Pacemakers and Internal Cardioverter Defibrillators in Adult Congenital Heart Disease

Bradyarrhythmias and Pacing in Congenital Heart Disease

Clinically, bradyarrhythmias are generally divided into two broad categories:

• 1.

  Those arising from a failure of impulse generation by, or impulse propagation from, the sinoatrial node (SAN) are collectively referred to as sinoatrial node dysfunction (SND).

• 2.

  Those arising from a failure of conduction from the atrium to the ventricle are referred to as atrioventricular (AV) conduction block.

As a rule of thumb, the risk of SND and AV conduction block is commensurate with the complexity of the CHD ( Table 19.1 ). Nevertheless, particular types of CHD have well-defined propensities to SND, AV conduction block, or even both. These propensities can be largely explained by understanding how the CHD, or any associated corrective surgery, affects the anatomy of the cardiac conduction system ( Table 19.2 ).

TABLE 19.1

Approximate Risk of Sinoatrial Node Dysfunction, Atrioventricular Block, Dyssynchrony, and Ventricular Arrhythmia by Congenital Heart Disease Type and Complexity

Modified from PACES/HRS Expert Consensus Statement on the Recognition and Management of Arrhythmias in Adult Congenital Heart Disease (2014).

Complexity of Congenital Heart Disease	Type of Congenital Heart Disease	Prevalence (in Congenital Heart Disease Population) (%)	Risk of
			Sinoatrial Node Dysfunction	Atrioventricular Block	Dyssynchrony	Ventricular Arrhythmia
Simple	Patent ductus arteriosus	6-8
	Pulmonary stenosis	6-8
	Ventricular septal defect	30-32
	Secundum atrial septal defect	8-10
Moderate	Aortic coarctation	5-7
	Anomalous pulmonary venous return	0.5-2.5
	Atrioventricular septal defect	3-5
	Aortic stenosis	3-5
	Ebstein anomaly	0.5-1.5
	Tetralogy of Fallot	8-10
	Primum atrial septal defect	2-3
Complex	Truncus arteriosus	1.5-2
	Pulmonary atresia	2-2.5
	Double outlet right ventricle	1.5-2
	d -transposition of the great arteries	6-7
	l -transposition of the great arteries	1-2
	Hypoplastic left heart syndrome	3-4
	Other (heterotaxy, other single ventricle)	7-10

Risk ranges from minimal (no shading) , mild (light blue shading) , moderate (medium blue shading) and high (dark blue shading) .

Normal Anatomy of the Cardiac Conducting System ( Fig. 19.1 )

With atrial situs solitus, the SAN will be found in the epicardium of the lateral right cavoatrial junction. The SAN spontaneously depolarizes (a property referred to as automaticity ), and impulses from this structure are conducted via the internodal tracts of the right atrium to the atrioventricular node (AVN). The normal AVN is situated in the midseptum of the right atrium, at the apex of the so-called triangle of Koch, before continuing anteriorly and superiorly as the penetrating bundle of His. The bundle of His passes through the right fibrous trigone and emerges at the base of the noncoronary aortic cusp in the upper interventricular septum before dividing into the left and right bundle branches.

Sinoatrial Node Dysfunction in Congenital Heart Disease

Congenital SND is relatively uncommon. When it does occur, it is usually a result of CHD that involves the right cavoatrial junction, where the normal SAN is situated. A well-known example is patients with left atrial isomerism, in whom the right cavoatrial junction is not normally developed, and the SAN is frequently hypoplastic, displaced, or even absent. Seventy percent of such patients will have sinus bradycardia by 15 years of age. Patients with left juxtaposition of the atrial appendages have a similar predisposition to SND.

Much more frequently, SND is a consequence of corrective surgery that inadvertently injures the SAN. Although SND can occur early, it is more usually a late consequence of corrective surgery. The risk can often be traced back to the surgical approach used—atrial reconstruction, deployment of an atriotomy line close to the SAN, insertion of intraatrial prosthetic baffles or patches all markedly increasing the risk. Therefore, surgery in which SND is a particular hazard includes atrial switch operations (Mustard and Senning), Glenn, hemi-Fontan and Fontan palliation of univentricular hearts, repair of supracardiac total anomalous pulmonary venous drainage, repair of partial anomalous pulmonary venous drainage involving the right upper pulmonary vein, and repair of superior sinus venosus defects. It is also increasingly recognized following repair of tetralogy of Fallot (TOF). In this latter case, SND may be related to the more recent use of a transatrial approach to the right ventricle in preference to a ventriculotomy (to avoid encouraging a substrate for late ventricular tachyarrhythmia and increased risk of sudden cardiac death in TOF, as discussed in the section Sudden Death in Adults With Congenital Heart Disease and Implantable Cardioverter Defibrillators).

