A Systematic Approach to Catheter Ablation of Atrial Flutter

Professor Luc De Roy, MD, Professor of Cardiology Université de Louvain, Cliniques Universitaires UCL de Mont Godinne, Belgium, and Michael Galloway, Manager of Clinical Programs, Electrophysiology, St. Jude Medical, Inc.
Professor Luc De Roy, MD, Professor of Cardiology Université de Louvain, Cliniques Universitaires UCL de Mont Godinne, Belgium, and Michael Galloway, Manager of Clinical Programs, Electrophysiology, St. Jude Medical, Inc.
Patient History The patient was a 70-year-old female who presented with a history of recurrent paroxysmal AFL. Echocardiogram demonstrated a normal heart; electrocardiogram (ECG) showed a typical atrial flutter characterized by a dominant negative F wave morphology in the inferior leads, II, III and aVF (Figure 1A). After failing anti-arrhythmic therapy, the patient was admitted for a diagnostic EP procedure and therapeutic catheter ablation of her arrhythmia. Electrophysiologic Procedure Vascular access was obtained via the right femoral vein. For the initial diagnosis, a Livewire Duo-Decapolar catheter was inserted into the right atrium (RA), and the 20 electrodes, connected in pairs, were positioned around the tricuspid annular side of the crista terminalis (Figure 2). The Duo-Decapolar catheter was positioned to provide mapping from the distal electrode pair (D1) at the medial aspect of the CTI, through the isthmus, lateral wall, the superior right atrium and around to the proximal electrode pair (D10) on the high septum. Observation of the electrograms during tachycardia demonstrated a continuous pattern of activation with a counter-clockwise rotation consistent with CTI-dependent AFL (Figure 1B). The isthmus dependency of this arrhythmia was confirmed by the technique of concealed entrainment. Therapeutic procedure In order to visualize the anatomy of the isthmus, which often has a slight, or even pronounced, concave pattern with a sometimes marked irregular base and varying length, we performed an angiogram of the RA. This was done with injection of 40 ml of contrast medium through the RAMP-1 8 French guiding introducer, placed at the junction of the inferior vena cava (IVC) and RA (Figure 3). The next step consisted of pulling the distal end of the Livewire Duo-Decapolar catheter out of the way, over to the lower lateral part of the RA wall, which allowed free access of the ablation catheter to the CTI ablation target (Figure 4). The RAMP-1 introducer was placed to the level of the isthmus and the ablation catheter was advanced through it in order to stabilize the catheter on the ventricular aspect of the isthmus. The ideal position is one where the distal bipole of the catheter records a distinct ventricular V wave of sufficient amplitude and a minimal amplitude of atrial A waves. Ablation may be performed during AFL or in sinus rhythm. Sequential burns are delivered from the distal ventricular part of the isthmus, dragging the ablation catheter progressively towards the IVC. Interruption of the AFL during ablation confirms the isthmus dependency of the arrhythmia, but the cyclic rapid movement of the isthmus during AFL may render ablation less effective due to smaller and incomplete lesions. These movements from the atrium and the rapid ventricular rate may actually prevent an optimal tip-tissue contact on the isthmus. This may result in superficial lesions with subsequent edema, prohibiting further complete isthmus interruption despite an initial termination of the AFL. In this specific situation, the RAMP-1 introducer appears to be an important tool to obtain an optimal contact of the catheter on the isthmus, even during tachycardia. When the AFL has been interrupted (Figures 5-6) and/or when ablation is attempted during sinus rhythm, we pace the low atrial septum. This can be achieved by stimulation from the proximal poles of the decapolar catheter which has been inserted within the CS to allow a stable and constant stimulation position. If there is no complete isthmus block after interruption of the AFL, or when we start ablation in sinus rhythm, septal pacing induces a wavefront which passes through the isthmus and collides with the other wavefront coming from the high lateral wall, descending toward the lower part of the RA. Collision is almost always visible on the distal duo-decapolar catheter electrode pairs positioned at the level of the lower RA (Figure 7). At that time, further applications of RF energy are directed toward sites where nearly fused double potentials are recorded on the ablation line during CS os pacing. When complete interruption of isthmus conduction is achieved, we observe a sudden shift of the collision front recorded on the distal duo-decapolar catheter electrodes, which changes to a straight alignment of the electrograms, indicating that the wavefront is exclusively coming from the upper part of the RA (Figure 8). This confirms the absence of conduction of the paced wavefront through the isthmus. This selective approach needs a straight and stable oriented ablation catheter, pulled back from the ventricular aspect of the isthmus to the vena cava junction. The RAMP-1 