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SND refers to physiologically inappropriate atrial rates, due to either sustained bradycardia or abrupt pauses in the intrinsic cardiac rhythm. In patients with isolated sinus bradycardia without symptoms due to cerebral or systemic hypoperfusion, there is no minimum heart rate or maximum pause duration where permanent pacing is recommended. Establishing a temporal correlation between symptoms and age-related bradycardia is of paramount importance when determining whether permanent pacing is needed.

Nonrandomized studies in both children and adults have demonstrated that pacing can provide symptomatic improvement when symptoms, particularly syncope and pre-syncope, are clearly attributable to SND. ^{Reference Breivik, Ohm and Segadal23–Reference Chiu, Lin and Wang26} However, there is no clear evidence that pacing in the setting of isolated SND without symptoms improves outcomes.

In symptomatic patients with SND, atrial-based pacing is generally recommended over single-chamber ventricular pacing. ^{Reference Kusumoto, Schoenfeld and Barrett2,Reference Kardelen, Celiker, Ozer, Ozme and Oto28} Furthermore, the decisions regarding pacemaker implantation for SND in patients with CHD or channelopathies should be made on an individualized basis and are discussed further in the corresponding sections. ^{Reference Gillette, Wampler and Shannon29}

Atrioventricular block

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Although the average ventricular rate in newborns (≤30 days old) and infants (≤12 months old) with isolated CCAVB provides an objective measure regarding the decision for pacemaker implantation, additional factors may equally influence the decision/timing of pacemaker implant. These include birth weight (size), ventricular dysfunction, and other comorbidities. ^{Reference Glatz, Rhodes and Gayno42} Furthermore, although symptoms such as poor feeding or tachypnea in the neonate may be due to multiple causes, they may be indicative of low cardiac output secondary to bradycardia. Therefore, a lower limit heart rate of 50 bpm is recommended for pacemaker implantation when overt symptoms related to low cardiac output do not appear to be present. One additional point of emphasis is that use of heart rate criteria for newborn or infant pacing should be based on heart rate consistency rather than a single measurement in time. ^{Reference Michaëlsson and Engle34,Reference Pinsky, Gillette and Garson37}

Beyond the first year of life, permanent pacemaker implantation is generally indicated in symptomatic patients. Contemporary studies suggest that approximately 66% of neonates and infants diagnosed with isolated CCAVB will undergo pacemaker implantation during their first year of life and that 90% of patients with CCAVB will undergo pacemaker implantation by 20 years of age. ^{Reference Jaeggi, Hamilton and Silverman30} Long-term natural history studies have demonstrated progressive left ventricular dysfunction and mitral insufficiency with cardiovascular mortality in the fourth or fifth decade of life in patients with CCAVB who did not undergo pacemaker implantation. ^{Reference Michaëlsson and Engle33,Reference Michaëlsson and Engle34,Reference Moak, Barron and Hougen43} On the other hand, some patients with CCAVB will develop left ventricular cardiomyopathy despite pacing due to either antibody-mediated myocarditis or pacing-induced dyssynchrony. ^{Reference Moak, Barron and Hougen43,Reference Janoušek, van Geldorp and Krupičková44}

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The diagnosis of advanced AV block during late childhood or adolescence is an uncommon but well-recognized phenomena. Advanced AV block may be congenital, may be related to infiltrative diseases, or may remain idiopathic. At times, late-onset AV block may be paroxysmal and quite difficult to document. ^{Reference Silver, Pass and Hordof49}

Exercise stress testing can be useful to detect the site and significance of AV block. Generally, supra-His block resolves with exercise by increased sympathetic tone. When second- and third-degree degree AV block are observed during exercise, conduction disturbance within the His-Purkinje system is suspected. Although progression to advanced second- and third-degree AV block during exercise is rare, it is associated with a poor prognosis in the absence of a pacemaker. ^{Reference Yandrapalli, Harikrishnan, Ojo, Vuddanda and Jain47,Reference Bonikowske, Barout, Fortin-Gamero, Lara, Kapa and Allison48}

With the exception of infiltrative or inflammatory causes of advanced AV block, the criteria for pacemaker implantation are similar to those for CCAVB. Permanent pacemaker implantation may be considered for advanced idiopathic AV block in adolescents with an acceptable ventricular rate, a narrow QRS complex, and normal ventricular function, based on an individualized consideration of symptoms and the risk/benefit ratio.

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Postoperative AV block complicates 3–8% of congenital heart surgeries, with 1–3% of patients requiring permanent pacemaker implantation for persistent postoperative AV block. ^{Reference Anderson, Czosek and Knilans56–Reference Liberman, Pass and Hordof58} A very poor prognosis has been established for CHD patients with permanent postoperative AV block who do not receive permanent pacemakers. ^{Reference Krongrad54,Reference Villain, Ouarda and Beyler55} Among patients who do regain AV conduction following a period of transient AV block, ≥85% have recovery of AV conduction by postoperative day 7 and ≥95% AV conduction by postoperative day 10. ^{Reference Weindling, Saul and Gamble50,Reference Romer, Tabbutt and Etheridge51} Although patients who spontaneously regain AV conduction have a favorable prognosis, ^{Reference Tracy, Epstein and Darbar7} there is a small but definite risk of late-onset complete AV block in transient postoperative AV block patients, with onset occurring as early as months, to as late as decades, following surgery. ^{Reference Aziz, Serwer and Bradley52,Reference Krongrad54,Reference Villain, Ouarda and Beyler55} Limited data suggest that some patients with a history of transient postoperative advanced second- or third-degree AV block may be at risk for late-onset AV block or sudden cardiac death (SCD) if they have postoperative bifascicular block on the electrocardiogram (ECG) that was not present preoperatively. ^{Reference Krongrad54,Reference Villain, Ouarda and Beyler55} Permanent pacemaker implantation may also be considered for transient postoperative third-degree AV block that reverts to intact AV node conduction when there is concern about the late development of AV block in patients with forms of CHD associated with progressive conduction abnormalities such as discordant AV connections, AV septal defects, and heterotaxy syndromes. ^{Reference Huhta, Maloney and Ritter59,Reference Moore and Aboulhosn60}

