Case History A 62-year-old man underwent a catheter ablation procedure for recurrent idiopathic paroxysmal atrial fibrillation (AF). He was having several daily episodes of AF that were inadequately controlled with antiarrhythmic therapy. While on propafenone, he had an episode of atrial flutter with 1:1 conduction resulting in a wide QRS complex tachycardia and syncope. A phased-array intracardiac echo catheter was advanced from the right femoral vein to the right atrium. From the right femoral vein, a bi-directional, steerable, octapolar catheter (SteeroCath-Dx Catheter model 2028BL, 7 French, 2.5/5/2.5 mm interelectrode spacing; Boston Scientific, San Jose, California) was placed in the coronary sinus (CS), and a double transseptal catheterization was performed. The baseline rhythm was sinus and neither spontaneous atrial ectopy nor AF were observed during the procedure. Wide-area left atrial ablation, guided by electroanatomic mapping and intracardiac echo, was performed using an 8 mm tip ablation electrode and radiofrequency current. Additional segmental ostial isolation was performed, guided by a circular mapping catheter positioned at the ostium of each pulmonary vein (PV), to achieve conduction block into all four PVs. Ablation of the cavotricuspid isthmus was also performed to achieve bi-directional conduction block. The patient tolerated the procedure well and there were no complications. Two months later, an ECG confirmed sinus rhythm and there were no reports of AF. Role of a CS Catheter During AF Ablation Catheter ablation has been shown to be an effective nonpharmacologic treatment option for patients with AF, and is associated with a high success rate in patients without structural heart disease.1,3 Placement of a catheter in the CS has many advantages during an ablation procedure for AF. These include the presence of a fluoroscopic marker within the CS, and the ability to pace and record from the left atrium. CS Catheter as a Fluoroscopic Marker Catheter ablation is increasingly anatomically based. A fluoroscopic marker in the CS facilitates localization of several important structures during the procedure, including the fossa ovalis during transseptal catheterization, the mitral annulus during left atrial mapping, and the CS ostium during ablation of the cavotricuspid isthmus. Figure 1 shows an octapolar catheter within the CS during transseptal catheterization. The catheter in the CS can be seen in the left anterior oblique view outlining the course of the CS above the mitral annulus. The presence of multiple electrodes improves the ability to identify the catheter fluoroscopically. Localization of the CS with the catheter can help orient the operator to the atrial anatomy. Pacing with a CS Catheter Left atrial pacing is necessary during catheter ablation for AF. When a segmental ostial isolation approach is used, it can be difficult to discriminate a left atrial signal from a pulmonary vein potential during sinus rhythm. Pacing from the distal coronary sinus often separates the LA from the PV potential.4 This can help make identification of the earliest PV potential easier when targeting the PV ostium or help determine if all PV potentials have been abolished after ablation. Figure 2 shows high-quality signals from the CS catheter during both sinus rhythm and CS pacing. The tracing also demonstrates the effect of pacing on the sequence of activation of the PV fascicles at the antrum. Pacing from within the coronary sinus can also be used to determine if there is conduction block between the left inferior PV and the mitral annulus after ablation for mitral isthmus-dependent flutter. Induction of AF has also been found to be a useful endpoint during AF ablation procedures.2 Most studies that have evaluated the utility of inducibility as an endpoint have used atrial pacing from the CS. Recording with a CS Catheter Intracardiac recordings from the CS also have value during AF ablation procedures. At the initiation of AF, recordings from the CS can be used to help localize the origin of the ectopy that triggers the AF. During sustained AF, recordings from elsewhere in the left atrium can be compared to the CS recordings to get a sense of relative frequency and amplitude. Left atrial sites that are associated with fractionated high-frequency potentials suggest the presence of a driver or rotor that could be targeted with ablation.5 Value for Left Atrial Flutter Left atrial flutter can occur after left atrial ablation for AF. Occasionally, it can be difficult to differentiate typical right atrial flutter from a left atrial flutter after wide-area circumferential left atrial ablation.6 Recordings from a CS catheter at the beginning of the case can help determine if the flutter circuit involves the left or right atrium. Measurement of the post-pacing interval from the CS can also rule in or rule out the left atrium when considering whether transseptal catheterization is needed to ablate an atrial flutter. Advantages of the SteeroCath-Dx Catheter Historically, electrophysiology catheters have been placed in the CS using a jugular approach. However, techniques were developed in the early 1990s to cannulate the CS from the femoral approach to avoid multiple central venous access sites.7 Facilitates a Femoral Approach. The familiar handle and bidirectional steering of the SteeroCath-Dx Catheter help guide the catheter through tortuous vasculature from the femoral vein up to the right atrium. After the catheter is positioned along the tricuspid annulus at the His-bundle location, it is deflected caudally and rotated posteriorly (clockwise) into the CS ostium. Fluoroscopic imaging in the LAO view and inspection of the electrograms can be used for guidance. Once the tip of the catheter is engaged in the ostium of the CS, the curve is relaxed and the catheter is advanced with continued clockwise rotation. The bi-directional curve can be used to point the tip of the catheter cranially as the catheter is advanced within the body of the CS to avoid entry into lateral branches. Soft Tip, Superior Steerability. Many features of the SteeroCath-Dx Catheter facilitate CS cannulation from an inferior approach. These include a soft tip, a curve radius that is appropriate for most patients, and a shaft that provides superior steerability, pushability, and torqueability. Navigation of the SteeroCath-Dx Catheter through tortuous vessels and within the heart is facilitated by two additional features: the adjustable curve-tension lock feature, and the in-plane steering feature that provides a measure of predictability by keeping the catheter tip deflection in the same plane as the flat part of the handle. Enhanced Stability. The SteeroCath-Dx Catheter provides excellent recordings and remains stable after positioning in the CS as demonstrated in Figures 2 and 3. Stability can be particularly important during AF ablations where the left atrial catheters commonly pass along the right atrial septum and can dislodge a CS catheter during LA mapping and catheter manipulation. An octapolar catheter, such as the one used in this case, can provide incremental information compared to a standard quadripolar catheter, including the atrial activation sequence along the mitral annulus. Multiple electrodes within the CS also provide the opportunity to pace from multiple left atrial sites without repositioning the catheter. For example, when analyzing left-sided PV recordings it is helpful to pace from the distal CS, but when determining whether or not there is cavotricuspid isthmus block, it is helpful to pace from the proximal CS closer to the isthmus. Conclusion In summary, there is an important role for a CS catheter in all catheter ablation procedures for AF and atrial flutter. The SteeroCath-Dx bi-directional CS octapolar Catheter can be placed using a femoral approach and has many advantages, including excellent catheter shape, steerability, and handling, as well as stable, high-quality electrograms during sinus rhythm and pacing.