PULMONARY VALVE ATRESIA WITH INTACT VENTRICULAR SEPTUM

In this cardiac malformation there is complete atresia of an otherwise well-formed pulmonary valve. The ventricular septum is intact; the right ventricular cavity is unusually small and the free wall is thick; the tricuspid valve annulus is usually small and the leaflets hypoplastic. The anomaly is to be distinguished from main pulmonary artery atresia with ventricular septal defect (severe tetralogy of Fallot or "pseudotruncus") and from severe pulmonary valve stenosis.

well-formed pulmonary valve. The ventricular septum is intact; the right ventricular cavity is unusually small and the free wall is thick; the tricuspid valve annulus is usually small and the leaflets hypoplastic. The anomaly is to be distinguished from main pulmonary artery atresia with ventricular septal defect (severe tetralogy of Fallot or "pseudotruncus") and from severe pulmonary valve stenosis. This is a relatively uncommon anomaly. It is estimated to represent 1%o of cases of congenital cardiac malformation, and to be present in 3%o of large collections of autopsied cases of congenital heart disease. Rowe and Mehrizel found three cases among 13,653 live births at National Women's Hospital in Auckland, New Zealand, but Keith, Rowe and Vlad2 mention an incidence of one in 70,000 children. Obviously, the incidence depends upon the age of the population being surveyed-the high neonatal mortality causes it to be much more common in studies of autopsy material or of heart disease in newborns.

PATHOLOGY
The obstruction to right vetricular outflow is complete. In most cases, the pulmonary leaflets are fused,4 and two or three raphes radiate from the center of the valve to the periphery. Occasionally there is also infundibular atresia (atresia of the bulbar ostium) or atresia of the main pulmonary artery. However, in the majority of cases, the main pulmonary artery is of normal or near normal size. The aorta is usually enlarged.
The size of the right ventricular cavity is variable and ranges from normal, or even enlarged, to extremely small and thick-walled. In the majority of cases, the right ventricular cavity is small. Keith et al.2 found a normal or large ventricle in only nine of 60 cases examined. Edwards3 likened the right ventricle to a peach, the stone of which has been removed. The endocardium is typically thickened, and occasionally the cavity contains a large thrombus.
The size of the tricuspid valve is proportionate to the size of the right ventricle. With a normal size right ventricle, there is usually anatomic evidence of tricuspid insufficiency (short or absent chordae tendineae; thick, rolled or redundant leaflets).2,4 When the ventricle is small, the tricuspid orifice and valve are hypoplastic. Occasionally a fully developed Ebstein's malformation is present.5 In some cases, where the right ventricle is very hypoplastic, intra-myocardial sinusoids permit communication from the cavity of the right ventricle directly to the coronary arteries.
The right atrium, left atrium, left ventricle and aorta are secondarily enlarged. The ductus arteriosus is usually patent, but tends to close in the first few weeks of life.1 The foramen ovale is always patent, but actual atrial septal defects occur in only about 20% of cases.2

Hemodynamics
Small right ventricle: Inflow obstruction predominates. The right atrial blood is diverted almost entirely to the left atrium. A small amount of right ventricular blood escapes into the coronary arteries.
Normal or large right ventricle: Outflow obstruction predominates. Blood passes in and out of the ventricle through the incompetent tricuspid valve. In both cases the ductus arteriosus is the only source of pulmonary blood flow.

Clinical Features
Cyanosis is usually marked, and occurs within a few hours after birth.
Approximately half of the patients are in congestive heart failure.1 The second heart sound is single. A murmur is audible in approximately two-thirds of the patients with this defect. It is usually a grade I-II/VI systolic ejection murmur along the left sternal border, and occasionally a continuous murmur is present.
Dyspnea, tachypnea, and hepatomegaly are common physical findings. Electrocardiogram The frontal plane QRS axis is usually between +600 and +1200, which helps distinguish this condition from tricuspid atresia with its typical left axis deviation. Between half and two-thirds of the patients have left ventricular hypertrophy (LVH)."-9 Although some authors report distinguishing type I cases (small right ventricle) and type II cases (normal right ventricle) on the basis of right ventricular hypertrophy (RVH) seen in the latter. there are many exceptions.6 The persistence of an LVH pattern as the infant grows seems to favor a type I lesion. However, the converse is not true, and many patients with type I lesions develop RVH as they grow older.8 Figure 1 shows the electrocardiogram from a 1 month old with pulmonary valve atresia and a diminutive right ventricle. Chest Roentgenogram The pulmonary vascular markings are usually, but not invariably, decreased. There is usually moderate cardiomegaly, the average cardiothoracic ratio being about 0.65. Patients with type II lesions tend to have more cardiomegaly. The pulmonary artery segment is frequently concave (Fig. 2).

