Patent foramen ovale and scuba diving: a practical guide for physicians on when to refer for screening
© Sykes and Clark; licensee BioMed Central Ltd. 2013
Received: 1 July 2012
Accepted: 11 January 2013
Published: 1 April 2013
Divers are taught some basic physiology during their training. There is therefore some underlying knowledge and understandable concern in the diving community about the presence of a patent foramen ovale (PFO) as a cause of decompression illness (DCI). There is an agreement that PFO screening should not be done routinely on all divers; however, when to screen selected divers is not clear. We present the basic physiology and current existing guidelines for doctors, advice on the management and identify which groups of divers should be referred for consideration of PFO screening. Venous bubbles after diving and right to left shunts are common, but DCI is rare. Why this is the case is not clear, but the divers look to doctors for guidance on PFO screening and closure; both of which are not without risks. Ideally, we should advise and apply guidelines that are consistent and based on best available evidence. We hope this guideline and flow chart helps address these issues with regard to PFOs and diving.
KeywordsPatent foramen ovale Decompression illness Arterial gas embolism Screening
Divers are taught some basic physiology during their training. There is therefore some underlying knowledge and understandable concern in the popular diving press about the presence of a PFO as a cause of DCI [9, 13, 14]. Unfortunately, DCI can occur after any dive, even within the depths and time limits of tables and computers, and after the diver has made many hundreds of dives without incident. All divers experiencing problems after diving should consult a diving physician, to whom this guideline is aimed. A list of contact details can be found at http://www.uksdmc.co.uk. Even when performing dives which are inside acceptable and safe decompression algorithms, venous bubbles are very common [2, 15, 16], and the Divers Alert Network states that:
While 20–30 percent of divers might be expected to have a PFO, decompression illness (DCI) in recreational divers occurs after only 0.005-0.08 percent of dives, clearly much lower than the one in five or six that might be expected if every diver with a PFO and venous bubbles developed DCI. Based on current experience, the estimated risk of a DCI incident characteristic of those correlated with PFO is between 0.002-0.03 percent of dives .
Therefore, routine screening of all divers for a PFO is not warranted primarily because the absolute risk of neurological DCI is low and the cost of screening is high , and beyond the recommendation not to screen all divers, there are no clear guidelines on when to screen for PFOs in divers who may be at risk of shunt-mediated DCI. Here, we present a practical approach to a common problem of what to do with a diver who may warrant or request a referral for a PFO check. These are guidelines for doctors treating divers and should not be used in place of diver training.
According to the UK Sports Diving Medical Committee :
Approximately one quarter of the population have a patent foramen ovale or a small atrial septal defect, but the risk of paradoxical embolism is much greater in those with large shunts [10, 19]. Decompression illness is very unusual in sport divers after dives to less than 20 metres and we have not observed neurological decompression illness that appears to be the result of paradoxical embolism in sport divers after dives to that depth. We have observed neurological decompression illness associated with a large shunt in a professional diver who did a working dive at 18 m, which required in-water stops that were performed correctly. It therefore seems reasonable that sport divers known to have intra-cardiac shunts should be allowed to dive shallower than 15 m, provided no other cardiac contra indications exists. If a diver with a shunt wishes to go deeper than 15 m the options include use of nitrox with an air decompression table (to reduce bubble liberation and tissue nitrogen load) and the use of a table such as the DCIEM (Defence and Civil Institute of Environmental Medicine) table which is believed to result in little or no bubble nucleation. It will also be possible for some individuals to return to unrestricted diving after trans-catheter closure of the defect.
For commercial divers, the Health and Safety Executive (HSE) state that :
Examination for the presence of an intra-cardiac shunt is not a requirement for either the initial or the annual examination. However, examination for patent foramen ovale should be performed in a diver who has suffered neurological, cutaneous or cardio-respiratory decompression illness, particularly where there is a history of migraine with aura or where the dive profile was not obviously contributory, since it may contribute to an assessment of the overall risk to the diver of continuing to dive. A positive finding is not necessarily a reason for a finding of unfitness. However, the opinion of a cardiologist with an interest in diving medicine is recommended.
The National Institute of Clinical Excellence (NICE) has produced guidelines on the closure of PFOs in divers,  which also emphasises the importance of involving a cardiologist knowledgeable in diving medicine. The assessment of the presence and size of a PFO can be poor and can therefore lead to people getting inappropriate advice and being put at risk. The Undersea and Hyperbaric Medical Society (UHMS) Best Practise Guidelines  state that PFO testing may be considered after severe or repetitive neurological DCS and may help in advising divers to modify their dive profiles. Carl Edmond's Diving Medicine agrees that the risk from a PFO is not great enough for it to be appropriate to test all divers, and repair of the hole is probably more dangerous than diving with it.
When to refer
There should probably be different advices for different divers, and we will cover the following categories, based on the current standard operating procedure at London Hyperbaric Medicine: (a) no DCI, (b) one episode of DCI, (c) more than one episode of DCI, (d) migraines and (e) commercial divers.
