By Divers Alert Network
With its unusual name, its connection to cardiovascular health, and its link to DCS risk, it’s easy to see why patent foramen ovale (PFO) is of particular interest to divers. The good news is that, while the condition is common, it’s typically low-risk—but it can sometimes require medical intervention. Because it may be present in as many as 1 in 3 adults and has been associated with increased DCS risk, it’s something you should be familiar with. Here’s what you should know about PFO:
What is a PFO?
A PFO is a relatively benign cardiac defect that creates a passage in a wall of the heart that normally separates the left and right upper chambers of the heart. Typically blood in an adult travels from the great veins of the body through the right atrium, into the right ventricle, then to the lungs via the pulmonary artery. The lungs oxygenate blood and filter out venous bubbles, and the blood is returned to the heart via the pulmonary veins. From the pulmonary veins blood travels into the left atrium and is then pumped into the left ventricle and back into various body tissues via the arteries. A PFO is a communication, or opening, between the right and left atria of the heart. In a developing fetus the lungs are nonfunctional, and blood bypasses them through this communication, which in a fetus is called just the foramen ovale. After birth, this opening is closed by a flap of tissue that acts as a valve. Because the pressure in the left atrium is slightly higher than in the right, the flap stays closed. In some individuals this flap never closes; this results in a PFO.
The condition was first introduced as a possible risk factor for DCS by researchers at Duke University in 1989 because of the potential for bubbles to shunt through a PFO, bypassing the pulmonary filter. Modern discussions have led to a wide variety of recommendations from various sources, which has led to some confusion. While some agencies and physicians recommend diving conservatively with a known PFO, others recommend surgical closure. Divers who perform long or deep dives with elevated risk of post-dive bubbling should be familiar with the condition and its associated risks, but an informed decision on screening and surgical closure can be made only in consultation with your physician.
What Are the Risks?
Discussions of risk must be couched in the understanding that the incidence of DCS in diving of all types is extremely low and that many divers with verified PFO will never have symptoms of DCS. There is, however, a strong association with the existence of a PFO and repeated or serious DCS. Divers without a PFO can still get DCS, and the risk can be mitigated in many situations by avoiding dive profiles that are likely to generate significant post-dive bubbling. Studies have found that divers who suffer from DCS have a PFO prevalence twice that of the general population. Divers who suffer from neurological DCS symptoms have been shown to have a PFO prevalence of twice that again—almost four times the prevalence of the general population. Note that only neurological, spinal vestibular, and cutaneous DCS have been associated with PFO presence, not DCS that presents only with pain. It is generally accepted that the risk of DCS seems to increase with the size of the PFO, and divers with a large PFO are at greater risk of DCS than those without. Studies on the relative risk of DCS in divers with a PFO are still ongoing, but the association is fairly well established and deserving of consideration.
Is There a Treatment?
Because a PFO doesn’t usually cause any symptoms, the condition is typically undiagnosed and rarely treated. It is possible to detect the communication between the atria with non-invasive transthoracic echocardiography (TTE), or transesophageal echocardiography (TEE). TTE involves placing an ultrasound probe on the outer wall of the chest, while TEE is more sensitive than TTE, but it is an invasive procedure that requires anesthesia. TTE with bubble contrast is typically a more appropriate test for PFO presence, and while it may miss some small PFO these are not as closely correlated with DCS occurrence as larger PFO. Because of the high incidence of PFO in the diving population, and the low incidence of DCS, it is not recommended to screen every diver for a PFO. Rather, current recommendations are that only dives with potentially indicative symptoms get tested for the condition. Divers with several incidents of DCS, DCS after a non-provocative dive profile, or DCS with neurological or cutaneous symptoms should consider undergoing an evaluation and PFO screening. After diagnosis, PFOs can be closed with a transcatheter closure procedure, or divers may elect to minimize their risks by using more conservative dive profiles. Recommendations on the acceptable indications for PFO closure may be vary, and divers with a suspected PFO should consult with a physician familiar with diving medicine to discuss the risks and benefits pertinent to their specific case.
For more information on safe diving practices visit www.DAN.org
Leave a Comment