An interesting article published by one of our staff and residents on morning report can be found here.A prior blog on the causes of platypnea and orthodeoxia can be found here.
Review of PFO formation:
- The endocardial cushions fuse, separating the heart into R and L sides.
- Early in utero the septum primum grows and fuses with the endocardial cushion, closing the formaen primum, however perorations have developed in the septum primum to fuse, forming the foramen secundum (still allowing right to left shunting)
- A second membrane, the septum secundum, grows on the right atrial side of the septum primum. The septum secundum overlaps the foramen secundum, forming an incomplete septal partition that becomes the foramen ovale. The remaining septum primum forms a flap-like valve over the foramen ovale.
- After birth, normal circulation is established (left sided pressures>right sided) and the flap fuses in 75% of people by age 2. The remainder have a PFO.
- The PFO is completed covered, but not sealed and shunting can occur if there is a reversal in intracardiac pressures (i.e. right to left shunt).
- If an open communication exits (no flap) this is an ASD.
A debate on PFO closure (with respect to cryptogenic stroke) can be found in these two Circulation articles: Close v. Don't Close (or at least do an RCT).
