Morphology of the sinus node in human and mouse hearts with isomerism of the atrial appendages

Rare variant of heterotaxy syndrome in childhood in pulmonology clinic

Heterotaxy syndrome is a congenital malformation in which the internal organs of the chest and abdominal cavity have an abnormal location. People suffering from this syndrome have multiple complex defects in the heart, blood vessels, spleen, liver, lungs and other organs. Heterotaxy is a rare pathology that requires a multidisciplinary approach to diagnosis. This article demonstrates a rare case of heterotaxy observed in the pulmonology clinic of the Veltischev Institute.

Twin atrioventricular nodes, arrhythmias, and survival in pediatric and adult patients with heterotaxy syndrome

BACKGROUND

Heterotaxy syndrome is likely to involve arrhythmias from associated conduction system abnormalities, which are distinct in different subtypes of isomerism and may change further after interventions and remodeling.

OBJECTIVE

The purpose of this study was to understand the risk of arrhythmias and its relation to isomerism subtypes.

METHODS

Patients diagnosed between 1980 and 2019 as having heterotaxy syndrome were enrolled and grouped as right atrial isomerism (RAI), left atrial isomerism (LAI), or indeterminate isomerism.

RESULTS

Of the 366 patients enrolled, 326 (89.1%) had RAI, 35 (9.6%) LAI, and 5 (1.4%) indeterminate isomerism; 71 (19.4%) patients were adults. Arrhythmias occurred in 37.2% of patients (109 supraventricular tachycardia [SVT], 8 atrial fibrillation/flutter, 12 ventricular tachycardia, and 14 paced bradycardia). Freedom from arrhythmias by the age of 1, 5, 10, 20, and 40 years was 0.849, 0.680, 0.550, 0.413, and 0.053, respectively. Twin atrioventricular nodes were identified in 51.5% of patients with RAI, 8.7% of patients with LAI, and 40.0% of patients with indeterminate isomerism and were the key predictors of SVT. Indeterminate isomerism was also a risk factor for SVT. Other forms of tachycardia appeared relatively late. Sinus bradycardia with junctional rhythm was common in LAI (48.7%) and less in indeterminate isomerism (20.0%), with none occurring in RAI. Only in patients with RAI who showed the poorest survival, ventricular tachycardia worsened the long-term survival.

CONCLUSION

RAI was the predominant subtype of heterotaxy in this cohort. Collectively, the median RAI/LAI ratio was 0.731 and 5.450 in Western and East Asian studies, respectively. Arrhythmias, tachycardia, or paced bradycardia were common, but the spectrum was distinct among subtypes.

Early outcomes of usage of cryoFORM® probe for cryomaze procedure in congenital heart surgery

OBJECTIVES

This study aimed to evaluate the early outcomes of patients who underwent a concomitant therapeutic maze procedure for congenital heart surgery.

MATERIALS AND METHODS

Between 2019 and 2020, eight patients underwent surgical cryoablation by using the same type of cryoablation probe.

RESULTS

Three patients had atrial flutter, two had Wolf-Parkinson-White syndrome, two intra-atrial reentrant tachycardia, and one had atrial fibrillation. Four patients underwent electrophysiological study. Preoperatively, one patient was on 3, two were on 2, five were on 1 antiarrhythmic drug. Six patients underwent right atrial maze and two underwent bilateral atrial maze. Five out of six right atrial maze patients underwent right atrial reduction. Nine different lesion sets were used. Some of the lesions were combined and applied as one lesion. In Ebstein's anomaly patients, the lesion from coronary sinus to displaced tricuspid annulus was delicately performed. The single ventricle patient with heterotaxy had junctional rhythm at the time of discharge and was the only patient who experienced atrial extrasystoles 2 months after discharge. Seven of the eight patients were on sinus rhythm. No patient needed permanent pacemaker placement.

CONCLUSION

Cryomaze procedure can be applied in congenital heart diseases with acceptable arrhythmia-free rates by selecting the appropriate materials and suitable lesion sets. The application of cryomaze in heterotaxy patients can be challenging due to differences in the conduction system and complex anatomy. Consensus with the electrophysiology team about the choice of the right-left or biatrial maze procedure is mandatory for operational success.

The heterotaxy syndrome: associated congenital heart defects and management

Heterotaxy syndrome (HS) constitutes a spectrum of anomalies arising from embryological errors that result in abnormalities of lateralization involving thoraco-abdominal viscera and culminate in loss of normal asymmetric arrangement of these organs. Besides the unique challenges involved in planning and execution of surgical procedures aimed at correction or palliation of these anomalies, they have the potential to cause profound physiological and immunological consequences in the individual patient due to their cardiac and extra-cardiac manifestations. This article aims to review the literature on this rare and extraordinary subset of developmental anomalies with the intention of familiarizing the reader on the modes of presentation, manifestations, and the variations thereof while dealing with this anomaly. In our institutional experience with HS, 75 consecutive patients were seen between January 2011 and September 2018. Of these, 48 (64%) were confirmed to have isomerism of right atrial appendages (IRAA) and the rest had isomerism of left atrial appendages (ILAA). The cardiac and extra-cardiac manifestations of these patients were listed out. Fifty-four patients (34 with IRAA and 20 with ILAA) underwent 83 surgical procedures. While 49 patients were palliated on the univentricular pathway, 5 underwent biventricular repair. The in-hospital mortality was 7 (13%) in both groups combined (5 for patients with IRAA and 2 for ILAA). In conclusion, the surgical management of HS is associated with satisfactory outcomes in current era.