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Patients with CHD often have important structural and functional lesions, ^{Reference Stout, Daniels and Aboulhosn70} which influence both the indications for pacing as well as the type of pacing lead(s) utilized. ^{Reference Glatz, Rhodes and Gayno42} Therefore, pacemaker implantation in these patients should not be viewed as an isolated procedure. The loss of vascular access or direct access to cardiac chambers and/or persistent right-to-left shunting require utilization of epicardial pacing leads (with concomitant sternotomy or thoracotomy), ^{Reference Lau, Gaynor and Fuller74} although novel hybrid approaches to lead placement are being developed. ^{Reference Termosesov, Kulbachinskaya and Polyakava75,Reference Clark, Kumthekar and Mass76}

Bradycardia and scar-related tachycardias are common following surgery, and in the absence of high-grade AV block, atrial pacing is preferred to avoid pacing-induced ventricular dysfunction. ^{Reference Tsao, Deal and Backer67,Reference Barber, Batra and Burch68} Permanent pacemaker and/or lead implantation may be considered prophylactically in patients with evidence of conduction disease and heart defects with a known natural progression to advanced heart block (e.g., discordant AV connections, heterotaxy syndrome) at the time of cardiac surgery. ^{Reference Huhta, Maloney and Ritter59,Reference Moore and Aboulhosn60,Reference Cohen, Rhodes and Spray77}

Similarly, in single-ventricle patients undergoing Fontan conversion, prophylactic antitachycardia pacemakers have been used. ^{Reference Tsao, Deal and Backer67} There may be a role for pacing in improving the hemodynamic status in patients with plastic bronchitis and protein-losing enteropathy without conventional pacing indications. ^{Reference Rychik, Atz, Celermajer and Deal78}

The decisions regarding pacemaker implantation should also consider the complexity of the patient’s anatomy and hemodynamic status, with complex defined as patients with palliative repairs or impaired ventricular function or circulatory physiology. ^{Reference Stout, Daniels and Aboulhosn70}

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Transient sinus bradycardia is relatively common immediately after transplantation and frequently resolves spontaneously. In rare cases, sinus bradycardia may persist and pacemaker implantation may be needed, but at least a week should be allowed for spontaneous recovery of sinus node function. Early post-transplant AV block has been reported in pediatric patients to be more frequent than in the adult population and may be related to donor age. ^{Reference Kertesz, Towbin and Clunie79,Reference El-Assaad, Al-Kindi and Oliveira80} An analysis of the United Network for Organ Sharing (UNOS) database reported that between 1994 and 2014, 1% of cardiac transplant patients <18 years of age required a pacemaker in the acute post-transplant interval. Factors associated with need for pacemaker implant were biatrial anastomosis, older donor age, and antiarrhythmic drug use. ^{Reference El-Assaad, Al-Kindi and Oliveira80}

Late-onset conduction disorders (sinus node or AV node dysfunction) may be related to cardiac allograft vasculopathy or allograft rejection. Patients should be evaluated for the presence or development of transplant coronary artery disease, as late-onset bradycardia may be the first manifestation. ^{Reference Kertesz, Towbin and Clunie79,Reference Cannon, Denfeld and Friedman84} Microvascular angiopathy that may not be seen during conventional angiography may also cause significant ventricular dysfunction and subsequent graft failure with an added risk for conduction abnormalities. ^{Reference Chang, Hruban and Levin85}

The role of prophylactic ICD implantation is not well established but may be considered in patients who require pacemakers. Risk factors to consider are coronary artery vasculopathy and left ventricular dysfunction, which may present as ventricular arrhythmias and have been associated with SCD. ^{Reference Daly, Chakravarti and Tresler86,Reference Carboni87}

Conditions include Duchenne muscular dystrophy, Becker muscular dystrophy, myotonic dystrophy type 1, Friedreich ataxia, Emery-Dreifuss muscular dystrophy, facioscapulohumeral muscular dystrophy, Barth syndrome, Kearns-Sayre syndrome, lamin A/C mutations, and desmin-related myopathies.

Progressive cardiac conduction diseases

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Progressive cardiac conduction diseases often involve genetic disorders with progressive deterioration of the conduction system occurring either in isolation or in conjunction with other cardiac and metabolic diseases including neuromuscular and mitochondrial diseases.

The severity and onset of cardiac complications differ among the diseases. Conduction disturbances are commonly observed in myotonic dystrophy type 1 and Emery-Dreifuss muscular dystrophy. ^{Reference Jones, Mortsell and Rajaruthnam81} Variable degrees of conduction abnormalities may occur, ranging from first-degree AV block to complete AV block with unpredictable progression. Laminopathy caused by mutations in the LMNA gene is a wide-spectrum disorder exhibiting peripheral neuropathy, skeletal muscle disorders, progerias, and dilated cardiomyopathy. Cardiac conduction abnormalities, such as sinus bradycardia, AV block, atrial fibrillation, atrial standstill, and ventricular tachycardia (VT), are common and are often observed before the onset of heart failure symptoms. ^{Reference Carboni87,Reference Groh, Groh and Saha92} In a meta-analysis, arrhythmias were observed in 36% of patients before 20 years of age, with heart failure observed in 10% before 30 years of age. ^{Reference Carboni87} A prolonged PR interval >240 ms in adults is reported to be a predictor of progressive AV block and/or ventricular arrhythmias in patients with myotonic dystrophy and in patients with laminopathy. ^{Reference Ha, Tarnopolsky and Bergstra91,Reference Groh, Groh and Saha92,Reference Van Berlo, de Voogt and van der Kooi94,Reference Hasselberg, Edvardsen, Petri and Berge99}

