The PFO Gets Blamed Again…Perhaps This Time it Is Real

Screening and Risk Stratification Strategy Reduced Decompression Sickness Occurrence in Divers With Patent Foramen Ovale

OBJECTIVES

This paper sought to evaluate the occurrence of decompression sickness (DCS) after the application of a patent foramen ovale (PFO) screening and risk stratification strategy.

BACKGROUND

PFO is associated with an increased risk of DCS. Recently, transcatheter closure was reported to reduce DCS occurrence in divers with a high-grade shunt. However, to date, there are no data regarding the effectiveness of any PFO screening and risk stratification strategy for divers.

METHODS

A total of 829 consecutive divers (35.4 ± 10.0 years, 81.5% men) were screened for PFO by means of transcranial color-coded sonography in the DIVE-PFO (Decompression Illness Prevention in Divers with a Patent Foramen Ovale) registry. Divers with a high-grade PFO were offered either catheter-based PFO closure (the closure group) or advised conservative diving (high grades). Divers with a low-grade shunt were advised conservative diving (low grades), whereas those with no PFO continued unrestricted diving (controls). A telephone follow-up was performed. To study the effect of the screening and risk stratification strategy, DCS occurrence before enrollment and during the follow-up was compared.

RESULTS

Follow-up was available for 748 (90%) divers. Seven hundred and 2 divers continued diving and were included in the analysis (mean follow-up 6.5 ± 3.5 years). The DCS incidence decreased significantly in all groups, except the controls. During follow-up, there were no DCS events in the closure group; DCS incidence was similar to the controls in the low-grade group (HR: 3.965; 95% CI: 0.558-28.18; P = 0.169) but remained higher in the high-grade group (HR: 26.170; 95% CI: 5.797-118.16; P < 0.0001).

CONCLUSIONS

The screening and risk stratification strategy using transcranial color-coded sonography was associated with a decrease in DCS occurrence in divers with PFO. Catheter-based PFO closure was associated with a DCS occurrence similar to the controls; the conservative strategy had a similar effect in the low-grade group, but in the high-grade group the DCS incidence remained higher than in all other groups.

High-grade patent foramen ovale is a risk factor of unprovoked decompression sickness in recreational divers

BACKGROUND

Patent foramen ovale (PFO), male sex, age, and body mass index (BMI) were all identified as potential risk factors of decompression sickness (DCS). It has been debated whether PFO might cause unprovoked DCS (i.e. without violation of decompression procedure) due to paradoxical embolization of venous gas emboli. To date, there are no data on the incidence or risk factors of unprovoked DCS. This study sought to evaluate the risk factors of unprovoked DCS in recreational divers.

METHODS

A total of 489 consecutive divers were screened for PFO between January 2006 and January 2014 by means of transcranial Doppler. All patients were prospectively included in the study registry. Survival analysis techniques were used to assess for risk factors for unprovoked DCS. Age, sex, BMI, PFO presence, and grade were analyzed. The total sum of dives was used as a measure of time.

RESULTS

The group performed a total of 169,411 dives (mean 346±636). Thirty-six (7%) of the divers suffered from an unprovoked DCS. The frequency of PFO was 97.2% in divers with a history of unprovoked DCS and 35.5% in controls (p<0.001). There was no difference in sex, age, BMI, or total number of dives between the respective groups. In the adjusted Cox proportional hazards model, PFO grade 3 was a major risk factor for unprovoked DCS; there was a slight protective effect of increasing age.

CONCLUSIONS

We demonstrated that a high-grade PFO was a major risk factor for unprovoked DCS in recreational scuba divers.

Reliability of right-to-left shunt screening in the prevention of scuba diving related-decompression sickness

OBJECTIVES

The aim of this study was to investigate the relationship between right-to-left shunt (RLS) and the clinical features of decompression sickness (DCS) in scuba divers and to determine the potential benefit for screening this anatomical predisposition in primary prevention.

METHODS

634 injured divers treated in a single referral hyperbaric facility for different types of DCS were retrospectively compared to 259 healthy divers. All subjects had a RLS screening by contrast Transcranial Doppler (TCD) ultrasound according to a standardized method. The number of bubbles detected defined the degree of RLS (small if 5-20 bubbles, large if >20 bubbles).

