Page 8 - Clinical Connections - Summer 2023
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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
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