Arrhythmia and Pacemaker Surgery in Congenital Heart Disease

The progress in the management of cardiac arrhythmias related to congenital heart disease (CHD) over the past 40 years mirrors the improvement in outcomes associated with heart disease in children. During the earliest era in the management of CHD, postoperative arrhythmias and heart block were a substantial cause of perioperative mortality. With the advent of direct myocardial pacing and cardiac defibrillation more than 50 years ago, mortality rates dropped substantially. In fact, the earliest history of pacing dates back to the repair of CHD. In 1958, Brockman and colleagues were the first to report the use of a myocardial pacing electrode after repair of a ventricular septal defect. Subsequent advances in arrhythmia detection and therapy coupled with the remarkable progress in pacemaker and defibrillator technology have resulted in a significant evolution in the field of arrhythmia therapy. As a result of the miniaturization of technology and the advances in transvenous techniques, cardiac surgeons have been displaced by the cardiologist in most primary electrophysiologic interventions, both diagnostic and therapeutic. This is especially true in the domain of adult cardiac surgery, where most ablative and pacemaker procedures have been transformed into a transvenous approach performed in the laboratory by cardiologists. Although the same is largely true in treatment of pediatric arrhythmias and arrhythmias associated with CHD, the inherent size and anatomic constraints in those patients often require more surgical participation in the arrhythmia therapy. There is also a growing population of adults with CHD who have an increasing need for reoperation and arrhythmia surgery as they age.

Indications and Techniques for Electrophysiologic Device Therapy in Pediatric and Congenital Heart Disease

When pacemakers were first developed in the early 1960s, the implants were all performed by cardiothoracic surgeons using an epicardial approach. Since then, the devices have been adapted to a transvenous approach, and in adults with normal cardiac anatomy, the implants are performed by a cardiologist more than 95% of the time. However, this is not the case for children and CHD patients, for whom congenital cardiac surgeons still perform nearly half of the device procedures. Indications and surgical techniques for the use of electrophysiologic devices in children and CHD patients present the surgeon with unique challenges. A child's chest cavity or vascular dimensions could be too small to host the generator and leads required, and once implanted, leads could stretch as the child grows, increasing the risk that the leads will later dislodge or fracture. A review of indications and techniques for optimal surgical placement of electrophysiologic devices in the pediatric population is presented.

Pacemakers

The recommendations for permanent pacing in children and patients with CHD are updated regularly. The last update was a practice guideline published in 2012 jointly by the American Heart Association (AHA), the American College of Cardiology Foundation (ACCF), and the Heart Rhythm Society (HRS), and its recommendations are listed in Box 132-1 . A class I indication for pacing exists for atrioventricular (AV) block that persists for more than 7 days after cardiac surgery. (The 7-day cutoff is the starting point, with longer waits for very small or unstable patients who have adequate backup temporary pacing.) The recommendations put special emphasis on age-appropriate heart rates and the presence of CHD or ventricular dysfunction to guide treatment decisions.

Box 132-1

Recommendations for Permanent Pacing in Children, Adolescents, and Patients with Congenital Heart Disease

Class I

1
Advanced second- or third-degree AV block associated with symptomatic bradycardia, ventricular dysfunction, or low cardiac output. (Level of evidence: C)
2
Sinus node dysfunction with correlation of symptoms during age-inappropriate bradycardia. The definition of bradycardia varies with the patient's age and expected heart rate. (Level of evidence: B)
3
Postoperative advanced second- or third-degree AV block that is not expected to resolve or that persists at least 7 days after cardiac surgery. (Level of evidence: B)
4
Congenital third-degree AV block with a wide QRS escape rhythm, complex ventricular ectopy, or ventricular dysfunction. (Level of evidence: B)
5
Congenital third-degree AV block in the infant with a ventricular rate less than 55 beats/min or with congenital heart disease and a ventricular rate less than 70 beats/min. (Level of evidence: C)

