Patent foramen ovale pathophysiology
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editors-In-Chief: Priyamvada Singh, M.B.B.S. [2]; Assistant Editor-In-Chief: Kristin Feeney, B.S. [3]
Overview
A patent foramen ovale is a flap-like structure in inter-atrial septum that is formed by failure of postnatal fusion of septum primum and septum secundum. It periodically opens and allows blood to shunt between the two atria. Thus, it is also sometimes called as a 'probe patent (PFO). This flap-like structure functions like a one-way valve mechanism that only opens to allow blood to flow from the right atrium to the left atrium during times where there is an increase flow or pressure in the right atrium. Elevation of pressure in the pulmonary circulatory system (i.e.: pulmonary hypertension, cough or valsalva maneuver) can cause the foramen ovale to open.
Pathophysiology
A patent foramen ovale or PFO is not considered an atrial septal defect because there is not a permanent hole or defect in interatrial septum. Instead there is a flap-like structure that periodically opens which allows blood to shunt between the two atria. As a result, it is also sometimes called as a probe patent (PFO). This flap-like structure functions like a one-way valve mechanism that only opens to allow blood to flow from the right atrium to the left atrium during times where there is an increase flow or pressure in the right atrium. Elevation of pressure in the pulmonary circulatory system (i.e.: pulmonary hypertension due to various causes, or transiently during a cough or valsalva maneuver) can cause the foramen ovale to open. Because of this one-way valve like mechanism and the dynamic nature of the right to left shunting, a patient is often asked to perform a Valsalva maneuver during a echocardiographic bubble study to facilitate transit of bubbles from the right atrium to the left atrium.
A patent foramen ovale is a flap-like structure that periodically opens and allows shunting of blood from right-to-left atria. As a result, it is also sometimes called as a 'probe patent' patent foramen ovale. The shunting could occur with a transient elevation of pressure in the pulmonary circulation that occurs during pulmonary hypertension, valsalva maneuver or cough. The size and the degree of right-to-left shunt appear to be important in determining the pathological significance of patent foramen ovale[1], [2], [3]. In a multi-center randomized trial, larger patent foramen ovale were found to be more associated with cryptogenic stroke than smaller patent foramen ovale[4].
Embryology
During fetal development, the presence of a patent foramen ovale is necessary for life as it allows for right-to-left shunting so that oxygenated blood can flow to the left side of the heart. At the time of birth, blood begins to flow through the pulmonary circulation and this results in a rise in left atrial pressure. This rise in left atrial pressure functionally closes the flap-like structure. This functional closure is usually followed by the mechanical or anatomic closure of the structure by the age of one. A patent foramen ovale or PFO forms by failure of postnatal fusion of the two components that form the inter-atrial septum i.e. septum primum and septum secundum.
References
- ↑ Homma S, Di Tullio MR, Sacco RL, Mihalatos D, Li Mandri G, Mohr JP (1994). "Characteristics of patent foramen ovale associated with cryptogenic stroke. A biplane transesophageal echocardiographic study". Stroke. 25 (3): 582–6. PMID 8128511.
- ↑ Hausmann D, Mügge A, Daniel WG (1995). "Identification of patent foramen ovale permitting paradoxic embolism". J Am Coll Cardiol. 26 (4): 1030–8. doi:10.1016/0735-1097(95)00288-9. PMID 7560596.
- ↑ Steiner MM, Di Tullio MR, Rundek T, Gan R, Chen X, Liguori C; et al. (1998). "Patent foramen ovale size and embolic brain imaging findings among patients with ischemic stroke". Stroke. 29 (5): 944–8. PMID 9596240.
- ↑ Homma S, Sacco RL, Di Tullio MR, Sciacca RR, Mohr JP, PFO in Cryptographic Stroke Study (PICSS) Investigators (2002). "Effect of medical treatment in stroke patients with patent foramen ovale: patent foramen ovale in Cryptogenic Stroke Study". Circulation. 105 (22): 2625–31. PMID 12045168.