Evaluation of heart rate and rhythm during exercise

Heart rate and heart rate variability in horses undergoing hot and cold shoeing

Heart rate variability (HRV) is a frequently used indicator of autonomic responses to various stimuli in horses. This study aimed to investigate HRV variables in horses undergoing cold (n = 25) or hot (n = 26) shoeing. Multiple HRV variables were measured and compared between horses undergoing cold and hot shoeing, including the time domain, frequency domain, and nonlinear variables pre-shoeing, during shoeing, and at 30-minute intervals for 120 minutes post-shoeing. The shoeing method interacted with time to change the HRV variables standard deviation of RR intervals (SDNN), root mean square of successive RR interval differences (RMSSD), very-low-frequency band, low-frequency band (LF), the LF to high-frequency band ratio, respiratory rate, total power, standard deviation perpendicular to the line of identity (SD1), and standard deviation along the line of identity (SD2). SDNN, RMSSD, and total power only increased 30 minutes after hot shoeing (all p < 0.05). Triangular interpolation of normal-to-normal intervals (TINN) and the HRV triangular index increased during and up to 120 minutes after hot shoeing (p < 0.05-0.001). TINN increased only during cold shoeing (p < 0.05). LF increased 30 and 60 minutes after hot shoeing (both p < 0.05). SD1 and SD2 also increased 30 minutes after hot shoeing (both p < 0.05). SDNN, TINN, HRV triangular index, LF, total power, and SD2 were higher in hot-shoed than cold-shoed horses throughout the 120 minutes post-shoeing. Differences in HRV were found, indicating increased sympathovagal activity in hot shoed horses compared to cold shoed horses.

Heart rate variability during high-speed treadmill exercise and recovery in Thoroughbred racehorses presented for poor performance

BACKGROUND

Heart rate variability (HRV) analysis measures the inter-beat interval variation of successive cardiac cycles. Measurement of these indices has been used to assess cardiac autonomic modulation and for arrhythmia identification in exercising horses.

OBJECTIVES

To report HRV indices during submaximal exercise, strenuous exercise and recovery, and explore relationships with clinical conditions (arrhythmias, lameness, equine gastric ulcer syndrome [EGUS], lower airway inflammation and upper respiratory tract obstructions [URTOs]) in Thoroughbred racehorses.

STUDY DESIGN

Retrospective, observational cross-sectional study.

METHODS

One hundred and eighty Thoroughbred horses underwent a treadmill exercise test with simultaneous electrocardiographic recording. Time-domain HRV indices (standard deviation of the R-R interval [SDRR]; root mean square of successive differences [RMSSD]) were derived for submaximal and strenuous exercise and recovery segments. Clinical conditions (arrhythmia [during each phase of exercise], lameness, EGUS, lower airway inflammation and URTO) were assigned to binary categories for statistical analysis. Relationships between selected HRV indices and the clinical conditions were explored using linear regression models.

RESULTS

During submaximal exercise, lameness was associated with decreased logRMSSD (B = -0.19 95% confidence interval [CI] -0.31 to -0.06, p = 0.006) and arrhythmia was associated with increased logRMSSD (B = 0.31 95% CI 0.01-0.608, p = 0.04). During strenuous exercise, arrhythmia was associated with increased HRV indices (logSDRR B = 0.51 95% CI 0.40-0.62, p < 0.001; RMSSD B = 0.60 95% CI 0.49-0.72, p < 0.001). During recovery, arrhythmia was associated with increased HRV indices (logSDRR B = 0.51 95% CI 0.40-0.62, p < 0.001, logRMSSD B = 0.60 95% CI 0.49-0.72, p < 0.001).

MAIN LIMITATIONS

The main limitations of this retrospective study were that not every horse had the full range of clinical testing, therefore some horses may have had undetected abnormalities.

CONCLUSIONS

The presence of arrhythmia increased HRV in both phases of exercise and recovery. Lameness decreased HRV during submaximal exercise.