Isomerism of the atrial appendages: morphology and terminology

BACKGROUND

Our aim is to identify the pathognomonic anatomical markers and the best terminology to describe the cardiac malformations associated with absent or multiple spleens, which are known as asplenia or polysplenia syndromes or isomerism.

MATERIALS AND METHODS

We have reviewed 65 hearts with isomerism of atrial appendages of the Anatomical Collections of Congenital Heart Disease, Institute of Pathological Anatomy of the University of Padua consisting of 1800 specimens. All the hearts were classified according to sequential segmental classification.

RESULTS

The incidence of isomerism was 3.6%. Of the total, 45 hearts with isomerism of right atrial appendages showed bilateral trilobed lungs, short bronchi, and absent spleen. The atrioventricular junction was univentricular in 49% of cases with a common atrioventricular valve in 91%. Pulmonary atresia and double outlet right ventricle were present in 40% and 47% of cases, respectively. Total anomalous pulmonary venous drainage and absent coronary sinus were always present. In 20 hearts with isomerism of left atrial appendages, bilateral bilobed lungs with long bilateral bronchi and multiple spleens were always found. The biventricular atrioventricular connection was present in 65% with a common valve in 30% of the hearts. The ventriculoarterial connection was concordant in 45% of cases, and aortic atresia and pulmonary atresia were both noted in 15% of each. An anomalous symmetric pulmonary venous drainage was observed in 65% of the hearts and interruption of inferior vena cava was found in 75% of cases.

CONCLUSIONS

We believe that the appropriate terminology is based on the symmetrical morphology of the atrial appendages. The absence of the coronary sinus and the total anomalous pulmonary venous drainage are the markers of isomerism of the right atrial appendages. Symmetric pulmonary venous drainage and interruption of inferior vena cava are the markers of isomerism of left atrial appendages. In recent years, thanks to the improvement of clinical diagnosis and of surgical techniques these patients have the possibility to survive to adult age.

Spontaneous Left Cardiac Isomerism in Chick Embryos: Case Report, Review of the Literature, and Possible Significance for the Understanding of Ventricular Non-Compaction Cardiomyopathy in the Setting of Human Heterotaxy Syndromes

The outer shape of most vertebrates is normally characterized by bilateral symmetry. The inner organs, on the other hand, are normally arranged in bilaterally asymmetric patterns. Congenital deviations from the normal organ asymmetry can occur in the form of mirror imagery of the normal arrangement (situs inversus), or in the form of arrangements that have the tendency for the development of bilateral symmetry, either in a pattern of bilateral left-sidedness (left isomerism) or bilateral right-sidedness (right isomerism). The latter two forms of visceral situs anomalies are called “heterotaxy syndromes”. During the past 30 years, remarkable progress has been made in uncovering the genetic etiology of heterotaxy syndromes. However, the pathogenetic mechanisms causing the spectrum of cardiovascular defects found in these syndromes remain poorly understood. In the present report, a spontaneous case of left cardiac isomerism found in an HH-stage 23 chick embryo is described. The observations made in this case confirmed the existence of molecular isomerism in the ventricular chambers previously noted in mouse models. They, furthermore, suggest that hearts with left cardiac isomerism may have the tendency for the development of non-compaction cardiomyopathy caused by defective development of the proepicardium.

Clinical Characteristics and Independent Factors Related to Long-Term Outcomes in Patients with Left Isomerism

BACKGROUND AND OBJECTIVES

We studied the results of patient management for left isomerism (LI) and sought to determine factors that may influence survival and prognosis.

SUBJECTS AND METHODS

We reviewed the medical records of 76 patients who were compatible with LI criteria between 1982 and 2014.

RESULTS

Of the total study population, 29 patients (38.1%) had functional univentricular heart disease, 43 patients (56.5%) had cardiac anomalies suitable for biventricular hearts, and four patients (5.2%) had normal heart structure. Extracardiac anomalies were noted in 38.1% of the study population, including biliary atresia in 7.8% of all patients. Of the 25 patients who underwent Kawashima procedures, 24.0% developed pulmonary arteriovenous fistulas (PAVFs). During the median follow-up period of 11.4 years (range: 1 day to 32 years), 14 patients died. The 10-year, 20-year, and 30-year survival rates were 87%, 84%, and 76%, respectively. Preoperative dysrhythmia and uncorrected atrioventricular valve regurgitation were significantly associated with late death. There was no significant difference in the number of surgical procedures and in survival expectancy between patients in the functional single-ventricle group and in the biventricular group. However, late mortality was higher in functional single-ventricle patients after 18 years of age.

