Observer agreement for detection of cardiac arrhythmias on telemetric ECG recordings obtained at rest, during and after exercise in 10 Warmblood horses

P>Reasons for performing study: Frequent supraventricular or ventricular arrhythmias during and after exercise are considered pathological in horses. Prevalence of arrhythmias seen in apparently healthy horses is still a matter of debate and may depend on breed, athletic condition and exercise intensity. Objectives: To determine intra- and interobserver agreement for detection of arrhythmias at rest, during and after exercise using a telemetric electrocardiography device. Materials and methods: The electrocardiogram (ECG) recordings of 10 healthy Warmblood horses (5 of which had an intracardiac catheter in place) undergoing a standardised treadmill exercise test were analysed at rest (R), during warm-up (W), during exercise (E), as well as during 0-5 min (PE0-5) and 6-45 min (PE6-45) recovery after exercise. The number and time of occurrence of physiological and pathological 'rhythm events' were recorded. Events were classified according to origin and mode of conduction. The agreement of 3 independent, blinded observers with different experience in ECG reading was estimated considering time of occurrence and classification of events. Results: For correct timing and classification, intraobserver agreement for observer 1 was 97% (R), 100% (W), 20% (E), 82% (PE0-5) and 100% (PE6-45). Interobserver agreement between observer 1 vs. observer 2 and between observer 1 vs. 3, respectively, was 96 and 92.6% (R), 83 and 31% (W), 0 and 13% (E), 23 and 18% (PE0-5), and 67 and 55% (PE6-45). When including the events with correct timing but disagreement for classification, the intraobserver agreement increased to 94% during PE0-5 and the interobserver agreement reached 83 and 50% (W), 20 and 50% (E), 41 and 47% (PE0-5), and 83.5 and 65% (PE6-45). The interobserver agreement increased with observer experience. Conclusions: Intra- and interobserver agreement for recognition and classification of events was good at R, but poor during E and poor-moderate during recovery periods. These results highlight the limitations of stress ECG in horses and the need for high-quality recordings and adequate observer training.