introducer is very helpful in that respect, allowing not only firm contact of the ablation catheter tip, but also very precise orientation and stabilization, permitting a careful exploration of the isthmus line, avoiding shifts and torsions of the catheter. In this way, more precise targeting can be achieved and, consequently, the duration of the ablation procedure and X-ray exposure could be reduced. Overall, the ablation procedure does not exceed 10 to 15 minutes in the majority of cases with a minimum of RF applications. After having interrupted the isthmus, the duo-decapolar catheter is again placed on the isthmus with its distal end placed in or near the coronary sinus. Pacing from that site and from the low lateral atrial wall is initiated in order to confirm the absence of isthmus conduction in both directions (Figure 9). In some instances, a marked slowed conduction through the isthmus can still be present despite an apparent complete interruption during the former pacing method with the recording catheter on the lateral wall. This can be revealed during careful analysis of clockwise and counter-clockwise conduction of the wavefront during pacing on both sides of the isthmus, while the duo-decapolar catheter is positioned on the isthmus, rather than on the lateral wall. After confirmation of complete block in the clockwise and counter-clockwise directions in the isthmus, a 15-20 minute wait time is observed during which a complete control electrophysiologic evaluation is performed. Afterwards, repeated pacing from both sides of the isthmus is performed, often after an isopronaline infusion, for assessing the absence of reconduction, which might occur if ablation lesions are either superficial and/or incomplete. Conclusions Ablation of CTI-dependent flutter has become a well-codified approach. The use of specific tools make it possible to refine and shorten the procedure and to improve the assessment of bidirectional conduction block. For this purpose, the Livewire Duo-Decapolar catheter is systematically used in our institution, not only for AFL, but for most of the ablation procedures because: 1. For AFL, the analysis of the electrical wavefront recorded by the duo-decapolar catheter permits a rapid confirmation of an isthmus related flutter, and can exclude left atrial flutter. 2. It has proven its handiness for easy positioning along the crista terminalis on the lateral RA wall, and more importantly, for a rapid insertion of its distal tip into the coronary sinus, which can almost always be catheterized without major difficulty. In AFL, this serves as a landmark for the introduction of another catheter for recording and pacing during ablation when the duo-decapolar catheter will be pulled back on the lateral RA wall. In these flutter patients, it indeed may sometimes be difficult to catheterize the CS because the atria are enlarged. 3. The duo-decapolar catheter as a landmark in the CS os allows us to orient more rapidly the CS catheter avoiding excessive X-ray exposure and time waste. Moreover, it gives us an almost complete mapping of the important sites of the RA and more specifically of the isthmus region, to avoid misinterpretation of bidirectional block during and after ablation. The sudden interruption of conduction clearly seen during RF delivery precludes further unnecessary energy applications. 4. Other ablation procedures may benefit greatly from this enhanced mapping. During pulmonary vein ablation in atrial fibrillation, an extensive view of atrial activation becomes available not only at the left atrial side (in the CS), but also on the right side. In addition, the Livewire Duo-Decapolar catheter allows us distal CS pacing during ostial ablation and validation of left isthmus block. 5. During electrophysiologic evaluation of paroxysmal supraventricular arrhythmias, a careful mapping of atrial depolarization is readily achieved allowing fast diagnosis of accessory pathways, assessment of slow AV nodal pathway conduction and the activation sequence of atrial beats, thereby facilitating accurate diagnoses. The RAMP-1 introducer is specifically useful for AFL ablation because: 1. It permits fast angiographic imaging of the RA and isthmus before ablation. 2. It serves as an extremely useful tool for stabilizing the ablation catheter on the isthmus, especially in the complex anatomy of a long isthmus. 3. It permits enhanced tip-to-tissue contact avoiding partial ablation, edema formation and inefficient energy delivery. 4. A straight ablation lesion may be formed precisely, achieving more rapid and complete isthmus conduction block, preventing irregular ablation lines. In summary, the use of adequate tools greatly facilitated our ablation procedures, not only in terms of efficacy, but also by reducing whole procedure and fluoroscopic time. Further studies are underway to evaluate the efficacy of the RAMP-1 approach versus common non-guiding introducer techniques. Acknowledgments. The authors would like to express thanks to Benoit Collet, Electrophysiology Technician, Gladys Alsteen and Isabelle Manchi for collaboration and support. Rx Only. 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