Authors: Lorenzo Caratti di Lanzacco, Nikolaos Vogiatzakis, Davide Fabbricatore, Charles Yao-Cheng Ho, Tsveta Rahneva, Michael Athanasios Gatzoulis, Tom Wong
Categories: Review Article, Adults congenital heart disease, Conduction system pacing, Leadless pacemaker
Source: International Journal of Cardiology Congenital Heart Disease
Authors: Lorenzo Caratti di Lanzacco, Nikolaos Vogiatzakis, Davide Fabbricatore, Charles Yao-Cheng Ho, Tsveta Rahneva, Michael Athanasios Gatzoulis, Tom Wong
Adults with congenital heart disease (ACHD) represent a rapidly growing population with a high burden of bradyarrhythmias and ventricular arrhythmias requiring cardiac implantable electronic devices. However, conventional transvenous pacing and defibrillator systems often present important challenges in this population due to complex anatomy, limited venous access, intracardiac shunts, and the cumulative risk of lead-related complications over a patient's lifetime.
Recent technological advances—including conduction system pacing, leadless pacemakers, subcutaneous and extravascular implantable cardioverter-defibrillators, and emerging modular pacing–defibrillator platforms—have expanded the range of device strategies available for ACHD patients. These innovations aim to reduce intravascular hardware, improve physiological ventricular activation, and enable device therapies tailored to complex congenital anatomy.
However, the evidence supporting both conventional and emerging technologies in ACHD patients remains limited and is derived largely from small observational studies and registry data. In addition, the substantial heterogeneity of congenital heart diseases and their prior surgical repair complicates extrapolation of outcomes across patient subgroups. Careful patient selection, anatomical assessment, and consideration of long-term device management therefore remain central to clinical decision-making.
In this narrative review, we summarise recent developments in pacing and defibrillator technologies and discuss their potential implications for adults with congenital heart disease. To support clinical decision-making, we also propose a pragmatic ACHD-specific device-selection algorithm integrating anatomical, electrophysiological, and long-term management considerations.
The prevalence of adults living with congenital heart disease is estimated at 3000 per million and now exceeds that of affected children in developed countries [1,2]. This population continues to grow as surgical interventions and medical therapies improve survival. As a result, arrhythmias have emerged as a major source of morbidity-mortality in adults with congenital hearts, driven by prior surgical repair, myocardial fibrosis, and altered haemodynamics. Cardiac implantable electronic devices (CIED) have therefore become central to the management of many adults with complex congenital heart disease (ACHD).
Current guideline recommendations for device therapy in ACHD are largely extrapolated from populations with structurally normal hearts and are supported mainly by observational studies and registry data [1]. The substantial anatomical and physiological heterogeneity of congenital heart disease further complicates the generalisation of evidence across this population. Consequently, device selection in ACHD often requires individualised decision-making that integrates the underlying anatomy, systemic ventricular morphology, prior surgical interventions, anticoagulation requirements, and anticipated long-term pacing needs [3].
Pacing is commonly used to treat bradyarrhythmias, including sinus node disease and atrioventricular (AV) block. These conditions may arise from developmental abnormalities, myocardial changes caused by abnormal pressure or volume loading, or complications after surgical repair. Pacing can also support management of atrial arrhythmias as part of a pace-and-ablate strategy [4].
[5] Cardiac resynchronisation therapy (CRT) is used to prevent and treat pacing-induced cardiomyopathy and correct ventricular dyssynchrony, while defibrillator therapy is indicated to prevent sudden cardiac death due to ventricular arrhythmias (Fig. 1, Fig. 2) [3,6]. Epicardial and endocardial leads, as well as transvenous implantable cardioverter-defibrillators (ICD), are commonly utilised but often face limitations due to factors such as lack of venous access, high rates of epicardial lead failure, infection and thromboembolic risks [7]. Emerging technologies in pacing systems and ICDs, including conduction system pacing (CSP), leadless pacing, advanced defibrillator systems, and modular systems that combine endocardial pacing with subcutaneous or extravascular ICDs (S/EV-ICD), demonstrate promise.Fig. 1Illustrative case highlighting the value of systematic electrogram interpretation. (A) ICD therapy in a patient with Tetralogy of Fallot. Initially mislabelled as inappropriate therapy in part because of dual arrhythmias. Preceding ventricular bigeminy, known baseline wide QRS on 12-lead ECG (B), poor morphology match of the QRS during the tachycardia, and a distinct appearance on the electrograms were consistent with ventricular tachycardia in the setting of atrial tachycardia. The VA relationship reflects retrograde atrial conduction. The patient underwent combined atrial tachycardia and ventricular tachycardia ablation.Fig. 1Fig. 2Pre-procedural computed tomography (A) integrated with electro-anatomical mapping (B) using InHEART ™ to guide catheter ablation in a patient with congenitally corrected transposition of the great arteries and recurrent atrial and ventricular tachycardias. Imaging integration allows visualisation of cardiac structures (phrenic nerves in green, coronary arteries in red, coronary veins in blue) and device leads (white), improving procedural safety combined with real-time fluoroscopy. This technology reduces the risks of inadvertently damaging or dislodging the leads.Fig. 2
In this review, we summarise and discuss the latest advancements in pacing and ICD therapies and explore their potential implications for ACHD patients., To assist clinicians in selecting the most appropriate device, we also propose a streamlined, four-step ACHD-specific device-selection algorithm, integrating anatomical, electrophysiological, and long-term management considerations.
