Use of a programmable, 'physiological' cardiac pacemaker in a dog with total atrioventricular block (with some comments on complications associated with cardiac pacemakers)

A collie-cross dog with syncopal attacks associated with total atrioventricular heart block was successfully fitted with a programmable, ‘physiological’ pacemaker, employing atrial sensing and ventricular pacing leads. Transvenous placement of leads under sedation and local analgesia, followed by temporary pacing, then general anaesthesia for the fitting of a permanent pacemaker, offers advantages over epicardial pacing. The use of a ‘tined’ ventricular lead appears to reduce the risk of lead displacement.     

Atrial-based pacing for sinus node dysfunction in dogs: initial results

Background

An important consideration for the treatment of sick sinus syndrome (SSS) lies in the function of the atrioventricular (AV) node because most patients with SSS retain the ability to conduct atrial impulses.

Hypothesis/Objectives

This retrospective study examined the feasibility of atrial pacing (AAI) in dogs with sinus node dysfunction (SND).

Animals

Sixteen dogs with SND and AAI pacing were identified.

Methods

Retrospective review of medical records.

Results

Follow‐up time ranged from 45 to 1,227 days (mean: 292 days). Only 1 dog developed AV block 3 days postoperatively. Complete lead dislodgment occurred in 3/16 dogs 1, 19, and 27 days postoperatively. Lead perforation into the pericardial space occurred in 2/16 dogs. Rising thresholds for pacing with possible lead microdislodgment or fibrosis were suspected in another 3/16 dogs 57, 192, and 1,016 days after implantation. None of these dogs had complete loss of capture but all required higher thresholds for pacing.

Conclusions and Clinical Importance

Based on this small group of dogs, clinically important AV block does not appear to occur in the long‐term for dogs with SND. Risks of lead perforation, complete dislodgment, and rising thresholds for pacing, possibly because of microdislodgment, may be related to the initial skill level of the operator or the leads that were used. Use of leads with reduced torque at the lead tip, higher flexibility, increased lead‐tip surface of contact with the endocardium or, more likely, use of alternate locations for pacing in the small right atrium of dogs with SND may decrease the frequency of these complications.     

Late cardiac perforation by a passive-fixation permanent pacemaker lead in a dog

CASE DESCRIPTION: A 12-year-old Miniature Dachshund with a history of permanent endocardial pacemaker implantation performed 7 weeks previously was admitted for routine dental prophylaxis. CLINICAL FINDINGS: Preanesthetic ECG revealed normal ventricular capture. Thoracic radiographic findings included caudomedial displacement of the endocardial pacemaker lead. Echocardiography revealed moderate chronic degenerative valve disease with moderate left atrial and ventricular dilation. After induction of anesthesia, loss of ventricular capture was detected. The dog recovered from anesthesia and had improved ventricular capture. The following day, surgical exposure of the cardiac apex revealed perforation of the right ventricular apex by the passive-fixation pacemaker lead. TREATMENT AND OUTCOME: A permanent epicardial pacemaker was implanted through a transxiphoid approach. Appropriate ventricular capture and sensing were achieved. The dog recovered without complications. Approximately 2 months later, the dog developed sudden respiratory distress at home and was euthanized. CLINICAL RELEVANCE: In dogs with permanent pacemakers and loss of ventricular capture, differential diagnoses should include cardiac perforation. If evidence of perforation of the pacemaker lead is found, replacement of the endocardial pacemaker lead with an epicardial pacemaker lead is warranted.     

Diagnostic imaging and pacemaker implantation in a domestic goat with persistent left cranial vena cava

Difficulty was encountered with the insertion of a right atrial pacing lead via the left jugular vein during lead and pacemaker implantation in a clinically normal goat as part of an ongoing rapid atrial pacing – induced atrial fibrillation research project. Fluoroscopic visualization of an abnormal lead advancement path prompted angiographic assessment which revealed a persistent left cranial vena cava (PLCVC) and prominent coronary sinus communicating with the right atrium. Angiography facilitated successful advancement and securing of the pacing lead into the right side of the interatrial septum. Cardiac magnetic resonance imaging/magnetic resonance angiography (MRI/MRA) allowed further characterization of this rare venous anomaly. Even though PLCVC has been reported once in a goat, to the authors' knowledge this is the first report to include MRI/MRA characterization of PLCVC and prominent coronary sinus with successful cardiac pacemaker implantation using the PLCVC.     

