A Look Inside the Galloping Horse Why We Need Overground Endoscopy Everyday

“A look inside the galloping horse – Why we need overground endoscopy everyday”

Patrick J Pollock BVMS, PhD, CertES(Soft Tissue), FHEA, DipECVS, FRCVS

European and RCVS Recognised Specialist in Equine Surgery

Introduction and Background to Overground endoscopy

The introduction of overground endoscopic examination of the upper portion of the equine airway is one of the most exciting innovations in veterinary medicine. The equipment, of which there are now a number ofcommercially available versions, allows the acquisition of images of the upper portion of the equine respiratory tract under normal exercise conditions and does not require the use of a high-speed treadmill (Franklin, etal., 2008; Pollock, et al., 2009). With the widespread use of the technique, availability of equipment and the expertise to use it, there has been a giant leap forward in the understanding of the structure and function of the equine upper airway and consequently a paradigm shift in the approach to and therapy for diseases of the equine airway.

It is now accepted that resting endoscopic examination poorly reflects the appearance of the airway during high speed exercise (Rakestrawet al., 1991; Kannegieter and Dore 1995; Tan et al., 2005; Lane et al., 2006b). The fact that many abnormalities of the upper portion of the airway of horses occur together further highlights the importance of overground respiratory tract evaluation (Lane et al., 2006a).

Prior to the introduction of overground endoscopy, high-speed treadmill endoscopy (HSTE) wasconsidered to be the ‘gold standard’ for diagnosis of diseases of the upper portion of the respiratory tract (URT). However, the lack of rider and tack, difference in surface, speed, incline and environment, potential difference in head position and lack of other horses has led workers to conclude that that treadmill endoscopy poorly emulates normal exercising conditions (Evans 2004; Franklin et al,. 2008, Pollock et al., 2009).

I was fortunate to be involved with the validation and development of the technique of overground endoscopy.I expected that having access to a system that allowed us to examine horses in their own environment, and in much larger numbers than those that presented for treadmill investigation, would result in greater numbers of airway surgeries for clinics that regularly treated horses. This however, has not been the case. Instead the technique has allowed clinicians to better understand the airway, monitor the development and progress of disease, and perhaps most importantly, assess its significance on the exercising horse. From a welfare perspective, there can be little doubt that the single biggest contribution that overground endoscopy has made is a reduction in the number of horses subject to surgical procedures of dubious efficacy.

The history of treatment of therapy for the upper airway

It is fair to say that the history of therapy for conditions affecting the upper portion of the equine respiratory tract, has not always been based on evidence. The pressure on veterinary surgeons from owners and trainers of horses, to intervene when presented with a poorly performing horse is often immense. As a profession we have a history of selecting a course of therapy for horses with apparent airway problems based on the presence of airway noise(Burn and Franklin 2006), resting endoscopic findings, the age of the horse, or just because that’s what has always been done on a particular premises (Cheethamet al. 2008; Reardon et al. 2008). The scientific basis for therapy has been further damaged by the, often outspoken, opinions of well-known trainers and veterinary surgeons. There is no doubt that the historic approach to the investigation and treatment of the equine airway has not been our professions finest hour. Thankfully all this has begun to change, because with the use of overground endoscopy, there is nowhere for the surgeon to hide. It is now possible for every horse to be examined undertaking the type and intensity of exercise in which it reportedly has a problem.Subsequently no horse should be treated without a diagnosis. In some cases that may even involve examining the horse on a racetrack, with other horses and performing under race conditions. Following the acquisition of the endoscopic video, a diagnosis can be made and an appropriate therapy selected.

In our clinic, all horses that are presented for overground endoscopy which have a subsequent surgical treatment are offered a free repeat overground examination following their return to exercise. Consequently the vast majority of procedures are audited allowing a great deal of evidence to be collected. In days gone by, the only measure of success was performance, and there is no doubt that performance is a poor index of surgical success.