CONCLUSION

Patients with LI need to be carefully followed, not only for late cardiovascular problems such as dysrhythmia, valve regurgitation, and the development of PAVFs, but also for noncardiac systemic manifestations.

Lateral Atrial Tunnel Fontan Operation Predisposes to the Junctional Rhythm

The goal of the study was to compare the early postoperative course after fenestrated lateral atrial tunnel (LT) and non-fenestrated extracardiac conduit (EC) Fontan operation (FO) in a single center where both techniques were parallelly used. Between 2004 and 2012, 56(32.7%) children underwent LT and 113(66.1%) EC FO. The mean age was 3.7 ± 2.9 years and mean weight was 14.6 ± 7.3 kg. The most common malformation was hypoplastic left heart syndrome (50.9%). The general approach was to perform LT in children after hemi-Fontan operation and EC in patients after Glenn anastomosis. Medical records were retrospectively reviewed. The hospital survival was 100%. In EC group, cardiopulmonary bypass time (CPB) was shorter (p = 0.004) and less patients needed aortic cross-clamping (p < 0.001). Children after EC stayed longer in the hospital (p = 0.016) and manifested more often prolonged effusions (p = 0.038). The incidence of all forms of junctional rhythm was higher in the LT group, early postoperatively (p < 0.001), during hospitalization (p = 0.004) and at discharge (p < 0.001). Children after LT required more often temporary pacemaker stimulation (p < 0.001). Patients without postoperative normofrequent sinus rhythm had longer CPB time (p = 0.008) and were more often operated on with aortic cross-clamping (p = 0.028). Lateral atrial tunnel Fontan operation with fenestration facilitates early adaptation to the total passive pulmonary flow, but predisposes the patients to the loss of sinus rhythm. The crucial role in the preservation of sinus rhythm plays the last step of the multistage surgery of the single ventricle malformations, probably not only the surgical technique but also factors associated with the cardiopulmonary bypass.

Surgical aspects of atrial arrhythmia : Right atrial ablation and anti-arrhythmic surgery in congenital heart disease

BACKGROUND

Atrial arrhythmias are frequently described in congenital heart disease.

OBJECTIVES

To provide a surgical perspective of anti-arrhythmic procedures and strategic approaches.

METHODS

Discussion of the history of anti-arrhythmic treatments in congenital heart disease.

RESULTS

Before the advent of the Maze procedure (first published in 1991), surgery mainly focused on patients with Wolff-Parkinson-White syndrome and also on arrhythmias in Ebstein's malformation. Atrial septal defects (ASD) subsequently received more attention, i.e., in terms of atrial arrhythmia in the natural prognosis and the surgically modified course and in terms of surgical versus transcatheter approaches. Based on the background of various atrial arrhythmia mechanisms of ASD, several surgical procedures have been reported, ranging from the bilateral full Maze procedure to simple modification of right atriotomy. The so-called right atrial Maze procedure occupies a special position from the viewpoint of cardiology in acquired heart disease, especially in cases of frequently occurring right heart failure. In hearts with more complex structural abnormalities, a detailed understanding of the conditions to improve overall surgical outcome and develop future "anti-arrhythmic" strategies is necessary.

CONCLUSIONS

It is important to precisely specify factors in the individual cases, not only morphological diversity but also technical and strategic variations and their consequences. A variety of anti-arrhythmic surgical procedures are currently available. How and when to use which procedure requires professional insight and cautious clinical decision-making.

Determining bronchial morphology for the purposes of segregating so-called heterotaxy

Introduction Heterotaxy is a unique clinical entity in which lateralisation of the thoraco-abdominal organs is abnormal, typically with isomerism of the bronchial tree and atrial appendages. This study was carried out to determine whether routine clinical imaging such as chest radiographs, angiographic images, and CT/MRI can determine bronchial isomerism, and how sidedness of bronchial isomerism correlates with overall features anticipated in hearts with isomeric atrial appendages. Methods and results We identified 73 patients with heterotaxy, in whom imaging clearly demonstrated the bronchial tree, seen at our institution since 1998. We calculated bronchial angles and lengths using all the available imaging modalities to determine the presence and sidedness of bronchial isomerism. This was then compared with the anticipated presence of isomeric atrial appendages based on the overall clinical findings, as the appendages themselves had not specifically been imaged. The ratio of bronchial lengths revealed bronchial isomerism in all patients, with bronchial angles permitting distinction of right as opposed to left isomerism. We noted discordances between the identified bronchial isomerism and the presumed arrangement of the atrial appendages in nearly 20% of the patients in our cohort.

CONCLUSION

Routine clinical imaging with chest radiographs, angiographic imaging, and CT/MRI can determine the presence of bronchial isomerism in patients with so-called heterotaxy. Right as opposed to left isomerism can be distinguished based on bronchial angles. The finding of bronchial isomerism correlates well, but not totally, with the presumed isomerism of the atrial appendages as predicted from the identified intra-cardiac morphology.

