You are in: eMedicine Specialties > Pediatrics: Cardiac Disease and Critical Care Medicine > Cardiology Pacemaker TherapyArticle Last Updated: May 5, 2006AUTHOR AND EDITOR INFORMATIONSection 1 of 12
  Author: Charles Berul, MD, Associate Professor of Pediatrics, Harvard Medical School; Senior Associate, Department of Cardiology, Children's Hospital of Boston Charles Berul is a member of the following medical societies: American Academy of Pediatrics, American College of Cardiology, American Heart Association, Heart Rhythm Society, and Society for Pediatric Research Editors: Jeffrey Towbin, MD, Associate Chair of Pediatric/Cardiology, Departments of Pediatrics, Molecular and Human Genetics, Cardiovascular, Professor, Baylor College of Medicine and Texas Children's Hospital; Mary L Windle, PharmD, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy, Pharmacy Editor, eMedicine.com, Inc; John W Moore, MD, MPH, Professor of Clinical Pediatrics, Division of Pediatric Cardiology, Mattel Children's Hospital of University of California at Los Angeles; Gilbert Herzberg, MD, Assistant Professor, Department of Pediatrics, Section of Pediatric Cardiology, New York Medical College; Stuart Berger, MD, Professor of Pediatrics, Division of Cardiology, Medical College of Wisconsin; Chief of Pediatric Cardiology, Medical Director of Pediatric Heart Transplant Program, Medical Director of The Heart Center, Children's Hospital of Wisconsin Author and Editor Disclosure Synonyms and related keywords: pacemaker therapy, pacing, permanent pacing, pacemaker implantation, transvenous pacemaker, implanted cardioverter/defibrillator, ICD INTRODUCTIONSection 2 of 12
  Pacemaker therapy in children involves unique issues regarding patient size, growth, development, and possible presence of congenital heart disease. This chapter reviews unique aspects of pediatric pacemaker implantation and follow-up, with particular attention to the difficulties encountered with smaller children and patients with coexistent congenital heart defects. History of the ProcedurePermanent pacing has been feasible for only the past 50 years. Since inception, the technique has advanced remarkably and now is a routinely prescribed therapy. Transvenous pacemaker implantation in young patients previously was limited by generator size and lead diameter in comparison to vascular dimensions and capacitance. Historically, epicardial pacing was more common in children. As technology has improved, generators and leads have become smaller and more advanced, allowing transvenous pacing systems in children and is even technically feasible in infants and neonates. ProblemPacemaker therapy in children primarily is used for abnormalities of sinus node or atrioventricular (AV) node function that lead to insufficient heart rate. Chronotropic incompetence is the term used to describe the inability of the sinus node to increase heart rate adequately as needed for degree of activity. Sinus node dysfunction is a related term that describes inappropriately low heart rate (either sinus or nonsinus) due to abnormal activity of the normal sinus node. Atrioventricular blocks can range in severity from first degree, where the impulse is conducted through the AV node albeit delayed, to second degree, where not all impulses are conducted through the AV node, to third degree, where AV block is complete and none of the impulses are conducted across the AV node. In addition, pacemakers are used less commonly for other disorders such as congenital long QT syndrome and cardiomyopathy. EtiologyCauses of sinus node dysfunction (SND) or atrioventricular node (AVN) dysfunction can be divided into 2 distinct categories: congenital and acquired. Congenital causes include congenital AV block and congenital SND, which is notably less common. Congenital heart block often is due to autoantibody production from maternal systemic lupus erythematosus (SLE). Acquired forms of heart block or SND are caused by infection or injury. Infections include viral myocarditis and Lyme disease. Surgical repair of congenital heart disease is the predominant cause of nodal or conduction tissue injury. INDICATIONSSection 3 of 12
Although indications for child and adult pacing differ, both include abnormalities in sinus node and AVN function. Recently, the American Heart Association (AHA) and American College of Cardiology (ACC) published updated guidelines for implanting pacing systems in children. The AHA's scientific statements on pacing in children and adolescents offer the following guidelines as "indications for pacemaker implantation in children": Class I - Pacing indicated
Class IIa - General agreement that pacing is indicated
Class IIb - No consensus, reasonable guidelines for implantation
RELEVANT ANATOMYSection 4 of 12
