Interatrial transseptal catheterization is a technique commonly used in the electrophysiology laboratory to access the left atrium. The procedure is being used more commonly as ablation of atrial fibrillation is more widely applied. Traditionally, transseptal catheterization has been done utilizing fluoroscopic markers with hemodynamic monitoring.1,2 Different variations of the technique have been described. Recently, intracardiac echocardiography (ICE) has been used to assist in needle localization during transseptal catheterization.3,4 Left atrial catheter ablation is frequently performed with use of one of several three-dimensional mapping systems available commercially. We describe a new technique that allows localization of the Brockenbrough needle tip within the cardiac images created in a three-dimensional nonfluoroscopic mapping system (EnSite NavX™, St. Jude Medical – Endocardial Solutions, St. Paul, Minnesota) to allow accurate localization during transseptal catheterization. Methods Six patients undergoing radiofrequency ablation and requiring transseptal catheterization were studied. The ages ranged between 14 and 72 years. Five patients were found to have a concealed left lateral accessory pathway with participation in orthodromic atrioventricular re-entry tachycardia, and 1 patient required ablation for atrial fibrillation. We use the non-contact mapping system — EnSite NavX — for localization of lesions for left atrial ablations. EnSite NavX was used in 2 cases to obtain a sequential activation map to localize earliest atrial activity during orthodromic atrioventricular re-entry tachycardia. This system was used to display the tip of the Brockenbrough needle on the mapping system, as described later. Use of the EnSite NavX technology involves applying three pairs of surface electrode patches on the patient. An electrical signal is transmitted between the patches. The catheter senses the electrical signal and sends the information to the EnSite System computer to determine the catheter’s position within the heart. To create an accurate model of the heart chamber, a catheter is dragged across the chamber. The resulting three-dimensional computer model assists in identifying key structures and landmarks of the heart and in facilitating the delivery of accurate ablation therapy. The EnSite NavX technology can simultaneously display up to 64 electrodes, on up to 12 catheters. It allows catheter visualization and manipulation within the cardiac chamber without use of fluoroscopy. We connected the proximal end of the Brockenbrough needle to the recording system by using an alligator clip; one end of this clip was connected to the proximal end of the transseptal needle, and the other end was connected to the distal electrode tip of a temporary pacing electrode. The pins of the temporary pacing electrode were then placed into the recording system (Figure H). This allowed the needle tip to be displayed on the EnSite NavX system as a unipolar electrode when the needle was advanced beyond the sheath tip. Transseptal catheterization was performed using the electrophysiology catheters (a quadripolar HIS bundle catheter and decapolar coronary sinus catheter) as fluoroscopic landmarks. Standard fluoroscopic views, i.e., left 45 degrees and right 30 degrees anterior oblique were used. A 110 cm, 9 Fr/9 MHz intracardiac echocardiography Ultra ICE™ catheter (Boston Scientific Corp., Natick, Massachusetts) was used in all cases. Once the dilator of the transseptal sheath assembly was thought to be at the fossa ovalis, the position was confirmed by intracardiac echocardiography and fluoroscopy. The needle was gently advanced beyond the dilator tip into the left atrium with pressure monitoring. Once a left atrial pressure waveform was seen, a blood oxygen saturation level was checked from the needle tip. Sheath and dilator assembly were advanced only if the above steps confirmed left atrial access. Once the needle was advanced beyond the dilator tip, it became visible on the EnSite NavX system. Images from the EnSite NavX were compared to intracardiac echocardiography and fluoroscopy. Patients were given intravenous heparin per protocol after completion of the transseptal catheterization, and the remainder of the procedure was then completed. Results In all cases, successful, uncomplicated transseptal catheterization was achieved. An example of the localization achieved is displayed in the images. The needle tip behaves as a unipolar electrode, as the majority of the needle body is within the dilator and is hence insulated. The needle tip only becomes visible on EnSite NavX when the needle is advanced beyond the dilator and is present in the intracardiac blood pool. Excellent visual correlation of the needle position is seen between fluoroscopy, intracardiac echocardiography and EnSite NavX. The needle tip was localized to the center of the interatrial septum on the cardiac geometry images created in EnSite NavX in all