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Pathophysiology, clinical course, and management of congenital complete atrioventricular block
CONTEMPORARY REVIEW
Pathophysiology, clinical course, and management of congenital complete atrioventricular block Pierre Bordachar, MD, PhD,*† Zachary Whinnett, MRCP, PhD,‡ Sylvain Ploux, MD,*† Louis Labrousse, MD,*† Michel Haissaguerre, MD,*† Jean-Benoit Thambo, MD, PhD*† From the *University Bordeaux 2, Bordeaux, France, yUniversity Hospital of Bordeaux, Bordeaux, France, and zImperial College NHS Trust, London, United Kingdom. patients presenting with profound bradycardia, left ventricular dysfunction, a wide QRS interval, or a prolonged QT interval. It is now recognized that a subset of paced patients develop dilated cardiomyopathy and heart failure, and therefore regular follow-up is important. They are also at high risk of developing complications related to the presence of intracardiac material as a result of prolonged exposure to pacing materials. Future areas of research to minimize these risks include assessing the impact of alternative stimulation sites and the development of new cardiac stimulation techniques.
ABSTRACT The incidence of congenital atrioventricular (AV) block is between 1 in 15,000 and 1 in 20,000 births. It may occur in isolation or as a consequence of anomalous development of the conduction tissue in the context of a cardiac malformation. In this review, we use the term congenital AV bock to describe complete heart block when it is diagnosed in utero or at birth. The pathophysiological process is believed to be due to immunemediated injury of the conduction system, which occurs as a result of transplacental passage of maternal anti-SSA/Ro-SSB/La antibodies. Many mothers are asymptomatic carriers, and less than onethird have a preexisting diagnosis of a rheumatological disorder. The AV block that develops months or years after birth probably occurs as a result of a different disease process that is poorly understood. The diagnosis of congenital AV block is usually confirmed by fetal echocardiography before birth and by electrocardiography after birth. The implantation of a pacemaker is recommended for symptomatic patients and for asymptomatic
(Heart Rhythm 2013;10:760–766) I 2013 Published by Elsevier Inc. on behalf of Heart Rhythm Society.
A. Introduction
B. Pathophysiology of congenital AV block
The estimated incidence of congenital atrioventricular (AV) block, a disorder that was first reported more than 100 years ago, is between 1 in 15,000 and 1 in 20,000 births.1,2 In clinical practice, the implantation of a permanent pacemaker is recommended for symptomatic patients as well as for a subset of patients presenting with clinical characteristics known to be associated with an increased risk of syncope and sudden death.3,4 In this review, we (1) focus on isolated congenital AV block in the absence of structural heart disease, (2) examine the key elements of an abundant, albeit sometimes antiquated literature, (3) present and discuss the pacing recommendations made in the guidelines issued by international professional societies, (4) discuss the adverse events that may affect the long-term outcome, and (5) examine whether new cardiac stimulation techniques might prevent these complications.
Congenital AV block is a passively acquired autoimmune disease of the fetus. It is believed to be the consequence of an inflammatory response that results in tissue injury, fibrosis, and scarring of the conduction system. The transplacental entry of autoantibodies into the fetal circulation are believed to be responsible for triggering this response.5,6 Signs of inflammation with deposition of antibodies, complement components, lymphocytic infiltrates, fibrosis, and calcifications are found in the vicinity of the conduction system.7,8 Using the recently developed technique of line immunoassay, it has been possible to detect SSA/Ro or SSB/La antibodies in the sera of 95% of the mothers of fetuses or newborns presenting with AV block.9 In contrast, autoantibodies have been detected in only a minority of mothers of children in whom AV block was diagnosed beyond the neonatal period. It has been shown that once maternal antibodies have been detected, they remain lifelong in the sera of the mothers, although the titers of the autoantibodies may change over time. This suggests a different distinct disease process.10–12 Therefore, it might be appropriate to
Address reprint requests and correspondence: Dr Pierre Bordachar, Hospital Haut Leveque, Service Pr Haissaguerre, Pessac 33604, France. E-mail address: [email protected].
KEYWORDS Congenital heart disease; AV block; Pacing ABBREVIATIONS AV ¼ atrioventricular; DCM ¼ dilated cardiomyopathy; LV ¼ left ventricular; RV ¼ right ventricular
1547-5271/$-see front matter B 2013 Published by Elsevier Inc. on behalf of Heart Rhythm Society.
http://dx.doi.org/10.1016/j.hrthm.2012.12.030
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reserve the term “congenital” to the subgroup presenting with autoantibody-associated AV block. Anti-Ro antibodies are detected in between 1% and 2% of randomly tested pregnant women.13,14 Between 2% and 5% of fetuses and infants whose mothers are autoantibody positive develop AV block, and in mothers who have had 1 child with congenital AV block, the risk to subsequent pregnancies is 12%–25%. In only 20%–30% of infants with congenital AV block does the mother have a previous diagnosis of a distinct autoimmune disease.13,14 The majority of mothers are asymptomatic despite the presence of autoantibodies. The diagnosis is usually made only after autoantibodies are detected as a result of testing after the diagnosis of congenital AV block in their newborn.15
C. Diagnosis C.1. Clinical presentation With the advent and development of fetal echocardiography, a high proportion of cases of autoimmune-mediated complete AV block are now identified in utero (in populations where routine fetal echocardiography is performed). The finding may be an incidental finding, or alternatively, investigations may have been performed because of concerns regarding fetal development.16,17 Postnatally, neonates and young children present in a wide variety of different ways. Some are asymptomatic with bradycardia and detected only during routine screening. Others may present with nonspecific symptoms, such as poor growth, abnormal tiredness, sleep disturbance, or frequent nightmares. Syncope, heart failure, or sudden death may be the first manifestation of congenital AV block in the absence of previous symptoms and signs of cardiovascular disease.18,19
D. Investigations D.1. Fetal echocardiography Despite recent developments in the field of electro- and magnetocardiography, fetal echocardiography remains the gold standard method for diagnosing congenital AV block.16,17,20–24 The diagnosis is made by establishing atrioventricular dissociation by using M mode or Doppler echocardiographic techniques. Reference values have been defined, and surveillance protocols have been designed to be implemented between 16 and 24 weeks of gestation, the period during which the fetus is at the highest risk of developing complete AV block. 20
D.2. Electrocardiogram D.2.1. AV block Complete AV block is by far the most common finding in children with AV conduction impairment. In a registry of 187 newborns with AV conduction impairment, 93% had complete AV block while 5% had first-degree and 2% had second-degree AV block.25
761 D.2.2. Bradycardia and QRS duration Micha¨elsson et al19 described the electrocardiographic characteristics in a large population of patients with congenital AV block. The mean heart rate was 41 beats/min. The heart rate usually decreased as the child grew older. A broad complex escape rhythm was observed in o10% of the patients.
