Page 1011 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

986 CHAPTER 8

VetBooks.ir Continuous murmurs are otherwise rare in the foal. components of complex congenital deformities.
Mitral valve dysplasia and parachute valve have
Complex cardiac abnormalities should be consid-
ered. Both systolic and diastolic murmurs may occur
vive beyond the fetal stages with tricuspid atresia,
in animals with VSDs that disrupt the aorta. Systolic been described as sole anomalies. For foals to sur-
murmurs (usually physiological flow murmurs) are concurrent VSDs and ASDs must also be pres-
common in the foal and may be normal during the ent. Obstruction to blood flow occurs in the right
first 2–3 months of life. heart and the ASD allows right-to-left blood flow.
The blood flows from the right atrium into the left
Diagnosis atrium, then into the left ventricle and into the right
A continuous machinery murmur loudest over the ventricle (across the VSD). This results in volume
left side is usually present. The diastolic compo- overload of the left heart.
nent may be quiet to inaudible. Enlargement of the
cardiac silhouette may be evident radiographically. Clinical presentation
Pulmonary overcirculation and oedema may also be With tricuspid atresia the foal may die suddenly in the
present. There are no radiographic changes to aid neonatal period or may survive for only a few months.
in the differentiation of PDA from more complex Cyanosis is common. Tachycardia and collapse are
congenital deformities. Similarly, no identifying also common. A grade 4–6/6 pansystolic murmur is
changes are present on electrocardiography. present with the PMI on the left side of the thorax.
Echocardiography is required for diagnosis. Heart failure may result from volume overload of the
Direct visualisation of the PDA may be possible left heart. Foals with pulmonic valve stenosis or tri-
far forward in the left cardiac window. Left atrial cuspid atresia are often severely stunted. Foals with
enlargement and left ventricular volume overload left AV valve deformities are variably stunted depend-
are common. Doppler echocardiography may show ing on the severity of the stenosis or regurgitation.
disturbed flow within the PDA and in the pulmo- With severe regurgitation, chamber failure may
nary artery. ensue. A loud systolic murmur is common.

Management/prognosis Differential diagnosis
The condition has not been thoroughly evalu- Acquired valvular disease, bacterial endocarditis,
ated in the horse. The prognosis is grave if other and complex congenital cardiac disease must also be
defects are present. Surgical correction is possible. considered.
Pharmacological closure with prostaglandin inhibi-
tors (indomethacin, ibuprofen) has been described in Diagnosis
other species. There are often no characteristic radiographic
changes; however, chamber enlargement may be
VALVULAR DEFORMITIES identified. Similarly, there are often no characteris-
tic electrocrdiographic changes. Echocardiography
Definition/overview may demonstrate stenosis or atresia. A single papil-
Congenital valvular deformities are uncommon in lary muscle is present with a parachute left AV valve.
the horse. Rare cases of pulmonic valve stenosis, Doppler and colour-flow Doppler are useful in order
tricuspid atresia, congenital mitral chordal rupture, to demonstrate blood flow, direction and the extent
papillary muscle deformity and parachute valve have of the regurgitation.
been described.
Management/prognosis
Aetiology/pathophysiology There are no therapeutic options for these diseases
All valvular deformities are developmental. and euthanasia is often indicated because of the
Tricuspid atresia and pulmonary valve stenosis are severity of clinical signs.