Among the mitochondrial diseases, patients with Kearns-Sayre syndrome, characterized by progressive external ophthalmoplegia and myopathy with an onset before the age of 20 years, are known to carry a high risk for AV block and SCD. ^{Reference Feingold, Mahle and Auerbach88–Reference Ha, Tarnopolsky and Bergstra91} Currently, an HRS expert consensus statement on the evaluation and management of arrhythmic risk in neuromuscular disorders is under development. Therefore, the above recommendations may be subject to modification as newer data become available.

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In the vast majority of cases, neurocardiogenic syncope is a limited disease and pacemaker implantation is not required. In some patients, however, recurrent syncopal events may significantly impair quality of life and may result in traumatic injury, particularly when the dominant feature of reflex syncope is cardioinhibitory. ^{Reference Kolterer, Gebauer, Janousek, Dähnert, Riede and Paech101–Reference Brignole, Menozzi and Moya104,Reference Bestawros, Darbar, Arain, Abou-Khalil, Plummer, Dupont and Rah108} Therefore, in a highly select group of patients who fail more conservative treatment options, pacemaker therapy may be useful by preventing profound bradycardia or prolonged asystole. Because the efficacy of pacing depends on the clinical setting, a clear relationship between symptoms and bradycardia should be established prior to pacemaker implantation. Bradycardia or asystole should be observed during episodes of clinical syncope, ideally on more than one occasion. ^{Reference Paech, Wagner, Mensch and Antonin Gebauer105} Event monitors and ICMs have been effective for documenting this relationship.

In pallid breath-holding spells, studies of predominantly infants and toddlers have demonstrated either complete resolution or a significant reduction in the number of syncopal events in 86% patients with pacing. ^{Reference Kolterer, Gebauer, Janousek, Dähnert, Riede and Paech101,Reference McLeod, Wilson, Hewitt, Norrie and Stephenson102} Single-chamber pacing with hysteresis appears as effective as dual-chamber pacing with rate drop response for the prevention of syncope and seizures. Pacemaker settings may be optimized to prevent sustained bradycardia by programming a relatively fast pacing rate at the time of the vasovagal reflex to augment cardiac output.

Attributed to vagal storm in the setting of epilepsy, ictal-induced bradyarrhythmia or asystole can impair both cerebral perfusion and cortical function and contribute to transient loss of consciousness and injury. ^{Reference Sutton, de Jong and Stewart106,Reference Benditt, van Dijk and Thijs107} While conventional antiepileptic medications and epilepsy surgery are the mainstay treatments for ictal-induced bradycardia, pacemaker implantation may be reasonable as an adjunct for reducing the severity of symptoms.

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The utility of pacing as adjunctive therapy in the various channelopathies is not well defined. Most data are based on observational reports of pacing in the context of long QT syndrome (LQTS). In certain high-risk patients with LQTS, permanent pacemaker implantation may provide a benefit to decrease bradycardia-related or pause-related initiation of ventricular tachyarrhythmias or so-called short-long-short episodes. ^{Reference Moss, Liu and Gottlieb109–Reference Viskin, Fish and Zeltser111} In infants with prolonged QT-related functional 2:1 AV block, one observational study reported that pacing in combination with other therapies resulted in favorable outcomes with no mortality. ^{Reference Aziz, Tanel and Zelster112} Additionally, in some patients with LQTS, atrial pacing faster than the intrinsic rate has been shown to shorten the QT interval and reduce the rate of recurrent syncopal events in high-risk LQTS patients. ^{Reference Moss, Liu and Gottlieb109,Reference Kowlgi, Giudicessi and Brake114} When SND and/or AV block are present in the setting of a channelopathy or as the result of antiarrhythmic medications needed for treatment of a channelopathy, the indications for permanent pacing detailed in the respective section on SND and/or AV block apply. In the setting of atrial standstill secondary to a channelopathy or laminopathy, single-chamber atrial pacemaker placement alone is not recommended due to the high probability of atrial noncapture. ^{Reference Bellmann, Roser and Muntean115,Reference Ishikawa, Tsuji and Makita116}

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Systemic infections may cause myocardial inflammation or infiltration presenting with bradycardia or complete AV block. Known causes are Lyme disease (Borrelia burgdorferi), Chagas disease in individuals from Trypanosoma cruzi–endemic areas in Central and South America, and rarely from diphtheria myocarditis. Other etiologies include infectious mononucleosis (Epstein-Barr virus), bacterial endocarditis, viral myocarditis with perivalvular abscess, rheumatic fever, and sarcoidosis.

In symptomatic AV block associated with Lyme disease, approximately 40% of patients may require temporary pacing, although AV block is typically reversible with antibiotic therapy. ^{Reference McAlister, Klementowicz and Andrews117,Reference Forrester and Mead118} Chronic Chagas disease can present with different degrees of conduction defects. Advanced heart block in Chagas is permanent, and pacemaker implantation is indicated. ^{Reference Nunes, Beaton and Acquatella119,Reference Bocchi, Bestetti and Scanavacca120} An ICD should be considered in Chagas cardiomyopathy in the presence of significant left ventricular dysfunction or ventricular arrhythmias. ^{Reference Bocchi, Bestetti and Scanavacca120} More recently, there have been reports of transient AV conduction abnormalities associated with the COVID-19–related multisystem inflammatory syndrome in children (MIS-C) with ventricular dysfunction. ^{Reference Dionne, Mah and Son121} Medical-directed therapy for the underlying condition should be maximized (including antibiotic therapy, steroids, intravenous immunoglobulins), and if tolerated, a waiting period of up to several months is warranted prior to pacemaker implantation to provide sufficient opportunity for spontaneous recovery of AV conduction.

