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Patent Foramen Ovale – Is It Important To Divers?

Alfred A. Bove, Richard E. Moon

Originally Published in Alert Diver Sept/Oct 2004

What is a PFO?

 The upper chambers of the heart (the atria) are separated into a right chamber that conveys blood from the veins to the right ventricle, then to the lungs, and a left atrium that conveys blood from the lungs to the left ventricle and then to the whole body.  In the unborn fetus, the lungs are not functioning, and in order to provide oxygen to the fetal circulation, an opening is present (the foramen ovale) in the wall between the two atria (the atrial septum).  The foramen ovale allows blood coming from the placenta to flow through the right atrium directly into the left atrium and then into the body to provide the oxygen needed for growth and development.  At birth, when the baby begins to breathe, a flap valve closes over the opening in the atrial septum and eventually becomes part of the atrial septum from growth of tissue sealing the opening.  However in about 30% of all people, the closure of the foramen ovale is incomplete, and the persistent foramen ovale (patent foramen ovale or PFO) becomes a potential location for blood from the veins to flow directly into the arterial circulation, thus allowing bubbles to enter the arteries and bypass the lung filter. In a small number of people, the flap valve is missing completely and a persistent opening occurs in the atrial septum (atrial septal defect or ASD). Concern for bubbles reaching the brain by this pathway seem to be validated by several reports in the medical literature of unexpected or unexplained decompression sickness, particularly involving the brain in divers who were subsequently found to have a PFO (see the heart diagram below).

 A medical report in 1986 suggested that neurological decompression sickness after a 15 minute dive to 38 m in a recreational scuba diver with an ASD was cause by venous gas emboli (VGE) passing through a previously undocumented atrial septal defect. Embolization through a patent foramen ovale has been described for over 50 years, and the concept of venous to arterial embolization led to the notion that venous gas bubbles, common after recreational dives but usually silent due to filtration by the pulmonary vasculature, could cross through the PFO and cause injury to the brain and spinal cord.  Since these initial observations, several other medical reports have suggested an association between PFO and cerebral, spinal cord, certain types of skin bends and, possibly, inner ear decompression sickness.

 Divers have enthusiastically latched onto this concept. During fitness to dive evaluations, questions about PFO are always near the top of divers’ lists; DAN is bombarded with PFO queries. With the development of devices that can be implanted without surgery to close the PFO, this interest has gained momentum.  In Europe these devices are commercially available and approved for closure of ASD and PFO. In the US, these occluders are still undergoing experimental study and are soon to be approved by the U.S. Food and Drug Administration (FDA) for treatment of certain forms of stroke caused by blood clots thought to come from the veins, which then flow to the right atrium and cross a PFO.

 Some professional divers have received the occluder device in an attempt to reduce the risk of DCI. In theses divers after occlusion there were no further neurological decompression episodes over a 3–12 month follow up period. However, without knowing more about their diving patterns before and after the procedure it is difficult to be sure that this represents a true reduction in risk. RETURN

 Should you dive with a PFO?

 While there is thought to be an association between PFO and severe neurological bends, causation is unproven. Indeed, important logical links between the purported mechanism and many of the facts, are missing. Venous bubbles are very common in recreational divers. In a DAN study of repetitive, multi-level dives, published in 2002, venous bubbles were observed by Doppler in 91% of recreational divers (Dunford RG, Vann RD, Gerth WA, Pieper CF, Huggins K, Wachholz C, Bennett PB. The incidence of venous gas emboli in recreational diving. Undersea & Hyperbaric Medicine 29: 247-59, 2002). While 20-30% of divers might be expected to have a PFO, DCI in recreational divers occurs after only 0.005-0.08% of dives, clearly much lower than the one in five or 6 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% of dives. In order for DCI to occur, there must therefore be other factors, such as bubble load or some other susceptibility factor, as yet unknown, possibly involving body tissues.

 Clinical observations to date have focused on the correlation of PFO with neurological injuries, particularly serious ones, but these represent only a third of DCI incidents. The majority of DCI cases in recreational diving consist of pain or sensory abnormalities, and no one has yet shown that PFO is related to these cases. The exception is skin bends, but this is uncommon. Only around one third of cases of DCI in recreational divers are considered severe. If 60% of these have a PFO, and 25% of the remainder have one, then it can be estimated that the majority of bends cases must occur in divers without a PFO.

 Associating a common finding (PFO) with an uncommon disease (DCI) is a common mistake and  this often-mistaken relationship is  likely to be involved in the data regarding DCI and PFO. RETURN

This is a diagram of the heart and its associated blood vessels. The location of the PFO is marked in yellow. The PFO is an opening betetween the right atrtium and the left atrium. These two chambers lie at the top of the heart and act as the priming pumps for the two main pumps of the heart - the right and left ventricles. In this diagram, the left atrium lies behind the aorta and the PFO communicates between the ritght and left atria. Bubbles coming into the right atrium from the veins can flow across the PFO and circulate in the arterial circulation where they can block blood flow in vital organs.

Should you have a PFO closed?

