Dear Readers, Transseptal puncture (TSP) was first described independently by Ross and Cope in 1959. Prior to this, the left atrium was accessed via a transbronchial or direct percutaneous infrascapular approach. Initially, transseptal left atrial access was used to assess hemodynamics and perform mitral valvuloplasty, and most of the expertise related to transseptal catheterization resided in the hands of interventional cardiologists. Many electrophysiologists did not have the training needed to perform TSP. In fact, in many EP labs, left-sided accessory pathways were ablated primarily using a retrograde aortic approach; in the rare cases, when transseptal catheterization was required, an interventional cardiologist was often summoned to help. Everything changed when catheter ablation for atrial fibrillation (AF) took off about ten years ago. Even though some of the initial pulmonary vein recordings were made using a retrograde aortic approach, electrophysiologists who wanted to ablate atrial fibrillation had to be proficient in TSP. Now the physicians who are the most experienced with TSP are clearly the interventional electrophysiologists. The numbers of transseptal catheterizations being performed around the world has soared over the last decade. This increase has been driven mostly, of course, by the increase in AF ablation procedures. However, new percutaneous procedures that require transseptal catheterization have also been developed. These procedures include percutaneous closure of atrial septal defects, left atrial appendage closure device implantation, and left ventricular assist device implantation. Transseptal catheterization can be performed with a very high success rate and low complication rate, in experienced hands using modern techniques. DePonti et al published a multicenter survey of 5,520 TSPs performed over 12 years in 33 Italian EP labs.1 Almost 80% of the cases were ablation procedures for atrial fibrillation. The success rate was 99.1% and the complication rate was only 0.79%. The complications were aortic perforation, pericardial tamponade, systemic embolization, ST segment elevation, cerebral air embolization, and thrombus formation on the sheath. Nevertheless, there is room for improvement. Tools that are now available to facilitate TSP include intracardiac echocardiography, radiofrequency (RF) powered wires and needles, and needle-tipped guidewires. One tool that is clearly useful during TSP is echocardiography. Fluoroscopy is used to guide nearly every case of TSP, but fluoroscopy cannot visualize soft tissue structures. Therefore, different ultrasound-based tools have been used to provide supplement imaging. These include transthoracic, transesophageal, and intracardiac echocardiography. In fact, transthoracic echocardiography can be used without fluoroscopy to guide TSP. There is a case report of TSP and balloon mitral valvuloplasty performed at the bedside solely with transthoracic echocardiographic guidance.2 Given the limitations of transthoracic and transesophageal echocardiography, intracardiac echocardiography is becoming the ultrasound tool of choice to guide TSP. It has the advantages of providing reliable high quality images of the fossa ovalis, and being easy to manipulate by the physician performing the TSP without the need for a second operator. Typically a standard Brockenbrough needle is used to puncture the fossa ovalis during TSP. However, the use of a standard needle and mechanical pressure can be difficult at times when the interatrial septum is thick or when TSP has been performed previously. Several options can be considered when the puncture is difficult. One option is an RF-powered guidewire from Baylis Medical Company. Although this guidewire can be useful, it does not provide the additional curvature and support that a needle does. Furthermore, because the wire has a diameter of 0.035”, it is not compatible with most transseptal dilators, which typically accept a wire no greater than 0.032”. Another alternative to conventional techniques is to deliver RF energy to the tip of a standard transseptal needle. Current can be delivered to the tip because most of the needle is insulated by the dilator. Several operators have reported using a standard transseptal needle attached to a conventional ablation RF generator or an electrosurgical generator. A recent study found that TSP was unsuccessful in 13 cases of 269 consecutive patients using a Brockenbrough needle and standard methods. Each of these patients had undergone a prior transseptal procedure. In each of the failed cases, TSP was ultimately achieved by the application of unipolar RF energy to the proximal hub of the needle via an ablation catheter. There is also an FDA-approved RF-powered needle (NRG™, Baylis Medical Company Inc., Montreal, Quebec, Canada). Energy is delivered to the tip of this specialized needle using a proprietary RF generator. The generator has built-in safety features to automatically shut off output under certain conditions including incorrect current or power delivery, or a very high or low impedance. Advantages of a powered needle are the ease of use, the need for little mechanical pressure to cross the fossa, and the fact that it is analogous to conventional transseptal techniques requiring little additional training. There does not appear to be additional risk. A recent study of 41 TSPs in 35 consecutive patients undergoing left-sided catheter ablation using the RF-powered transseptal needle found the system to be safe and effective.3 Prior TSP had been performed in one-third of the patients. Energy was delivered at 10 watts for 2 seconds as gentle pressure was applied to the needle after it was engaged in the fossa ovalis using ICE guidance. In 5 of the 41 TSPs, the needle crossed into the left atrium before RF energy was delivered. In 35 of the remaining 36 punctures, the needle was successfully advanced into the left atrium after application of RF current. In one patient, the TSP with the powered needle was unsuccessful but was accomplished using a standard needle. The only complication was a transient right atrial thrombus, which occurred in two patients. An additional alternative to puncturing the septum with a standard or powered needle is to advance a specialized guidewire that has a sharp needle at the end of it (“needle wire”) through the lumen of a conventional needle. Such a wire is commercially available (SafeSept™ transseptal guidewire, Pressure Products, Inc. San Pedro, CA). This needle wire is a J-shaped, 120-cm long, 0.014” diameter nitinol needle that replaces the stylet and forms a J-shape as it comes out of the tip of the needle. It allows for confirmation that the needle has entered the left atrium by advancing it into a left-sided pulmonary vein before advancing the standard needle over the needle wire.4 Advancing the J-shaped wire ahead of the transseptal apparatus protects the needle and dilator from puncturing the wall of the left atrium after the septum is punctured. The needle at the end of the wire is so small that it is difficult to see on fluoroscopy. However, it crosses the fossa with little effort and might be useful when the fossa is difficult to puncture using a standard needle and to provide additional confirmation that the puncture was accurate when intracardiac echo is not available for direct visualization. There are several other new technologies in development that might prove useful to perform or guide TSP, including the LA-Crosse system (St. Jude Medical, St. Paul, MN) designed for punctures from a superior approach, and an excimer laser catheter. An investigational TSP catheter that allows direct color visualization of the septum has also been used successfully in animal models. Although the complication rate of TSP is low, anything that can help get the complication rate closer to zero should be considered. Given the nature of the potential complications related to TSP, variations in atrial septal anatomy, the need at times for double transseptal catheterization, the rise in repeat TSPs, and the inexperience of some physicians performing TSP, the use of new tools should be considered as we strive for a zero complication rate in the EP lab.