Introduction

What is Tricuspid atresia?

Tricuspid atresia (TA) is a type of cyanotic congenital heart disease (CCHD), characterised by a complete obstruction of the atrioventricular valve, which is consistent with the right ventricular anatomical configuration. TA is an example of single-ventricle physiology. In addition, it is the third most common type of CCHD.¹

Overview of heart failure (HF) in congenital heart disease

Heart failure is related to high morbidity and mortality and is considered to be the most common cause of death in adults with congenital heart disease (ACHD). A combination of clinical suspicion from subjective patient history, anatomic imaging, functional diagnostic studies, and rhythm evaluation establishes the diagnosis of heart failure. Once diagnosed, the management of HF in this population varies widely and by lesion.²

Pathophysiology of Tricuspid atresia

The exact cause of tricuspid atresia (TA) remains unclear, but it is believed to result from a disruption in the development of the tricuspid valve. The process of atrioventricular (AV) valvulogenesis is complex and involves several pathways, including Wnt/β-catenin, bone morphogenetic protein/transforming growth factor-β, and Ras/extracellular-signal-regulated kinase (ERK). Certain genetic mutations in these pathways have been linked to specific instances of TA, such as a germline homozygous missense mutation in the RASA1 gene, which is responsible for regulating the Ras/ERK signaling cascade. Additionally, compound heterozygous missense mutations in the NFATC1 gene, which functions further downstream in the Ras/ERK pathway, have also been identified. While the familial occurrence of TA is considered to be very rare, there have been reports of an autosomal recessive inheritance pattern in some cases.³

Types and staging of heart failure in TA patients

• Type I: This type is characterised by normal anatomy of the great arteries
• Type II: This type comprises D-transposition of the great arteries (D-TGA)
• Type III: This type consists of malposition defects, like truncus arteriosus, atrioventricular septal defects, and double outlet right ventricle, involving the great arteries other than D-TGA⁴

Blood flow in patients with pulmonary obstruction

Pulmonary atresia is seen in patients who have normally positioned great arteries and no ventricular septal defect (VSD). In this condition, the lungs receive blood supply primarily through a patent ductus arteriosus (PDA). In type Ia tricuspid atresia, blood flows from the right atrium through the atrial septum into the left atrium, and then it moves down through the mitral valve into the left ventricle.

Blood flow in patients without pulmonary obstruction

Patients with transposition of the great arteries usually present with ventricular septal defects (VSDs) and generally experience unrestricted pulmonary blood flow (type IIc). Unlike patients with other types, these individuals do not depend on the patent ductus arteriosus (PDA) for pulmonary blood flow. In type II tricuspid atresia, blood from the right atrium is redirected into the left atrium via the mitral valve, flows into the left ventricle, and is then pumped out through the pulmonary artery (see Image: Blood Flow in Patients Without Pulmonary Obstruction).

Acute and chronic heart failure in TA

Chronic heart failure can be "compensated" or "decompensated". In the compensated state, symptoms are stable, and most overt features of fluid retention and pulmonary oedema are absent. Acute heart failure may be related to an extensive myocardial infarction, sustained cardiac arrhythmias or mechanical problems.⁵

Right ventricular vs. left ventricular failure

Thus, most patients with advanced heart failure with reduced ejection fraction assessed for an LVAD have some form of right ventricular dysfunction. Therefore, RVF remains an extremely common complication associated with LVAD placement. Severe RVF following LVAD implantation increases perioperative mortality and lengthens hospital stays. RVF may also lead to coagulopathy, altered metabolism of drugs, worsening nutritional status, diuretic resistance, and inferior quality of life.⁶

Clinical presentation and diagnosis

Echocardiogram This non-invasive imaging technique uses sound waves to depict images displaying the blood flowing through the heart and heart valves and shows the congenital absence of one valve (the tricuspid) and irregularities of blood flow. Two-dimensional echocardiography is capable of showing the absence of the tricuspid.⁴

Electrocardiograms, pulse oximeter, chest X-ray, cardiac catheterisation and laboratory tests are diagnostic tools.

Management and treatment approaches

The first management of the condition is stabilisation of the patient. For cyanotic patients presenting in severe or critical PS or a very small VSD and who depend on a ductal-dependent pulmonary blood supply, initiation of prostaglandin within a short time after birth is crucial. Those who present later in infancy with heart failure and pulmonary overcirculation may require diuretics as part of the indicated treatment.⁴

The Fontan procedure is a procedure to redirect systemic venous blood directly into pulmonary arteries without the need to traverse the right ventricle. This is a palliative procedure bypassing the atretic tricuspid valve. In practice, creating a Fontan circulation often involves multiple stages of repair.⁴

Patients with pulmonary obstruction

In patients presenting pulmonary obstruction, the first step is providing adequate pulmonary blood flow using a systemic-to-pulmonary artery shunt. Often, this is best done with a modified Blalock-Taussig (BT) shunt, also known simply as a BT-Thomas shunt. This involves creating an anastomosis between the right subclavian and pulmonary arteries, typically done using a polytetrafluoroethylene tubular graft.

Patients without pulmonary obstruction

For patients with unobstructed pulmonary blood flow (type IC), a pulmonary artery band may be placed initially to limit the overwhelming flow to the pulmonary vascular bed. In some instances, the VSD is small enough that pulmonary blood flow is limited naturally, there is, therefore, a balanced circulation. Therefore, pulmonary artery banding is not required for these patients, as they have balanced circulation and proceed to the second stage of palliation, as described below.

Patients with D-TGA and subaortic obstruction

For the patients with type II lesions in which the VSD is obstructive to aortic flow, the first stage may consist of enlargement of the VSD or use of the Damus-Kaye-Stansel procedure, an anastomosis between the main pulmonary artery and ascending aorta, combined with a modified BT shunt.⁴

Prognosis 

The risk of mortality in these unoperated patients is quite high, particularly within the first year of life. The current era of early diagnosis and effective surgical interventions has allowed most patients with tricuspid atresia to survive into adulthood, maintaining good functional capacity. Operative mortality associated with the Fontan procedure is always less than 2%. A detailed assessment by Sittiwangkul et al., in 2004, addressing specifically the result in patients who had tricuspid atresia (over the period 1971 through 1999), showed overall survival rates were 82% at 1 year, 72% by 5 years, and 61% for 20-year survivors.

Advances in surgical techniques and innovations to address the conditions of patients have improved surgical outcomes. A recent study by Mery et al, who analysed outcomes of patients undergoing the Fontan procedure for various pathologies, including tricuspid atresia, showed a transplant-free survival rate of 92% at 15 years and an 87% freedom from Fontan failure.⁴

Future directions and research perspectives

Several studies are also examining neurodevelopmental results in the tricuspid atresia cohort, who is at risk for delayed development, attention-deficit hyperactivity disorder, and learning disorders. As people with tricuspid atresia now live longer, the ACHD specialist assumes a more vital role in providing care and monitoring for potential long-term complications. The 2018 guidelines for adult congenital heart disease treatment point out that care should be transitioned from paediatric cardiologists to ACHD specialists smoothly and effectively, especially at the end of late adolescence into early adulthood. This interprofessional team paradigm, collaborative in nature, is expected to produce better results.⁴

Summary

Tricuspid atresia is a complex congenital heart disease, associated with marked morbidity and mortality. Awareness of the varied presentations of the condition, required investigations, and multiple stages in surgical palliation is critical. Future research should aim to focus on pathophysiology, interstage outcomes, and postoperative or long-term management in TA patients. It is an area that may grow in importance with the improvement in the longevity of patients' lives.