Appropriate threshold levels of cardiac beat-to-beat variation in semi-automatic analysis of equine ECG recordings

Abstract

BackgroundAlthough premature beats are a matter of concern in horses, the interpretation of equine ECG recordings is complicated by a lack of standardized analysis criteria and a limited knowledge of the normal beat-to-beat variation of equine cardiac rhythm. The purpose of this study was to determine the appropriate threshold levels of maximum acceptable deviation of RR intervals in equine ECG analysis, and to evaluate a novel two-step timing algorithm by quantifying the frequency of arrhythmias in a cohort of healthy adult endurance horses.ResultsBeat-to-beat variation differed considerably with heart rate (HR), and an adaptable model consisting of three different HR ranges with separate threshold levels of maximum acceptable RR deviation was consequently defined. For resting HRs <60 beats/min (bpm) the threshold level of RR deviation was set at 20%, for HRs in the intermediate range between 60 and 100 bpm the threshold was 10%, and for exercising HRs >100 bpm, the threshold level was 4%. Supraventricular premature beats represented the most prevalent arrhythmia category with varying frequencies in seven horses at rest (median 7, range 2–86) and six horses during exercise (median 2, range 1–24).ConclusionsBeat-to-beat variation of equine cardiac rhythm varies according to HR, and threshold levels in equine ECG analysis should be adjusted accordingly. Standardization of the analysis criteria will enable comparisons of studies and follow-up examinations of patients. A small number of supraventricular premature beats appears to be a normal finding in endurance horses. Further studies are required to validate the findings and determine the clinical significance of premature beats in horses.

The use of heart rate variability analysis to detect arrhythmias in horses undergoing a standard treadmill exercise test

“…The study by Flethøj et al showed healthy Arab horses have very narrow % R‐R variation of approximately 4% at a HR of greater than 100/min during ridden exercise . Data from our study provide similar results using a different analysis technique.…”

“…Resting heart rate variability (HRV) has been well described in horses . However, during exercise, publications documenting the normal R‐R variation are limited . It is challenging during analysis of an exercising electrocardiograph (ECG) to separate truly premature beats from normal beat‐to‐beat variation, when the degree of normal variation is unclear, P‐QRS‐T morphology is difficult to differentiate and motion artifacts impair ECG quality.…”

“…At the onset of exercise, withdrawal of vagal tone increases HR to approximately 100‐120 beats/min. Sympathetic tone and neurohumoral regulation further elevate the HR above 120 beats/min . As HR rises, differences between R‐R intervals become less apparent.…”

“…A recently published study suggests that normal % R‐R variation of falls between −4 and +4% of the preceding R‐R interval at HRs above 100/min. This is based on data from 11 healthy Arabian endurance horses during ridden exercise, obtained from computer modeling of the width of a cluster of “normal” beats within an R‐R deviation plot, but it is unknown if this variation is consistent across breeds and types of exercise …”

Frequency of cardiac arrhythmias in horses during straight and untethered swimming

“…18 Higher threshold values were applied for HRs between 60 and 100 bpm (10%) and below 60 bpm (20%). 18 Each ECG was checked manually to ensure accurate detection of the QRS complexes. Raw data were exported for HR analysis and each ECG was manually inspected for arrhythmias by two operators [S.M, R.L] as described below.…”