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REVI E W Open Access
Patent foramen ovale and scuba diving: a
practical guide for physicians on when to refer
for screening
Oliver Sykes
1*
and James E Clark
2
Abstract
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.
Keywords: Patent foramen ovale, Decompression illness, Arterial gas embolism, Screeni ng
Review
Introduction
Decompression illness (DCI) encompa sses decompres-
sion sickness (DCS) and arterial ga s embolism (AGE).
The differentiation of the pathological processes in prac-
tice can be difficult, but the treatment is similar; hence,
both are given the mod ern overarching term of decom-
pression illness. DCS occurs as a result of venous bub-
bles forming in the tissues and vessels, which can cause
mechanical, embolic and biochemical effects with mani-
festations ranging from trivial to fatal [1]. AGE is caused
by arterial bubbles as a result of ruptured lung alveoli
from gas trapping in the lungs or blood shunting from
the venou s right atrial side to the arterial left atrial side
of the heart. This is known as a right to left shunt.
Symptoms usually appear short ly after, or within 30 min
of surfacing, but can have delayed onset. These symp-
toms are frequently neurological in nature [2-4] and can
be profound. The lungs are an effective filter, and a right
to left shu nt, such as a patent foramen ovale (PFO), is
therefore a route for bubbles to avoid this filter and
enter the arterial system. This is known as a paradoxical
embolism and is depicted in Figure 1. Usually, the blood
pressure on the arterial left side is higher than the ve-
nous right, which prevents right to left flow. However,
this pressure differential is reversed on releasing a Valsalva
manoeuvre, causing the right atrium to fill before the left
atrium. Unfortunately, 30 to 60 min post-dive is the peak
time for bubble liberation [5], which coincides with divers
climbing into boats, lifting heavy kit, straining and uncon-
sciously performing Valsalva manoeuvres.
In the fetus, the foramen ovale is vital to allow blood
to bypass the lungs, which are not in use. On breathing
at birth, there is a flap valve effect [6] (Figure 2), and the
negative intra-thoracic pressure helps closes this route.
While in about 30% there remains a leak, DCI is still a
rare event [1,7]. This suggests that not all divers with a
PFO are at increased risk of DCI [8]. However, those
that are susceptible appear to get the more serious
neurological symptoms. Moon examined 91 patients
with a two-dime nsional echocardiogram, who were eva-
luated and/or treated for DCS at Duke University
* Correspondence: o.sykes@nhs.net
1
London Hyperbaric Medicine, Whipp's Cross University Hospital, London E11
1NR, UK
Full list of author information is available at the end of the article
© 2013 Sykes and Clark; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative
Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and
reproduction in any medium, provided the original work is properly cited.
Sykes and Clark Extreme Physiology & Medicine 2013, 2:10
http://www.extremephysiolmed.com/content/2/1/10
Medical Center. Of these 91, 39 had a PFO and 64 of
the 91 had more serious symptoms (weakness, dizziness
or symptoms of brain abnormalities); 32 of these 64 had a
PFO [9] (50%). The risk of DCI by right to left shunting is
related to the tissu e nitrogen load (i.e . pressure–time
profile), the size and characteristics of the shunt and the
presence of other factors likely to cause right to left
shunting [10,11]. These include occult lung disease,
smoking, lung shunts, Vals alva, straining and functional
size of the PFO. According to Dr. Peter Wilmshurst,
cardiologist of the UK Sport s Diving Medical Commit-
tee, the requirement s for shunt-mediated D CI are a
large right to left shunt, a PFO, atrial septal defe ct or
pulmonary arteriovenous lung malformation, a dive pro-
file that liberates venous bubbles profile and also an
appropriate inert ga s load in critical tissue to amplify
embolic bubbles [12].
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 guide-
line is aimed. A list of contact details can be found at
www.uksdmc.co.uk. Even when performin g dives which
are inside acceptable and safe decompression algorithms,
venous bubbles are very common [2,15,16], and the Di-
vers 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 [17].