As adults with congenital heart disease represent a highly heterogeneous population, pacing and defibrillator therapy cannot be approached uniformly across ACHD patients, and phenotype-specific considerations are often necessary when evaluating device options.
Patients with a systemic left ventricle—such as those with repaired ventricular septal defects, AV septal defects, or tetralogy of Fallot—often resemble patients with acquired structural heart disease in terms of ventricular mechanics and response to pacing therapies. In this group, conventional pacing strategies and CRT may be more closely applied using principles similar to those used in non-congenital populations [8]. In particular, CRT response appears greatest in patients with systemic LV dysfunction and left bundle branch block (LBBB) or pacing-induced LV dysfunction. However, prior surgical repairs, right ventricular dilation, and patch-related septal myocardial scarring may still complicate RV lead placement and influence electrical activation patterns [9].
In patients with a systemic right ventricle—such as those with congenitally corrected transposition of the great arteries (ccTGA) or those who have undergone atrial switch repair for D-transposition of the great arteries—the often already compromised right ventricle demonstrates increased susceptibility to the deleterious effects of electrical dyssynchrony [10,11]. Conventional CRT strategies have traditionally been considered less effective in this population than in patients with acquired heart failure or systemic LV dysfunction. This may reflect several factors, including late referral, the predominance of right bundle branch block rather than left bundle branch block, and the technical difficulty of achieving effective resynchronisation in this complex anatomical setting [11]. Although conduction system pacing has shown promising results in selected ACHD populations, overall experience in patients with a systemic right ventricle remains limited.
Patients with Fontan circulation or functionally single ventricles represent one of the most challenging subgroups for device therapy. Venous access to the heart may be absent or significantly compromised due to surgical rerouting of systemic venous return, limiting the feasibility of transvenous pacing systems. In addition, intracardiac shunts or fenestrations in univentricular hearts may increase the risk of paradoxical embolism especially when transvenous leads are present [12]. Epicardial pacing has traditionally been the preferred approach in this population, although more reliable leadless pacing systems have recently emerged as a potential alternative in carefully selected patients. In Fontan patients, subcutaneous or extravascular ICD systems are often attractive options for not relying on the intravascular medium.
In ACHD patients with fenestrations, residual intracardiac shunts or cyanotic physiology, the presence of transvenous leads may increase the risk of systemic thromboembolism [12,13]. In such cases, leadless pacing systems or extravascular defibrillator technologies offer clear advantages by minimising or avoiding intravascular material. Assessment of thromboembolic and haemorrhagic risks, life-long anticoagulation requirements, and long-term access considerations is essential when selecting device strategies in these patients [12].
Epicardial pacing has traditionally been the preferred approach for surgically corrected complex ACHD patients due to its ability to be implanted concurrently during surgery [7,14]. It is particularly beneficial for cases where vascular access is limited or absent such as in univentricular hearts, where the diversion of venous flow after surgery limits endocardial pacing options [15,16]. However, epicardial pacing has its own issues. It is associated with up to fivefold higher lead failure rates compared to endocardial leads, due to factors such as exit block, lead fracture from inadequate contact, fibrosis, and displacement [7,14,15]. (Fig. 3). Epicardial lead revision or replacement also requires repeated thoracotomy or sternotomy, which may be undesirable in complex ACHD patients who often undergo several cardiothoracic surgeries during their lifetime. Moreover, epicardial pacing is less physiological compared to endocardial pacing, which more closely engages the His-Purkinje system.Fig. 343-year-old patient with tricuspid atresia and double outlet left ventricle, after Fontan surgery. The patient had a coronary sinus transvenous pacemaker for complete heart block, later replaced with a right-sided dual-chamber epicardial system (white arrows) After atrial lead failure and during an elective generator change, the patient underwent implantation of a new left-sided epicardial atrial lead (black arrow) with a capping of the ventricular epicardial backup lead adjacent to the abdominal generator (asterisk).Fig. 3
Comparatively, endocardial pacing offers the advantage of lower lead failure rates and better lead stability with internal active fixation [17]. However, vascular access can be challenging due to inherent vascular variations, occlusions, or abnormal anatomy resulting from previous surgeries, including baffles, conduits, and valve replacements [18,19]. Complexities also arise from altered chamber geometry due to chamber dilation or hypertrophy. In addition to the complexities of lead implantation in the ACHD cohort, the risk factors associated with traditional transvenous systems are further amplified. ACHD patients tend to be younger with decades of reintervention ahead of them. Mechanical stress in the growing vasculature can lead to stenosis, thrombosis, and occlusion; indeed, partial or complete venous obstruction has been reported in up to 18% of congenital heart patients [20]. Repetitive intervention with multiple generator changes increases the risk of pocket haematoma and infection in a population that is already at higher risk of systemic infection and endocarditis. Active lifestyle and mechanical stress over time can also lead to earlier lead failure from lead fracture or insulation break needing lead extraction and new system implant [21]. (Fig. 4).Fig. 4Multiple transvenous pacing leads in a patient with repaired sinus venosus defect and AV node ablation. The image illustrates cumulative hardware burden following repeated lead failure and generator replacement, including abandoned atrial (∗) and ventricular (∗∗) leads.Fig. 4
Cardiac resynchronisation therapy has become an important therapeutic option for selected ACHD patients with electrical dyssynchrony and ventricular dysfunction [3,5,10]. Electromechanical dyssynchrony, frequently arising from long-standing right ventricular apical pacing or native bundle branch block (notably left bundle branch block [LBBB] in a systemic left ventricle [LV] or possibly right bundle branch block [RBBB] in a systemic right ventricle [RV] [22,23]), contributes significantly to progressive ventricular dysfunction in this population. CRT aims to restore coordinated ventricular contraction and has been associated with improvements in symptoms, ventricular pro-remodelling, and systolic function [[24], [25], [26]].
