These are the people most at risk of the ill-effects of a PFO, and suffering the consequences.
It is good to see that you have come to the realisation that VGE can be harmful.
Screening does not require a full TTE/TEE exam. There is a simple indicator test that is reliable enough to sort out and find the PFO people.
Unfortunately, a very complex and nuanced issue is being grossly over-simplified here.
The transcranial Doppler (TCD) test is no more simple, nor safer, nor cheaper than a transthoracic echocardiogram (TTE) test. Both tests involve the injection of bubble contrast into a vein and measuring the appearance of those bubbles in the arterial circulation. In the TCD test bubbles are detected in one of the brain blood vessels and in a TTE test they are vizualised in the heart chambers. Both tests require expertise and carry risks (albeit small). In our jurisdiction a `specialised tech` would not be allowed to independently inject bubbles into a patient and then try to detect them in the patient`s cerebral circulation. It would always involve a specialist doctor. Moreover, the TCD test only tells you there is a right to left shunt. It does not characterise it (the shunt could be a pulmonary shunt or PFO or atrial septal defect). If a diver had a positive TCD test and was interested in proceeding (eg seeing whether it is possible to close the shunt) then they would need second study with TEE or transesophageal echo (TEE). So they would end up having two tests instead of one.
There are very good reasons why TTE with bubble contrast (and not TCD) has been identified as the preferred test for a PFO by all the world`s major diving medical societies [1,2]
Those PFO people don't know of their elevated risk status, because the current system says they can only learn about it, after they get injured.
No, `the system` does not say that. We do bubble contrast TTE on divers (particularly technical divers) who have never had DCS often enough at their request. But this is always preceded by careful counselling about what they are getting into. Key elements of such counselling were recently outlined in Diving and Subaquatic Medicine [3]:
1. The bubble contrast echo test is relatively safe, but there are some risks. Transient symptoms of cerebral arterial gas embolism have been reported following strongly positive tests for right to left shunt.
2. The test is likely to be positive in at least 30% of cases (depending on the context) and the diver may then have some difficult options to choose from. To mitigate the risk implied by a large PFO the diver effectively has 3 options: give up diving, modify their diving practice in an attempt to reduce VGE production, or have the PFO repaired. If the diver does not intend to take one of those options, then there is little practical point in having the test.
3. A positive test after an episode of DCS does not guarantee that the PFO was the cause of the DCS.
4. As a corollary to point 3, repairing a PFO discovered after an episode of DCS does not guarantee that another event will not occur.
5. A negative test does not mean that the diver is “resistant” to DCS as many seem to believe.
6. The finding of a PFO may have unexpected negative ramifications for things such as career choices, diving insurance, general health insurance.
So, currently, it is entirely possible for a diver to be tested for a PFO if they want to be, whether they have had DCS or not; but we are careful to fully inform them what they are getting themselves into. It is also notable that the majority of divers with significant PFOs discovered after DCS have them found after recurrent mild events (like skin rashes) rather than serious events. So l
earning about it after they get injured is a slightly dramatic characterisation of the typical scenario.
What 'the system'
does say is that mandatory pre-participation screening for PFO is not justified [1,2]. This is certainly true for diving as a whole and probably also for technical diving, but it is technical diving where things start to get tricky; mainly because of a lack of accurate data on the risk of major DCS events linked to PFO among this group. There is considerable anecdotal evidence suggesting that DCS is more common in technical diving than scuba air diving; perhaps dramatically so. Moreover, it is probably significantly under-reported (many mild cases ignored, or treated with surface oxygen / in-water recompression). Nevertheless, major cases are much more visible because they almost all find their way to a recompression chamber, and those cases still seem relatively rare and herein lies the essential problem. Pre-participation screening for PFO (which has some risk) would be hugely expensive, would prompt many to have closures (which has risks), all to prevent an unknown proportion of a relatively rare event. Can I be clear that there is some wooliness in all of the relevant numbers (the risk of screening, the risk of closure, and the risk of serious DCS events in technical diving). But at this time the medical community does not believe that pre-participation screening is justified purely on a risk vs benefit bases.
There are also other problems with the idea. For a start, the need to be screened would deter a lot of people who might not like the idea of having bubbles injected into them. The cost would also deter some (bubble contrast TTE costs around $800 in Auckland). Moreover, the test
would detect a PFO in 30% of candidates. Although many of these would be small and insignificant lesions, once a diver has the PFO label it is often hard to make such distinctions no matter how rational. I expect a huge proportion of that 30% would decline to proceed. In short, pre-participation screening for PFO would likely devastate the technical diving industry. This would not be a reason for avoiding it were it justified. But see my above comment about risk vs benefit.
I would also like to note that some commentators seem to believe that if we took PFOs out of the equation we would no longer have to worry about VGE. This is not true. The presence of VGE probably incites inflammatory reactions in the blood, and if there are enough of them they can cause pulmonary DCS ("the chokes"). More importantly, VGE can access the arterial circulation via pulmonary shunts (blood vessels which bypass the capillary beds of the lungs) which are variable (they can open and close) and therefore not reliably detectable. There is nothing we can do about these, so VGE will always be a consideration whether we screen for PFOs or not.
Finally, I would like to be clear that my comments above which relate to mandated pre-participation screening are not to be interpreted as suggesting that there is no merit in PFO testing and closure under any circumstances. Like all diving physicians I refer divers who report indicative DCS events for PFO testing, and after careful counselling, sometimes recommend closure for those who have a large PFO, who wish to continue diving, and who have limited scope for increasing conservatism. There is emerging evidence that closure of a significant PFO is effective in preventing DCS events [4,5].
Simon M
1. SMART D, MITCHELL SJ, WILMSHURST P, TURNER M, BANHAM N. Joint position statement on persistent (patent) foramen ovale and diving. South Pacific Underwater Medicine Society (SPUMS) and the United Kingdom Sports Diving Medical Committee (UKSDMC).
Diving Hyperbaric Med. 45, 129-131, 2015.
2. MOON RE, MITCHELL SJ, BOVE AA. PFO statement. In: Denoble PJ, Holm JR (Editors). Patent Foramen Ovale and Fitness to Dive Consensus Workshop Proceedings. Durham, NC, Divers Alert Network, 141-144, 2016
3. MITCHELL SJ. Prevention of decompression sickness. In: EDMONDS C, BENNETT MH, LIPPMANN J, MITCHELL SJ (editors).
Diving and Subaquatic Medicine (5th ed). Florida, USA, Taylor and Francis, 153-166, 2015
4. EBERSOLE D. Risk-benefit analysis of PFO closure: a prospective study. In: Denoble PJ, Holm JR (Editors). Patent Foramen Ovale and Fitness to Dive Consensus Workshop Proceedings. Durham, NC, Divers Alert Network, 100-106, 2016
5. BILLINGER M, ZBINDEN R, MORDASINI R, et al. Patent foramen ovale closure in recreational divers: effect on decompression illness and ischaemic brain lesions during long-term follow-up.
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