Five Things You Should Know About PFO
By: Douglas Ebersole, MD
The relationship between decompression illness (DCI) and patent foramen ovale (PFO) has been popularized in the diving community over the past 5-10 years.
Here are five things you should know about PFOs
- A PFO is NOT a disease. As a fetus, we all have a patent foramen ovale. It is a “flap” in the wall between the top two chambers of the heart which directs oxygenated blood from the placenta to the left side of the heart, thereby bypassing the lungs. Once we are born and begin to use our lungs to oxygenate blood, this “flap” closes in about 75% of people and forms a solid wall between the top chambers of the heart. However, in about 25%, it remains open and can be a pathway for blood clots or bubbles to get to the left side of the heart and cause a stroke or DCI.
- Having a PFO increases the risk of decompression illness by about fivefold. For sport diving, this increase is from about 2 episodes of DCI per 10,000 dives to about 1 episode per 1000 dives. For technical diving, this fivefold increase persists but is now 5 times a much larger baseline risk depending on the particular dive profile.
- PFOs are associated with certain types of decompression illness but not others. The types of DCI associated with PFO are cerebral (stroke), spinal (paralysis, urinary retention), cutaneous (a distinctive skin rash), and inner ear (vertigo). Joint pain as a manifestation of DCI is NOT felt to be related to PFO.
- The problem is the “bubble” not the PFO. The problem in DCI is with the inert gas load. Anything the diver can do to lessen his or her inert gas load such as fewer dives per day, shallower dives, shorter dives, “padding” decompression, etc., will lessen the risk of DCI – whether or not he or she has a PFO.
- Closure of the PFO is an option in carefully selected cases. If a diver has recurrent episodes of the type of DCI associated with a PFO (cerebral, spinal, cutaneous, inner ear), he or she has several options. First of all, the diver could stop diving. Most divers reading this would probably not choose this option, but it is always a consideration. Secondly, the diver could dive more conservatively. This approach has been shown to reduce the incidence of DCI in sport diving for patients with PFO. The restrictions include diving shallower than 100 feet, no more than one or two dives per day, no decompression diving, diving nitrox on air profiles, and long safety stops. For technical diving, though it has not been validated in controlled studies, the same considerations of fewer, shorter, and shallower dives along with “padding” decompression should be effective as well. Finally, divers could elect to have the PFO closed. This is an outpatient procedure done through a needle stick in the groin with a success rate of well above 95% and a complication rate of around 2-3%, the vast majority of which are minor complications such as palpitations and groin bruising. Serious complications are rare but do occur and must be considered when weighing the risks and benefits of PFO closure. After the procedure, patients are usually on aspirin and clopidogrel (Plavix) for 3-6 months.
Decompression illness is a poorly understood risk for scuba divers and especially for technical divers. Conservative diving practices are the best way to lower the risk of DCI. Despite these practices, some divers have recurrent Type II or skin bends – the types associated with PFO – and should consider being evaluated for PFO. The best screening test is a “regular” transthoracic echocardiogram with the injection of agitated saline (“bubble study”). If this is inconclusive and the clinical suspicion is high, a transesophageal echo could be performed. If a PFO is found, the diver could choose to stop diving, dive more conservatively, or, in selected cases, have the PFO closed.