Recovery of AV conduction in patients with complete heart block due to acute myocarditis has been reported to occur in 67% of young patients within 7 days of the onset of AV block. ^{Reference Batra, Epstein and Silka122} Late monitoring for possible recurrence of symptoms or unrecognized recurrences of AV block or other arrhythmias is advised in these patients.

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ICD guidelines specific to pediatrics must consider the unique aspects of device implantation and follow-up in children as well as the pathogenesis of the disease, which may evolve over time. A pediatric cardiologist should be involved in the decision to implant an ICD in pediatric patients, and the procedure should be performed by a cardiologist or cardiothoracic surgeon with special training and/or experience in CIED implantation in the pediatric age-group. ICD implantation should be a shared decision between the patient, family, and physician considering specific pediatric characteristics including age, size of the patient, need for an epicardial device, religious/cultural beliefs, and patient quality of life. This includes the physical as well as the psychological impact of an ICD on the patient’s well-being. ^{Reference Sears, Hazelton and St Amant137} In addition, all ICD recommendations are based on the premise that meaningful survival of >1 year is expected; meaningful survival means that a patient has a reasonable quality of life and functional status. ^{Reference Shen, Sheldon and Benditt11} It is further recommended that the indications for an individual patient’s ICD be reconsidered at each reintervention with respect to current guidelines, especially after a period of nonuse, as discontinuation of device therapy may be considered in select cases. ^{Reference Kini, Soufi and Deo138}

Long QT syndrome

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Congenital LQTS refers to genetically heterogeneous disorders characterized by the phenotypes of QTc prolongation on the ECG and risk of potentially life-threatening cardiac arrhythmias. Both phenotypic and genotypic characteristics are used to guide risk stratification of patients with LQTS and consideration for ICD. ^{Reference Mazzanti, Maragna and Vacanti153} Phenotypic risk factors include the onset of symptoms at age <10 years, prior SCA, or recurrent syncope. ^{Reference Bos, Bos and Johnson143–Reference Biton, Rosero and Moss146,Reference Mazzanti, Maragna and Vacanti153} Additional high risk factors include a QTc ≥ 550 ms regardless of genotype, QTc ≥ 500 ms with LQT1 genotype, females with LQT2 genotype, and males with LQT3 genotype. ^{Reference Wedekind, Burde and Zumhagen141,Reference Giudicessi and Ackerman150}

Patients with rare conditions such as the Jervell and Lange-Nielson syndrome, Timothy syndrome, or calmodulinopathies may be at highest risk for SCA or SCD. ^{Reference Giudicessi and Ackerman150–Reference Crotti, Spazzolini and Tester152} Infants presenting with bradycardia, functional 2:1 AV block, or cardiac arrest are also at significant risk. ^{Reference Moore, Gallotti and Shannon155}

Nonselective beta-blockers are considered first-line therapy and can significantly decrease subsequent cardiac events in patients, especially in those with KCNQ1 mutations. ^{Reference Priori, Wilde and Horie14,Reference Vincent, Schwartz and Denjoy140} In addition, beta-blockers and cardiac sympathetic denervation without ICD may be appropriate alternatives in carefully selected patients. ^{Reference Priori, Wilde and Horie14,Reference Schwartz, Priori and Cerrone142,Reference Bos, Bos and Johnson143}

In highest-risk patients, observational studies support effectiveness of the ICD in preventing SCD, with consideration of left cardiac sympathetic denervation to reduce the frequency of ICD shocks. ^{Reference Schwartz, Spazzolini and Priori139,Reference Schwartz, Priori and Cerrone142,Reference Bos, Bos and Johnson143} However, implantation of an ICD in asymptomatic low-risk patient with LQTS for a positive family history of LQTS-related SCD is not clearly supported by published data, and individual decision-making is important. ^{Reference Priori, Wilde and Horie14}

Catecholaminergic polymorphic ventricular tachycardia

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CPVT is characterized by exertion-related polymorphic or bidirectional VT and is associated with syncope and SCA. SCA/SCD is reported in 3–13% of CPVT patients. ^{Reference Priori, Napolitano and Memmi158} High risk factors include male sex, previous history of cardiac arrest, multiple genetic variants, and younger age at diagnosis. ^{Reference Priori, Napolitano and Memmi158,Reference Roston, Haji-Ghassemi and LaPage159} Continued complex ventricular ectopy on exercise testing despite optimal medical therapy is also associated with worse outcome. ^{Reference Hayashi, Denjoy and Extramiana160} Studies evaluating CPVT patients with >2 genetic variants suggest that these patients may also be at higher risk for SCA. ^{Reference Roston, Haji-Ghassemi and LaPage159}

Treatment with nonselective beta-blockers is associated with a reduction in adverse cardiac events. ^{Reference Priori, Blomström-Lundqvist and Mazzanti13,Reference Priori, Wilde and Horie14,Reference Priori, Napolitano and Memmi158} The addition of flecainide to refractory patients in addition to maximally tolerated beta-blocker may suppress ventricular ectopy by as much as 85%. ^{Reference Kannankeril, Moore and Cerrone161}

