Congenital heart block: development of late-onset cardiomyopathy, a previously underappreciated sequela

Congenital complete heart block: fetal management protocol, review of the literature, and report of the smallest successful pacemaker implantation

Fetuses with complete heart block have an increased mortality with most deaths occurring in utero or during infancy. The cardiac evaluation of these fetuses is difficult since the ventricular rate is low and the heart is dilated. We have implemented a strategy that includes the biophysical profile, which assesses fetal well-being, in combination with the cardiovascular profile that assesses cardiac function and the circulation. We present two cases of fetal complete heart block in which early delivery was recommended due to worsening cardiovascular profile scores. Biophysical profile scores were normal. Both babies were successfully treated, despite having risk factors that predicted poor outcomes. We hypothesize that our management protocol initiated intervention before fetal compromise, hydrops, and myocardial damage occurred. We recommend an evaluation of heart function in addition to an assessment of fetal well-being in fetuses with complete heart block. Early delivery should be considered if there is evidence of distress and/or deteriorating cardiac function.

Anaesthetic management in a neonate with congenital complete heart block

We present the case of a neonate undergoing surgery on the first day of life for the installation of a permanent pacemaker because of the existence of congenital complete heart block (CCHB) with a basal heart rate of 43 b.min(-1) and minimal elevation after initiating an isoproterenol perfusion. The intervention was under general anaesthesia with laryngeal mask airway (LMA) and spontaneous ventilation. The principal anaesthetic goals were to assure adequate anaesthesia, with haemodynamic and respiratory stability, to maintain the best possible heart rate and to avoid postoperative respiratory depression or apnoea.

Genetics of atrioventricular conduction disease in humans

Atrioventricular (AV) conduction disease (block) describes impairment of the electrical continuity between the atria and ventricles. Classification of AV block has utilized biophysical characteristics, usually the extent (first, second, or third degree) and site of block (above or below His bundle recording site). The genetic significance of this classification is unknown. In young patients, AV block may result from injury or be the major cardiac manifestation of neuromuscular disease. However, in some cases, AV block has unknown or idiopathic cause. In such cases, familial clustering has been noted and published pedigrees show autosomal dominant inheritance; associated heart disease is common (e.g., congenital heart malformation, cardiomyopathy). The latter finding is not surprising given the common origin of working myocytes and specialized conduction system elements. Using genetic models incorporating reduced penetrance (disease absence in some individuals with disease gene), variable expressivity (individuals with disease gene have different phenotypes), and genetic heterogeneity (similar phenotypes, different genetic cause), molecular genetic causes of AV block are being identified. Mutations identified in genes with diverse functions (transcription, excitability, and energy homeostasis) for the first time provide the means to assess risk and offer insight into the molecular basis of this important clinical condition previously defined only by biophysical characteristics.

Immunohistologic evidence supports apoptosis, IgG deposition, and novel macrophage/fibroblast crosstalk in the pathologic cascade leading to congenital heart block

OBJECTIVE

To assess in vivo the pathologic cascade leading to fibrosis in congenital heart block (CHB). In vitro studies suggest that CHB is initiated via apoptosis, resulting in translocation of SSA/Ro and SSB/La antigens and surface binding by maternal autoantibodies. These opsonized cardiocytes are phagocytosed by macrophages, which secrete factors inducing fibrosis.

METHODS

Immunohistochemistry analysis was performed on formalin-fixed sections of 4 fetal hearts identified in utero as having CHB or isolated myocarditis; mothers had anti-SSA/Ro and anti-SSB/La antibodies.

RESULTS

Apoptosis was most extensive in fetuses dying early and most pronounced in regions containing conduction tissue. Deposition of IgG was observed in hearts from fetuses with CHB/myocarditis, but not in 3 control hearts, and was colocalized with apoptotic cells. Giant cells and macrophages (frequently seen proximal to IgG and apoptotic cells) were present in septal and thickened fibrous subendocardial regions, most apparent in the youngest fetuses. Septal tissue also revealed extensive areas of fibrosis and microcalcification in which a predominant smooth muscle actin (SMA)-positive infiltrate (myofibroblast scarring phenotype) was observed. In contrast, there were no macrophages or SMA-positive cells (other than those lining blood vessels) in septal tissue from control hearts, although rare macrophages were seen in the working myocardium.

CONCLUSION

In summary, findings in this unique autopsy material paralleled those in in vitro studies. These data support the notion of exaggerated apoptosis, probably due to ongoing inflammation caused by IgG binding and ingestion by macrophages. Transdifferentiation of cardiac fibroblasts to a scarring phenotype may be a pathologic process initiated by maternal antibodies, and persistence of this phenotype even after birth may relate to the progression of block seen in some infants postpartum.