D.2.3. QT interval It is recognized that Bazett’s formula may overcorrect QT interval in patients with extreme bradycardia. However, in the absence of a better alternative, it remains the most widely used method in this population.26 Seven percent of the patients were identified as having a prolonged QT interval (corrected QT interval 4450 ms) at the time of presentation in the study by Micha¨elsson et al.19 We recommend serial measurements are made, as the incidence may be as high as 22% if multiple measurements are made. 27 It is important to distinguish between patients with congenital heart block and prolonged QT interval and those with congenital long QT syndrome who may present with pseudo 2:1 AV block. The latter have normal AV conduction, but as a consequence of prolonged ventricular repolarization, every other P wave occurs during the ventricular refractory period and consequently does not result in ventricular depolarization. Two mechanisms have been proposed for the development of QT prolongation in patients with congenital AV block. First, the conduction disorder and resultant bradycardia may be the initial phenomenon that subsequently leads to the development of altered repolarization. This is supported by data from animal models of chronic complete AV block.28,29 Alternatively, patients with congenital AV block who develop QT prolongation may have a phenotypic manifestation of latent congenital long QT syndrome.
D.3. Holter monitoring We routinely perform 24-hour electrocardiographic recordings as part of our assessment of patients with congenital heart bock. This allows mean heart rate to be assessed and episodes of RR prolongation to be documented. A certain proportion of sudden deaths occurred during sleep. A study reported an incidence of 35% of pause during the night with long R-R intervals (3000–6000 ms).30
D.4. Exercise testing Despite the conduction disorder, many patients have a normal exercise treadmill evaluation in terms of performance. Neither exercise tolerance nor the maximum heart rate achieved with exercise can be predicted from the resting heart rate. Ectopy with exercise is frequent and occurs in 50%–70% of the patients.31–33
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D.5. Echocardiography Echocardiography is an important investigation in the postnatal population. It allows intracardiac structural malformations to be identified and provides an assessment of ventricular function.34
D.6. Other investigations Once heart block has been diagnosed, the mother should be screened for evidence of connective tissue disease. Immoassays for SSA/Ro or SSB/La antibodies should be performed.
E. Natural history of patients with congenital AV block Spontaneous recovery from congenital AV block is very rare, though it has been reported in exceptional cases.35 The estimated overall mortality of nonpaced patients with isolated complete congenital AV block is 8%–16% in infants and 4%–8% in children and adults.18,19 The high mortality observed in neonates appears to occur as a consequence of the complications of prematurity and bradycardia owing to the delayed initiation of pacing therapy. The morbidity and mortality associated with congenital AV block remains high even as the child grows and becomes an adult.19
F. Management F.1. Prenatal management Left untreated, congenital, antibody-mediated AV block is associated with a fetal and neonatal mortality ranging between 14% and 34%.36,37 Transplacental treatment with dexamethasone to prevent myocardial inflammation as well as beta-adrenergic stimulation to increase the ventricular rate have been proposed as treatment options. They were found to significantly lower fetal mortality in a recent study.37 However, the transplacental administration of corticosteroids to treat congenital heart block remains controversial. A recent retrospective multicenter study found no significant reduction in the occurrence of hydrops fetalis. There is the potential for harm to both mother and baby as a result of steroid use, in particular fetal neurological development may be impaired.38–40 Prospective randomized studies are required to evaluate these treatments before definitive guidance can be given. Percutaneous in utero pacing has been investigated as a method for providing heart rate support. However, with use of currently available techniques it appears to be a very high risk procedure, with fetal deaths occurring within a few hours of the procedure in a high proportion of cases.41,42 Further studies are required to improve our understanding of the natural history of congenital AV block in order to identify more accurately the fetuses at the highest risk from not being paced. Moreover, development in the techniques and technologies available to deliver in utero pacing are required before this treatment can be adopted into routine clinical practice.
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F.2. Postnatal management F.2.1. Indications for pacing Decisions regarding the indications for, and timing of, pacing therapy must take into account the technical peculiarities associated with the pacing in young children. F.2.1.1. Symptomatic patients. Both the North American and European guidelines recommend implantation of a pacemaker in children with congenital heart block and any of the following symptoms: syncope, congestive heart failure, or chronotropic incompetence with the limitation of physical activity. There is a consensus that patients with heart failure or syncope should be implanted without delay. The decision-making process can be more complex in patients presenting with more subtle symptoms such as tiredness, poor growth, frequent nightmares, or naps. If clinically bradycardia is felt to be the most likely cause of the symptoms, then the recommendation is usually to advise pacing. However, the decision regarding timing of implantation warrants careful consideration, weighing up the benefits of symptom improvement against the risks associated with long-term pacing therapy. F.2.1.2. Asymptomatic patients. As with patients who have mild symptoms, the critical decision is usually not if but rather when to initiate pacing therapy since the majority of patients require pacing at some time during their lifetime, even if they are asymptomatic when they are first diagnosed. A number of different parameters have been assessed as markers of risk, sometimes with conflicting results. F.2.1.2.1. Ventricular impairment. There is evidence from an observational study that cardiac pacing is beneficial in asymptomatic patients presenting with echocardiographically apparent left ventricular (LV) dilatation or dysfunction. Reductions in ventricular dimensions and improvement in ventricular function were observed after the initiation of pacing therapy.34 As a result of these findings, the international guidelines recommend pacing symptomatic or asymptomatic patients with clinical or echocardiographic signs of LV dysfunction or dilatation. F.2.1.2.2. Heart rate. Conflicting results have been found with regard to the usefulness of heart rate to predict syncope or sudden death. In their large observational study, Micha¨elsson et al43 found that patients with a resting heart rate o55 beats/ min had significantly higher mortality than those with a higher heart rate (29% vs 4.3%). These results were, however, not replicated in 2 subsequent observational studies.19,44 Our practice is to implant a pacemaker in asymptomatic patients when heart rate is found to be o55 beats/min in neonates or o50 beats/min in children, adolescents, and adults. F.2.1.2.3. Pauses during spontaneous rhythm. The predictive value of pauses detected with Holter monitoring is also controversial. In an observational study, Dewey et al45 found that patients who had a heart rate o50 beats/min or pauses 43 seconds on Holter monitoring had an increased incidence of syncope and sudden death.45 However, in