Safety and feasibility of transesophageal pacing in a dog

This study investigated the feasibility of using a modified transesophageal atrial pacing system for dogs requiring temporary ventricular pacing. Atrial pacing was readily achieved in the one dog studied, but it caused considerable diaphragmatic movement. Ventricular pacing could not be achieved at any lead configuration or energy stimulation. While transesophageal cardiac pacing was a safe procedure, the large variation in the chest anatomy of dogs requires further study to explore this model as a substitute for transvenous or transthoracic ventricular pacing.     

Permanent Transvenous Pacemaker Implantation in Forty Dogs

Permanent transvenous cardiac pacemakers were implanted in 40 dogs. Electrocardiographic diagnoses included persistent atrial standstill (3 dogs), sick sinus syndrome (8 dogs), and high-grade second-degree or third-degree atrioventricular (AV) block (29 dogs). Thirteen dogs were alive and well 4 to 42 months after pacemaker implantation (mean, 16.9 months). The mean and median survival times of the 26 dogs that died or were euthanatized during the study were 17.9 months and 13 months, respectively. Most of these dogs succumbed to problems unrelated to the arrhythmia and pacemaker implant. One dog was lost to follow-up. Complications associated with permanent transvenous pacemaker implantation included lead dislodgement, infection, hematoma formation, skeletal muscle stimulation, ventricular arrhythmia, migration of the pulse generator, and skin erosion. Lead dislodgement was the most common complication, occurring in 7 of 9 dogs paced using untined electrode leads and in 6 of 30 dogs paced using tined leads. Lead dislodgement did not occur in the only dog paced using an actively fixed endocardial lead. It was concluded that permanent transvenous cardiac pacing is a feasible, less traumatic alternative to epimyocardial pacing in dogs, but that successful use of this technique requires careful implantation technique and anticipation of the potential complications.     

Secure pacemaker fixation critical for prevention of Twiddler's syndrome

A two year old, female spayed border collie presented three weeks after permanent pacemaker implantation for weakness, lethargy and collapse. Electrocardiogram documented complete (3^rd degree) atrioventricular (AV) block, the absence of pacing and a ventricular escape rhythm. Thoracic radiographs revealed retraction and dislodgement of the passive fixation lead from the right ventricular apex. During a procedure to reposition the lead, it was noted that lead retraction had resulted from rotation of the generator with twisting and entanglement of the lead on itself and around the generator, a complication recognized in human patients as “Twiddlers syndrome”. The pacemaker lead was removed, a new lead securely placed at the right ventricular apex, and the generator was secured into a revised subcutaneous pocket. Pacing was re-established and the Twiddler's syndrome has not reoccurred.     

Pacemaker malfunction due to mechanical failure of the lead–header interface

An 8 year old female spayed Boxer dog, diagnosed with concurrent vasovagal syncope and arrhythmogenic right ventricular cardiomyopathy, presented for routine evaluation approximately three months following epicardial pacemaker implantation. Routine device interrogation revealed intermittent loss of ventricular capture and intermittent failure to appropriately sense. Following evaluation of chronic impedance data, failure of the pacemaker lead–header interface or lead conductor fracture was suspected. Radiographic and pacemaker interrogator findings suggested incomplete lead insertion into the device header with intermittent loss of ventricular capture and variable pacemaker sensing. We hypothesize that either the presence of a loose or cross-threaded set screw or operator error at the time of device implantation may have caused this complication. This report details the diagnosis of mechanical failure of the lead–header interface, a complication not previously reported in a veterinary patient.     

