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Mitral/Tricuspid Regurgitation Due to Myxomatous Valve Disease 659

• Class B: dogs without clinical signs but • The fibroblast-like valvular interstitial endocarditis) or congential heart disease, or
presenting with a systolic click (early stage) cells transform into a more active myofi- • Other causes of respiratory distress
functional flow murmurs
VetBooks.ir divided into two subclasses: induce signaling pathways, resulting in an ○ Upper respiratory causes such as tracheal Diseases and Disorders
broblast phenotype, and these cells can
and/or systolic heart murmur. This class is
○ Class B1: asymptomatic with heart
abnormal structural integrity of the valve,
disease
murmur and (if an echocardiogram is
performed) echocardiographic signs of mediated through various proteolytic ○ Lower respiratory causes such as bronchial
disease, pneumonia, pulmonary edema due
enzymes.
AV valve lesions and regurgitation • Accumulation of glycosaminoglycans, to noncardiac or other cardiac diseases,
○ Class B2: asymptomatic with AV valve proteoglycans, and collagen fibers lead to pleural effusion, pneumothorax, hernias,
lesions and hemodynamically significant disorganization in the fibrosa layer and or neoplasia
regurgitation, as evidenced by radiographic marked expansion of the spongiosa layer. ○ Nonrespiratory diseases such as neuromus-
or echocardiographic cardiomegaly ± elec- • The valve leaflets, which normally are thin, cular disease, metabolic/endocrine disease,
trocardiographic changes (electrocardiogram translucent, and soft, become thickened and anemia, or abdominal disease
[ECG] is an insensitive method to detect elongated with disease progression. ○ Other causes of respiratory effort, such as
cardiomegaly): P mitrale (increased P-wave • The chordae tendineae also are affected pain, fear, physical exertion, fever, heat,
duration) and/or P pulmonale (increased by myxomatous degeneration, resulting in stress, obesity, or drug-related causes
P-wave amplitude), increased R-wave elongation. • Other causes of reduced exercise capacity
amplitude, and increased QRS duration. • Distortion of the valve architecture contrib- ○ Hypoxia of noncardiac causes such as
• Class C: dogs with AV valve lesions, utes to systolic atrial displacement of the anemia or respiratory disease, or other
hemodynamically significant regurgitation, valve leaflets. cardiac diseases.
and presenting with clinical signs of CHF • Insufficient coaptation of the leaflets leads ○ Orthopedic- or neuromuscular-related
(usually left-sided) or that have had episodes to AV valve regurgitation and to chronic disorders
of CHF in the past that resolved with volume overload with atrial and ventricular ○ Other systemic disease (e.g., renal or
ongoing medical therapy dilation. hepatic failure, and endocrinologic- or
• Class D: dogs with end-stage disease; clinical • Slight to moderate AV valve regurgitation immune-related diseases)
signs of AV valve regurgitation–induced CHF is often completely compensated for years • Other causes for syncope (p 953)
that are refractory to standard CHF therapy and is not expected to cause clinical signs ○ Arrhythmic syncope or sudden changes
of disease. in heart rate
HISTORY, CHIEF COMPLAINT • Compensatory mechanisms include cardiac ○ Cardiostructural syncope such as due to
• Often, incidental finding of murmur before dilation and eccentric hypertrophy, increased right-to-left shunting cardiac diseases or
CHF occurs force of contraction, increased heart rate, obstruction to blood flow
• Respiratory: tachypnea/dyspnea/orthopnea; increased pulmonary lymphatic drainage ○ Neurologically mediated syncope, such
cough (often worse at night) (left-sided AV valve regurgitation), fluid as due to vasodepressor syncope (loss of
• Systemic: lethargy, reduced exercise tolerance, retention, and neurohormonal modulation sympathetic tone) or cardioinhibitory
syncope, anorexia, weight loss, ascites of cardiovascular function. syncope (predominance of parasympathetic
• With progression, valvular regurgitation tone)
PHYSICAL EXAM FINDINGS can no longer be compensated, and CHF ○ Conditions associated with reduced
Patients without overt clinical signs: develops due to increased venous pressures preload, such as dehydration, hemorrhage,
• Systolic click (early stage) and reduced cardiac output. hypotensive drugs, or cardiac tamponade
• Systolic heart murmur due to AV valve • Pulmonary edema develops with left-sided • Other causes of abdominal distention due
regurgitation; murmur increases in duration CHF, and ascites develops with right-sided to ascites
and intensity with progression of disease. CHF. ○ Liver disease, protein-losing enteropathy,
Patients showing overt clinical signs: glomerulopathy, right-sided heart failure
• Moderate to loud heart murmur, unless there DIAGNOSIS caused by other cardiac/pericardial diseases,
is significant myocardial failure (e.g., with neoplasia, vasculitis, infectious diseases,
concurrent myocardial disease) Diagnostic Overview pancreatitis, trauma, coagulopathies, or
• Tachycardia and/or loss of respiratory sinus • The diagnosis is suspected based on the postoperative complications
arrhythmia characteristic left apical location of a systolic Radiographic:
• Arrhythmia and pulse deficit may be present, heart murmur in an adult dog. • Other causes of cardiac enlargement
most commonly supraventricular premature • Echocardiography is the diagnostic test of ○ Other heart diseases, hernia, pericardial
beats, atrial fibrillation, or ventricular ectopies choice for demonstrating the valve lesion; effusion, or enlargement related to normal
• Weak femoral pulse a high index of suspicion usually exists breed and/or individual variation
• Prolonged capillary refill time, pallor before echocardiography is employed, and • Other causes of increased pulmonary
• Tachypnea/dyspnea/orthopnea it functions as a confirmatory test, to identify interstitial or alveolar radiopacity due to
• Respiratory crackles/rales severity of secondary changes, and for treat- ○ Pulmonary edema due to other cardiac
• Pink froth (i.e., pulmonary edema may be ment decisions. and noncardiogenic processes
evident in the nostrils and oropharynx in • Thoracic radiographs may alternatively be ○ Primary respiratory or systemic disease
cases with severe CHF) used for staging purposes (to assess for heart processes
• Ascites (tricuspid disease, pulmonary enlargement) and are indicated, particularly ○ Artifacts or expiratory radiographs
hypertension) if cough and/or dyspnea is present, to dif-
ferentiate pulmonary edema from unrelated Initial Database
Etiology and Pathophysiology comorbid conditions such as collapsing Assessment of disease severity and complica-
• Primary inciting factor for the valvular trachea or chronic bronchitis. tions; specific diagnostic tests chosen based on
degeneration is unknown. Current leading clinical progression
hypothesis is that a genetically determined Differential Diagnosis • Auscultation: a low-intensity murmur
dystrophic process initiates valve degeneration. Physical: with or without a systolic click in an
• Damage occurs to the endothelial cell lining • Other causes of systolic heart murmurs such otherwise healthy dog usually indicates
covering the valve surface. as AV regurgitation caused by acquired (e.g., mild disease severity. Murmur intensity

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