Patent foramen ovale: to close or not to close – still the question

Introduction

Patent foramen ovale (PFO) is a physiological remnant of the foramen ovale, a connection between atria which is essential in fetal circulation. It is assumed to be a normal variant, as it is present in 20-27% of the population in autopsy studies but only in 10-15% of patients in contrast transesophageal echocardiography (TEE) [1]. This discrepancy may be due to increase in size of PFO with age.

Patent foramen ovale is a flap-like tunnel between atrial septa: primum and secundum in the location of the fossa ovalis. It is potential communication for right-to-left shunt. Patent foramen ovale usually opens during Valsalva manoeuvre and other physiological situations when pressure in the right atrium exceeds the left atrium, that is when negative pressure in the chest (e.g. during deep breath, cough, sneezing) raises systemic venous return. Patent foramen ovale remains unrecognized and silent in most cases.

The Mayo Clinic autopsy study showed that the size of a PFO increases from a mean of 3.4 mm in the first decade to 5.8 mm in the 10th decade of life, as the valve of the fossa ovalis stretches with age [1]. The prevalence of PFO presence decreasing with age may be due to shorter life of patients with PFO or spontaneous closure. Recent evidence from surgical data show the opposite, that PFO prevalence is not related to age [2].

Patent foramen ovale (PFO) is associated with cryptogenic strokes, recurrent transient neurological deficits, sleep apnoea, decompression illness, and migraines [3].

Patent foramen ovale and cryptogenic stroke

Cryptogenic stroke represents up to 40% of all ischaemic strokes [4]. It is a diagnosis by exclusion, based on thorough investigation of other established causes of stroke.

The first paradoxical embolism related to PFO was described by Cohnheim in 1877. The most likely mechanism of cryptogenic stroke is paradoxical embolization through the PFO, but other possible hypotheses, such as the formation and release of thrombus from within the PFO tunnel and the passage of vasoactive humoral substances that are normally degraded in the pulmonary circulation, have also been suggested [5].

It is hard to show clearly, according to evidence-based medicine, that the PFO is worth closing, because there are no randomized positive studies showing a benefit of the closing strategy over...


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