Use of transesophageal atrial pacing to provide temporary chronotropic support in a dog undergoing permanent pacemaker implantation

A 14.5-kg, 13-year-old female spayed Cocker spaniel was evaluated because of episodic hind limb weakness. Results of examination were consistent with sick sinus syndrome with intermittent second-degree atrioventricular block. Transesophageal atrial pacing was successful in providing chronotropic support during permanent pacemaker implantation. Transesophageal atrial pacing appears to be a viable option for temporary atrial pacing in dogs with hemodynamically marked bradycardia without significant atrioventricular blockade.     

Successful use of an acceleration rate response pacemaker with a transvenous steroid-eluting screw-in lead for third-degree atrioventricular block in a labrador retriever

Permanent pacemakers are commonly used in veterinary practice and can have a dramatic effect on the treatment of heart block. A Labrador Retriever dog suffering from exercise intolerance secondary to third degree atrioventricular block was treated with a new pacemaker system. A steroid-eluting screw-in type lead that has the advantage of being more fixed to the myocardial wall without increasing the pacing threshold was used. The heart rate was regulated with an acceleration sensing pacemaker generator that included several automatic modulation systems. Nineteen months after implantation, the dog has a normal level of activity. The present case suggests that this pacemaker design may offer important advantages for canine patients.     

Permanent Pacemaker Implantation for Treatment of Symptomatic Bradycardia in Two Cats

Two cats with bradycardia and syncope were treated by permanent pacemaker implantation. Cat 1 had multiple episodes of syncope intermittently over a 10-month period and then multiple episodes within 24 hours; cat 2 had episodes of collapse over a 3-month period. Clinical signs included disorientation, vocalization, and collapse. High-grade second-degree AV block was recorded in both cats, with left and right bundle branch block in cat 1 and right bundle branch block in cat 2. Neither responded to pharmacologic therapy. In cat 1, an epimyocardial electrode was implanted into the left ventricular apex by a ventral abdominal transdiaphragmatic surgical approach. Cat 2 had a permanent smooth endocardial pacing lead introduced into the fight external jugular vein and directed into the right ventricular apex. Both cats were clinically normal within three days after implantation. Complications in cat 2 included failure of pacemaker capture, endocardial lead dislodgement, and pulse generator pocket seroma. Cats with symptomatic bradycardia caused by second-degree and third-degree AV block can be effectively treated by pacemaker implantation by surgical endomyocardial or perivenous endocardial lead placement.     

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

IntroductionIn 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.AnimalsEighteen client-owned dogs with VVIR pacemakers for third degree atrioventricular block.Materials and methodsThis 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.ResultsHeart 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.ConclusionDefault 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.     

Atrial and Ventricular Electrical and Contractile Remodeling and Reverse Remodeling Owing to Short‐Term Pacing‐Induced Atrial Fibrillation in Horses

Background: In humans, atrial fibrillation (AF) induces electrical, contractile, and structural remodeling leading to AF stabilization. Little is known about AF‐induced atrial remodeling in horses. Hypothesis: Induced AF produces rapid atrial electrical and contractile remodeling in horses. Animals: Six horses, 5 animals completed the study. Methods: Each horse was instrumented with a pulse generator and pacemaker to maintain AF by burst pacing and to study atrial and ventricular electrophysiology (AF cycle length [AFCL], AF duration, and atrial/ventricular effective refractory period [AERP/VERP] at different pacing cycle lengths [PCL]). Left atrial and ventricular contractile remodeling were assessed echocardiographically by calculation of fractional changes in atrial and ventricular dimensions, respectively, during the cardiac cycle. Measurements were performed at baseline, a 7‐day AF period and a 2‐day recovery period. Results: Atrial electrical and contractile remodeling could be demonstrated after 4 and 12 hours of AF, respectively. A progressive shortening of the AERP (261 ± 39–171 ± 18 ms at a PCL of 1,000 ms, P < .0001), an attenuation of the AERP rate adaptation, a decrease in AFCL (239 ± 39–194 ± 7 ms, P < .0001), and a decrease in atrial FS (12 ± 3% to 0 ± 2%, P < .05) occurred. AF duration increased progressively and became persistent in 2 animals. VERP did not change significantly. Upon restoration of sinus rhythm, values returned to baseline within 48 hours. Conclusions and Clinical Importance: Atrial electrical and contractile remodeling appears rapidly. After 7 days of AF, reverse remodeling occurred within 2 days. These observations suggest that early conversion of AF might be beneficial for success rate and early return to training.     

