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.     

CARDIAC MAGNETIC RESONANCE IMAGING IN NORMAL DOGS AND TWO DOGS WITH HEART BASE TUMOR

We describe the technique for in vivo cardiac‐gated magnetic resonance imaging (MRI) in normal dogs and its application in two dogs with a large right atrial tumor. The dogs with a cardiac tumor were also imaged using contrast‐enhanced magnetic resonance angiography (CE‐MRA). Cardiac‐gated MRI and CE‐MRA are both feasible in animals with short acquisition times compatible with breath‐hold imaging under anesthesia, and provide detailed two‐ and three‐dimensional (3D) depiction of the cardiac anatomy and great vessels with or without contrast medium. Although cardiac MRI will not replace echocardiography, it is a powerful alternative technique to use when knowledge of the 3D anatomy of the vasculature is required, when precise volume measurements are needed or when myocardial characterization is indicated. As opposed to contrast‐enhanced computed tomography angiography, cardiac MRI does not use ionizing radiation or iodinated contrast medium.     

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.     

Dual-chamber pacemaker implantation via the cephalic vein in healthy equids

The purpose of the present study was to develop a feasible and safe technique for dual-chamber pacemaker implantation in healthy horses. Implantation was performed in a standing, tranquilized horse and in ponies. Atrial and ventricular leads were transvenously inserted through the cephalic vein, and a subcutaneous pacemaker pocket was created between the lateral pectoral groove and the manubrium sterni in 6 equids. Positioning of each lead was guided by echocardiography and by measuring the electrical characteristics of the lead. The implantation procedure lasted about 4 hours in each animal and was well tolerated. In all animals, dual-chamber pacemaker function was obtained, and these results remained good throughout the follow-up period. At the time of implantation, atrial and ventricular sensing were between 2.1 and 7.2 mV and 7.8 and 16.8 mV, respectively, and atrial and ventricular pacing thresholds at 0.5 millisecond varied from 0.5 to 0.7 V and from 0.3 to 1.0 V, respectively. Six months after the implantation, sensing values varied from 2 to 10 mV for the atrial lead and from 2 to 16 mV for the ventricular lead, while pacing thresholds at 0.5 millisecond varied from less than 0.5 to 2.5 V for the right atrium and from less than 0.5 to 5.0 V for the right ventricle. Atrial lead dislodgment occurred in 2 animals, requiring insertion of a new lead. Ventricular lead dislodgment was not observed.     

COMPUTED TOMOGRAPHY AND MAGNETIC RESONANCE IMAGING OF CAVERNOUS SINUS ENLARGEMENT IN A DOG WITH UNILATERAL EXOPHTHALMOS

Computed tomography (CT), magnetic resonance imaging (MRI) and magnetic resonance angiography (MRA) were performed on a dog with a two year history of unilateral exophthalmos occurring two years following head trauma. On CT images, an expansile enhancing mass was present along the right intracranial cavernous sinus and extended through the orbital fissure into the retrobulbar space. With MRI, the structure appeared as a signal void due to the presence of rapidly flowing blood. Gadolinium enhancement of the adjacent brain was not present. A vascular origin of the lesion was confirmed with MRA. Based on the CT and MRI findings, the enlarged cavernous sinus and associated ophthalmic plexus were believed to represent an arterialized aneurysm, most likely the result of traumatic arteriovenous fistulization. Treatment consisted of surgical enucleation. At the time of this report, 29 mouths later, the dog remains free of clinical signs.     

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.     

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.     

Noninvasive transthoracic temporary cardiac pacing in dogs

Temporary cardiac pacing is used in the emergency treatment of life-threatening bradyarrhythmias and for the support of heart rate and blood pressure of patients with sick sinus syndrome or high-grade atrioventricular (AV) block undergoing general anesthesia, typically for permanent pacemaker implantation. We retrospectively evaluated the safety and efficacy of a noninvasive transthoracic external cardiac pacing system in 42 dogs treated for bradyarrhythmias. Optimal placement of the patch electrodes on the skin of the thorax was initially established on 2 anesthetized normal dogs. The optimal electrode placement was determined to be on the right and left hemithoraces, directly over the heart. Afterward, by means of this electrode placement all 42 dogs treated for bradyarrhythmias in this study were successfully paced with the noninvasive transthoracic system. Dogs ranged in age from 1 to 15 years and weighed between 3.2 and 40 kg. Miniature Schnauzers, German Shepherds, and mixed breeds were most common in the study population. Indications for noninvasive transthoracic pacing included emergency treatment of hemodynamically unstable 3rd-degree AV block (2 dogs): support of heart rate during general anesthesia for permanent pacemaker implantation or lead-wire adjustment (38 dogs): and support of heart rate during general anesthesia for ophthalmologic surgery in dogs with sick sinus syndrome (2 dogs). Complications included pain and skeletal muscle stimulation, which required general anesthesia. We conclude that the noninvasive transthoracic pacing system evaluated is satisfactory for clinical veterinary use.     

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.     

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.     

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.     

Complex cardiac congenital defects in an adult dog: An ultrasonographic and magnetic resonance imaging study

This article describes a complex and not previously reported combination of congenital cardiac defects. Echocardiography showed dilation of right and left chambers, accompanied with patent ductus arteriosus, persistence of the left cranial vena cava, atrial septal defect (ASD), subaortic stenosis, and tricuspid dysplasia. The interatrial wall was examined and the diameter of the ASD was measured by magnetic resonance imaging (MRI).     

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.     

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.     