Findings to date

To date our clinic has performed approximately 3500 examinations and many more have been undertaken across the globe. The technique is straightforward, reliable and safe. Breeds examined have included thoroughbreds, thoroughbred crosses, standardbreds, sporthorses, clydesdales and a number of native breed ponies. In the population of horses scoped to date, a number of pathological conditions have been identified including: recurrent laryngeal neuropathy, dynamic laryngeal collapse, intermittent dorsal displacement of the soft palate, medial deviationaryepiglottic folds, vocal fold collapse, dynamic pharyngeal collapse, retroversion of the epiglottis, cricotracheal membrane collapse and fourth brachial arch defects among others. A number of new conditions have also been described (Pollock et a.., 2013). Diagnosis of these conditions, many of which were only visible during strenuous exercise is encouraging. Many questions arise regarding their significance with reference to effect on performance, links to abnormal respiratory noise and repeatability of diagnosis. It has rapidly become clear that there is a considerable amount of work to be done investigating upper airway pathology in ridden horses under normal exercise conditions.

The new system has resulted in the presentation of horses not traditionally or regularly presented for treadmill examination, and to the re-presentation and serial examination of horses after tack changes or conservative or surgical treatment. Furthermore, the system requires very few operators, and does not require hospitalisation and is therefore considerably cheaper than treadmill endoscopy.

Complications

Although the scope has generally been very easy to use and has provided some excellent images, there have been some complications and technical problems associated with its use.

The scope is generally very well tolerated, with only very few individuals in which we were unable to pass the scope. The greatest resistance to the technique appears to occur during the passage of the scope through the rostral third of the ventral meatus, similar to the experience when using a standard endoscope. Following placement and twitch removal a number of horses demonstrated snorting behaviour and a minority showed some initial reluctance to go forward. In all cases these early behavioural signs rapidly resolved and did not recur once exercise was initiated. As the various companies that produce overground endoscopes refine and develop their products, it is likely that we will see further innovations and a reduction in size and invasiveness. A recent addition includes the ability to record sound at the same time as video.

Is there any evidence that overground endoscopy has changed our approach to upper respiratory tract disease?

An increasing number of scientific studies have been performed using overground endoscopy, some of these have given rise to changes in the approach to treatment.

In a group of 100 racehorses presented due to the presence of abnormal respiratory noise, a comparison of recorded noise and overground endoscopy findings suggested that the use of respiratory noise alone as a diagnostic criteria would result in an incorrect diagnosis in approximately 50% of horses presented (Witte et al., 2011). In a significant proportion of horses in this study, abnormal noises were actually recorded in horses with no evidence of airway disease.

A number of longitudinal studies have been performed suggesting that overground endoscopy, when performed in young horses is able to identify individuals that may subsequently develop significant and career limiting airway problems (Kelly et al., 2013).

Conservative therapy for problems of the equine airway have never been all that popular, the pressure on vets to “do something” has often led to the use if surgical treatments which are at best ineffective and at worst damaging. This is particularly true for treatment of intermittent dorsal displacement of the soft palate (IDDSP). Due to the ease at which overground endoscopy can be performed, it has been possible to serially examine large groups of horses with this condition. The findings suggest that in young horses this condition is likely to be self-limiting in the majority of cases(over 70%). Currently a study assessing the association between overground endoscopic findings and laryngeal ultrasonography is ongoing.

Discussion and Conclusion

From the results of horses examined to dateit is evident that, using overground endoscopyallows operators to obtain an accurate assessment of the URT of horses in a safe and reliable manner. The URT abnormalities diagnosed have generally been comparable to those reported by others during HSTE (Dart et al. 2001; Tan et al. 2005; Franklin et al. 2006; Lane et al. 2006) suggesting that the diagnostic usefulness of the overground technique is at least comparable to HSTE.

Diagnosis of URT disease is sometimes partly based on the horse having a history of making a respiratory noise as described by the rider. In our experience riders’ observations of noise made during the exercise test were poorly associated with overground diagnoses. One further advantage that became evident during overground studies was that the end point of the test was the end of the gallop, such that changes in speed were dictated by the horse (and to some extent the rider), and not, as is the case with HSTE, the treadmill operator. Therefore the appearance, or lack thereof, of an abnormality had no effect on the outcome of the test. As a result, the overground technique is more closely comparable to race conditions than HSTE in which the end point of the exercise test is typically the point when an abnormality is detected (Tan et al. 2005; Lane et al. 2006).

Overground endoscopy is well tolerated and few complications occur during its use. It is probable that this technique will go from strength to strength and be used even more widely. The goal will be to diagnose correctly and treat conditions that were previously often diagnosed presumptively and treated by management methods and/or surgical procedures assumed to be efficacious but lacking objective evidence. Continued use of overground endoscopy should lead to increased understanding of and improvement in equine health and welfare.

