title: Influence of 2nd-degree AV blocks, ECG recording length, and recording time on heart rate variability analyses in horses.
abstract: OBJECTIVE
  To assess the influence of 2nd-degree AV blocks (AVB) on RR interval-based heart rate variability (HRV) variables; to investigate the effect of using PP interval time series and of artifact filtering on HRV analyses; to investigate the influence of electrocardiogram (ECG) recording length and time of recording; and to calculate day-to-day variability and reference intervals of HRV variables.
  
  
  METHODS
  Thirty healthy adult horses.
  
  
  METHODS
  RR and PP interval time series were extracted from 10-h Holter ECGs and an automated filter was applied to the RR time series (RRf). Time-domain HRV variables were calculated based on RR, PP, and RRftime series and their relation to the number of AVBs was assessed. Hourly 10- and 60-min segments were extracted to investigate the influence of segment length and recording time on HRV variables. Day-to-day variability and reference intervals of HRV variables were calculated.
  
  
  RESULTS
  Variables of short-term HRV were significantly influenced by the number of AVBs when based on RR, but not when based on PP- and RRftime series. PP- and RRf-based HRV variables were in good agreement. The majority of HRV variables were influenced by recording time and ECG segment length. Day-to-day variability of HRV variables was low when based on 10-h ECG recordings but moderate to high when based on 60-min and 10-min recordings.
  
  
  CONCLUSIONS
  Second-degree AVBs significantly influence conventional RR-based, but not PP- and RRf-based time-domain HRV variables. However, PP and RRfanalyses have limitations and recording length and time of recording must be considered.
authors.affiliation: Clinic for Equine Internal Medicine, Equine Department, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland.
authors.forename: B H
authors.initials: BH
authors.lastname: Eggensperger
authors.affiliation: Clinic for Equine Internal Medicine, Equine Department, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland. Electronic address: cschwarzwald@vetclinics.uzh.ch.
authors.forename: C C
authors.initials: CC
authors.lastname: Schwarzwald
mesh_terms: D000818:Animals; D002940:Circadian Rhythm; D004562:Electrocardiography / Q000662:veterinary; D005260:Female; D006327:Heart Block / Q000503:physiopathology / Q000662:veterinary*; D006339:Heart Rate / Q000502:physiology*; D006734:Horse Diseases / Q000503:physiopathology*; D006736:Horses / Q000502:physiology*; D008297:Male; D012016:Reference Values; D013997:Time Factors
keywords: Automated artifact filtering; PP interval; RR interval; Sinus arrhythmia; Time domain