Typical right atrial flutter (AFL) commonly occurs in patients who have been previously treated with biventricular pacemakers and defibrillators. Such patients may benefit substantially from catheter ablation, but may not be approached due to concerns over coronary sinus (CS) lead dislodgement. Three cases of radiofrequency (RF) ablation of atrial flutter in the presence of CS pacing leads are presented along with an approach that allows for confirmation of bidirectional isthmus block. Our method, which utilizes a 10-mm, high-output ablation catheter, minimizes the number of diagnostic catheters required and restricts their location to areas that are less likely to result in CS lead dislodgement. Typical right atrial flutter is a common arrhythmia that often complicates congestive heart failure (CHF) and can be challenging to treat medically. Catheter ablation is an effective treatment for AFL with a high success and low recurrence rate.1-3 Many CHF patients are now treated with biventricular pacemakers and defibrillators utilizing a coronary sinus (CS) lead that is passively fixed within the CS. Such patients may not be referred for catheter ablation of typical right AFL due to concern that introduction of mapping and ablation catheters may result in CS lead dislodgement. The safety, efficacy, and feasibility of right AFL ablation in the setting of CS leads have not been reported. We present three consecutive patients who were treated with catheter ablation for typical right AFL in the presence of a CS pacing lead, and present an ablation approach including demonstration of bidirectional block. Case Studies Patient #1 is a 63-year-old female with advanced nonischemic cardiomyopathy who presented with recurrent, highly symptomatic AFL, with an atrial cycle length of 250 ms and 2:1 conduction. The surface ECG suggested typical right AFL. Because of severe symptoms of dyspnea, fatigue, and lightheadedness, AFL was pace-terminated using the atrial lead of her biventricular ICD, and she was referred for AFL ablation. In the electrophysiology laboratory, a 10-mm-tip RF ablation catheter (Blazer II XP™ Catheter, Boston Scientific, San Jose, CA) and a deflectable quadripolar mapping catheter were advanced to the right atrium. The baseline rhythm was sinus and AFL was noninducible with burst pacing and single atrial extrastimuli. Using the EPT-1000 XP™ Cardiac Ablation System (Boston Scientific), power was adjusted from 60–100 W, with a target temperature of 65 °C and an RF delivery time of 120 seconds. An ablation line was created on the medial aspect of the tricuspid valve annulus - inferior vena cava (TV-IVC) isthmus (Figure 1A). Following initial diminution of electrogram amplitude along the ablation line, we placed the deflectable catheter in the roof of the CS ostium with great care to avoid interaction with the CS lead, and assessed for block by proximal CS pacing. Further ablation was carried out during proximal CS pacing with assessment for block by moving the ablation catheter lateral to the line in the LAO projection after each lesion. After 12.3 minutes of RF delivery, double potentials with an isoelectric delay of 102 ms were seen along the entire ablation line (Figure 2A). Following the creation of bidirectional block along the TV-IVC isthmus, pacing was performed from the CS ostium using a deflectable mapping catheter; when recording from the medial aspect of the ablation line (Figure 1B), the conduction time was 114 ms (Figure 2B). Recording immediately lateral to the ablation line (Figure 1C) was associated with a conduction time of 218 ms (Figure 2C) from the proximal CS. Finally, recording from the far lateral isthmus (Figure 1D) during CS pacing demonstrated a conduction time of only 168 ms (Figure 2D), consistent with a lateral-to-medial depolarization sequence toward the lateral aspect of the ablation line. These intervals were consistent when pacing from the lateral ablation line and recording from the proximal CS, and supported the presence of bidirectional block. After six-month follow-up, the patient has had no recurrent AFL. Patient #2 is a 68-year-old male with a history of ischemic cardiomyopathy status post-biventricular ICD implantation and advanced oxygen-dependent chronic obstructive pulmonary disease (COPD). He presented with AFL that was refractory to treatment with sotalol and amiodarone. Surface ECG suggested typical right AFL. In the electrophysiology laboratory, the approach was the same as for patient #1. The baseline rhythm was AFL with a cycle length of 310 ms. Confirmation of a lateral-to-medial direction of isthmus activation was obtained by moving the ablation catheter across the isthmus. Concealed entrainment was demonstrated with a post-pacing interval less than 10 ms of the tachycardia cycle length. With power set between 60–100 W, and a target temperature of 65 °C, an ablation line was created on the medial aspect of the TV-IVC isthmus. Atrial flutter terminated after 6.9 minutes of ablation. The ablation catheter was placed at the lateral aspect of the ablation line. Pacing from the proximal CS reached the lateral TV-IVC isthmus in only 50 ms, inconsistent with a line of