EQUINE VETERINARY EDUCATION / AE / MAY 2018
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Fig 1: Modified base-apex ECG during sliding stops in a reining horse. Note the premaure QRS complex (black arrow) with aberrant morphology and followed by a compensatory pause (black segment) consitent with a VPC. Note the baseline artifact during the sliding stop (red segment).
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113 113 114 Fig 2: Modified base-apex ECG during spins in a reining horse. Note the baseline artifact during the spins (black segment). Upper respiratory tract dysfunction is a major cause of
exercise intolerance. In Thoroughbred racehorses, the incidence of dynamic obstructions ranges from 23 to 78% (Lane et al. 2006; Desmaizieres et al. 2009) and common upper respiratory abnormalities include axial deviation of the aryepiglottic folds (6–40%), abnormal laryngeal function (9– 33%), dorsal displacement of the soft palate (25–50%), and palatal instability (33%) (Lane et al. 2006; Pollock et al. 2009). The prevalence of dynamic obstructions observed in this population of horses is low compared to that reported in Thoroughbred racehorses and perhaps a more strenuous exercise protocol would have identified additional abnormalities. The most common abnormality observed was laryngeal asymmetry and this is consistent with other breeds of horses. Importantly, none of the horses in this study had a complaint of exercise intolerance or respiratory noise and results represent the prevalence of incidental and subclinical functional respiratory abnormalities in this population of reining horses. The cytological profile of BALF showed an inflammatory
response in three horses, using a fairly exclusive definition, and two horses had an increased amount of mucus in the trachea. An increased amount of tracheal mucus is associated with poor performance in racehorses (Holcombe et al. 2006) and reduced willingness to perform in sports horses (Widmer et al. 2009). When asked prospectively, signs associated with lower respiratory disease were not reported but when trainers were asked retrospectively, two of the horses with lower airway inflammation or increased mucus were reported to cough. The cytological results obtained are similar to those reported in sport horses (Gerber et al. 2003) and pleasure horses (Robinson et al. 2006) without signs of poor performance. To the best of our knowledge, ECGs during a reining test
have not been previously described. This study shows that diagnostic ECG can be obtained during reining manoeuvres.
The rare presence of exercising arrhythmias contrasts with the higher prevalence reported in horses of other disciplines (Ryan et al. 2005; Barbesgaard et al. 2010; Buhl et al. 2010) and arrhythmias observed in the study group are unlikely to be of clinical relevance. Arrhythmias during and after exercise can be more common in horses exercising at higher intensities (Ryan et al. 2005) and the moderate level of exercise performed in these horses could partially explain the differences when compared to racehorses. However, the frequency of arrhythmias was also less when compared to studies in which showjumpers and dressage horses performed exercise tests with similar or lower HRs than the ones obtained in this study using the same arrhythmia definition (Barbesgaard et al. 2010; Buhl et al. 2010). It is possible that there are breed differences, differences due to the particular exercise tests or that a higher intensity test would have yielded different results. The changes in laboratory tests provide baseline data
to evaluate groups performing at similar levels. In contrast, the previously described routines can be used in horses exercising at higher intensities (Webb et al. 1988; Rammerstorfer et al. 2001). The outlier found in post-exercise CK plasma concentration underscores the potential utility of exercise tests in performance horses. This horse subsequently tested positive for GYS1 mutation evidencing polysaccharide storage myopathy. It is plausible that the diagnosis of a subclinical myopathy in this horse and implementation of exercise and diet changes will help prevent further episodes of rhabdomyolysis. Similarly, it can be speculated that managing the environment to reduce the exposure to airborne particles, awareness of cardiac disease in one horse with mitral regurgitation, or of upper airway disease in four horses, could help riders and trainers recognise early signs of progression before these subclinical problems become severe and affect performance, health or welfare.
© 2017 EVJ Ltd
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