Patent foramen ovale (PFO)
Patent foramen ovale (PFO) is a valvular opening in the region of the fossa ovalis of the interatrial septum. Normally it remains closed due to higher pressure on the left atrial side than on the right atrial side. The direction of the foramen is such that it will permit only shunting of blood from right atrium from left atrium when the right atrial pressure is transiently higher than left atrial pressure as in certain phases of Valsalva manoeuvre. In conditions with grossly elevated right atrial pressures as in tricuspid stenosis, the valvular mechanism does not function as the foramen is stretched open (stretched open PFO). This can lead to paradoxical embolism and stroke even in the absence of grossly elevated right sided pressures. Some have advocated closure of the PFO by specially made devices in cases of recurrent strokes due to paradoxical embolism. PFO closure device differs from ASD (atrial septal defect) closure device in that the right atrial disc is larger than the left atrial disc.