Atrial septal pacing in small dogs: A pilot study

ObjectiveTo determine the feasibility of atrial septal pacing via a delivery catheter-guided small non-retracting helix pacing lead.AnimalsSix healthy beagles (8.3-12.9 kg).MethodsUsing single plane fluoroscopic guidance, Medtronic^® 3830 SelectSecure leads were connected to the atrial septum via Medtronic® Attain Select® II standard 90 Left Heart delivery catheter. Pacing threshold and lead impedance were measured at implantation. The Wenckebach point was tested via atrial pacing up to 220 paced pulses per minute (ppm). Thoracic radiographs were performed following implantation to identify the lead position, and repeated at 24 h, 1 month, and 3 months post-operatively.ResultsMacro-lead dislodgement occurred in two dogs at 24 h and in three dogs at one-month post-implantation. Lead impedance, measured at the time of implantation, ranged from 583 to 1421 Ω. The Wenckebach point was >220 ppm in four of the six dogs. The remaining two dogs had Wenckebach points of 120 and 190 ppm.ConclusionsThis pilot study suggests the selected implantation technique and lead system were inadequate for secure placement in the atrial septum of these dogs. The possible reasons for inadequate stability include unsuitable lead design for this location, inadequate lead slack at the time of implantation and inadequate seating of the lead as evidenced by low impedance at the time of implantation. Other implantation techniques and/or pacing leads should be investigated to determine the optimal way of pacing the atria in small breed dogs that are prone to sinus node dysfunction.     

Noise Reversion in Paced Dogs

Pacemakers are commonly implanted by veterinary cardiologists in dogs with bradyarrhythmias. In the past, these pacemakers were placed with little attention to programming except for the basic heart rate. However, the availability of pacing programmers has permitted a better appreciation of the needs for proper and safe pacing in dogs. An awareness of the problems that can result from improper programming is imperative. We report the identification of noise reversion (inappropriate asynchronous pacing) in 42% of dogs consecutively paced (n = 19) at Cornell University during a 2 year period. Noise reversion is the operation that causes the pacemaker to switch to asynchronous pacing with repetitive refractory sensing. It was developed as a protective mechanism against noise being mistaken for cardiac events with the consequence of inhibition of pacing. However, in the dog, this operation can cause inappropriate, and potentially dangerous pacing. In the dog, this common complication is associated with the coexistence of a bradycardia and tachycardia. Proper programming of the refractory period (shortening) in conjunction with the sensitivity (decreasing the sensitivity) can eliminate noise reversion in dogs with both ventricular and atrial pacing.     

Transvenous pacemaker placement in a dog with atrioventricular block and persistent left cranial vena cava

The case reported herein describes the placement of a permanent transvenous pacemaker in an older dog with a previously undiagnosed persistent left cranial vena cava (PLCVC) and recent onset symptomatic third-degree atrioventricular (AV) block. On presentation the dog was found to have atrial flutter and third-degree AV block and echocardiography demonstrated evidence of chronic valvular disease and pulmonary arterial hypertension. The persistent left cranial vena cava was discovered via angiography when difficulties were encountered with pacemaker placement. Successful right ventricular pacing necessitated passage of the lead through the coronary sinus. The attendant complications in pacemaker placement in the presence of a PLCVC are well-described in man but, to the authors' knowledge, have not been described in companion animals.     