Arrhythmias in Adult Congenital Patients With Bodily Isomerism

There are an increasing number of adults with congenital heart disease, some of whom have bodily isomerism. Bodily isomerism or heterotaxy is a unique clinical entity associated with congenital malformations of the heart which further increases the risk for future cardiovascular complications. We aimed to investigate the frequency of arrhythmias in adults with bodily isomerism. We utilized the 2012 iteration of the Nationwide Inpatient Sample to identify adult inpatient admissions associated with arrhythmias in patients with isomerism. Data regarding demographics, comorbidities, and various procedures were collected and compared between those with and without isomerism. A total of 6,907,109 admissions were analyzed with a total of 861 being associated isomerism. The frequency of arrhythmias was greater in those with isomerism (20.8 vs. 15.4 %). Those with isomerism were also more five times more likely to undergo invasive electrophysiology studies. Length and cost of hospitalization for patients with arrhythmias also tended to be greater in those with isomerism. Mortality did not differ between the two groups. Arrhythmias are more prevalent in those with isomerism, with a majority of arrhythmias in isomerism being atrial. Those with isomerism and arrhythmias also tended to have greater length and cost of hospitalization.

Decreased baseline variability on fetal heart rate pattern in a fetus with heterotaxy syndrome

In a fetus with suspected heterotaxy syndrome, a decreased/absent baseline variability of fetal heart rate pattern developed at gestational week 36(+5) and continued for 5 days until birth at gestational week 37(+2), while repeat biophysical profile scorings with ultrasound were consistently unremarkable. This neonate weighing 2404 g with Apgar scores of 7 (1-min) and 8 (5-min) and umbilical arterial cord blood pH of 7.28 with base deficit of 3.9 mmol/L, showed a heart rate of 120 b.p.m. for 3 h after birth, but subsequently developed sinus bradycardia (84 b.p.m.) unresponsive to crying. Isoproterenol initiated 9 h after birth was effective in the increase of heart rate to 120 b.p.m. in this neonate. Brain magnetic resonance imaging at 16 days of age was unremarkable. The decreased/absent baseline variability of fetal heart rate pattern was speculated to have been caused by sinus node dysfunction, and not by reduced fetal oxygenation in this case.

An adult case of polysplenia syndrome associated with sinus node dysfunction, dextrocardia, and systemic venous anomalies

A 54-year-old woman was referred to our hospital for symptomatic sinus bradyarrhythmia with a sinus pause of 8 seconds. She was diagnosed with dextrocardia during childhood and discovered to have heterotaxy syndrome when she had an appendectomy during her teenager years. Chest and abdominal examinations by computed tomography showed multiple spleens located on the right side and abnormal drainages of the superior and inferior vena cava. Left isomerism was diagnosed by bilaterally bilobed lungs. Because of a patent bilateral superior vena cava, pacemaker leads were implanted using the right cephalic vein approach. Her fainting symptoms disappeared after pacemaker implantation.

Molecular analysis of patterning of conduction tissues in the developing human heart

BACKGROUND

Recent studies in experimental animals have revealed some molecular mechanisms underlying the differentiation of the myocardium making up the conduction system. To date, lack of gene expression data for the developing human conduction system has precluded valid extrapolations from experimental studies to the human situation.

METHODS AND RESULTS

We performed immunohistochemical analyses of the expression of key transcription factors, such as ISL1, TBX3, TBX18, and NKX2-5, ion channel HCN4, and connexins in the human embryonic heart. We supplemented our molecular analyses with 3-dimensional reconstructions of myocardial TBX3 expression. TBX3 is expressed in the developing conduction system and in the right venous valve, atrioventricular ring bundles, and retro-aortic nodal region. TBX3-positive myocardium, with exception of the top of the ventricular septum, is devoid of fast-conducting connexin40 and connexin43 and hence identifies slowly conducting pathways. In the early embryonic heart, we found wide expression of the pacemaker channel HCN4 at the venous pole, including the atrial chambers. HCN4 expression becomes confined during later developmental stages to the components of the conduction system. Patterns of expression of transcription factors, known from experimental studies to regulate the development of the sinus node and atrioventricular conduction system, are similar in the human and mouse developing hearts.

CONCLUSIONS

Our findings point to the comparability of mechanisms governing the development of the cardiac conduction patterning in human and mouse, which provide a molecular basis for understanding the functioning of the human developing heart before formation of a discrete conduction system.

