Atrial Flutter Ablation Made Quick and Easy

Efficiency and cost effectiveness have always been laudable goals in the electrophysiology laboratory, but have taken on increasing importance recently as ablation of complex arrhythmias has become more commonplace. Complex ablation procedures require a variety of sophisticated and expensive technologies and tend be lengthy, labor-intensive affairs. For the busy electrophysiology laboratory, this means that efforts to improve the efficiency and reduce the costs of other laboratory procedures, such as type 1 atrial flutter ablation, should help to ease the burden on staff and facilities. Background Atrial flutter is one of the most common problems for which patients are referred for ablation. The majority of these patients have right atrial cavotricuspid (CT) isthmus-dependent atrial flutter. In our laboratory, this arrhythmia accounts for more than 50% of ablation procedures. The goal of ablation for this particular arrhythmia is the creation of a line of bidirectional conduction block in the CT isthmus. This seems like a simple enough endpoint; however, it is surprising how widely the techniques used to achieve this endpoint vary from one laboratory to another. One commonly used method is to apply radiofrequency (RF) energy continuously while “dragging” the ablation catheter from the tricuspid annulus back to the junction of the inferior vena cava (IVC) and right atrium, while monitoring the local atrial electrogram for a reduction in voltage. Compared to discrete point-by-point application of RF, continuous RF application may shorten procedure and fluoroscopy times and reduce the total amount of RF energy applied.1 However, this method may result in gaps in the ablation line. Irrigated RF ablation catheters may minimize the production of gaps, but the smaller tip size may create smaller lesions. It is also surprising how frequently expensive technologies, like 3D electroanatomic mapping, are used to confirm the diagnosis of CT isthmus-dependent atrial flutter and to assess the effects of ablation. Three-dimensional electroanatomic mapping often adds expense but very little value to the procedure. In our laboratory, we utilize a technique that maximizes the efficiency of the ablation procedure while reducing the need for 3D electroanatomic mapping. Ablation Technique From the right femoral vein a duodecapolar electrode catheter is advanced into the right atrium and positioned in a “halo” configuration, so that the proximal poles descend from the high to low right atrium along the crista terminalis, the middle poles span the CT isthmus and the distal poles pass through the os into the proximal coronary sinus (Figure 1). From the left femoral vein, a quadripolar electrode catheter is advanced into the right ventricular apex. This catheter provides backup pacing capability in the event that sinus arrest appears after termination of flutter and allows one to assess patterns of ventriculo-atrial conduction after restoration of sinus rhythm, which can uncover other mechanisms of organized supraventricular tachycardia, like AV node reentry, which may have led to development of atrial flutter in the first place. A hexapolar electrode catheter (CRD™, St. Jude Medical, St. Paul, MN) is also advanced from the left femoral vein and positioned across the tricuspid valve in the His bundle position. This catheter has 5-5-5-175-5 mm spacing, which results in the proximal poles being located in the inferior vena cava below the diaphragm. One of these proximal poles is utilized as the anode, instead of Wilson’s Central Terminal, during unipolar pacing from the ablation catheter distal electrode. Finally, an ablation catheter is advanced from the right femoral vein into the right atrium and positioned in the CT isthmus. A wide variety of ablation catheters are available for use in the treatment of typical atrial flutter. In our laboratory, we frequently use the Blazer II XP™ Temperature Ablation Catheter (Boston Scientific, Natick, MA). This catheter has bidirectional steering and excellent handling characteristics for creating lesions along the CT isthmus. We use the 8-mm-tip electrode (a 10-mm tip is also available), which helps create large lesions, thereby reducing procedure time.2,3 In most cases, proper positioning of this catheter can be accomplished easily without using a long venous sheath. For patients in atrial flutter at the start of the procedure, the ablation catheter is initially placed in the midportion of the CT isthmus, usually described as the “6 o’clock position” as viewed in the left anterior oblique projection, with the tip electrode as close as possible to the tricuspid valve, where the local atrial and ventricular electrograms are of approximately equal