First-degree heart block in the fetus of an anti-SSA/Ro-positive mother: Reversal after a short course of dexamethasone treatment

Isolated congenital heart block is almost invariably associated with the presence of antibodies to SSA/Ro and SSB/La antigens in the maternal circulation. Once established, third-degree congenital heart block is permanent. However, a lesser degree of autoantibody-associated heart block in a fetus can be reversed if it is recognized and treated early enough with fluorinated glucocorticosteroids. The only method available clinically for the recognition of first-degree heart block in a fetus is measurement of the mechanical PR interval by pulsed Doppler echocardiography. This is the first report of a fetus in whom a diagnosis of first-degree heart block and the consequent decision to intervene were based solely on this technique. In addition, the first-degree heart block resolved completely after only 2 weeks of dexamethasone treatment, and the heart rhythm remained stable throughout the remainder of the pregnancy despite early discontinuation of therapy due to oligohydramnios.

[Neonatal lupus syndrome: review of the literature]

PURPOSE

Neonatal lupus syndrome include skin lesions, hematological and hepatic disorders, and congenital heart block (CHB) in the absence of severe cardiac malformation. This rare disorder is closely linked to transplacental transport of anti-SSA/Ro and anti-SSB/La maternal antibodies.

CURRENT KNOWLEDGE AND KEY POINTS

The prevalence of CHB in newborns of anti-Ro/SSA positive women with known connective tissue disease is 2% and the risk of recurrence ranges from 10 to 17%. Skin and systemic lesions are transient, whereas CHB is definitive and is associated with significant morbidity and mortality (estimated at 16-19%). A pacemaker must be implanted in 2/3 of cases. Myocarditis may be associated or may appeared secondarily. Mothers of children with CHB are usually asymptomatic or have Gougerot-Sjögren, or undifferentiated connective tissue disease. Mothers of children with cutaneous manifestations may present with more severe disease and systemic lupus erythematosus. In anti-Ro/SSA positive pregnant women, echocardiograms should be performed at least every 2 weeks from 16 to 24 weeks gestation. Electrocardiogram should be performed for all children.

FUTURE PROSPECTS AND PROJECTS

The efficiency of prophylactic treatment of CHB is not established. Therapy for CHB detected in utero is not standardized and involves fluorinated steroids (especially betamethasone).

Autoantibody-associated congenital heart block: the clinical perspective

Congenital heart block (CHB) can occur in association with structural heart disease, such as atrioventricular septal defects, left atrial isomerism, and abnormalities of the great arteries, with tumors, such as mesotheliomas, or as an isolated defect. In 1928, Aylward reported the occurrence of CHB in two children whose mother "suffered from Mikulicz's disease." This curious clinical observation was further solidified by the 1970s, with reports of CHB in children whose mothers had autoimmune diseases and that the maternal sera contained antibodies to Ro ribonucleoproteins. It was subsequently reported that many mothers also had antibodies to La. Other abnormalities affecting the skin, liver, and blood elements were associated with anti-Ro/La antibodies in the maternal and fetal circulation, and are now grouped under the heading of neonatal lupus syndromes. Neonatal lupus was termed because the cutaneous lesions of the neonate resembled those seen in systemic lupus erythematosus.

Cytokine polymorphisms and histologic expression in autopsy studies: contribution of TNF-alpha and TGF-beta 1 to the pathogenesis of autoimmune-associated congenital heart block

Although Abs to SSA/Ro-SSB/La are necessary for the development of congenital heart block (CHB), the low frequency suggests that fetal factors are contributory. Because CHB involves a cascade from inflammation to scarring, polymorphisms of the TNF-alpha promoter region and codons 10 and 25 of the TGF-beta gene were evaluated in 88 children (40 CHB, 17 rash, 31 unaffected siblings) and 74 mothers from the Research Registry for Neonatal Lupus (NL). Cytokine expression was assessed in autopsy material from two fetuses with CHB. Significantly increased frequency of the -308A (high-producer) allele of TNF-alpha was observed in all NL groups compared with controls. In contrast, the TGF-beta polymorphism Leu(10) (associated with increased fibrosis) was significantly higher in CHB children (genotypic frequency 60%, allelic frequency 78%) than unaffected offspring (genotypic frequency 29%, p = 0.016; allelic frequency 56%, p = 0.011) and controls, while there were no significant differences between controls and other NL groups. For the TGF-beta polymorphism, Arg(25), there were no significant differences between NL groups and controls. In fetal CHB hearts, protein expression of TGF-beta, but not TNF-alpha, was demonstrated in septal regions, extracellularly in the fibrous matrix, and intracellularly in macrophage infiltrates. Age-matched fetal hearts from voluntary terminations expressed neither cytokine. TNF-alpha may be one of several factors that amplify susceptibility; however, the genetic studies, backed by the histological data, more convincingly link TGF-beta to the pathogenesis of CHB. This profibrosing cytokine and its secretion/activation circuitry may provide a novel direction for evaluating fetal factors in the development of a robust animal model of CHB as well as therapeutic strategies in humans.