Congenital heart disease in pacemaker recipients Congenital (or acquired) structural heart disease presents additional issues for pacemaker therapy in children. These patients may have a more critical reliance on adequate hemodynamic status. Optimal hemodynamic performance is achieved with atrial synchronous pacing. Maintaining AV synchrony in this population often is more important than in children who have structurally normal hearts. For example, in a newborn with congenital complete heart block (CHB) but a structurally normal heart, an epicardial ventricular pacing system initially suffices to meet hemodynamic needs. In contrast, a newborn with significant structural heart disease and CHB may benefit more from a dual-chamber system to obtain AV synchrony and meet hemodynamic needs. In general, the transvenous route is a reasonable approach for children weighing at least 10 kg, although other authors have reported successful transvenous pacing in neonates without complications. Physical considerations include absence of intracardiac shunting, low-flow states, and anatomic barriers (eg, mechanical valves that block pacing leads). Transvenous lead placement in congenital heart patients often requires nonstandard positioning because of variations in venous and intracardiac anatomy. The atrial appendage often is amputated concurrently with cannulation for cardiac bypass, and atrial anatomy is often different from usual in pacemaker patients. Use of active-fixation leads allows for easier sampling of nonstandard pacing sites and easier removal. In specific congenital heart surgeries, such as the Fontan procedure, the right medial wall often is viable; in postoperative Mustard and Senning procedures, superior aspects of the systemic venous atrium are most optimal. High-output pacing is imperative testing for diaphragmatic or phrenic nerve stimulation, particularly in lateral pacing sites. The active pacing lead tip may be used for mapping of optimal tissue implant sites. Although not universally recommended, anticoagulation may help patients who have leads implanted in low-flow chambers. Also consider the possibility of future rhythm complications in children who have undergone palliative repairs. For example, a child who develops heart block after a Fontan procedure needs ventricular pacing. These children also risk developing SND, so placing an atrial pacing lead concurrent with ventricular lead placement may prove beneficial. Certain populations also have greater risk of developing atrial tachycardia; therefore, pacemaker type is important. A patient with SND who is at risk for atrial tachycardia should probably have a generator placed that also allows for antitachycardia pacing, either manually or automatically. There are now automatic atrial antitachycardia pacemakers that have been shown to be effective in pediatrics and congenital heart disease patients. Additional concerns include patients who require a pacemaker but who also are at risk of developing ventricular arrhythmias (eg, an older patient with previous repaired tetralogy of Fallot). If these patients require a pacemaker, avoiding placement in the left subclavian vein and pectoral pocket may be prudent, thus reserving this area for future potential placement of an implantable cardioverter defibrillator (ICD). CONTRAINDICATIONSSection 5 of 12
See Class III guidelines for general nonindications for pacemaker implantation in children. Expected survival of less than 6 months is a relative contraindication to permanent pacing therapy for patients who are terminally ill. Patients who fully regain normal conduction after transient postoperative heart block typically do not need to receive a permanent pacemaker (Class III guideline). WORKUPSection 6 of 12
Lab Studies
Imaging Studies
Other Tests
TREATMENTSection 7 of 12
Surgical therapyPacemaker Pulse Generators in ChildrenSize is an important factor in pacemaker selection, particularly for infants and smaller children. Modern generators have markedly reduced mass, width, and circumference, and no significant size difference now exists between single-chamber and dual-chamber devices. No pacemaker is designed specifically for pediatric use. Each generator has special features and options, which vary among different manufacturers and specific models. Some features may be particularly appropriate or inappropriate for children. For example, because pacemakers are designed primarily for adults, resting heart rate is expected to be less than 100 bpm. Most pacemakers released prior to 1996 had a maximum rate limit of 120-130 bpm, which may be inadequate for a neonate or critically ill postoperative infant. A programmable lower and upper rate limit may require a higher setting in children to compensate for increased demands on myocardial oxygen consumption, cardiac output response to exercise, and increased predicted maximum heart