Atrial septal defect (ASD) is a heart defect in which blood flows between the atria (upper chambers) of the heart. Some flow is a normal condition both pre-birth and immediately post-birth via the foramen ovale, however when this does not naturally close after birth it is referred to as a patent (open) foramen ovale (PFO). Normally, after PFO closure, the atria are separated by a dividing wall, the interatrial septum. If this septum is defective or absent, then oxygen-rich blood can flow directly from the left side of the heart to mix with the oxygen-poor blood in the right side of the heart, or vice versa. This can lead to lower-than-normal oxygen levels in the arterial blood that supplies the brain, organs, and tissues. However, an ASD may not produce noticeable signs or symptoms, especially if the defect is small. Also, in terms of health risks, people who have had a cryptogenic stroke are more likely to have a PFO than the general population.
A “shunt” is the presence of a net flow of blood through the defect, either from left to right or right to left. The amount of shunting present, if any, determines the hemodynamic significance of the ASD. A “right-to-left-shunt” typically poses the more dangerous scenario.
During development of the baby, the interatrial septum develops to separate the left and right atria. However, a hole in the septum called the foramen ovale, allows blood from the right atrium to enter the left atrium during fetal development. This opening allows blood to bypass the nonfunctional fetal lungs while the fetus obtains its oxygen from the placenta. A layer of tissue called the septum primum acts as a valve over the foramen ovale during fetal development. After birth, the pressure in the right side of the heart drops as the lungs open and begin working, causing the foramen ovale to close entirely. In about 25% of adults, the foramen ovale does not entirely seal. In these cases, any elevation of the pressure in the pulmonary circulatory system (due to pulmonary hypertension, temporarily while coughing, etc.) can cause the foramen ovale to remain open.
Patent Foramen Ovale
Most patients with a PFO are asymptomatic and do not require any specific treatment. However, those who develop a stroke require further workup to identify the etiology. In those where a comprehensive evaluation is performed and an obvious etiology is not identified, they are defined as having a cryptogenic stroke. The mechanism for stroke is such individuals is likely embolic due to paradoxical emboli, a left atrial appendage clot, a clot on the inter-atrial septum, or within the PFO tunnel.
Until recently, patients with PFO and cryptogenic stroke were treated with antiplatelet therapy only. Previous studies did not identify a clear benefit of PFO closure over antiplatelet therapy in reducing recurrent ischemic stroke. However, based on new evidence and systematic review in the field, percutaneous PFO closure in addition to antiplatelet therapy is suggested for all who meet all the following criteria.
Age ≤ 60 years at onset of first stroke,
Embolic-appearing cryptogenic ischemic stroke (i.e., no evident source of stroke despite a comprehensive evaluation), and PFO with a right-to-left interatrial shunt detected by bubble study (echocardiogram) A variety of PFO closure devices may be implanted via catheter-based procedures.
Based on the most up to date evidence, PFO closure is more effective at reducing recurrent ischemic stroke when compared to medical therapy. In most of these studies, antiplatelet and anticoagulation were combined in the medical therapy arm. Although there is limited data on the effectiveness of anticoagulation in reducing stroke in this population, it is hypothesized that based on the embolic mechanism, that anticoagulation should be superior to antiplatelet therapy at reducing risk of recurrent stroke. A recent review of the literature supports this hypothesis recommending anticoagulation over the use of antiplatelet therapy in patients with PFO and cryptogenic stroke. However, more evidence is required comparing of PFO closure with anticoagulation or anticoagulation with antiplatelet therapy.
Atrial Septal Defect
Once someone is found to have an atrial septal defect, a determination of whether it should be corrected is typically made. If the atrial septal defect is causing the right ventricle to enlarge a secundum atrial septal defect should generally be closed. If the ASD is not causing problems the defect may simply checked every two or three years.Methods of closure of an ASD include surgical closure and percutaneous closure.