Heterotaxy syndrome

Heterotaxy is defined as an abnormality where the internal thoraco-abdominal organs demonstrate abnormal arrangement across the left-right axis of the body. This broad term includes patients with a wide variety of very complex cardiac lesions. Patients with heterotaxy can be stratified into the subsets of asplenia syndrome and polysplenia syndrome, or the subsets of heterotaxy with isomerism of the right atrial appendages and heterotaxy with isomerism of the left atrial appendages. Treatment of patients with isomerism is determined by the nature and severity of the associated cardiac and extracardiac lesions. Most cardiac operations for patients with isomerism are palliative in nature, since normal anatomy is rarely achieved and mortality rates remain high for patients with heterotaxy syndrome. Patients with left isomerism in general have less severe cardiac malformations than those with right isomerism and, hence, more chance of biventricular repair. For almost all patients with right isomerism, and for many with left isomerism, biventricular repair will not be feasible, and all palliative protocols are then staging procedures prior to a Fontan-type repair. Recent advances in medical management, and improvements in surgical techniques have resulted in improved survival for these patients, and the surgical outcomes are comparable to those with Fontan circulation irrespective of the presence or absence of heterotaxy.

Challenges of Univentricular Physiology in Heterotaxy

Patients with heterotaxy syndrome exhibit an extensive constellation of congenital cardiac malformations, making these patients a challenging group to manage surgically. Many of these patients' hearts do not lend themselves to separation of the pulmonary and systemic circulations except by some modification of the Fontan procedure. Palliative procedures early in life are directed at creating a satisfactory balance of pulmonary and systemic blood flow and at the same time ensuring unobstructed pulmonary venous return. Early conversion from parallel pulmonary and systemic circulations to superior cavopulmonary connections is important, to reduce volume work of the systemic ventricle. Heterotaxy patients are generally considered a high-risk population with respect to eventual Fontan procedure. It is important to appreciate the unique and variable anatomy of the sinus node and conduction system and the potential for occult pulmonary venous obstruction, atrioventricular valve regurgitation, and recurrent cyanosis, which may be related to the development of pulmonary arteriovenous malformations.

A novel autosomal dominant condition consisting of congenital heart defects and low atrial rhythm maps to chromosome 9q

Congenital heart defects (CHDs) occur mostly sporadic, but familial CHD cases have been reported. Mutations in several genes, including NKX2.5, GATA4 and NOTCH1, were identified in families and patients with CHD, but the mechanisms underlying CHD are largely unknown. We performed genome-wide linkage analysis in a large four-generation family with autosomal dominant CHD (including atrial septal defect type I and II, tetralogy of Fallot and persistent left superior vena cava) and low atrial rhythm, a unique phenotype that has not been described before. We obtained phenotypic information including electrocardiography, echocardiography and DNA of 23 family members. Genome-wide linkage analysis on 12 affected, 5 unaffected individuals and 1 obligate carrier demonstrated significant linkage only to chromosome 9q21-33 with a multipoint maximum LOD score of 4.1 at marker D9S1690, between markers D9S167 and D9S1682. This 48-cM critical interval corresponds to 39 Mb and contains 402 genes. Sequence analysis of nine candidate genes in this region (INVS, TMOD1, TGFBR1, KLF4, IPPK, BARX1, PTCH1, MEGF9 and S1PR3) revealed no mutations, nor were genomic imbalances detected using array comparative genomic hybridization. In conclusion, we describe a large family with CHD and low atrial rhythm with a significant LOD score to chromosome 9q. The phenotype is representative of a mild form of left atrial isomerism or a developmental defect of the sinus node and surrounding tissue. Because the mechanisms underlying CHD are largely unknown, this study represents an important step towards the discovery of genes implied in cardiogenesis.

Diagnosis and management of common fetal arrhythmias

Fetal arrhythmias are detected in at least 2% of unselected pregnancies during routine obstetrical scans. Most common are transient, brief episodes of a slow or fast heart rate or of an irregular heart rhythm. Less common are prolonged or persistent abnormalities such as supraventricular tachycardia and complete heart block which may lead to low cardiac output, fetal hydrops and demise. The objectives of this review are to update the reader on the diagnosis and management of the more common arrhythmias.

A mouse model of conduction system patterning abnormalities in heterotaxy syndrome

Duplication or absence of parts of the specialized cardiac conduction system in patients with heterotaxy syndrome causes significant clinical disease, but the mechanistic basis by which embryonic disruption of left-right patterning alters conduction system patterning in these patients is not well understood. We sought to determine whether a mouse model of X-linked human heterotaxy recapitulates conduction system abnormalities identified in patients with heterotaxy. Cardiac structure and conduction system patterning were evaluated in Zic3 null embryos from e9.5 to e16.5 using genetic and molecular methods. Severe structural abnormalities involving atrial, ventricular, and conotruncal development were associated with a spectrum of disorganized and ambiguous arrangements throughout the conduction system, including the appearance of duplicated structures. The severity and location of conduction system abnormalities correlated with the severity and location of associated structural heart disease and were identifiable at the earliest stages examined. The Zic3 mouse model provides a novel tool to dissect the mechanistic underpinnings of conduction system patterning and dysfunction and its relationship to cardiovascular malformations, making it a promising model to improve understanding and risk assessment in the clinical arena.

