Anatomic distribution and electrophysiologic properties of accessory atrioventricular pathways in dogs

ObjectiveçTo evaluate the anatomic distribution and electrophysiologic properties of accessory pathways (APs) in dogs. DesignçCase series. Animalsç10 dogs with tachyarrhythmias associated with an AP. ProceduresçEach dog underwent electrophysiologic testing to determine the inducibility of documented and undocumented arrhythmias and to identify location, conduction properties, and antegrade and retrograde effective refractory periods of the APs. Radiofrequency catheter ablation was then performed. Resultsç15 APs were identified; 7 dogs each had a single AP, and 3 had multiple APs. Fourteen of the 15 APs were right-sided (6 right free wall, 4 posteroseptal, 3 midseptal, and 1 anteroseptal), and 1 was left-sided (left free wall). All APs conducted in an all-or-none fashion. Unidirectional retrograde conduction was observed in 11 APs, and bidirectional conduction was observed in 4. All documented tachyarrhythmias could be induced during electrophysiologic testing; atrial fibrillation was also inducible in 2 dogs. Mean ± SD cycle duration of orthodromic atrioventricular reciprocating tachycardia was 215.80 ± 44.87 milliseconds. Mean shortest R-R interval during atrial fibrillation was 247.33 ± 83.17 milliseconds. Conclusions and Clinical RelevanceçResults suggested that in dogs, most APs are rightsided, had unidirectional retrograde conduction, and are associated with various arrhythmias, including orthodromic atrioventricular reciprocating tachycardia and atrial fibrillation without evidence of pre-excitation.