Two-dimensional echocardiography using second harmonic imaging for the diagnosis of intracardiac right-to-left shunt: a meta-analysis of prospective studies

Right-to-left shunting (RLS), usually through a patent foramen ovale (PFO), has been associated with migraine, cryptogenic stroke and hypoxemia. With emerging observational studies and clinical trials on the subject of PFO, there is a need for accurate diagnosis of PFO in patients being considered for transcatheter closure. While transesophageal echo (TEE) bubble study is the current standard reference for diagnosing PFO, transthoracic echo with second harmonic imaging (TTE-HI) may be a preferable screening test for RLS due to its high accuracy and non-invasiveness. The aim of this meta-analysis was to determine the accuracy of TTE-HI compared to TEE as the reference. A systematic review of Medline, Cochrane and Embase was done for all the prospective studies assessing for intracardiac RLS using TTE-HI compared to TEE as the reference; both TTE-HI and TEE were performed with a contrast agent and a maneuver to provoke RLS in all studies. A total of 15 studies with 1995 patients fulfilled the inclusion criteria. The weighted mean sensitivity and specificity for TTE-HI were 91 and 93 % respectively. Likewise, the positive and negative likelihood ratios were 13.52 and 0.13 respectively. TTE-HI is a reliable, non-invasive test with proficient diagnostic accuracies. The high sensitivity and specificity of TTE-HI make it a useful initial screening test for RLS. If the precise anatomy is required, then TEE can be obtained before scheduling a patient for transcatheter PFO closure.