The clinical indications for pacemaker implantation in children, adolescents, and young adults with congenital heart disease (CHD) are summarized below.

Epicardial pacing systems (Fig. 107.1) are generally utilized in younger patients (<5 years or so), patients with single ventricle physiology and intracardiac shunts. In a multicenter study by Khairy and colleagues comparing transvenous versus epicardial pacing systems, the authors found a greater than twofold increase in thromboembolic events with transvenous devices in patients with significant left-to-right or right-to-left shunts. The advantage of transvenous systems is that transvenous leads tend to have lower pacing thresholds, higher lead impedances, and longer battery longevity in comparison to the epicardial leads. Of course, epicardial systems also obviate the need for a sternotomy or thoracotomy. The risks of venous occlusion and lead compromise are significantly increased in infants with transvenous pacemakers because of smaller patient and vessel lumen size. The major disadvantage of epicardial systems in young children is the higher risk of lead fracture due to mechanical stress. More importantly, maintaining long-term vessel integrity is imperative for infants requiring life-long pacing and, therefore, an epicardial system is ideal at a young age until adequate vascular growth is achieved and transvenous leads are an option.

Transvenous leads in the pediatric patient pose a unique challenge. Adhesions between the leads and endocardial or vascular tissue and patient growth can cause shear and stress tension on the lead and may compromise lead function. To circumvent this issue of growth, many implanters leave an extra loop of lead (such as right atrial loops) to minimize tension (Fig. 107.2). However, looping may create the presence of more surface lead area in the heart and promote further adhesions, thus complicating future lead extraction if needed.

Though epicardial systems are preferred in infants, the decision regarding implantation type in young children is more difficult. The risk of thromobembolism in young patients must be balanced with the risk of compromise to lead integrity. In a study of 63 children, echocardiography and venography were routinely performed to assess the risk of thrombus formation. Twenty-one percent were found to have moderate or severe thrombosis at follow-up. Patients found to have thrombosis were younger (4.5 vs. 8.2 years) and had larger lead diameter to body surface area ratio suggesting that children <5 to 6 years of age should have epicardial systems implanted. Dual chamber (two lead) systems were also found to be prothrombotic (because of two leads occupying a larger vessel diameter) and should be avoided in the younger patient population.

Epicardial systems (Fig. 107.1) are preferred in all patients with CHD and intracardiac shunting, regardless of age, because of increased risk of systemic thromboembolism. Unipolar leads (Fig. 107.1) have a single electrode with the pacemaker generator acting as the anode. Steroid-eluting leads provide lower (better) pacing thresholds and therefore preserve battery longevity. Bipolar leads (suture on) offer better sensing
thresholds as compared with unipolar leads since they avoid far-field cardiac or skeletal muscle sensing. Ideally, bipolar leads (Fig. 107.3) should be placed on the myocardium free of scar to optimize sensing and pacing thresholds. Bipolar screw-in leads are also available for use in older patients with thicker myocardium (Fig. 107.4). In patients with multiple prior sternotomies, the left thoracotomy approach enables the surgeon to access more posterior structures such as left atrium and ventricle and avoid scar tissue ( from sternotomies), thus facilitating dissection.

Subpectoral devices are preferred in children as they offer the most optimal cosmetic result. However, the implant may be more technically challenging (more submuscular dissection) and need an experienced implanter. Muscular protection of the proximal lead, header, and generator improve longevity as well. Since subpectoral implants are anteriorly and posteriorly surrounded by muscular tissue, bipolar sensing and pacing are preferred to minimize muscular interference and muscular stimulation, respectively.

The indications for pacemaker implantation in patients with and without CHD are important to distinguish. In patients with normal cardiac anatomy, bradycardia, even advanced atrioventricular heart block, can be well tolerated from a symptomatic standpoint and is not an indication alone for pacemaker implantation. However, patients with operated CHD may require closer evaluation for residual hemodynamic issues, which may influence pacemaker implantation decision-making. One such example is an adolescent with single ventricle physiology with AV valvar insufficiency who has SND with bradycardia and junctional rhythm. Such a subject may be a candidate for pacing (atrial pacing) to improve his symptoms and hemodynamics. Consideration must be given to residual hemodynamic issues such as AV valve or semilunar valve insufficiency and chamber enlargement in addition to the presence of sinus or AV node dysfunction.

Implantation of pediatric pacemakers is best performed by a team (cardiologists, surgeons, and anesthesiologists) skilled in the management of children. Particular appreciation for anatomical considerations is often the key in patients with CHD as anatomical variations often dictate the surgical approach. Ideally, general anesthesia should be performed by a pediatric cardiac anesthesiologist with special attention to effects of anesthesia on the hemodynamics of the cardiac lesion.

Careful screening for patients deemed pacemaker dependent (defined as an unreliable underlying escape rhythm) is a crucial part of surgical preparation. Anesthesia commonly suppresses conduction and may exacerbate brady arrhythmias. Pacemaker-dependent patients undergoing generator changes must also have an appropriate mechanism for maintaining hemodynamic stability. Isuprel administration or a temporary transvenous pacing lead via the femoral vein are useful adjuncts in preparation for pacemaker implantation in patients with unreliable escape rhythms.