DILATED CORONARY SINUS IN A DOG WITH PERSISTENT LEFT CRANIAL VENA CAVA

This paper describes the electrocardiographic, echocardiographic (two-dimensional, M-mode, contrast and Doppler) and non-selective angiocardiographic features in a 3 year old female Beagle with dilated coronary sinus due to persistent left cranial vena cava. Negative P waves in leads III and aVR and a positive P wave in lead aVL were seen. Echocardiographically, a hipoechoic circular structure was seen between the left atrium and the pericardium in the area where the coronary sinus is located. A velocity pattern with two peaks was obtained, one systolic with velocity = 0.44 ± 0.05 m/sec and the other diastolic with velocity = 0.27 ± 0.01 m/sec. By M-mode echocardiography, at level of the aorta and the left atrium, a linear structure was identified between the left atrium and the pericardium; this structure was characterized by phasic movements of the anterior wall during the cardiac cycle. Following a left cephalic vein injection of saline, bubbles were seen within the coronary sinus; when saline was injected into the right cephalic vein, bubbles were also seen within the coronary sinus and right atrium and ventricle. Non-selective angiocardiography confirmed a dilated coronary sinus with persistent left cranial vena cava. The right cranial vena cava was absent. The dog was clinically normal and the unusual vessel was an incidental finding.     

AORTOILIAC THROMBUS SECONDARY TO A MINERALIZED ARTERIOSCLEROTIC LESION

A 12-year-old, neutered female, Siberian Husky dog presented with a hind limb weakness of one month duration. To facilitate making a diagnosis multiple imaging modalities were performed. These modalities included radiography, ultrasonography, magnetic resonance imaging (MRI), magnetic resonance angiography (MRA) and selective angiography of the abdominal aorta. In this dog, the MRI/MRA studies provided the first documentation of the external iliac thrombi and the collateral circulation via the lumbar arteries. At necropsy, an aortoiliac thrombus caused by a mineralized arteriosclerotic plaque was noted.     

Estimation of left ventricular filling pressure by use of Doppler echocardiography in healthy anesthetized dogs subjected to acute volume loading

OBJECTIVE: To identify Doppler echocardiographic (DE) variables that correlate with left ventricular filling pressure (LVFP). ANIMALS: 7 healthy dogs (1 to 3 years old). PROCEDURES: Dogs were anesthetized and instrumented to measure left atrial pressure (LAP), left ventricular pressures, and cardiac output. Nine DE variables of LVFP derived from diastolic time intervals, transmitral and pulmonary venous flow, and tissue Doppler images were measured over a range of hemodynamic states induced by volume loading and right atrial pacing. Associations between simultaneous invasive measures of LVFP and DE measures of LVFP were determined by use of regression analysis. Receiver operating characteristic analysis was used to predict increases in mean LAP on the basis of DE variables. RESULTS: Mean LAP was correlated with several DE variables: the ratio between peak velocity during early diastolic transmitral flow and left ventricular isovolumic relaxation time (peak E:IVRT) during sinus rhythm and during right atrial pacing, IVRT, the ratio between late diastolic transmitral flow velocity and pulmonary venous flow duration, and the interval between onset of early diastolic mitral annulus motion and onset of early diastolic transmitral flow. Cutoff values of 2.20 and 2.17, for peak E:IVRT in dogs with sinus rhythm and atrial pacing predicted increases in mean LAP (> or = 15 mm Hg) with sensitivities of 90% and 100% and specificities of 92% and 100%, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: Doppler echocardiography can be used to predict an increase in LVFP in healthy anesthetized dogs subjected to volume loading.     

Tricuspid valve stenosis caused by fibrous adhesions to an endocardial pacemaker lead in a dog

Acquired tricuspid valve stenosis (TVS) is a rare complication of endocardial lead placement in humans that has not been described in the veterinary literature. We describe a 6.5-year-old Border terrier that was presented with right-sided congestive heart failure 5.5 years after placement of a transvenous pacemaker. Severe TVS was confirmed by cardiac ultrasonography and appeared to be secondary to excessive endocardial pacemaker lead within the right atrium. Repositioning of the lead proved impossible and subsequent postmortem examination demonstrated fusion of the tricuspid valve (TV) leaflets around the endocardial lead with associated narrowing of the tricuspid valve orifice. In addition, the loop of the endocardial lead was anchored by thick fibrous tissue to the right atrial wall. This case report suggests that if sufficient endocardial lead is left inside the heart, in dogs undergoing transvenous pacemaker therapy, the redundant lead can become adherent to the tricuspid valve apparatus and cause valvular stenosis.     

The optimal size and placement of transdermal electrodes are critical for the efficacy of a transcutaneous pacemaker in dogs

Transcutaneous cardiac pacing (TCP) can be used in dogs with a high risk for bradyarrhythmias prior to anesthesia, either in an emergency room or intensive care unit setting. Furthermore, TCP can also be used on patients diagnosed with bradyarrhythmias that require temporary pacing at the induction of anesthesia for the implantation of a permanent pacemaker. Despite the importance of TCP in emergency medicine, no studies have evaluated the optimal size and placement of the transdermal electrodes crucial for the efficacy of TCP in dogs.This study evaluated four different sizes of electrodes (10.5, 20, 30 and 40 cm²), and four different anatomical sites (anterior–posterior, left–right, apex–base, modified left–right) in order to optimize the efficacy of TCP in dogs. Electrodes with a surface area of 20 cm² and a modified left–right placement minimized the pacing current and involuntary skeletal muscular contraction (muscular twitching) and so achieved the most optimal effect of TCP in dogs.     

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.