Austria Vienna, 3 September 2007:
A PFO and an ASD are congenital structural heart diseases characterized by a communication between heart chambers at the level of the wall (septum) separating them. These chambers are the left and right atrium as shown on the picture below. The right atrium receives (dark) oxygen-depleted blood from the great veins, while the left atrium receives (red) oxygen-rich blood from the lungs.
In case of an ASD there is a permanent hole in the septum, allowing blood to flow back into the right heart circulation (pressure is higher in the left circulation). This chronic volume overload causes dilatation of the right heart chambers and although usually well tolerated, over time it may cause functional failure of the right heart (fatigue, dyspnea) or arrhythmia (heart rhythm disturbances). Echocardiography is the diagnostic tool of choice as it enables to visualize the ASD.
Furthermore, it allows physicians to choose the optimal treatment, which is defect closure. This can be done either by heart surgery (suturing of a patch for very large and particular defects) or by the implantation of an umbrella-type device through a catheter inserted into a vein in the groin.
This percutaneous technique has been around for many years with excellent results both from a clinical (symptoms) and objective (regression of the dilatation of the right heart chambers) point of view. It is therefore the treatment of choice for any ASD if technically feasible.
Contrary to the ASD, the PFO is not a permanent defect. This remnant from the fetal heart rather acts like a door capable of opening from the right to the left side. Normally, this defect should close after birth but autopsy studies have shown that up to 25% of the general population has a PFO. This condition generally causes no harm during the course of life but over the last decades it has been associated with several diseases so much so that manner that percutaneous closure (technically basically almost identical to ASD closure) has been advocated.
A first condition is stroke of unknown cause in young (<55 years) patients. The prevalence of PFO is significantly higher in these patients compared to stroke patients with known cause. Even more, patients at risk for recurrence of stroke have been identified based on clinical and anatomic characteristics. The proposed mechanism for stroke in these patients is the embolisation of a blood clot from the veins into the heart and passing through the PFO into the arterial circulation up to the brain. These clots may for example be formed during a period of prolonged rest and the PFO door is mostly opened during the so-called Valsalva maneuver. This maneuver (to forcibly exhale while keeping the mouth and nose closed) occurs often during daily life (lifting objects, moving the bowels). Randomized controlled trials (RCT) comparing device closure versus “best” medical therapy (antiplatelet or anticoagulation therapy) have been ongoing for years and are still not terminated. Therefore, most cardiology centers that practice PFO closure in Europe adapt a pragmatic approach and close PFO’s estimated at high risk for recurrence. In the U.S., the HDE rule is applied.
Secondly, PFO has been been associated with migraine and aura. It has been shown that the prevalence of large PFO’s in migraine with aura patients is up to 6 time higher than in the general population. A proposed mechanism in this condition is the passage of chemical substances from the right circulation through the PFO to the brain to trigger constriction of the brain vessels. A RCT (the MIST trial) has been concluded, presented at international meetings and will be published in due course. This study, comparing device closure to a sham procedure, did not demonstrate complete elimination of migraines but revealed less frequent and shorter migraine periods. Several other RCT are currently ongoing with final results to be expected within 2 years.
Third, it has been shown that divers with a PFO have a 5 fold risk of unexplained and severe decompression illness. Scuba divers may, depending on duration and depth of diving, develop bubbles in the veins. These bubbles are mostly small and are therefore trapped in the lung circulation and filtered out. In case of a large PFO, these bubbles may cross the PFO to the brain circulation and thereby cause decompression illness. Although it is generally accepted that large PFO’s are a contra-indication for diving, there are no real European recommendations on screening or treatment of “PFO – divers”.
The presence of a PFO has been associated with other more rare clinical entities and research is ongoing in emerging conditions such as the “sleep-apnea syndrome”.
In conclusion, if the diagnosis of an ASD has been established, percutaneous closure by an umbrella-type device is preferred if technically feasible. The presence of a PFO is no longer considered as an “innocent bystander” in the general population. It has been associated with stroke of unknown cause in young patients, with migraine with aura and decompression illness in divers. Further clinical research will establish candidates for percutaneous closure. In the meantime, closure is proposed under certain circumstances.