Patients with CHD frequently have variations in venous anatomy, thereby complicating the transvenous approach. As such, venography of the subclavian, innominate, and superior vena cava can document patency and provide a “road map” for venopuncture. Clear elucidation of intracardiac anatomy and the presence or absence of shunts is also imperative. The presence of an unrecognized patent foramen ovale may lead to inadvertent placement of the ventricular lead in the left ventricle (Fig. 107.5). This could be avoided by careful fluoroscopic imaging of the leads using different angles to confirm anterior lead placement. On the other hand, the ventricular lead placement in a patient with transposition of the great arteries (in the pulmonary ventricle-anatomically left ventricle) will be posterior fluoroscopically compared with a patient with normal segmental anatomy (Fig. 107.6). Demonstration of patent systemic venous return in patients with atrial switch operations (Mustard, Senning) is imperative as occlusion prevents transvenous access to endocardial tissue. Narrowing, stenosis, or interatrial leaks of the atrial baffle needs to be recognized by angiography and addressed (surgically, by stent or atrial septal defect device placement) before transvenous leads are placed (Figs. 107.6 and 107.7). Cardiac angiography in this patient population is also indicated to assess for baffle leaks that are a risk for paradoxical emboli and stroke. Baffle leaks need to be closed (either by device closure or surgical approach) before transvenous leads are inserted. The use of transvenous approach for atrial and ventricular pacing has been described in patients with single ventricle physiology and Fontan palliation. However, this poses technical challenge of finding viable atrial tissue capable of capture (in Fontan baffle with prosthetic material) and also obviates the need for chronic anticoagulation and its associated complications.

The most common class I indication for lead extraction is pocket/device infection (Fig. 107.8). Successful treatment of pacemakerrelated infection requires complete removal of all prosthetic (pacemaker and lead) material. In a study from the Cleveland Clinic of 123 patients undergoing hardware removal for infection, four patients experienced recurrence of infection and all four patients had retained device remnants, both transvenous and epicardial. Complete extraction was achieved in 118 patients, all of whom had no infection recurrence. Lead malfunction in the pediatric population is the most common indication for lead extraction. Lead insulation disruption and inner pacing or sensing coil fracture (Fig. 107.9) are common causes of lead malfunction, particularly in pediatrics as trauma and patient growth can compromise lead integrity. Traditionally, epicardial leads are abandoned (after new lead/s placement) without the need for extraction.

Thrombus formation around the lead is the major impediment to extraction. Fibrous tissue then forms over the lead in the course of days to months. Typical sites of fibrous accumulation (on the lead) include the venous entry site, the anastomosis of the superior vena cava and innominate vein, and the distal lead tip. In younger patients with older leads, calcification may further strengthen the fibrous matrix, thereby complicating extraction.

Several tools have been devised to facilitate lead extraction. In the past, direct traction was the only available method. Not surprisingly, direct traction often led to complete lead fracture with retained fragments requiring surgical removal. The advent of locking stylets allows for traction to be placed on the distal lead tip, increasing the likelihood of complete extraction. Telescoping sheaths and laser sheaths provide counterpressure and countertraction, both disrupting fibrous tissue adhesion to vascular structures thus facilitating lead removal.

Life-threatening complications of lead extraction include myocardial avulsion, vascular tear, pneumothorax, pulmonary embolism, arteriovenous fistula, and death. Minor complications are pericardial effusion, hematoma, venous thrombosis, and arrhythmia. Recent reported complication rates are between 0.4% and 1.0% with lead extraction success rates of >95%. The most important factors predicting extraction failure are increased implant duration, physician inexperience, younger patient age, and ventricular versus atrial leads. The risk of failed extraction, based on this database, doubles for every 3 years of implant duration. Operators who have performed fewer than 20 extractions had lower success rates. As described earlier, the pediatric population is more likely to develop calcified fibrous matrices lending to lower success rates in younger patients. Because of the increased risks, such complicated procedures should be limited to experienced operators with all available resources including surgical operating room backup for emergency surgical intervention in the event of any of the above-mentioned life-threatening complications.

The objective of pacemaker follow-up is to optimize device function, prolong battery longevity, and identify possible lead/generator issues. At implant, threshold margins (both pacing and sensing) are programmed with 2 to 3× safety margin. This is because myocardial edema and scaring may transiently affect threshold values in a fresh lead implant. Lead maturation occurs over the course of 6 weeks to 3 months at which time thresholds remain stable (chronic thresholds) and reprogramming to optimize battery longevity is indicated.

Pacemaker status evaluation can be performed in a variety of settings. Conventionally, device checks are performed in the office by an electrophysiologist or a cardiologist with pacemaker programming
expertise. With the advent of remote monitoring, transtelephonic checks can provide information regarding sensing/pacing thresholds, stored electrograms in the device for arrhythmia troubleshooting, and battery longevity. However, formal device interrogations by a technician or an electrophysiologist are required on a yearly basis, and more often for those patients with CHD or ongoing pacemaker issues.