Tricuspid atresia: current concepts in diagnosis and treatment

Tricuspid atresia with atrial and ventricular septal defects in a kitten

A 45-days-old mixed-breed female cat was referred to a veterinary specialty hospital for evaluation due to poor general condition, dyspnea of possible cardiac origin, and a heart murmur. The results of the physical examination, thoracic radiography, and echocardiography led to a diagnosis of hypotrophy of the right ventricle, tricuspid atresia, and atrial septal defect. Cardiovascular pathological findings confirmed the clinical diagnosis in addition to the observation of a ventricular septal defect. To the authors' knowledge, this is the first report of tricuspid atresia with atrial septal defect and ventricular septal defect in a cat.

The Superior Cavopulmonary Connection: History and Current Perspectives

The development of the superior cavopulmonary connection is a rich illustration of international influences in congenital cardiac surgery. The bidirectional Glenn and hemi-Fontan procedures have improved survival as both definitive and staged functional single ventricle palliation. The optimal timing of the second-stage superior cavopulmonary procedures varies by center but for low- and intermediate-risk patients, this may be within three to six months after the Norwood procedure. The list of risk factors continues to grow but the most frequently cited factors include atrioventricular valve regurgitation, decreased ventricular function, need for reintervention, and failure to attain nutritional and growth goals. Ongoing prospective, multi-institutional studies, particularly those fostered internationally by the World Society for Pediatric and Congenital Heart Surgery and other associations, will hopefully provide further clarification of the complex management issues related to patients with functional single ventricle physiology.

Canonical wnt signaling regulates atrioventricular junction programming and electrophysiological properties

RATIONALE

Proper patterning of the atrioventricular canal (AVC) is essential for delay of electrical impulses between atria and ventricles, and defects in AVC maturation can result in congenital heart disease.

OBJECTIVE

To determine the role of canonical Wnt signaling in the myocardium during AVC development.

METHODS AND RESULTS

We used a novel allele of β-catenin that preserves β-catenin's cell adhesive functions but disrupts canonical Wnt signaling, allowing us to probe the effects of Wnt loss of function independently. We show that the loss of canonical Wnt signaling in the myocardium results in tricuspid atresia with hypoplastic right ventricle associated with the loss of AVC myocardium. In contrast, ectopic activation of Wnt signaling was sufficient to induce formation of ectopic AV junction-like tissue as assessed by morphology, gene expression, and electrophysiological criteria. Aberrant AVC development can lead to ventricular pre-excitation, a characteristic feature of Wolff-Parkinson-White syndrome. We demonstrate that postnatal activation of Notch signaling downregulates canonical Wnt targets within the AV junction. Stabilization of β-catenin protein levels can rescue Notch-mediated ventricular pre-excitation and dysregulated ion channel gene expression.

CONCLUSIONS

Our data demonstrate that myocardial canonical Wnt signaling is an important regulator of AVC maturation and electric programming upstream of Tbx3. Our data further suggest that ventricular pre-excitation may require both morphological patterning defects, as well as myocardial lineage reprogramming, to allow robust conduction across accessory pathway tissue.

Factors associated with development of atrial septal restriction in patients with tricuspid atresia involving the right-sided atrioventricular valve

BACKGROUND

Clinical practice is discrepant regarding routine enlargement of the interatrial communication (IAC) in patients with right-sided atrioventricular valve atresia. We determined the percentage and risk factors of those who develop a restrictive IAC.

METHODS

Medical records were reviewed for patients treated from 1985 to 2006, including those admitted in the first 6 weeks of life (group A), and those referred at a later age (group B), some of whom had routine atrial septal procedures. In group A, we analyzed the initial postnatal echocardiogram.

RESULTS

Group A consisted of 79 patients, 16 of whom had an atrial septectomy as part of the initial surgical procedure. Of the remaining 63 patients, 9 (14%) developed atrial septal restriction. In group A, an atrial septal aneurysm (ASA) (OR 16, P = .006) and IAC diameter < 5 mm (OR 13, P = .009) were associated with atrial septal restriction. Atrial septal restriction occurred in 80% of patients with both features, 20% with IAC > or = 5 mm and ASA, 18% with IAC < 5 mm and no ASA, and 2% with neither feature. Group B consisted of 95 patients, 27 of whom had an atrial septal procedure. Of the remaining 68 patients, 11 (16%) developed atrial septal restriction.

CONCLUSION

Routine enlargement of the IAC is not necessary in patients with right-sided atrioventricular valve atresia. Patients with ASA or IAC < 5 mm are at increased risk for development of atrial septal restriction.

Outcome of listing for cardiac transplantation for failed Fontan: a multi-institutional study

BACKGROUND

The Fontan procedure is a successful palliation for children with single-ventricle physiology; however, many will eventually require heart transplantation. The purpose of this study was to determine risk factors for death awaiting transplantation and to examine results after transplantation in Fontan patients.

