Since its introduction by Ross et al¹ and Cope² in 1959, transseptal catheterization has gained widespread acceptance among cardiologists as an important tool in the interventional laboratory. Although originally embraced mainly by interventional cardiologists, during recent years the electrophysiology community has used the technique more frequently to gain access to the left atrium, as atrial fibrillation ablation has entered the mainstream. Recent advances demonstrating involvement of the pulmonary veins (PV) for initiation of atrial fibrillation (AF) led to the development of different ablative approaches for the treatment of AF, and transseptal catheterization became an integral part of these approaches. While the original technique relied mainly on fluoroscopic imaging, additional imaging provided by intracardiac echocardiography (ICE) has become a very useful tool to reduce potential complications and avoid pitfalls that might arise from complicated cases.
       Anatomy. The left atrium is positioned posterior, leftward, and inferior to the right atrium. The interatrial septum originates embryologically from the septum primum and the septum secundum. The fossa ovalis is the thinnest portion of the interatrial septum. In up to 20% of adults, the fossa ovalis remains open, resulting in a patent foramen ovale. Access to the left atrium is obtained either via a needle puncture through the fossa ovalis or direct catheter introduction across a patent foramen ovale.
       Transseptal sheaths and dilators. Multiple transseptal sheaths by different manufacturers have been developed, with each designed for better access to a specific location in the left atrium. St. Jude Medical’s Daig™ SL sheaths (St. Paul, Minnesota) are designated SL1 to SL4, with the higher-numbered sheaths designed for closer proximity to the mitral annulus. In our lab we mainly use SL1 sheaths for transseptal puncture and subsequent pulmonary vein isolation.
       The Brockenbrough needle. The Brockenbrough needle has been designed with different curvatures. In our lab we usually use BRK-1™ (Daig Corporation, Minnetonka, Minnesota) Brockenbrough needle for transseptal puncture. We believe that its enhanced curvature will result in a better reach to the septum and avoid the possibility of the needle sliding up the septum and perforating the left atrium or right superior pulmonary vein. In cases where we use the BRK Brockenbrough needle, we manually enhance the proximal curvature of the needle to simulate the BRK-1 curvature.
       Transseptal catheterization. We place a His bundle catheter via a 6 Fr venous sheath introduced through the left femoral vein to identify the most inferior aspect of the noncoronary cusp of the aorta. Of course this is only true when the His bundle catheter is recording a His bundle electrogram. We also place a coronary sinus catheter, usually via right internal jugular access, to adjust for the effects of cardiac rotation. During transseptal puncture, the transseptal unit is kept parallel to the coronary sinus catheter and posterior to the His bundle catheter. This prevents damage to the structures close to the fossa ovalis like the aorta or coronary sinus.
       All patients undergo ICE using a 9 Fr, 10.5 MHz phased-array ICE catheter imaging system (Accuson™, Siemens Medical Inc., Malvern, Pennsylvania) introduced through the left femoral vein.³ The ICE images are used to locate the thinnest portion of the interatrial septum and confirm the location of the transseptal needle. It is also useful in monitoring the posterior portion of the left atrium wall, ensuring that the transseptal needle does not puncture the posterior wall of the left atrium. We believe that the addition of ICE images to standard fluoroscopic imaging provides an additional significant safety net to the procedure, justifying its extra cost.
       In the current issue of the Journal of Invasive Cardiology, Verma et al report on the innovative use of a nonfluoroscopic mapping system (EnSite NavX™, St. Jude Medical - Endocardial Solutions, St. Paul, Minnesota) for real-time, three-dimensional localization of the Brockenbrough needle tip. The authors show that by using the three-dimensional images produced by the EnSite NavX system, they were able to overcome the limitations of two-dimensional imaging provided by fluoroscopic and ICE images. They connected the proximal end of the Brockenbrough needle to the recording system by using a sterile alligator clip, while the other end of the clip was connected to the distal electrode tip of a temporary pacing electrode. The temporary pacing electrode was then connected to the recording system. Using this approach, the tip of the needle was displayed on the EnSite NavX system as a unipolar electrode when the needle was advanced beyond the sheath tip, since the dilator and sheath behave as the insulator. This introduces an interesting new approach to recording the location of the transseptal puncture, a use of the electrical and three-dimensional recording system to follow the needle tip. However, as the authors themselves acknowledge, the needle can only be localized after the needle tip has been advanced beyond the dilator. Intracardiac electrocardiograms have been previously used to improve the safety of transseptal catheterization.⁴ Although all these approaches provide interesting new techniques for transseptal catheterization, use of fluoroscopic and ICE images remains the mainstay of transseptal access in the everyday practice of cardiology.

1. Ross J Jr, Braunwald E, Morrow AG. Transseptal left atrial puncture: New technique for the measurement of left atrial pressure in man. Am J Cardiol 1959;3:653–655.
2. Cope C. Technique for transseptal catheterization of the left atrium: Preliminary report. J Thorac Surg 1959;37:482–486.
3. Martin RE, Ellenbogen KA, Lau YR, et al. Phased-array intracardiac echocardiography during pulmonary vein isolation and linear ablation for atrial fibrillation. J Cardiovasc Electrophysiol 2002;13:873–879.
4. Bidoggia H, Maciel JP, Alvarez JA. Transseptal left heart catheterization: Usefulness of the intracavitary electrocardiogram in the localization of the fossa ovalis. Cathet Cardiovasc Diagn 1991;24:221–225.