Cardiology Resident University of Guelph Guelph, Ontario, Canada
Third degree atrioventricular block (3rdAVB) is a common bradyarrhythmia in dogs for which pacemaker implantation is the gold-standard treatment. Pacemakers with rate responsive mode (VVIR) capability are usually implanted, as these provide the option of heart rate adjustment in response to activity. The aim of the present study was to determine the efficacy of the rate responsive setting of VVIR pacemakers in dogs that have pacemakers for 3rdAVB. Medical records of the Ontario Veterinary College were retrospectively searched and a total of 28 dogs with VVIR pacemakers for 3rdAVB were identified. Pacemaker interrogations, 6-12 months after placement, detected that the dogs spent the most time at the programmed lower rate with only minor heart rate variation. In 9/28 (32%) dogs, the activity daily living (ADL) and exertion responses were increased one or two levels to improve pacemaker response to activity. In 5/9 (55%) dogs, this did not elicit heart rate variation; in one dog this resulted in heart rate variation (this dog had an epicardial lead with abdominal generator, contrary to the other dogs); 3/9 (33%) dogs died before re-evaluation. In the majority of dogs with VVIR pacemakers for 3rdAVB, the default rate responsive mode did not result in heart rate variation. An increase of the activity response settings did not improve pacemaker response to activity, and it is possible that further adjustments are required. Furthermore, positioning of the pacemaker generator might influence rate responsiveness of a VVIR pacemaker.