Implantable Cardiac Devices and Congenital Heart Disease
Survival of children with congenital heart disease (CHD) continues to improve in lockstep with advances in surgical and medical therapy, and more than 90% now reach adulthood. Despite the impressive anatomic repairs that are now achievable, even adults with fully repaired CHD cannot be regarded as having normal hearts, and many will be prone to arrhythmias. More and more will meet indications for implantable cardiac devices—pacemakers as definitive therapy for bradycardia, implantable cardioverter-defibrillators (ICDs) for ventricular arrhythmias, and cardiac resynchronization devices for impaired myocardial function and dyssynchrony. However, device implantation in adults with CHD is fraught with unique technical and management challenges, as described in this chapter.
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 ).
| Congenital Sinoatrial Node Dysfunction | Congenital Atrioventricular Block |
|---|---|
| Left atrial isomerism (heterotaxy syndrome)Left-sided juxtaposition of the atrial appendages | CC-TGAAVSDLooped single ventriclesAnomalous left coronary artery arising from the pulmonary artery |
| Postoperative SND | Postoperative AV Block |
| Mustard and Senning atrial redirectionHemi-Fontan or Fontan surgery (atriopulmonary and TCPC)Glenn shuntSinus venosus ASDEbstein anomalyArterial switch for d -TGATetralogy of Fallot | CCTGAAVSD with or without left atrial isomerismASDVSDValve surgery, especially mitral valve and multivalve surgery involving the tricuspid valveLeft ventricular outflow tract surgerySubaortic stenosis |
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.
Right Bundle Branch Block Following Repair of Tetralogy of Fallot
Electrocardiographic RBBB is seen in greater than 90% of patients following repair of ToF. This is seen irrespective of whether surgical repair involves a ventriculotomy. QRS widening early after surgical repair reflects injury to the right bundle branch or myocardium, whereas late QRS widening reflects right ventricular (RV) dilation. Injury to the right bundle branch is partly dependent on the surgical approach and can occur at three levels : (1) at the proximal right bundle at the posterior inferior rim of the VSD, (2) at the level of the moderator band, or (3) terminal RBBB at the distal ramifications of the RV Purkinje system. Generally, most repaired patients will have terminal or distal RBBB and do not progress to complete heart block. Electrocardiographically, this corresponds to RV apical endocardial or epicardial activation in the first third of the QRS complex; if this ECG pattern is present, then proximal RBBB can be effectively excluded. However, in the uncommon patient with postoperative transient complete heart block that persists as bifascicular block subsequently, the risk of late higher degree or complete AV block may be as high as 33%.
Note that congenital complete AV block can also occur in the absence of structural CHD or surgical procedures. Although it can be an isolated abnormality, many cases of fetal congenital CHD are strongly associated with maternal autoimmune connective tissue disease. In these cases, it is presumed to be related in some way to the transplacental passage of anti-Ro and anti-La antibodies, which are present in greater than 90% of mothers during pregnancy or at the time of delivery. (Late cases of congenital complete heart block are less likely to be associated with antibodies.) Another rare cause of congenital AV block is the hereditary diseases such as Hurler and Hunter cardiomyopathy.
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.