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
[1], and bey ond 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
Pulmonary
Vein
Left
Atrium
Left Ventricle
Right Ventricle
Pulmonary
Artery
Right Atrium
To the
body
To the Lungs
A
o
r
t
a
Right Atrium
To the
body
To the Lungs
Aorta
PFO
A
B
J
.
C
l
a
r
k
Figure 1 Paradoxical gas embolism. Schematic drawing
demonstrating the paradoxical gas embolism in a diver with a PFO
(A); migration of a bubble of gas from the venous system to the left
atrium via a PFO, with subsequent systemic embolisation (B).
Figure 2 Intra-cardiac echocardiogram. Showing the patent
foramen ovale, in an adult and in real time, acting as a flap valve
between the right atrium (RA) and left atrium (LA) [6].
Sykes and Clark Extreme Physiology & Medicine 2013, 2:10 Page 2 of 7
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DCI. Here, we present a practical approach to a com-
mon problem of what to do with a diver who may war-
rant 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.
Current guidelines
According to the UK Sports Diving Medical Committee [18]:
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 Execu-
tive (HSE) state that [20]:
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 continu ing 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 di-
vers, [21] which also emphasises the importance of
involving a cardiologist knowledgeable in diving medi-
cine. The assessment of the presence and size of a PFO
can be poor and can therefore lead to people getting in-
appropriate advice and being put at risk. The Undersea
and Hyperbaric Medical Societ y (UHMS) Best Practise
Guidelines [22] state that PFO testing may be considered
after severe or repetitive neurological D CS and may help
in advising divers to modify their di ve profiles. Carl
Edmond's Diving Medic ine [23] agrees that the risk from
a PFO is not great enough for it to be appropriat e to test
all divers, and repair of the hole is probably more dan-
gerous 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
If the diver has not had DCI, discourage the diver from
seeking a PFO check. However, consider what the reason
for the request might be. Divers often deny symptoms of
DCI but worry they may have a PFO. No diving is the only
way to guarantee no DCI. Consider also the expense,
worry, risk and the possible impact on medical insurance.
If concerned about a PFO and the diver wants to continue
diving, encourage safe diving practices (Figure 3). A diver's
safest profile is a rapid descent to the deepest part of the
dive with a gradual ascent, whereas a reverse profile dive
is one where the diver spends a prolonged time at the
shallowest part of the dive before going deeper for the lat-
ter part of the dive. A reverse profile dive maximises nitro-
gen uptake during the dive and results in a greater risk of
bubble formation and, consequently, DCI following as-
cent. If the diver wants to dive outside these recommen-
dations, then suggest referral to a cardiologist with an
interest in diving.
One episode of DCI
Discuss whether the diver want s to continue diving,
despite being susceptible to D CI. If the diver wants to
continue diving, encourage safe diving practices and
decide whether there are any factors suggestive of a
PFO (Figure 4). If any factors are present , then have a
lowerthresholdforPFOcheck.Ifthedivewaspro-
vocative (Figure 5) and the re were no other factors,
then encourage safe diving practices and not a PFO
check. There is no re commendation to che ck for a
PFO after all types of D CI.
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More than one episode of DCI
As with divers after one episode of DCI, discuss whether
the diver wants to continue diving, despite being suscep-
tible to DCI. If the diver wants to continue diving, en-
courage 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 [24] or
British Sub-Aqua Club 1988 decompression tables [25]
to ‘prove’ whether the dive profiles are relatively safe, al-
though 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 [22]. We would therefore suggest that a PFO
check is discussed with the diver.
Migraines
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 rec-
ommendation to screen for a PFO in divers simply with
Figure 3 Safe
diving practices. Courtesy of London Hyperbaric Medicine.
Figure 4 Factors suggestive of a PFO. Courtesy of London
Hyperbaric Medicine.
Figure 5 Provocative
dive profile. Courtesy of London Hyperbaric Medicine.
Figure 6 Guidewire and patent foramen ovale occluder device
(courtesy of St. Jude Medical).
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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
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 inc entives to continue diving; therefore, stop-
ping 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 [20].