In general, ICD implantation should be reserved for CPVT patients with prior SCA or with arrhythmogenic syncope on combination medical therapy and/or cardiac sympathetic denervation. ^{Reference Priori, Blomström-Lundqvist and Mazzanti13,Reference Priori, Wilde and Horie14,Reference van der Werf, Lieve and Bos126,Reference Miyake, Webster and Czosek157} Inappropriate shocks are reported in 20–30% of CPVT patients with ICDs. ^{Reference Miyake, Webster and Czosek157,Reference Olde Nordkamp, Postema and Knops163,Reference Roses-Noguer, Jarman and Clague164} Device programming in patients with CPVT should be optimized to deliver therapy for ventricular fibrillation (VF) and to minimize inappropriate shocks and the risk of potentially fatal electrical storms. ^{Reference Miyake, Webster and Czosek157,Reference Roses-Noguer, Jarman and Clague164}

Cardiac sympathetic denervation is recommended in patients who continue to have syncope or significant arrhythmias despite optimal medical therapy, are intolerant of medical therapy, or experience recurrent ICD shocks. ^{Reference De Ferrari, Dusi and Spazzolini162} In selected patients with aborted SCA as the initial presentation of CPVT, pharmacologic therapy and/or cardiac sympathetic denervation without ICD may be considered as a possible alternative. ^{Reference Priori, Wilde and Horie14,Reference van der Werf, Lieve and Bos126}

Brugada syndrome

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Brugada syndrome (BrS) is an inherited arrhythmogenic disorder characterized by a coved-type ST-segment elevation in the right precordial ECG leads and an increased risk of SCD. ^{Reference Al-Khatib, Stevenson and Ackerman12–Reference Priori, Wilde and Horie14,Reference Gonzalez Corcia, de Asmundis and Chierchia165} The phenotypic expression of the disease spans from patients who are completely asymptomatic to those who experience a lethal arrhythmia. ^{Reference Gonzalez Corcia, de Asmundis and Chierchia165,Reference Gonzalez Corcia, Sieira and Sarkozy166} The syndrome presents typically in the fourth to fifth decade, but in rare cases may have an early onset during childhood. ^{Reference Moore, Gallotti and Shannon155} Pediatric cases are rare but can express as a rapidly progressive form and lead to life-threatening arrhythmias. ^{Reference Minier, Probst and Berthome128,Reference Gonzalez Corcia, Sieira and Sarkozy166–Reference Michowitz, Milman and Andorin169}

The placement of an ICD remains the only therapy with proven efficacy for the management of ventricular arrhythmias and prevention of SCD in patients with BrS. ^{Reference Gonzalez Corcia and Sieira170} Adult recommendations for risk stratification including ventricular stimulation have been established but have not been validated in pediatrics. ^{Reference Al-Khatib, Stevenson and Ackerman12–Reference Priori, Wilde and Horie14} Findings associated with high risk of ventricular arrhythmias and SCD in children include, in order of relevance: the presence of symptoms (SCD or arrhythmogenic syncope), spontaneous coved-type ST elevation (type I pattern) ECG, atrial arrhythmias and/or SND, and conduction abnormalities (AV block or intraventricular conduction delay). ^{Reference Gonzalez Corcia, de Asmundis and Chierchia165} Although attempts have been made to create a noninvasive risk stratification scoring system, ^{Reference Gonzalez Corcia, Sieira and Pappaert167} such recommendations are based on small cohorts. Patients with a type I ECG pattern and a history of syncope or SCD have a class I indication for an ICD implantation. ^{Reference Hayashi, Denjoy and Extramiana160} In this study, 9 of 35 (26%) BrS patients with an ICD implanted at age <20 years received an appropriate therapy during a median follow-up of 7.3 years. ^{Reference Hayashi, Denjoy and Extramiana160} Conversely, implantation of an ICD is not indicated in asymptomatic patients in the absence of risk factors. Large multicentric studies are necessary to further characterize risk factors and support primary prevention indications for BrS in pediatric patients.

Hypertrophic cardiomyopathy

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Hypertrophic cardiomyopathy (HCM) is a genetic cardiovascular condition manifested by pathologic left ventricular hypertrophy in the absence of loading conditions. The phenotypic expression of HCM is variable, resulting in a diverse clinical course and highly variable long-term prognosis. Estimates for SCD rates in childhood HCM vary widely, with recent epidemiologic studies that have reported rates of between 1 and 7.2% per year. ^{Reference Maron, Rowin and Casey172,Reference Miron, Lafreniere-Roula and Steve Fan174} While ICDs have improved the outcomes for patients with HCM resuscitated from SCA, the accurate identification of risk factors for SCD to guide primary prevention ICD implantation remains a challenge, particularly given the potential progression of the disease process over time. ^{Reference Maron, Rowin and Casey172–Reference Norrish, Cantarutti and Pissaridou175} A multicenter pediatric HCM registry study reported the 5-year risk of SCA was 9%. ^{Reference Miron, Lafreniere-Roula and Steve Fan174} Primary and secondary prevention ICDs were implanted in 18 and 4% of the cohort, respectively. Only 2.5% of the patients with a primary prevention ICD received an appropriate discharge at 5 years’ follow-up, highlighting the major gaps in knowledge for accurate prediction of SCD risk in pediatric HCM patients. ^{Reference Miron, Lafreniere-Roula and Steve Fan174}

