Continuing Education Activity

Pulmonary atresia with ventricular septal defect is a rare congenital anomaly with poor prognostic outcomes. It is a serious anomaly affecting the development of pulmonary trunk and the membranous portion of the interventricular septum. To avoid the high morbidity and mortality associated with this condition, it must be promptly diagnosed and treated. This activity reviews the evaluation and treatment of pulmonary atresia with interventricular septal defect and highlights the role of the interprofessional team in evaluating and treating patients with this condition.

Objectives:

• Identify the etiology of pulmonary atresia with ventricular septal defect medical conditions and emergencies.
• Outline the evaluation of pulmonary atresia with ventricular septal defect.
• Review the management options available for pulmonary atresia with ventricular septal defect.

Introduction

Pulmonary atresia with ventricular septal defect (PAVSD) is one of the cyanotic congenital heart diseases. It occurs due to under or maldevelopment of the right ventricular outflow tract along with atresia of the pulmonary valve and trunk. It also involves overriding of the aorta and a large ventricular septal defect.[1] Previously it was termed as truncus arteriosus type IV. Whether it is a different entity or a severe form of Tetralogy of Fallot (TOF) is still controversial, but there is no denying the occurrence of PAVSD.

The spectrum of this defect varies in presentation and severity largely depending on the degree to which the pulmonary artery atresia is present. The major difference between the usual presentation of TOF and PAVSD is the presence of normal pulmonary trunk and arteries in TOF. A second prominent difference is the presence of major aortopulmonary collateral arteries (MAPCA) in PAVSD. Another notable difference is the presence of pulmonary valve atresia in PAVSD, unlike TOF where the pulmonary valve stenosis is prominent. Some physicians prefer to call this entity as TOF with pulmonary atresia and MAPCA.[2] 

Although when severe enough, TOF overlaps significantly with PAVSD and may even be managed as such, the management hardly changes so there is no ambiguity about consensus at least treatment-wise. For the purpose of this article, we are going to consider PAVSD as a separate entity from classical TOF. 

Etiology

The etiology of PAVSD is yet unknown. But several risk factors have been linked with the incidence of it. A genetic component has been suggested in literature but the level of evidence is weak.[3] Among the risk factors are reported so far are:

• History of congenital heart diseases in either father or mother.
• History of intake of teratogenic drugs by mother
• Smoking during or before pregnancy
• Poorly controlled diabetes
• Pregnancy in elderly

These risk factors are not specific to PAVSD and are also found frequently associated with other congenital anomalies.

Epidemiology

The incidence of congenital heart diseases is decreasing day by day because of the avoidance of known teratogens and risk factors by the patients through their education and counseling. The incidence of pulmonary atresia is also falling down. The prevalence of pulmonary atresia in the years 1999 to 2000 was 12.1% of all congenital heart diseases, which gradually went down to 9.6% in 2008 (p=0.01).[4]

Pathophysiology

In PAVSD, the degree of pulmonary artery involvement steers the clinical picture and the treatment options. It may present as isolated valvular atresia or with proximal pulmonary trunk involved. The right and left pulmonary arteries may or may not communicate. Major aortopulmonary collateral arteries (MAPCA) usually supply the lung parenchyma. These MAPCA arise may arise from the thoracic or abdominal aorta, subclavian arteries, internal mammary arteries, intercostal arteries, etc. MAPCA are usually aberrant and stenosed at either end. In other instances, patent ductus arteriosus (PDA) may also contribute to supplying pulmonary circulation.

The intrapulmonary arterial structure mainly relies on the size and flow of PDA. In the absence of PDA, or too many aberrant MAPCA, the intrapulmonary arteries may not be developed properly leading to pulmonary hypertension. The associated VSD is usually membranous in origin. Other defects like atrial septal defects are also not uncommon but their association with PAVSD is not well understood. The right ventricle may hypertrophy in response to pulmonary atresia. The left chambers of the heart are usually normal. The coronary artery network is usually normal but may rarely present with fistulas.[5][6]

Due to the atresia of the pulmonary arteries and valve, the right ventricle is unable to pump the blood adequately towards pulmonary circulation. This situation is incompatible with life in severe cases where the valve is completely atretic since the blood oxygenation is severely diminished. The pressure in the right ventricle increases equal or above to that of the left ventricle. The presence of the associated defect in the interventricular septum (VSD) plays a key role. Blood then flows towards the path offering the least resistance which in this case is left ventricle via the VSD leading to the right-to-left shunting of blood.