The overall incidence of SND varies between 15% for lateral tunnel total cavopulmonary connection (TCPC) and 28% for extracardiac tunnel TCPC early postoperatively, and up to 29% on long-term follow-up, with no difference between surgical techniques. Following Mustard or Senning atrial switch operations, the incidence of SND is reported as 60% at 20 years of follow-up. Following repair of a sinus venosus atrial septal defect (ASD), SND is reported in as many as 35% of patients.

Atrioventricular Conduction System Block in Congenital Heart Disease

CHD that displaces and disrupts AV conduction tissue includes cases involving discordant AV chamber connections, malalignment between atrial and ventricular septae (endocardial cushion defects), or a univentricular heart. Such displaced tissue is often abnormally fragile and prone to early degeneration, leading to AV conduction block. It is also more prone to iatrogenic injury during corrective surgery or catheter ablation procedures.

Examples of CHD lesions predisposing to spontaneous AV conduction block are:

• Endocardial cushion defects : The AV node is usually displaced posteriorly and inferiorly to its normal location, and is in proximity with the junction of the posterior rims of the atrial and ventricular septae. The bundle of His runs along the lower rim of the ventricular septum; more distally, the left anterior fascicle is frequently hypoplastic. This accounts for the characteristic ECG appearance of first-degree AV block with complete or incomplete right bundle branch block (RBBB) and left axis deviation. In addition to pure endocardial cushion defects, more complex CHD that includes this abnormality will also share a predisposition to spontaneous AV block.

• Congenitally corrected transposition of the great arteries (CCTGA): Such patients can have one or two AV nodes that can be connected by a sling of conduction tissue (so-called Monckeberg sling), together with inversion of the bundle branches. The functional AV node is normally the anterior and right-sided one, which is situated anterolateral to the mitral-pulmonary valve junction. If a second AV node is present, it is situated posteriorly and is usually hypoplastic. Whether there are solitary or twin AV nodes, early fibrosis and development of AV block is frequent. The risk of complete AV block is 3% to 5% at birth, and approximately 2% a year thereafter.

Numerous surgical procedures in CHD patients can be complicated by AV block; these include ventricular septal defect (VSD) closure, AV valve repair or replacement surgery, atrial reduction surgery, and left ventricular outflow tract surgery. The overall incidence is approximately 1% to 3%. Complete AV block in the early postoperative period has a low chance of recovery if it persists beyond 10 days. Complete recovery of AV conduction usually indicates a favorable prognosis, but residual impairment of AV conduction on the surface ECG as indicated by a pattern of bifascicular block with first-degree AV block carries a high risk of late recurrence of complete AV block.

Investigation of Bradyarrhythmias in Congenital Heart Disease and Indications for Pacing

The surface ECG alone may be sufficient, but ambulatory 24-hour recordings and/or exercise testing is frequently helpful in ambiguous or borderline cases ( Fig. 19.2 ). In SND, the sinus rate is usually low with failure to increase appropriately with exertion—so-called chronotropic incompetence . In AV conduction block, the most helpful feature is worsening of AV conduction as the sinus rate increases. Formal cardiopulmonary exercise testing can also be very helpful to clarify the cause of symptoms such as breathlessness or effort intolerance. Although impaired chronotropism is a frequent finding in CHD, it limits exercise tolerance in only 20% of cases with other factors such as impaired myocardial performance and right-to-left shunting accounting for the rest.

Symptoms of bradyarrhythmia include lethargy, presyncope, and syncope (as for non-CHD patients). In children, bradyarrhythmia can lead to failure to thrive and poor growth. In CHD patients with a Fontan circuit, low cardiac output states may lead to uncommon and unique manifestations such as protein-losing enteropathy, plastic bronchitis, and hepatic dysfunction. After exclusion of other causes, these states can sometimes be corrected by atrial pacing. Apart from these relatively unusual conditions, the indications for pacing are broadly similar to the non-CHD population ( Table 19.3 ). However, considerations specific to CHD patients must be taken into account when recommending implantable device therapies:

• CHD patients are often considerably younger compared to the non-CHD population requiring a device implant, and they will require more device changes and lead extractions on average; growth of young patients who have not yet reached their adult size will also need to be taken into account.