No decompression illness
One episode of DCI
More than one episode of DCI
As with divers after one episode of DCI, discuss whether the diver wants to continue diving, despite being susceptible to DCI. If the diver wants to continue diving, encourage safe diving practices (Figure 3) and have a lower threshold for screening for a PFO. If the diver clearly understands the risks and agrees to dive to less than 15 m, then no PFO check is necessary. However, the diver may have unrealistic views on what makes a safe dive, and these cases can be difficult. Use the DCIEM  or British Sub-Aqua Club 1988 decompression tables  to ‘prove’ whether the dive profiles are relatively safe, although DCI can still occur within these tables. A PFO check with a cardiologist with an interest in diving can also be useful in these cases, as this will allow a realistic discussion of the risks of continuing to dive with the diver's cardiac status, as per the UHMS Best Practise Guidelines . We would therefore suggest that a PFO check is discussed with the diver.
Divers with migraine with aura are at increased risk of neurological DCI [26–28]. However, we should encourage safe diving practices (Figure 3) and check whether the medications are appropriate for diving. There is no recommendation to screen for a PFO in divers simply with migraines with aura. However, those with migraines with aura and at least one episode of DCI should probably have a PFO check. Diagnosing migraine with aura is important as migraine without aura and other headaches are not considered a risk factor for DCI or having a PFO.
Commercial divers could be defined as those requiring an HSE Commercial Diving Medical for their work. These divers cannot modify their dive profiles and have very clear incentives to continue diving; therefore, stopping diving or encouraging safe diving is not a realistic option. Check whether there are any factors suggestive of a PFO and follow the HSE guidelines above .
Referral, screening and closure
Guidelines for screening for PFOs are difficult to create because the relationship between PFOs and DCI is not clear and also because DCI is rare and most of the tests involve expense, worry and some risk. Cardiac investigations are not always of sufficient quality to pick up all right to left shunts such as pulmonary arteriovenous malformations. There are also a number of ways of testing for a PFO, which may explain why the rates vary. Deciding when to check for and close a PFO can also be difficult but ultimately lies with the cardiologist performing the procedures. PFO checks and closures are done at many centres, but screening and advice on continued diving must come from a cardiologist with an interest in diving.
The screening procedure
A small dose of bubbles is injected into a large ante-cubital fossa vein, and the diver is asked to perform a Valsalva. Since bubbles show up well on ultrasound, there is then opacification of the right atria and ventricle, and any bubbles that traverse the septum can be easily seen. As far as we know, there have been no reported problems after the dose of intravenous bubbles.
The closure procedure
This is performed using a local anaesthetic and sedation, or general anaesthesia, and can be done as a day case. A guidewire and catheter (Figure 6) are inserted through a vein usually in the groin into the heart and through the PFO using imaging guidance  (Figure 7). A device is then inserted via the catheter, closing the hole. There is a NICE guidance on Percutaneous closure of patent foramen ovale for the secondary prevention or recurrent paradoxical embolism in divers (issued December 2010) . In terms of efficacy and risks, the guidance for patients includes five studies with a total of 1,283 patients who had the procedure for a number of different conditions; the PFO was immediately closed in 1,268 patients (99%)  and a further study of 29 divers treated by the procedure for neurological decompression sickness: 23 had returned to diving and experienced no more decompression sickness and 6 were not diving (three as they had only recently had the procedure and three for reasons unrelated to the procedure) . In terms of risks and possible problems, the NICE guidance is useful again :
In a study of 280 patients, cardiac tamponade was reported in 2 patients (0.71%) who both required further surgery.
In 2 studies with a total of 992 patients, the device used to close the PFO caused a tear in a large blood vessel of the heart requiring emergency surgery in 1 patient (0.10%). The device fell out and entered the circulation in 7 patients (0.71%).
Abnormal heart rhythm during or after surgery was reported in 13 of 95 patients (13.68%) in 2 studies of a total of 213 patients.
As well as looking at these studies, NICE also asked expert advisers for their views who said that in theory, a problem with the heart valves could occur.
It is worth emphasising that the risk post-closure of DCI returns to normal and not zero. The closure also requires checking with repeat echocardiography to ensure closure and a period of antiplatelet therapy which must be completed before returning to diving.
OS is currently a senior registrar in anaesthetics in SW London, a PADI Divemaster and a hyperbaric doctor at Whipp's Cross University Hospital, where there are over 100 cases of DCI every year. Some are referred for PFO screening. The guideline for referral of divers for a PFO check was developed by OS in order to help other doctors at the unit refer appropriate cases. OS also writes regularly for Sport Diver and contributes to the discussions on the UK Sport Diving Medical Committee forum, where PFO screening is a common theme. JEC is a lecturer and independent researcher at King's College, London within the Centre for Human Aerospace Physiological Sciences and the Cardiovascular Division, respectively. He teaches on the M.Sc. in Human & Applied Physiology programme and undergraduate physiology courses including Human Physiology in Extreme Environments (MSc) and Extreme Physiology (BSc) in diving medicine. He is a British Sub-Aqua Club advanced diver and instructor.
Defence and Civil Institute of Environmental Medicine
Health and Safety Executive
National Institute of Clinical Excellence
Patent foramen ovale
Undersea and Hyperbaric Medical Society.
The authors would like to thank London Hyperbaric Medicine for the use of the guideline: Referral of Divers for PFO Check.
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