Expression and distribution of voltage-gated ion channels in ferret sinoatrial node

Spontaneous diastolic depolarization in the sinoatrial (SA) node enables it to serve as pacemaker of the heart. The variable cell morphology within the SA node predicts that ion channel expression would be heterogeneous and different from that in the atrium. To evaluate ion channel heterogeneity within the SA node, we used fluorescent in situ hybridization to examine ion channel expression in the ferret SA node region and atrial appendage. SA nodal cells were distinguished from surrounding cardiac myocytes by expression of the slow (SA node) and cardiac (surrounding tissue) forms of troponin I. Nerve cells in the sections were identified by detection of GAP-43 and cytoskeletal middle neurofilament. Transcript expression was characterized for the 4 hyperpolarization-activated cation channels, 6 voltage-gated Na(+) channels, 3 voltage-gated Ca(2+) channels, 24 voltage-gated K(+) channel α-subunits, and 3 ancillary subunits. To ensure that transcript expression was representative of protein expression, immunofluorescence was used to verify localization patterns of voltage-dependent K(+) channels. Colocalizations were performed to observe any preferential patterns. Some overlapping and nonoverlapping binding patterns were observed. Measurement of different cation channel transcripts showed heterogeneous expression with many different patterns of expression, attesting to the complexity of electrical activity in the SA node. This study provides insight into the possible role ion channel heterogeneity plays in SA node pacemaker activity.

Molecular pathway for the localized formation of the sinoatrial node

The sinoatrial node, which resides at the junction of the right atrium and the superior caval vein, contains specialized myocardial cells that initiate the heart beat. Despite this fundamental role in heart function, the embryonic origin and mechanisms of localized formation of the sinoatrial node have not been defined. Here we show that subsequent to the formation of the Nkx2-5-positive heart tube, cells bordering the inflow tract of the heart tube give rise to the Nkx2-5-negative myocardial cells of the sinoatrial node and the sinus horns. Using genetic models, we show that as the myocardium of the heart tube matures, Nkx2-5 suppresses pacemaker channel gene Hcn4 and T-box transcription factor gene Tbx3, thereby enforcing a progressive confinement of their expression to the forming Nkx2-5-negative sinoatrial node and sinus horns. Thus, Nkx2-5 is essential for establishing a gene expression border between the atrium and sinoatrial node. Tbx3 was found to suppress chamber differentiation, providing an additional mechanism by which the Tbx3-positive sinoatrial node is shielded from differentiating into atrial myocardium. Pitx2c-deficient fetuses form sinoatrial nodes with indistinguishable molecular signatures at both the right and left sinuatrial junction, indicating that Pitx2c functions within the left/right pathway to suppress a default program for sinuatrial node formation on the left. Our molecular pathway provides a mechanism for how pacemaker activity becomes progressively relegated to the most recently added components of the venous pole of the heart and, ultimately, to the junction of the right atrium and superior caval vein.

Cardiac perforation 6 weeks after percutaneous atrial septal defect repair using an Amplatzer septal occluder

A 14-year-old boy presented to the emergency department unaccompanied by his parents with a decreased level of consciousness, bradycardia, and hypotension after a syncopal episode. The patient's electronic chart revealed a percutaneous closure of a secundum atrial septal defect using an Amplatzer septal occluder (AGA Medical, Golden Valley, MN) 6 weeks before this presentation. An urgent echocardiogram revealed a moderate pericardial effusion, and 320 mL of fresh blood was evacuated by subxiphoid pericardiocentesis. The child underwent surgical exploration and was found to have a perforation in the superior-posterior aspect of the right atrium, which was corrected. The septal occluder was extracted, and the atrial septal defect was closed with a pericardial patch. This case illustrates a rare but life-threatening complication of percutaneous closure of atrial septal defect using an Amplatzer septal occluder and the importance of timely access to patient records when available history and physical examination are limited.

The diverse cardiac morphology seen in hearts with isomerism of the atrial appendages with reference to the disposition of the specialised conduction system

Congenital cardiac malformations which include isomerism of the atrial appendages are amongst the most challenging of problems for diagnosis and also for medical and surgical management. The nomenclature for pathological description is controversial, but difficulties can be overcome by the use of a segmental approach. Such an approach sets out the morphology and the topology of the chambers of the heart, together with the types and modes of the atrioventricular, ventriculo-arterial, and venous connections. We have applied this method to a study of 35 hearts known to have isomerism of the atrial appendages. We have already published accounts of 27 of these cases, but these were reviewed for this study in the light of our increased awareness of the implications of isomerism, and 8 new cases were added. After examining, or re-examining, the morphology of every heart in detail, we grouped them together according to their ventricular topology and modes of atrioventricular connection. Then we studied the course of the specialised conduction system, by the use of the light microscope, first in each individual case, and then together in their groups. We conclude that the pathways for atrioventricular conduction in hearts with isomerism of the atrial appendages are conditioned both by ventricular topology, and by the atrioventricular connections. Based on our experience, we have been able to establish guidelines that direct the clinician to the likely location of the conduction tissues.

