Physiologic VDD versus Nonphysiologic VVI Pacing in Canine 3rd-Degree Atrioventricular Block

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.

The perioperative management of small animals with previously implanted pacemakers undergoing anaesthesia

OBJECTIVE

There is little information in the veterinary literature about the perioperative management of small animal patients with previously implanted pacemakers undergoing elective or emergency non-cardiac procedures. The purpose of this article is to review the current literature with regard to human patients, with previously implanted pacemakers, undergoing general anaesthesia. Using this and the current information on pacemakers and anaesthesia in dogs and cats, we provide recommendations for small animal patients in this situation.

DATABASES USED

Google Scholar, PubMed and CAB Abstracts using and interlinking and narrowing the search terms: "dog", "cat", "small animals", "anaesthesia", "pacemaker", "perioperative", "transvenous pacing", "temporary pacing". Scientific reports and human and small animal studies from the reference lists of the retrieved papers were reviewed. In addition, related human and veterinary cardiology and anaesthesia textbooks were also included to create a narrative review of the subject.

CONCLUSIONS

The best perioperative care for these animals comes from a multidisciplinary approach involving the anaesthetist, cardiologist, surgeon and intensive care unit team. When such an approach is not feasible, the anaesthetist should be familiar with pacemaker technology and how to avoid perioperative complications such as electromagnetic interference, lead damage and reprogramming of the device. The preanaesthetic assessment should be thorough. Information regarding the indication for pacemaker placement, complications during the procedure, location, type and programming of the pacemaker should be readily available. The anaesthetic management of these veterinary patients aims to preserve cardiovascular function while avoiding hypotension, and backup pacing should be available during the perioperative period. Further prospective studies are needed to describe the best perioperative care in small animals with a previously implanted pacemaker.

Optimizing single-chamber pacing in dogs Part 1: Rate determinations, rate interventions and hysteresis

Determining ideal pacing rates to meet physiological needs and optimizing programming to prevent unnecessary right ventricular pacing in dogs requires an understanding of heart rate profiles and applicable pacing technology. The heart rate and rhythm of the dog is complex necessitating investigation of rate requirements of activity and circadian influences. Overlaying this information are a multiplicity of other factors such as age, breed, temperament, cardiovascular disease and underlining rhythm disorders that contribute to the difficulty in making general conclusions. However, all such information permits better implementation of programming options with the goal of better outcomes. In this review (Part 1 of a two-part review) instantaneous heart rate, rolling average heart rate, simple average heart rate, heart rate tachograms, RR interval tachograms (2D, 3D and dynamic), and Poincaré plots (2D, 3D and dynamic) are discussed as they apply to decisions in the determination and examination of pacing rates for dogs programmed in the VVI pacing mode (Ventricular paced, Ventricular sensed, Inhibited pacing). The applicable pacing operations available for three pacemaker companies are reviewed (Abbott, Biotronik/Dextronix, and Medtronic). The programmable options considered include: slowest pacing rate without additional features to extend the pacing interval, sleep/rest rate preferences, hysteresis to lengthen pacing interval following intrinsic beats, and intermittent increases in pacing following abrupt loss of intrinsic rhythm. Recommendations are suggested for follow-up of individual dogs with examination of pacing statistics and Holter monitoring.

Instantaneous and averaged heart rate profiles: Developing strategies for programming pacing rates in dogs

Pacemakers use heart rate histograms (% beats) and sensor indicated rate histograms (% time) to illustrate rate distributions. When programmed to the rate adaptive modes, these data are used to determine the appropriateness of rate response to activity. These histograms are generated from instantaneous heart rate calculations. In humans, such data are compared to known histographic rate profiles. Such rate profiles during 24 h in the dog are not available. Moreover, data representation differ between Holter monitoring and pacemakers making comparisons challenging. The rate distribution in dogs >7-years of age was determined over 24 h using instantaneous and rolling average heart rate. Such data could serve as a guide to programming pacing rates for dogs. Sinus arrhythmia resulted in dissimilar heart rate profiles depending on the method of determining rate. The long intervals of sinus arrhythmia resulted in median values for the percent of time with an instantaneous heart rate of <50 beats/min (bpm) of 15%, whereas a rolling average heart rate of <50 bpm was 0.2%. Based on the cumulative time of the rolling average rate, dogs spent 26.3% of the day between 70-90 bpm with rates <65 bpm and >90 bpm approximating 30% for each. Rates >160 bpm were uncommon (<1%). However, high variability existed between dogs. This study demonstrated the shortcomings of both instantaneous and averaging methods to evaluate heart rate profiles in the dog and that both methods should be incorporated when making pacing rate decisions during programming.

