Hidden Heart Defect Raises DCS Risk Five Fold

Scuba divers with a relatively common heart defect appear to be at higher risk than normal for decompression sickness, a new report in the European Heart Journal (June 2004) shows. The defect – patent foramen ovale (PFO) – is a tiny opening between the heart’s two upper chambers. While it normally closes during fetal development, it remains open in as much as 30 percent of the population.

Researchers from University Hospital in Bern, Switzerland found that divers with PFO were five times more likely to get bent than people without the defect. The study supports previous research, which also showed that divers with a PFO have double the risk of bubbles traveling to the brain, where they can do serious damage.

Researchers used ultrasound to examine the hearts of 230 diver who had logged at least 200 dives. Among them, 63 divers, or 27 percent, had PFO. None had known they had the defect. Approximately 29 percent of the divers with PFO had experienced at least one major DCS episode – impaired bowel or bladder control or loss of consciousness after the dive – compared with only six percent of divers without the heart defect.

The researchers also found that the risk of major DCS increased as PFO size increased. However, people with the smallest PFO had the same risk of DCS as people without PFO.

The researchers recommend that people with a relatively large opening between the left and right atria of the heart refrain from diving. And people with smaller defects who have experienced decompression sickness should avoid dives deeper than 100 feet, and refrain from repetitive dives during a single day

Since few people know whether they have PFO, we asked underwater medicine expert Dr. Ernest Campbell (www.scubadoc.com) whether divers should have a costly PFO exam before diving. Here is what he told us.

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In the light of the high incidence of venous gas bubbles even after dives in shallow water, and the presence of a PFO in at least a quarter of the population, bubbles passing into the arterial circulation might be more prevalent than we would like to think! There are several diagnostic screening studies, but the best is the most invasive and expensive: a trans esophageal electrocardiogram. Others, in descending order of validity, include the trans thoracic echo, the trans cranial echo, carotid Doppler studies, oximetry, and dilutional studies of blood flow in the ear lobe.

Across the board screening for PFO in all divers would not be productive, but some divers should be examined to rule out a PFO before they dive again:

• All divers who have had neurological decompression sickness.

• All divers with “undeserved” DCS — DCS that occurs when there are no errors in ascent rates or decompression stops – who also had several of the minor DCS risk factors – fatigue, stress, alcohol, dehydration before and after diving, physical stress, cold, and post dive exercise.

• Migraine with aura, which is the feeling of impending headache, flashes of light or other sensory experiences that presage a migraine headache.

• Skin rashes during early stages of off-gassing.

If PFO is present, deep diving or any diving where there would be a heavy load of venous gas bubbles on ascent would be a particular risk. This could include wreck diving, cave diving, multi-day, multi-dive excursions, possibly even live aboard diving.