Hello,
There is a lot of misinformation in this thread, and this is an important subject. I will attempt to put the medical community's perspective on it.
There are simple screening tests available that are 90+% accurate. DAN Europe did this on a study of 700(?) divers. This can isolate the problematic patients for further investigation via TEE / TTE, or the diver can decide if its worth the risk to repair the PFO, or change diving style.
Ross, this has all been explained to you before by specialists in the field, yet you continue to misrepresent the issue in a place where divers come to acquire knowledge because it suits your position that we should not have to be concerned about venous gas emboli. You do the community no favours with perpetration of poor quality information.
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 any test involving injecting bubbles into the patient's veins and then trying to detect them in the cerebral circulation would always involve a specialist doctor. Moreover, the TCD test only tells you that bubbles have crossed 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 TTE 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]
Kevrumbo:
I exceptionally disagree with this expert panel, looking at it from the perspective of a hypothetical beginning tech diver starting training with an unknown -and unaware of- a PFO condition not previously discovered or diagnosed.
Again, it all comes down to a statistical/epidemiological vs clinical dilemma in a personal risk management perspective
Yes it does Kev, but your evaluation of that is at odds with that of true experts in the field for the reasons outlined below. I can't really tell from your posts whether you are arguing for an individual's right to ask for PFO testing, or whether you are saying we should encourage or even make it compulsory for
everyone entering technical diving to be screened, but I am suspecting the latter.
Two separate consensus documents published within the last few years, which represent the views of the world's major diving medical societies, clearly state 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 I accept 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 [3 - 8]) would be hugely expensive, would prompt many to have closures (which has risks [9]), all to prevent an unknown proportion of cases suffering a relatively rare event. I am happy to admit 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 expert medical community does not believe that pre-participation screening is justified purely on a
risk / cost vs benefit basis.
There are also other problems with screening of all prospective tech divers. 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. There are other potential problems too, including the very important one made at point 6 on the counselling list below.
I would like to be clear that my comments above which relate to pre-participation screening of all divers 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 individual divers who report indicative DCS events for PFO testing, and sometimes divers who have never had DCS 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 [10].
Every diver wanting a PFO test gets told:
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 [3 - 8].
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 (which has risks [9]). 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, travel 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 this.....
rossh:
The current approach is to let you experience an accident first, and only then investigate that you are a high risk diver
.......is a slightly dramatic characterisation of the typical scenario.
Finally, Kev, your citation of a very old passage written by Richard Moon is misleading. His current thoughts are clearly represented in the contemporary guideline on which he is lead author [2]. Finally, for the OP, as someone trained as a cardiac anaesthesiologist, I could easily test myself for a PFO but never have.
Simon M
References:
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. Wilmshurst et al. Relation between interatrial shunt and decompression sickness in divers. Lancet December 1989:1302-1306.
4. Srivastava TN and Undesser EK. Transient ischemic attack after air contrast echocardiography in patients with septal aneurysm. Ann Intern Med. 1995;122:396.
5. Holcomb BW et al. Iatrogenic paradoxical air embolism in pulmonary hypertension. Chest 2001;119:1602-1605.
6. Christin F et al. Paradoxical symptomatic air embolism after saline contrast transesophageal echocardiography. Echocardiography. 2007;24:867–9.
7. Romero JR et al. Cerebral Ischemic Events Associated With ‘Bubble Study’ for Identification of Right to Left Shunts. Stroke 2009;40:2343-2348.
8. Sorenson SG et al. Transient neurological symptoms during contrast transcranial Doppler right-to-left shunt testing in patients with cryptogenic neurological disease. J Interv Cardiol 2010;23:284-290.
9. Abaci A et al. Short and long term complications of device closure of atrial septal defect and patent foramen ovale. Catheterization and Cardiovascular Interventions 2013;82:1123–1138.
10. 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