Current guidelines support CRT in ACHD patients with symptomatic heart failure, systemic LV dysfunction, and LBBB, particularly when there is an ongoing need for substantial ventricular pacing [3,5]. The burden is often amplified by intensive anti-arrhythmic regimens – betablockers, class III antiarrhythmic, etc., prescribed to control atrial or ventricular arrhythmia and thereby increasing pacing-dependence. However, delivering optimal CRT in this group remains complex due to anatomical heterogeneity and technical limitations inherent to congenital heart disease (Fig. 5, Fig. 6).Fig. 5Upgrade to cardiac resynchronisation therapy in a patient with repaired Tetralogy of Fallot and pacing-induced cardiomyopathy. A coronary sinus lead was added and subcutaneously tunnelled (white arrows) to an abdominal generator (asterisk) of a pre-existing epicardial system (black arrows).Fig. 5Fig. 6Peri- (A,B) and post-procedural (C) implantation of two coronary sinus leads (black arrows) in a repaired Tetralogy of Fallot patient with severe tricuspid stenosis to mitigate pacing-induced cardiomyopathy and reduce the risk of ventricular loss of capture. The asterisk points to the abdominal generator).Fig. 6
One of the main technical hurdles is the requirement for multi-lead systems, which introduces increased procedural risk and long-term lead-related complications. Coronary sinus (CS) anatomy may be variable or abnormal in ACHD patients, making left ventricular lead placement particularly challenging. CS anomalies such as a persistent left superior vena cava, unroofed CS, or complete absence of the CS are more prevalent in congenital heart disease, especially after surgical interventions as the atrial switch procedure for D-transposition of the great arteries, which may render the CS ostium inaccessible.
Evidence supporting the efficacy of CRT in this population is growing, although it remains largely derived from small cohorts. A study of 54 ACHD patients showed early improvements in NYHA class, QRS duration, and cardiothoracic ratio following CRT. Those with a systemic LV (85%) had sustained gains in LVEF and end-systolic volume, while the ones with a systemic RV (15%) showed early right ventricular remodelling that was not maintained long term [24].
In a cohort of 32 ACHD patients, the systemic ventricle was left-sided in 44%, right-sided in 44%, and functionally single in 12%. CRT led to significant improvements in ejection fraction or fractional area change, primarily in those with a systemic LV, with an overall long-term response rate of ∼50% [25].
In a study of 85 ACHD patients (mean age 40), 37% had a systemic RV. CRT response (systemic VEF ≥10% and/or improvement in NYHA class ≥1) rate at 6, 12, and 24 months were similar between systemic RV and LV groups, particularly in the context of pacing-induced dyssynchrony [26].
In a multicentre retrospective study of 80 ACHD patients with a systemic RV (mean age 45 years), most had congenitally corrected transposition of great arteries (ccTGA) (79%) or dextro transposition of great arteries (D-TGA) (21%). Over a 4-year median follow-up, those upgraded from ventricular pacing to CRT (n = 49) showed improved NYHA class, QRS duration, and a modest rise in systemic RV function. De novo CRT recipients (n = 31) saw no significant functional gains. Heart failure readmission occurred in 25%, and mortality was 21% [27].
These findings underscore several important considerations and discordances amongst studies. Firstly, CRT can provide significant symptomatic and structural benefits in all ACHD subgroups with varying results. Secondly, patients with systemic RVs, who were historically considered less likely to respond, may derive benefit comparable to those with systemic LV in selected settings. In systemic RV, upgrade CRT for pacing-induced cardiomyopathy appears more effective than de novo implantation. Thirdly, with anatomical complexities, the need for multiple leads increases the procedural complexity and risk of complications, highlighting the need for evolving technologies to improve outcomes and broaden the applicability of CRT in ACHD.
