Equine Electrocardiography

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.

Electrocardiographic Reference Values in Clinically Healthy Lusitano Horses

The Lusitano horse is gaining popularity in the equestrian world, and as a result, the significance of applied sports medicine for this breed is growing. As cardiology plays a crucial role in this field, numerous studies have been conducted to establish electrocardiographic reference values in various breeds to ensure a more accurate evaluation. However, studies regarding healthy Lusitano horses are lacking. So, this study aimed to establish electrocardiographic reference values for Lusitano horses, utilizing a sample of 82 clinically healthy animals. The evaluation involved lead II and base-apex lead measurements, with a median heart rate of 39 beats per minute being recorded. The P wave demonstrated a predominantly bifid configuration, while the QRS complex exhibited various forms. The most common QRS configurations were QR and R in lead II, and RS in the base-apex lead. Additionally, most T waves displayed a biphasic shape in both methods. Furthermore, statistically significant differences were noted based on age and gender. Some of the electrocardiographic values obtained differed from those previously published for other breeds. Given the relevance of electrocardiogram in cardiovascular evaluation, these findings bring valuable insights regarding the specific parameters for Lusitano horse and emphasize the importance of obtaining breed-specific electrocardiographic reference values.

Validation of an Equine Smart Textile System for Heart Rate Variability: A Preliminary Study

Electrocardiograms (ECGs), and associated heart rate (HR) and heart rate variability (HRV) measurements, are essential in assessing equine cardiovascular health and fitness. Smart textiles have gained popularity, but limited validation work has been conducted. Therefore, the objective of this study was to compare HR and HRV data obtained using a smart textile system (Myant) to the gold-standard telemetric device (Televet). Simultaneous ECGs were obtained using both systems in seven horses at rest and during a submaximal exercise test. Bland-Altman tests were used to assess agreement between the two devices. Strong to perfect correlations without significant differences between the two devices were observed for all metrics assessed. During exercise, mean biases of 0.31 bpm (95% limits of agreement: -1.99 to 2.61) for HR, 1.43 ms (-11.48 to 14.33) for standard deviation of R-R intervals (SDRR), and 0.04 (-2.30 to 2.38) for the HRV triangular index (TI) were observed. A very strong correlation was found between the two devices for HR (r = 0.9993, p < 0.0001) and for HRV parameters (SDRR r = 0.8765, p < 0.0001; TI r = 0.8712, p < 0.0001). This study demonstrates that a smart textile system is reliable for assessment of HR and HRV of horses at rest and during submaximal exercise.

A Smart Textile Band Achieves High-Quality Electrocardiograms in Unrestrained Horses

Electrocardiography (ECG) is an essential tool in assessing equine health and fitness. However, standard ECG devices are expensive and rely on the use of adhesive electrodes, which may become detached and are associated with reduced ECG quality over time. Smart textile electrodes composed of stainless-steel fibers have previously been shown to be a suitable alternative in horses at rest and during exercise. The objective of this study was to compare ECG quality using a smart textile girth band knit with silver and carbon yarns to standard adhesive silver/silver chloride (Ag/AgCl) electrodes. Simultaneous three-lead ECGs were recorded using a smart textile band and Ag/AgCl electrodes in 22 healthy, mixed-breed horses that were unrestrained in stalls. ECGs were compared using the following quality metrics: Kurtosis (k) value, Kurtosis signal quality index (kSQI), percentage of motion artifacts (%MA), peak signal amplitude, and heart rate (HR). Two-way ANOVA with Tukey’s multiple comparison tests was conducted to compare each metric. No significant differences were found in any of the assessed metrics between the smart textile band and Ag/AgCl electrodes, with the exception of peak amplitude. Kurtosis and kSQI values were excellent for both methods (textile mean k = 21.8 ± 6.1, median kSQI = 0.98 [0.92−1.0]; Ag/AgCl k = 21.2 ± 7.6, kSQI = 0.99 [0.97−1.0]) with <0.5% (<1 min) of the recording being corrupted by MAs for both. This study demonstrates that smart textiles are a practical and reliable alternative to the standard electrodes typically used in ECG monitoring of horses.

Electrocardiographic characteristics of trained and untrained standardbred racehorses

Background

Long‐term exercise induces cardiac remodeling that potentially influences the electrical properties of the heart.

Hypothesis/objectives

We assessed whether training alters cardiac conduction in Standardbred racehorses.

Animals

Two hundred one trained and 52 untrained Standardbred horses.

Methods

Cross‐sectional study. Resting ECG recordings were analyzed to assess heart rate (HR) along with standard ECG parameters and for identification of atrial and ventricular arrhythmias. An electrophysiological study was performed in 13 horses assessing the effect of training on sinoatrial (SA) and atrioventricular (AV) nodal function by sinus node recovery time (SNRT) and His signal recordings. Age and sex adjustments were implemented in multiple and logistic regression models for comparison.

Results

Resting HR in beats per minute (bpm) was lower in trained vs untrained horses (mean, 30.8 ± 2.6 bpm vs 32.9 ± 4.2 bpm; P = .001). Trained horses more often displayed second‐degree atrioventricular block (2AVB; odds ratio, 2.59; P = .04). No difference in SNRT was found between groups (n = 13). Mean P‐A, A‐H, and H‐V intervals were 71 ± 20, 209 ± 41, and 134 ± 41 ms, respectively (n = 7). We did not detect a training effect on AV‐nodal conduction intervals. His signals were present in 1 horse during 2AVB with varying H‐V interval preceding a blocked beat.

Conclusions and Clinical Importance

We identified decreased HR and increased frequency of 2AVB in trained horses. In 5 of 7 horses, His signal recordings had variable H‐V intervals within each individual horse, providing novel insight into AV conduction in horses.

