Patent Foramen Ovale

The foramen ovale is a valve-like opening in the fossa ovalis region of the atrial septum, the wall that lies between the right and left atria. It normally closes spontaneously after birth; when it fails to do so, it persists as a small, flap-like communication known as a patent foramen ovale (PFO). A PFO is in fact present in one in every five people in the general population, yet fewer than 1% of them have a condition that requires closure.

When a PFO is present, conditions that raise intrathoracic pressure — such as coughing, sneezing or straining (the Valsalva manoeuvre) — may open this small flap, and blood may then cross in either direction between the two atria. In some unfavourable circumstances, deoxygenated blood in the right atrium may pass through the PFO into the left atrium without first passing through the filtering system of the lungs. In such cases, particularly in people predisposed to thrombus formation in the leg veins, small clots carried in the venous blood may pass into the left atrium and from there into the left ventricle, reaching the brain and other organs (paradoxical embolisation) and causing stroke and paralysis, as well as acute ischaemic injury and acute events in other organs.

Because one in every five people in the population has a PFO, the clinical settings that may be relevant to the indications for PFO closure need to be clearly understood. They can be summarised as:

• Cryptogenic stroke (stroke of undetermined cause)
• Migraine
• Platypnoea-orthodeoxia syndrome
• Decompression sickness in divers

In a patient with a cryptogenic stroke, a PFO may also be an incidental finding. It is therefore important first to establish whether there is a clear relationship between the stroke and the PFO. A risk scoring system has been developed for this purpose, which assesses the risk factors present in the individual patient, and applying it can be very helpful. According to this score, a high score indicates an increased risk of a “PFO-associated” stroke, suggesting that the PFO has itself taken part in the event rather than being an incidental finding.

The type of PFO differs from patient to patient, and certain anatomical types have been shown to carry high-risk features for stroke. These features can be summarised as:

• a large (>4 mm) or long tunnel-type PFO
• atrial septal aneurysm
• a prominent Eustachian valve (>10 mm)
• a right-to-left shunt present at rest

When a PFO is detected in a patient with a cryptogenic stroke, the circumstances that may call for closure of the PFO can be summarised as:

• recurrent cryptogenic stroke despite conventional blood-thinning (anticoagulant) therapy;
• recurrent PFO-associated transient ischaemic attack, or embolism to a leg or to a coronary artery, despite medical therapy;
• an inability to take anticoagulant medication;
• a PFO in a young patient together with deep vein thrombosis of the leg, or with a disorder that increases the tendency to clot (thrombophilia).

A definite relationship between migraine and PFO has not been clearly established. There are therefore insufficient data to support the view that PFO closure may be of benefit in patients with migraine.

Breathlessness that appears on sitting up or standing and resolves on lying down is known as platypnoea-orthodeoxia syndrome. It is a relatively uncommon but striking clinical syndrome, characterised by dyspnoea and deoxygenation on moving from a recumbent position to sitting or standing. It is seen mainly in older patients, in whom coexisting conditions such as elongation of the aorta, removal of lung tissue (pneumonectomy), pulmonary emphysema and liver cirrhosis may be present. In such situations, standing upright may displace the great vein (the vena cava), and when a PFO accompanies anomalies of this kind, blood flow may be directed straight towards the vena cava; a right-to-left shunt, from the right atrium to the left atrium, may then be triggered. Where this syndrome is present and a PFO is demonstrated, the PFO should be closed.

Current evidence indicates that routine PFO screening is not required in divers, miners, cosmonauts and astronauts who are at risk of decompression sickness. It has been suggested, however, that when decompression sickness develops in professional divers, industrial divers and those undertaking deep and technical diving who also have a PFO, the symptoms are considerably more pronounced and the risk of demonstrating injury in the brain is higher. Screening could therefore be considered for professional divers, in view of their frequent dives, and for deep and technical divers, given the higher risk of decompression lesions. In such at-risk individuals, if a PFO with high-risk features is detected in the presence of symptoms, closure of the PFO may be considered, taking into account the type and the number of dives and the person’s wish to continue the activity.

How is the diagnosis made?

A PFO can readily be diagnosed today with the advanced ultrasound technology known as echocardiography. Once a PFO is suspected on transthoracic echocardiography — performed simply by placing an ultrasound probe on the front of the chest — the definitive diagnosis is established by transoesophageal echocardiography (TEE), in which a probe is swallowed and positioned in the oesophagus. After the colour Doppler jet has been visualised across the foramen ovale region on two-dimensional TEE, three-dimensional echocardiography readily demonstrates the location, the shape and the size of the opening, whether it carries high-risk features, and whether it is suitable for device closure. Two- or three-dimensional TEE is today accepted as the gold standard both for establishing the diagnosis of a PFO and for determining the method of treatment. In our clinic, two- and three-dimensional TEE is performed in every patient in whom a PFO is suspected.

How is the percutaneous (transcatheter) method performed?

The veins in the groin region carry the deoxygenated blood of the legs and of the region below the groin to the right side of the heart through the large lower vein called the inferior vena cava. In the angiography laboratory, the groin vein is punctured with a small needle and a sheath is placed in it.

Through this sheath, the right atrium is reached with atraumatic dedicated guidewires and catheters (small tubes) that do not injure the vessel; from there, the opening between the two atria is crossed to reach the left atrium, and then the pulmonary veins, which drain into the left atrium.

A supportive guidewire is placed within the pulmonary veins, and over this wire a balloon is positioned at the site of the opening.

The balloon is inflated and the diameter of the opening is determined by balloon sizing; the balloon is then withdrawn, and over the supportive wire positioned in the pulmonary vein the dedicated delivery system — the tube system in which the closure device is collected and carried — is advanced and positioned in the left atrium.

Under two- or three-dimensional echocardiographic guidance, the closure device, which may be described as a kind of “double-disc” implant, is deployed with its left disc in the left atrium, its waist exactly in the middle of the opening, and its right disc in the right atrium, so that the opening is closed completely.

Once a dedicated manoeuvre has confirmed that the device is seated precisely over the opening, the device is released from the delivery cable and left in place.

Following the procedure, within approximately 6 months to 1 year the outer surfaces of the device become covered spontaneously by the body’s own surface lining, the endothelium (endothelialisation). Images from the transcatheter closure procedures performed in our clinic are presented below.

Are there any risks of the percutaneous method or of the devices used?

Complications are far less frequent with this treatment performed by the percutaneous method than with open surgery. Complications that may arise during open surgery — such as serious bleeding, the complications of prolonged anaesthesia, and injury to vessels and to the cardiac chambers — are not commonly seen. The cosmetic advantage of the procedure is also clear, since it is carried out without opening the chest, through no more than a small needle puncture and the placement of a sheath in the groin. Most of these devices are manufactured from nitinol, a special shape-memory metal; other devices, such as platinum-coated closure devices, are also available to us. Other than in people with nickel allergy, no side effect of these devices has been reported. In procedures performed by operators without specific training in this field, however, the device may dislodge and embolise into the cardiac chambers if appropriate measurements have not been made or an appropriate device has not been selected. Even then, dedicated snares are available with which the device can be captured within the body and removed without difficulty. Other complications, such as bleeding, air embolism and a collection of blood around the heart within the pericardial sac (pericardial effusion or tamponade), may also arise during the procedure, although very rarely indeed compared with open surgery.

Images of the Closure Procedure