Conduction system pacing (CSP), encompassing His bundle pacing (HBP) and left bundle branch area pacing (LBBAP) (Fig. 7), aims to stimulate the heart's native conduction system to achieve physiological ventricular activation [28,29]. Compared to traditional right ventricular apical pacing, CSP has been associated with improved electrical synchrony, reduced risk of heart failure progression, lower incidence of atrial fibrillation, and fewer device-related complications [30,31]. However, direct comparisons with CRT in congenital studies are lacking [32]. Emerging data supports the feasibility and safety of LBBAP in ACHD patients with procedural and fluoroscopy times in proficient hands comparable to those in non-ACHD populations [33]. In systemic left ventricular ACHD patients, CSP has been shown to be reliably achievable, offering similar improvements in LVEF and greater QRS narrowing compared to CRT at one year [34]. Among CSP modalities, electrical parameters tend to be more favourable with LBBAP than with HBP [34]. Lead performance has generally been satisfactory and stable over short-term follow-up [34]. However, CSP in ACHD presents several unique anatomical and technical challenges [35,36]. Anatomical complexities such as variation in the location and structure of the conduction system—particularly in conditions like transposition of the great arteries or tetralogy of Fallot—can make lead positioning unpredictable [37]. Surgical patches, scarring in the interventricular septum, and altered myocardial architecture may further complicate lead deployment and stability [9]. Electro-anatomical mapping can be utilised to differentiate scarred from viable tissue and to guide optimal lead placement based on conduction system potentials (Fig. 8). [38] Additional procedural difficulties include marked right atrial and right ventricular dilatation, which can compromise lead support and delivery, as well as hypoplastic right ventricles, which limit space for manoeuvring and accurate lead placement. Severe tricuspid or pulmonary regurgitation as well as right ventricular hypertrophy may also impede access to the left bundle branch area [38]. These challenges sometimes necessitate the use of specialised delivery systems and tools, or altering current available systems, in order to adapt to the unique anatomy and physiology of ACHD patients. O'Connor and colleagues showed that CSP could be achieved in almost all ACHD cases with or without modifying the sheath curvature, to better suit the underlying anatomy [33].Fig. 712-lead ECGs (A) pre- and (B) post-implantation of a LBBAP pacemaker in a patient with repaired Tetralogy of Fallot and intermittent 1 AV block. Confirmation of true left bundle capture may be challenging during the procedure due to the marked anatomical heterogeneity in congenital heart disease.Fig. 7Fig. 8In a patient with prior Mustard procedure for transposition of the great (A) Electroanatomical mapping of the systemic ventricle (RAO 30° view) to identify bundle branch potential(s) and delineate scar.(B) CSP implantation in an anteroposterior fluoroscopic view, with lead placement guided by mapping catheter (Octaray™) localisation of conduction tissue.(C) Final lead position confirmed on cardiac CT.Systemic ventricular leads require long-term anticoagulation to minimise the risk of stroke and systemic thromboembolism.Fig. 8
Long-term lead performance in ACHD also remains insufficiently defined. Although early procedural success and short-term electrical parameters are encouraging, chronic lead behaviour in surgically altered septa is uncertain. Progressive septal fibrosis/calcification, including around prior VSD repair sites or patch material, may potentially contribute to threshold rise over time and could reduce long-term lead durability although this rare event in the general population remains to be elucidated [39]. Transvenous lead extraction in patients with repaired congenital hearts is prone to heightened extraction failure and complications excess due to the presence of post-surgical intravascular and/or intracardiac adhesions along the lead trajectory [40]. Unsurprisingly, both the number of prior cardiac surgeries and lead dwell time independently correlate with procedural failure [41].
Finally, true CSP in ACHD is technically demanding and should be viewed as an expertise-dependent procedure. The learning curve is substantial even in structurally normal hearts and is likely to be steeper in congenital populations due to variable conduction system location, unusual chamber orientation, and the frequent need for tailored delivery tools or adjunctive imaging [29]. For this reason, CSP in ACHD is best performed in centres with expertise in both congenital heart disease and advanced device implantation.
Leadless pacing systems offer a compelling alternative to conventional transvenous pacemakers by eliminating the complications related to leads and generator pockets (Fig. 9). [42,43]. Despite these benefits, leadless pacing in ACHD poses technical and anatomical challenges. One of the major limitations is the size of the delivery sheath required for device implantation, which may be unsuitable for small adults and paediatric patients. Moreover, complex lower limb and central venous anomalies may preclude the conventional femoral approach [44]. For example, an interrupted inferior vena cava, as seen in atrial isomerism, necessitates alternative access routes. In these scenarios, internal jugular venous access has been successfully employed, with case reports demonstrating the feasibility of both MICRA™ (Medtronic) and AVEIR™ (Abbott) leadless pacemaker implantations via the right internal jugular vein [45,46]. Furthermore, in selected cases, the trans-carotid approach has been utilised effectively, including in patients with Fontan physiology [47].Fig. 9Atrial leadless pacemaker implantation using AVEIR™ system in a patient with prior Mustard repair and sinus pauses. (A) Contrast injection outlining the left atrial appendage during before device deployment. (B) Post-procedure chest X-ray showing the released device in the LAA (arrow).Fig. 9
Accessing the sub-pulmonary ventricle in patients with univentricular circulation or surgically modified anatomy presents an additional layer of complexity. In such cases, trans-baffle puncture can facilitate access. This has been illustrated in a case involving a woman with double inlet left ventricle and complete AV block, post–lateral tunnel Fontan, where leadless pacing was successfully achieved through fenestration [48]. The lack of trabeculations in the non-systemic left ventricle may compromise device stability. The AVEIR™ leadless pacemaker, with its helix fixation and retrievability, may offer superior anchoring in such anatomies.
