What is Patent Foramen Ovale in Diving?
Patent foramen ovale (PFO) is a medical condition where a natural opening in the wall between the two upper chambers of the heart, known as the foramen ovale, doesn’t close as it should after birth. This condition is significant especially among divers, as it has been linked to serious decompression sickness which affects both the brain and the inner ear, as well as a skin condition known as cutis marmorata.
What Causes Patent Foramen Ovale in Diving?
During a baby’s development in the womb, there’s a small opening called the foramen ovale that allows blood to flow from the right side to the left side of the heart, allowing it to bypass the baby’s lungs. Normally, this opening closes on its own within a few years after a baby is born.
However, if this opening doesn’t close, it can lead to a small amount of blood from the veins entering the left side of the heart. Despite this, it’s generally not a cause for concern because the pressure in the body’s blood circulation usually keeps the effect minimal.
Risk Factors and Frequency for Patent Foramen Ovale in Diving
The foramen ovale, a hole in the heart, is naturally open in about 20% to 34% of adults. However, this opening only creates an actual shift of blood (called shunting) in 8% to 10% of cases. Decompression sickness, a risk for divers, is generally rare, happening in only 0.01% to 0.095% of the general diving population, depending on where and what type of diving is done. But interestingly, in groups of divers who have a known open foramen ovale, this sickness happens slightly more often – in about 0.5% to 1.8% of cases.
Signs and Symptoms of Patent Foramen Ovale in Diving
A patent foramen ovale, a condition where a small hole in the heart doesn’t close after birth, generally goes unnoticed and doesn’t have symptoms. It might be linked to migraines with aura and some stroke types, but the scientific community hasn’t reached a consensus on such links.
Having decompression sickness, normally connected with diving, can indicate the existence of a patent foramen ovale. The risk of this condition is likely if the person has recurrent episodes of severe decompression sickness, with sudden onset of symptoms, even after following standard diving safety rules and without additional risk factors.
However, it’s essential to remember that a patent foramen ovale isn’t the only reason for developing decompression sickness. Testing for patent foramen ovale doesn’t make sense among divers who have shown only minor decompression sickness symptoms, like joint pain, swelling or a type 1 skin rash.
Decompression sickness is more likely after long and deep dives, aggressive decompression protocols, rapid ascents or heavy duty at depth. Other risk factors include skipping necessary decompression stages, being under cold conditions during decompression and multiple dives over consecutive days.
Testing for Patent Foramen Ovale in Diving
Regular screening for a heart condition known as patent foramen ovale (PFO) isn’t typically advised for divers. Nonetheless, it’s sensible to screen individuals who are at a higher risk. These are people who have experienced severe migraines (migraines with aura), were born with heart disease (congenital heart disease), or have a family history of PFO.
Echocardiography with bubble contrast is what doctors usually rely on to diagnose PFO. This test utilizes sound waves and a specially prepared fluid (bubble contrast), and it is executed when the patient is at rest. The doctor might also ask the patient to perform certain actions, like attempting to exhale while the mouth and nose are closed (this is called the Valsalva maneuver). The Valsalva maneuver allows doctors to see if the condition changes when the body is under strain.
Transcranial Doppler is another test that’s both inexpensive and noninvasive. It’s used for patients with a suspected abnormality in the heart circulation, known as a right-to-left shunt, however, it can’t identify the shape and size of the gaps that might exist in the heart (intracardiac shunt morphology).
Another test called transthoracic echocardiography with bubble contrast works well for clinically significant PFO detection. However, some doctors might choose to perform a more detailed test, a transesophageal echocardiography with bubble contrast.
Treatment Options for Patent Foramen Ovale in Diving
If a diver experiences a sudden case of decompression sickness, which occurs when a diver ascends too quickly causing gas bubbles to form in the body, they need to undergo a treatment called hyperbaric oxygen therapy. This involves breathing pure oxygen in a pressurized room to help alleviate the symptoms.
However, if a diver experiences severe unexplained decompression sickness, inner ear decompression sickness, or a specific skin condition called cutis marmorata and they also have a heart condition known as a patent foramen ovale (PFO), diving again should be approached with caution. PFO is a hole in the heart that didn’t close the way it should after birth. Multiple instances of decompression sickness make this even more crucial. A qualified and experienced practitioner must be consulted before diving again. If they do return to diving, they must be very careful, such as using a mixed gas called nitrox and avoiding decompression diving.
People with PFO may wonder about having it closed. This decision should be made together with a heart specialist and a doctor trained in diving medicine. The risk of the procedure needs to be compared with the individual risk of decompression sickness for divers with PFO. There is a certain complication rate for the device and procedure, and divers should be aware of this.
The likelihood of serious decompression sickness in divers with PFO varies but is relatively low. However, some studies suggest that larger PFO sizes in divers may increase their risk of decompression sickness.
Divers with PFO who have not had decompression sickness should not usually consider getting it closed. They should instead be advised to dive in a careful and measured way. Only in rare cases, such as preparing for extensive expedition-level dives, might closure be requested. The risks of device and procedure complications need to be evaluated against the unique risks of decompression sickness for that individual.
If a diver has had their PFO closed, they may resume diving once cleared by their cardiologist and a certain type of doctor trained in examining divers. They must have an ultrasound of the heart (echocardiography) showing the PFO is adequately closed, and not be on any blood-thinning medications other than aspirin. It has been suggested that closing a PFO may lower the risk of decompression sickness in divers who have PFO and have had decompression sickness before.
What else can Patent Foramen Ovale in Diving be?
When diagnosing patent foramen ovale (a hole in the heart that didn’t close after birth), doctors also consider similar conditions to make sure they’re making the right diagnosis. They look into the possibility of the following conditions:
- Coronary sinus atrial septal defects (a hole in the wall between the two upper chambers of the heart)
- Ostium primum atrial septal defects (another type of hole in the heart’s wall)
- Partial anomalous pulmonary venous connection (when some of the blood vessels from the lungs don’t correctly connect to the heart)
- Sinus venosus atrial septal defect (an uncommon type of hole in the upper chambers of the heart)
- Total anomalous pulmonary venous connection (all the blood vessels from the lungs are wrongly connected)