 Those who undertake or sign up for such a procedure should be aware of several issues:  Insertion of an occluder has some risk risk. According to data submitted to the US Food and Drug Administration by the manufacturer of the AMPLATZER PFO Occluder™, in 442 insertions there were 7 major adverse events, including cardiac arrhythmia requiring major treatment, device embolization (the device breaking free from its position in the atria of the heart and being carried away by the bloodstream), requiring either percutaneous or surgical removal, and failure of the system by which the device is inserted (http://www.fda.gov). More recent articles in medical journals have continued to report complications such as device malposition, device embolization, changes in heart rhythm, perforation of the heart, vein damage, bleeding and both right and left atrial blood clot formation. Late complications have included sudden death.

 One of the purposes for which these occluder devices will be marketed is to prevent blood clots from passing through a PFO and into the left side of the heart, from which they could travel to the brain and cause a stroke. However, even for prevention of recurrent blood clots, the effectiveness of transcatheter devices has not been proven. Regarding closure of a PFO to prevent DCI, scientific evidence is presently non-existent..

 If it is proven with certainty that a PFO in a diver with VGE predisposes to DCI by providing a route through which bubbles can pass into the arterial circulation, then the safest strategy would be to reduce the venous bubble load by developing different decompression procedures, limiting bottom time or by the appropriate use of oxygen-enriched breathing mixes. RETURN

CORRESPONDENCE WITH DIVERS

 The Diver:
I recently made 13 dives in the Caribbean over a 7 day period (max depth 104’). I did not come close to violating any depth, time, or ascent rules. I also had a surface interval of at least 90 minutes between dives. Sometime during the week I started getting a mottled rash on my right upper arm and some moderate abdominal pain accompanied by diarrhea. I attributed the rash to sunburn and the abdominal pain to bad food. I flew home without further incident. However, 10 or so days after my last dive I started having severe chest pain, high BP and HR (130 bpm at rest). I went to the hospital, was admitted, given O2, and an EKG, as well as stress test, all of which showed no abnormalities. I attributed the whole thing to stress and it went on with life.
 
I went back to the Caribbean 6 months later, and after the 4th dive (max depth 80’) I once again noticed a rash on my arm as well as some abdominal discomfort (sort of like having done too many sit-ups). Again all my dives were well within limits.
 
A local physician diagnosed me with skin bends. He treated my elevated BP (145/100) with meds, and my abdominal pain with antibiotics. The rash went away in a couple of days, the abdominal pain did not. I got on the internet and read up on my symptoms and suspected a PFO was the problem.   Ten days after my last dive I started having the same symptoms as before (elevated HR and BP). At home, a transesophageal echocardiogram showed a moderate PFO.  


I would like to go back to diving, or get the PFO fixed. I am concerned about the risk v. benefit of the procedure as weighed against the chance of stroke without the procedure.

Dr. Bove:

First of all, there are no data suggesting that a PFO is a contraindication to diving. There are some people  who feel that a PFO should be a prohibition, but given that fact that 30% of all divers have a PFO, it is not likely that it causes a high risk.  Abdominal cramps and diarrhea are not part of a decompression syndrome.  Many people who go to Caribbean islands get abdominal cramps and diarrhea, whether diving or not.  In addition your symptoms 10 days after diving are also not likely to be related to diving.  They are however worrisome, and could have been related to a blood clot in the lungs (pulmonary embolism) that sometimes happens after a long air flight.

The local physician was correct in not treating an  uncomplicated case of skin bends.  In the absence of other findings, recompression therapy is not needed.  

 

 Data on stroke and PFO are still not well established.  There is some suggestion that a large PFO is a risk for stroke, and many cardiologists advocate closure.  Looking at the complications of closure, and the residual PFO rate after closure, in the absence of any stroke symptoms, closure is likely to be more risky that non-closure.  

 
You should be cognizant of your nitrogen load when diving.  Many computers are liberal and would put you in a decompression stop situation based on USN tables.  To get bends, you must have bubbles.  Minimizing bubbles can be done by being conservative about depth and bottom time. DCIEM tables would be a good guideline for bubble free diving.   RETURN


CLOSING A PFO

Closure of both PFO and atrial septal defects is done using a catheter method that does not require surgery. The diagram on the right demonstrates how this is done using an occluder that is advanced through the PFO and deployed to close the defect using a catheter that is inserted in a vein at the groin then advanced into the PFO or ASD. Inset in the upper right is a diagram of the catheter entering the right atrium from the Inferior Vena Cava and passing through the PFO with the occluder deployed. in the lower right inset, the two halves of the occluder are tightened together and the PFO is closed. Diagram is from Kizer, JR and Devereaux RB, New England Journal of Medicine 2005; 353:2361-72. Copyright © 2005 Massachusetts Medical Society. All rights reserved.

Below is an echocardiogram of the closed PFO.

The pictures on the right show a set of echocardiograms. In the upper left, the channel that makes up the PFO (arrow) can be seen connecting the right atrium (RA) and the left atrtium (LA). In the upper right the right atrium is filled with bubbles and there are bubbles (small white dots) in the left atrium. In the lower left, an occluder has been placed in the PFO. The arrow points to the disk on the right side of the septum. In the lower left there are many bubbles in the right atrium, but none in the left atrium, indicating that the PFO has been closed. SVC denotes the superior vena cava, the large vein that enters the atrium from above. Image from www.cardiosource.com RETURN