Patent foramen ovale (PFO) is a small opening in the wall of the heart that separates the two upper chambers or atria. It is due to a persistence of the fetal circulation where a flap-like opening does not close as it normally should after birth. It is very common to have a PFO and is found in approximately 20% of the adult population. This flap-like valve enables shunting (abnormal mixture of blood between the right and left sides of the heart), which is often dynamic and of variable degree.
PFO has been associated with a variety of clinical syndromes afflicting hundreds of thousands of people in the United States alone and is to be equally common in Europe and other regions of the world. These clinical syndromes include cryptogenic stroke, migraine headache, hypoxemia (low blood oxygen), decompression illness in divers, high altitude sickness, and sleep apnea. Standard of care for these clinical syndromes may vary but generally have focused on medications.
Open heart surgery to close PFO has been largely replaced by the development of catheter based therapies. PFO closure for these clinical syndromes has been an area of active clinical investigation. Multicenter randomized trials to evaluate treatment strategies include catheter closure of PFO versus sham closure with medical management for migraine sufferers. Other trials have compared closure of PFO versus medical therapy to reduce clot formation to prevent recurrent stroke in stroke victims. Most clinical trials have struggled to finish due to slow enrollment. There has also been concern that the patients with the most severe clinical syndromes and abnormal PFO anatomy and physiology have been underrepresented due to patient and provider unwillingness to accept randomization in FDA supervised clinical trials.
PFO closure has been advocated based on clinical evidence of effectiveness and safety from single center reports as well as an acceptance of a causative link between the presence of a PFO and several clinical syndromes. Specifically cryptogenic stroke and transient ischemic attacks (TIA) are felt to often be the result of presumed paradoxical embolism and hypoxemia from right to left atrial shunting. The causative link with migraines is under study. The causative link to hypoxemia is suggested by larger amounts of low oxygen content blood flowing thru the PFO from the right to left atrium.
The absence of FDA approval for any implantable PFO closure device or alternative strategies for catheter-based PFO closure has resulted in the off-label use of several devices approved for the closely related but distinct congenital heart defect, secundum atrial septal defect. CE Mark approval has been obtained for a number of PFO closure devices in Europe. Estimates of the number of PFO closures currently being performed in clinical practice using both approved devices in Europe and off-label devices in the United States are in the thousands to tens of thousands worldwide. The results from ongoing, properly controlled clinical trials of catheter PFO closure for a variety of clinical syndromes are anxiously awaited in order to guide and inform clinical practice.