Leadless pacing is especially advantageous in patients who have undergone tricuspid valve surgery or replacement. In these cases, traditional transvenous systems may jeopardise the integrity or function of the prosthetic valve. Leadless systems, by avoiding transvalvular lead passage, offer a solution that is both safer and effective [49,50]. Additional challenges include the absence of trabeculations in some congenital ventricles, potential interaction with prosthetic valves, and the need for precise device positioning.
A major limitation of the early-generation single-chamber leadless pacemakers is their inability to maintain AV synchrony particularly at higher heart rates, which is an important concern in younger and more active patients. Loss of AV synchrony may reduce cardiac output and increase the risk of atrial arrhythmias. The MICRA™ AV model leadless pacemaker addresses this limitation to an extent by providing a certain level of rate-responsive ventricular pacing and AV synchrony through accelerometer-based sensing of atrial contractions [51].
More recently, the AVEIR™ dual-chamber leadless pacing systems allows sequential sensing and pacing of the atrium and ventricle, thereby providing more reliable AV synchrony than the MICRA™ AV model [42]. This innovation is of particular interest in the ACHD population, where preserving AV synchrony improves haemodynamics, symptoms, and exercise tolerance [52]. As Reddy et al. recently demonstrated the feasibility of leadless CSP in non-ACHD populations, this promising technique may eventually be extended to congenital [53].
Infections involving leadless pacemakers have been reported, although their incidence appears to be lower than with conventional transvenous systems, likely because of their limited intravascular exposure and the absence of a pocket [54] The smaller device surface area and rapid endothelialisation further reduce susceptibility to microbial colonisation. When leadless device infections do occur, usually in the setting of persistent bacteraemia or endocarditis, their management may require device retrieval. The long-term infection risk of LP in ACHD patients remains poorly defined, particularly across cyanotic and non-cyanotic, repaired and unrepaired subgroups.
Unlike conventional systems, in which depleted generators can be replaced while the leads remain in place, current generation leadless pacemakers require implantation of a new device at end of service. Battery longevity therefore remains a major concern in younger patients with lifelong pacing needs. In this setting, the availability of a retrievable system, such as for the AVEIR™ leadless pacemaker, provides a valuable therapeutic solution [46]. Contemporary data from a recent large-scale international registry in a general population demonstrated that transvenous LP removal, including retrieval of chronically implanted devices, was feasible in 87.6% of cases [55]. Failure to explant the device was most commonly attributable to the inability to successfully engage and snare docking button. Predictors of failure included horizontally oriented devices, basal implantation site within the ventricle, and suspected adhesions involving the docking apparatus—such as tethering to the tricuspid valve apparatus or fibrotic ingrowth from adjacent endomyocardial tissue. These features are not uncommon in operated congenital hearts, and further studies are required to assess retrieval success in ACHD.
In younger patients with lifelong pacing needs, this also raises the possibility of sequential implantation of multiple devices over time. Although most targeted ventricles can generally accommodate more than one device, the long-term haemodynamic implications of multiple intracardiac devices remain uncertain, particularly in patients with abnormal ventricular geometry or prior surgical reconstructions. This issue may be particularly relevant in ACHD patients with systemic right ventricles, single-ventricle physiology, Ebstein's disease, in whom available implantation space may already be anatomically or functionally limited.
Consequently, when considering leadless pacing in ACHD patients, clinicians should incorporate long-term pacing strategy into the initial device selection process. Factors such as expected device longevity, anatomical space for future implants, and the potential need for device retrieval should be carefully factored in.
Implantable cardioverter-defibrillator therapy plays a vital role in the prevention of sudden cardiac death among ACHD patients, many of whom are at elevated risk for life-threatening ventricular arrhythmias [[1], [2], [3]]. [56, 57] Because younger age and primary prevention indications are associated with lower ICD acceptance, pre-implantation screening for anxiety and depression is important [58]. In addition, optimal medical and heart failure management remains essential to reduce arrhythmic occurrence and burden, minimise ICD therapies, and potentially avoid the need for an ablation or ICD implantation in selected cases [59].
When a transvenous ICD lead and an LBBAP lead are implanted together, case reports have described pacing inhibition through oversensing caused by mechanical interaction between the two closely spaced leads. This rare phenomenon appears more likely when the ICD lead is positioned basally, close to the distal portion of the LBBAP lead, and when ventricular space is limited [60]. Altered ventricular dimensions in congenital hearts may predispose to this uncommon interaction.
