- Right-sided heart failure treatment given at the onset of clinical signs.
- Symptomatic treatments are also given if clinical signs persist while the animal is on heart failure medications.
Complications
- Arrhythmias
- Bronchial Compression
- Ruptured Chordae Tendineae
- Atrial Rupture
Prognosis
-Asymptomatic patients may live for many years.
-Some patients remain stable for years on heart failure medications
Valvular Endocardiosis
Incidence:
The most common cardiovascular lesion in dogs. In dogs over 9 years old 97% show lesions, of which approximatley 40% are clinically significant.
Often found at post mortem as an incidental age related change.
Aetiology is not currently known but breeds affected include chondrodystrophoid breeds E.g. Pomeranian. Males show a significantly higher prevalence of disease than females.
Potential genetic influence based on connective tissue degeneration. The disease appears similar to prolapsed mitral valve syndrome in humans which is associated with abnormalities in collagen metabolism.
Pathology:
The pathological lesion occurs when collagen in the fibrosa layer of the valve leaflet degenerates and loose fibrelastic tissue and glycosaminoglycans are laid down in the spongiosa layer. This is mucoid or myxomatous degeneration. Endocardiosis is a sterile degenerative disease so no inflammatory infiltrate will be present, perhaps only a few chronic inflammatory cells E.g. lymphocytes. The valve leaflet becomes thickened, the edges often rolling in on themselves. The lesions progress from small nodular areas to larger plaques to make the valve incompetent. Large lesions result in distortion of the valve leaflets and potentially rupture of the chordae tendinae.
In most cases the mitral valve is affected, the tricuspd valve is less commonly involved and the semilunar valves even less commonly involved. Incompetent valves allow mitral regurgitation and left atrial dilation. The regurgitant jet applies damaging forces on the atrial endocardium which may result in endocardial mineralisation and in extreme cases may facilitate left atrial rupture and haemopericardium.
Cinical Signs:
The eventual sequale of endocardiosis is left sided heart failure. The resultant increase in pressure within the pulmonary circulation will be seen as pulmonary oedema.
The enlarged left atrium compresses the left main stem bronchus inducing a soft, moist cardiac cough. A cough is usually the first presenting sign noticed by the owner. Exercise intolerance and dyspnoea may also be evident.
A harsh pansystolic murmur will often be evident, more intense over the left heart apex. A mid-systolic click may indicate the prolapse of AV-valves into the atria. The left atrium enlargement will be clearly visible on radiographs and is identifiable on ECG.
Complications:
Further to the left sided heart failure the heart may not be able to adequately perfuse the coronary circulation resulting in focal myocardial necrosis and then fibrosis. This will impair conduction within the myocardium and potentially induce arrhythmias and further heart failure. In these cases syncope may be seen due to the arrhythmia.