Effects of a 15° Variation in Poll Flexion during Riding on the Respiratory Systems and Behaviour of High-Level Dressage and Show-Jumping Horses

From previous studies, the International Society for Equitation Science has advised that further research be conducted on the physiological/psychological effects of less-exacerbated poll flexion angles. We aimed to evaluate the effects of two riding poll flexion positions with a difference of only 15° on the respiratory systems and behaviour of horses through an evaluation of dynamic airway collapse via over-ground endoscopy, the pharyngeal diameter, pleural pressure, arterial oxygenation and lactate, HR/RR, and the occurrence of conflict behaviours. Twenty high-level dressage and twenty show-jumping horses underwent a 40 min ridden test at a ground angle of 85°; 3 weeks later, they underwent a ridden test at a 100° ground angle (the angle between the ground and the line from the forehead to the muzzle) and in a cross-over design. Using a mixed model for repeated measures, Wilcoxon/Friedman tests were carried out according to the experimental design and/or error normality. For both groups, at 100°, conflict behaviours and upper airway tract abnormalities were significantly more frequent, and the pleural pressure was higher, and the pharyngeal diameter was lower. At 85°, relaxation behaviours were significantly more frequent. Lactate was significantly higher at 100° only in the dressage horses. Compared to the first test at 85°, the HR/RR were significantly lower at the beginning of the second test (at 100°) but higher at the end. The significant differences identified in these dressage and show-jumping horses support the idea that an increase of just 15° in riding poll flexion can have negative effects on the respiratory system and behaviour of a horse and therefore on its welfare.

Fluctuations of Physiological Variables during Conditioning of Lipizzan Fillies before Starting under Saddle

Simple Summary

Equine exercise physiological research has led to the development of scientifically sound programs that improve the physical fitness of horses. However, there are few scientific studies on the physical responses of young horses during initial training, although they are known to be sensitive to exercise overload. Our study focused on purebred Lipizzan fillies, aged 4 years in the early stages of training. To investigate the response of the fillies to a workload achieved by lunging, heart, and respiratory rates, rectal and skin temperatures, and blood parameters, cortisol and lactate concentrations were measured. All measured values, which were within a normal range for warm-blooded horses, increased after exercise due to the increased requirements of the working muscles and heat production. Despite the increase in surface temperatures of different body regions after exercise, their distributions remained unchanged. It was highest in the front regions, followed by the rear regions, and lowest in the lower parts of the legs. Our study contributes to the knowledge of physiological processes in young horses during exercise, as well as supplements research in the field of equine exercise testing, sports physiology, and animal welfare, and provides important knowledge for the conservation and development of the Lipizzan breed.

Abstract

Scientific studies on the physiological responses of young horses to workloads are limited. Therefore, the aim of our study was to determine the basal values of some cardiovascular, thermoregulatory, hematological, and biochemical parameters in 10 purebred Lipizzan fillies aged 4 years in the initial phase of training, and their responses to a graded workload, i.e., by lunging for 15 min in four exercise tests at 2-week intervals. The basal values of the measured parameters were within a range for warm-blooded horses and mostly increased after exercise in all four exercise tests. Resting heart rates were above physiological values at the baseline but decreased as the study progressed. Bilateral symmetry of body surface temperatures (BSTs) was confirmed at rest and after exercise. The highest BSTs were measured at the cranial, followed by the caudal and distal body regions. A moderate increase in cortisol and a small increase in lactate concentration indicated a low intensity of workload. The results presented contribute to the knowledge of the complex physiological processes that occur in young horses during exercise and provide a basis for further research into the field of sports physiology and welfare, as well as the conservation and development of the Lipizzan breed.

Validation of an equine fitness tracker: ECG quality and arrhythmia detection

BACKGROUND

Cardiac arrhythmias in exercising horses are the focus of much interest, both in terms of what is considered normal and potential associations with poor performance and sudden cardiac death. One barrier to performing large-scale studies is the lack of an easily applicable device, to allow recording of large numbers of high-quality exercising electrocardiograms (ECGs). The EquimetreTM is a new wearable device which records a single lead ECG, amongst other parameters. Validation of such wearable devices is essential before further studies are undertaken.

OBJECTIVES

To evaluate the quality of ECG using the EquimetreTM and compare arrhythmia detection during exercise with the reference TelevetTM system.

STUDY DESIGN

Prospective blinded clinical study.