Sinus node dysfunction after Fontan modifications--influence of surgical method

BACKGROUND

Sinus node dysfunction (SND) is reported to be a troublesome complication following various types of Fontan operations. The correlation of post-Fontan SND with surgical methods was evaluated in this study.

METHODS

By reviewing the medical records, surface ECGs, and Holter monitoring, the range of heart rate (HR) and the risk of SND at intermediate term after Fontan type operation (follow up: 41.3+/-13.1 months) were analyzed between two age matched groups of patients, consisting of the extracardiac conduit group (EC, n=33) and the lateral tunneling group (LT, n=35).

RESULTS

Junctional rhythm was observed in nine out of 35 patients in LT and five out of 33 patients in EC during the follow-up period. Resting HR was faster in EC than that in LT (108+/-15 vs. 82+/-21, P<0.001). Average and maximal HR in Holter monitoring were also faster in EC than those in LT. SND was found in 13 cases (10 in LT, three in EC) during follow-up and one required pacemaker implantation. In the case of situs solitus heart, SND was less frequent in EC than in LT (0/16 vs. 8/26, P=0.01). In the case of heterotaxy syndrome, SND occurred in similar number of cases (3/17 vs. 2/9). The staged approach to Fontan completion did not influence SND. LT repair was the only factor causing sinus node dysfunction according to multivariate logistic regression (P=0.03, OR 5.96).

CONCLUSIONS

Lateral tunnel type surgical repair was more likely to lead to the development of sinus node dysfunction than extracardiac conduit operation. In the case of heterotaxy syndrome, surgical method had no significant influence.

Cardinal vein isomerism: an embryological hypothesis to explain a persistent left superior vena cava draining into the roof of the left atrium in the absence of coronary sinus and atrial septal defect

BACKGROUND

A persistent left superior vena cava (PLSVC) is a relatively frequent systemic venous anomaly associated with congenital heart defects. This anomaly has been explained with the persistence of the left superior cardinal vein. PLSVC usually drains into the right atrium, via coronary sinus, but it joins the left atrium in approximately 8% of the cases either directly in the setting of atrial isomerism, or via an unroofed coronary sinus, or through a coronary sinus type atrial septal defect.

CASE REPORT

We describe a case of an adult patient with atria in the situs solitus, PLSVC draining into the left atrium, atresia of coronary sinus without atrial septal defect, and with additional cardiac anomalies (ventricular septal defect and discrete subaortic stenosis).

CONCLUSION

A possible embryological explanation to this case rises from a right partial isomerism of the superior cardinal veins, which gives reason for both the coexistence of the PLSVC draining into the left atrium and the absence of coronary sinus, atrial septal defect, or coronary sinus ostium.

Complications associated with heterotaxy syndrome in Fontan patients

Enormous progress has been made in the last decade toward decreasing the risk of the Fontan operation and optimizing early and intermediate outcomes. Heterotaxy syndrome patients, with their extensive constellation of anatomic abnormalities, constitute a challenging group to manage surgically. Palliative procedures early in life are directed at creation of a satisfactory balance between pulmonary and systemic blood flow and at the same time assurance of unobstructed pulmonary venous return. For heterotaxy patients who survive beyond the newborn period, and are considered to have nonseptatable hearts, early reduction of the volume load of the functional single ventricle is extremely important. Early conversion from parallel pulmonary and systemic circulations to a superior cavopulmonary anastomosis (bidirectional Glenn or hemi-Fontan) is the preferred strategy. Traditionally, those patients with heterotaxy who survive initial surgical management have been considered a very high-risk population with respect to an eventual Fontan procedure. In heterotaxy patients it is particularly important to understand the unique and variable anatomy of the sinus node and conduction system, the potential for occult pulmonary venous obstruction, the tendency for development of atrioventricular valve regurgitation in volume loaded ventricles, and the potential for recurrent or persistent cyanosis because of intrahepatic shunting or pulmonary arteriovenous malformations.

An approach to dissecting the congenitally malformed heart in the forensic autopsy: the value of sequential segmental analysis

The demonstration of congenital heart disease at autopsy necessitates the careful preservation and examination of the heart, the vessels, and their connections. Techniques preserving these connections and using a reproducible and systematic approach are preferred. The Rokitansky method of organ block dissection, in combination with a system of heart examination termed sequential segmental analysis, provides such an approach. This study is based on the examination of heart specimens accessioned into the Frank E. Sherman, M.D., and Cora C. Lenox, M.D., Heart Museum (containing approximately 2400 specimens) of the Pathology Department, Children's Hospital of Pittsburgh. Specimens received in consultation during a 25-year period from hospitals and coroners'/medical examiners' offices were examined, and the corresponding reports were reviewed. Of 46 total heart specimens examined (1975-1999), 29 (63%) were dissected properly or left intact for dissection at Children's Hospital of Pittsburgh, and 17 (37%) were incorrectly dissected for the demonstration of congenital heart disease. Of these 17 cases, 11 (24%) displayed dissection errors, which did not hinder a complete diagnosis, 3 cases (6.5%) had errors that enabled only an incomplete diagnosis, and in 3 cases (6.5%), no diagnosis of congenital heart disease could be made. Dissection mistakes and means of avoiding them are discussed. Review of medical and family history, external and internal examination, and a reproducible and sequential method of examining the heart and its connections enables documentation of even the most complex cardiovascular anomalies.