METHODS AND RESULTS

A retrospective, multi-institutional review was performed of 97 Fontan patients <18 years of age listed at 17 Pediatric Heart Transplant Study centers from 1993 to 2001. Mean age at listing was 9.7 years (0.5 to 17.9 years); 25% were <4 years old; 53% were United Network for Organ Sharing status 1; 18% required ventilator support. Pretransplantation survival was 78% at 6 months and 74% at 12 months and was similar to 243 children with other congenital heart disease (CHD) and 747 children without congenital heart disease (No-CHD), who were also awaiting transplantation. Patients who were younger, status 1, had shorter interval since Fontan, or were on a ventilator were more likely to die while waiting. At 6 months, the probability of receiving a transplant was similar for status 1 and 2 (65% versus 68%); however, the probability of death was higher for status 1 (22% versus 5%). Seventy patients underwent transplantation. Survival was 76% at 1 year, 70% at 3 years, and 68% at 5 years, slightly less than CHD and No-CHD patients. Causes of death included infection (30%), graft failure (17%), rejection (13%), sudden death (13%), and graft coronary artery disease (9%). Protein-losing enteropathy (present in 34 patients) resolved in all who survived >30 days after transplantation.

CONCLUSIONS

Heart transplantation is an effective therapy for pediatric patients with a failed Fontan. Although early posttransplantation survival is slightly lower than other patients with CHD, long-term results are encouraging, and protein-losing enteropathy can be expected to resolve.

ZFPM2/FOG2 andHEY2 genes analysis in nonsyndromic tricuspid atresia

Tricuspid atresia (TriAt), the third most common cyanotic congenital heart defect (CHD), consists of complete lack of tricuspid valve formation, with no connection between the right atrium and the right ventricle. To date, the genetic mechanism responsible of TriAt is still obscure. However, animal models have suggested a role of cardiogenic Zfpm2/Fog2 and Hey2 genes in the pathogenesis of TriAt. Therefore, we screened 40 individuals affected by nonsyndromic TriAt for ZFPM2/FOG2 and HEY2 gene mutations. No pathogenetic mutation has been identified, thus failing to demonstrate a major role of ZFPM2/FOG2 and HEY2 genes in the pathogenesis of human TriAt.

Outcomes of tricuspid atresia in the Fontan era

BACKGROUND

Whereas indications expand and results improve with increasing refinements to the Fontan procedure the overall impact on outcomes related to tricuspid atresia remains suboptimally defined.

METHODS

We reviewed 225 consecutive patients presenting between 1971 and 1999. All patients had classic tricuspid atresia with absent right atrioventricular connection and with D-transposition of the great arteries in 21%, pulmonary outflow obstruction in 75%, and aortic outflow obstruction in 11%.

RESULTS

Ten patients died before any intervention and 3 patients were lost to follow-up. Palliative procedures (includes 151 with systemic shunt, 27 pulmonary artery banding, 60 venous shunt) were performed in 203 patients, with 44 deaths, 8 patients awaiting Fontan, 12 patients Fontan contraindicated, and 11 patients lost-to-follow-up. A total of 137 patients had the Fontan procedure (9 patients without previous procedures) with 7 early deaths, 11 late deaths, and 3 patients progressing to heart transplantation. Total survival for the cohort was 90% at the age of 1 month, 81% at 1 year, 70% at 10 years, and 60% at 20 years with no significant change over the time period. Independent factors associated with ineligibility or death without Fontan (n = 68, 30%) included earlier birth date, lower birth weight, presence of aortic arch anomaly and greater right ventricular hypoplasia, and no palliative procedure. There were no significant changes in mortality with Fontan over the study time period with survival of 95% at 1 month, 93% at 1year, and 82% at 10 years.

CONCLUSIONS

Improvements in outcomes with tricuspid atresia will require attention to management and risk factors before Fontan.

Molecular embryogenesis of the heart

Development of the heart is a complex process involving primary and secondary heart fields that are set aside to generate myocardial and endocardial cell lineages. The molecular inductions that occur in the primary heart field appear to be recapitulated in induction and myocardial differentiation of the secondary heart field, which adds the conotruncal segments to the primary heart tube. While much is now known about the initial steps and factors involved in induction of myocardial differentiation, little is known about induction of endocardial development. Many of the genes expressed by nascent myocardial cells, which then become committed to a specific heart segment, have been identified and studied. In addition to the heart fields, several other "extracardiac" cell populations contribute to the fully functional mature heart. Less is known about the genetic programs of extracardiac cells as they enter the heart and take part in cardiogenesis. The molecular/genetic basis of many congenital cardiac defects has been elucidated in recent years as a result of new insights into the molecular control of developmental events.

