Four dogs were referred to our institution for incessant supraventricular tachycardias causing weakness; congestive heart failure was present in one dog. At admission, all dogs had a surface electrocardiogram showing a narrow QRS complex tachycardia with a ventricular rate ranging from 80 to 300 bpm, variable atrioventricular conduction ratio from 1:1 to 3:1, and positive atrial depolarizations in inferior leads (II, II, III, and aVF), with isoelectric lines between them. Three of four dogs had a dilated cardiomyopathy phenotype; one dog had a heart base tumor involving the cranial vena cava wall. According to the electrocardiographic findings, a presumptive diagnosis of reverse typical or atypical atrial flutter was considered, and endocardial mapping was planned for each dog. During the electrophysiologic study, continuous atrial activation compatible with atypical atrial flutter was observed in all dogs, with concealed entrainment obtained at the level of the isthmus located at the distal portion of the cranial vena cava, close to the entrance into the right atrium. A linear radiofrequency catheter ablation was performed from the right atrial wall to the distal part of the cranial vena cava with a permanent interruption of the isthmic conduction in all dogs at a 6-month follow-up.

四只狗因持续的室上性心动过速导致虚弱而被转诊到我们的机构；一只狗出现充血性心力衰竭。入院时，所有犬的体表心电图显示窄 QRS 波群心动过速，心室率范围为 80 至 300 bpm，房室传导比为 1:1 至 3:1，下导联心房除极阳性（II、II 、III 和 aVF)，它们之间有等电位线。四只狗中有三只有扩张型心肌病表型；一只狗的心脏基底肿瘤累及颅腔静脉壁。根据心电图结果，考虑推定诊断为反向典型或非典型心房扑动，并对每只狗进行心内膜标测。在电生理研究期间，在所有狗中都观察到与非典型心房扑动相一致的持续心房激动，在位于颅腔静脉远端部分的峡部水平处获得隐性夹带，靠近右心房的入口。在 6 个月的随访中，从右心房壁到颅腔静脉远端进行了线性射频导管消融，所有犬的峡部传导均被永久性中断。