Page 8 - Clinical Connections - Summer 2023

RVC RESEARCH STUDY VETERINARY SERVICES RVC.AC.UK
Equine
CARDIAC ARRHYTHMIAS IN HORSES

Jenny Reed, Lecturer in Equine Medicine

quine arrhythmias result in a range involves the placement of an intra-cardiac
of effects, from poor performance steerable catheter and the creation of a
E and reduced exercise capacity to magnetic field over the heart via which the
sudden cardiac death – but are also present location of the catheter is ‘visualised’.
in healthy equine athletes. By combining both 3D anatomical and
On identifying an arrhythmia, the ECG image demonstrating several premature electrophysiological data, an electrical map
veterinarian’s role is to determine whether ventricular depolarisations identified at rest in of the inner surface of the heart is created.
a physiological or pathological arrhythmia a horse presented for poor performance Initial studies utilised this 3D mapping
exists and to assess the risk to the rider. system to describe the normal activation
Unfortunately, this is often difficult, and whilst Heart rate variability, the difference in pattern of the myocardium throughout the
auscultation is useful, a definitive diagnosis heart rate between consecutive cycles, is a cardiac cycle, and while initially performed
is usually achieved via electrocardiography normal phenomenon related to changes in in anaesthetised horses, the technology has
(ECG). the autonomic nervous system. However, also been used in standing horses.
The introduction of smartphone-based abnormal variations in heart rate during In addition to demonstrating the normal
ECG technology has allowed for the exercise suggest premature or late beats propagation of the electrical impulse
diagnosis of rhythm disturbances at rest which are identified by computer-aided through the heart, the depolarisation of the
and under field conditions, however the evaluation of beat-beat intervals. Despite ventricular myocardium was also shown to
identification of arrhythmias occurring at the advancement of technology aiding be reflected in the QRS morphology, and
exercise requires a telemetric system with the analysis of ECG’s, characterisation of subsequently, 12-lead ECG’s have also
detailed analysis of the ECG following arrhythmias remains a challenge. been evaluated as a method for identifying
collection – a service offered at RVC Equine. The presence of morphological and/ the origin of focal premature atrial and
Exercising ECG recordings are difficult or temporal changes in the ECG can be ventricular depolarisations.
to analyse due to the presence of motion suggestive of the source of an ectopic beat, The ability to detect the source of ectopy
artefacts and the lack of P-waves and short however occasionally these findings do not also allows for the treatment of arrhythmias
QRS intervals associated with physiological agree to the source, and as a result a more with intra-cardiac radiofrequency ablation.
tachycardia. Whilst morphological descriptive approach to arrhythmias has Several atrial arrhythmias have been
changes may be identified on subjective been suggested. successfully treated in this way, including
analysis, heart rate variability has more While ECG analysis may help to locate atrial tachycardia and an atrioventricular
recently been utilised in the detection of the likely source of an arrhythmia, catheter- accessory pathway.
arrhythmias in horses at exercise, and aids based intra-cardiac electroanatomic Whilst these technologies are not
in interpretation of ECGs notwithstanding mapping is being used to provide universally available, one catheter-based
the aforementioned challenges. information on the precise location of treatment that has been performed at the
electrophysiological abnormalities. This RVC Equine Hospital is trans-venous electro-
conversion (TVEC). Atrial fibrillation (AF)
is the most common arrhythmia affecting
performance in horses, and conversion
to sinus rhythm can be accomplished via
several methods. Quinidine sulphate is
effective for pharmacological conversion of
atrial fibrillation in horses, but undesirable
side effects are frequently encountered. A
general anaesthesia is required for TVEC,
however both methods have high success
rates and recurrence rates are similar.
While it remains a constantly evolving
field, our ability to more accurately detect,
describe and locate equine arrhythmias
has improved with the introduction of
these technologies, and the opportunities
for successful resolution of arrhythmias
continue to grow.

For equine referrals, please call: 01707
666297
Email:
The Televet telemetric ECG system in use to collect a resting ECG equinehospital@rvc.ac.uk

8 Summer 2023