Determination of the Optimum Number of Cardiac Cycles to Differentiate Intra‐Pulmonary Shunt and Patent Foramen Ovale by Saline Contrast Two‐ and Three‐Dimensional Echocardiography

Patent foramen ovale ( PFO ) and intra‐pulmonary shunt ( IPS ) are potential causes of stroke. The most optimum cardiac cycle cutoff for bubbles to appear in the left heart on saline contrast transthoracic echocardiography ( TTE ) as criteria to differentiate the 2 entities is unknown. Methods Ninety‐five adult patients had saline contrast transesophageal echocardiography ( TEE ), two‐dimensional (2D) and 3 DTTE . Sensitivity and specificity of each cardiac cycle as cutoff to differentiate a PFO and IPS were obtained. Results Transesophageal echocardiography showed IPS in 28 and PFO in 15 patients. If bubbles appeared in the left heart within the first 4 cardiac cycles (the 4th cardiac cycle rule) as compared to alternate cutoffs, a PFO was most accurately diagnosed by both 2D and 3 DTTE . Bubbles appearing at or after the 5th cardiac cycle most accurately determined an IPS . 3D versus 2 DTTE had a trend for a higher sensitivity (61% vs. 36%, P = 0.06), but similar specificity (94% vs. 91%) for IPS . Accuracy of 3 DTTE was 84% and 2 DTTE was 75% (P = 0.08) for IPS . For PFO , 2 DTTE sensitivity (87%) and specificity (98%) did not differ (P = NS) from that of 3 DTTE sensitivity (73%) and specificity (100%). Conclusions This study demonstrates for the first time that the 4th cardiac cycle rule differentiates PFO and IPS most optimally by 2D and 3 DTTE . 3 DTTE appears to have higher sensitivity for diagnosing IPS . These data suggest that 3 DTTE is preferable when IPS is to be diagnosed. Both methods are similar for diagnosing PFO .