Referral, screening and closure
Guidelines for screening for PFOs are difficult to cre-
ate be cause the relationship between PFOs and DCI is
not clear and also be cause D CI is rare and most of the
tests involve e xpense, worry and some risk. Cardiac in-
vestigations a re not always of sufficient quality to pick
up all right to left shunts such as pulmonary arterio-
venous malformations. There are als o a number of
ways of testing for a PFO, which may explain why the
rates vary. De ciding when to check for and close a
PFO can also be difficult but ultimately lies with the
cardiologist performing the proce dures. PFO checks
and closures are done at many centres , but screening
and advice on continued diving must come from a car-
diologist with an interest in diving.
Figure 7 Intra-cardiac echocardiography. The guidewire and
catheter can be seen in the heart, passing from the right atrium (RA),
through the patent foramen ovale, into the left atrium (LA). The
bright white area (echo dense) on the wall of the LA opposite the RA
is the occlude device with the guidewire attached [29].
Figure 8 Flow chart on when to refer for screening by a cardiologist with an interest in diving. Courtesy of London Hyperbaric Medicine.
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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 ven-
tricle, 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 sed-
ation, or general anaesthesia, and can be done a s a day
case. A guidewire and catheter (Figure 6) are inserted
through a vein usua lly in t he groin into the heart
and through the PFO using imaging guidance [29]
(Figure 7). A device is then inserted via the catheter,
closing the hole. There is a NICE guidance on Percu-
taneous closure of patent foramen ovale for the second-
ary prevention or recurrent paradoxical embolism in
divers (issued December 2010) [21]. In terms of effi-
cacy and risks, the guidance for patients includes five
studies with a total of 1,2 83 patient s who had the pro-
cedure for a number of different conditions; the PFO
was immediately closed in 1,268 patients (99%) [30]
and a further study of 29 divers treated by the proced-
ure for neurological de compression sickne ss : 23 had
returned to diving and experie nced no more de com-
pression sickness and 6 were not diving (three as they
had only recently had the procedure and three for re a-
sons unrelated to the procedure) [30]. In terms of risks
and possible problems, the NICE guidance is useful
again [30]:
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 stu dies, NICE also
asked expert advisers for their views who said
that in theory, a problem with the heart va lves
could occ ur.
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 en-
sure closure and a period of antiplatelet therapy which
must be completed before returning to diving.
Conclusions
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 seek doctors' 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 (Figure 8) help ad-
dress these issues with regard to PFOs and diving.
Abbreviations
DCI: Decompression Illness; DCIEM: Defence and Civil Institute of
Environmental Medicine; HSE: Health and Safety Executive; NICE: National
Institute of Clinical Excellence; PFO: Patent foramen ovale; UHMS: Undersea
and Hyperbaric Medical Society.
Competing interests
JEC is a lecturer in Aerospace and Applied Physiology at King's College,
London and runs the B.Sc. Extreme Physiology and M.Sc. in Human
Physiology in Extreme Environments and a diving medicine module. OS is
paid as a doctor at the hyperbaric unit at Whipp's Cross Hospital and, as part
of this work, refers divers for PFO checks.
Authors' contributions
Both authors (JEC and OS) have made substantive intellectual contributions
in conceiving, designing, interpreting, drafting and revising the manuscript
critically for important intellectual content and have given final approval of
the version to be published. Notably, OS conceived the idea and provided
the guideline at London Hyperbaric Medicine. JEC advised on changes to
the guidelines and produced graphics. Both authors read and approved the
final manuscript.
Authors' information
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.
Acknowledgements
The authors would like to thank London Hyperbaric Medicine for the use of
the guideline: Referral of Divers for PFO Check.
Author details
1
London Hyperbaric Medicine, Whipp's Cross University Hospital, London E11
1NR, UK.
2
Centre of Human & Aerospace Physiological Sciences, King's
College, London SE1 1UL, UK.
Received: 1 July 2012 Accepted: 11 January 2013
Published: 1 April 2013
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doi:10.1186/2046-7648-2-10
Cite this article as: Sykes and Clark: Patent foramen ovale and scuba
diving: a practical guide for physicians on when to refer for screening.
Extreme Physiology & Medicine 2013 2:10.
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