Closing patent foramen ovale in cryptogenic stroke: The underscored importance of other interatrial shunt variants

Abstract

Recent trials and metanalysis even not fully conclusive and still debated, at least suggested that mechanical device-based closure of patent foramen ovale (PFO) is more effective than medical therapy in prevent recurrence of stroke. In a proportion ranging from 20% to nearly 40% of patients in literature, PFO is associated to atrial septal aneurysm (ASA): ASA is a well-known entity often associated with additional fenestration. Additionally small atrial septal defects ("Flat ASD") can present with signs of paradoxical embolism and cannot be easily detected by transthoracic echocardiography or even by transesophageal echocardiography and are usually discovered by intracardiac echocardiography at the moment of transcatheter closure. This evidence might change potentially the anatomical diagnosis from PFO to fenestrated ASA or as we called it to "hybrid defect", being a bidirectional flow through a small ASD or/and an additional fenestration, often present. Despite the differences in anatomy, pathophysiology and haemodynamic paradoxical embolism may occur in both entities and also may be the first appearance of fenestrated ASA. Because some overlapping do really exist between PFO and hybrid defects, which are often not clearly differentiable by standard diagnostic tools, it is likely that a proportion of patients evaluated for potential transcatheter closure of PFO had actually a different anatomical substrate. These different anatomical and pathophysiologic entities have not been address in any of the previous trials, potentially having an impact on overall results despite the similar mechanical treatment. Neurologists and general cardiologists in charge of clinical management of PFO-related cryptogenic stroke should be aware of the role of hybrid defects in the pathophysiology of paradoxical embolism - mediated cerebral ischemic events in order to apply the correct decision - making process and avoid downgrading of patients with paradoxical embolism-related interatrial shunt variants different from PFO.

Keywords: Anatomy; Atrial septal defect; Echocardiography; Patent foramen ovale.

Figure 1

Secundum atrial septal defect is a defect located into the limit of the fossa ovalis. The shunt usually is left-to-right because of the pressure gradient between the left (high pressure) and right (low pressure) atrium. ASD: Atrial septal defect; IVC: Inferior vena cava; L: Left; R: Right; SVC: Superior vena cava.

Figure 2

Patent foramen ovale is a communication between the right and left atrium caused by the incompetence of the fossa ovalis valve. The shunt is usually right-to-left despite the gradient pressure between the atria. IVC: Inferior vena cava; L: Left; PFO: Patent foramen ovale; R: Right; SVC: Superior vena cava.

Figure 3

Spectrum of interatrial shunt associated with possible paradoxical embolism and potential related haemodynamic and functional characteristics. ASA: Atrial septal aneurysm; ASD: Atrial septal defect; FO: Fossa ovalis; IVC: Inferior vena cava; PAP: Pulmonary artery pressure; PFO: Patent foramen ovale; R-to-L: Right to left shunt; SVC: Superior vena cava; TCD: Transcranial doppler; TEE: Transesophageal echocardiography.