Endocardiosis (or Degenerative Valve Disease)
Endocardiosis (or Degenerative Valve Disease) is an acquired disease characterized
by degeneration and fibrosis of the cardiac valves. As endocardiosis progresses,
the affected valve becomes increasingly insufficient. For mitral valve disease,
the valve most commonly affected in dogs, insufficiency allows blood to jet back
into the left atrium during ventricular contraction. Blood jetting back into the
left ventricle increases the pressure within the left atrium which decreases venous
flow from the lungs. This results in pulmonary venous congestion and ultimately
pulmonary edema. In addition, as the left atrium dilates, there is a high likelihood
that atrial arrhythmias (APCs, atrial fibrillation) will occur, further decreasing
cardiac output. The constant jetting of blood from the high pressure left ventricle
physically damages the endocardium of the left atrium, and may result in left atrial
rupture in chronic cases. The decrease in the amount of blood ejected by the left
ventricle (cardiac output) forces several compensatory mechanisms into action. The
body responds to decreases in cardiac output by increasing sympathetic tone and
activating angiotensin converting enzyme (ACE). Chronic elevation of these compensatory
mechanisms become deleterious rather beneficial. Chronic elevation of sympathetic
tone causes sustained tachycardia which increases the oxygen demand of the heart
and predisposes the animal to arrhythmias. ACE activation results in the formation
of angiotensin II which causes sustained arteriolar and venous constriction and
release of aldosterone. Vasoconstriction increases the cardiac afterload, hampering
ventricular ejection of blood. Aldosterone release results in sodium and water retention
and predisposes the animal to pulmonary edema.
Endocardiosis is the most common cardiac disease in veterinary medicine. This disorder
most commonly affects the left atrioventricular (mitral) valve in dogs, cats, and
horses. Approximately 60% of dogs older that 8 years are affected. This disease
is uncommon in cats. Endocardiosis occurs primarily in small breed, older dogs,
particularly in the miniature poodle, Shetland sheepdog, lhasa apso, dachshund,
and cocker spaniel. The severity of clinical signs depends upon the degree and chronicity
of the valvular disease. Early in the course of the disease, there are no clinical
signs present, although a systolic murmur of low intensity (grade 1-2) can be heard
at the left apex. As the disease progresses, exercise intolerance gradually increases,
and respiratory rate increases, followed by coughing and labored breathing. In general,
as this disease progresses, the intensity of the murmur increases (up to grade 6)
and a precordial thrill develops. A complete blood count, serum chemistry profile,
and urinalysis are usually within normal limits. Radiographically, left atrial enlargement
is the hallmark finding. Other changes include left ventricular enlargement, and
enlargement of the pulmonary veins. As heart failure develops, there is a progressive
increase in interstitial densities, and ultimately the appearance of air bronchograms,
indicative of an alveolar pattern and severe pulmonary edema. Echocardiography reveals
a thickened, enlarged, and irregular valvular leaflet of normal echogenicity. Chordae
tendineae may be ruptured, and the atrioventricular leaflets may prolapse into the
atrium during ventricular contraction. Ventricular enlargement is common. Contractility
in most cases appears normal to exaggerated as the left ventricle is able to eject
a significant portion of blood into left atrium rather than the high pressure aorta.
A decrease in fractional shortening (contractility) signals the presence of myocardial
failure. Electrocardiographically, the rhythm in most cases is normal sinus rhythm
or sinus tachycardia. When congestive heart failure occurs, sinus arrhythmia converts
to a very regular sinus rhythm and the rate increases. Left atrial enlargement promotes
the occurrence of atrial arrhythmias such as atrial premature complexes and atrial
fibrillation. Cardiac hypoxia causes ventricular arrhythmias - VPCs are common when
congestive heart failure is present. There may be evidence of left atrial enlargement
(P-mitrale or widened P waves) and left ventricular enlargement (tall and widened
R waves) when the mitral valve is involved.
The essentials of treatment are 1) to slow the progression of clinical signs early
with vasodilators, 2) control pulmonary edema with vasodilators and diuretics when
it occurs, and 3) reduce the heart rate and increase contractility later in the
course of the disease when vasodilators and diuretics begin to lose their effectiveness.
It is most convenient to plan the optimal therapy for each stage of this disease:
Stage I: A soft (grade 1-2) systolic murmur is present, but there are no clinical
signs of heart failure and the left atrium is not enlarged radiographically. No
cardiac medications are indicated. The client should be instructed to avoid feeding
any foods or snacks high in sodium.
Stage 2: A systolic murmur (grade 2-3) is present, there are no clinical signs,
yet the left atrium is enlarged radiographically. Vasodilator therapy will likely
be beneficial at this early stage. Enalapril therapy at 0.4 to 0.5 mg/kg once daily
is recommended. Owners should avoid excessive sodium - a senior diet would be ideal.
Stage 3: A systolic murmur (grade 3-4) is present and there is cough at night and
following activity. There is left atrial enlargement radiographically. Continue
enalapril therapy but increase to 0.4 to 0.5 mg/kg BID. Add furosemide at 1 mg/kg
SID to BID and determine the lowest effective dose. A senior diet should be part
of the therapy.
Stage 4: A loud (grade 4-6) systolic murmur is present. There are signs of heart
disease throughout the day consisting of exercise intolerance and cough. There is
moderate to marked left atrial enlargement radiographically. The heart rate has
increased. Enalapril (0.5 mg/kg BID), furosemide (1-2 mg/kg SID to BID) and digoxin
at 0.22 mg/m2 are indicated. A diet moderately restricted in sodium should be part
of the therapy.
Affected dogs can live for years with clinical signs of degenerative valve disease
and proper treatment. The use of ACE inhibitors, such as enalapril, has greatly
increased our ability to control the signs of heart failure and to maximize survival.