METHODS

Simultaneous ECGs were recorded with both systems in 49 healthy horses during exercise. High intensity exercise (>40km/h) was performed by 29 racehorses, and lower intensity exercise for the remainder of the racehorses and show jumpers. Tracings were excluded if >10% artefact was present (duration of artefact relative to duration of exercise). For included ECGs, the duration of artefact was recorded and compared. ECGs were evaluated using Kubios premium software. Arrhythmia detection (yes/no) and arrhythmia classification (sinus arrhythmia, narrow complex of similar morphology to the sinus complexes or wide complex with a different morphology) were compared using Cohen's Kappa coefficient.

RESULTS

Nine TelevetTM ECGs and 3 EquimetreTM ECGs were excluded due to artefact >10%. TelevetTM ECGs included significantly more artefact during exercise than EquimetreTM ECGs (5% vs. 0.25% p<0.001). Arrhythmia analysis was performed on 38 horses' paired ECGs. The Kappa coefficient was excellent for arrhythmia detection (K=0.97) and arrhythmia classification (K=0.93).

MAIN LIMITATIONS

Relatively low numbers of horses with arrhythmias (n=21) were included. The ECG recordings only provided one lead, making arrhythmia classification challenging in some cases.

CONCLUSIONS

The Equimetre device provides a reliable ECG for arrhythmia detection during exercise. This system may be useful clinically and for future large-scale investigations into the occurrence and significance of exercising arrhythmias.

Application of an electrocardiography device (iECG) for heart rhythm analysis after exercise in Thoroughbred horses

AliveCor is a smartphone electrocardiography device (iECG) providing automated heart rate (HR) and rhythm determination. Atrial fibrillation (AF) in horses often is paroxysmal and rapid ECG acquisition is needed for diagnostic confirmation. iECGs were collected post-race from 15 horses with AF and 64 horses in sinus rhythm (SR). Results of manual assessment were compared to 3 commercial algorithms for HR and rhythm. Agreement between manually derived HR (HR_M ) and HR derived by the AliveECG Vet (HR_VET ) and Kardia version-1 (K_V1 HR) and Kardia advanced (K_ADV HR) algorithms was quantified by the Bland-Altman limits of agreement test. Agreement between manual rhythm classification and K_V1 and K_ADV algorithms for AF and SR was calculated by the Kappa statistical coefficient. The agreement (bias, 95% limits), between HR_M and HR_VET was 7.1 BPM (-29 to 43) in AF and -4.2 BPM (-38 to 30) in SR, between HR_M and K_V1 HR, was -0.3 BPM (-31 to 30) in AF and 0.2 BPM (-3 to 4) in SR, and between HR_M and K_ADV HR was 7.0 BPM (-29 to 43) in AF and 0.2 BPM (-3.9 to 4.2) in SR. Agreement between manual rhythm classification and K_V1 was 0.36 (0.13-0.59), and K_ADV was 0.84 (0.68-0.99). Sensitivity and specificity for identification of AF and SR of the K_V1 algorithm were 60, 100% and 83, 100%, respectively, and of K_ADV was 87, 100% and 93, 100% respectively. The Kardia algorithms improved precision for HR determination in SR but not AF. The advanced algorithm accurately distinguished between AF and SR. The iECG is suitable for recording episodes of AF following exercise.

A Preliminary Investigation into Ridden Water Submersion Training as an Adjunct to Current Condition Training Protocols in Performance Horses

Simple Summary

Superficial Digital Flexor Tendon (SDFT) injuries are the most common musculoskeletal injury reported in equestrian jumping disciplines. In an attempt to reduce incidences of injuries in elite event horses, Ridden Water Submersion Training (RWST) is a form of condition training that involves submerging the horse up to sternum height in water and trotting for set intervals. It is used by a small number of trainers to increase cardiovascular fitness whilst potentially minimising tendon temperature increase, which is typically reported during traditional condition training sessions. The results of this study suggest that RWST acted as a moderate sub-maximal intensity level of exercise in a group of elite international event horses whilst preventing the accompanying increase of distal limb temperature commonly associated with condition training on land. RWST could thus be a useful adjunct to current condition training protocols, particularly for horses that compete in disciplines that have high incidence rates of tendon injury. However, further research is required to provide a more comprehensive understanding of the workload imposed during RWST training.