Cardiac Catheterization
There is usually significant systemic arterial desaturation. In type I lesions, RV pressure is usually equal to or greater than systemic. In type II lesions with severe tricuspid insufficiency, RV pressure tends to be lower. Right ventricular angiography is essential for an accurate diagnosis. In type I lesions, the findings are (1) a very small ventricular cavity with a narrow outflow tract ending blindly at the usual location of the pulmonary valve, (2) marked stasis of contrast media in the right ventricular cavity, (3) presence of myocardial sinusoids and (4) tricuspid regurgitation. Figure 3 demonstrates this type of lesion. The findings are similar in type II lesions except that the right ventricular cavity is larger. It is occasionally difficult to make an accurate assessment of cavity size. Type I lesions with large myocardial sinusoids which communicate and become confluent may be mistaken for part of the true cavity.
Freedom et al. 10 Fig. 2. Chest roentgenogram from a 2-month-old with pulmonary atresia. The heart is enlarged, with decreased pulmonary vascular markings. Etiology of the densities in right chest has not been determined-they may represent callus from fractured ribs. '152 artery (reached via a systemic-pulmonary anastomosis). They feel thistechnique allows better evaluation of the length of the atretic area, and may help plan subsequent surgery. Differential Diagnosis The most common cause for cyanosis when there is no murmur in the newborn period is transposition of the great arteries; cardiac catheterization may be necessary to distinguish transposition from pulmonary valve atresia.
Tricuspid atresia can usually be distinguished by the electrocardiogram'-which typically reveals left axis deviation. Ebstein's anomaly may= be as-sociated with severe cyanosis; but typically produces a triple or quadp--le rhythm and marked right atrial enlargement. Furthermore, in Ebstein's the heart may seem disproportionately large for the degree of respiratory distress and the echocardiogram is frequently diagnostic.
Tetralogy of Fallot usually causes a more prominent systolic ejection murmur, does not cause congestive heart failure, and is associated with RVH and right axis on the electrocardiogram. Natural History Although adults have been reported with this anomaly, the majority of patients die in the first year of life, usually in the first three months. Treatment Essentially, all infants with pulmonary valve atresia and intact ventricular septum require early palliative surgery. A variety of operative procedures have been employed. Early attempts focused on the pulmonary valve, using either a direct pulmonary valvotomy or a closed (Brock) procedure. Systemic to pulmonary artery anastomoses have also been utilized, especially the Potts procedure. More recently, Rashkind balloon atrial septostomy has been combined with either a systemic to pulmonary artery anastomosis, or an anastomosis and a pulmonary valvotomy. The early surgical results were very poor. Trusler and Fowler," reporting their early experience with valvotomies, noted ten early and four late deaths among 14 patients. They combined infundibulectomy with valvotomy in six cases-all died. Gersony8 reported 13 deaths in 15 cases employing a variety of approaches-Blalock-Taussig anastomoses, Brock procedures, and caval-pulmonary anastomoses.
Dhanavaravibul et al.6 reported 11 survivors among 15 patients treated with systemic-pulmonary anastomosis (three had Rashkind septostomy as well). However, there were seven late deaths, five at the time of a second operation.
Bowman et al.12 recommended combining balloon septostomy with transventricular pulmonary valvotomy and an ascending aorta-to-right pulmonary artery anastomosis, the latter procedures being performed through a right anterior thoracotomy incision. Of five patients treated in this manner, four survived and two have undergone intracardiac repair of the defect. Others recommend performing the shunt and an atrial septectomy early, followed by a valvotomy three to four months later.'3 Shams et al.14 reviewing recent experiences in Toronto, reported seven survivors in eight patients treated with balloon septostomy, ligation of the ductus arteriosus, and a Potts anastomosis.
The overall surgical results in 133 cases are summarized in Table 1. Valvotomy alone, or creation of a shunt alone, has a very high mortality. The outlook for those treated with valvotomy and a shunt appears somewhat better, but the number of patients treated in this manner is still relatively small. The underlying assumption behind this form of treatment is that the right ventricular cavity can grow if antegrade flow can be established by valvotomy. Although there is evidence that this may occur in some cases,12 further experience is necessary to determine if this is a common phenomenon. Even in the presence of a normal size right ventricle, abnormalties of the tricuspid valve may preclude complete correction.'9