Page 1025 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

1000 CHAPTER 8

VetBooks.ir concerns often preclude their use. Hydralazine is an Prognosis
Once signs of heart failure have developed, it is
arterial dilator and has proven to be of some value
in other species in cases of left AV valve disease.
Nitroglycerine or nitroprusside, which are venodila- unlikely that cardiac function can be restored suf-
ficiently that the animal is able to perform ade-
tors, have been of value in the management of pul- quately. Appropriate management may, in some
monary oedema in other species, but they have not cases, result in an animal that is capable of pasture
been fully evaluated in horses. All vasodilators have turnout and of reproductive service for a limited
the potential for hypotension, and the risk of col- period. Euthanasia is often appropriate, due to the
lapse should be considered. poor prognosis.

MISCELLANEOUS CARDIOVASCULAR DISEASES

AORTIC ROOT DISEASE Diagnosis
Clinical examination, including careful ausculta-
Definition/overview tion, is very important. Clinical pathology such as
Rupture of the aortic ring, or root, is an uncommon cTnI levels and cardiac isoenzymes may be of benefit
condition that is most commonly reported in aged in identifying active myocardial inflammation. No
stallions. An increase in incidence of aortic root rup- radiographic abnormalities typify this condition, but
ture/aortopulmonary fistulas in Friesian horses has if acute left-heart failure is a component, increased
been recently reported. pulmonary opacity may be observed.
Sinus tachycardia is commonly observed on an
Aetiology/pathophysiology ECG. Other arrhythmias may also occur. These
The aetiology is uncertain; however, necrosis of the may be junctional or ventricular in origin. In chronic
aortic wall connective tissue has been implicated. cases, atrial dilatation may predispose to the devel-
The rupture usually dissects through the right coro- opment of AF.
nary sinus into the interventricular septum. Sinus of Echocardiography is important for a definitive
Valsalva aneurysms may have a similar aetiology. In diagnosis (Fig. 8.29). An area of hypoechogenicity
these cases, there may be an abnormal appearance at may be present at the aortic root or into the intra-
the junction between the aortic root and the junc- ventricular septum. Colour-flow Doppler is particu-
tion of the right ventricle and right atrium, which larly useful. In some cases, abnormal flow from the
may appear similar to a VSD on echocardiography. aortic root may be observed. With dissection into
both ventricles, an acquired VSD may be observed.
Clinical presentation Flow would not be observed across an aneurysm
The horse may die acutely or present in acute heart unless it was ruptured. Valvular regurgitation may
failure. Tachycardia, distress and discomfort are also be present. The rupture is often near the right
common. A continuous murmur over the right ven- coronary cusp of the aortic valve and extension into
tricle is characteristic. The presence of the diastolic the right ventricle is common.
component of the murmur on the right side is almost
diagnostic. Management/prognosis
The prognosis is poor. For those animals that do not
Differential diagnosis die suddenly, temporary recovery may occur; how-
VSD and aortic regurgitation are the main differen- ever, signs may recur or the horse may die suddenly
tial diagnoses for the echocardiographic findings. In at a later date. The owners should be informed of the
cases of sudden collapse or death, pulmonary artery danger posed by the condition. Horses with a sinus
rupture, various arrhythmias and non-cardiac dis- of Valsalva aneurysm should be considered unsafe
ease should be considered. and at risk of rupture.