Page 1005 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

980 CHAPTER 8

VetBooks.ir Clinical presentation/diagnosis Clinical presentation/diagnosis
Ventricular contraction occurs prematurely in rela-
An abnormally short PR interval combined with a
prolonged QRS is present. It may appear for a cou-
is often bizarre (Fig. 8.19). Heart rate is normal.
ple of cycles and then disappear. QRS conforma- tion to the sinus complexes. QRS conformation
tion may be variable. A delta wave (slurring of the Premature contractions may be single or in trains.
R wave upstroke) is found at the beginning of QRS The ectopic beat is often followed by a pause before
(Fig. 8.18). the next sinus beat.

Management Management
There are no treatment options. No treatment is required for single beats or for short
trains of 2–3 complexes. Some horses may respond
PREMATURE VENTRICULAR COMPLEXES to rest and corticosteroid administration.

Overview/aetiology/pathophysiology VENTRICULAR TACHYCARDIA
Premature ventricular complexes are common and
are variable in their clinical significance. Single ecto- Overview/aetiology/pathophysiology
pic complexes are likely to be clinically insignificant. Ventricular tachycardia is a clinically significant
Long trains or frequent occurrence of complexes may condition that usually involves underlying myocar-
be associated with myocardial inflammation or disease. dial or systemic disease.

8.18

Fig. 8.18 Pre-excitation (Wolff–Parkinson–White) syndrome. Base–apex lead recorded from a 7-year-old
Standardbred gelding with a variable performance record. An extremely short PR interval and a positive delta
wave are present at the beginning of the QRS complex, giving it a widened appearance. Variable conduction with
some normal sinus complexes was present at elevated heart rates during treadmill exercise. The horse continued
to race following this diagnosis, with variable results.

8.19

Fig. 8.19 Premature ventricular complexes. Base–apex electrocardiogram recorded from a normal horse
at rest. There is a normal PQRST (note negative deflection of QRS complex), followed by a P wave with an
abnormal QRS almost obliterating the P wave. This premature ventricular complex is followed by another with
the same conformation (note the absence of a P wave with this complex). A compensatory pause is then present,
followed by normal complexes.