Page 1013 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

988 CHAPTER 8

VetBooks.ir Degenerative valve disease is most common. Aortic oedema may develop in cases with chordae tendinae
rupture. Frequently, the left-sided heart failure signs
and left AV valve changes have been reported com-
monly. Valvular insufficiency is a common cause of
the horse is not presented to the veterinarian until
heart murmur in the horse and may or may not be are overlooked as primary respiratory disease, and
associated with degenerative changes in the valve. signs of right-sided heart failure develop.
The extent of regurgitation determines the haemo-
dynamic significance. Valvular insufficiency of mod- Differential diagnosis
erate to severe extent will influence performance and Outflow tract murmurs (innocent flow murmurs),
could be of concern if the horse has to undergo gen- VSD or endocarditis involving the left AV valve
eral anaesthesia. should be considered. Respiratory diseases such as
heaves may also have similar clinical signs if left-
LEFT ATRIOVENTRICULAR sided heart failure is present.
VALVE DISEASE
Diagnosis
Definition/overview The most common clinical finding is a band-shaped,
Murmurs associated with left AV valve disease are soft, blowing, holosystolic murmur over the left
relatively common in the horse, occurring in an esti- heart base just above the area of the left AV valve.
mated 3.5% of the equine population, and are the A mid-systolic crescendo murmur may be detected
most common cause for referral for cardiac evalu- in cases with valve prolapse. In those cases, a beat-
ation. Insufficiency of this valve is more commonly to-beat variability in the murmur characteristics
associated with performance limitations than that of may be present. The correlation between intensity
the right AV valve, and it is the most likely valvular of murmur and severity of regurgitation is poor.
insufficiency to lead to congestive heart failure. Usually, no other clinical signs are apparent.
There are no characteristic radiographic changes.
Aetiology/pathophysiology Atrial enlargement is difficult to discern in equine
There is no breed predilection for left AV valve dis- thoracic radiographs. There are no characteris-
ease. Structural changes in the left AV valve may tic electrocardiographic changes. AF in the face of
contribute to regurgitation. Valvular thickening, moderate to severe left AV valve insufficiency should
fenestration and cystic changes have been reported. raise concern of atrial enlargement.
Pathological changes similar to those of endocardio- Echocardiography is required for diagnosis
sis in other species have also been reported. (Fig. 8.23). Thickened AV valve margins may be
With valvular insufficiency, blood leaks from the detected on 2-D echocardiography. Prolapse of
left ventricle to the left atrium during systole. This a valve leaflet may also be visible in some cases.
increases the volume load on the left atrium. With Careful examination of the papillary muscles and
time, atrial dilatation may occur, which predisposes chordal attachments is indicated, especially in
to the development of AF. Left-sided heart failure those cases with sudden onset of left-heart signs.
may occur. This progresses to pulmonary hyperten- M-mode evaluation can be used to assess left ven-
sion and right-sided pressure overload. Right-sided tricular dimensions and functional indices. Atrial
heart failure may then occur. dimensions should be assessed. Colour-flow and
pulsed-wave Doppler examinations are benefi-
Clinical presentation cial in determining the extent of regurgitation. If
Typically, no clinical signs are apparent, and the the jet is extensive or if there are signs of atrial
murmur is detected during routine examination. enlargement, the diameter of the pulmonary
With severe regurgitation, respiratory signs such as artery should be compared with that of the aorta.
laboured breathing, increased respiratory effort and Dilatation of the pulmonary artery such that it is
rate, prolonged recovery following exercise and a ten- larger than the aorta is an indication of pulmonary
dency to cough may be detected. Overt pulmonary hypertension.