Pulmonary atresia with intact ventricular septum (PAIVS)

What is Atresia of the Pulmonary Artery?

Atresia of the pulmonary artery with an intact interventricular septum is a congenital heart defect characterized by membranous or muscular atresia of the right ventricle outflow tract with an intact interventricular septum. It is an extremely severe defect with high morphological heterogeneity.

Embryology

Pulmonary atresia with VSD develops in the early stages of cardiac morphogenesis, during and immediately after ventricular separation. Pulmonary atresia with an intact interventricular septum forms thereafter. This conclusion is based on an analysis of a number of morphological factors - the diameter of the pulmonary trunk, anatomy of the ductus arteriosus and its valve.

Anatomy

This defect is characterized by normally formed atria and concordant atrioventricular connections. The interventricular septum is intact. The right ventricular outflow tract is completely closed. The right ventricle is hypoplastic to varying degrees and hypertrophied.

A normal tricuspid valve is rare; abnormalities vary from severe stenosis to severe regurgitation.

The left ventricle may be hypertrophied and rigid, especially in toddlers. In half of the patients mitral chordae tendineae are short and dysplastic. In patients with blood pressure in dysplastic right ventricle higher than systemic BP, the outflow part of the interventricular septum sometimes bulges into the left ventricular cavity.

Very often, this defect is accompanied by abnormalities of the coronary arteries.

Classification

The most commonly used classification is the Bull classification, based on the integrity of the right ventricle:

1. all departments are preserved (inlet, trabecular, infundibular);
2. trabecular part is absent;
3. trabecular and infundibular parts are absent.

Hemodynamics

Hemodynamic disturbances are determined by the absence of antegrade blood flow from the right ventricle into the pulmonary artery and impossibility to discharge this blood through the VSD into the left heart.

Severe hypoplastic ventricle (and tricuspid valve) filling with blood insignificantly, almost all blood flow from the right atrium is shunted through the patent foramen ovale into the left atrium. In cases where blood still enters the cavity of the right ventricle (in slightly hypoplastic right ventricle), its volume overload occurs, since emptying occurs only retrograde through the tricuspid valve and / or preserved sinusoids.

The absence of a natural outflow of blood from the right ventricle predetermines the presence of a right-left shunt at the atrial level through the patent foramen ovale or secondary ASD. Cases of prenatal closure of the foramen ovale lead to inevitable fetal death.

A patent foramen ovale and an alternative blood supply to the lungs (collaterals extending from the aorta) are essential for child’s survival. In this situation blood flows through the PDA from the aorta into the pulmonary artery already in the prenatal period (in contrast to the normal blood flow directed from the pulmonary artery to the aorta), hence the duct becomes a thin convoluted vessel.

After birth, in most cases, there is also ductus-dependent pulmonary circulation. In this case, the left ventricle pumps blood into both blood circulation circles.

For atresia of the pulmonary artery with an intact interventricular septum, severe disorganization of the coronary circulation is characteristic. It develops due to ventriculo-coronary connections and myocardial sinusoids.

Workup

• EchoCG, CT. The main method for visualizing the defect, assessing the degree of the right ventricle hypoplasia.
• ECG. The changes are nonspecific. The presence of a deviation of the heart axis to the left is possible.
• X-ray of the chest organs. Unclear pulmonary pattern.
• Angiocardiography is used to evaluate additional parameters.

Clinical presentation

The main symptoms are cyanosis, shortness of breath, drug-refractive right ventricular failure.

During the first hours of life, cyanosis can sharply worsen after the closure of the PDA. In rare cases, when the interatrial communication is insignificant, cardiac output and pulmonary blood flow, dependent on the volume of the right-to-left shunt, are reduced.

On auscultation, tones I and II are not split, a soft murmur of tricuspid insufficiency or a continuous murmur of the PDA is heard, especially after the start of the infusion of prostaglandin E. In severe tricuspid valve insufficiency, the murmur increases.

If the interatrial communication is not restrictive, the peripheral arterial pulse is palpable.

The liver is usually slightly enlarged. Significant hepatomegaly suggests inadequate interatrial communication and severe tricuspid valve insufficiency. Typical signs are hypoxemia, refractory to high concentrations of inhaled oxygen, and hypocapnia as a consequence of tachypnea.

Treatment

Basic therapy is aimed at reducing the body's needs for oxygen and correction of metabolic disorders. The emergency treatment is a prostaglandin infusion, which maintains the PDA and increases pulmonary blood flow. As an emergency care for obstructive foramen ovale and right ventricular failure, Rashkind procedure may be used. Objectives of surgical treatment: decompression of the right ventricle and creation of conditions for its development, restoration of effective pulmonary blood flow. As a rule, surgical interventions are multi-stage interventions. The choice of surgical tactics depends on the size of the right ventricle, the presence or absence of sinusoids, and coronary artery abnormalities.

In a right ventricle of adequate size and with perspective of growth, an outflow tract to the pulmonary artery is formed; thereby two-ventricular blood circulation is created. At the same time, a systemic-pulmonary shunt is formed to increase arterial saturation, since the hypoplastic right ventricle does not initially provide sufficient pulmonary blood flow. Since the first months of life are most important for optimizing tricuspid valve and right ventricular growth, the greatest possible decompression should be performed as early as possible.

There are several ways to create an anatomical connection between the right ventricle and the pulmonary artery:

1. reconstruction of the right ventricular outflow tract using transannular plasty, supplemented with a systemic-pulmonary anastomosis, is the optimal solution for subsequent biventricular correction later;
2. transpulmonary valvotomy, supplemented by a left-sided modified Blalock – Taussig shunt;
3. radiofrequency or laser perforation of the pulmonary valve, with or without balloon dilatation and stenting.

Two-ventricle repair is impossible in patients with the right ventricle, represented only by the inlet section. The only possible palliative method is the systemic-pulmonary shunt without right ventricle outflow tract repair. During diagnostic catheterization, balloon atrioseptostomy is performed, since the possibility of ventricular growth is excluded. Subsequently, the treatment adopted for the functionally single ventricle defect is carried out, i. E. Fontan circulation correction.

A particular problem is presented by patients with a rudimentary right ventricle, lack of proximal aortocoronary connection, distal stenosis and with sinusoids, which are the main source of coronary circulation, perfused by venous blood. The nature of the coronary arteries pathology determines operation method choice.