Successful ventricular sensing, and inhibition mode pacemaker placement and clinical improvement in a dog with third-degree atrioventricular block: a case report

A 9-year-old spayed female Labrador Retriever (body weight, 26.2 kg) was referred for evaluation of progressive lethargy and a single episode of syncope. Physical examination revealed marked bradycardia (40 bpm) with ventricular premature complexes (VPCs). The electrocardiogram (ECG) documented third-degree atrioventricular (AV) block accompanied by VPCs that were unresponsive to atropine administration. Owing to anatomical limitations and the device’s design specifications intended for human use, single-chamber ventricular pacing was implanted. A single-chamber ventricular pacing, ventricular sensing, and inhibition mode (VVI) pacemaker (Medtronic, USA) was surgically implanted in the right ventricular apex and programmed with a lower rate limit of 60 beats per minute. After implantation, ECG evaluation identified predominantly second‐degree AV block (Mobitz type II) with intermittent episodes of third‐degree AV block in the absence of VPCs. Following implantation, the patient showed marked improvement in lethargy and exercise intolerance, as well as complete resolution of syncopal episodes. No device-related complications were noted during the 3-month follow-up period. The case demonstrates that pacemaker implantation in a dog with high‐grade AV block and bradycardia resulted in marked improvement in arrhythmia and associated clinical signs.