Patent Foramen Ovale
Patent foramen ovale is a persistent opening in the wall of the heart which did not close completely after birth (opening required before birth for transfer of oxygenated blood via the umbilical cord). This opening can cause a shunt of blood from right to left , but more often there is a movement of blood from the left side of the heart (high pressure) to the right side of the heart (low pressure).
Fetuses have a normal opening between the left and right atria (upper chambers) of the heart. If this opening fails to close naturally soon after the baby is born, the condition is called patent foramen ovale (PFO). Patent foramen ovale is the persistence of a fetal opening between the left and right atria (upper chambers) of the heart. This hole allows blood to bypass the lungs, because they are not used until a baby is born. The foramen ovale normally closes soon after the infant is born. The foramen ovale may remain open in as many as 1 out of 5 people. The cause is unknown and there are no known risk factors for developing a patent foramen ovale or PFO.
A patent foramen ovale represents an interatrial communication that is common in children. The presence of patent foramen ovale rarely has clinical significance in situations where no other congenital heart defect is present.
People with shunts are less likely to develop fainting or low blood pressure with diving than are obstructive valve lesions (such as mitral valve stenosis or aortic stenosis), but are more likely to develop fluid accumulation in the lungs from heart failure and severe shortness of breath from the effects of combined exercise and water immersion. Ordinarily, the left to right shunt will cause no problem; the right to left shunt, if large enough, will cause low arterial O2 tension (hypoxia) and severely limited exercise capacity. In divers there is the risk of paradoxical embolism of gas bubbles (passage of bubbles into the arterial circulation) which occur in just about all divers in the venous circulation during decompression.
Several echocardiography and postmortem studies indicate that the foramen remains competent in 30% of patent foramen ovale patients with otherwise normal cardiac anatomy.
* The vast majority of patients with patent foramen ovale experience no symptoms throughout life.
* Morbidity, though rare, is predominantly due to paradoxical embolism. Cerebrovascular ischemic events can be attributed to paradoxical embolism through patent foramen ovale. This occurs more frequently in adults who experience deep-vein thrombosis or a hypercoagulable state. Risk of paradoxical air embolism is high in children and adults who undergo neurosurgical procedures. In particular, the sitting position for neurosurgery carries high risk for paradoxical air embolisms. Additionally, patients with pulmonary disease and high pulmonary vascular resistance are at risk for right-to-left shunting and paradoxical embolism.