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another study, no significant difference was observed in the incidence of syncope between patients with and without 43-second pauses during Holter monitoring.44 Our practice is to implant a pacemaker in patients with 43-second pauses, without differentiating between day and night. We justify this approach on the basis that patients with congenital complete heart block are at risk of nocturnal sudden cardiac death, which is most likely due to very low nocturnal ventricular rates. F.2.1.2.4. QRS duration. Data are available only from a relatively small numbers of patients with a broad complex escape rhythm and as yet no study has identified an increased risk of death or syncope in this group of patients.19–44 However, data from other populations of patients suggest that a broad complex escape rhythm occurs because of more distal block in the His-Purkinje system. Therefore, even though definitive evidence is lacking in the congenital heart block population, the international guidelines recommend implanting a pacemaker in asymptomatic patients who have a broad ventricular escape rhythm (QRS duration 4120 ms). F.2.1.2.5. Complex ventricular ectopy. Importance of ventricular ectopy as a predictor for sudden cardiac death has not been determined. 44 F.2.1.2.6. Prolonged QT interval. There is good evidence that QT prolongation is a risk factor for syncope or sudden death in patients with congenital heart block.19,27,46 The international guidelines recommend implantation of a pacemaker in patients with congenital AV block and a prolonged QT interval. The implantation of a defibrillator is limited to patients with repeated episodes of syncope or documented torsades de pointes despite optimal medical therapy. This is supported by the findings from observational studies that report favorable outcomes after the implantation of a pacemaker. 46
763 2. Historically, concerns regarding high initial and longterm capture thresholds of epicardial leads have sometimes steered implanters away from epicardial leads. However, these concerns are now less relevant since the advent of epicardial leads with steroid-eluting tips that appear to be equivalent to endocardial leads in terms of performance, prolonging the battery life and limiting the need for repeat operations.52,53 3. Concerns regarding the risk of vascular or valvular injury caused by endocardial leads as well as the increasing likelihood of mismatch between leads and their recipients associated with somatic growth. 4. The potentially fatal complications associated with the extraction of transvenous leads, which remains a relatively high-risk dangerous procedure, particularly in children.54 5. The functional and hemodynamic potential advantages offered by an epicardial LV placement in small children compared with right ventricular (RV) apical pacing.55–58
Pending direct comparison in prospective randomized studies, an initial epicardial approach seems preferable in early childhood, with a view to preserve the venous network for expected lifelong pacing.
H. Outcome of paced patients After the implantation of a pacemaker, it was often assumed that children presenting with congenital AV block would go on to enjoy an average quality of life. However, various studies have demonstrated that some patients are prone to developing severe systolic dysfunction despite the early institution of cardiac pacing.56–63
G. Pacing strategies
I. Development of dilated cardiomyopathy
In this specific population, the pacing strategy is highly center specific and may vary widely between North American and European centers. Children presenting with complete AV block and a normal ventricular function may initially be paced in the VVIR mode, pending an upgrade to the VDD/DDD mode in adolescence; alternatively, they may receive a dualchamber pacemaker as initial therapy.47–49 Epicardial systems are usually chosen for the youngest children, while endocardial pacing is postponed until the child weighs 410 kg or is Z2 years of age. An intracardiac approach is, therefore, usually chosen when allowed by the anatomical substrate. In some medical centers, transvenous implants are offered to the youngest patients, a strategy enabled by the development of thinner leads.50,51 In contrast, other centers defer endocardial implantation until at least 5–8 years of age. A number of factors are taken into consideration when deciding between an epicardial and an endocardial approach to pacing and include the following:
In published studies of congenital complete AV block diagnosed in utero or at birth, the prevalence of dilated cardiomyopathy (DCM) ranges between 5% and 30%.56–59 Late-onset DCM in patients with complete heart block may be a sequela of in utero autoimmune myocarditis or due to its postnatal reactivation.6–8 The detrimental effects of maternal antibodies directed against fetal cardiac tissue provided evidence in favor of the immunopathologic role played by the SSA/Ro and SSB/La antibodies in congenital AV block. The deposition of immunoglobulin G throughout the myocardium observed in postmortem immunofluorescent studies also suggests a strong relationship between SSA/Ro and SSB/ La antibodies and the development of DCM. Most patients with congenital AV block implanted with a pacemaker will be ventriculary paced 100% of the time. In view of the myocardial dystrophic changes and adverse remodeling caused by ventricular desynchronization, RV pacing has been proposed as a potentially important cause of DCM in this patient group.56–59 In some patients, normalization of systolic function has been observed after the discontinuation of RV pacing or after upgrade to CRT; this
1. Preference of the family and local expertise; some families prefer to opt for the least invasive approach.
764 would not be expected to occur if ongoing myocarditis or other autoimmune factors were the only cause of DCM.64,65 However, doubts persist with respect to the relationship between RV pacing and the development of DCM. Indeed, a study has linked the presence of antibodies to the development of DCM with RV pacing.66 Finally, a high mean paced heart rate is also a hypothetical cause of DCM, particularly after the implantation of dual-chamber pacemakers, though DCM has been observed in patients with normal average heart rates.67 The testing of these various hypotheses has been limited by small sample sizes. Furthermore, the relative importance of these putative mechanisms is complex and indeed they may interact with each other.
J. Complications due to intracardiac leads The reported average 5-year survival rate of endocardial leads in children ranges between 76% and 89%, while reoperations for failure or complications due to epicardial leads have been observed in 15%–20% of the patients.47–54 While long-term data are lacking, lead failure rates over several decades are likely to be close to 100%. Venograms obtained after the implantation of permanent transvenous leads have revealed the presence of nearly occluded or highgrade stenoses of the great cardiac veins in nearly 25% of children and young adults, as well as a high prevalence of occlusions occurring after 420 years of cardiac pacing.62 While infectious complications have been described, the precise risk of endocarditis over a lifetime of pacing is not known.60,63
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K. Alternate treatment options Heart rate, rhythm, and ventricular function should be followed closely by using serial echocardiograms at regular intervals since ventricular dysfunction may appear at a young age or after decades of cardiac pacing.68 There is an increasing focus on developing methods that do not use intracardiac leads.
L. Robot-assisted thoracoscopic implantation of LV epicardial leads Robot-assisted pacemaker implantation allows the benefits of epicardial pacing to be obtained with minimally invasive surgery. It requires a short hospitalization and, like transvenous implantation, is cosmetically sparing (Figure 1). It has recently been developed in a few highly specialized medical centers and is promising because it overcomes some of the limitations of conventional cardiac pacing.69,70 It eliminates the risk of endovascular lead endocarditis and venous thromboses. It also allows the pacing stimulus to be delivered to the LV lead and thus may overcome the risks associated with chronic RV pacing. Long-term data and controlled trials will be required to demonstrate the advantages of LV pacing over RV pacing. The main limitation with robot-assisted pacemaker implantation is that currently it is available only in a few specialized centers.