• Activity levels can be significantly higher, with an adverse impact on lead longevity.

• Endocardial leads are relatively contraindicated in CHD patients with a right-to-left shunt because of the risk of systemic thromboembolism; if used, such patients warrant anticoagulation.

• Vascular access to the target cardiac chamber can be problematic (see section Technical Considerations for Transvenous Device Implantation ), and must take into account the need for multiple lead and device changes over the lifetime of the average CHD patient.

• Epicardial access in patients with prior surgery can also be difficult or impossible because of scarring and fibrous tissue formation.

Decisions that must be made ahead of time include:

• Timing of device implant, and whether it can be delayed to allow the child to reach adulthood.

• Choosing between endocardial and epicardial pacing.

• Choice of device (ie, pacemaker versus defibrillator, discussed in the section Sudden Death in Adults With Congenital Heart Disease and Implantable Cardioverter Defibrillators).

• Cardiac chambers to be paced (ie, atrial, right ventricular, and/or left ventricular pacing, discussed in the section Adults With Congenital Heart Disease Living With a Pacemaker or Implantable Cardioverter Defibrillators: Medium- and Long-Term Consequences), and the anatomical route available to reach the target chambers.

Technical Considerations for Transvenous Device implantation

Understanding the anatomy of the particular CHD is a key determinant of success, particularly in complex CHD. Hence, preprocedural imaging with some combination of echocardiography computed tomography (CT), magnetic resonance imaging (MRI), and/or contrast venography, and discussion with CHD specialists (as part of a multidisciplinary team) is mandatory. The aim is to help the implanting physician answer three specific questions (prior to any incision being made):

• Is it possible to place a lead in a venous atrium or ventricle leading to the pulmonary circulation? Where is the coronary sinus, and is it usable for ventricular pacing?

• Is there a patent vascular access route to the target cardiac chamber(s)?

• What are the expected fluoroscopic appearances?

Particularly for cardiac resynchronization therapy (CRT) (see the section Cardiac Resynchronization Therapy ), questions about the location and extent of scarring, and areas of late electrical and/or mechanical ventricular activation may be pertinent. In CHD patients with prior surgical correction, the operative note can also be immensely helpful. For example, in patients treated with Fontan palliation, the surgical details may be crucial in deciding whether it is possible to place a transvenous atrial lead.

An exhaustive treatment of implantation techniques in CHD is beyond the scope of this text, but we will describe some common CHDs, their associated pitfalls, and helpful strategies for successful transvenous pacing.

Persistent Left-Sided Superior Vena Cava ( Fig. 19.3 )

The incidence of isolated persistent left-sided superior vena cava (PLSVC) is approximately 0.5% in the general population, but it is encountered considerably more frequently in combination with other CHD (up to 10%). PLSVCs drain into the coronary sinus (CS), which is consequently greatly dilated. The CS almost always empties into the right atrium (as normal), but rare cases where the CS drains into the left atrium have been described. Almost all patients with PLSVC will also have a right-sided superior vena cava (SVC), and 30% will have a bridging innominate vein that connects the left to the right SVC. Isolated PLSVC poses no great problem when the target chamber for pacing is the right atrium, but siting the right ventricular lead can be problematic. The options for the implanter in this case are: (1) implant via a pocket on the right side using the right SVC to enter the RA and RV as usual; (2) implant via a pocket on the left side but cross to the right SVC via the bridging innominate vein, if it is present; (3) implant from the left side and pass through the PLSVC, the CS, the right atrium, and then the right AV valve in succession to reach the subpulmonic ventricle—in this case, a looping maneuver using a succession of curved stylets can be used to bounce the lead off the lateral atrial wall and into the subpulmonic ventricle. For both atrial and ventricular leads implanted on the left side, longer lead lengths will be required. With modern leads and stylets, an experienced implanter is usually successful. If implantation of a CS lead (for CRT) is also desired, retrograde cannulation of the CS (through a right-sided pocket or from the PLSVC and a bridging innominate vein) is often preferred. This is because antegrade cannulation of the CS via the PLSVC disallows balloon occlusion venography, and direct contrast injection may not reveal any tributaries in a dilated, high-flow CS. Furthermore, because of the sharp angulations, some branches may be inaccessible if the CS is cannulated antegradely via a PLSVC.