A retrospective evaluation of the indications, complications, and outcomes associated with epicardial pacemakers in 20 cats from a single institution☆
Introduction
Artificial cardiac pacing (AP) is the standard treatment for life-threatening bradyarrhythmias, like advanced second-degree atrioventricular block (AVB) and third-degree AVB, that have a high risk of sudden death in dogs [1]. It is also indicated in dogs with bradyarrhythmias that have signs of low cardiac output or congestive heart failure (CHF) that are refractory to medical management alone; this may include dogs with sick sinus syndrome, permanent atrial standstill, and vasovagal syncope [[2], [3], [4], [5], [6], [7], [8], [9]]. Pacemaker implantation has been used in cats with clinical signs associated with bradyarrhythmias, such as syncope, lethargy, or signs associated with CHF [4,6,10]. However, cats may be more tolerant of bradyarrhythmias than dogs and less susceptible to sudden death as a consequence of advanced AVB [11]. A study evaluating the clinical outcomes in cats with third-degree AVB showed that the majority of cats with third-degree AVB that did not undergo pacemaker implantation (13/20; 65%) survived for more than 1 year after diagnosis regardless of presenting clinical signs, underlying structural cardiac disease, or presence of CHF [11]. These findings are in contrast to survival data reported in dogs with third-degree AVB with a 41% occurrence rate of sudden death and 40% of dogs dying within 6 months of diagnosis [1]. Cats may be more tolerant of third-degree AVB than dogs; however, there are reports that suggest a potential benefit of AP by documenting cessation of clinical signs and a seemingly improved quality of life after surgery [[4], [5], [6]]. Although AP has only been reported in a small number of cats with symptomatic bradyarrhythmias, the findings of these studies suggest that the severity of clinical signs and the severity of the bradycardia may be an indication of the need for AP [4,6,10].
Transvenous implantation of pacing leads into the right ventricular apex is the most commonly used method of pacemaker implantation in dogs [2,3,7]. Although less surgically invasive than epicardial pacing (EP), transvenous pacing places the lead in direct contact with intracardiac structures and blood flow, which can lead to potentially life-threatening, albeit uncommon, complications such as cranial vena caval syndrome, right ventricular outflow tract obstruction, intracardiac thrombosis, acquired tricuspid stenosis, cardiac perforation, and lead-associated infection [2,6,10,[12], [13], [14], [15]]. Cats may be predisposed to some of these complications because of a relatively large lead size: patient size ratio and cats’ unique predisposition to thrombus formation, and therefore the placement of EP leads may be more appropriate in cats [6,10,16]. However, much of the available literature regarding complications and outcomes associated with EP has been focused on dogs [2,4,[17], [18], [19]]. Major complications reported in dogs include lead dislodgement, loss of capture, pacemaker generator failure, and cardiac arrest, whereas minor complications that have been reported include minor arrhythmias, oversensing, inappropriate programming, muscle twitching, minor hemorrhage, and seroma formation [2,4]. Although some of these complications have also been reported in cats that have received EP systems [4,6], there are so few reports that the true prevalence of major and minor complications remains unknown.
Improved understanding of EP indications, complications, and outcomes is important when recommending intervention and long-term management for cats with symptomatic bradyarrhythmias. Therefore, the objective of this retrospective study was to describe these factors in a larger population of cats that receive EP systems.
Section snippets
Animals, materials and methods
Medical records (January 1, 2003–January 1, 2020) of cats that had surgical implantation of an EP lead and pulse generator at the University of Wisconsin Veterinary Care were reviewed and included in the data analysis. Owners, referring veterinarians, or both were contacted to obtain information about the current status of each animal if this information could not be elucidated by medical record review. Follow-up ended at the end of the review period (January 1, 2020). All cats included in the
Patient characteristics
Twenty cats received a total of 26 EP systemsc in the 17-year study period with two cats requiring generator replacement and four cats requiring both pulse generator and lead replacement. The median age was 12.9 years (range 9.8–17.6 years). There were seven spayed females, one intact female, and 12 castrated males. Breeds included domestic shorthaired (13/20), Siamese (3/20), domestic longhaired (2/20), and Burmese
Discussion
This is the first study to report the indications, complications, and outcomes associated with EP in a larger population of cats. The indications for AP in dogs are well-established although this information is limited in cats [9]. Around one-third of cats with third-degree AVB are asymptomatic and sudden death is not an inevitable outcome of this bradyarrhythmia in cats [11], suggesting that the presence and severity of clinical signs may be a better indicator of a need for AP. In the present
Conclusions
Cats with syncope secondary to a bradyarrhythmia appear to experience a clinical benefit from the placement of an EP system. Although complications were common in this population after EP, major and minor complications could be successfully resolved and were not associated with reduced survival. Cats that undergo EP have a long MST and preexisting heart disease, the presence of CHF, or older age did not negatively impact their survival.
Conflict of Interest Statement
The authors do not have any conflicts of interest to disclose.
Acknowledgements
The authors would like to thank Nicholas Keuler for his assistance with statistical analysis.
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Data were presented as an ePoster at the 2020 ACVIM Forum.