The subcutaneous ICDs has emerged as an alternative to traditional transvenous systems in this population, especially for individuals with challenging vascular access, intracardiac shunts, or increased risk of systemic thromboembolism [61]. However, 23-48.4% ACHD patients are rendered ineligible for both right- and left-sided S-ICD after screening, because of unfavourable sensing-vector orientation [47,62,63]. In addition, S-ICDs alone cannot deliver anti-tachycardia pacing (ATP), and inappropriate shocks may occur because of oversensing of the T waves. T wave oversensing appears to be promoted by broader QRS complexes, R:T max ratio <3 or T wave inversion, greater time to peak T wave amplitude, and long QTc, all of which may be more prevalent in ACHD patients after surgical repair [17,64]. Abnormal QRS morphologies commonly seen in repaired tetralogy of Fallot, systemic right ventricular physiology, or prior ventricular septal defect patch repair, may compromise sensing vector eligibility and increase the risk of inappropriate therapies. Whether QRS duration >148 ms is definitely an independent predictor of inappropriate shocks remains uncertain. Prompt recognition and treatment of supraventricular tachyarrhythmias is essential to reduce inappropriate ICD therapies [65]. Overall, between 12.5 and 15% of the ACHD population with the first generations S-ICD encountered inappropriate shocks [65].
Further advances in defibrillator technology include the development of the extra-vascular ICD, which employs a lead positioned in the substernal space rather than within the vasculature [66]. EV-ICDs offer several advantages over traditional S-ICDs, including reduced defibrillation and pacing energy requirements, approximately 60% longer projected battery life, and a smaller form factor similar to transvenous ICD generators [67,68]. The EV-ICD is capable of delivering ATP, pause-prevention pacing at 40 bpm for up to 30 s, and post-shock pacing at the same rate, expanding its functionality well beyond that of the S-ICD [[66], [67], [68]].
Despite these benefits, the EV-ICD is not without limitations. Inappropriate shocks have been reported in approximately 9.7% of recipients, often due to oversensing of P-waves—emphasizing the need for meticulous lead placement [[66], [67], [68]]. Moreover, several exclusion criteria restrict its use, including prior sternotomy, pericardial or mediastinal disease, previous pericardial surgery, chest radiation, and history of mediastinitis [[66], [67], [68]]. Given the complexity of many ACHD patients’ surgical histories, collaboration between electrophysiologists and congenital cardiac surgeons is essential when evaluating candidacy for these devices. Finally, neither the S-ICD nor the EV-ICD provides prolonged bradycardia pacing. Because many ACHD patients are treated with anti-arrhythmic drugs that may render them pacing-dependent, some will still need an additional pacing system.
A growing proportion of congenital adults require both bradycardia pacing and protection from malignant ventricular arrhythmias. While S/EV-ICDs offer the advantage of avoiding intravascular hardware and reducing the risk of lead-related complications, the interaction between pacing systems and sensing algorithms – especially with epicardial leads– represents an important clinical consideration [69].
The principal concern is oversensing of large pacing artefacts by the S/EV-ICD, which may result in inappropriate therapies because paced events are misclassified as ventricular tachycardia. Conversely, abnormal QRS morphology and extensive myocardial scarring may alter surface electrocardiographic signals, resulting in undersensing fatal ventricular arrhythmias such as ventricular fibrillation. Initial strategies to mitigate sensing issues include bipolar pacing, minimising pacing output where feasible, minimising pacing, optimising sensing vectors, and adjusting blanking intervals. [70]. If all fail, lead repositioning may be required.
Additional considerations arise when CSP is combined with a S-ICD. In particular, unipolar pacing, when required to achieve bundle branch capture, may adversely affect S-ICD sensing behaviour.
Despite these potential challenges, combined S/EV-ICD and pacemaker therapy has been successfully implemented in selected patients [71]. Emerging modular systems, such as communicative leadless pacemaker–S-ICD platforms (EMPOWER™), aim to overcome these limitations by enabling coordinated therapy delivery, including anti-tachycardia pacing (Fig. 10) [72]. However, these technologies remain investigational, and long-term reliability of inter-device communication and real-world clinical performance remain to be established. Most currently available data are derived from early feasibility studies and controlled clinical evaluations, with relatively little real-world experience in complex congenital populations. In addition, the long-term reliability of inter-device communication, which relies on wireless signal transmission between the leadless pacemaker and the S-ICD, introduces potential vulnerabilities related to signal interference, transmission failure, or unintended device interaction.Fig. 1026-year-old patient with complex congenital heart disease and prior Damus–Kaye–Stansel and Glenn procedures with RV lead failure. Previously had a transvenous dual-chamber pacemaker in 2011 and subcutaneous implantable cardioverter-defibrillator (black box; white coil tip). Lead extraction was considered high risk due to potential superior vena cava and shunt injury, epicardial pacing challenging due to multiple prior sternotomies and extensive mediastinal venous collaterals. A dual chamber AVEIR™ leadless pacemaker (a. atrial, v. ventricular) was implanted to preserve atrio-ventricular synchrony.Fig. 10
As implantable cardiac devices increasingly incorporate wireless communication and remote monitoring capabilities, cybersecurity considerations have become an important aspect of device safety. Although current systems use encrypted communication protocols and proprietary telemetry, the long-term resilience of these technologies to cyber threats or signal disruption in real-world environments remains an area requiring continued evaluation [73].