M. The next anticipated breakthrough: Leadless pacing Since the majority of complications are due to the presence of leads within the vascular system and ventricular cavity, the
Figure 1 A: The chest roentgenogram of a 17-year-old man who has been implanted with a “traditional” transvenous dual-chamber pacemaker system (1 right atrial lead and 1 right ventricular lead). B: The chest roentgenogram of a 17-year-old woman who received an epicardial system using a robot-assisted thoracoscopic approach (1 left atrial lead and 1 left ventricular lead) (C–E). Both patients healed rapidly and were discharged from the hospital within 72 hours.
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development of a leadless pacing system with capsules containing a battery implanted directly inside the heart chamber seems to represent the most promising future of cardiac pacing.71 The prototypes tested in animals have been implanted in the RV cavity via the femoral vein. The small size of the device should allow its rapid endothelialization, limiting the risk of dislodgement or endocarditis. Its implementation in humans is expected within 1–3 years. Further technological developments should later enable the implantation of these devices within the LV cavity, which should allow more physiological pacing. Biological pacing is also under active investigation, but the road to the first clinical applicability may be much longer.72
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765 22. Chia EL, Ho TF, Rauff M, Yip WC. Cardiac time intervals of normal fetuses using noninvasive fetal electrocardiography. Prenat Diagn 2005;25:546–552. 23. Gardiner HM, Belmar C, Pasquini L, et al. Fetal ECG: a novel predictor of atrioventricular block in anti-Ro positive pregnancies. Heart 2007;93:1454–1460. 24. Wakai RT, Leuthold AC, Cripe L, Martin CB. Assessment of fetal rhythm in complete congenital heart block by magnetocardiography. Pacing Clin Electrophysiol 2000;23:1047–1050. 25. Askanase AD, Friedman DM, Copel J, et al. Spectrum and progression of conduction abnormalities in infants born to mothers with anti-SSA/Ro-SSB/La antibodies. Lupus 2002;11:145–151. 26. Benatar A, Ramet J, Decraene T, Vandenplas Y. QT interval in normal infants during sleep with concurrent evaluation of QT correction formulae. Med Sci Monit 2002;8:351–356. 27. Esscher E, Micha¨elsson MQ-T. interval in congenital complete heart block. Pediatr Cardiol 1983;4:121–124. 28. Volders PG, Sipido KR, Vos MA, Kulcsa´r A, Verduyn SC, Wellens HJ. Cellular basis of biventricular hypertrophy and arrhythmogenesis in dogs with chronic complete atrioventricular block and acquired torsade de pointes. Circulation 1998;98:1136–1147. 29. Volders PG, Sipido KR, Vos MA, et al. Downregulation of delayed rectifier K(þ) currents in dogs with chronic complete atrioventricular block and acquired torsades de pointes. Circulation 1999;100:2455–2461. 30. Levy AM, Camm AJ, Keane JF. Multiple arrhythmias detected during nocturnal monitoring in patients with congenital complete heart block. Circulation 1977;55: 247–253. 31. Winkler RB, Freed MD, Nadas AS. Exercise-induced ventricular ectopy in children and young adults with complete heart block. Am Heart J 1980;99:87–92. 32. Ikkos D, Hanson JS. Response to exercise in congenital complete atrioventricular block. Circulation 1960;22:583–590. 33. Reybrouck T, Vanden Eynde B, Dumoulin M, Van der Hauwaert LG. Cardiorespiratory response to exercise in congenital complete atrioventricular block. Am J Cardiol 1989;64:896–899. 34. Beaufort-Krol G, Schasfoort-Van Leeuwen MJ, Stienstra Y, Bink-Boelkens M. Longitudinal echocardiographic follow-up in children with congenital complete atrioventricular block. Pacing Clin Electrophysiol 2007;30:1339–1343. 35. De Raet J, Rega F, Meyns B. Late recovery of atrioventricular conduction after pacemaker implantation for complete heart block in congenital heart disease: fact or fluke? Acta Chir Belg 2010;110:323–327. 36. Groves AM, Allan LD, Rosenthal E. Outcome of isolated congenital complete heart block diagnosed in utero. Heart 1996;75:190–194. 37. Jaeggi ET, Fouron JC, Silverman ED, Ryan G, Smallhorn J, Hornberger LK. Transplacental fetal treatment improves the outcome of prenatally diagnosed complete atrioventricular block without structural heart disease. Circulation 2004;110:1542–1548. 38. Saleeb S, Copel J, Friedman D, Buyon JP. Comparison of treatment with fluorinated glucocorticoids to the natural history of autoantibody-associated congenital heart block: retrospective review of the research registry for neonatal lupus. Arthritis Rheum 1999;42:2335–2345. 39. Pisoni CN, Brucato A, Ruffatti A, et al. Failure of intravenous immunoglobulin to prevent congenital heart block: findings of a multicenter, prospective, observational study. Arthritis Rheum 2010;62:1147–1152. 40. Modi N, Lewis H, Al-Naqeeb N, Ajayi-Obe M, Dore CJ, Rutherford M. The effects of repeated antenatal glucocorticoid therapy on the developing brain. Pediatr Res 2001;50:581–585. 41. Walkinshaw SA, Welch CR, McCormack J, Walsh K. In utero pacing for fetal congenital heart block. Fetal Diagn Ther 1994;9:183–185. 42. Assad RS, Zielinsky P, Kalil R, et al. New lead for in utero pacing for fetal congenital heart block. J Thorac Cardiovasc Surg 2003;126:300–302. 43. Micha¨elsson M, Engle MA. Congenital complete heart block: an international study of the natural history. Cardiovasc Clin 1972;4:85–101. 44. Sholler GF, Walsh EP. Congenital complete heart block in patients without anatomic cardiac defects. Am Heart J 1989;118:1193–1198. 45. Dewey RC, Capeless MA, Levy AM. Use of ambulatory electrocardiographic monitoring to identify high-risk patients with congenital complete heart block. N Engl J Med 1987;316:835–839. 46. Solti F, Szatma´ry L, Vecsey T, Re´nyi-Va´mos F Jr, Bodor E. Congenital complete heart block associated with QT prolongation. Eur Heart J 1992;13:1080–1083. 47. Berul CI, Cecchin F. American Heart Association American College of Cardiology. Indications and techniques of pediatric cardiac pacing. Expert Rev Cardiovasc Ther 2003;1:165–176. 48. Cohen MI, Bush DM, Vetter VL, et al. Permanent epicardial pacing in pediatric patients: seventeen years of experience and 1200 outpatient visits. Circulation 2001;103:2585–2590.
