Accuracy of conventional transthoracic echocardiography for the diagnosis of intracardiac right-to-left shunt: a meta-analysis of prospective studies. Background: Paradoxical embolization through a right-to-left shunt (RLS), often from a patent foramen ovale (PFO), has been associated with cryptogenic stroke. While transesophageal echo (TEE) bubble study is the current standard reference for diagnosing PFO, transthoracic echo (TTE) remains the most commonly used screening test for RLS due to its noninvasiveness and easy availability. The aim of this meta-analysis was to determine the accuracy of TTE compared to TEE as the reference. Methods and Results: A systematic review of Medline, Cochrane, and EMBase was done to look for all the prospective studies assessing for intracardiac RLS using conventional TTE compared to TEE as the reference; both TTE and TEE were performed with a contrast agent and a maneuver to provoke RLS in all studies. A total of 13 studies with 1436 patients fulfilled the inclusion criteria. The weighted mean sensitivity and specificity for TTE were 46% and 99%, respectively. Likewise, the positive likelihood ratio and negative likelihood ratio were 20.85 and 0.57, respectively. Using different contrast agents, different microbubble cutoffs for a positive TTE/TEE, and different cardiac cycle cutoffs for a positive TTE/TEE did not affect the accuracy of TTE. In a population of patients with cryptogenic stroke, a TTE that tests positive for RLS has a 95% probability of being a true positive. Conclusion: Transthoracic echocardiogram has a low sensitivity and extremely high specificity, making it a poor rule out test but an excellent rule in test for the detection of intracardiac RLS.

The addition of blood to agitated saline improves the sensitivity of TCD for the detection of RLS to 100% when compared to other conventional contrast agents; these findings support the addition of blood to agitated saline during TCD bubble studies.

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