2 The procedure
2.1.1 A PFO is the persistence of an opening (the foramen ovale) in the septum between the right atrium and left atrium of the heart. In the fetus, the foramen ovale allows blood to bypass the lungs, directly from the venous to the arterial side of the circulation. After birth the foramen ovale normally closes but in approximately 25% of people it remains either fully or partially patent throughout life. Usually a PFO causes no symptoms, although a 'shunt' or movement of blood from the right to left side of the heart may be demonstrable using specialist tests.
2.1.2 During a dive, inert gas (usually nitrogen or helium) accumulates within blood and tissues. On ascent, provided that appropriate decompression schedules are followed, excess gas is excreted via the lungs. However, during deep or long duration dives, venous gas emboli (VGE) often form, and in the presence of a PFO, VGE may become arterialised, resulting in neurological symptoms that may resemble a stroke (termed 'neurological decompression illness').
2.1.3 There is currently no consensus on the optimal management of divers with a PFO and a history of neurological decompression sickness.
2.2.1 Percutaneous closure of PFO for the secondary prevention of recurrent paradoxical embolism in divers is carried out with the patient under local anaesthesia and intravenous sedation, or general anaesthesia. A guidewire and delivery sheath are introduced via a small incision in the femoral vein into the heart and across the PFO. A closure device is then inserted through the opening via the delivery sheath and released, closing the PFO.
2.2.2 A range of different devices are available for this procedure.
2.3.1 Immediate closure of the PFO (confirmed with echocardiography) was reported in 99% (148/150), 89% (42/47), 97% (179/185), 100% (76/76) and 99.8% (823/825) of patients in studies across a range of indications.
2.3.2 A case series of 29 divers treated by percutaneous closure of PFO for neurological decompression sickness reported that 79% (23/29) had returned to diving (3 had only recently had closure and 3 had not returned to diving for other unrelated reasons). In the 23 who returned to diving, no recurrences of decompression sickness were reported.
2.3.3 The Specialist Advisers stated that a key efficacy outcome is adequate closure of the PFO assessed by a suitable technique (such as bubble contrast echocardiography).
2.4.1 The following safety data were obtained from studies of PFO closure for a range of indications because:
safety data are likely to be similar for the various indications
the larger numbers of patients provide more robust evidence on safety than those from studies specifically relating to divers.
2.4.2 Cardiac tamponade requiring surgery was reported in 2 patients in a non randomised comparative study of 280 patients: 1 occurred 5 weeks after the procedure because of left atrial laceration.
2.4.3 Late perforation of the aortic root by the device requiring pericardiocentesis and emergency cardiothoracic surgery occurred in 1 patient in a case report.
2.4.4 Device embolisation was reported in 0.6% (5/825) and 1% (2/167) of patients treated by the procedure in a case series of 825 patients and a non randomised comparative study of 280 patients respectively (device removed percutaneously in the first study but no further details given for the second).
2.4.5 Post- or peri-procedural arrhythmia was reported in 17% (8/47) and 10% (5/48) of patients in non-randomised comparative studies of 121 and 92 patients respectively.
2.4.6 The Specialist Advisers considered an additional theoretical adverse event to be valve dysfunction.