Class IIA

1
Congenital heart disease and sinus bradycardia for the prevention of recurrent episodes of intra-atrial reentrant tachycardia; sinus node dysfunction may be intrinsic or secondary to antiarrhythmic treatment. (Level of evidence: C)
2
Congenital third-degree AV block beyond the first year of life with an average heart rate less than 50 beats/min, abrupt pauses in ventricular rate that are two or three times the basic cycle length, or associated with symptoms resulting from chronotropic incompetence. (Level of evidence: B)
3
Sinus bradycardia with complex congenital heart disease with a resting heart rate less than 40 beats/min or pauses in ventricular rate longer than 3 seconds. (Level of evidence: C)
4
Congenital heart disease and impaired hemodynamics because of sinus bradycardia or loss of AV synchrony. (Level of evidence: C)
5
Unexplained syncope in the patient with prior congenital heart surgery complicated by transient complete heart block with residual fascicular block after a careful evaluation to exclude other causes of syncope. (Level of evidence: B)

Class IIB

1
Transient postoperative third-degree AV block that reverts to sinus rhythm with residual bifascicular block. (Level of evidence: C)
2
Congenital third-degree AV block in asymptomatic children or adolescents with an acceptable rate, a narrow QRS complex, and normal ventricular function. (Level of evidence: B)
3
Asymptomatic sinus bradycardia after biventricular repair of congenital heart disease with a resting heart rate less than 40 beats/min or pauses in ventricular rate longer than 3 seconds. (Level of evidence: C)

Class III

1
Transient postoperative AV block with return of normal AV conduction in the otherwise asymptomatic patient. (Level of evidence: B)
2
Asymptomatic bifascicular block with or without first-degree AV block after surgery for congenital heart disease in the absence of prior transient complete AV block. (Level of evidence: C)
3
Asymptomatic type I second-degree AV block. (Level of evidence: C)
4
Asymptomatic sinus bradycardia with the longest relative risk interval less than 3 seconds and a minimum heart rate greater than 40 beats/min. (Level of evidence: C)

AV, Atrioventricular.

Additional indications for permanent pacing may not be as obvious as those listed in the AHA/ACCF/HRS guidelines. If a child with a congenital heart defect requires surgery, it may be prudent to preemptively implant a pulse generator or epicardial leads during the surgery. This can benefit children with preoperative rhythm abnormalities who do not meet the indications listed in Box 132-1 , but for whom pacing will be needed postoperatively based on the known natural history of a particular cardiac anomaly or type of surgery. For example, an infant with l -transposition of the great arteries ( l -TGA) undergoing ventricular septal defect closure is at risk for complete AV block, even without cardiac surgery, and may benefit from prophylactic epicardial lead placement. Such placement can also assist children undergoing Fontan revision surgery in conjunction with an atrial maze procedure that is likely to result in sinus node dysfunction. Careful preoperative screening with 24-hour Holter monitors and electrocardiography (ECG) can help to select the patients who would benefit from prophylactic epicardial lead placement.

Epicardial pacing, the predominant method of pediatric pacing until relatively recently, is now used mainly for patients in whom transvenous pacing is contraindicated or who are undergoing concomitant heart surgery. Some of the contraindications to transvenous pacing include prosthetic tricuspid valves, right-to-left intracardiac shunts, CHD or surgery precluding transvenous access to the cardiac chambers, and small patient size. Although there are no absolute technical limitations to a transvenous route except in premature infants, venous capacitance and lead failure resulting from growth are important considerations. Although each institution should make individual decisions on the basis of local procedural capabilities and experience, we generally consider transvenous pacemaker implants in children weighing more than 10 kg.

