Variability Inter-observer between Three Methods of Electrocardiographic (Conventional, Computerized and Computerized Printed) on Healthy Cats

Abstract

Background: Electrocardiography is an exam widely used in feline medicine. It consists of recording the electrical activity of the heart in waves representing myocardial depolarization and repolarization. Two electrocardiographic evaluation methods are employed in dogs and cats: computerized and conventional. However, possible differences in ECG results performed by the different methods have been reported. This paper aims to evaluate the observer's interference in the interpretation of the electrocardiographic exams and possible differences between the methods: conventional single channel, computerized screen and computerized printed of healthy cats.Materials, Methods & Results: Electrocardiographic tracings were obtained from 58 healthy cats, aged between 1 and 10 years-old, of both sexes, of the Persian and mixed breed and therefore interpreted by four observers with similar degree of experience. The examinations were performed in a sequential manner, the computerized method first, and then the conventional method. The animals were gently contained in the right lateral decubitus position. The tracings obtained by the conventional method were printed on thermally sensitive graph paper. The computerized method was performed in computer by means of specific software (TEB® ECGPC version 6.2), being the waves delimited by the observer. The tracings were also printed by means of a jet printer, and also interpreted. The morphology of P waves, QRS complexes and T waves were analyzed in the derivations: I, II, III, aVR, aVL and aVF. Heart rate, amplitude and duration of the P, QRS and T waves, PR, QT and heart rate (HR) intervals were calculated in derivation II. Mean electric axis was determined in leads I and III. Comparing the methods, there was a difference observed in the values of P and R waves, QRS complex, QT and PR intervals and T wave polarity. The interpretation of the evaluators presented statistical differences in the duration of the P wave, QRS, QT and HR. The three methods used presented differences during the mean of the interpretation of the evaluators.Discussion: Some factors such as the positioning of the animal and the use of chemical containment may influence the electrocardiographic tracings, as well as variations between electrocardiographic devices. In our study, the non-use of sedation and the use of the same equipment in all animals reduced the variability of the results. The interpretation of the computerized method printed and on the screen presented different results which can be explained by the reduced human visual capacity when compared to the computers. It is known that the interpretation of different tracings by the observers might influence the results of the examination. The evaluators of the present study evaluated the same tracings, but there was a difference in the interpretation of the observers. Regarding the methods, there was a difference between the three methods evaluated in relation to the ST segment. The computerized on-screen method demonstrated in its totality isoelectric ST segments that represent normal pattern for the species. The conventional and computerized printed methods presented results of elevation in ST segments that represent alterations in the diagnosis. There was a difference between the measurements performed by different observers, however this fact did not influence the results of the tests, since the parameters remained within the normality standards for species. It can be concluded that the variation between observers and among the three methods evaluated suggests that the ST segment interpretation is subtle and less influenced when performed in the computerized method.