Anatomic biventricular repair by intraatrial and intraventricular re-routing in patients with left isomerism

OBJECTIVE

To determine the efficacy of anatomic biventricular repair by a combination of intraatrial and intraventricular re-routing in patients with isomerism of the left atrial appendages.

METHODS

Anatomic biventricular repair by means of combined intraratrial and intraventricular re-routing was achieved in 5 of the 63 patients with left isomerism in whom we attempted a definitive surgical procedure. The inferior caval vein was interrupted in 3. The Mustard procedure was chosen for intraatrial redirection of blood in 4, and the Senning procedure in the other. Intraventricular re-routing was carried out via a right ventriculotomy in all patients, using an external conduit to reconstruct the morphologically right ventricular outflow tract.

RESULTS

One patient died one month after the procedure because of low cardiac output and bronchial bleeding. Obstruction across the superior caval venous channel occurred after the Senning procedure in this particular patient, related to the interrupted inferior caval vein draining via the azygous vein. The other 4 patients are currently doing well. Postoperative catheterization showed excellent cardiac performance, with no obstruction across the venous channels or the ventricular outflow tracts in these 4. No episode of significant arrhythmia has been noted, all patients having a regular atrial rhythm, although the P wave vector was unusual in each patient. Reoperation has been needed thus far in one patient, 128 months after the initial repair, because of obstruction of the external conduit.

CONCLUSION

With precise recognition of the morphologic features, a combination of intraatrial and intraventricular re-routing can successfully be established in patients with isomeric left atrial appendages, with functional results in the intermediate term being reasonable.

Arrangement of the systemic and pulmonary venous components of the atrial chambers in hearts with isomeric atrial appendages

BACKGROUND

The morphological definition of atrial chambers, and the determination of atrial laterality, are based on analysis of the structure of the atrial appendages. The systemic and pulmonary venous connections to the heart, nonetheless, are important in the management of patients having isomeric appendages. In this study, therefore, we analysed the morphology of the postero-superior walls of the atrial chambers so as to provide evidence concerning the morphogenetic background of those hearts, and to improve operative management.

METHODS

We reviewed 15 autopsied specimens with isomeric right appendages, and 10 with isomeric left appendages, paying particular attention to the morphology of the systemic and pulmonary venous connections. The postero-superior walls of the atrial chambers can be made up of the atrial body, the systemic venous components, or the pulmonary venous component. We analysed the contributions made by each of these components.

RESULTS

The postero-superior walls of the atrial chambers were markedly variable, but could be grouped into five patterns. Bilaterally well-developed systemic venous components and absence of the pulmonary venous component within the hypoplastic atrial body were present in 9 hearts with extracardiac pulmonary venous connections in the setting of right isomerism. Bilaterally well-developed systemic venous components, and a hypoplastic pulmonary venous component within the hypoplastic atrial body, were present in 5 hearts with intracardiac pulmonary venous connections in right isomerism. Bilaterally well-developed systemic venous components, and a hypoplastic pulmonary venous component within the sizable atrial body, were present in 1 heart with an intracardiac pulmonary venous connection in right isomerism. A well-developed pulmonary venous component within the atrial body, and hypoplasia of one systemic venous component, were present in 7 hearts with left isomerism. A well-developed pulmonary venous component within the atrial body, and hypoplasia of bilateral systemic venous components, were present in 3 hearts with left isomerism.

CONCLUSIONS

The postero-superior walls of the atrial chambers in hearts with isomeric atrial appendages can be analysed on the basis of a compound structure made of bilateral systemic venous components, a central pulmonary venous component, and the body of the atrium. Hearts with isomeric right appendages have absence or hypoplasia of the pulmonary venous component, while hearts with isomeric left appendages have hypoplastic systemic venous components.

How should we optimally describe complex congenitally malformed hearts?

BACKGROUND

There is still no agreement on how best to describe the arrangement of complex congenitally malformed hearts. Some favor a system using short coded segmental combinations. Others favor a more descriptive approach.

METHODS AND RESULTS

I have reviewed my own experience in examining congenitally malformed hearts. This shows that it is possible to select in all such hearts the most constant anatomic components to define the morphology of the atrial and ventricular chambers and the arterial trunks. These components are the appendages for the atriums, the apical trabecular regions for the ventricles, and the branching pattern for the arterial trunks. Thereafter, it is possible in all hearts to base description on the fashion in which the chambers and trunks are or are not joined together, describing separately any pertinent additional morphologic features or abnormal relationships.

CONCLUSIONS

By using this simple descriptive approach, which owes nothing to concepts of development, it is possible to give a basic description of each heart, and predict the location of the conduction tissues, even if the heart in question has never previously been encountered.