Evaluation of myocardial performance with conventional single-site ventricular pacing and biventricular pacing in a canine model of atrioventricular block

INTRODUCTION

The aim of this study was to evaluate epicardial biventricular pacing as a means of maintaining synchronous ventricular activation in an acute canine model of AV block with normal ventricular anatomy and function. Chronic single-site ventricular pacing results in dyssynchronous ventricular activation and may contribute to ventricular dysfunction. Biventricular pacing has been used successfully in adult patients with congestive heart failure.

METHODS AND RESULTS

This was an acute study of open chest mongrel dogs (n = 13). ECG, left ventricular (LV), aortic, and pulmonary arterial pressures were measured. LV impedance catheters were used to assess cardiodynamics using instantaneous LV pressure-volume relations (PVR). Following radiofrequency ablation of the AV node, a temporary pacemaker was programmed 10 beats/min above the intrinsic atrial rate, with an AV interval similar to the baseline intrinsic PR interval. The pacing protocol consisted of 5-minute intervals with the following lead configurations: right atrium-right ventricular apex (RA-RVA), RA-LV apex (LVA), and RA-biventricular using combinations of four ventricular sites (RVA, RV outflow tract [RVOT], LVA, LV base [LVB]). RA-RVA was used as the experimental control. LV systolic mechanics, as measured by the slope of the end-systolic (Ees) PVR (ESPVR, mmHg/cc), was statistically greater (P < 0.05) with all modes of biventricular pacing (RA-RVA/LVA 20.0 +/- 2.9, RA-RVA/LVB 18.4 +/- 2.9, RA-RVOT/LVA 15.1 +/- 1.8, RA-RVOT/LVB 17.6 +/- 2.9) compared to single-site ventricular pacing (RA-RVA 12.8 +/- 1.6). Concurrent with this improvement in myocardial performance was a shortening of the QRS duration (RA-RVA 97.7 +/- 2.9 vs RA-RVA/LVA 75.7 +/- 4.9, RA-RVA/LVB 70.3 +/- 4.9, RA-RVOT/LVA 65.3 +/- 4.4, and RA-RVOT/LVB 76.7 +/- 5.9, P < 0.05).

CONCLUSION

In this acute canine model of AV block, QRS duration shortened and LV performance improved with epicardial biventricular pacing compared to standard single-site ventricular pacing.

Proposal for a new definition of congenital complete atrioventricular block

The classic old definition of congenital heart block by Yater (1929) is still generally accepted: 'Heart block established in a young patient. There must be some evidence of the existence of the slow pulse at a fairly early age and absence of a history of any infection which might cause the condition after birth: notably diphtheria, rheumatic fever, chorea and congenital syphilis'. However, other definitions are used. We systematically reviewed 1825 cases from 38 separate studies. We conclude that complete AV blocks detected in utero in the absence of structural abnormalities differ from blocks detected later in life with respect to pathogenesis (they are generally associated with maternal anti-Ro/SSA antibodies), poorer childhood prognosis, increased risk of developing late-onset dilated cardiomyopathy, different maternal clinical features and increased risk of recurrence in future pregnancies. For these reasons we propose a new modern definition of congenital complete AV block which might be acceptable to cardiologists, rheumatologists, pediatricians and obstetricians: 'an AV block is defined as congenital if it is diagnosed in utero, at birth or within the neonatal period (0-27 days after birth)'.

Prenatal diagnosis of sustained bradycardia with 1 : 1 atrioventricular conduction

OBJECTIVES

The aims of this study were to elucidate the clinical course of fetal bradycardia with 1 : 1 atrioventricular conduction, and to discuss the optimal management of affected fetuses in the second and third trimesters of pregnancy.

METHODS

The hospital records of five fetuses with the diagnosis of bradycardia (100 bpm) with 1 : 1 atrioventricular conduction between 1981 and 2000 in our institution were reviewed. Atrioventricular conduction was evaluated by simultaneous M-mode echocardiographic tracing of the atria and the ventricles.

RESULTS

The gestational ages at referral ranged from 19 to 36 (median, 25) weeks, and fetal heart rates ranged from 60 to 80 (median, 80) bpm. Postnatal electrocardiography revealed sinus bradycardia in four (two of which were siblings) of the five cases, and junctional rhythm in the remaining case. Two fetuses with congenital heart defects (CHDs) were delivered by Cesarean section but died postnatally. The three fetuses without CHDs were delivered vaginally and have survived to date for 6, 8 and 15 years.