rates with exertion. Unfortunately, battery longevity is sacrificed in favor of optimizing hemodynamic performance. Because cardiac output is more critically dependent on heart rate in children, the requirement for faster pacing rates increases battery expenditure. Single versus dual-chamber pacing debate Experts now debate whether dual-chamber synchronous pacing is superior to single-chamber ventricular pacing. Atrial-based pacing, which includes AAI(R), DDD, and VDD(R) pacing modes, has been shown superior to ventricular-based (VVIR) pacing in studies of adults, although controversy regarding DDD versus VVI pacing continues. Several large-scale prospective studies are underway to help illuminate these issues. In adult studies, dual-chamber pacing may have lower morbidity and mortality compared to ventricular pacing in patients with CHF, valvular heart diseases, and hypertensive heart disease. Recent studies indicate higher incidences of death, stroke, atrial fibrillation, pacemaker syndrome, and heart failure during VVI pacing, compared to DDD pacing modes. An apparently convincing argument advocates atrial-based pacing (either single-chamber AAI(R) or dual-chamber modes) over ventricular-based pacing modalities, although whether DDD is better than AAI(R) for patients with intact atrioventricular conduction is less clear. Experimental data that addresses pacing in children are more limited, and some conclusions are extrapolated from adult patient series. Common pacing indications in children are similar to adults (eg, SND, AVN dysfunction), although concomitant cardiac, medical, psychological, and size-related issues often differ markedly. Rate-responsive ventricular pacing often has been used in children with complete AV block. Rate-responsive ventricular pacing also adequately responds to physiological demands of healthy active children. Many pediatric patients, however, have underlying structural heart disease, tachyarrhythmia, and hemodynamic derangements that compromise ventricular performance. In addition, pediatric patients frequently have structural anatomic barriers to implantation and limited access to cardiac chambers. Many patients with prior atrial surgery (ie, Fontan, Mustard, Senning procedures) have both bradyarrhythmia and tachyarrhythmia. Some studies have demonstrated higher atrial-pacing failure rate in these patients, presumably due to higher atrial pressures, scarring, and ischemia. A large retrospective series from Boston Children's Hospital revealed no significant differences between many patients who had undergone Fontan or atrial switch surgeries. Investigators compared these patients with others who underwent Fontan surgery and received no permanent pacemaker, atrial single-chamber pacemaker, ventricular-based pacing system, or dual-chamber pacing system. No clear choice of pacing modality emerged for the pediatric single-ventricle patient. Pacemaker Leads in ChildrenEpicardial versus endocardial pacing sites The main difference in lead implantation is route of placement. While the vast majority of adult pacemaker patients have transvenous lead placement, children have an almost even distribution of transvenous and epicardial lead implantation. Advantages of epicardial implantation include the lack of need to provide vascular continuity with cardiac chambers and avoidance of concerns about venous thrombosis. Disadvantages include more frequent reports of sensing and capture failure, higher rates of insulation and conductor fractures, and the need for an open chest approach (eg, thoracotomy, sternotomy, subxiphoid, subcostal incision). Advantages of the transvenous route include avoidance of a thoracotomy, lower pacing thresholds (with subsequent longer battery longevity), and lower incidences of exit block and lead fractures. Disadvantages include a slightly higher dislodgment rate (particularly with passive fixation devices), potential venous occlusion, danger of embolic vascular events (especially from an intracardiac shunt), slight risk of endocarditis, and subclavian crush syndrome. Leaving a generous amount of slack in the lead to allow for uncurling may decrease the likelihood of lead fracture or dislodgment with linear growth. Studies have been performed to estimate the amount of intracardiac lead redundancy necessary to allow for anticipated growth. Twiddler's syndrome also can occur in children with potential lead dislodgment, generator migration, or pacing failure due to twisting of leads or generator in the pocket. Significant vascular access challenges also can relate to congenital heart diseases and surgical corrections. Transvenous pacing leads in children Transvenous pacing certainly is feasible in infants and small children. Smaller pacemaker generators and thinner lead diameters now simplify placement of permanent transvenous