Mitral valve
dysplasia is congenital defect affecting both the dog and the cat.
This abnormality is very common in cats; in fact it may be the
most common congenital defect in felines. In dogs, it is usually seen in
large breed dogs such as the Great Dane, Rottweiler, Bull terrier, and
German Shepherd. Rolling,
shortening, notching, and/or thickening of the valve leaflets are a few
of the characteristics of mitral valve dysplasia.
Others include leaflet adhesion to the septal wall, thickening or
fusion of the chordae tendinae, and malformed papillary muscles.
This lesion typically produces regurgitant blood flow
across the valve plain identical to that produced by mitral valve
degeneration. The lesion
usually auscultates as a holosystolic murmur loudest on the left side at
the level of the 5th intercostal space.
Hemodynamically the lesion produces a volume overload of the left
atrium and ventricle, which produces eccentric hypertrophy. If the lesion is not of significant size and the
regurgitation is minimal, most dogs will be asymptomatic.
With larger lesions, symptoms may include exercise intolerance,
coughing, and/or signs of left-sided congestive heart failure.
In larger dogs, mitral valve dysplasia can easily be confused
with primary dilated cardiomyopathy. With both diseases, affected dogs will present with similar
clinical signs and diagnostic findings than that seen with myocardial
failure. The use of
echocardiography allows for differentiation between the two heart
problems. Three main
criteria distinguish mitral valve dysplasia from DCM on
echocardiography: 1) a large mitral jet regurgitation (accompanied by a
loud murmur), 2) a fractional shortening greater than 20%, and 3) left
ventricular free wall failure with a normal functioning septum.
Other diagnostic tests should include radiographs and
ECG. Initial radiographs
also functions as a baseline for treatment management and disease
progression. Radiographs
are not as sensitive of an indicator of change as is echocardiography,
but moderate changes can be observed on follow-up radiographs and
corrections in treatment can be made accordingly.
Common radiographic presentations include left atrial and
ventricular enlargement and perihilar edema (not seen on ultrasound).
An ECG also functions as a baseline for therapy success and
progression. Common
findings include wide P waves, tall R wave in lead II and aVF.
If CHF is present, it is not uncommon to see atrial fibrillation.
Tricuspid valve dysplasia is also a congenital defect that commonly
affects both cats and dogs. While
Labrador retrievers are over represented, other breeds commonly affected
include the Old English Sheepdog, Great Dane, German Shepard, and Irish
setter.
Anatomically, dysplasia of the tricuspid vale can
present in numerous ways. Abnormalities
include short or absent chordae tendinae, which results in attachment of
the leaflets to the papillary muscles and shortened, irregular valves
and leaflets. Most murmurs
associated with this abnormality are present at birth but most animals
are asymptomatic until 2 years of age.
The most common clinical presentation secondary to
tricuspid valve dysplasia is ascites.
This is the result of a marked regurgitation leading to right
atrial enlargement, which leads to volume overload and subsequent right
ventricular dilation. Ventricular
dilation worsens the regurgitation to the right atrium causing further
dilation, which in turn further overloads the right ventricle, setting
up a detrimental cycle. The
high right-sided volume overload increases caudal vena cava pressures,
which causes increased hydrostatic pressure at the level of the
capillary beds causing leakage and ascites.
Other clinical signs include syncope and exercise intolerance
attributable to decrease blood return to the left heart.
This is the most common cause of true right-sided congestive
heart failure leading to ascites in cats.
Echocardiography is the cornerstone of diagnostics.
As with mitral valve dysplasia, it helps define the lesion,
assess the heart hemodynamically, and develop a sound baseline.
Common findings on echo include massive right atrial enlargement
(in severe cases, this chamber may be larger than the rest of the
heart), right ventricular enlargement, ventricular septal flattening
(causing a “D” shaped left ventricle), and abnormally shaped
tricuspid leaflets. Radiographic findings include severe cardiomegaly secondary
to the enlarged right atrium and ascites.
ECG reveals deep P waves in leads I, II, III, and aVF along with
atrial fibrillation.