Previously published clinical practice guidelines define high risk for SCD in HCM by the presence of ≥1 clinical risk factors based on primarily adult data. ^{Reference Epstein, Dimarco and Ellenbogen6,Reference Tracy, Epstein and Darbar7,Reference Priori, Wilde and Horie14} Recent studies, however, suggest that the significance of the various risk factors may differ in children compared to adults. ^{Reference Miron, Lafreniere-Roula and Steve Fan174–Reference Norrish, Ding and Field177} Conventional risk factors include survival from an SCA, spontaneous sustained VT, unexplained syncope, nonsustained VT, family history of early HCM-related SCD, and massive left ventricular hypertrophy. ^{Reference Priori, Wilde and Horie14,Reference Maron, Spirito and Ackerman173} While a left ventricular wall thickness ≥30 mm is considered a risk factor in adults, left ventricular hypertrophy is determined relative to age and body size and therefore should be converted to a z score when evaluating this as a risk factor in smaller children. ^{Reference Miron, Lafreniere-Roula and Steve Fan174,Reference Norrish, Ding and Field177} A multicenter pediatric study showed that a left ventricular posterior wall thickness z score ≥5 was associated with VT/VF or SCA, while a meta-analysis of pediatric studies reported a maximum left ventricular wall thickness ≥30 mm or a z score ≥6 associated with an increased risk of SCD. ^{Reference Norrish, Cantarutti and Pissaridou175,Reference Balaji, DiLorenzo and Fish176}

Other secondary risk factors for SCD, such as late gadolinium enhancement (LGE) on cardiac magnetic resonance imaging (MRI), have been investigated, but the predictive value of LGE for SCD in children is still unclear. ^{Reference Briasoulis, Mallikethi-Reddy and Palla179,Reference Prinz, Schwarz and Ilic180} The evolving role of genetic testing for specific “malignant” sarcomere mutations remains debated and requires further investigation before inclusion as specific risk factors for SCD in pediatric patients with HCM. ^{Reference Vermeer, Clur and Blom181,Reference Maron, Maron and Semsarian183}

Restrictive cardiomyopathy

There are limited data regarding the use of ICDs in patients with restrictive cardiomyopathy. ^{Reference Muchtar, Blauwet and Gertz184,Reference Walsh, Grenier and Jeffries185} The underlying cause of the restrictive cardiomyopathy is most commonly due to abnormalities in the sarcomeric genes, resulting in overlap with the HCM phenotype as well as risk for both tachyarrhythmias and conduction block. ^{Reference Walsh, Grenier and Jeffries185} Given the overlap with HCM, ICD recommendations for patients with restrictive cardiomyopathy are included under the HCM and general guidelines. However, these patients do require unique consideration as, in comparison to those with HCM, patients with purely restrictive cardiomyopathy may not display the typical risk factors such as thickening of the intraventricular septum but do appear to be at higher risk for SCD, SCA, and cardiac transplant. ^{Reference Webber, Lipshultz and Sleeper186,Reference Wittekind, Ryan and Gao187} Given this, ICD implantation may be appropriate in patients with a restrictive cardiomyopathy who present with heart failure or unexplained syncope when transplant is not an immediate option. ^{Reference Zangwill, Naftel and L’Ecuyer188}

Arrhythmogenic cardiomyopathies

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Arrhythmogenic cardiomyopathy (ACM) encompasses a spectrum of disorders of the myocardium with the distinguishing feature of presentation with sustained arrhythmias. ^{Reference Towbin, McKenna and Abrams16} It includes, but is not limited to, genetic disorders such as arrhythmogenic right/left ventricular cardiomyopathy, lamin A/C, filamin-C, phospholamban, and cardiac amyloidosis. ^{Reference Towbin, McKenna and Abrams16} Under this definition, infectious processes such as myocarditis and Chagas disease and inflammatory disorders such as sarcoidosis may also be classified. Most of these entities are infrequent before puberty and often overlap with other cardiomyopathies in presentation, particularly dilated cardiomyopathy. ^{Reference Towbin, McKenna and Abrams16}

The diagnosis of ACM requires a high degree of suspicion. The initial evaluation should include clinical history, physical examination, detailed family history, 12-lead ECG, echocardiography, ambulatory electrocardiography monitoring, exercise testing, and cardiac MRI. Additional testing includes signal-averaged ECG and genetic testing. ^{Reference Towbin, McKenna and Abrams16,Reference DeWitt, Chandler and Hylind189}

The most frequent form of ACM in the pediatric age-group is arrhythmogenic right ventricular cardiomyopathy (ARVC). ^{Reference DeWitt, Chandler and Hylind189} ARVC is characterized by predominant right ventricular involvement with fibro-fatty replacement of the myocardium resulting in conduction abnormalities and ventricular arrhythmias. Biventricular disease is associated with younger age of onset. ^{Reference Mazzanti, Ng and Faragli190,Reference Te Riele, James and Sawant191} ARVC is either de novo or inherited in an autosomal dominant pattern involving variances in desmosomal genes or desmosome-associated proteins. ^{Reference Towbin, McKenna and Abrams16,Reference Ortiz-Genga, Cuenca and Dal Ferro193} Syncope is reported in 16–40% of ARVC patients at the time of diagnosis, is frequently exercise related, and has been associated with high arrhythmic risk. ^{Reference Towbin, McKenna and Abrams16,Reference Te Riele, James and Sawant191} In adult ARVC cohorts, risk factors for SCD include syncope presumed due to ventricular arrhythmia, sustained or nonsustained VT, and severe right ventricular and/or left ventricular systolic dysfunction. ^{Reference Al-Khatib, Stevenson and Ackerman12,Reference Towbin, McKenna and Abrams16} Due to the relatively low prevalence of manifest ARVC in the young, there is a paucity of data regarding risk stratification for SCD in pediatric patients with ARVC.

