Page 1024 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Cardiovascular system 999

VetBooks.ir 8.27 8.28

Fig. 8.28 Left atrial dilatation. Left-sided long-
axis view taken from the left 5th ICS. Two-year-old
Standardbred colt with a history of poor performance
and a grade 5/6 left-sided holosystolic murmur. Left
atrial measurements indicated left atrial dilatation
Fig. 8.27 Ventral oedema. Severe ventral oedema with a diameter of 16.05 cm. The horse was in sinus
in a 7-year-old Standardbred mare in heart failure. rhythm, with no signs of heart failure. LV = left
The mare was tachycardic, had venous distension, ventricle; LA = left atrium.
AF, cardiac dilatation, reduced functional indices and
severe left AV valve regurgitation. The ventral oedema
resolved following 1 week of therapy with furosemide
and digoxin.

Electrocardiography should be performed. i/m or p/o q8–12 h) is indicated to decrease pulmo-
Tachycardia is present, although the extent is vari- nary fluids. Bronchodilators (e.g. salbutamol) may
able. AF is a common finding in horses with heart improve respiratory function. Salt supplementation
failure. Ventricular and supraventricular ectopic should cease, but salt restriction is not indicated.
activity may also occur. Adequate hydration is indicated to avoid exacerbation
Enlargement of multiple chambers may be evident of reduced renal perfusion. Fluid therapy, however,
on echocardiography (Fig. 8.28). The left ventricle should be judicious, because of the risk of volume
often has a globoid rather than a tapered appearance. overload. Digoxin is of benefit due to its positive
Multiple valvular insufficiencies may be present. If pul- inotropic and negative chronotropic effects, thereby
monary hypertension is a component, the pulmonary improving cardiac output (Table 8.4). Digoxin has a
artery will be enlarged, approaching or exceeding the narrow therapeutic index (1–2 ng/ml), however, and
measurements for the aorta. With chordae tendinae digoxin levels should be monitored. Once stabilised,
rupture, part of the AV valve may appear to flail. diuretics should only be administered as needed, as
excessive or prolonged diuretic therapy may result in
Management dehydration and reduced cardiac output. Furosemide
Since heart failure is dynamic, the goal of therapy may result in potassium depletion, which may poten-
is to restore cardiac function sufficiently, such that tiate digoxin toxicity. Venous vasodilatation is a
failure is abated. Decreasing cardiovascular demands common therapy in humans and small animals. ACE
by placing the horse in a stall is advised. Initially, inhibitors have proven beneficial in those species
administration of furosemide (0.5–2 mg/kg i/v, and may be useful in the horse; however, financial