amplitude (Figures 2 and 3). This starting position is preferred because it is here that the CT isthmus is narrowest. The isthmus is broader at the lateral end of the isthmus (8 o’clock position), which increases the difficulty in achieving block in the isthmus. When the catheter is placed at the septal end of the isthmus (4 o’clock position), the risk of damage to the slow AV node pathway or inadvertent RF application in the middle cardiac vein is increased. With the ablation catheter placed in its ideal starting position, entrainment by unipolar pacing is then performed using the ablation tip electrode as the cathode, a proximal pole of the His bundle catheter as the anode, a stimulus amplitude of 10 mA and a pulse duration of 2 ms. Unipolar pacing is used rather than bipolar pacing. because it ensures that capture occurs at the distal tip electrode rather than at a proximal ring electrode.4 This, in turn, ensures that the tip is in good contact with underlying tissue and improves the accuracy of measurement when assessing the post-pacing interval (PPI) after cessation of pacing.5,6 The flutter is entrained, usually at a rate 20-30 ms faster than the atrial flutter cycle length. A PPI after cessation of pacing that equals or nearly equals the flutter cycle length confirms the presence of isthmus-dependent atrial flutter, without having to resort to 3D electroanatomic mapping (Figure 3). If one wishes, entrainment mapping can be repeated at the septal and lateral ends of the isthmus to confirm that the entire isthmus is a part of the reentry circuit. Even for flutters that are atypical, 3D electroanatomic mapping may be avoided by using this unipolar entrainment mapping technique. With the catheter positioned in the middle portion of the isthmus as close as possible to the tricuspid valve, a radiofrequency lesion is created. For the 8-mm-tip ablation catheter, we apply RF using the EPT-1000XP™ Cardiac Ablation System (Boston Scientific) for a total of 60 seconds at each site in temperature control mode (maximum power of 70 W, maximum temperature of 60˚ C). After completion of this lesion, without moving the catheter, unipolar pacing from the ablation catheter is repeated. If capture still occurs, another lesion is made at the same site. If capture does not occur, this indicates that an adequate lesion has been created.7 The catheter is then slowly withdrawn while continuing to pace, until capture reappears. This identifies the next site for RF application (Figures 4 and 5). The process is repeated at each ablation site until the catheter has been withdrawn across the entire CT isthmus to the IVC-right atrial junction. Frequently, the flutter will terminate during RF application, but this does not always correspond to the development of bidirectional conduction block in the CT isthmus. For this reason, the entire ablation line should be completed before the presence or absence of conduction block in the CT isthmus is assessed. Once the line has been completed, routine pacing maneuvers are performed to assess whether isthmus block has been achieved. If conduction through the isthmus is still present, the process described above is repeated with the ablation catheter positioned slightly septal or lateral to the first ablation line. If patients are in sinus rhythm at the start of the procedure or if flutter terminates during the procedure, the same technique of unipolar pacing from the ablation catheter distal electrode is used to assess electrode/tissue contact and adequacy of the RF lesion at each site, although in such cases pacing is typically performed at a much slower rate (Figures 6 and 7). Using the Blazer II XP 8-mm-tip catheter and this technique, the CT isthmus can usually be spanned with only three or four RF applications. It is rare that more than one or two ablation lines across the CT isthmus are required before flutter terminates and bidirectional conduction block in the isthmus is achieved. In some instances, capture of local tissue during unipolar pacing with the catheter tip perpendicular to the target site is difficult because the entire surface area of the ablation catheter is not in contact with tissue, resulting in less electrode-to-tissue electrical coupling. In such cases, orienting the ablation catheter so that the tip electrode is in a parallel position along the isthmus can be helpful (Figure 8). Conclusions Utilizing the method described here, ablation of isthmus-dependent atrial flutter can usually be completed in 45 minutes or less, timed from initiation of local anesthesia to removal of all catheters. This technique may also help to avoid creation of gaps in the ablation line that can occur when one applies RF continuously while “dragging” the ablation catheter across the CT isthmus.