References

Burn, J. F. and S. H. Franklin (2006). "Measurement of abnormal respiratory sounds during over-ground exercise." Equine Vet J38(4): 319-323.

Cheetham, J., Pigott, J.H., Thorson, L.M., Mohammed, H.O. and Ducharme, N.G. (2008) Racing performance following the laryngeal tie-forward procedure: a case control study. Equine vet. J.40, 501-507.

Dart, A. J., B. A. Dowling, et al. (2001). "Evaluation of high-speed treadmill videoendoscopy for diagnosis of upper respiratory tract dysfunction in horses." Aust Vet J79(2): 109-112.

Evans, D. (2004) Exercise testing in the field. In: Equine Sports Medicine and Surgery,Eds: K.W. Hinchcliff, A.J. Kaneps and R.J. Geor, W.B. Saunders, Philadelphia. pp 19-31.

Franklin, S.H., Naylor, J.R. and Lane, J.G. (2006) Videoendoscopic evaluation of the upper respiratory tract in 93 sport horses during exercise testing on a high-speed treadmill. Equine vet. J., Suppl. 36, 540-545.

Franklin, S.H., Burn, J.F. and Allen, K.J. (2008) Clinical trials using a telemetric endoscope for use during over-ground exercise: A preliminary study. Equine vet.J.40, 712-715.

Kannegieter, N. J. and M. L. Dore (1995). "Endoscopy of the upper respiratory tract during treadmill exercise: a clinical study of 100 horses." Aust Vet J72(3): 101-107.

Kelly, P.,G., Reardon, R.,M., Johnston, M., Pollock, P.J. (2013). Comparison of dynamic and resting endoscopy of the upper portion of the respiratory tract in 57 thoroughbred yearlings. Eq. Vet. J. DOI:10.1111/evj.12061

Lane, J. G., B. Bladon, et al. (2006a). "Dynamic obstructions of the equine upper respiratory tract. Part 1: observations during high-speed treadmill endoscopy of 600 Thoroughbred racehorses." Equine Vet J 38(5): 393-399.

Lane, J. G., B. Bladon, et al. (2006b). "Dynamic obstructions of the equine upper respiratory tract. Part 2: comparison of endoscopic findings at rest and during high-speed treadmill exercise of 600 Thoroughbred racehorses." Equine Vet J 38(5): 401-407.

Pollock, P. J., R. J. Reardon, et al. (2009). "Dynamic respiratory endoscopy in 67 Thoroughbred racehorses training under normal ridden exercise conditions." Equine Vet J41(4): 354-360.

Pollock, P.J., Kelly, P.G., Reardon, R.J.M., Kelly, G.M. (2013) Dynamic ventrorostral displacement of the dorsal laryngeal mucosa. Vet. Record. doi: 10.1136/vr.101319

Rakestraw, P. C., R. P. Hackett, et al. (1991). "Arytenoid cartilage movement in resting and exercising horses." Vet Surg20(2): 122-127.

Reardon, R.J., Fraser, B.S.L., Heller, J., Lischer, C., Parkin, T. and Bladon, B.M. (2008) The use of race winnings, ratings and a performance index to assess the effect of thermocautery of the soft palate for treatment of horses with suspected intermittent dorsal displacement. A case-control study in 110 racing Thoroughbreds. Equine vet. J.40, 508-513.

Tan, R. H., B. A. Dowling, et al. (2005). "High-speed treadmill videoendoscopic examination of the upper respiratory tract in the horse: the results of 291 clinical cases." Vet J170(2): 243-248.

Witte, S.H, Witte, T.H., Harriss, F., Kelly, G., Pollock, P.J. (2011). Association of owner-reported noise with findings during dynamic respiratory endoscopy in Thoroughbred racehorses.

Equine Vet. J. 43(1) 9-17.

Figure 1. An early version of an overground endoscope (jockey mounted)is tested on an all weather gallop. Another horse accompanies the horse of interest emulating normal exercise conditions.

Figure 2. High speed treadmill endoscopy was the gold standard, however, this was a very abnormal environment for a horse

Figure 3. The overground endoscope is safe and easy to place, and is well tolerated

Figure 4. Multiple abnormalities are common, as is seen here (laryngeal neuropathy, vocal cord collapse, and medial deviation of the aryepiglottc folds (MDAF))