| Recommendations for Permanent Pacemaker Therapy According to the PACES/HRS Expert Consensus Statement on Arrhythmias in Adult Congenital Heart Disease 2014 | Class of Recommendation | Level of Evidence |
|---|---|---|
| Permanent pacing is recommended for adults with CHD and symptomatic sinus node dysfunction, including documented sinus bradycardia or chronotropic incompetence that is intrinsic or secondary to required drug therapy. | I | c |
| Permanent pacing is recommended in adults with CHD and symptomatic bradycardia in conjunction with any degree of AV block or with ventricular arrhythmias presumed to be due to AV block. | I | B |
| Permanent pacing is recommended in adults with congenital complete AV block and a wide QRS escape rhythm, complex ventricular ectopy, or ventricular dysfunction. | I | B |
| Permanent pacing is recommended for adults with CHD and postoperative high-grade second- or third-degree AV block that is not expected to resolve. | I | C |
| Permanent pacing is reasonable for adults with CHD and impaired hemodynamics, as assessed by noninvasive or invasive means, due to sinus bradycardia or loss of AV synchrony. | IIa | C |
| Permanent pacing is reasonable for adults with CHD and sinus or junctional bradycardia for the prevention of recurrent IART. Devices with atrial antitachycardia pacing properties are preferred in this subpopulation of patients. | IIa | C B |
| Permanent pacing is reasonable in adults with congenital complete AV block and an average daytime resting heart rate <50 bpm. | IIa | B |
| Permanent pacing is reasonable for adults with complex CHD and an awake resting heart rate (sinus or junctional) <40 bpm or ventricular pauses >3 s. A device with antitachycardia pacing properties may be considered if the underlying anatomic substrate carries a high likelihood of developing IART. | IIa | C B |
| Permanent pacing may be reasonable in adults with CHD of moderate complexity and an awake resting heart rate (sinus or junctional) <40 bpm or ventricular pauses >3 s. A device with antitachycardia pacing properties may be considered if the underlying anatomic substrate carries a high likelihood of developing IART. | IIb | C B |
| Permanent pacing may be considered in adults with CHD, a history of transient postoperative complete AV block, and residual bifascicular block. | IIb | C |
| Pacing is not indicated in asymptomatic adults with CHD and bifascicular block with or without first-degree AV block in the absence of a history of transient complete AV block. | III | C |
| Endocardial leads are generally avoided in adults with CHD and intracardiac shunts. Alternative approaches for lead access should be individualized. | III | B |
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.
Atrial Septal Defect
ASD does not usually pose a challenge for implantation of endocardial leads. Where there is an indication to close the ASD, this should be done first as the presence of an atrial lead makes placement of an atrial septal occlusion device more challenging. If the ASD remains open and a right-sided lead is implanted, anticoagulation should be considered because of the risk of systemic thromboembolism. Particularly in patients with an undiagnosed ASD (or patent foramen ovale) at the time of implant, there is also a danger of inadvertently placing the lead(s) through to the systemic circulation. This can be easily recognized during fluoroscopy by an alert operator. Additionally, the surface ECG will show a paced right bundle branch-like morphology (in contrast to the usual left bundle branch-like morphology and left superior QRS axis characteristic of RV pacing). In general, such leads should be removed and re-sited correctly within the pulmonary venous circulation.
Dextrocardia and Mesocardia
This simply requires a suitable adjustment of the fluoroscopic views. For dextrocardia, right and left anterior oblique views are interchanged.
Ebstein Anomaly
Overall, pacing is necessary in about 3% to 4% of patients with Ebstein anomaly. There can be difficulty in placing atrial leads because a significant proportion will have a coexistent ASD. However, the most common problem is siting of the ventricular lead. In milder forms of Ebstein anomaly, it may be possible to pass a lead through the displaced and oftentimes narrowed tricuspid valve orifice, but in more severe forms, this can be exceptionally difficult. In such cases, ventricular pacing can be achieved by siting the lead at the atrialized portion of the right ventricle, without crossing the tricuspid valve at all. This has the advantage of avoiding lead-related tricuspid regurgitation, but the pacing threshold may be high. If pacing of the atrialized RV is also unsuccessful, then placing a lead within a CS branch (as in CRT) can be attempted. In cases of surgically repaired Ebstein anomaly, future need for pacing may have been anticipated, in which case the surgeon will have left a lead tunneled to the subclavicular or abdominal areas. If this is not the case, and in the less common case where surgical repair includes a mechanical tricuspid valve, then the only transvenous option left is to place a lead through the coronary sinus and its tributaries to pace the left ventricle. However, a potential pitfall is that the surgeon may sometimes position the prosthetic tricuspid valve above the coronary sinus (which therefore will empty into the ventricular side of the prosthesis), in which case the CS is no longer usable and an epicardial system will be needed. The operation note describing the position of the prosthetic tricuspid valve relative to the CS is essential in such cases.