cases. In the images presented here, “tenting” of the fossa ovalis is seen on intracardiac echocardiography. The EnSite NavX images show the needle tip to be located beyond the right atrial geometry created before the transseptal needle and dilator assembly were introduced. This was felt to be due to the tenting effect of the needle on the interatrial septum. One of the patients undergoing atrial fibrillation ablation had previously failed transseptal catheterization using fluoroscopy and intracardiac echocardiography. Despite aortic localization with a pigtail catheter in the ascending aorta, the transseptal needle tip had entered the aortic wall due to aortic root dilatation. No acute sequelae occurred during the initial attempt, and she was referred for a repeat attempt 6 weeks later. During the repeat attempt, the aortic root margins were clearly defined by manipulating an electrode catheter in the ascending aorta. These locations were tagged in detail using the EnSite NavX system, and successful transseptal catheterization was completed (Figure 1). This technique allowed us to clearly visualize the aortic outline as well as other critical landmarks. Discussion Three-dimensional cardiac mapping is commonly used for diagnosis and treatment of complex arrhythmias. With the increasing use of this technology for ablation of atrial fibrillation, there is also an increasing need for left atrial access via interatrial catheterization. Our experience described here suggests that localization of a transseptal needle can be achieved with the EnSite NavX system. This technology certainly does not replace the need for an experienced operator and usual care necessary for transseptal catheterization. Most physician operators are trained to perform this just with the use of fluoroscopic and hemodynamic monitoring, while others routinely add intracardiac echocardiography. The EnSite NavX mapping system is available in some electrophysiology laboratories, and this system allows the additional benefit of being able to display a Brockenbrough needle as an electrode. We have not attempted to perform this test with other commercially available three-dimensional cardiac mapping systems. We found that the degree of localization achieved is visually accurate and consistent within the different modalities tested. In addition, needle tip movement in the EnSite system corresponds to needle tip movement on fluoroscopy and intracardiac echocardiography. This is the only method we are aware of that allows three-dimensional localization of a Brockenbrough needle tip. All other methods of needle localization, including intracardiac echocardiography, have the limitation of providing only two-dimensional localization at a given instant. In cases where there is atrial septum “tenting” on intracardiac echocardiography, it is possible that the needle may “slide” up the septum instead of puncturing it. This may not be immediately apparent with intracardiac echocardiography, as views are limited to the ultrasound plane. We recognize that the needle can only be localized after the needle tip has been advanced beyond the dilator. However, in our experience, advancement of the needle tip alone without advancement of the dilator or sheath in an incorrect location does not lead to perforation. During this study, this technique allowed us to orient the needle tip in a very precise manner, i.e., a slight posterior orientation of the needle was preferred to avoid aortic entry and direct the sheath towards the posterior mitral annulus. Also, the posterior wall of the right atrium could be clearly defined in the EnSite map. The technique allows for “tagging” or marking of critical anatomical structures such as the atrioventricular node, coronary sinus and aorta, and assesses the location of the needle tip in relation to these structures prior to dilator and sheath advancement. Conclusion EnSite NavX is an accurate and useful adjunctive technology for transseptal catheterization. The technique described is easy to implement and requires an easy-to-build connector. In this preliminary series, we fashioned a connector using an alligator clip and a temporary pacemaker wire, however, a simple connector can easily be constructed. The localization and needle tip movement achieved are visually accurate compared to fluoroscopy and intracardiac echocardiography. The technique allows for real-time localization of the needle tip in relation to other right atrial anatomical landmarks and the aorta prior to dilator and sheath advancement. Accurate three-dimensional localization of the needle tip should help improve safety of transseptal catheterization, especially in patients with difficult anatomy. We hope that this preliminary series will open the door for further investigation in this field. Acknowledgments. The authors wish to acknowledge the invaluable technical assistance provided by Jeff Schultz from St. Jude Medical.
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