SAEVA Congress 2018 Proceedings | 12-15 February 2018 | ATKV Goudini Spa
cardioversion is not an option and the horse is intended to be used for performance,
an exercising ECG is indicated to be sure that the exercising HR remains at 220
beat/minute or below when working at the desired effort and that no ventricular
ectopy, aberrant conduction or R on T phenomenon are detected. The exercise test
should be performed with the horse exercising slightly more rigorously than normal
to be sure that the exercising heart rate is not excessively high.
Atrial Premature Complexes (APCs) and Ventricular Premature Complexes
(VPCs)
Premature beats interrupting an otherwise regular rhythm are most consistent with
atrial premature complexes and when followed by a compensatory pause, are more
likely to be ventricular premature complexes. APCs are a risk factor for atrial
fibrillation while VPCs are a risk factor for ventricular tachycardia and possibly
sudden cardiac death.
An electrocardiogram can confirm whether the premature complexes are atrial or
ventricular in origin. The APC has a premature P wave that can be conducted with a
variable P-R interval or blocked at the AV node. The conducted QRS is generally
normal in morphology, but aberrant ventricular conduction can occur resulting in
wider, taller or bizarre QRS and T complexes. VPCs are characterized by a
premature QRS that is typically wide and bizarre and followed by a large T wave of
opposite polarity, without an associated P-wave. VPCs that are multiform, occurring
on top of the preceding T wave, repetitive or occurring in runs of ventricular
tachycardia are complex VPCs and are more likely to be associated with an adverse
cardiac event.
Horses with occasional APCs that are overdriven with exercise or that are infrequent
during exercise are generally considered safe to ride but the risk of AF needs to be
recognized. These APCS are unlikely to be affecting performance. Occasional
uniform VPCs that are overdriven with exercise or only detected in the immediate
post-exercise period are also not usually a cause for poor performance. VPCs that
are detected during exercise are a cause for concern and may be associated with
poor performance.
Ventricular tachycardia (VT)
Horses with uniform VT and no evidence of structural heart disease often recover
and return to normal work but recurrences can occur. Horses with complex
ventricular arrhythmias should not be ridden until their rhythm has returned to
normal and is normal during exercise. These horses should only be ridden by an
informed adult rider, as their safety is uncertain. Rigorous athletic work is not
recommended for horses that have underlying structural heart disease and VT and
these horses should only be used by an informed adult rider.
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