D-Transposition of the Great Arteries
This condition is generally not compatible with survival to adulthood without corrective surgery; therefore, the adult implanter will only encounter patients who have undergone surgical correction. This can take the form of an arterial switch (the Jatene procedure) or the older atrial switch (Mustard or Senning procedures). The arterial switch is a full anatomical correction, so the implant procedure is essentially the same as for a non-CHD patient. In the case of the Mustard or Senning procedures, the implanter must understand the anatomy of the intraatrial baffle, but the procedure itself is usually straightforward ( Fig. 19.4 ). Using a modestly curved stylet, the atrial lead is placed through the superior vena cava, then along the intraatrial baffle to reach the anatomic left atrium and the left atrial appendage. Placement at the proximal left atrial appendage or even more medial (rightward) placement near the roof of the atrium is usually desirable because there is a significant risk of phrenic nerve stimulation. This must be tested for carefully using a maximal 10 V output stimulus through the pacing system analyzer before accepting the lead position. The ventricular lead can be placed in a fashion similar to the atrial lead, except it should be directed inferiorly through the left AV valve to the body of the ventricle. Care to avoid phrenic nerve stimulation from the ventricular lead is also necessary. A potential pitfall to placing atrial and ventricular leads in Mustard and Senning patients is venous or baffle stenosis, which is present in as many as 22% of patients. This may not be clinically evident because the azygos vein, if present, will permit venous runoff to the inferior vena cava. Preprocedural CT, MRI, or contrast venography is recommended to rule this out. Finally, the presence of baffle leaks may increase the risk of paradoxical thromboembolism, and although the data are scanty, anticoagulation or antiplatelet therapy should be considered under these circumstances.
Congenitally Corrected l-Transposition of the Great Arteries
Device implantation is usually straightforward in CCTGA. Atrial lead placement is as normal. However, in the case of the ventricular lead, it is helpful to know that the interventricular septum may not lie in the expected plane and is rotated compared to normal—it will tend to lie close to the anteroposterior plane ( Fig. 19.5A ). Therefore, in the pulmonary artery (PA) projection, the ventricular lead can sometimes be seen to come straight toward the implanter rather than taking a leftward curve. A ventricular lead that takes a more normal, leftward course suggests the systemic ventricle is dilated, or alternatively, the pacing lead (PL) has entered the coronary sinus or middle cardiac vein (see Fig. 19.5B-E ).
Repaired Ventricular Septal Defects
Cardiac morphologists have accurately described the AV conduction axis for perimembranous, muscular and doubly committed subarterial VSDs, and surgeons are now well aware of the danger areas where careless suture placement and retraction can irrevocably damage AV conduction during VSD repair. In modern series, the incidence of AV block requiring a pacemaker is less than 1%. A small incidence of AV block is probably inevitable because of uncertainties about the AV conduction axis in complex patients (eg, those with AV discordance, malaligned VSDs, and double-outlet right ventricles) or a genetic predisposition to VSD and AV block (as seen in patients with Tbx 5 and Nkx 2.5 mutations). Although the anatomy for endocardial lead placement is straightforward, in practice, it can be difficult to find a stable position with satisfactory pacing parameters because of RV dilation, extensive scarring, and the presence of surgical prosthetic material. Active fixation leads should probably be preferred.
Repaired Tetralogy of Fallot
As for repaired VSDs, the anatomy here is straightforward, but finding a satisfactory position may be difficult in practice. Additional factors that may need to be taken into account include: (1) completeness of the surgical correction, (2) presence of any previous palliative shunts that may affect the vascular access route, (3) possible presence of free pulmonary regurgitation and/or tricuspid regurgitation impinging on the RV lead and affecting lead stability—therefore, an active fixation lead should be used, (4) need for serial cardiovascular magnetic resonance (CMR) imaging as part of follow-up (see the section Mechanism of Arrhythmic Sudden Death and Indications for Implantable Cardioverter Defibrillators Therapy in Specific Congenital Heart Disease Pathologies ) so an MRI-conditional system is recommended.
Univentricular Heart With Fontan Palliation
These are some of the most challenging patients for transvenous lead implantation because of access issues. Patients with univentricular physiology will usually have been palliated with one of a number of similar operations, aiming to direct (SVC) blood into the pulmonary circulation (classic Glenn, bidirectional Glenn, and hemi-Fontan) or to direct inferior vena cava (IVC) and SVC blood into the pulmonary circulation (classic and modified atriopulmonary Fontan and extracardiac and lateral tunnel TCPC). Because these operations usually exclude the right ventricle from the systemic venous pathway, endocardial right ventricular pacing is typically not possible, although endocardial atrial pacing may be feasible. Because the dominant problem at presentation is usually SND, a single atrial lead may suffice; however, late development of AV block is not uncommon and a dual-chamber system is then strongly recommended because loss of AV synchrony often leads to marked clinical deterioration in the Fontan patient. Given the large variety of Fontan-type operations, it is essential to review the operative notes and imaging to determine the exact systemic venous pathways to the atrium that are available (if any) before attempting pacing. Of course, the ideal situation is that the surgeon has left epicardial leads in place at the time of the original surgery, which would obviate the need for transvenous leads or further surgery for epicardial leads.
