Noise reversion in paced dogs

Insulation break of the ventricular lead in a dog with a pacemaker

A 10-year-old female spayed mixed breed dog that had a transvenous pacemaker implanted four years prior was presented for the evaluation of episodes of transient loss of consciousness without any history of trauma that were unresponsive to anticonvulsant therapies. Intermittent failure to capture coupled with low impedance and high capture threshold were noted upon interrogation of the pacemaker. Radiography and fluoroscopy demonstrated a possible break in the insulation of the lead. After the placement of another transvenous pacemaker, the dog had no additional syncopal episodes, and anticonvulsants were tapered off. The dog developed an implant infection from the newly placed pacemaker, which prompted the removal of the infected pacemaker and the implantation of an epicardial pacemaker. However, the epicardial lead dislodged seven days after placement, and the dog was euthanized. During necropsy, the first transvenous lead was removed, and the insulation break was visually confirmed. Although an insulation break is a rare delayed complication of pacemaker implantation, this report shows how the diagnosis, suspected by typical interrogation findings, can be aided by radiographic and fluoroscopic investigations.

Quiet timer blanking in a dog with sick sinus syndrome and a permanent transvenous pacemaker

A 14-year-old, 5.8 kg (12.7 lb) male castrated Jack Russell Terrier was referred for investigation of syncope and an arrhythmia. Electrocardiogram showed pronounced variation in the sinus rate including long periods of sinus arrest and an inconsistent escape rhythm. Sick sinus syndrome was the presumptive diagnosis. A single lead permanent transvenous pacemaker was implanted and was programmed to perform ventricular-demand pacing. Postoperative pacemaker interrogation revealed undersensing and asynchronous pacing during episodes of supraventricular tachycardia (SVT). This intermittent pacemaker malfunction was attributed to a specific pacemaker programming feature called quiet timer blanking. Adjustment of pacemaker parameters did not restore normal function. Treatment with sotalol (5 mg per os q 12 h) was used to medically treat the SVT, and asynchronous pacing was not observed during follow-up visits. To the authors' knowledge, this is the first documented case of quiet timer blanking causing paroxysmal undersensing and asynchronous pacing in a dog with a permanent pacemaker.

Transvenous pacing implantation: techniques, tips, and lessons learned along the way

The right ventricular apex has been the traditional site for lead placement in veterinary patients who require permanent cardiac pacing therapy for atrioventricular block and sick sinus syndrome. Implantation of leads in this location is a straightforward procedure that most veterinary cardiologists perform routinely. Pacing at the right ventricular apex, however, has been demonstrated to have long-term deleterious effects on the left ventricular function in numerous patient populations and animal models. Alternative lead placement sites and pacing system configurations have been developed, and the purpose of this review article is not to review the literature or the decision-making process in selecting a specific pacing system but rather to share the experiences of our group with the use of alternative pacing implantation techniques for veterinary patients in need of permanent cardiac pacing.