What are the recommended diagnostic criteria for identifying a patent foramen ovale (PFO) in patients who have experienced a stroke?

Recommended diagnostic criteria for identifying a patent foramen ovale (PFO) in patients who have experienced a stroke focus primarily on imaging evidence of right-to-left shunting, especially in the context of cryptogenic stroke or transient ischaemic attack (TIA).

According to UK guidelines (NG128), the initial diagnostic approach involves transthoracic echocardiography (TTE) with bubble contrast during a Valsalva manoeuvre to detect right-to-left shunt, which is suggestive of PFO presence. If TTE is inconclusive or if clinical suspicion remains high, transoesophageal echocardiography (TOE) with bubble contrast is recommended as the gold standard for definitive diagnosis due to its superior sensitivity and specificity ¹.

Meta-analyses of diagnostic accuracy support TOE as the most reliable modality, demonstrating higher detection rates of PFO compared to TTE (Mojadidi et al., 2014). The diagnostic criteria on TOE include visualization of microbubbles crossing from the right atrium to the left atrium within three cardiac cycles after contrast injection, confirming a right-to-left shunt (Mojadidi et al., 2014).

Additional factors considered in diagnosis include the size of the shunt and the presence of an atrial septal aneurysm, which increase the likelihood that the PFO is clinically relevant in stroke pathogenesis (Mazzucco et al., 2018). The presence of a PFO alone is common in the general population, so diagnosis in stroke patients requires correlation with clinical context, especially cryptogenic stroke without other identifiable causes [1, (Mazzucco et al., 2018)].

In summary, the recommended diagnostic criteria for PFO in stroke patients are:

• Detection of right-to-left shunt by bubble contrast echocardiography, initially by TTE and confirmed by TOE if needed ¹.
• Visualization of microbubbles crossing the interatrial septum within three cardiac cycles on TOE (Mojadidi et al., 2014).
• Assessment of shunt size and associated atrial septal abnormalities to evaluate clinical significance (Mazzucco et al., 2018).
• Integration of imaging findings with clinical presentation, particularly in cryptogenic stroke cases ¹.

This integrated approach ensures accurate identification of PFO as a potential stroke mechanism, guiding appropriate management decisions.