Scuba divers with patent foramen ovale at higher risk for decompression illness

Key takeaways:

• High-risk patent foramen ovale was independently linked to a higher risk for decompression illness in scuba divers.
• Divers with high-risk PFO should use a more conservative protocol or refrain from diving.

Scuba divers with high-risk patent foramen ovale, or a hole in the heart, may be more susceptible to decompression illness than previously thought and should adhere to a conservative diving protocol or avoid diving, according to researchers.

Previous studies have indicated that patent foramen ovale (PFO) prevalence is higher among scuba divers who experienced decompression illness (DCI) than those who did not, Hyun-Jong Lee, MD, PhD, a researcher and professor at Sejong University in South Korea, and colleagues wrote in Annals of Internal Medicine.

DCI is a disease in which nitrogen that has been inhaled is dissolved in blood or tissues during a diver’s descent under high pressure and forms gas bubbles as they rise, inhibiting blood flow or mechanically affecting the tissue, the researchers wrote. A PFO “enables venous nitrogen bubbles to embolize into the arterial system,” they added.

“In patients with cryptogenic stroke with a pathophysiology similar to that of DCI, the PFO has been reported as a pathway in which deep venous thrombi pass into the systemic circulation,” Lee and colleagues wrote.

They conducted a prospective cohort study to evaluate the connections between high-risk PFO and DCI in scuba divers. Both event adjudicators and participating divers were blinded to the absence or presence of PFO.

The researchers included 100 experienced divers who completed more than 50 dives per year from 13 diving organizations. The participants underwent a transesophageal echocardiography with a saline bubble test to determine PFO presence and were then divided into low-risk and high-risk groups. The participants then completed questionnaires to self-report symptoms. The researchers used logistic regression analysis to determine the OR of the primary endpoint of the study: PFO-related DCI.

Lee and colleagues observed PFO in 68 divers, 37 of whom were at high risk and 31 of whom were low risk. The prevalence of PFO in this study was more than double that of the general population — 20% to 34%.

During a mean follow-up of 28.7 months, 12 divers in the PFO group had PFO-related DCI events (high-risk PFO vs. low-risk PFO: 8.4 vs. 2 incidences per 10,000 person-dives; P = 0.001).

The incidence of DCI was 12.8%, which is higher than the incidence reported in previous literature, the researchers wrote. Of the 12 divers diagnosed with DCI, just one had a history of DCI. However, 11 reported experiencing similar symptoms in a follow-up questionnaire.

“Our results indicated that DCI events with mild symptoms occurred frequently in divers with PFO, and many divers did not recognize them as DCI,” Lee and colleagues wrote.

Multivariable analysis additionally showed that high-risk PFO was independently linked to a higher risk for PFO-related DCI (OR = 9.34; 95% CI, 1.95-44.88). The findings indicate that high-risk divers should adhere to a more conservative diving protocol or refrain from diving altogether, the researchers wrote.

“Patients with DCI have various types of pains and discomfort, including generalized constitutional symptoms,” they wrote. “Symptoms of DCI range from mild constitutional symptoms to fatal events. Even mild DCI events are potentially associated with fatal events underwater.”

Lee and colleagues further noted that routine PFO screening is not currently recommended for divers without previous DCI episodes.

“The necessity of PFO evaluation should be determined individually by comprehensive assessment of the severity of DCI, diving situation in which DCI occurs, repeatability of symptoms, daily diving environment, and whether diving is discontinued,” they wrote.