The position of ground electrode affects electrocardiographic parameters in horses

Background and Aim:

Improper attachment of the grounding lead is one of the artifacts and causes difficulty in interpretation of ECG. This study aimed to examine the effects of the position of a ground electrode on electrocardiographic (ECG) parameters in horses.

Materials and Methods:

Sixteen Arabian horses without any cardiac problems were included in this study. The animals were divided into two groups, the base-apex lead method 1 (BA1 method) and the base-apex lead method 2 (BA2 method) with the reposition of the ground limb electrode to the xiphoid. ECG recordings (paper speed=25 mm/s and calibration=10 mm/mV) were performed to obtain six limb leads (leads I, II, III, aVR, aVL, and aVF). The amplitude and duration of P waves and QRS complexes, PR interval, QT interval, and T duration were analyzed. T wave morphology was observed. Heart rate was evaluated by using R-R interval in each recording.

Results:

Heart rate, P duration and amplitude, PR interval and T duration, and QRS duration and amplitude were not significantly different between the BA1 and the BA2 method, except that the BA2 method had a significantly higher QT interval than did the BA1 method (p<0.05). A higher significance of the percentage of coefficient of variation was seen on the P wave amplitude and the ORS amplitude in the BA1 method when compared to BA2 method (p<0.05).

Conclusion:

These data indicated that base-apex lead method with reposition of the ground limb electrode to the xiphoid can decrease variation of ECG configuration and might be useful for routine ECG evaluation and monitoring in horses. The limitation of this study was the evaluation of cardiac morphology and function by echocardiography to exclude cardiac problems. In further, the studies should examine the effect of breed, age, body weight, and sex on electrocardiography parameters in horses.

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.

Comparison of novel wearable cardiac monitors to yield accurate exercising ECG and heart rate data in horses

Exercise associated deaths (EADs) in horses are a problem for the equestrian industry. Sudden death (SD) is responsible for approximately 20% of EADs. The underlying cause of SD is suspected to be cardiovascular disease but often cannot be determined post-mortem. User-friendly cardiac monitors are needed for large scale investigations of arrhythmias associated with SD in horses. We hypothesised that novel wearable devices would provide exercising electrocardiograms (ECGs) of sufficient diagnostic quality for this purpose. Diagnostic quality of ECGs generated by two wearable devices (W2nd™ and Polar Equine™) were compared to simultaneous recordings with a telemetry unit (Televet™) in 5 Thoroughbreds completing 43 separate submaximal exercise tests on a high-speed treadmill. Maximal heart rate (HRmax) generated by mobile applications (HRmaxapp), HRmax after manual correction (HRmaxcorr), percentage of diagnostic ECGs (%diag) at the gallop, and overall quality assessed by visual analogue scale (VAS) were assessed by a blinded observer. HRmaxcorr did not differ significantly between groups. HRmaxapp was significantly lower for W2nd (166.8/min, 95% confidence interval (CI): 160.5-173.1/min) but did not differ significantly between Televet (178.8/min 95% CI: 165.8-191.1/min) and Polar (181.3/min, 95% CI: 174.5-188.1/min). HRmaxcorr was accurate and precise in all runs. HRmaxapp was within a priori limits of agreement in 16/23 W2nd and 18/19 Polar recordings. %diag was significantly lower (77.1%, 95% CI: 67.4-86.8) for W2nd than Polar (100%, 95% CI: 89.9-110.3). VAS was lower for W2nd (46.2, 95% CI: 35.5-57.0) than Polar (90.6, 25% CI: 79.4-101.9). In conclusion, wearable devices appear to be promising tools for investigation of equine exercising arrhythmias in large-scale studies.

Validation of an equine fitness tracker: heart rate and heart rate variability

The adoption of fitness tracker devices to monitor training in the equine market is in full expansion. However, the validity of most of these devices has not been assessed. The aim of this study was to examine the validity of heart rate (HR) and heart rate variability (HRV) measurements during high-intensity exercise by an integrated equine fitness tracker with an electrocardiogram (ECG) (Equimetre) in comparison to an ECG device (Televet). Twenty Thoroughbred racehorses were equipped with the two devices and completed a training session at the track. Data from 18 horses was readable to be analysed. Equimetre HR was compared to Televet HR derived from the corrected Televet ECG. HRV parameters were computed in a dedicated software (Kubios) on uncorrected and manually corrected ECG from both devices, and compared to the Televet corrected data. The HR was recorded on the entire training session and HRV parameters were calculated during the exercise and recovery periods. A strong correlation between the Equimetre HR and Televet HR on corrected data was found (Pearson correlation: r=0.992, P<0.001; root mean square error = 4.06 bpm). For HRV, the correlation was good for all parameters when comparing corrected Equimetre to corrected Televet data (Lin’s coefficient = 0.998). When comparing data obtained from uncorrected Equimetre data to the corrected Televet data, the correlation for HR was still good (Lin’s coefficient = 0.995) but the correlation for all HRV parameters was poor, except for the triangular index (Lin’s coefficient = 0.995). However, correlation between the uncorrected Televet HRV data and the corrected Televet data was equally poor (Lin’s coefficient <0.9). In conclusion, the integrated equine fitness tracker Equimetre satisfies validity criteria for HR monitoring in horses during high intensity exercise. When using corrected ECG data, it provides accurate HRV parameters as well.

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.

Pathological bradyarrhythmia in horses

Pathological bradyarrhythmia is rare in horses but should be especially considered when presented with a horse that has signs consistent with episodic weakness or collapse. This paper reviews the literature describing our current knowledge of, and possible mechanisms causing, clinically significant bradyarrhythmia in horses.