Practical factors such as system cost, availability, and integration into existing device follow-up infrastructure may also influence adoption. Consequently, while modular pacing–defibrillator platforms represent a promising technological development, further real-world experience and longer-term data will be necessary to fully define their roles in ACHD populations.
Wearable cardioverter-defibrillators (WCD), such as the LifeVest™, may provide temporary protection from sudden cardiac death in selected adults with congenital heart disease who are at transiently increased arrhythmic risk but are not immediate candidates for permanent ICD implantation [74]. Although data in ACHD populations remain limited, the device may be considered in situations where arrhythmic risk is uncertain or potentially reversible. Potential indications include patients undergoing optimisation of heart failure therapy, those recovering from acute haemodynamic deterioration, or individuals awaiting definitive surgical or electrophysiological intervention. The WCD may also be useful as a bridging strategy following device extraction due to infection, particularly in patients in whom immediate reimplantation may not be feasible.
However, several limitations should be considered when extrapolating these findings to ACHD. The extent to which data from non-ACHD populations can be generalised remains uncertain, given the relatively low incidence of lethal ventricular tachyarrhythmias and the non-negligible risk of inappropriate shocks in this heterogeneous population [74,75]. In addition, adherence to continuous WCD wear may be variable, especially in younger ACHD patients. Importantly, the LifeVest™ does not provide pacing support, which represents a major limitation in patients with concomitant bradyarrhythmias or pacing dependence. Therefore, in selected ACHD patients, the WCD is best regarded as a temporary bridging or risk-stratification tool.
Selection of ICD therapy in adults with congenital heart disease requires careful consideration of pacing requirements, vascular access, and the anatomical consequences of prior surgical repair. In recent years, the development of extravascular defibrillator systems has expanded the therapeutic options available for patients in whom conventional transvenous leads are undesirable or infeasible. Table 1 summarises key advantages and limitations that may influence device choice in ACHD.Table 1Comparative features of ICD technologies in adults with congenital heart disease (ACHD).Table 1CharacteristicsTransvenous ICDSubcutaneous ICDExtravascular ICDLead locationIntravascularSubcutaneous parasternalSubsternalATP✔✖✔Extended bradycardia pacing✔✖TemporaryIntravascular infection risk↑↓↓Suitability with intracardiac shuntsLimitedFavourableFavourableVenous access requirement✔✖✖Long-term lead complicationsHigher riskMinimalUnknown long-term dataEvidence in ACHDEstablished (limited)Growing registry dataEarly clinical experience
Given the anatomical complexity and lifelong device needs of adults with congenital heart disease, device selection should follow a structured and multidimensional evaluation. To facilitate this process, we propose a pragmatic four-step framework (A-C-H-D) integrating clinical indication, anatomical constraints, electrophysiological substrate, and long-term management considerations.
(A-C-H-D; Fig. 11):Fig. 11ACHD Device-selection algorithm.Fig. 11
Assess the clinical
The initial step is to clearly define the therapeutic objective. Clinicians should determine whether the primary indication •Bradyarrhythmia requiring permanent pacing or chronotropic support•Anticipated high ventricular pacing burden or pacing dependence•Ventricular dyssynchrony requiring cardiac resynchronisation therapy•Primary or secondary prevention of sudden cardiac death, including the need for ATP
Characterise the
A detailed anatomical roadmap should then be established. This includes assessment •Venous access pathways•Surgical baffles or conduits•Intracardiac shunts or fenestrations•Prosthetic valves•Prior sternotomies or thoracic surgeries•Chamber size, rotation, and cardiac axis•Chest size and chest wall deformities
Pre-procedural imaging using computed tomography or cardiac magnetic resonance imaging may be particularly valuable in complex congenital anatomy to guide device planning and anticipate procedural challenges. Patients with chest malformations may be unsuitable for S-ICD or EV-ICD.
Hit the right
Identification of the systemic ventricle and assessment of electrical activation patterns are critical for selecting the optimal pacing strategy. Clinicians should •Presence of electromechanical dyssynchrony and ventricular dysfunction•QRS duration/bundle branch block morphology•Risk of pacing-induced cardiomyopathy
Based on these findings, potential pacing strategies may include conduction system pacing, epicardial pacing (surgically placed), coronary sinus lead placement, or hybrid approaches combining multiple techniques.
