Page 149 - Small Animal Internal Medicine, 6th Edition

CHAPTER 6 Acquired Valvular and Endocardial Disease 121

Massive left (or right) atrial distention can result in
BOX 6.1 partial- or full-thickness tearing. Atrial wall rupture can
VetBooks.ir Potential Complications of Chronic Mitral Valve Disease cause acute cardiac tamponade or an acquired atrial septal
defect. There appears to be a higher prevalence of this com-
Causes of Acutely Worsened Pulmonary Edema
Arrhythmias plication in male Cocker Spaniels, Dachshunds, and possibly
Miniature Poodles. In Cavalier King Charles Spaniels, the
Frequent atrial premature complexes prevalence seems to be similar between females and males.
Paroxysmal atrial/supraventricular tachycardia Severe valve disease, marked atrial enlargement, atrial jet
Atrial fibrillation lesions, and ruptured first-order chordae tendineae are
Frequent ventricular tachyarrhythmias common findings in these cases.
Ruptured chordae tendineae
Iatrogenic volume overload CLINICAL FEATURES
Excessive volumes of IV fluids or blood
High-sodium fluids Middle-aged and older small to mid-size breeds are most
Erratic or improper medication administration often affected; a strong hereditary basis is thought to exist,
Insufficient medication for stage of disease and disease prevalence and severity increase with age. The
Increased cardiac workload majority of small-breed dogs older than 10 years of age are
Physical exertion affected. Common breeds include Cavalier King Charles
Anemia Spaniels, Toy and Miniature Poodles, Miniature Schnauzers,
Infections/sepsis Chihuahuas, Pomeranians, Fox Terriers, Cocker Spaniels,
Hypertension Pekingese, Dachshunds, Boston Terriers, Miniature Pin-
Disease of other organ systems (e.g., pulmonary, schers, and Whippets. An especially high prevalence and
renal, liver, endocrine)
Hot, humid environment early onset of CMVD occurs in Cavalier King Charles Span-
Excessively cold environment iels, in which the disease is suspected to be a complex auto-
Other environmental stresses somal polygenic trait with variable penetrance. The overall
High salt intake prevalence of MR murmurs and degenerative valve disease
Myocardial degeneration and poor contractility appears similar in male and female dogs, but males have
earlier onset and faster disease progression. Some large-
Causes of Reduced Cardiac Output or Weakness breed dogs are also affected, although the degree of valve
Arrhythmias (see previously) thickening and prolapse tends to be less pronounced than in
Ruptured chordae tendineae small-breed dogs. German Shepherd Dogs may be overrep-
Cough-syncope resented. Larger-breed dogs also are prone to dilated cardio-
Pulmonary hypertension myopathy (DCM, which may coexist) or are more susceptible
Secondary right-sided heart failure
Left atrial tear to myocardial dysfunction secondary to chronic volume
Intrapericardial bleeding overload.
Cardiac tamponade Many dogs with CMVD have no clinical signs, even with
Myocardial degeneration and poor contractility fairly advanced disease. In those that do, early signs of CHF
Hypertension usually include reduced exercise tolerance, and tachypnea or
Anemia or other systemic disease cough with exertion. Because a persistent increase in base-
line respiratory rate (RR) often signals the onset of pulmo-
nary interstitial edema before other signs develop, owner
tachyarrhythmias may be severe enough to cause decompen- monitoring of resting (sleeping) RR is useful even in dogs
sated CHF, syncope, or both. Frequent atrial premature con- with early evidence of disease (see Chapter 3, p. 74). Cough-
tractions, paroxysmal atrial tachycardia, or atrial fibrillation ing might occur at night and in the early morning, as well as
can reduce ventricular filling time and cardiac output, with activity. However, the genesis of coughing in many dogs
increase myocardial oxygen needs, and worsen pulmonary with CMVD could relate more to concurrent chronic airway
congestion and edema. Ventricular tachyarrhythmias also disease, rather than CHF itself. A study of dogs with CMVD
occur but are less common. showed CHF (as assessed by radiographic evidence of pul-
Acute rupture of diseased chordae tendineae acutely monary edema) was not significantly associated with cough-
increases regurgitant volume and can quickly precipitate ful- ing; however, an abnormal airway pattern as well as enlarged
minant pulmonary edema and signs of low cardiac output in LA size were. A persistent cough without progressive increase
previously asymptomatic or compensated dogs. Ruptured in RR and effort usually is associated with airway disease,
minor chordae tendineae can be an incidental finding in rather than CHF. The cough caused by airway compression
some dogs. Marked LA enlargement itself might contribute or collapse often is described as dry or “honking.” Severe
to left mainstem bronchus compression or collapse, and pulmonary edema causes obvious respiratory distress, often
stimulate persistent coughing even in the absence of CHF. with a soft, moist cough. Signs of severe pulmonary edema
Concurrent airway inflammatory disease and bronchomala- can develop gradually or acutely. Intermittent episodes of
cia are common in small-breed dogs with chronic MR. symptomatic pulmonary edema interspersed with periods of