Atriopulmonary Fontan
Here, upper limb venous drainage is usually preserved, and it is therefore possible to access the right atrium through the usual subclavian-SVC route. If there is venous obstruction of the upper body, then the femoral route may be available (but much less desirable because there is a markedly increased risk of infection associated with inguinal placement of the generator box). The principal difficulty is usually not with access to the right atrium, but with finding a stable atrial pacing location with satisfactory pacing parameters. This is because right atrial pressures are typically high in atriopulmonary Fontans, and the atrium is therefore usually severely dilated, thickened, and scarred. Customized stylets with larger radius curves and testing of multiple anatomic positions are usually needed. If available, review of pre-implant electrophysiological 3D voltage maps to assess and avoid regions of scarring can be very helpful. In this type of Fontan, for those cases requiring ventricular pacing, the coronary sinus may be accessible, and has been reported as a viable route for pacing the systemic ventricle.
Total Cavopulmonary Connections
For intracardiac variants of TCPC, atrial lead placement may be theoretically and practically possible from either the subclavian or femoral routes because a portion of the intracardiac lateral tubular path connecting the IVC and PA consists of the lateral right atrial wall. If a fenestration is present (either preexisting and created at the time of surgery, or by transcatheter perforation), it may be technically possible to use the perforation to reach the neopulmonary and pulmonary atria, but in general, endocardial lead placement via this route is strongly discouraged—the epicardial route should be preferred. For extracardiac variants of TCPC, the tunnel lies outside the heart so epicardial pacing will be necessary.
Choice of Pacing Mode
The choice of pacing mode in CHD patients is extrapolated from studies in non-CHD patients, or small studies of the acute hemodynamic effects of different pacing modes and parameters. For most cases, the principles are the same as for non-CHD patients. Atrial pacing is generally preferred to try and avoid the deleterious effects associated with long-term right (subpulmonic) ventricular pacing, but this is not always possible. AAI(R) pacing or DDD(R) pacing with a long AV delay and low backup rate is usually programmed but this can be problematic: long AV delays increase the total atrial refractory period, limiting the maximum tracking rate of the pacemaker. This is particularly important in young patients (who may be very active otherwise). This type of programming will also affect atrial tachycardia detection and mode switch. Unless there is permanent atrial fibrillation, VVI(R) pacing should generally be avoided if possible because this will result in loss of AV synchrony. Device-specific algorithms such as managed ventricular pacing (MVP; Medtronic), RYTHMIQ, and AV Search+ (Boston Scientific) and ventricular intrinsic preference (VIP; St. Jude Medical) should be used to promote atrial-only pacing, but if AV conduction is very poor, it may be judged preferable to use a shorter AV delay to reduce AV dyssynchrony (which can have severe consequences such as significantly worsening AV valve regurgitation) and accept ventricular pacing instead. In such cases, CRT upgrade can be considered if there is evidence of a fall in ejection fraction, as discussed in the section Adults With Congenital Heart Disease Living With a Pacemaker or Implantable Cardioverter Defibrillators: Medium- and Long-Term Consequences. In general, rate-response should be programmed “on” if there is evidence of SND.
Special Considerations for Univentricular Physiology and Fontan Circulations
The hemodynamics of the Fontan circulation is complex. Atrial pacing at higher rates in such patients does not always augment cardiac output because of a concomitant fall in stroke volume. This is at least in part because in the Fontan circulation (where the subpulmonic pump is absent), cardiac output is constrained by preload. Hence it is possible to view the chronotropic incompetence seen in Fontan patients as an adaptive response. As a result, pacing for chronotropic incompetence alone (without significant resting bradycardia) may not lead to clinical improvement, and the optimal programming pacemaker parameters for such patients have not yet been clearly defined. It is common to program an atrial rate of more than 70 beats per minute, with rate-response turned on, but with a relatively low upper tracking rate. Atrial tachyarrhythmias are especially deleterious in Fontan patients (as a result of loss of AV synchrony with worsening of AV valve regurgitation and left ventricular function), and in a small percentage, atrial antitachycardia pacing (AAIT or DDDRT) has been used to effectively terminate recurrent atrial tachycardia. In the presence of significant atrial tachyarrhythmias, particularly atrial flutter, the preferred solution would be to opt for early catheter ablation or arrhythmia surgery.
