Abstract
A patent foramen ovale is a remnant of the foetal circulation that exists between the right atrium and the left atrium of the heart. It is estimated to be present in 1 in 4 adults in the general population. The presence of this residual hole can allow the passage of microemboli into the arterial system, which can then travel to the brain causing an ischemic stroke. A subtype of ischemic stroke is a cryptogenic stroke, which occurs when the initial cause of ischemia cannot be determined. The presence of a patent foramen ovale is more common in patients with cryptogenic stroke, suggesting a relationship. Currently, the most common method of detection for a patent foramen ovale is transthoracic echocardiography, which is often followed by transoesophageal echocardiography if the remnant is suspected and requires further investigation. An alternative method of diagnosis is transcranial Doppler, which has demonstrated diagnostic superiority in some studies. The use of all three imaging techniques are commonly utilized clinically, but the optimal method is still under debate.
In this thesis, the two bedside techniques transthoracic echocardiography and transcranial Doppler were applied to a case series of three patients with suspected patent foramen ovale that were referred on to the cardiology unit after an ischemic stroke, or possible cryptogenic stroke. Additionally, a systematic review and meta-analysis was undertaken to assess the status of the two diagnostic techniques in literature.
The case studies uncovered some significant pitfalls and advantages of both transthoracic echocardiography and transcranial Doppler, while still diagnosing all three case studies positively with a patent foramen ovale.
The systematic review and meta-analysis found that the sensitivity of the two bedside techniques changed when the gold standard reference technique, transoesophageal echocardiography, was included. Prior to its inclusion, the two techniques had similar levels of sensitivity, but on inclusion, transcranial Doppler appeared to be the optimal technique for the ruling in of a patent foramen ovale, while transthoracic echocardiology appeared to be the optimal technique for the ruling out of a patent foramen ovale.
Discrepancies between the detection techniques continue to emerge throughout literature, indicating the need for further investigation into the determination of the optimal technique, as well as methods that can be applied to optimize each technique. The treatment of a patent foramen ovale can be lifesaving, but an accurate initial diagnosis is needed to facilitate making the right treatment decision.