766 49. Villain E, Martelli H, Bonnet D, Iserin L, Butera G, Kachaner J. Characteristics and results of epicardial pacing in neonates and infants. Pacing Clin Electrophysiol 2000;23:2052–2056. 50. Robledo-Nolasco R, Ortiz-Avalos M, Rodriguez-Diez G, et al. Transvenous pacing in children weighing less than 10 kilograms. Pacing Clin Electrophysiol 2009;32:177–181. 51. Kammeraad JA, Rosenthal E, Bostock J, Rogers J, Sreeram N. Endocardial pacemaker implantation in infants weighing o or ¼10 kilograms. Pacing Clin Electrophysiol 2004;27:1466–1474. 52. Karpawich PP. Technical aspects of pacing in adult and pediatric congenital heart disease. Pacing Clin Electrophysiol 2008;31:28–31. 53. Fortescue EB, Berul CI, Cecchin F, Walsh EP, Triedman JK, Alexander ME. Comparison of modern steroid-eluting epicardial and thin transvenous pacemaker leads in pediatric and congenital heart disease patients. J Interv Card Electrophysiol 2005;14:27–36. 54. Cecchin F, Atallah J, Walsh EP, Triedman JK, Alexander ME, Berul CI. Lead extraction in pediatric and congenital heart disease patients. Circ Arrhythm Electrophysiol 2010;3:437–444. 55. van Geldorp IE, Vanagt WY, Prinzen FW, Delhaas T. Chronic ventricular pacing in children: toward prevention of pacing-induced heart disease. Heart Fail Rev 2011;16:305–314. 56. Udink ten Cate FE, Breur JM, Cohen MI, et al. Dilated cardiomyopathy in isolated congenital complete atrioventricular block: early and long-term risk in children. J Am Coll Cardiol 2001;37:1129–1134. 57. Thambo JB, Bordachar P, Garrigue S, et al. Detrimental ventricular remodelling in patients with congenital complete heart block and chronic right ventricular apical pacing. Circulation 2004;110:3766–3772. 58. Karpawich PP, Rabah R, Haas JE. Altered cardiac histology following apical right ventricular pacing in patients with congenital atrioventricular block. Pacing Clin Electrophysiol 1999;22:1372–1377. 59. Moak JP, Barron KS, Hougen TJ, et al. Congenital heart block: development of late-onset cardiomyopathy, a previously underappreciated sequela. J Am Coll Cardiol 2001;37:238–242. 60. Klug D, Vaksmann G, Jarwe M, et al. Pacemaker lead infection in young patients. Pacing Clin Electrophysiol 2003;26:1489–1493.
Heart Rhythm, Vol 10, No 5, May 2013 61. Rozmus G, Daubert JP, Huang DT, Rosero S, Hall B, Francis C. Venous thrombosis and stenosis after implantation of pacemakers and defibrillators. J Interv Card Electrophysiol 2005;13:9–19. 62. Bar-Cohen Y, Berul CI, Alexander ME, et al. Age, size, and lead factors alone do not predict venous obstruction in children and young adults with transvenous lead systems. J Cardiovasc Electrophysiol 2006;17:754–759. 63. Cohen MI, Bush DM, Gaynor JW, Vetter VL, Tanel RE, Rhodes LA. Pediatric pacemaker infections: twenty years of experience. J Thorac Cardiovasc Surg 2002;124:821827. 64. Moak JP, Hasbani K, Ramwell C, et al. Dilated cardiomyopathy following right ventricular pacing for AV block in young patients: resolution after upgrading to biventricular pacing systems. J Cardiovasc Electrophysiol 2006;17:1068–1071. 65. Janousek J, Tomek V, Chaloupecky V, Gebauer RA. Dilated cardiomyopathy associated with dual-chamber pacing in infants: improvement through either left ventricular cardiac resynchronization or programming the pacemaker off allowing intrinsic normal conduction. J Cardiovasc Electrophysiol 2004;15:470–474. 66. Sagar S, Shen WK, Asirvatham SJ, et al. Effect of long-term right ventricular pacing in young adults with structurally normal heart. Circulation 2010;121:1698–1705. 67. Chen CA, Chang CI, Wang JK, et al. Restoration of cardiac function by setting the ventricular pacing at a lower range in an infant with congenital complete atrioventricular block and dilated cardiomyopathy. Int J Cardiol 2008;131:38–40. 68. Balmer C, Fasnacht M, Rahn M, Molinari L, Bauersfeld U. Europace: long-term follow up of children with congenital complete atrioventricular block and the impact of pacemaker therapy. Europace 2002;4:345–349. 69. Jansens JL, Jottrand M, Preumont N, Stoupel E. de Canniere D. Roboticenhanced biventricular resynchronization: an alternative to endovenous cardiac resynchronization therapy in chronic heart failure. Ann Thorac Surg 2003;76: 413–417. 70. DeRose JJ, Ashton RC, Belsley S, et al. Robotically assisted left ventricular epicardial lead implantation for biventricular pacing. J Am Coll Cardiol 2003;41: 1414–1419. 71. Beck H, Boden WE, Patibandla S, et al. 50th anniversary of the first successful permanent pacemaker implantation in the United States: historical review and future directions. Am J Cardiol 2010;106:810–818. 72. Rosen MR, Robinson RB, Brink PR, Cohen IS. The road to biological pacing. Nat Rev Cardiol 2011;8:656–666.
Pathophysiology, clinical course, and management of congenital complete atrioventricular block Pierre Bordachar, MD, PhD,*† Zachary Whinnett, MRCP, PhD,‡ Sylvain Ploux, MD,*† Louis Labrousse, MD,*† Michel Haissaguerre, MD,*† Jean-Benoit Thambo, MD, PhD*† From the *University Bordeaux 2, Bordeaux, France, yUniversity Hospital of Bordeaux, Bordeaux, France, and zImperial College NHS Trust, London, United Kingdom. patients presenting with profound bradycardia, left ventricular dysfunction, a wide QRS interval, or a prolonged QT interval. It is now recognized that a subset of paced patients develop dilated cardiomyopathy and heart failure, and therefore regular follow-up is important. They are also at high risk of developing complications related to the presence of intracardiac material as a result of prolonged exposure to pacing materials. Future areas of research to minimize these risks include assessing the impact of alternative stimulation sites and the development of new cardiac stimulation techniques.