CONCLUSIONS

Fetal bradycardia with 1 : 1 atrioventricular conduction caused by sustained sinus bradycardia or wandering pacemaker is an important type of fetal arrhythmia. Further investigations with a larger number of cases are required to determine the risk factors for predicting the outcome of affected fetuses.

Successful outcome in a fetus with an extremely low heart rate due to isolated complete congenital heart block

Isolated complete congenital heart block (CCHB) in a fetus is usually associated with the presence of autoantibodies to SSA (Ro) and SSB (La) antigens in the maternal circulation. Although the prognosis for the majority of fetuses is good, it is less favorable in fetuses with a ventricular rate < 55 bpm in early pregnancy or with a decrease in the ventricular rate by >/= 5 bpm during pregnancy. It is not known if the same prognostic criteria apply for the occasional fetus with isolated non-autoimmune CCHB. We report a case of a single fetus with an isolated non-autoimmune CCHB with an extremely low ventricular rate (37 bpm) in which the outcome was favorable. Dilated cardiomyopathy is a rare complication in patients with isolated CCHB, despite early institution of cardiac pacing, and is usually recognized after several months of relative well-being. It is assumed that in the majority of patients it represents a sequel to in utero autoimmune or postnatal reactivation myocarditis. However, the possibility of a tachycardia-induced cardiomyopathy caused by an excessively high pacing rate should also be taken into consideration, as was clearly demonstrated in our patient.

Calreticulin in cardiac development and pathology

Calreticulin is a Ca(2+) binding/storage chaperone resident in the lumen of endoplasmic reticulum (ER). The protein is an important component of the calreticulin/calnexin cycle and the quality control pathways in the ER. In mice, calreticulin deficiency is lethal due to impaired cardiac development. This is not surprising because the protein is expressed at high level at early stages of cardiac development. Overexpression of the protein in developing and postnatal heart leads to bradycardia, complete heart block and sudden death. Recent studies on calreticulin-deficient and transgenic mice revealed that the protein is a key upstream regulator of calcineurin-dependent pathways during cardiac development. Calreticulin and ER may play important role in cardiac development and postnatal pathologies.

Congenital heart block in neonatal lupus: the pediatric cardiologist's perspective

CLINICAL PRESENTATION

Congenital heart block (CHB) in the absence of major structural abnormalities is associated with maternal antibodies to Ro (SS-A) and La (SS-B). CHB is most commonly diagnosed between 18 and 24 wk of gestation, and may be first, second or third degree (complete). Mortality approaches approximately 20%, and most surviving children require pacemakers. Affected infants may develop cardiomyopathy. Abnormalities in the skin, liver and blood of neonates are also associated with anti-Ro/La antibodies, and are usually self-limiting; these manifestations and CHB are collectively referred to as neonatal lupus syndromes (NLS).

INVESTIGATION OF PATHOGENESIS

Recent studies demonstrate that Ro/La ribonucleoproteins appear on the surface of apoptotic fetal cardiocytes and are recognized by their cognate antibodies, promoting an inflammatory response. Mice immunized with Ro/La proteins have offspring with conduction abnormalities. In vitro, human serum and IgG with anti-Ro/La antibodies affect the conducting properties of isolated animal heart tissue.

DIAGNOSTIC PROBLEMS

If fetal bradycardia is identified, a 2-dimensional and M-mode fetal echocardiographic and Doppler ultrasound should be obtained to determine whether there is an atrial arrhythmia or atrioventricular (AV) block, and to what degree, and whether there are major structural abnormalities of the heart. The mother's serum should be tested by ELISA for anti-Ro and/or anti-La antibodies.

THERAPEUTIC OPTIONS

To date, only anecdotal and retrospective evidence guides in utero therapy of CHB. A prospective trial is currently underway to evaluate the efficacy of maternal oral dexamethasone in treating newly identified first, second or third degree block. Established third-degree block appears to be irreversible. Dexamethasone and sympathomimetics may be of some benefit in treating hydrops fetalis. In pregnant women with anti-Ro/La antibodies, prophylactic therapy is not indicated but serial echocardiographic analysis is strongly recommended, with emphasis on the mechanical PR interval to identify a reversible block.

CONCLUSION

CHB occurs in approximately 1-5% of pregnancies in mothers with anti-Ro/La antibodies, independent of the mother's disease status, and in approximately 15-20% of pregnancies following the birth of a child with NLS. Treatment of CHB identified in utero is not established but guidelines are provided. Serial echocardiographic monitoring of high-risk pregnancies, using the mechanical PR interval to identify first degree block, may afford the earliest opportunities for therapeutic intervention.