The pathophysiology of patent foramen ovale and its related complications

The foramen ovale plays a vital role in sustaining life in-utero; however, a patent foramen ovale (PFO) after birth has been associated with pathologic sequelae in the systemic circulation including stroke/transient ischemic attack (TIA), migraine, high altitude pulmonary edema, decompression illness, platypnea-orthodeoxia syndrome (POS) and worsened severity of obstructive sleep apnea. Importantly, each of these conditions is most commonly observed among specific age groups: migraine in the 20 to 40s, stroke/TIA in the 30-50s and POS in patients > 50 years of age. The common and central pathophysiologic mechanism in each of these conditions is PFO-mediated shunting of blood and its contents from the right to the left atrium. PFO-associated pathologies can therefore be divided into (1) paradoxical systemic embolization and (2) right to left shunting (RLS) of blood through the PFO. Missing in the extensive literature on these clinical syndromes are mechanistic explanations for the occurrence of RLS, including timing and the volume of blood shunted, the impact of age on RLS, and the specific anatomical pathway that blood takes from the venous system to the left atrium. Visualization of the flow pattern graphically illustrates the underlying RLS and provides a greater understanding of the critical flow dynamics that determine the frequency, volume, and pathway of flow. In the present review, we describe the important role of foramen ovale in in-utero physiology, flow visualization in patients with PFO, as well as contributing factors that work in concert with PFO to result in the diverse pathophysiological sequelae.