The overriding position of the aorta has a compensatory role by receiving the blood from both the ventricles and pump it to both systemic circulation and pulmonary circulation via the patent ductus arteriosus. Patency of ductus arteriosus is crucial in the initial survival of these patients. In mild to moderate cases where the pulmonary vasculature and valve are mildly atretic, the right ventricle can pump adequate blood in the pulmonary circuit for oxygenation. PDA in these cases may spontaneously collapse before the presentation.

History and Physical

Although evident in fetal ultrasound at 18 to 22 weeks gestation, many cases may go unrecognized in whom the mother refuse prenatal care or does not have access to the appropriate maternal healthcare resources. In these situations, the case may be first recognized on history and physical examination usually at birth. The clinical presentation of the PAVSD is highly variable depending on the degree of pulmonary atresia. Some of the common symptoms in history include:

• Central cyanosis may present as bluish discoloration of the face, particularly around the mouth and lips. In severe cases, it may be seen in peripheral limbs as well.
• Increased respiratory rate or shortness of breath due to poor oxygenation of blood. May not be evident at rest and only present at exertion i.e during crying or breastfeeding.
• Easy fatigability may present as weak cry, loss of tone, and poor latch to breast.
• Difficulty feeding.

The physical exam may reveal central cyanosis, a holosystolic murmur at the left sternal border that may radiate to the back or axilla, single accentuated second heart sound S2, a machine-like continuous murmur of PDA best heard at upper chest or the interscapular region on the back, weak grip, low weight for age, and lethargy. Peripheral edema, clubbing, and worsening cyanosis may indicate congestive heart failure if presented very late.[6]

Evaluation

Following investigations is a part of the comprehensive evaluation of PAVSD patients:

• Pulse oximetry to evaluate oxygen saturation (especially in dark-skinned infants where cyanosis may be missed on physical exam).
• Arterial blood gasses.
• Baseline hemoglobin and blood cell indices.
• Genetic testing particularly if other congenital defects are present.
• Chest X-ray (absent pulmonary artery shadow, boot-shaped heart or cardiomegaly, poor lung vasculature markings, etc).
• Echocardiography (pulmonary valve atresia, overriding of the aorta, VSD, ASD, some MAPCA if present, the pressure gradient across valves, ejection fraction).[6]
• MRI/CT (important to delineate vascular anatomy before surgery to plan correction, may reveal other MAPCA which are hard to see on echocardiography).[7]
• Cardiac categorization and angiography (anatomy, size, and distribution of the arterial vasculature, pressure in the right ventricle, the pressure gradient across the pulmonary valve).

Treatment / Management

Medical management: Oxygen saturation is critical and should be monitored continuously. Similarly, fluid balance and acidosis if present are needed to be addressed urgently. Since the neonate is usually unable to feed well, nutritional rehabilitation might be needed as well. In severe cases where the pulmonary valve is completely atretic and is the pulmonary circulation is entirely dependent on ductus arteriosus, prostaglandin E2 should be considered to keep it open until surgical correction can take place. Symptomatic treatment with diuretics or digoxin is indicated if the patient is going into congestive heart failure. 

Surgical management: Mainly, the size of the pulmonary arteries, presence/absence of MAPCAs, and PDA drive the surgical plan. Although the ideal surgical approach lacks consensus due to the extreme variation in anatomy, staged palliation is favored by most surgeons over early total correction.

Staged Palliation

The surgical treatment of PAVSD is a staged approach that involves several admissions and many operations without any fixed number. The steps of correction are as follows.

1) Blood flow is established first in the pulmonary arteries by connecting it directly to the aorta through a modified Blalock-Taussig shunt.