block. Further ablation was carried out during proximal CS pacing, and assessment for block was performed by moving the ablation catheter lateral to the line in the LAO projection after each lesion. Following 13.7 minutes of ablation time and completion of the line, there were double potentials along the line of block and the conduction time from proximal CS to the lateral isthmus increased to 190 ms, consistent with block. During six-month follow-up, the patient remains free of AFL with a markedly improved functional capacity. Patient #3 is an 86-year-old male with a history of aortic valve replacement, sick sinus syndrome previously treated with a permanent pacemaker, and persistent AFL. He has a biventricular ICD implanted for CHF with left ventricular dyssynchrony. He became highly symptomatic with fatigue and dyspnea during AFL and his arrhythmia was refractory to sotalol therapy. Surface ECG suggested typical right AFL. In the electrophysiology laboratory, our approach was the same as for patient #1. Upon arrival to the lab, his rhythm was typical AFL with an atrial cycle length of 257 ms. Entrainment mapping confirmed a mechanism of typical, counterclockwise right AFL. A 10-mm-tip Blazer II XP Catheter was placed along the TV-IVC isthmus and set to a power of 80 W and a temperature of 65 °C. After approximately two minutes of RF energy delivery, AFL terminated and persistent bidirectional block was present with double potentials separated by 181 ms across the ablation line during CS ostial pacing. A total of 11.2 minutes of RF energy was applied to ensure persistence of bidirectional block. At three-month follow-up, interrogation of the patient’s pacemaker confirms that he has been free of atrial arrhythmias. Discussion Typical isthmus-dependent right AFL is a common, curable arrhythmia. The most common mapping and ablation approach to right AFL involves catheters placed in the CS and around the TV annulus, which may pose a significant dislodgment risk to passively fixed, endocardial pacing leads. Placement of a single ablation catheter causes little dislodgment risk; however, bidirectional isthmus conduction block is rarely present upon ablation-induced termination of AFL. Absence of bidirectional block is associated with recurrent AFL4-5 and may even be proarrhythmic due to residual slow conduction in the isthmus.6 A second pacing catheter is required for demonstration of block, and our approach outlines a simple method to show block while posing minimal CS lead dislodgement risk. The 10-mm Blazer II XP Catheter and 100 W RF generator used in these cases offer distinct advantages in the ablation of AFL in the presence of CS pacing leads. This catheter is easily maneuverable, minimizing CS lead dislodgement risk. The geometry of the 10-mm-tip catheter is well suited to the anatomy of the TV-IVC isthmus; the 1-cm tip can cover a large percentage of the isthmus with fewer lesions. Longer electrode tips have been shown to create longer lesions and achieve bidirectional block in fewer lesions during RF ablation. 2,9 This can result in less tissue destruction lateral to the ablation line, and gives a crisp appearance to the double potentials seen when pacing medial or lateral to the ablation line. While cooled or irrigated catheters are also capable of producing large ablation lesions, it is our lab’s experience that a longer ablation catheter minimizes the number of lesions for a successful AFL ablation. The presence of double potentials along the ablation line that are spaced by at least 90 ms during proximal CS pacing are suggestive of conduction block. 7 However, in cases where the ablation line is broad rather than narrow or when extensive ablation is required, double potentials may not readily be observed. In such cases, differential pacing is helpful. 8 Differential pacing demonstrates that the conduction times when pacing from a fixed point on one side of a complete ablation line are increased as one record increasingly close to the opposite side of the line. As shown in Figure 2, a complete line of block is associated with a relatively short conduction time from the proximal CS to the medial aspect of the line. In contrast, the conduction interval is longer on the lateral aspect of the line and demonstrates a lateral-to-medial direction as the paced wavefront approaches the ablation line. In previous studies, a conduction time of 110 ms is associated with 100% specificity for the presence of isthmus block. 7 Conclusion In summary, typical right AFL ablation is feasible and effective in the presence of a CS pacing lead. Coronary sinus lead dislodgement risk can be managed by limiting the number and locations of diagnostic catheters. The unique 10-mm-tip RF ablation catheter offers advantages of maneuverability and 100 W output for predictable, precise lesion formation along the TV-IVC isthmus. Bidirectional conduction block can be ascertained through the use of double potentials and differential pacing techniques. Conflict of Interest Disclosure: The author discloses support of this article from Boston Scientific. Editor’s Note: This article was peer reviewed by one or more members of EP Lab Digest’s editorial board.