Epicardial pacemaker implantation in small animals

Cardiovascular images: pacemaker-lead fracture and excessive coiling in a dog

A seven-year-old male castrated Labrador Retriever presented emergently due to concern for pacemaker malfunction five years after successful transvenous pacemaker implantation to treat partial atrial standstill. On presentation, the dog's pulse rate was 30-50 beats per minute. An electrocardiogram showed no spontaneous atrial activity or paced ventricular activity. Pacemaker interrogation revealed an increased impedance of 7557 ohms, indicating a lead malfunction. Thoracic radiographs confirmed the lead was fractured and had excessive coiling. The transvenous pacing system was turned off, left in place, and an epicardial pacing system was implanted the following day. The dog was discharged with no perioperative complications. The dog eventually required escalated medical therapy for progressive cardiac disease and was euthanized two years after implantation of the replacement pacemaker. This manuscript illustrates a complete lead fracture and excessive lead coiling, which has not previously been detailed in veterinary medicine.

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.

Single center retrospective clinical audit and comparison of outcome between epicardial and transvenous endocardial permanent pacemaker implantations in dogs

The aim of this retrospective cohort study was to provide a single-center clinical audit of complications for single chamber permanent pacemaker implantation (PPI) techniques and determine if the clinical parameters, PPI technique or complications were associated with outcome. The electronic medical records were searched for dogs treated for bradyarrhythmia with PPI. Data related to presenting complaint, signalment of the dog, ECG diagnosis, echocardiographic findings, PPI technique, and programing of the pacemaker were recorded. Survival length (days) was recorded as the last veterinary visit; if the dog was dead the reason was documented. Cumulative survival of each pacemaker was examined by a Kaplan-Meier survival curve and the two techniques compared with a logrank test. Chi-square was used to determine the association between major complications and death. A total of 66 dogs with 52 transvenous and 30 epicardial PPIs were included. All epicardial pacemakers were implanted via transdiaphragmatic approach. A total of 31 life-threatening complications were reported. There were nine deaths related to major complications (13.6% of the study sample). The median follow-up period was 366 days, with a median survival of 255 days, and a significant difference in cumulative survival of each pacemaker (P = 0.01) between epicardial (93 days, range 0-1882 days) and transvenous (334 days, range 0-2745) PPIs but no significant difference in cumulative survival between the two techniques when only the first pacemaker was considered (p = 0.07). The presence of a major complications had a significant association with death due to pacemaker complications (P<0.001). The decision to perform epicardial PPI in failed transvenous PPI patients may have skewed the cumulative survival as was evident in the lack of significant difference in survival when only first PPI were examined. Major complication rates between the two techniques were similar and the authors consider both techniques equally reliable to manage symptomatic bradycardia in dogs.

Heart rate distribution in dogs with third degree atrioventricular block and rate responsive pacemakers

INTRODUCTION

In dogs, single lead ventricular pacing, ventricular sensing, inhibition response, rate adaptive (VVIR) pacemakers are routinely used to treat third degree atrioventricular block. The objectives of this study were to investigate the heart rate distribution in dogs with VVIR pacemakers, and report changes when activity settings were adjusted.

ANIMALS

Eighteen client-owned dogs with VVIR pacemakers for third degree atrioventricular block.

MATERIALS AND METHODS

This observational study consisted of a review of medical records of dogs with VVIR pacemakers. For dogs with >50% of paced beats at the lower pacing rate, the activity daily living (ADL) and exertion responses were increased. Re-evaluations were performed after 6-12 months.

RESULTS

Heart rate distribution similar to healthy dogs was absent for all dogs. In nine dogs, the ADL and exertion responses were increased to the highest level. Of these, three dogs showed no improvement in heart rate distribution; for two dogs, one with an epicardial pacemaker, several activity settings were adjusted and pacing at higher heart rates was observed at re-evaluation. Four dogs died or were lost to follow-up. Clinical signs had resolved for all dogs after pacemaker implantation.

CONCLUSION

Default activity settings of VVIR pacemakers do not result in heart rate distribution equivalent to healthy dogs. Increasing the ADL and exertion response settings to the highest levels did not improve the pacemaker rate response. Further investigations into the role of dog size, generator positioning, pacemaker settings, and whether rate responsiveness is required for dogs' quality and quantity of life are warranted.

A retrospective evaluation of the indications, complications, and outcomes associated with epicardial pacemakers in 20 cats from a single institution

INTRODUCTION

The objective of this retrospective study was to describe the indications, complications, and long-term outcomes in a group of cats that received an epicardial pacing (EP) system.

ANIMALS

Twenty client-owned cats.

MATERIALS AND METHODS

Medical records were reviewed for signalment, presenting complaint, primary electrocardiogram (ECG) diagnosis, presence of structural heart disease, presence of congestive heart failure (CHF), presence of major or minor complications, and survival time.

RESULTS

The majority of cats were presented for syncope (n = 11), and the most common ECG diagnosis was advanced second-degree atrioventricular block (n = 9). Fifteen cats (15/20, 75%) had one or more major or minor complications. One cat died in the perioperative period as a result of a major complication. None of the variables evaluated were associated with a statistically significant increase in the occurrence of major or minor complications. The most common major complication was loss of ventricular capture (seven instances in six cats), which was successfully treated in all cases by increasing pacemaker output or replacing both the lead and the pulse generator. The most common minor complications were arrhythmias (n = 7) and sensing issues (n = 8). The overall median survival time (MST) was 948 days. No statistical difference in survival time was identified between cats that experienced a major complication and those that did not.

CONCLUSIONS

Although complications were common in this feline population after EP, major and minor complications were successfully treated.

Paroxysmal high-grade second-degree and persistent third-degree atrioventricular block in cats

INTRODUCTION

Both paroxysmal high-grade second-degree and persistent third-degree atrioventricular block (AVB) are recognised in cats. Our aim was to document the presentation, echocardiographic data, comorbidities and outcome in affected cats from a single referral hospital, including those that underwent epicardial pacemaker implantation (EPI).

ANIMALS, MATERIALS AND METHODS

This retrospective study included 64 cats diagnosed with persistent third-degree or paroxysmal high-grade AVB, for which detailed patient history was available. Non-parametric testing, Kaplan-Meier curves and Cox proportional hazard testing were performed.

RESULTS

Atrioventricular block was persistent in 43 cats (67%) and paroxysmal in 21 (33%). Forty-seven cats (74%) were referred for cardiac complaints (e.g. collapse, arrhythmia, tachypnea), 6 (9%) had non-specific complaints and AVB was an incidental finding in 11 cats (17%). Median duration of clinical signs prior to presentation was 21 days (1-1138 days). Thirty-nine (63%) cats had echocardiographic abnormalities; 13 (20%) presented with congestive heart failure. Forty-five (70%) cats had one or more comorbidities. Fifteen cats underwent EPI with immediate resolution of signs in 12 cats. Following EPI, two and four cats experienced major and minor complications, respectively. Forty-seven cats died; median survival time was 799 days (all-cause mortality). Cardiac-related death occurred in 17 cats (36%); median survival in these cats was 132 days. Heart failure on presentation was the only independent risk factor for cardiac death (p=0.002).

CONCLUSIONS

Outcome in cats with AVB was variable, although most had good medium- to long-term survival. Cardiac death occurred in a minority of cats. Pacemaker implantation was effective in relieving clinical signs.