New Data Back Closing Large PFOs to Prevent Decompression Sickness in Divers

In scuba divers with patent foramen ovale (PFO) featuring high-grade shunts, percutaneous closure is more effective than conservative diving recommendations at preventing decompression sickness (DCS), suggest new observational data.

Now widely accepted as a means to prevent PFO-associated stroke, closure has also shown potential to reduce migraines, but evidence is still lacking to support referring patients routinely for anything other than secondary prevention of stroke. Also, screening for PFO isn’t widely recommended in the general population, even though the incidence is known to be about 25%.

The findings from this study, published online yesterday ahead of print in JACC: Cardiovascular Imaging, however, at least support the screening of all divers.

“Once you know you have a PFO, even when you are a new diver, you can start diving more responsibly or more conservatively,” lead author Jakub Honěk, MD, PhD (Charles University, Prague, Czech Republic), told TCTMD. “Of course, there's the question of reimbursement, but as a sports activity, this can be paid individually by the diver as a preventive measure.”

The new data, follow similar findings from the same group last year demonstrating that closure seems to prevent DCS in divers with large shunts. This time around, the researchers went a step further by comparing closure against conservative diving, which involves “measures that should lead to lower bubble production and a reduction in the incidence of clinically overt DCS,” they explain.

While DCS is something to take seriously, the potential for significant morbidity with this condition is less likely than it is with stroke, according to David Thaler, MD, PhD (Tufts Medical Center, Boston, MA), explaining why the latter has received more research attention. However, “the relationship and the concern from the diving community is a legitimate one,” he told TCTMD. “What to do about it has long been a question that all of who've been in the PFO business have been confronted occasionally: a freaked-out diver who found they had a PFO from one reason or another—sometimes they've had a stroke—and they want to know if they can still dive.”

Thaler can remember two occasions where he sent patients for PFO closure because of diving-related reasons and said the observational data may lead to a change in guidelines. “There is some legitimacy for someone who is diving even recreationally to want to know if they have a PFO, and they might say, ‘Well look, I like diving but it's not my life, and if I have a PFO and there is some risk, I'd like to know and then I'll stop diving. I'll go snorkeling instead,’” he observed. “I would not prohibit a patient from diving even if they knew they had a PFO, but it might change somebody's own view of how they want to do it.”

No DCS in Closure Group

For the study, Honěk and colleagues screened 829 divers (mean age 35.4 years; 81.5% men) for inclusion in the DIVE PFO registry between 2006 and 2018. Of the 702 with follow-up data who continued diving after enrollment, 153 (22%) were diagnosed with high-grade PFO. Slightly more than one-third (n = 55; 35.9%) underwent catheter-based closure while the rest (n = 98; 64.1%) were advised “to dive within the limits of recreational diving.” Additionally, 128 were diagnosed with low-grade PFO shunts and advised to practice conservative diving, while 421 without PFO served as controls and were allowed to continue unrestricted diving.

Over a mean follow-up period of 6.5 years in patients with high-grade PFOs, the closure group reported more dives than did those in the conservative diving group (30,689 vs 25,328; P < 0.001). However, DCS was reported only in the latter (0 vs 11%; P = 0.012).

The risk of DCS in the low-grade PFO group was similar to that in controls (HR 3.97; 95% CI 0.56-28.18), but for the high-grade PFO group who did not undergo closure, the risk was elevated (HR 26.17; 95% CI 5.80-118.16).

“This is consistent with the results of numerous retrospective studies that strongly suggest that PFO is the clinically relevant route of paradoxical embolization in divers,” the authors write, noting that PFO closure is not without its risks.

The obvious way to reduce risk is to stop diving, they continue, “but in our experience this suggestion is rarely accepted. In this study, only 5% of the divers reportedly quit diving. We believe that catheter-based PFO closure may be an effective and safe preventive measure for divers who are unable to adopt to strict conservative recommendations (ie, professionals) or who wish to continue frequent or technical diving (ie, deep diving, diving with gas mixtures, etc).”

What to Do Depends on Diver

While Honěk now supports PFO screening in all divers, both those who dive professionally and those who only dive occasionally on vacation, he said what to do with the diagnosis of a PFO will vary.

“The recommendation for the low-grade [shunt] is conservative diving,” he said, although the specifics of what this might mean tends to vary from person to person. Honěk defined it as “one dive per day, very short, with longer decompression.”

This is an area where he’d like to see further research. “We should define the precise measures that would lower the [DCS] incidence to the same level as the PFO closure or the recommendation for conservative dives in low-grade shunts,” Honěk said. Also, “there are some individual variables that [indicate] some patients get more DCS than others, [though] none of them have been proved from our data,” including the diver’s age or sex.

For those with high-grade PFOs, “this is a more difficult discussion that should be done individually with the doctor and the patient,” taking into account the diver’s lifestyle and professional needs, he said.

Thaler argued the data in this study aren’t enough to yet warrant PFO screening in all divers. “It doesn't say at all why the ones who underwent closure, underwent closure and the ones who didn't, didn't. And that kind of self-selected population makes it much harder to know how to interpret this,” he said, adding that only a randomized trial would give a definitive answer.

Also, the fact that the study showed no DCS in the closure group is “almost hard to believe,” Thaler observed. “If you believe that, that means that you never get decompression sickness unless you have a PFO, which obviously is not the case. So that's probably an underrepresentation.”

The general incidence of PFO would mean that one-quarter of all divers have one, Thaler pointed out. “And if decompression sickness was so common amongst divers with PFOs, I would think there would be a lot more decompression sickness,” he said. “If you dive well, diving is pretty safe. You shouldn't get decompression sickness if you do it properly. This is for the subgroup who for whatever reason come up too quickly or stay down too long or go flying too soon after. Those are the reasons people end up with decompression sickness. But otherwise, you probably shouldn't get it.”

If someone wanted to get tested for a PFO in the United States, Thaler said it’s easy to do, although not part of a usual physical exam. “It's not hard to get a physician to order a PFO test if you make an argument for why it should be done,” he said. “If I had an otherwise recreational diver who had no neurological history and just bumped into a PFO and they said to me, ‘What should I do?’, I would not for the most part refer that patient for PFO closure.” As for diving, he added, it hasn’t been proven to be so dangerous with a PFO that he would advise against it.