Page 1014 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Cardiovascular system 989

VetBooks.ir 8.23

Fig. 8.23 Left atrioventricular
(AV) (mitral) valvular regurgitation.
Left heart long-axis view taken
from the left 5th ICS. Two-year-
old Standardbred colt with poor
performance and a grade 5/6 left-
sided holosystolic murmur. Colour-
flow Doppler echocardiography
reveals high-velocity regurgitant
flow at the left AV valve in green
in the right-hand image. LV = left
ventricle; LA = left atrium.

Management/prognosis An incidence of 9% has been reported, with a higher
There is no treatment for correcting left AV valvular incidence in Thoroughbred and Standardbred race-
regurgitation. In horses with small focal jets of regur- horses. This increased incidence is considered to
gitation, the prognosis for life and for performance be associated with hypertrophic changes follow-
is excellent without any treatment. In those horses ing intensive training rather than with hereditary
with valve thickening or more extensive regurgita- factors.
tion, the prognosis is less favourable. The regurgi-
tant fraction tends to increase with time. This may Aetiology/pathophysiology
result in a gradual decrease in performance capacity. Deformities of the right AV valve are uncommon at
Chordal rupture is rare and usually results in sud- post-mortem examination, but regurgitation through
den onset of heart failure, pulmonary oedema and the right AV valve is common. The three-valve leaflet
respiratory distress. The case mortality rate with conformation may predispose the valve to incomplete
chordal rupture is high. Cardioversion of AF may closure. Regurgitation of blood into the right atrium
be attempted; however, the prognosis for restora- during systole may result in volume overload.
tion and maintenance of sinus rhythm is guarded in Right AV valvular regurgitation may be primary
cases with evidence of atrial dilatation. The onset of or may occur secondarily to left-sided heart failure.
signs of congestive heart failure is a poor prognostic Signs of right-sided heart failure are most commonly
indicator. Clinical signs of heart failure should be associated with left-sided heart disease and left-sided
treated as outlined on p. 999. heart failure. Pulmonary hypertension causes pres-
sure overload of the right heart and results in right-
RIGHT ATRIOVENTRICULAR sided failure. Chordal rupture is less common than
VALVE DISEASE in the left heart.

Definition/overview Clinical presentation
Murmurs associated with right AV valvular regurgi- There are usually no clinical signs associated with
tation are common in the horse; however, pathology right AV valvular regurgitation. The murmur is clas-
of the right AV valve is seldom detected, and right sically holosystolic to pansystolic, band-shaped, soft
AV valvular regurgitation is not commonly associ- and blowing. The PMI is on the right side of the
ated with any clinical signs or performance effects. chest, usually in the 4th ICS. Crescendo, mid-systolic