Pulmonary atresia with intact ventricular septum (PA/IVS) is one of the rare cyanotic congenital heart diseases, accounting for about 1% of congenital heart malformations. More than 50% of untreated cases die in the neonatal period and 85% die within 6 months of age.
Lesions include septal atresia with fusion of the pulmonary valve junction, varying degrees of stenosis of the annulus, and mild or moderate narrowing of the common pulmonary artery trunk. The tricuspid valve and right ventricle are hypoplastic, the ventricular septum is intact with secondary foramen ovale septal defect or patent foramen ovale, and an arteriovenous ductus arteriosus is necessary for survival of the child. Cardiac macrovascular connections are normal.
I. Pathologic anatomy
The main pathological features are the absence of direct right ventricle-pulmonary artery continuity and intact ventricular septum, both combined with secondary foramen ovale septal defect or patent foramen ovale. Pulmonary atresia generally occurs in the valve or valve and funnel. In the former case, the pulmonary valve is septal-like atresia, with complete fusion of the triple leaflet junction, and the pulmonary annulus and pulmonary trunk can be close to normal in diameter; in the latter case, it is less common, with muscular tissue at the base of the pulmonary valve and only shallow concave changes, atresia or severe dysplasia of the funnel, and dysplasia of the pulmonary valve annulus and pulmonary trunk.
In 45% of children, a right ventricular-coronary fistula is present, especially in children with severe right ventricular hypoplasia and small tricuspid valve openings, with a unique anatomic pattern of dependence on the right ventricular coronary circulation. Less than 10% of children have a combined inferior tricuspid valve malformation (Ebstein’s malformation), in which the right ventricle may be normal in size or even enlarged. Aortopulmonary collateral circulation is rare.
Clinical classification
There is no uniform clinical classification at home and abroad, and PA-IVS is classified according to the development of the right ventricle and tricuspid valve due to the need for surgical selection.
Bull and de Leval et al. classified PA-IVS into three types according to the different development of the right ventricular input, trabeculation, and funiculation parts: type I, in which all parts of the right ventricle are present but with some degree of dysplasia; type II, in which only the input and funiculation parts are present and the trabeculation part is occluded; and type III, in which only the input part is present and neither the funiculation nor the trabeculation part is developed.
Billingsley and colleagues classified PA/IVS as mild, moderate, or severe by combining the classification of Bull and Hanley et al. Hanley and Agnoletti et al. suggested that the diameter of the tricuspid valve and the size of the right ventricular cavity were positively correlated and that the diameter of the tricuspid annulus (Z value) was the determining factor for right ventricular development and the choice of procedure. The correction of the tricuspid orifice diameter (Z value) measured by right ventriculography or 2-dimensional echocardiography can be used to evaluate the surgical indications and guide the clinical procedure.
Mild dysplasia: The right ventricle is well developed, with a well-developed input and funneled, trabeculated portion and a well-developed outflow tract. The size of the right ventricular cavity is approximately 2/more than that of the normal control. The tricuspid valve Z value was between 0–2; moderate dysplasia type: the right ventricular cavity and tricuspid valve size were approximately 1/–2/ of normal controls. Three parts of the right ventricle are present, all hypoplastic. The degree of right ventricular outflow tract development allows for pulmonary valvuloplasty.
Tricuspid valve Z value between -2 and 4; severe dysplasia type: right ventricular cavity and tricuspid valve size less than 1/ of normal control. Only the inflow tract or three parts of the right ventricle are present and unrecognizable; the outflow tract is absent or the degree of development does not allow for pulmonary valvuloplasty. Tricuspid valve Z-values between -4 and 6. It is often combined with a right ventricular coronary fistula or even a coronary circulation dependent on the right ventricle.
III. Pathophysiology
Cyanosis is present in the neonatal period due to right ventricular hypertension and right-to-left shunt at the atrial level. The open arterial duct is the only source of pulmonary blood, and the child’s postnatal pulmonary blood flow and oxygen saturation are completely dependent on the shunt from the arterial duct. If the arterial duct is constricted or functionally closed after birth, this will result in pulmonary blood deficiency, progressively increasing hypoxemia and metabolic acidosis, and even death.
In right ventricular hypertension, blood entering the right ventricle flows back into the right atrium via the tricuspid valve or retrogradely into the coronary circulation through the myocardial sinusoidal gap, leading to severe consequences of coronary underperfusion and myocardial ischemia once right ventricular decompression is performed. Blood returning from the body vein enters the left ventricle and aorta through the foramen ovale or atrial septal defect to mix with pulmonary venous blood. However, the diameter of the foramen ovale or atrial septal defect can limit the amount of right-to-left shunt, and if its diameter is small, it can lead to high pressure in the right atrium and produce body vein stasis and low heart displacement in the body circulation.
Incidence
PA/IVS is one of the rare cyanotic congenital heart diseases, which accounts for about 1% of congenital heart malformations as reported by different cardiac centers abroad. More than 50% of untreated cases die in the neonatal period, and 85% die within 6 months.
V. Etiology
The embryologic mechanism of ventricular septal atresia is unknown, but it has been hypothesized that it is caused by a significant reduction in blood flow through the tricuspid valve and the right ventricle. In contrast, the mechanism of right ventricle-coronary artery fistulae is due to direct return of normal coronary venous return from the right ventricle into the right ventricle itself via the minimal cardiac vein (Thebesian) rather than back into the coronary sinus. The right ventricle is under high pressure due to pulmonary atresia and the return blood flows back into the coronary artery via the Thebesian vein.
VI. Clinical manifestations
Symptoms: Most children present with cyanosis of the cheeks, lips, and fingertips a few days after birth, pauses in breastfeeding, excessive sweating, short periods of shortness of breath, increased cyanosis, dyspnea, progressive hypoxemia, and moderate metabolic acidity. The degree of cyanosis depends on the amount of blood flow from the ductus arteriosus to the pulmonary artery, if accompanied by a large ductus arteriosus the degree of cyanosis, metabolic acidosis can be mild.
Signs: cyanotic face, inspiratory trismus, poor peripheral perfusion of the extremities. Most of the tricuspid regurgitant all-systolic murmur can be heard at the left edge of the sternum, or a systolic-dominant continuous murmur from the arterial duct can be heard, and the first and second heart sounds are single and the heart murmur is more variable.