Abstract

This observational study aimed to elucidate the effects of RWST on the cardiovascular and musculoskeletal systems of horses and concurrently determine whether RWST limits distal limb temperature increases previously reported during gallop training on land. A group of 15 clinically sound international event horses were recruited, and heart rate (HR), speed (km/h) and thermal images of the distal limb were analysed at set intervals during RWST training. Intervals of RWST produced a total mean HR_max value of 65.18 ± 3.76%, which is within the parameters for increased aerobic stamina. Mean HR increased significantly (p < 0.01) while mean distal limb temperature decreased significantly (p < 0.01) between warm-up and RWST, which contrasts with positive correlations previously reported during gallop training on land. These preliminary results suggest that RWST can be classed as a moderate submaximal intensity exercise in elite international event horses whilst restricting an increase in temperature of the distal limb that is commonly associated with tendon rupture. Horses competing at very elite levels of eventing only represent a small percentage of the total performance population; therefore, further research is needed to ascertain the physiological effects of RWST in non-elite performance horses, as well as horses competing across various equestrian disciplines.

Incidence, recurrence, and outcome of postrace atrial fibrillation in Thoroughbred horses

BACKGROUND

Atrial fibrillation (AF) impacts performance and horse and jockey safety. Understanding the outcomes of AF identified postrace will better inform regulatory policy.

HYPOTHESIS/OBJECTIVES

To investigate the outcomes after episodes of AF identified postrace and determine whether affected horses are at increased risk of additional episodes compared to the general racing population.

ANIMALS

Total of 4684 Thoroughbred racehorses.

METHODS

Race records for Thoroughbred horses racing in Hong Kong from 2007 to 2017 were reviewed. Horses that performed below expectation were examined by cardiac auscultation and ECG. Incidence and recurrence of AF were compared between horses with and without a history of AF and between horses with paroxysmal and persistent episodes using Fisher's exact test.

RESULTS

There were 96 135 race starts during the study. Atrial fibrillation was identified in 4.9% of horses, with an overall incidence of 2.7 episodes per 1000 starts. The incidence of AF in horses after any previous episode (12.8 per 1000 starts) was higher than for horses with no previous episode (2.4 per 1000 starts; odds ratio [OR], 5.3; 95% confidence interval [CI], 3.8-7.6). Recurrence was seen in 64% of horses previously treated for persistent AF, which was higher than recurrence in horses with paroxysmal AF (23%; OR, 5.9; 95% CI, 1.6-21.2). Median duration between episodes was 343 days (range, 34-1065).

CONCLUSIONS AND CLINICAL IMPORTANCE

Thoroughbreds are at increased risk of recurrent AF after both paroxysmal and persistent episodes, but the duration of time between episodes varies widely. These findings support a substantial burden of AF among individual Thoroughbred racehorses.

Using Different Combinations of Body-Mounted IMU Sensors to Estimate Speed of Horses-A Machine Learning Approach

Speed is an essential parameter in biomechanical analysis and general locomotion research. It is possible to estimate the speed using global positioning systems (GPS) or inertial measurement units (IMUs). However, GPS requires a consistent signal connection to satellites, and errors accumulate during IMU signals integration. In an attempt to overcome these issues, we have investigated the possibility of estimating the horse speed by developing machine learning (ML) models using the signals from seven body-mounted IMUs. Since motion patterns extracted from IMU signals are different between breeds and gaits, we trained the models based on data from 40 Icelandic and Franches-Montagnes horses during walk, trot, tölt, pace, and canter. In addition, we studied the estimation accuracy between IMU locations on the body (sacrum, withers, head, and limbs). The models were evaluated per gait and were compared between ML algorithms and IMU location. The model yielded the highest estimation accuracy of speed (RMSE = 0.25 m/s) within equine and most of human speed estimation literature. In conclusion, highly accurate horse speed estimation models, independent of IMU(s) location on-body and gait, were developed using ML.

Evaluation of a novel ambulatory electrocardiogram monitor (the Carnation Ambulatory Monitor) for use in horses

INTRODUCTION

Short-term electrocardiogram (ECG) examinations of horses may not detect paroxysmal arrhythmias. Twenty-four hour Holter equipment can be unwieldy and inconvenient for long-term use. This study evaluated a novel long-term ECG patch recorder, the Carnation Ambulatory Monitor (CAM) in horses, determining ideal placement, practicality, durability and performance.

ANIMALS

Twenty-one adult mixed-breed horses.

