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PloS one2018; 13(3); e0194008; doi: 10.1371/journal.pone.0194008

Cardiac electrophysiological adaptations in the equine athlete-Restitution analysis of electrocardiographic features.

Abstract: Exercising horses uniquely accommodate 7-8-fold increases in heart rate (HR). The present experiments for the first time analysed the related adaptations in action potential (AP) restitution properties recorded by in vivo telemetric electrocardiography from Thoroughbred horses. The horses were subjected to a period of acceleration from walk to canter. The QRS durations, and QT and TQ intervals yielded AP conduction velocities, AP durations (APDs) and diastolic intervals respectively. From these, indices of active, λ = QT/(QRS duration), and resting, λ0 = TQ/(QRS duration), AP wavelengths were calculated. Critical values of QT and TQ intervals, and of λ and λ0 at which plots of these respective pairs of functions showed unity slope, were obtained. These were reduced by 38.9±2.7% and 86.2±1.8%, and 34.1±3.3% and 85.9±1.2%, relative to their resting values respectively. The changes in λ were attributable to falls in QT interval rather than QRS duration. These findings both suggested large differences between the corresponding critical (129.1±10.8 or 117.4±5.6 bpm respectively) and baseline HRs (32.9±2.1 (n = 7) bpm). These restitution analyses thus separately identified concordant parameters whose adaptations ensure the wide range of HRs over which electrophysiological activation takes place in an absence of heart block or arrhythmias in equine hearts. Since the horse is amenable to this in vivo electrophysiological analysis and displays a unique wide range of heart rates, it could be a novel cardiac electrophysiology animal model for the study of sudden cardiac death in human athletes.
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Publication Date: 2018-03-09 PubMed ID: 29522557PubMed Central: PMC5844547DOI: 10.1371/journal.pone.0194008Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

This study explores how horses adapt their heart rate during exercise, demonstrating electrophysiological changes which enable a broad range of heart rates. The research can potentially advance our understanding of sudden cardiac death in human athletes, with horses serving as a feasible experimental model due to their unique electrophysiological characteristics.

Research context and objectives

  • While it is known that exercising horses can accommodate significant increases in heart rate, the electrophysiological adaptations associated with this are less understood.
  • The purpose of this study is to investigate these physiological changes through analysis of the horses’ action potential or AP (the short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls).

Research Methodology

  • The study used in vivo telemetric electrocardiography (ECG) to record data from Thoroughbred horses subjected to exercise conditions, transitioning from a walk to a canter.
  • Various ECG features were measured, including the durations of the QRS complex, QT interval (time between start of the Q wave and the end of the T wave in the heart’s electrical cycle), and TQ interval (time from end of the T wave to the start of the next QRS complex), providing insights into AP conduction velocities, AP durations (APDs), and diastolic intervals.
  • From these measurements, the researchers calculated indices of active and resting AP wavelengths, respectively labeled λ and λ0. The critical values at which these functions showed unity slope were also obtained.

Findings

  • The study found that these critical values reduced by significant percentages relative to their resting values. The changes in λ were due to decreases in QT interval rather than changes in QRS duration.
  • They observed large differences between baseline heart rates and the critical values, indicative of the electrophysiological adaptations that allow a wide range of heart rates without inducing heart block or arrhythmias.

Implications

  • The results provide insights into adaptive mechanisms in the equine heart that allow for enhanced heart rate performance during exercise.
  • Given the unique range of heart rates exhibited by horses, they could serve as an appropriate animal model for studying cardiac electrophysiology, potentially aiding our understanding of sudden cardiac deaths in human athletes.

Cite This Article

APA
Li M, Chadda KR, Matthews GDK, Marr CM, Huang CL, Jeevaratnam K. (2018). Cardiac electrophysiological adaptations in the equine athlete-Restitution analysis of electrocardiographic features. PLoS One, 13(3), e0194008. https://doi.org/10.1371/journal.pone.0194008

Publication

PloS one
ISSN: 1932-6203
NlmUniqueID: 101285081
Country: United States
Language: English
Volume: 13
Issue: 3
Pages: e0194008
PII: e0194008

Researcher Affiliations

Li, Mengye
  • Physiological Laboratory, University of Cambridge, Cambridge, United Kingdom.
Chadda, Karan R
  • Physiological Laboratory, University of Cambridge, Cambridge, United Kingdom.
  • Faculty of Health and Medical Sciences, University of Surrey, Guildford, United Kingdom.
Matthews, Gareth D K
  • Physiological Laboratory, University of Cambridge, Cambridge, United Kingdom.
Marr, Celia M
  • Rossdales Equine Hospital and Diagnostic Centre, Exning, Suffolk, United Kingdom.
Huang, Christopher L-H
  • Physiological Laboratory, University of Cambridge, Cambridge, United Kingdom.
  • Division of Cardiovascular Biology, Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom.
Jeevaratnam, Kamalan
  • Physiological Laboratory, University of Cambridge, Cambridge, United Kingdom.
  • Faculty of Health and Medical Sciences, University of Surrey, Guildford, United Kingdom.

MeSH Terms

  • Action Potentials
  • Adaptation, Physiological
  • Animals
  • Electrocardiography / veterinary
  • Female
  • Heart Conduction System / physiology
  • Horses / physiology
  • Male
  • Physical Conditioning, Animal / physiology
  • Running / physiology
  • Telemetry / veterinary
  • Walking / physiology

Grant Funding

  • Wellcome Trust
  • MR/M001288/1 / Medical Research Council
  • PG/14/79/31102 / British Heart Foundation

Conflict of Interest Statement

The authors have declared that no competing interests exist.

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Citations

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