Heart Defect PFO
The oxygen supply of a child in the womb is independent of the lungs. Therefore the blood flow is deviated and the lungs are bypassed by a connection between the two atria. This connection is called the foramen ovale. After birth, the child starts to breathe independently and the connection between the atria closes. In as many as 1 out of 4 people the atria does not close properly, and a trap-door-like opening a few millimeters wide is left open, known as a Patent Foramen Ovale (PFO).
As the PFO is constructed like a trap-door, the opening is normally closed, since the pressure in the left atrium is higher than in the right atrium and this pressure closes the lid of the door. However, when the pressure on the right side of the heart increases and becomes much higher than the pressure on the left side of the heart, the trap-door will be pushed open. This may occur in situations with heavy pressure development inside the chest, such as gasping for breath, coughing or sneezing, or with chest infections. Other typical examples are lifting a heavy weight or even when diving.
When the door is pushed open, oxygen-poor blood from the right heart (venous) side may mix with oxygen-rich (arterial) blood from the left heart side. Unfortunately, there are usually many small blood clots in the venous system arising from smaller injuries as well as low flow conditions when patients do not move for several hours (e.g. sitting in an airplane, etc.). These blood clots are normally transported with the blood stream into the lungs, filtered there and finally resolved. If, however, pressure in the lungs rises, a clot can then come from the right atrium into the left atrium, which would otherwise remain stuck in the filter system of the lungs. This is called a paradoxical embolism. Such clots can be the cause an occlusion of a small blood vessel, and if in the brain, can cause a stroke.
As many as 20% of all people have a PFO. Infants with PFOs have no symptoms if they do not have other heart defects. Unless there are other defects, there are usually no complications from a PFO. The situation in adults is similar. Adults or older people however may suffer more frequently from clotting disorders based on risk factors typical for older age (i.e. smoking, obesity, hormonal contraception (the pill), high blood pressure, arteriosclerosis, etc.) Therefore adults with a PFO may have a higher risk of getting certain types of strokes, namely a stroke via a paradoxical embolism. In these circumstances, medication to prevent blood clots can be advantageous.
Once a person has had a stroke caused by a clot in the brain, and a PFO is diagnosed with the likelihood of a paradoxical embolism, a closure of the PFO is recommended to avoid future strokes.
Closure of ASD and PFO
Once the diagnosis of an ASD suitable for interventional closure, or a PFO responsible for paradoxical embolism is made, it is time to close it. Today, in most cases of patients with an ASD and in nearly all patients with a PFO, closure can be achieved without open-heart surgery but by using interventional catheterization.
Interventional closure: The closure is performed in a cardiac catheterization laboratory, known as a cath lab. Techniques vary between clinics and physicians active in catheter intervention. The procedure can be done under local anesthesia, with the support of sleeping medication (sedation) or by general anesthesia and will be performed by a (pediatric) cardiologist. A thin tube – a catheter – is inserted into a blood vessel in the groin and guided to the heart. The exact size of the PFO or ASD is measured by ultrasound transesophageal echography(TEE), intracardiac echography(ICE) and the surrounding tissue is assessed. In many cases of PFO and in most patients with an ASD, the size of the defect is measured exactly by inserting a soft balloon, known as balloon sizing. Everything is constantly controlled by X-ray. Then the catheter is exchanged for a larger catheter, the delivery sheath.
The appropriate device, an ASD occluder or a PFO occluder is pushed through to be placed across the hole, through the delivery sheath. The occluders consist of a left-sided disk and a right-sided disk. The left-sided disk is deployed first and then retracted directly to the septum. Then the right-sided disk is deployed and thus the occluder will seal the defect between the two disks. Once the device is in the correct position, the physician will release the device and withdraw the delivery sheath. The defect is now closed and the tissue will grow around the device and be a permanent part of the septum. Typically the procedure takes approximately 60 minutes.
Occluder and MRI
This device contains no magnetic parts. An MRI or any other conventional X-ray can be carried out immediately after the procedure.
Occluders and airports
Illustrations of PFO
PFO area shown on a normal, healthy heart
A heart with a PFO defect
A Patent Foramen Ovale (PFO) is an opening or trap-door between the right and left atrium. Usually this opening is closed but it can open in situations with elevated blood pressure in the right side of the heart.
Closing the PFO defect
The closure is performed in a cardiac catheterization laboratory, a cath lab. A thin tube – a catheter – is inserted into a blood vessel in the groin and guided to the heart. The size of the PFO is measured by ultrasound (TEE, ICE) or with a balloon catheter. The catheter is then exchanged for a larger catheter, the delivery sheath. The appropriate device, a PFO occluder is pushed through to be placed across the hole through the delivery sheath.
Once the device is in the correct position and firmly attached on both sides, the physician will release the device and withdraw the delivery sheath.
Movie showing in a general way the mechanism of a PFO related cryptogenic stroke
Movie showing in a general way how an Occlutech PFO Occluder is implanted
The Occlutech device used to close a PFO defect is called the Occlutech Figulla Flex II PFO. The device is made of braided Nitinol threads. Nitinol is a very elastic alloy with wide-ranging memory skills. Nitinol alloys exhibit two unique properties: The shape memory effect and the superelasticity effect, both guarantee that it goes back into its “programmed” shape after being deformed, a Nitinol device can be folded to be guided to its intended place of implantation. This helps stop the blood going through the meshwork of the device*. The device will be pushed through the delivery catheter across the defect, then both discs will fix the device at the septum wall and the device will then be released when placed in the correct position to close the defect.
* 2017_Hildick-Smith_Occlutech percutaneous patent foramen ovale closure: Safety and efficacy registry (OPPOSE)