Patent foramen ovale (PFO) and atrial septal defects (ASDs) are both openings in the interatrial septum, but they differ substantially with respect to morphology and functional consequences. Accordingly, although technical treatment details match in several aspects, treatment indications vary.
The interatrial septum is made from two overlapping embryological structures, the left-sided partially fibrous septum primum and the right-sided muscular septum secundum, forming the foramen ovale, a one-way slit valve for the physiological right-to-left shunt during in utero development located within the fossa ovalis. The postnatal enhancement of the pulmonary circulation and the decrease of right atrial pressure result in immediate functional closure of the foramen ovale by apposition of the septum primum against the septum secundum. In the months post partum, the septum primum on the left side and the septum secundum on the right side fuse permanently in the majority of cases. However, autopsy studies have shown that the foramen ovale remains patent in about one quarter of the general population1. Particularly in individuals with an atrial septal aneurysm (ASA), a congenital abnormality of the interatrial septum characterised by an enlarged septum primum with hypermobility and large pressure-depending excursions into the atria (>10 mm), the prevalence of a PFO is increased, ranging between 50% and 85%2,3. It can be said that ASA begets PFO and the same holds true for an Eustachian valve, cannulating the inferior vena cava inflow onto the foramen.
ASDs represent the second most common congenital heart defect, accounting for about 10% of all congenital heart defects in the adult population4. Familial occurrence is rare but described in about 2% of patients. There is an association with genetic diseases, like Down’s syndrome and the Holt-Oram syndrome.
Depending on the localisation in the atrial septum, ASDs are basically divided into four different types (Table 1). Briefly, the secundum ASD, which is the most common atrial septal defect type, is located in the centre or the septum; the primum ASD, the second most common type, is located adjacent to the atrioventricular valves and is usually associated with a valvular malformation (e.g., mitral cleft). The sinus venosus ASD is a defect near the junction of the superior or inferior caval vein and frequently associated with an anomalous connection of the right pulmonary veins to the right atrium or the superior vena cava. The coronary sinus defect (unroofed coronary sinus) directly connects the coronary sinus with the left atrium. All of them have similar haemodynamic consequences. However, only the secundum ASD can be treated interventionally and will be discussed in this paper.
The purpose of this manuscript is to provide a technical overview on PFO and ASD closure like a useful “how to” recipe rather than providing a review on the latest publications in this field.