METHODS

Prospective observational study. Three horses had ECG patches fitted at selected sites (phase 1); the two most promising sites were used for further wear testing (phase 2) and the best site was chosen for a trial in 18 horses (phase 3), 16 of which had presented for evaluation of cardiac disease. In phase 1, the CAM was compared with a standard telemetric ECG. The CAM ECGs were analysed using proprietary software.

RESULTS

The most promising sites for CAM placement were the ventral midline caudal to the xiphisternum and left thorax caudal to the girth. The ventral midline was chosen for further evaluation. The CAM provided reliable and generally excellent ECG quality at rest (median quality score 4.5/5, range 3-5), over extended periods, allowing detection of arrhythmias. The ECG quality was poor during exercise (median quality score 1, range 1-5), except in three horses. In 15/17 placements in the standing horse, greater than 85% of the potential recording time was achieved.

CONCLUSIONS

The CAM is a convenient and well-tolerated device for evaluating equine cardiac rhythm at rest over long periods. Further evaluation of the ideal placement site during exercise may increase its diagnostic utility.

Prevalence of cardiac arrhythmias and R-R interval variation in healthy Thoroughbred horses during official Chuckwagon races and recovery

The prevalence and severity of cardiac arrhythmias in healthy racehorses undergoing competition is not well defined. The aim was to characterize arrhythmias in Thoroughbreds participating in official Chuckwagon races and to determine normal beat-to-beat (R-R) variability during supramaximal exercise. Electrocardiograph (ECG) recordings were obtained during pre-race, race, and active-recovery from 82 clinically healthy Thoroughbreds. ECG recordings were analyzed for arrhythmias and mean percent R-R deviation. Plasma lactate and high-sensitivity troponin (hs-cTnT) were also measured. Fifty-two ECGs were included in the analysis. Arrhythmias were seen in 48/52 horses (92%) and were predominantly isolated events. No complex rhythms were observed. During the race, 92% of horses had arrhythmias (81% supraventricular premature complex [SVPC]; 33% ventricular premature complex [VPC]). Eleven percent of racing arrhythmias were VPCs (all singlets except for two couplets). During active-recovery, 58% of horses had arrhythmias (56% SVPC; 15% VPCs): Three horses had VPC couplets and one horse had a VPC triplet. All plasma hs-cTnT were within normal limits. The measured lactate was 28.5 ± 4.5 mmol/L, confirming supramaximal exercise. R-R variation ranged between -9.5 to +18.8% during pre-race (mean heart rate [HR], 155 ± 22 beats per min [bpm]), -27.8 to +45.3% during racing (mean HR, 200 ± 9 bpm) and -16.4 to +40.1% during active-recovery (mean HR, 165 ± 14 bpm). Maximal and 1st percentile R-R shortening and lengthening were significantly greater at race than pre-race and active-recovery (P < 0.0001). Racing and active-recovery maximal R-R lengthening were significantly greater than pre-race (P = 0.0003). Supraventricular premature complexes and VPCs are prevalent in healthy horses undergoing Chuckwagon racing. R-R variation is greater during racing than has previously been described.

Smart textiles biotechnology for electrocardiogram monitoring in horses during exercise on treadmill: Validation tests

BACKGROUND

There are several bioengineering solutions aimed at improving human health and welfare. Smart electrodes based on textile substrates have met the growing demand for comfort, reliability, and robustness when acquiring physiological signals.

OBJECTIVES

Given the importance of good quality electrocardiograms (ECG) in equine sports medicine, this study focuses on the validation of smart textile electrodes to acquire ECG signals in horses during treadmill exercise.

STUDY DESIGN

The performance of the smart textile electrodes is compared with standard silver/silver chloride (Ag/AgCl) electrodes in terms of signal quality.

METHODS

Five healthy Standardbred mares were fitted with two identical electronic systems for the simultaneous recording of ECGs during a standardised exercise test (SET) on a treadmill. One system was equipped with smart textile electrodes, whereas the second was equipped with standard Ag/AgCl electrodes. The Ag/AgCl electrodes were positioned on shaved skin with self-adhesive pads, and without (SET1) or with glue (SET2). The textile electrodes were positioned without shaving the skin. The Kurtosis (k) value for each ECG trace recorded was calculated as an index of ECG signal quality.

