Anomalies of Pulmonary Venous Return

Definition

APVR is defined as abnormal drainage of pulmonary venous blood into the systemic venous system. Total APVR is characterized by the anomalous drainage of all the pulmonary veins, whereas partial APVR is characterized by the anomalous drainage of one, two, or three of the four pulmonary veins.

Prevalence and Epidemiology

The incidence of APVR has been reported to be 1 : 10,000 live births, with an incidence of approximately 2.2% of patients with congenital heart disease (CHD).

Etiology and Pathophysiology

The main consequence of APVR is interruption of the normal circulation of blood that enters the left atrium after closure of the foramen ovale. In total APVR, there is virtually no oxygenated blood return to the left atrium, left ventricle, and aorta. Immediate and increasing hypoxemia and acidosis are the rule, which can be reversed only by emergency postnatal cardiac surgery.

APVR can be classified by the location of the abnormal drainage and further designated as being with or without obstruction, as follows :

• Type I: supracardiac (50%). The four pulmonary veins drain into a venous collector located behind the left atrium, from which a vertical vein runs up to reach the innominate vein, and this terminates in the right superior vena cava and right atrium. It has been reported that the vertical vein may be obstructed, but this is rarely severe in the perinatal period.

• Type II: cardiac (25%). The pulmonary veins drain through the coronary sinus or directly into the right atrium. Usually, there is no obstruction.

• Type III: infracardiac or infradiaphragmatic (20%). The pulmonary veins converge into a descending vertical vein that reaches the abdomen through the diaphragm. It usually drains into the portal vein or, more rarely, into the ductus venosus or the inferior vena cava. Almost always, the vertical vein is significantly obstructed.

• Type IV: mixed (5%). The pulmonary veins drain separately to different sites.

APVR can be an isolated lesion or occur in combination with other cardiac defects, such as single ventricle, hypoplastic left heart syndrome, truncus arteriosus, transposition of the great arteries, and heterotaxies. Associated chromosomal anomalies are rare, but some cases are described (unbalanced translocations).