A syndrome of tricuspid atresia in mice with a targeted mutation of the gene encoding Fog-2

Tricuspid atresia (TA) is a common form of congenital heart disease, accounting for 1-3% of congenital cardiac disorders. TA is characterized by the congenital agenesis of the tricuspid valve connecting the right atrium to the right ventricle and both an atrial septal defect (ASD) and a ventricular septal defect (VSD). Some patients also have pulmonic stenosis, persistence of a left-sided superior vena cava or transposition of the great arteries. Most cases of TA are sporadic, but familial occurrences with disease in multiple siblings have been reported. Gata4 is a zinc-finger transcription factor with a role in early cardiac development. Gata4-deficient mice fail to form a ventral heart tube and die of circulatory failure at embryonic day (E) 8.5 (refs 6,7). Zfpm2 (also known as Fog-2) is a multi-zinc-finger protein that is co-expressed with Gata4 in the developing heart beginning at E8.5 (refs 8-10). Zfpm2 interacts specifically with the N-terminal zinc finger of Gata4 and represses Gata4-dependent transcription. Here we use targeted mutagenesis to explore the role of Zfpm2 in normal cardiac development. Zfpm2-deficient mice died of congestive heart failure at E13 with a syndrome of tricuspid atresia that includes an absent tricuspid valve, a large ASD, a VSD, an elongated left ventricular outflow tract, rightward displacement of the aortic valve and pulmonic stenosis. These mice also display hypoplasia of the compact zone of the left ventricle. Our findings indicate the importance of Zfpm2 in the normal looping and septation of the heart and suggest a genetic basis for the syndrome of tricuspid atresia.

Tricuspid valve disease. Clinical evaluation, physiopathology, and management

The tricuspid and mitral valves are homologous whose function depends on coordination among components. Isolated tricuspid valve abnormalities are relatively uncommon. Rheumatic disease, chemicals, immunologic and degenerative disorders alter leaflet anatomy and may result in either stenosis, insufficiency or a combination. More often, tricuspid disorders present as a component of congenital syndromes or secondary to pulmonary vascular or let heart disease which alter geometry and function of nonleaflet components.

Cardiac evaluation of infants. The first year of life

Many structural congenital heart defects present at birth, and most are diagnosed by 1 year of age. Arrhythmias also are common during this time and may be particularly problematic. Identification of infants who may have a serious underlying congenital heart defect is important because many require prompt medical and surgical treatment. This article is a guide to the clinical findings that may assist the practitioner in the evaluation of infants with potential cardiac problems.

Magnetic resonance imaging of hearts with atrioventricular valve atresia or double inlet ventricle

OBJECTIVE

To investigate the effectiveness and limitations of magnetic resonance imaging in defining cardiac anatomy in patients with double inlet ventricle or atrioventricular valve atresia.

DESIGN

Magnetic resonance images were reviewed retrospectively without reference to other morphological data.

SETTING

A tertiary referral centre for paediatric cardiology.

PATIENTS

18 patients (aged 8 days to 27 years) with a suspected univentricular atrioventricular connection.

METHODS

Imaging by a 1.5 T whole body magnetic resonance system with imaging planes adjusted to individual patient anatomy to best define the cardiac morphology. A complete sequential diagnosis obtained from an independent interpretation of the images was compared with the diagnosis obtained from cross sectional echocardiography and angiocardiography.

RESULTS

There was substantial accord between the diagnosis from magnetic resonance alone and that from other methods. In the six instances where there was not accord the magnetic resonance diagnosis was considered to be correct in two cases and incorrect in three cases. In the remaining case no consensus could be reached. In eight patients magnetic resonance imaging provided anatomical information additional to that from other methods. The strengths of magnetic resonance were in imaging the pulmonary arteries and their abnormalities and identifying juxtaposed atrial appendanges but there were some deficiencies in identifying Blalock-Taussig shunts.

CONCLUSION

Magnetic resonance imaging provided detailed information about all aspects of cardiac morphology in patients with a suspected diagnosis of univentricular atrioventricular connection. Often it provided additional information to echocardiography. Its use in selected patients should give valuable complementary information.

Anaesthetic management of phaeochromocytoma associated with tricuspid atresia

The anaesthetic management of a patient with phaeochromocytoma, tricuspid atresia and pulmonary vascular stenosis is reported. The patient received no preoperative preparation with adrenergic blockers. Anaesthesia was induced and maintained with fentanyl, diazepam and sevoflurane. Intraoperative blood pressure was controlled with sodium nitroprusside, sevoflurane, phentolamine, and propranolol. For hypotension after resection of the tumour norepinephrine was required. This patient did not have a systemic to pulmonary shunt procedure performed, so the maintenance of pulmonary blood flow in the presence of haemodynamic instability during operation for phaeochromocytoma was a major concern. Monitoring of oxyhaemoglobin saturation (SpO2) with a pulse oximeter was considered to be useful because SpO2 may reflect pulmonary flow. During serious haemodynamic disturbances due to the manipulation of the tumour, the heart rate was inversely correlated with SpO2, but the relationship between mean arterial pressure and SpO2 was weak. Therefore, control of heart rate appeared to be more important than control of blood pressure in this case.