ABSTRACT The incidence of congenital atrioventricular (AV) block is between 1 in 15,000 and 1 in 20,000 births. It may occur in isolation or as a consequence of anomalous development of the conduction tissue in the context of a cardiac malformation. In this review, we use the term congenital AV bock to describe complete heart block when it is diagnosed in utero or at birth. The pathophysiological process is believed to be due to immunemediated injury of the conduction system, which occurs as a result of transplacental passage of maternal anti-SSA/Ro-SSB/La antibodies. Many mothers are asymptomatic carriers, and less than onethird have a preexisting diagnosis of a rheumatological disorder. The AV block that develops months or years after birth probably occurs as a result of a different disease process that is poorly understood. The diagnosis of congenital AV block is usually confirmed by fetal echocardiography before birth and by electrocardiography after birth. The implantation of a pacemaker is recommended for symptomatic patients and for asymptomatic
(Heart Rhythm 2013;10:760–766) I 2013 Published by Elsevier Inc. on behalf of Heart Rhythm Society.
A. Introduction
B. Pathophysiology of congenital AV block
The estimated incidence of congenital atrioventricular (AV) block, a disorder that was first reported more than 100 years ago, is between 1 in 15,000 and 1 in 20,000 births.1,2 In clinical practice, the implantation of a permanent pacemaker is recommended for symptomatic patients as well as for a subset of patients presenting with clinical characteristics known to be associated with an increased risk of syncope and sudden death.3,4 In this review, we (1) focus on isolated congenital AV block in the absence of structural heart disease, (2) examine the key elements of an abundant, albeit sometimes antiquated literature, (3) present and discuss the pacing recommendations made in the guidelines issued by international professional societies, (4) discuss the adverse events that may affect the long-term outcome, and (5) examine whether new cardiac stimulation techniques might prevent these complications.
Congenital AV block is a passively acquired autoimmune disease of the fetus. It is believed to be the consequence of an inflammatory response that results in tissue injury, fibrosis, and scarring of the conduction system. The transplacental entry of autoantibodies into the fetal circulation are believed to be responsible for triggering this response.5,6 Signs of inflammation with deposition of antibodies, complement components, lymphocytic infiltrates, fibrosis, and calcifications are found in the vicinity of the conduction system.7,8 Using the recently developed technique of line immunoassay, it has been possible to detect SSA/Ro or SSB/La antibodies in the sera of 95% of the mothers of fetuses or newborns presenting with AV block.9 In contrast, autoantibodies have been detected in only a minority of mothers of children in whom AV block was diagnosed beyond the neonatal period. It has been shown that once maternal antibodies have been detected, they remain lifelong in the sera of the mothers, although the titers of the autoantibodies may change over time. This suggests a different distinct disease process.10–12 Therefore, it might be appropriate to
Address reprint requests and correspondence: Dr Pierre Bordachar, Hospital Haut Leveque, Service Pr Haissaguerre, Pessac 33604, France. E-mail address: [email protected].
KEYWORDS Congenital heart disease; AV block; Pacing ABBREVIATIONS AV ¼ atrioventricular; DCM ¼ dilated cardiomyopathy; LV ¼ left ventricular; RV ¼ right ventricular
1547-5271/$-see front matter B 2013 Published by Elsevier Inc. on behalf of Heart Rhythm Society.
http://dx.doi.org/10.1016/j.hrthm.2012.12.030
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reserve the term “congenital” to the subgroup presenting with autoantibody-associated AV block. Anti-Ro antibodies are detected in between 1% and 2% of randomly tested pregnant women.13,14 Between 2% and 5% of fetuses and infants whose mothers are autoantibody positive develop AV block, and in mothers who have had 1 child with congenital AV block, the risk to subsequent pregnancies is 12%–25%. In only 20%–30% of infants with congenital AV block does the mother have a previous diagnosis of a distinct autoimmune disease.13,14 The majority of mothers are asymptomatic despite the presence of autoantibodies. The diagnosis is usually made only after autoantibodies are detected as a result of testing after the diagnosis of congenital AV block in their newborn.15
C. Diagnosis C.1. Clinical presentation With the advent and development of fetal echocardiography, a high proportion of cases of autoimmune-mediated complete AV block are now identified in utero (in populations where routine fetal echocardiography is performed). The finding may be an incidental finding, or alternatively, investigations may have been performed because of concerns regarding fetal development.16,17 Postnatally, neonates and young children present in a wide variety of different ways. Some are asymptomatic with bradycardia and detected only during routine screening. Others may present with nonspecific symptoms, such as poor growth, abnormal tiredness, sleep disturbance, or frequent nightmares. Syncope, heart failure, or sudden death may be the first manifestation of congenital AV block in the absence of previous symptoms and signs of cardiovascular disease.18,19
D. Investigations D.1. Fetal echocardiography Despite recent developments in the field of electro- and magnetocardiography, fetal echocardiography remains the gold standard method for diagnosing congenital AV block.16,17,20–24 The diagnosis is made by establishing atrioventricular dissociation by using M mode or Doppler echocardiographic techniques. Reference values have been defined, and surveillance protocols have been designed to be implemented between 16 and 24 weeks of gestation, the period during which the fetus is at the highest risk of developing complete AV block. 20
D.2. Electrocardiogram D.2.1. AV block Complete AV block is by far the most common finding in children with AV conduction impairment. In a registry of 187 newborns with AV conduction impairment, 93% had complete AV block while 5% had first-degree and 2% had second-degree AV block.25
761 D.2.2. Bradycardia and QRS duration Micha¨elsson et al19 described the electrocardiographic characteristics in a large population of patients with congenital AV block. The mean heart rate was 41 beats/min. The heart rate usually decreased as the child grew older. A broad complex escape rhythm was observed in o10% of the patients.
D.2.3. QT interval It is recognized that Bazett’s formula may overcorrect QT interval in patients with extreme bradycardia. However, in the absence of a better alternative, it remains the most widely used method in this population.26 Seven percent of the patients were identified as having a prolonged QT interval (corrected QT interval 4450 ms) at the time of presentation in the study by Micha¨elsson et al.19 We recommend serial measurements are made, as the incidence may be as high as 22% if multiple measurements are made. 27 It is important to distinguish between patients with congenital heart block and prolonged QT interval and those with congenital long QT syndrome who may present with pseudo 2:1 AV block. The latter have normal AV conduction, but as a consequence of prolonged ventricular repolarization, every other P wave occurs during the ventricular refractory period and consequently does not result in ventricular depolarization. Two mechanisms have been proposed for the development of QT prolongation in patients with congenital AV block. First, the conduction disorder and resultant bradycardia may be the initial phenomenon that subsequently leads to the development of altered repolarization. This is supported by data from animal models of chronic complete AV block.28,29 Alternatively, patients with congenital AV block who develop QT prolongation may have a phenotypic manifestation of latent congenital long QT syndrome.