pacing systems. Easier placement of transvenous leads in small patients, however, does not imply superiority over other methods. Current practice suggests that transvenous pacing leads routinely can be placed in children weighing more than 10 kg. This figure is likely to continue to decrease as pacing technology continues to reduce lead body diameter. Because of continued growth and vigorous activity, however, pediatric patients have lead fracture and failure rates distinctly higher than adults. Actual survival comparisons have been performed for transvenous pacing leads in children. These comparisons show progressive lead failure over time from fracture, insulation discontinuities, adapter/header failures, or pacing exit block. Fixation mechanisms in transvenous leads are divided into active-fixation tips and passive-fixation leads. In general, modern active-fixation leads are now more commonly used in children because of the easier removal, if necessary. Active-fixation leads have a screw on the end that penetrates the endocardium. These mechanisms either are covered in a dissolvable material (eg, gelatin, sugar cap) to protect the delicate veins during insertion or have an intricate screw extension-retraction mechanism, allowing the operator to enter the vein and cardiac chambers without an exposed screw. Advantageously, active-fixation leads can be fixated almost anywhere in the endocardium; they may be especially valuable for patients with left ventricular lead placements (eg, corrected transposition of great arteries) or for patients who lack a right atrial appendage (eg, most postoperative patients with congenital heart disease). Active-fixation transvenous leads are removed more easily, even after implantation for many years. Ease of removal is a distinct advantage for young patients who may need multiple pacemaker system replacements over a lifetime. Passive-fixation mechanisms use small tines or fins near the distal tip, which become entrapped in the right ventricular trabeculations and lodge within scar over time. These leads do not require a screw-in device but are facilitated by placement in a trabeculated region, which may not be routine in patients with congenital heart disease. Passive-fixation leads are more difficult to extract when implanted for long periods and may be less appropriate for pediatric patients because multiple revisions are anticipated. Tips of leads may have special coatings to improve pacing characteristics or to decrease surrounding tissue inflammation. The most common is a steroid-eluting tip, which continually disperses a tiny amount of dexamethasone (or other corticosteroid) into the local tip-tissue interface. These steroid-eluting leads, available in both passive-fixation and active-fixation tips, prevent subacute threshold rise, which is seen several weeks after lead implantation. This benefit can be critically important in children, who typically have a greater inflammatory response to tissue injury and larger threshold rise. Titanium nitride and other metallic compounds also have been used to increase surface area at tip-tissue interface; this increased surface area should improve pacing and sensing performance. Epicardial pacing leads in children Until recently, epimyocardial pacing was the most common pediatric pacing application. Epicardial pacing now is used primarily when transvenous pacing is contraindicated or for patients undergoing concomitant heart surgery. Contraindications to transvenous pacing include prosthetic tricuspid valves, right-to-left intracardiac shunts, congenital heart disease, surgery precluding transvenous access to cardiac chambers, recurrent transvenous lead dislodgment, and, probably minimum patient size. Preoperative detailsProvide a thorough and adequate explanation of pacemaker implantation procedures to the patient. Document indications for permanent pacing and outline the plan for route of access. Make relevant surgical decisions after comprehensive consideration of the following factors:
Intraoperative detailsA sterile environment is absolutely essential for implantation. Proper facilities include an operating room, cardiac catheterization lab, or electrophysiology laboratory. The implantation procedure may be performed under general or local anesthesia, depending on patient age and route of implantation. For the transvenous approach, one can perform either a cephalic vein cutdown or percutaneous subclavian (or axillary) vein puncture to access the venous system. Position a wire in the right heart with pacing leads positioned in the right atrium or ventricle. Testing is performed using cables to a pacing system analyzer, which can ascertain adequate sensing of intrinsic waves, capture thresholds, and lead impedances. The generator is then connected to the leads, and a pacemaker pocket is fashioned