Experience with using a safe landmark the fossa ovalis in transseptal procedures

Background and Objectives: Pressure monitoring and injection of contrast media after piercing the fossa ovalis are used to avoid life-threatening complications during transseptal procedures. However, when performing those maneuvers, the information provided can only be obtained after having pierced structures that may not have been the intended target. When we injected the contrast media through a Brockenbrough needle before piercing the fossa, the dye that had collected under the membranous septum tented by the transseptal equipment (tenting) was observed on the left anterior oblique (LAO) projection and this indicated the fossa ovalis. This study was performed to evaluate the usefulness and safety of tenting in order to identify the membranous septum during transseptal procedures. Subjects and Methods: Contrast injections were performed on the fossa ovalis and the septal wall surrounding it during 64 transseptal procedures. The rates of dye staining and tenting in both the muscular and membranous septums were compared. Results: No areas of the muscular septum exhibited any tenting. Various rates of dye staining of those areas were observed. However, the membrane of the fossa exhibited tenting without dye staining in all 64 cases. The sensitivity of the tenting without dye staining to identify the Fossa was 98%, and the specificity was 100%. Conclusion: Tenting without dye staining could differentiate the membranous septum from the muscular one with high diagnostic accuracy. This method could be used as a safe landmark for the fossa ovalis before piercing it during transseptal procedures.