D.3. Holter monitoring We routinely perform 24-hour electrocardiographic recordings as part of our assessment of patients with congenital heart bock. This allows mean heart rate to be assessed and episodes of RR prolongation to be documented. A certain proportion of sudden deaths occurred during sleep. A study reported an incidence of 35% of pause during the night with long R-R intervals (3000–6000 ms).30
D.4. Exercise testing Despite the conduction disorder, many patients have a normal exercise treadmill evaluation in terms of performance. Neither exercise tolerance nor the maximum heart rate achieved with exercise can be predicted from the resting heart rate. Ectopy with exercise is frequent and occurs in 50%–70% of the patients.31–33
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D.5. Echocardiography Echocardiography is an important investigation in the postnatal population. It allows intracardiac structural malformations to be identified and provides an assessment of ventricular function.34
D.6. Other investigations Once heart block has been diagnosed, the mother should be screened for evidence of connective tissue disease. Immoassays for SSA/Ro or SSB/La antibodies should be performed.
E. Natural history of patients with congenital AV block Spontaneous recovery from congenital AV block is very rare, though it has been reported in exceptional cases.35 The estimated overall mortality of nonpaced patients with isolated complete congenital AV block is 8%–16% in infants and 4%–8% in children and adults.18,19 The high mortality observed in neonates appears to occur as a consequence of the complications of prematurity and bradycardia owing to the delayed initiation of pacing therapy. The morbidity and mortality associated with congenital AV block remains high even as the child grows and becomes an adult.19
F. Management F.1. Prenatal management Left untreated, congenital, antibody-mediated AV block is associated with a fetal and neonatal mortality ranging between 14% and 34%.36,37 Transplacental treatment with dexamethasone to prevent myocardial inflammation as well as beta-adrenergic stimulation to increase the ventricular rate have been proposed as treatment options. They were found to significantly lower fetal mortality in a recent study.37 However, the transplacental administration of corticosteroids to treat congenital heart block remains controversial. A recent retrospective multicenter study found no significant reduction in the occurrence of hydrops fetalis. There is the potential for harm to both mother and baby as a result of steroid use, in particular fetal neurological development may be impaired.38–40 Prospective randomized studies are required to evaluate these treatments before definitive guidance can be given. Percutaneous in utero pacing has been investigated as a method for providing heart rate support. However, with use of currently available techniques it appears to be a very high risk procedure, with fetal deaths occurring within a few hours of the procedure in a high proportion of cases.41,42 Further studies are required to improve our understanding of the natural history of congenital AV block in order to identify more accurately the fetuses at the highest risk from not being paced. Moreover, development in the techniques and technologies available to deliver in utero pacing are required before this treatment can be adopted into routine clinical practice.
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F.2. Postnatal management F.2.1. Indications for pacing Decisions regarding the indications for, and timing of, pacing therapy must take into account the technical peculiarities associated with the pacing in young children. F.2.1.1. Symptomatic patients. Both the North American and European guidelines recommend implantation of a pacemaker in children with congenital heart block and any of the following symptoms: syncope, congestive heart failure, or chronotropic incompetence with the limitation of physical activity. There is a consensus that patients with heart failure or syncope should be implanted without delay. The decision-making process can be more complex in patients presenting with more subtle symptoms such as tiredness, poor growth, frequent nightmares, or naps. If clinically bradycardia is felt to be the most likely cause of the symptoms, then the recommendation is usually to advise pacing. However, the decision regarding timing of implantation warrants careful consideration, weighing up the benefits of symptom improvement against the risks associated with long-term pacing therapy. F.2.1.2. Asymptomatic patients. As with patients who have mild symptoms, the critical decision is usually not if but rather when to initiate pacing therapy since the majority of patients require pacing at some time during their lifetime, even if they are asymptomatic when they are first diagnosed. A number of different parameters have been assessed as markers of risk, sometimes with conflicting results. F.2.1.2.1. Ventricular impairment. There is evidence from an observational study that cardiac pacing is beneficial in asymptomatic patients presenting with echocardiographically apparent left ventricular (LV) dilatation or dysfunction. Reductions in ventricular dimensions and improvement in ventricular function were observed after the initiation of pacing therapy.34 As a result of these findings, the international guidelines recommend pacing symptomatic or asymptomatic patients with clinical or echocardiographic signs of LV dysfunction or dilatation. F.2.1.2.2. Heart rate. Conflicting results have been found with regard to the usefulness of heart rate to predict syncope or sudden death. In their large observational study, Micha¨elsson et al43 found that patients with a resting heart rate o55 beats/ min had significantly higher mortality than those with a higher heart rate (29% vs 4.3%). These results were, however, not replicated in 2 subsequent observational studies.19,44 Our practice is to implant a pacemaker in asymptomatic patients when heart rate is found to be o55 beats/min in neonates or o50 beats/min in children, adolescents, and adults. F.2.1.2.3. Pauses during spontaneous rhythm. The predictive value of pauses detected with Holter monitoring is also controversial. In an observational study, Dewey et al45 found that patients who had a heart rate o50 beats/min or pauses 43 seconds on Holter monitoring had an increased incidence of syncope and sudden death.45 However, in
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another study, no significant difference was observed in the incidence of syncope between patients with and without 43-second pauses during Holter monitoring.44 Our practice is to implant a pacemaker in patients with 43-second pauses, without differentiating between day and night. We justify this approach on the basis that patients with congenital complete heart block are at risk of nocturnal sudden cardiac death, which is most likely due to very low nocturnal ventricular rates. F.2.1.2.4. QRS duration. Data are available only from a relatively small numbers of patients with a broad complex escape rhythm and as yet no study has identified an increased risk of death or syncope in this group of patients.19–44 However, data from other populations of patients suggest that a broad complex escape rhythm occurs because of more distal block in the His-Purkinje system. Therefore, even though definitive evidence is lacking in the congenital heart block population, the international guidelines recommend implanting a pacemaker in asymptomatic patients who have a broad ventricular escape rhythm (QRS duration 4120 ms). F.2.1.2.5. Complex ventricular ectopy. Importance of ventricular ectopy as a predictor for sudden cardiac death has not been determined. 44 F.2.1.2.6. Prolonged QT interval. There is good evidence that QT prolongation is a risk factor for syncope or sudden death in patients with congenital heart block.19,27,46 The international guidelines recommend implantation of a pacemaker in patients with congenital AV block and a prolonged QT interval. The implantation of a defibrillator is limited to patients with repeated episodes of syncope or documented torsades de pointes despite optimal medical therapy. This is supported by the findings from observational studies that report favorable outcomes after the implantation of a pacemaker. 46
763 2. Historically, concerns regarding high initial and longterm capture thresholds of epicardial leads have sometimes steered implanters away from epicardial leads. However, these concerns are now less relevant since the advent of epicardial leads with steroid-eluting tips that appear to be equivalent to endocardial leads in terms of performance, prolonging the battery life and limiting the need for repeat operations.52,53 3. Concerns regarding the risk of vascular or valvular injury caused by endocardial leads as well as the increasing likelihood of mismatch between leads and their recipients associated with somatic growth. 4. The potentially fatal complications associated with the extraction of transvenous leads, which remains a relatively high-risk dangerous procedure, particularly in children.54 5. The functional and hemodynamic potential advantages offered by an epicardial LV placement in small children compared with right ventricular (RV) apical pacing.55–58
Pending direct comparison in prospective randomized studies, an initial epicardial approach seems preferable in early childhood, with a view to preserve the venous network for expected lifelong pacing.