In complex ACHD anatomy, pre-procedural imaging plays an important role in defining the electrophysiological substrate and planning device implantation. Cardiac magnetic resonance imaging or computed tomography can help delineate ventricular morphology, measure septal thickness, identify surgical patches or areas of myocardial fibrosis, and clarify the relationship between intracardiac structures and potential lead targets. These modalities may also assist in identifying anatomical constraints, such as abnormal chamber orientation, coronary sinus anomalies, or limited septal access, which may influence the feasibility of conduction system pacing or transvenous lead placement.
In patients with prior septal surgery, particularly VSD patch repair, planned CSP should prompt early consideration A.Modification of sheath delivery to improve engagement and penetration of the lead in a thickened fibrotic or calcified septum; andB.Electro-anatomical mapping to identify scar and directly target conduction tissue.
Decide the device
The final step involves selecting the most appropriate device platform, taking into account anatomical feasibility, pacing requirements, and long-term management considerations. Options may •Conventional transvenous pacing or ICD systems•Epicardial pacing systems•Conduction system pacing•Cardiac resynchronisation therapy•Leadless pacemakers (single chamber if in permanent atrial fibrillation; dual chamber particularly if young patient).•Subcutaneous or extravascular ICD systems•Modular systems combining leadless pacing and EV/S-ICD therapy
Screening for S-ICD eligibility and evaluation of potential pacing–defibrillator interactions should be performed when combined therapies are anticipated.
Given the young age of many ACHD patients and the likelihood of multiple future interventions, device selection should also incorporate a “10-year test,” considering the anticipated durability of the system, potential need for lead extraction or replacement, and the cumulative burden of hardware over a patient's lifetime.
In younger ACHD patients, the long-term implications of sequential leadless pacemaker implantation, including cumulative intracardiac device burden and retrieval feasibility, should be considered when selecting pacing strategies.
Given the complexity of many ACHD patients, device planning should ideally occur within a multidisciplinary setting involving congenital cardiologists, electrophysiologists, imaging specialists, and congenital cardiac surgeons. Such collaboration allows multidimensional integration of anatomical, electrophysiological, and surgical considerations, ensuring that pacing strategies are tailored to each unique patient.
Important unanswered questions remain in ACHD, in particular regarding the long-term durability of conduction system pacing leads, the cumulative device burden associated with repeated leadless pacemaker implantation, and the real-world performance of non-transvenous defibrillator systems in ACHD populations. Future prospective registries/studies and multicentre collaborations will be essential to clarify optimal patient selection and long-term outcomes.
Cardiac rhythm management in adults with congenital heart disease presents unique challenges due to complex anatomy, prior surgical reconstruction, and the lifelong device dependency [76]. Conventional transvenous pacing and defibrillator systems remain essential tools but are frequently limited by restricted venous access, increased thromboembolic risk, and a high cumulative burden of lead-related complications over decades of follow-up.
Recent technological advances—including conduction system pacing, leadless pacemakers, extravascular defibrillator systems, and emerging modular pacing–defibrillator platforms—have expanded the therapeutic options available for this population. These technologies offer potential advantages by reducing intravascular hardware, improving physiological ventricular activation, and enabling device strategies tailored to complex anatomy. However, the current evidence supporting their use in ACHD remains limited and largely derived from small observational cohorts, case series, and registry data. The substantial heterogeneity of congenital heart disease further complicates extrapolation of outcomes across patient subgroups.
Device selection in ACHD should therefore be individualised and guided by a comprehensive assessment of anatomical constraints, systemic ventricular physiology, pacing requirements, and long-term management considerations. Multidisciplinary collaboration between electrophysiologists, congenital cardiologists, imaging specialists, and congenital cardiac surgeons is essential when planning device therapy in complex cases. The ACHD-specific algorithm proposed in this review provides a practical stepwise framework to support device selection in this challenging population.
Future studies are needed to better define the long-term performance of emerging technologies in ACHD populations, particularly with respect to lead durability, device interactions, and the cumulative impact of repeated device interventions over a patient's lifetime. Until such evidence becomes available, careful patient selection and structured decision-making frameworks—such as the ACHD-specific device-selection algorithm proposed in this review—may help clinicians navigate the expanding landscape of pacing and defibrillator technologies in adults with congenital heart disease.
Lorenzo Caratti di Lanzacco: Writing – review & editing, Writing – original draft, Visualization, Resources, Methodology, Investigation, Conceptualization. Nikolaos Vogiatzakis: Writing – original draft, Resources, Methodology, Conceptualization. Davide Fabbricatore: Writing – review & editing, Supervision, Conceptualization. Charles Yao-Cheng Ho: Writing – review & editing, Conceptualization. Tsveta Rahneva: Resources. Michael Athanasios Gatzoulis: Resources. Tom Wong: Validation, Supervision, Resources, Methodology, Investigation, Data curation, Conceptualization.
Author Michael A. Gatzoulis is Editor-in-Chief of International Journal of Cardiology – Congenital Heart Disease and was not involved in the peer review or decision-making process for this manuscript.
The authors declare that they did not receive any funding or grant for this work.
TW and MAG are serving the IJCCHD Editorial Board but had no involvement in the handling of this paper. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.