Overall, SCD affects 2–15% of young patients with ACM. ^{Reference DeWitt, Chandler and Hylind189,Reference Te Riele, James and Sawant191} Patients presenting with SCD and/or sustained ventricular arrhythmias have a class I indication for an ICD implantation. ^{Reference Al-Khatib, Stevenson and Ackerman12,Reference Towbin, McKenna and Abrams16} The limited available data on risk stratification in the young hamper the indication for a primary prevention ICD in this population. However, ICD implantation is reasonable in patients with ACM with hemodynamically tolerated sustained VT, syncope presumed due to ventricular arrhythmia, or an LVEF ≤ 35%. Candidacy and timing of cardiac transplantation and whether a wearable external defibrillator is a reasonable alternative should be taken into consideration on an individual basis for those patients with advanced heart failure. ^{Reference Kusumoto, Calkins and Boehmer5}

Nonischemic dilated cardiomyopathy

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The incidence of SCD in pediatric patients with idiopathic/NIDCM is only 1–5%, which is significantly less than that in adult patients. ^{Reference Bharucha, Lee and Daubeney195,Reference Pahl, Sleeper and Canter196} Although studies have shown some ICD survival benefit for secondary prevention in pediatric dilated cardiomyopathy, the low incidence of SCD has made it quite difficult to establish risk factors to guide recommendations for primary prevention ICD implantation. ^{Reference Bharucha, Lee and Daubeney195} In contrast to some studies of adult patients with NIDCM and LVEF ≤ 35%, ^{Reference Bardy, Lee and Mark198} there is no clear evidence that ICDs implanted for primary prevention improve survival for pediatric patients with NICDM. ^{Reference El-Assaad, Al-Kindi and Oliveira199,Reference Rhee, Canter and Basile200} However, primary prevention ICDs may be considered for patients with syncope or severe impairment of left ventricular function despite optimal medical therapy (beta-blockers and afterload reduction) and after careful consideration of device-related complication risks, candidacy and timing of cardiac transplantation, and whether a wearable external defibrillator is a reasonable alternative. ^{Reference Kusumoto, Calkins and Boehmer5,Reference Kirk, Dipchand and Rosenthal17,Reference Dubin, Berul and Bevilacqua194,Reference Middlekauff, Stevenson, Stevenson and Saxon197}

The phenotype of NIDCM may overlap with other types of pediatric cardiomyopathies resulting in variable risks of SCD. For example, the Sudden Death in Childhood Cardiomyopathy study showed that the risk of SCD varied according to cardiomyopathy phenotype. ^{Reference Bharucha, Lee and Daubeney195} The cumulative incidence of SCD at 15 years was 5% for idiopathic dilated cardiomyopathy compared to 23% for left ventricular noncompaction. Myocardial dysfunction and/or a history of clinically significant arrhythmias are strongly associated with mortality in left ventricular noncompaction. ^{Reference Jefferies, Wilkinson and Sleeper201,Reference Brescia202} Therefore, factors that may influence the decision regarding implantation of a primary prevention ICD include the underlying etiology of the NIDCM, the cardiomyopathy phenotype, the degree of ventricular dysfunction, and the presence of cardiac arrhythmias. ^{Reference van Waning, Caliskan and Hoedemaekers203}

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The association between CHD and arrhythmias has been well established. First demonstrated in repaired Tetralogy of Fallot, multiple studies since have identified risk factors for VT or SCD including residual cardiac defects, alterations in hemodynamics, and scars from prior interventions/surgeries. ^{Reference Khairy, Harris and Landzberg204–Reference Nieminen, Jokinen and Sairanen206} Correction of residual abnormalities or ablation of arrhythmogenic substrate may improve ventricular function and reduce symptoms. However, this may be inadequate to prevent the risk of subsequent VT or SCA in all but a select group of patients. ^{Reference Miyazaki, Sakaguchi and Ohuchi207,Reference Zeppenfeld, Schalij and Bartelings208} ICD placement may therefore be appropriate in patients with, or at high risk of, potentially life-threatening arrhythmias. ^{Reference Khairy, Van Hare and Balaji9,Reference Al-Khatib, Stevenson and Ackerman12,Reference Priori, Blomström-Lundqvist and Mazzanti13}

While ICDs are commonly placed for both primary and secondary prevention in patients with CHD, those with CHD appear to have an increased risk of inappropriate shocks compared to those with ICDs and without CHD. ^{Reference Berul, Van Hare and Kertesz130,Reference Von Bergen, Atkins and Dick131,Reference Jordan, Freedenberg and Wang211–Reference Krause, Müller and Wilberg213} Appropriate ICD shock rates of 3–6% per year have been shown with an increased frequency of appropriate shocks for secondary prevention indications. ^{Reference Khairy, Harris and Landzberg204} Antitachycardia pacing has been shown to be effective in VT termination and reducing ICD shocks. ^{Reference Kalra, Radbill and Johns214} Patients with CHD receiving an ICD have an increased rate of complications as high as 26–45%, as well a high rate of inappropriate shocks. ^{Reference Berul, Van Hare and Kertesz130,Reference Von Bergen, Atkins and Dick131,Reference Dechert, Bradley and Serwer212,Reference Krause, Müller and Wilberg213} The role of programmed stimulation and presence and degree of ventricular dysfunction as risk factors for SCD in CHD and thus primary prevention ICDs continues to be debated. ^{Reference Sandhu, Ruckdeschel and Sauer215–Reference Khairy, Landzberg and Gatzoulis217} ICD implantation can be especially challenging in patients with CHD due to anatomic complexity, intracardiac shunts, or limited vascular access. This may require nonstandard approaches such as epicardial leads, nontransvenous defibrillation coils or a subcutaneous ICD. ^{Reference Radbill, Triedman and Berul218,Reference von Alvensleben Johannes, Dechert and Bradley David219}

