Preprocedural Evaluation
For patients with congenital or idiopathic atrioventricular (AV) block, test for maternal lupus antibodies (anti-Ro, anti-La), and measure Lyme titers. AV block due to Lyme carditis is typically reversible with appropriate antibiotic treatment.
Echocardiography is used to determine the underlying anatomy, particularly the presence of L-looping of the ventricles (ie, physiologically corrected transposition of the great arteries), which has a high association with the development of AV block. Echocardiographic data are also useful to assess ventricular function and to determine the presence of congenital heart disease or intracardiac shunts.
Phlebography may be helpful before transvenous pacemaker implantation, particularly for patients who have undergone prior surgery or central venous line placement. Arm phlebography can outline the course of the venous system and confirm continuity with the heart. Variants (eg, left superior vena cava to coronary sinus connections and other vascular anomalies) can be easily identified.
Performing chest radiography before pacemaker implantation to identify heart chamber sizes and potential vascular abnormalities (eg, right aortic arch) is reasonable. In addition, imaging should be performed in patients with existing pacing systems to visualize the lead positions.
Electrocardiography (ECG) is essential for documenting the rhythm before the pacemaker is implanted (see the images below).
This electrocardiogram reveals a sinus atrial mechanism with complete atrioventricular block and a ventricular paced rhythm.
This electrocardiogram illustrates third-degree atrioventricular block in a 2-year-old child.
This electrocardiogram illustrates an atrial-synchronous, ventricular paced rhythm.
Equipment
A pacemaker is an electronic device, approximately the size of a pocket watch, that senses intrinsic heart rhythms and provides electrical stimulation when indicated. Cardiac pacing can be either temporary or permanent.
Permanent pacing is most commonly accomplished through transvenous placement of leads to the endocardium (ie, right atrium or ventricle) or epicardium (ie, to the left ventricular surface via the coronary sinus), which are subsequently connected to a pacing generator placed subcutaneously in the infraclavicular region.
Implantable pacemakers
Permanent pacemakers are implantable devices that sense intrinsic cardiac electric potentials and, if these are too infrequent or absent, transmit electrical impulses to the heart to stimulate myocardial contraction. A specialized type of pacemaker therapy, cardiac resynchronization therapy (CRT) with biventricular pacing, with or without an implantable cardioverter-defibrillator (ICD), has been used as adjunctive therapy for patients with heart failure.
Implantable defibrillators
The implantable cardioverter-defibrillator (ICD) is first-line treatment and prophylaxis for patients at risk for ventricular tachycardia (VT) or ventricular fibrillation (VF). Current devices offer tiered therapy with programmable antitachycardia pacing schemes, as well as low-energy and high-energy shocks in multiple tachycardia zones.
Dual-chamber, rate-responsive bradycardia pacing is available in all ICDs, and sophisticated discrimination algorithms minimize shocks for atrial fibrillation, sinus tachycardia, and other non–life-threatening supraventricular tachyarrhythmias. Diagnostic functions, including stored electrograms, allow for verification of shock appropriateness.
Pacemaker size and type
Size is an important factor in pacemaker selection, particularly for infants and smaller children. Modern generators have markedly reduced mass, width, and circumference, and single-chamber and dual-chamber devices are similarly sized.
No pacemaker is specifically designed 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, the resting heart rate is expected to be lower than 100 beats/min. Most pacemakers released before 1996 had a maximum rate limit of 120-130 beats/min, 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.
Pacemaker leads
Fixation mechanisms in transvenous leads are divided into active-fixation tips and passive-fixation leads. In general, active-fixation leads are more commonly used in children because they can be more easily removed 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 that allows the operator to enter the vein and cardiac chambers without an exposed screw.
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 those without a right atrial appendage (eg, most postoperative patients with congenital heart disease). Active-fixation leads are more easily removed, even after being implanted for many years. This feature 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 scars over time. These leads do not require a screw-in device but are facilitated by placement in a trabeculated region, which may not be routinely available in patients with congenital heart disease. Passive-fixation leads are more difficult to extract when implanted for long periods and, therefore, may be less appropriate for pediatric patients because multiple revisions are anticipated.
The tips of the 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 another corticosteroid) into the local tip-tissue interface. [27]
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 a larger threshold rise.
Titanium nitride and other metallic compounds have also been used to increase the surface area at the tip-tissue interface; this increased surface area should improve pacing and sensing performance.
Relatively recent advances in leadless pacemaker technology allow for a pacemaker to be inserted using a transcatheter approach; the Nanostim leadless pacemaker (approved for use in select international markets only) [28] and the Micra transcatheter pacing device [29, 30] are only approved for use in patients older than 18 years. These devices can provide VVIR pacing only and have not been studied in the pediatric population, but they may prove to be a viable option in the future.
Monitoring and Follow-up
Postoperative follow-up is routine and simplified. During the initial few months after surgery, evaluate the patient to assess for a possible rise in the 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 or non–steroid-eluting leads.
Remote monitoring of pacing systems is simple and convenient, and it is done wirelessly over a cellular network in the majority of cases. Remote monitoring technology has become more sophisticated, allowing for seamless transmission of events or symptoms, adequate detection of clinically relevant events, and decreased frequency of outpatient clinic visits. [31, 32]
For patients who are pacemaker-dependent, dizziness, presyncope, or syncope warrants a full device interrogation of both the leads and pulse generator to ensure proper function of the device.
Children with implanted devices are generally more active than adults; the child’s continuing bodily 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. In a multivariate analysis of 1905 pediatric patients implanted with a cardiac device from a single device company and monitored remotely, the overall daily average activity was 5.4 hours, and increased level of activity was associated with being male and younger, as well as having experienced a shock and having a pacemaker versus an implantable cardioverter-defibrillator, an epicardial device site, and the rate response turned off. [33]
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.
In 2015, the American Heart Association (AHA) and American College of Cardiology (ACC) published their recommendations regarding competitive athletics and cardiovascular abnormalities. [34] There are specific recommendations for athletes with permanent pacemakers, all of which are class 1:
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Generally, athletes with permanent pacemakers should be cleared for athletic participation if there are no limiting structural heart conditions or symptoms.
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Athletes who are completely pacemaker dependent should not engage in sports in which there is a risk of collision that could result in damage to the pacemaker system.
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Athletes treated with a pacemaker who are not pacemaker dependent may participate in sports with a risk of collision or trauma if they understand and accept the risk of damage to the pacemaker system and they have no structural heart disease that precludes participation.
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For athletes with permanent pacemakers, protective equipment should be considered for participation in contact sports that have the potential to damage the implanted device.
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This electrocardiogram reveals a sinus atrial mechanism with complete atrioventricular block and a ventricular paced rhythm.
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This electrocardiogram illustrates third-degree atrioventricular block in a 2-year-old child.
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This electrocardiogram illustrates an atrial-synchronous, ventricular paced rhythm.
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The normal cardiac conduction system is illustrated. AV = atrioventricular, IVC = inferior vena cava, SA = sinoatrial, SVC = superior vena cava.
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This radiograph depicts a transvenous ventricular pacemaker in 2-year-old child. Note the abundant slack in the lead to allow for growth.
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An epicardial dual-chamber implantable cardioverter defibrillator is shown in a neonate with congenital complete atrioventricular block. Two bipolar suture-on leads (one on the atrium and one on the ventricle) are attached to the DDDR pacemaker in the abdomen.