H. Outcome of paced patients After the implantation of a pacemaker, it was often assumed that children presenting with congenital AV block would go on to enjoy an average quality of life. However, various studies have demonstrated that some patients are prone to developing severe systolic dysfunction despite the early institution of cardiac pacing.56–63
G. Pacing strategies
I. Development of dilated cardiomyopathy
In this specific population, the pacing strategy is highly center specific and may vary widely between North American and European centers. Children presenting with complete AV block and a normal ventricular function may initially be paced in the VVIR mode, pending an upgrade to the VDD/DDD mode in adolescence; alternatively, they may receive a dualchamber pacemaker as initial therapy.47–49 Epicardial systems are usually chosen for the youngest children, while endocardial pacing is postponed until the child weighs 410 kg or is Z2 years of age. An intracardiac approach is, therefore, usually chosen when allowed by the anatomical substrate. In some medical centers, transvenous implants are offered to the youngest patients, a strategy enabled by the development of thinner leads.50,51 In contrast, other centers defer endocardial implantation until at least 5–8 years of age. A number of factors are taken into consideration when deciding between an epicardial and an endocardial approach to pacing and include the following:
In published studies of congenital complete AV block diagnosed in utero or at birth, the prevalence of dilated cardiomyopathy (DCM) ranges between 5% and 30%.56–59 Late-onset DCM in patients with complete heart block may be a sequela of in utero autoimmune myocarditis or due to its postnatal reactivation.6–8 The detrimental effects of maternal antibodies directed against fetal cardiac tissue provided evidence in favor of the immunopathologic role played by the SSA/Ro and SSB/La antibodies in congenital AV block. The deposition of immunoglobulin G throughout the myocardium observed in postmortem immunofluorescent studies also suggests a strong relationship between SSA/Ro and SSB/ La antibodies and the development of DCM. Most patients with congenital AV block implanted with a pacemaker will be ventriculary paced 100% of the time. In view of the myocardial dystrophic changes and adverse remodeling caused by ventricular desynchronization, RV pacing has been proposed as a potentially important cause of DCM in this patient group.56–59 In some patients, normalization of systolic function has been observed after the discontinuation of RV pacing or after upgrade to CRT; this
1. Preference of the family and local expertise; some families prefer to opt for the least invasive approach.
764 would not be expected to occur if ongoing myocarditis or other autoimmune factors were the only cause of DCM.64,65 However, doubts persist with respect to the relationship between RV pacing and the development of DCM. Indeed, a study has linked the presence of antibodies to the development of DCM with RV pacing.66 Finally, a high mean paced heart rate is also a hypothetical cause of DCM, particularly after the implantation of dual-chamber pacemakers, though DCM has been observed in patients with normal average heart rates.67 The testing of these various hypotheses has been limited by small sample sizes. Furthermore, the relative importance of these putative mechanisms is complex and indeed they may interact with each other.
J. Complications due to intracardiac leads The reported average 5-year survival rate of endocardial leads in children ranges between 76% and 89%, while reoperations for failure or complications due to epicardial leads have been observed in 15%–20% of the patients.47–54 While long-term data are lacking, lead failure rates over several decades are likely to be close to 100%. Venograms obtained after the implantation of permanent transvenous leads have revealed the presence of nearly occluded or highgrade stenoses of the great cardiac veins in nearly 25% of children and young adults, as well as a high prevalence of occlusions occurring after 420 years of cardiac pacing.62 While infectious complications have been described, the precise risk of endocarditis over a lifetime of pacing is not known.60,63
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K. Alternate treatment options Heart rate, rhythm, and ventricular function should be followed closely by using serial echocardiograms at regular intervals since ventricular dysfunction may appear at a young age or after decades of cardiac pacing.68 There is an increasing focus on developing methods that do not use intracardiac leads.
L. Robot-assisted thoracoscopic implantation of LV epicardial leads Robot-assisted pacemaker implantation allows the benefits of epicardial pacing to be obtained with minimally invasive surgery. It requires a short hospitalization and, like transvenous implantation, is cosmetically sparing (Figure 1). It has recently been developed in a few highly specialized medical centers and is promising because it overcomes some of the limitations of conventional cardiac pacing.69,70 It eliminates the risk of endovascular lead endocarditis and venous thromboses. It also allows the pacing stimulus to be delivered to the LV lead and thus may overcome the risks associated with chronic RV pacing. Long-term data and controlled trials will be required to demonstrate the advantages of LV pacing over RV pacing. The main limitation with robot-assisted pacemaker implantation is that currently it is available only in a few specialized centers.
M. The next anticipated breakthrough: Leadless pacing Since the majority of complications are due to the presence of leads within the vascular system and ventricular cavity, the
Figure 1 A: The chest roentgenogram of a 17-year-old man who has been implanted with a “traditional” transvenous dual-chamber pacemaker system (1 right atrial lead and 1 right ventricular lead). B: The chest roentgenogram of a 17-year-old woman who received an epicardial system using a robot-assisted thoracoscopic approach (1 left atrial lead and 1 left ventricular lead) (C–E). Both patients healed rapidly and were discharged from the hospital within 72 hours.
Bordachar et al
Congenital Complete Atrioventricular Block
development of a leadless pacing system with capsules containing a battery implanted directly inside the heart chamber seems to represent the most promising future of cardiac pacing.71 The prototypes tested in animals have been implanted in the RV cavity via the femoral vein. The small size of the device should allow its rapid endothelialization, limiting the risk of dislodgement or endocarditis. Its implementation in humans is expected within 1–3 years. Further technological developments should later enable the implantation of these devices within the LV cavity, which should allow more physiological pacing. Biological pacing is also under active investigation, but the road to the first clinical applicability may be much longer.72
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