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The 2017 MRI and Radiation Exposure in Patients with CIEDs Consensus Statement provides comprehensive recommendations for individuals with both conditional and nonconditional transvenous devices. ^{Reference Indik, Gimbel and Abe19} With MRI, there is potential risk for heating of the lead, increase in pacing thresholds, sudden battery depletion, and inappropriate sensing/pacing. The consensus statement also provides guidance for CIED programming and evaluation pre-, during, and post-MRI along with a protocol of testing and patient-specific considerations. However, these recommendations are not specific for patients with abandoned or epicardial CIED leads and make no specific recommendations for MRI in these cases. ^{Reference Nazarian, Hansford and Rahsepar283,Reference Padmanabhan, Kella and Mehta284}

Regarding epicardial lead considerations, younger patients and those with CHD have a greater likelihood of requiring epicardial leads. Additionally, as there are no MRI conditional epicardial leads, even when used with a conditional device, the system is considered nonconditional. The 2017 recommendations suggest a possible contraindication to MRI, and in the pediatric section no recommendations regarding epicardial leads are made. However, when attached to a device, the limited data show only a small increase in risk for substantial alterations of the pacing threshold or changes in sensing after MRI. ^{Reference Bireley, Kovach and Morton279–Reference Gakenheimer-Smith, Etheridge and Niu281,Reference Rahsepar, Zimmerman and Hansford285,Reference Balmer, Gass and Dave286}

Regarding abandoned leads, in vitro data suggest that epicardial leads are more likely to generate heat than transvenous leads; however, small studies evaluating MRIs in patients with both epicardial and transvenous abandoned leads suggest that it can be done safely in the majority of cases. ^{Reference Schaller, Brunker and Riley282,Reference Nazarian, Hansford and Rahsepar283,Reference Langman, Goldberg and Finn287–Reference Higgins, Gard and Sheldon289} Even so, these studies do not imply lack of an effect on the myocardium underlying the abandoned lead. In summary, the data on MRI use in epicardial or abandoned leads are inadequate to provide specific recommendations or an absolute contraindication.

Acknowledging the sparsity of data, but also appreciating the importance of MRI for diagnosis, prognosis, and surgical planning, individualized consideration of the risk/benefit ratio of MRI in young patients must be made on a “case-by-case basis.” ^{Reference Indik, Gimbel and Abe19}

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The safety of sports participation for patients with CIEDs remained fundamentally unstudied until the past decade. Despite a dearth of research, initial published guidelines recommended against strenuous competitive sports participation (greater than class Ia) for patients with pacemakers or ICDs. ^{Reference Zipes, Link and Ackerman295–Reference Mitchell, Haskell and Snell298} Subsequent to publication of guidelines in 2005, evidence emerged suggesting that risks of sports participation for athletes with CIEDs may be lower than hypothesized. ^{Reference Saarel, Pilcher and Etheridge290–Reference Saarel, Law and Berul293}

Surveys from HRS (2006) and PACES (2013) suggested that many patients with pacemakers and ICDs had participated in sports without adverse events. ^{Reference Saarel, Pilcher and Etheridge290,Reference Mitchell, Haskell and Snell298} Thus, an international ICD Sports Registry was initiated and reported in 2013–2018. ^{Reference Lampert, Olshansky and Heidbuchel292,Reference Saarel, Law and Berul293} The registry consisted of 129 patients <21 years of age including varsity high school and college athletes. While shocks occurred during sports, there were no deaths, no resuscitated arrests, and no arrhythmia-related injuries during sports. In addition, the rate of lead malfunction was similar to previously reported rates in unselected populations. ^{Reference Lampert, Olshansky and Heidbuchel292} The conclusion was made that despite the potential for exercise to be arrhythmogenic, some young patients with ICDs can participate in sports without injury or failure to terminate the arrhythmia.

When questions arise about sports participation in youth with CIEDs, it is now standard practice to counsel patients and families about the risks, including potential for increased rate of ventricular tachyarrhythmias and damage to the pacemaker or ICD system. Counseling is patient specific; the underlying cardiac disease, type of device, indication for implant, position of leads and pulse generators, underlying heart rhythm, patient age, and type of athletic activity are considered when estimating risk. ^{Reference Mitchell, Haskell and Snell298,Reference Lampert, Cannom and Olshansky299} Shared decision-making processes that include the patient, family, coach, school, team, and other community members should be utilized to determine the best course of pursuit for individuals with CIEDs and sporting endeavors.

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Shared decision-making is a process whereby patients, families, and providers exchange information and dialogue about medical diagnostic and treatment options. ^{Reference Elwyn, Frosch and Thomson310} The goal is for patients and their families to reach evidence-informed and value-congruent medical decisions collaboratively with their clinicians. This modern model for health care decision-making has superseded paternalism, a previous model whereby providers made medical decisions on behalf of their patients using the ethical principal of beneficence. A shared decision-making approach, combining the ethical principles of professional beneficence and patient autonomy, has been shown to improve patient outcomes. ^{Reference Greenfield and Kaplan311,Reference Legare, Adekpedjou and Stacey312}

The use of shared decision-making should occur prior to all CIED implantation procedures. Clinicians must estimate and clearly describe the potential benefits and risks for the patient and their family. Some decisions will be relatively straightforward; for example, the decision to implant a permanent pacemaker to treat postoperative surgical complete heart block in a patient who is pacemaker dependent will be largely uncontestable. However, other treatment decisions, such as implantation of an ICD for primary prevention of SCD, are more complex and nuanced and include choice of ICD system, device location, and personalized estimation of risk of life-threatening arrhythmia for the particular patient over time.

Finally, the shared decision-making process is also important and applicable to post-implant diagnostic and treatment decisions for our patients with CIEDs including genetic testing, MRI, sports participation, pregnancy, cardiac surgery, and device reprogramming, removal, or revision.