Dual Chamber Pacemaker Implantation in Dogs with Atrioventricular Block

Background: Pacemaker implantation is the treatment of choice for symptomatic bradyarrhythmias. In dogs, a single chamber system is commonly used. In human patients with high-grade 2nd- or 3rd-degree atrioventricular (AV) block, physiologic pacing is recommended, because it improves cardiac output, blood pressure, exercise tolerance, and quality of life. In dogs, this type of pacing is seldom used.
Hypothesis: The implantation of a dual chamber pacemaker in dogs with AV block is a feasible procedure for restoring AV synchrony.
Animals: Thirty-three privately owned dogs with high-grade 2nd- or 3rd-degree AV block were included.
Methods: Patient data of all dogs with AV block presented for pacemaker implantation between December 1997 and November 2004 were reviewed.
Results: Dual chamber pacemaker implantation with AV synchronous stimulation was successfully performed in 33/33 dogs (100%). In 9/33 (27%) major and in 12/33 (36%) minor complications were observed. Mean survival time for the patients discharged from hospital (n = 32) was 33.6 ± 20.4 months (range, 3.9–83.5 months).
Conclusion and Clinical Importance: Dual chamber pacing is a feasible procedure in dogs with 2nd- or 3rd-degree AV block and is not associated with a higher complication rate compared with single chamber pacemaker systems. A major advantage over ventricular demand pacemaker systems is the restoration of AV synchrony for a substantial period of time.     

Changes in concentrations of neuroendocrine hormones and catecholamines in dogs with myocardial failure induced by rapid ventricular pacing

OBJECTIVE: To describe neuroendocrine responses that develop in dogs subjected to prolonged periods of ventricular pacing. ANIMALS: 14 adult male hound-type dogs. PROCEDURE: Samples were obtained and neuroendocrine responses measured before (baseline) and after 3 periods of ventricular pacing. A pacemaker was used to induce heart rates of 180, 200, and 220 beats/min (BPM). Each heart rate was maintained for 3 weeks before increasing to the next rate. Atrial natriuretic peptide, antidiuretic hormone, aldosterone, norepinephrine, epinephrine, and dopamine concentrations and plasma renin activity were measured. Severity of left ventricular compromise was estimated. RESULTS: Shortening fraction decreased significantly with increasing heart rates (mean +/- SE, 35.5 +/- 1.4, 25.0 +/- 1.4, 19.5 +/- 1.9, and 12.2 +/- 2.3 for baseline, 180 BPM, 200 BPM, and 220 BPM, respectively). Atrial natriuretic peptide concentrations increased significantly at 180 BPM (44.1 +/- 3.0 pg/mL) and 200 BPM (54.8 +/- 5.5 pg/mL), compared with baseline concentration (36.8 +/- 2.6 pg/mL). Dopamine concentration increased significantly at 200 BPM (70.4 +/- 10.4 pg/mL), compared with baseline concentration (44.2 73 pg/mL). Norepinephrine concentrations increased significantly from baseline concentration (451 +/- 46.2 pg/mL) to 678 +/- 69.8, 856 +/- 99.6, and 1,003 +/- 2676 pg/mL at 180, 200, and 220 BPM, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: Dogs subjected to ventricular pacing for 9 weeks developed neuroendocrine responses similar to those that develop in humans with more chronic heart failure and, except for epinephrine concentrations, similar to those for dogs subjected to ventricular pacing for < 6 weeks.     

Transvenous cardiac pacing in 19 dogs and one cat

Eighteen dogs and one cat with symptomatic bradycardias were equipped with cardiac pacemakers. One further dog died during anaesthesia for pacemaker placement. Each animal was sedated, and a ‘tined’ transvenous pacing lead was passed to the apex of the right ventricle from the jugular vein. Following temporary pacing and general anaesthesia, the permanent pacemaker was placed subcutaneously at the neck in the dogs and at the abdominal wall in the cat. In 11 dogs and the cat, the pacemaker was implanted in a dacron pouch. Complications (mainly serous reaction to the pacemaker) developed in four out of seven dogs in which no pouch had been employed. The pacing lead was retained after discharge from hospital in all except one dog. Pacing successfully relieved clinical signs in all cases. Fifteen out of 18 dogs and the cat survived one year after pacing and the mean survival time was greater than 18 months. Transvenous pacing is a simple and reliable technique that avoids transthoracic or transabdominal surgery for pacemaker lead placement.     

Follow-up of troponin I concentration in dogs with atrioventricular block and dual-chamber pacing in a case-matched study

Background

Increased cardiac troponin I (cTnI) concentration has been reported in dogs with atrioventricular (AV) block before and shortly following pacemaker implantation. The role of AV dyssynchrony, age, or concurrent cardiac disease on cTnI concentration remains unknown.