RESULTS

TCD detected 63% RLS in DCS group versus 32% in the control group (p<0.0001) The overall prevalence of RLS was higher in divers presenting a cerebral DCS (OR, 5.3 [95% CI, 3.2-8.9]; p<0.0001), a spinal cord DCS (OR, 2.1 [95% CI, 1.4-3.1]; p<0.0001), an inner ear DCS (OR, 11.8 [95% CI, 7.4-19]; p<0.0001) and a cutaneous DCS (OR, 17.3 [95% CI, 3.9-77]; p<0.0001) compared to the control group, but not in divers experiencing ambiguous symptoms or musculoskeletal DCS. There was in increased risk of DCS with the size of RLS. The determination of diagnostic accuracy of TCD testing through the estimation of likelihood ratios revealed that predetermination of RLS did not change significantly the prediction of developing or not a DCS event.

CONCLUSION

The assessment of RLS remains indicated after an initial episode of spinal cord, cerebral, inner ear and cutaneous form of DCS but this approach is definitely not recommended in routine practice.

Correlation between Patent Foramen Ovale, Cerebral "Lesions" and Neuropsychometric Testing in Experienced Sports Divers: Does Diving Damage the Brain?

SCUBA diving exposes divers to decompression sickness (DCS). There has been considerable debate whether divers with a Patent Foramen Ovale of the heart have a higher risk of DCS because of the possible right-to-left shunt of venous decompression bubbles into the arterial circulation. Symptomatic neurological DCS has been shown to cause permanent damage to brain and spinal cord tissue; it has been suggested that divers with PFO may be at higher risk of developing subclinical brain lesions because of repeated asymptomatic embolization of decompression-induced nitrogen bubbles. These studies however suffer from several methodological flaws, including self-selection bias. We recruited 200 volunteer divers from a recreational diving population who had never suffered from DCS; we then randomly selected 50 of those for further investigation. The selected divers underwent brain Magnetic Resonance Imaging to detect asymptomatic brain lesions, contrast trans-oesophageal echocardiography for PFO, and extensive neuro-psychometric testing. Neuro-psychometry results were compared with a control group of normal subjects and a separate control group for subjects exposed to neurotoxic solvents. Forty two divers underwent all the tests and are included in this report. Grade 2 Patent Foramen Ovale was found in 16 (38%) of the divers; brain Unidentified Bright Objects (UBO's) were found in 5 (11.9%). There was no association between PFO and the presence of UBO's (P = 0.693) or their size (p = 0.5) in divers. Neuropsychometric testing in divers was significantly worse from controls in two tests, Digit Span Backwards (DSB; p < 0.05) and Symbol-Digit-Substitution (SDS; p < 0.01). Compared to subjects exposed to neurotoxic solvents, divers scored similar on DSB and SDS tests, but significantly better on the Simple Reaction Time (REA) and Hand-Eye Coordination (EYE) tests. There was no correlation between PFO, number of UBO's and any of the neuro-psychometric tests. We conclude that for uneventful recreational diving, PFO does not appear to influence the presence of UBO's. Diving by itself seems to cause some decrease of short-term memory and higher cognitive function, including visual-motor skills; this resembles some of the effects of nitrogen narcosis and we suggest that this may be a prolonged effect of diving.

Patent Foramen Ovale in Recreational and Professional Divers: An Important and Largely Unrecognized Problem

Patent foramen ovale (PFO) is associated with an increased risk of decompression sickness (DCS) in divers that results from a paradoxical embolization of nitrogen bubbles. The number of scuba divers worldwide is estimated in the millions, and the prevalence of PFO is 25%-30% in adults. It is interesting that despite these numbers, many important issues regarding optimal screening, risk stratification, and management strategy still remain to be resolved. Recently published data suggest the possible effectiveness of both PFO closure and conservative diving measures in preventing arterial gas embolization. This review aims to introduce the basic principles of physiology and the pathophysiology of bubble formation and DCS, summarize the current literature on PFO and diving, and review the possibilities of diagnostic workup and management.