Indications for permanent pacing in dogs and cats

Pacemaker implantation is considered as a standard procedure for treatment of symptomatic bradycardia in both dogs and cats. Advanced second-degree and third-degree atrioventricular blocks, sick sinus syndrome, persistent atrial standstill, and vasovagal syncope are the most common rhythm disturbances that require pacing to either alleviate clinical signs or prolong survival. Most pacemakers are implanted transvenously, using endocardial leads, but rarely epicardial leads may be necessary. To decide whether a patient is a candidate for pacing, as well as which pacing modality should be used, the clinician must have a clear understanding of the etiology, the pathophysiology, and the natural history of the most common bradyarrhythmias, as well as what result can be achieved by pacing patients with different rhythm disturbances. The goal of this review was, therefore, to describe the indications for pacing by evaluating the available evidence in both human and veterinary medicine. We described the etiology of bradyarrhythmias, clinical signs and electrocardiographic abnormalities, and the choice of pacing modality, taking into account how different choices may have different physiological consequences to selected patients. It is expected that this review will assist veterinarians in recognizing arrhythmias that may require permanent pacing and the risk-benefit of each pacing modality and its impact on outcome.

Cardiac pacemakers: a basic review of the history and current technology

In the 60 years since the first human implant of a cardiac pacemaker, tremendous improvements have been made to devices themselves as well as the lead systems. Improvement in battery materials has allowed for production of smaller devices with greater longevity and a vast array of technologies allowing for communication between the device and the operator. Lead wires, typically to as the weakest part of the pacing system, have also seen a metamorphosis as improvements in conductor materials and hybrid insulation have been shown to improve reliability. With the recent development of leadless pacing systems, the downfalls of implantable leads can be avoided. These improvements have allowed a more widespread use of cardiac pacing in veterinary applications since the first reported canine implant in 1967.

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.

Upper rate behavior in six dogs with dual-chamber pacemakers

INTRODUCTION

This report provides clinical examples of upper rate behavior in dogs with dual-chamber pacemakers, with suggestions for programming alterations to avoid detrimental upper rate behavior.

ANIMALS

Six dogs with dual-chamber pacemakers displaying upper rate behavior at upper atrial tracking rates.

METHODS

Medical records of dogs with dual-chamber pacemakers with evidence of upper rate behavior were reviewed retrospectively from two institutions. Two of the six dogs were followed prospectively, and 24 h Holter monitors were placed to evaluate upper rate behavior correlated to programming settings.

RESULTS

Pacemaker Wenckebach or 2:1 atrioventricular block was documented in four of six dogs, and automatic mode switch was documented in two of six dogs. Twenty-four-hour Holter monitors placed on two dogs after pacemaker optimization documented a pacemaker Wenckebach window at increased atrial rates with neither dog reaching their respective 2:1 block point throughout the recording period.

CONCLUSIONS

Clinicians who implant dual-chamber pacemakers should be aware of upper rate behavior in animal species with high heart rates. Optimal programming of dual-chamber pacemakers can be achieved by selecting programmed timing intervals to limit deleterious upper rate behavior and create a more physiologic ventricular response at maximum tracking rates.

Synchronous diaphragmatic contraction associated with dual-chamber transvenous pacing in a dog

A 3-year-old, 20-kg, spayed female, mix-breed dog received a dual-chamber pacemaker for management of symptomatic 3rd-degree atrioventricular block. Synchronous diaphragmatic contraction was documented to occur with atrial pacing. Various methods to reduce the occurrence of pacemaker-related phrenic nerve stimulation are discussed.

Permanent dual chamber epicardial pacemaker implantation in two dogs with complete atrioventricular block

Between November 2013 and December 2013, two dogs with complete atrioventricular (AV) block had a permanent, dual chamber epicardial pacing system implanted. Steroid-eluting unipolar, button-type epicardial leads(a) were sutured to the right atrial appendage and right ventricular wall via a right thoracotomy in both dogs. The pacemakers were programmed in VDD mode. Permanent dual chamber epicardial pacemaker implantation was successful in both dogs with no intra-operative complications. One dog had an acute onset of neurologic signs two days post-operatively that resolved within 24 h. Both dogs have had complete resolution of the clinical signs related to the bradyarrhythmia, and one dog has had complete resolution of chylothorax. One dog had a major lead complication characterized by intermittent loss of capture that resolved by increasing the pacemaker output. Based on the outcome of these two cases, implantation of permanent dual chamber epicardial pacing systems is possible in dogs providing an alternative to dual chamber transvenous systems.

Use of transcutaneous external pacing during transvenous pacemaker implantation in dogs

The aim of this retrospective study was to evaluate the utility of transcutaneous external pacing (TEP) during transvenous pacemaker implantation in dogs. Eighty-two pacemakers were implanted in 77 dogs because of third-degree atrioventricular block (AVB) (58 cases; 70.7 per cent), sinus node dysfunction (SND) (nine cases; 11.0 per cent), high-grade second-degree AVB (six cases; 7.3 per cent), persistent atrial standstill (PAS) (four cases; 4.9 per cent), post-radiofrequency catheter ablation of the bundle of His (four cases; 4.9 per cent) and vasovagal syncope with atrial fibrillation (one case; 1.2 per cent). TEP was initiated during general anaesthesia after the onset of asystole or profound bradycardia, and stopped when permanent pacing was started. The use of TEP was necessary in 27 cases: 19 cases of third-degree AVB, five of SND, two of PAS and one of vasovagal syncope. External pacing was successful in all but two dogs.