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

Abstract

BackgroundHeart 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.ObjectivesTo 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 designRetrospective, observational cross‐sectional study.MethodsOne 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.ResultsDuring 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 limitationsThe 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.ConclusionsThe presence of arrhythmia increased HRV in both phases of exercise and recovery. Lameness decreased HRV during submaximal exercise.

Effects of pregnancy on electrocardiographic, vasovagal tonus index, and echocardiographic variables in horses

“…The balance of sympathetic and parasympathetic activity can be analyzed by variability in HR for assessing stress and different welfare states in farm animals [ 16 ]. In addition, HRV has been reported as useful for diagnosing arrhythmias in horses [ 17 , 18 ].…”

“…The balance of sympathetic and parasympathetic activity can be analyzed by variability in heart rate or HRV for assessing stress and different welfare states in farm animals [16]. In addition, HR variability (HRV) is useful for diagnosing arrhythmias in sports horses [17,18] and was widely used in horses [19][20][21][22]. Vasovagal tonus index or VVTI (time domain analyses of HRV) is a simple method of assessing sympathetic and parasympathetic tone balance in horses [23].…”

Evaluation of vasovagal tonus index and electrocardiographic parameters in horses using a new modified base apex lead method

“…Assessing heart rate variability (HRV) in a clinical context aids the evaluation of autonomic nervous functions. It is valuable for diagnosing cardiac arrhythmias, tracking recovery, determining overtraining status, and evaluating sport horse performance [ 2 – 4 ]. Telemetric ECG and ambulatory Holter systems enable rapid and noninvasive HRV assessments.…”

“…Telemetric ECG and ambulatory Holter systems enable rapid and noninvasive HRV assessments. Telemetric electrocardiography (Holter monitoring), with ECG configuration and HRV records, is used for monitoring arrhythmias during exercise [ 2 , 5 – 7 ]. The equipment is limited to stable rest or low-intensity exercises such as endurance for accurate evaluation in horses due to constraints like following the horse’s path or staying within a radio signal’s range [ 8 ].…”