2) The right ventricle is also connected to the aorta temporarily if the overriding is insufficient.

3) As the pulmonary arteries grow in size due to sustained blood supply from the aorta, the pulmonary circulation is then connected to the pulmonary artery.

4) The right ventricle is connected back to the pulmonary artery.

5) The MAPCAs are closed in the next step usually at six months of age if the respective lung segments are receiving enough supply through the now developed pulmonary arteries.

6) VSD is repaired at the end usually at age 1 to 3 years. The major benefit of this approach is the whole procedure becomes more tolerable by the already feeble neonate and breaks are available to it for healing. In contrast to staged repair, the other approach is complete repair in one surgery. This procedure is only suitable for limited candidates who are on the low end of the severity spectrum. 

Early Total Correction

In this less popular approach preferred mostly in mild cases, surgeons usually correct the anatomy within the same admission if not the same operation. The patients are carefully picked and risks versus benefits are analyzed critically before picking this option.

Cardiac Transplant

In patients with the completely atretic pulmonary system, or who have failed the surgical corrective measures, a cardiac transplant can be the viable option.[6]

Differential Diagnosis

Differential diagnoses of PAVSD include:[8][9]

• Severe tetralogy of Fallot
• Transposition of the great arteries with pulmonary stenosis
• A single ventricle with severe pulmonary stenosis 
• Tricuspid atresia
• Pulmonary atresia with the intact interventricular septum
• Double-outlet right ventricle with pulmonary atresia
• Double-inlet left ventricle with pulmonary atresia
• Congenitally corrected transposition of the great arteries (L-TGA) with ventricular septal defect (VSD) and pulmonary atresia

Prognosis

The prognosis of PAVSD is especially poor if left untreated. About 50% of patients die within the first two years of life. With proper treatment and follow-up, 65% of the patients who are alive at 1 year are able to live beyond the age of 10.[10]

Complications

On top of surgical and anesthesia complications in treated patients, some of the complications of PAVSD are:

• Congestive heart failure (CHF)
• Reactive erythrocytosis in response to chronic hypoxia
• Infective endocarditis due to the aberrant flow of blood
• Sepsis either due to infective endocarditis or poor immune system development
• Delayed growth and puberty
• Arrhythmias
• Sudden death

Consultations

Pediatric cardiologists, pediatric cardiac anesthesiologists, pediatric surgeons, and geneticists should be consulted for appropriate assessment and management.

Deterrence and Patient Education

Education of parents regarding congenital heart diseases is important as the prognosis is particularly poor and the patient usually requires multiple surgeries for correction of anomalies. Parents should also be counseled regarding performing cardiopulmonary resuscitation in children. Genetic counseling should be provided to plan future pregnancies. Possible termination of pregnancy should be discussed as an option if presented in the early fetal stage.

Enhancing Healthcare Team Outcomes

PAVSD is a rare disease and presents with a wide variety of clinical signs and symptoms overlapping with other congenital anomalies. Patients may initially present with vague symptoms like feeding difficulty and lethargy. A comprehensive evaluation is required to reach a final diagnosis and that too with the consultation from different departments like pediatric cardiology, pediatric surgery, geneticists, etc. History and physical exam are usually not enough and investigations are required to diagnose it. [Level 4]

Mostly, the pediatricians are the ones who see these patients first. Since it is a rare condition, they are usually referred to pediatric cardiologists when echocardiographic or CT/MRI scans reveal the cardiac defects. Radiologists play a vital role in determining the underlying defect. It is vital to get the pediatric surgeons involved in plan and assessment. The nutritionists are an essential part of the team to take care of the nutritional requirement of the patient as they often face feeding difficulties.

Geneticists are also an important part of the team to provide counseling on future pregnancies. As the mainstay of treatment is surgery, the preoperative, as well as postoperative management, is crucial and needs anesthetists to play their role effectively. Pharmacists are responsible for the correct dosage of the medicine. A team-based approach is crucial to providing the best possible care to these patients. The outcomes of a PAVSD depend on the time of presentation and extent of severity. However, to improve outcomes, prompt consultation with an interprofessional group of specialists is recommended.