How does PFO closure reduce stroke risk?

What is a PFO?

Before birth, a natural passage called the foramen ovale sits between the heart's two upper chambers (atria). After birth it closes in most people. In roughly one in four, it does not fully close and remains a patent foramen ovale (PFO). In most people a PFO never causes symptoms and is found incidentally.

How can a PFO cause a stroke?

A small clot forming in the leg veins is normally filtered by the lungs. When a PFO is present, such a clot can pass through the opening between the atria and reach the arteries supplying the brain. This is called paradoxical embolism, and it is most relevant in strokes for which no other cause can be found (cryptogenic stroke). A PFO is found more often in people who have had a cryptogenic stroke than in those without stroke or with a known cause.

How does PFO closure reduce stroke risk?

The procedure is performed with a thin catheter advanced through a vein in the groin. An umbrella-like closure device is placed across the opening and is gradually covered by the body's own tissue. This blocks the passage of a clot between the atria, closing off the paradoxical embolism route. In clinical practice the goal is not to treat the current stroke but to prevent a second stroke in a carefully selected patient. PFO closure belongs to the family of structural heart interventions (PFO/ASD/LAA closure).

What have clinical studies shown?

The strongest evidence comes from randomized controlled trials and their pooled analyses. Early trials, limited by small numbers and short follow-up, were inconclusive, but newer trials and long-term follow-up have clarified the picture:

• Long-term follow-up (RESPECT trial, 2017): With 980 patients followed for a median of about six years, recurrent ischemic stroke occurred less often in the closure group than in the medical group (roughly 0.58 vs 1.07 events per 100 patient-years). The reduction was even clearer for strokes of undetermined cause. ^[1]
• Pooled analyses (five randomized trials, ~3,440 patients, mean ~4 years): Closure significantly reduced the risk of recurrent stroke compared with medication. One analysis reported a number needed to treat (NNT) of about 37 to prevent one recurrent stroke. ^[2]
• Atrial fibrillation: In the same analyses, the risk of new-onset AF after closure was clearly increased. This AF is mostly early and transient but requires follow-up. ^[2,3]
• No significant difference was shown between the two treatments for all-cause death, transient ischemic attack, or major bleeding. ^[2–5]

In short, in selected patients the stroke protection from closure is judged to be a net clinical benefit against the increased AF risk. This balance is set individually for each patient. ^[1–5]

Who is it considered for?

PFO closure is not recommended for everyone with a PFO, but for a specific group. In the trials, the average patient age was in the early forties. Features typically assessed in clinical practice:

• Usually under 60 years of age
• A stroke whose cause remains unexplained despite thorough investigation (cryptogenic stroke)
• A strong likelihood that the PFO is causally linked to the stroke
• High-risk PFO features such as a large shunt or an accompanying atrial septal aneurysm

Tools such as the RoPE score help estimate the probability that the PFO is related to the stroke. In older patients, or when another clear cause of stroke exists, the benefit of closure becomes uncertain.

How is the decision made?

The decision rests on an overall assessment rather than a single test: brain imaging, cardiac ultrasound (particularly a bubble study to demonstrate the shunt), heart-rhythm monitoring, and clotting evaluation. Neurology and cardiology assess together. The aim is to select patients in whom the stroke is highly likely to be related to the PFO.

Risks and limits

The procedure is generally well tolerated but is not without risk. Possible events include new-onset atrial fibrillation after the procedure (mostly transient), problems at the access site, rarely device-related complications, and venous thromboembolism. Closure also does not eliminate stroke risk in every patient; any other risk factors are managed separately. The choice is individualized, and the same outcome is not expected in every patient.