Epicardial leads are available with sutureless (screw-on) or suture-on methods of fixation. Alternatively, a standard transvenous lead can be used in postoperative CHD patients with epicardial scarring. The transvenous lead can be placed using a transmural technique, with the lead passed through the myocardial wall and attached to the endocardium. The steroid-eluting suture-on epicardial leads are our preferred lead, because the steroid can suppress the subacute threshold rise resulting from tissue inflammatory response. Several studies have shown that these steroid-eluting leads have good intermediate-term performance, with stable acute and chronic pacing and sensing thresholds and longevity similar to transvenous leads. However, screw-on leads may be preferable for patients who have undergone prior heart surgery, as the depth of scarring can hinder suture-on techniques.

Bipolar pacing is particularly advantageous in patients with abdominal muscle stimulation, those at risk for phrenic nerve stimulation, and those with oversensing problems. Bipolar steroid-eluting suture-on epicardial leads are available, or two unipolar sutureless leads can be joined together into a bipolar pulse generator.

The surgical access can be from a midline sternotomy, a left thoracotomy, or a subxiphoid approach or via video-assisted thoracoscopy. Each method has advantages, but the aim is to allow implantation of the proper number of leads in an individual patient. Finding an optimal site for maintenance of acceptable long-term pacing and sensing thresholds can be difficult because of bleeding, limited myocardial access, myocardial scarring, and pericardial adhesions. In patients with prior extensive right atrial (RA) surgery, left atrial pacing sites and the Bachmann bundle in general have better chronic pacing and sensing thresholds than do right lateral or anterior atrial sites. A left thoracotomy can be used for implantation of left atrial epicardial leads in children with CHD. In small infants, short leads (15-25 cm) should be used because long leads left in the pericardial space can ensnare the heart, as noted in several case reports of cardiac strangulation or constriction of a great vessel by pacing leads.

The site of pacing is being recognized as an important determinant of ventricular performance. The systemic ventricle is the chamber of choice to pace and best if it is performed in an apical location. Annular and high outflow tract locations produce worse dyssynchrony. The effects of pacing site on ventricular performance depend on baseline ventricular function. If ventricular dysfunction is present, it is better to expand the surgical entry access than to pace at a site known to produce ventricular dysfunction.

Once the leads are placed and tested, the pacemaker is typically set in a subrectus pocket, but in very small infants (<3 kg), the generator and leads can be left in the pleural cavity. Although uncommon, the abdominal-positioned generators can migrate into the pericardium, peritoneum, or pelvic space—a complication most often seen in very small infants.

Cardiac Resynchronization Therapy

Biventricular pacing is a treatment used in patients with symptomatic drug-refractory heart failure secondary to dilated cardiomyopathy and associated interventricular conduction delay or dyssynchrony. The aim of cardiac resynchronization therapy (CRT) treatment is to correct AV asynchrony, nonuniformity of ventricular activation, contraction, and relaxation sequences, while providing sequences that are as homogeneous as possible. The data in children for this therapy consist of retrospective reviews rather than the randomized trials seen in adults.

Indications for CRT are well established for adults with normal cardiac anatomy, but not for children and patients with CHD. The standard adult indication for CRT is a QRS duration of greater than 120 msec, an ejection fraction less than 35%, and class II heart failure. Unfortunately, this combination rarely occurs in children. Although 90% of adults meeting these criteria have left bundle branch block, it is more common in patients with CHD such as tetralogy of Fallot to have right bundle branch block and right ventricular (RV) dysfunction. Thus standard criteria for CRT rarely are applicable in the CHD population. CRT in CHD is thus used mainly in cases of poor ventricular function and increased QRS duration (>120 msec) regardless of the QRS morphology.

Types of CRT available are biventricular, dual site, multisite, and temporary. In biventricular pacing, two distinct ventricles are present, with a pacing lead on each ventricle. If two sites on the same ventricle are paced, then it is called dual-site pacing . When the systemic ventricle is a single ventricle, then dyssynchrony can be decreased by pacing two widely separate sites on the same ventricle, a maneuver called multisided pacing . For children, temporary CRT has been used to improve cardiac output in the early postoperative setting.

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