Atrial depolarization electrocardiographic features during orthodromic atrioventricular reciprocating tachycardia mediated by right-sided accessory pathway in the dog

Introduction/Objectives: Electrocardiographic features of atrial depolarization (AD) during orthodromic atrioventricular reciprocating tachycardia (OAVRT) have been widely studied to localize accessory pathways (APs) in humans. The aim of this study was to determine whether AD characteristics might also be used to determine AP anatomical sites in dogs. Animals, Materials and Methods: Clinical records for 83 dogs that underwent electrophysiologic studies for AP ablation were retrospectively analyzed. Accessory pathways were classified into three groups according to localization: right anterior (RA, 13.3%), right postero-septal (RPS, 36.1%), and right posterior (RP, 50.6%). Electrocardiographic characteristics of AD (duration, amplitude, and axis) and OAVRT (AD-AD, peak of R wave - atrial depolarization (R-AD)/atrial depolarization - peak of R wave (AD-R), peak to peak of R wave (RR) interval, and QT duration) were analyzed in all 12 leads. Results: Mean AD duration in RA, RPS, and RP was 48.0 ± 10.3 ms, 46.1 ± 10.6 ms, and 47.1 ± 10.2 ms, respectively, and the mean amplitude was 􀀀 0.25 ± 0.12 mV, 􀀀 0.28 ± 0.20 mV, and 􀀀 0.28 ± 0.18 mV, respectively. The median electrical axis on the frontal plane was 􀀀 90.0 ◦ (interquartile range [IQR]: 26.5 ◦ in RA, 9.4 ◦ in