Sudden Death in Adults With Congenital Heart Disease and Implantable Cardioverter Defibrillators
Although the prognosis for patients with CHD has improved greatly over the years as a result of surgical and medical advances, late sudden death is a well-recognized risk. In long-term follow-up studies of CHD, it accounts for 19% to 26% of all deaths. Although the absolute incidence of sudden death is generally low (0.9 per 1000 patient years in one large US series), this is 25- to 100-fold higher than age-matched controls. This risk is not equally distributed among the different CHDs, and the pathologies at highest risk include congenital aortic stenosis (0.5% per year), TGA (0.5% per year), repaired ToF (0.15% per year), and univentricular heart (0.15% per year).
Reported causes of late death include acute heart failure, pulmonary emboli, myocardial infarction, aortic dissection or rupture, pulmonary hemorrhage, and cerebrovascular accident, but consistently in all large series, the most frequent reported mechanism of death is arrhythmia, which accounts for perhaps three-quarters of all late deaths. Atrial arrhythmias, complete AV conduction block, and ventricular arrhythmias have all been implicated (as discussed later), but overall, the dominant arrhythmia associated with late sudden death is ventricular tachycardia (VT) and ventricular fibrillation (VF). This explains the keen interest in ICD therapy for reducing late mortality in CHD patients ; in the non-CHD setting, ICDs have already been shown in large trials to be extremely effective in reducing arrhythmic death in suitably selected patients.
Mechanism of Arrhythmic Sudden Death and Indications for Implantable Cardioverter-Defibrillator Therapy in Specific Congenital Heart Disease Pathologies
Repaired Tetralogy of Fallot
This is probably the best-studied CHD in terms of late death. Survival following complete surgical repair of ToF is generally excellent. However, in large series, the prevalence of ventricular tachyarrhythmias is 3% to 4%, with a risk of sudden death of 8.3% at 35 years of follow-up, or 1% to 2% per decade of follow-up. In a landmark multicenter study that included 793 patients with repaired ToF, the main predictors of VT and late sudden death were similar, supporting the idea that in repaired ToF, ventricular arrhythmias are the main cause of death. Despite this, nonsustained VT on its own does not appear to be a strong predictor of sustained ventricular arrhythmia and sudden death. In this study, the main predictors of death were age at time of repair, QRS duration greater than 180 ms, rate of change of QRS duration, transannular patch repair, and moderate or severe pulmonary regurgitation.
In a separate landmark study of repaired ToF patients, which utilized ICD discharge as a surrogate marker of sudden death risk, no single factor was strongly predictive of sudden death and it was also necessary to combine several variables to achieve reasonable risk stratification. Synthesizing these data, it suggests that multiple adverse clinical, anatomic, hemodynamic, and electrophysiologic factors must intersect to meaningfully raise the risk of sudden death in repaired ToF (and perhaps in other forms of CHD). Traditionally, hemodynamic assessment has focused on RV mechanical function, but it is now clear that there is also an association between LV systolic function, ventricular arrhythmias, and sudden death.
Currently, the consensus opinion is that ICD therapy is indicated for patients with repaired ToF who have aborted sudden death from ventricular arrhythmia and in those with demonstrable sustained VT (ie, secondary prevention), but the indication for ICD implantation for primary prevention is less clearly defined. Guideline recommendations for ICD implantation are summarized in Table 19.4A and B . Patients need to be selected carefully because there is significant comorbidity attributable to ICDs (inappropriate shocks with attendant psychological distress, infection, lead fracture, device infection, etc.; see the section Cardiac Resynchronization Therapy ). Electrophysiology study (programmed ventricular stimulation) may be helpful in this setting because adults without inducible sustained VT appear to be at low risk. It is also important to address pulmonary (or aortic) valve regurgitation with a valve replacement, if necessary, to fully reduce the risk of sudden death.