either prepectorally or subpectorally, usually using blunt dissection and/or cautery. The generator is placed in the pocket, and the incision is closed in multiple layers. The epicardial approach is typically performed via subcostal, subxiphoid, thoracotomy, or sternotomy procedures. The pacing leads are attached to epicardial surfaces and then tested for capture, sensing, and lead impedances. Similar to the transvenous procedure, a pocket, typically in the subrectus region of the abdomen (or in the pectoral region), is created, with subcutaneous tunneling of leads from epicardial sites to the pocket. Postoperative detailsIn general, most patients remain hospitalized for 12-48 hours, depending on age, complexity, and route of access. Postoperative patients may resume normal activities of daily living other than several weeks' restriction from heavy lifting, extreme stretching of the accessed shoulder (for transvenous implants), and vigorous activities. These restrictions are particularly important following passive lead implantation to avoid dislodgement. The incision needs to be kept clean and dry and typically heals within 7-10 days. Prophylactic antibiotics after the first 24 hours have not been demonstrated to reduce risk of pacemaker system or pocket infection. Patients are instructed to immediately report any symptoms of possible infection. Follow-upFollow-up is routine and simplified. During the initial few months following surgery, evaluate the patient to assess for a possible rise in capture thresholds, secondary to inflammation and exit block. Program a safety margin to avoid possible loss of capture because of a subacute threshold rise, which may be seen in the first several weeks, particularly with epimyocardial implants and/or nonsteroid eluting leads. Transtelephonic pacing system evaluation is simple, convenient, and relatively inexpensive, allowing follow-up with fewer cardiology office visits. These systems have become more sophisticated and more automated over the past few years, allowing extensive pacemaker system information to be transmitted over the telephone and internet. COMPLICATIONSSection 8 of 12
Complications involve immune response to artificial materials and response of the body to the pacemaker system. Pacemaker generators typically are very reliable and have a low failure rate. The lithium iodide battery has a limited longevity of 5-15 years. Battery depletion is not a complication but a normal occurrence. Pacing leads are more prone to failure, particularly in children. Leads may fail at the conductor wires or in insulation material (polyurethane or silicone). Lead failure typically results in inappropriate sensing or capture (underpacing or overpacing). Infection of the pacemaker system is a serious complication and almost always necessitates complete system removal, IV antibiotics, and system replacement at a remote site. However, in selected individualized cases, pacemaker system infection can occasionally be effectively treated with a prolonged course of antibiotics, without system removal. Twiddler's syndrome is an interesting finding caused by repetitive and often unintentional twisting of the generator in the pacemaker pocket, causing lead dislodgement or fracture and pacemaker failure. It is most commonly observed in patients with behavioral issues. OUTCOME AND PROGNOSISSection 9 of 12
Permanent pacing in children is a successful procedure that results in physiologic heart rates. Pacing also allows the patient to return to normal activity and lifestyle. Prognosis is excellent, because modern generation pacing systems allow for physiologic atrial-synchronous, rate-responsive pacing in the vast majority of patients, even small infants and children with congenital heart disease. FUTURE AND CONTROVERSIESSection 10 of 12
Pacemakers and sports Children with implanted devices generally are more active than adults; the child's continuing body growth and development create additional concerns and further increase demands on pacing systems. Contact sports add stress and strain on pacemaker generators and leads. Children with pacing devices have higher incidences of lead-related complications than adults, presumably secondary to growth and vigorous exertion. Younger patients are more apt to participate in contact sports and to continue to engage in vigorous activities. Resumption of normal activities, as feasible, and promotion of healthy development without incurring significant additional risks are important goals of pediatric health care. Physicians must identify potential concerns and obstacles that patients and families may encounter and must offer strategies to guide them through their adjustment. MULTIMEDIASection 11 of 12
REFERENCESSection 12 of 12
Article Last Updated: May 5, 2006 | |||||||||||||||||||||||||||||||||||||||||||||||
