Page 1007 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

982 CHAPTER 8

VetBooks.ir 8.21

Fig. 8.21 Torsades de pointes. Base–apex lead recorded from a 2-year-old Standardbred colt undergoing
quinidine therapy for AF. Polymorphic ventricular tachycardia with twisting around the baseline is present in
this recording. A ventricular rate of 240 bpm is present in the latter third of the recording.

CONGENITAL CARDIAC DISEASE

Congenital cardiac disease is uncommon in the poor performance in an animal of sufficient age to
horse. It may occur as single or complex anomalies. perform, as ill-thrift or poor growth in a foal or as
The most common congenital cardiac anomaly is cyanosis or heart failure in a neonatal animal.
VSD. Other defects, such as patent ductus arteriosus A full physical examination should be performed,
(PDA), persistent truncus arteriosus and tetralogy of with particular attention paid to mucous mem-
Fallot, have also been reported. Isolated anomalies branes, jugular veins, arterial pulses and cardiac and
involving the AV or pulmonic valves are infrequent thoracic auscultation. Electrocardiography often
in the horse. Complex congenital disease or severe does not provide additional information aside from
single defects are more likely to present at an early cardiac rate and rhythm and waveform morphology.
age. In contrast, a small VSD may be an incidental It does not provide details of chamber dimensions
finding in a mature horse. or enlargement in the horse. Thoracic radiography
The causes for congenital heart disease are not may indicate evidence of pulmonary changes asso-
known in the horse and there is no proven herita- ciated with cardiac disease or may provide evidence
bility, although congenital heart disease has been of cardiac enlargement. 2-D echocardiography, as
more commonly reported in Arabians. Contributory well as Doppler and contrast echocardiography, are
factors may include maternal infection, hypoxia due the most valuable tools for determining the site and
to placental insufficiency, fetal infection or toxin extent of a lesion. Arterial blood-gas analysis may
exposure. help determine the presence of a right-to-left shunt.
Suspicion of congenital cardiac disease should be
raised if a continuous holosystolic or holodiastolic VENTRICULAR SEPTAL DEFECT
murmur is detected in a foal. Innocent murmurs are
common in the neonatal period, therefore detection Definition/overview
of a quiet, soft murmur in a foal might not indicate VSD is the most commonly reported congenital car-
congenital disease. Early investigation is indicated diac anomaly in the horse. It occurs both as a lone
when a palpable thrill is detected or when the mur- anomaly and as part of a complex of anomalies. The
mur radiates widely. Cyanosis at rest may occur with following discussion addresses VSD as it occurs alone.
complex cardiac disease. Cyanosis should raise suspi- Complex congenital defects will be addressed sepa-
cion of right-to-left shunting of blood. rately. Breed predispositions for VSD have not been
The severity of clinical signs is variable. well documented in the horse, although the Arabian
Congenital heart disease may be an incidental diag- breed appears overrepresented, and in one study, an
nosis at post-mortem examination. It may present as increased incidence was reported in Welsh mountain