The most severe variant involves the presence of severely hypoplastic main pulmonary arteries and branch pulmonary arteries, alongside agenesis of the patent ductus arteriosus. Blood flow to the lungs comes from various dysplastic (malformed) blood vessels from the thoracic aorta called major aortapulmonary collateral arteries, these blood vessels narrow down as time goes on. Causes
Although this birth defect is congenital, the exact cause is unknown, and it may vary between children with the condition, the following factors have been known to influence the risk of a baby being born with the condition:

Genetics
The molecular genetics of this condition isnt known in most people with PA(VSD), however, there have been candidate genes found to be possibly implicated in the pathogenesis of this condition:
DNAH10
DST
FAT1
HMCN1
HNRNPC
TEP1
TYK2
NDRG4
TBX5
NKX2.5
GATA4There have also been copy number variants described in the medical literature as associated with PA(VSD):
Deletion in chromosome 16p11.2
Deletion in chromosome 5q35.3
Deletion in chromosome 5p13.1
Deletion in chromosome 22q11.2
Deletion in chromosome 15q11.2
Deletion in chromosome 8p23.2
Deletion in chromosome 17p13.2
Duplication in chromosome 5q14.1
Duplication in chromosome 10p13A 1998 study done in Britain revealed that children with a mother who had a congenital heart defect (including PAVSD) had a higher risk of being born with a congenital heart defect themselves than those whose father had a congenital heart defect. Syndromes
Some cases of PA(VSD) have been associated with genetic syndromes such as VACTERL association, Alagille syndrome, CHARGE syndrome, trisomy 13, 18, and 21. Environmental
While congenital heart defects cant be acquired, they can also be caused by environmental factors the mother exposed herself to before and/or during pregnancy, these include:
Smoking
Certain medications (e.g.
Complications
Children with this condition are at a higher risk of developing the following complications:
Failure to thrive
Recurrent chest infections
Endocarditis
Epilepsy
Stroke
Arrhythmia
Heart failure
Premature deathChildren whose PAVSD is caused by DiGeorge syndrome (also known as 22q11.2 deletion syndrome) are more likely to suffer from the post-surgical complications (especially respiratory ones) associated with surgeries that treat this defect.Women with PAVSD are at a slightly higher risk of being infertile and having miscarriages or children with a congenital heart defect.Airway hyperresponsiveness is a commonly seen co-morbidity among those afflicted with PAVSD. Pathogenesis
Pulmonary atresia in PAVSD takes place during the first 8 weeks of fetal life, when the pulmonary valve that is supposed to form, fails to form, this doesnt allow blood to flow through the pulmonary artery from the right ventricle. The ventricular septal defect associated with PAVSD lets the right ventricule form.In some cases of PAVSD, major aortopulmonary collateral arteries develop; in a normal fetus, these arteries usually develop but then start deteriorating after pulmonary arteries grow, in fetuses with PAVSD, the pulmonary arteries dont develop, and this gives a chance to the major aortopulmonary collateral arteries to develop fully. Pathophysiology
The mildest variant of pulmonary atresia with ventricular septal defect involves pulmonary atresia with normally developed main pulmonary artery and branch pulmonary arteries, the blood that flows to the lungs from the right side of the heart goes to the left side of the heart through the ventricular septum which then flows through the patent ductus arteriosus.