RESULTS

For the textile electrodes, k values were higher, and closer to ideal compared to Ag/AgCl electrodes. The median values of the Signal Quality Indexes (kSQI) were higher for textile compared to Ag/AgCl electrodes. These differences were significant in SET 2 (P < .001), but not in SET 1 (P = .08).

MAIN LIMITATIONS

This study was limited to treadmill exercise that did not include a rider or harness.

CONCLUSIONS

During treadmill exercise, textile electrodes are a practical solution for collecting good quality ECG traces.

Exercise Induced Laryngeal Obstruction in Humans and Equines. A Comparative Review

Dynamic obstructions of the larynx are a set of disorders that occur during exercise in equines and humans. There are a number of similarities in presentation, diagnosis, pathophysiology and treatment. Both equines and humans present with exercise intolerance secondary to dyspnea. During laryngoscopy at rest, the larynx appears to function normally. Abnormalities are only revealed during laryngoscopy at exercise, seemingly triggered by increased ventilatory demands, and quickly resolve after cessation of exercise. Lower airway disease (asthma being the most prevalent condition), cardiac disease and lack of fitness are the major differentials in both species. Laryngoscopic examination during exercise should be performed from rest to peak exertion to allow for a comprehensive diagnosis, including where the airway collapse begins, and thereafter how it progresses. Dynamic disorders with most visual similarity between humans and equines are: aryepiglottic fold collapse (both species); equine dynamic laryngeal collapse (DLC) relative to some forms of human combined supraglottic/glottic collapse; and epiglottic retroversion (both species). Quantitative grading techniques, such as airway pressure measurement, that have proven effective in veterinary research are currently being piloted in human studies. Conditions that appear visually similar are treated in comparable ways. The similarities of anatomy and certain types of dynamic collapse would suggest that the equine larynx provides a good model for human upper respiratory tract obstruction during exercise. Thus, close collaboration between veterinarians and medical personal may lead to further advancements in understanding pathophysiologic processes, and enhance the development of improved diagnostic tests and treatments that will benefit both species.

Cardiovascular Response to Exercise and Training, Exercise Testing in Horses

The physiology of exercise and training is fascinating, and hundreds of interesting studies have given insight into its mechanisms. Exercise testing is a useful clinical tool that can help veterinarians assess poor performance, fitness, and performance potential and prevent injuries. The clinically applicable aspects of cardiovascular adaptions to training and exercise testing are highlighted in this review. Different exercise tests should be used to evaluate horses performing in different disciplines and levels. Exercise tests that simultaneously assess several body systems can be beneficial when assessing poor performance, because this is often a multifactorial problem with signs not detectable at rest.

Cardiac/Cardiovascular Conditions Affecting Sport Horses

Cardiac murmurs are not uncommonly detected in the equine athlete. Although most are benign in nature, differentiation and quantification of murmurs due to valvular regurgitation are important for prognosis and recommendations. Arrhythmias can be associated with structural disease or occur independently and may range in severity from minimal clinical effect to poor performance to presenting a safety risk to rider and horse. This article discusses commonly encountered cardiac conditions in the sport horse. Physical examination, diagnostic approach, valvular disease, and arrhythmias with an impact on performance or ridden safety are discussed.

The heart remains the core: cardiac causes of poor performance in horses compared to human athletes

Cardiac remodelling occurs in response to exercise and is generally beneficial for athletic performance due to the increase in cardiac output. However, this remodelling also may lead to an increased prevalence of cardiac murmurs and arrhythmias. In most cases, these are not considered to be significant. However, in some cases, there may be potentially deleterious consequences. Whilst sudden cardiac death (SCD) is a rare occurrence, the consequences are catastrophic for both the horse and potentially the rider or driver. Furthermore, the sudden death of a horse in the public arena has negative connotations in regards to public perception of welfare during equestrian sports. Prediction of which individuals might be susceptible to potential deleterious effects of exercise is a focus of interest in both human and equine athletes but remains a challenge because many athletes experience cardiac murmurs and exercise-induced arrhythmias that are clinically irrelevant. This review summarises the effects of exercise on cardiac remodelling in the horse and the potential effects on athletic performance and SCD. The use of biomarkers and their future potential in the management of athletic horses is also reviewed.