Application of Voltage Mapping Using a Novel High-Density Mapping System to Quickly Identify and Terminate an Atypical Atrial Flutter

Introduction

High-density electroanatomical mapping, coupled with advancements in catheter technology, have advanced the knowledge of atrial flutter (AFL) mechanisms as well as enabled refinements in the diagnosis and treatment with catheter ablation.¹ More specifically, it is now recognized that the term AFL encompasses a wide range of mechanisms including macro- and micro-reentrant circuits involving both the right and left atria, each of which requires precise characterization and targeting in order to optimize ablation. Additionally, there is increasing recognition of the complex relationship between AFL and atrial fibrillation (AF):² AFL can coexist or precede AF, and AFL may develop subsequent to AF ablation. Recurrences in patients with persistent AF may be characterized as atypical AFLs, which can be difficult to treat medically and can involve long procedure times when retreated.^3,4 In this case report, we describe the use of the EnSite Precision Cardiac Mapping System (Abbott) with the AutoMap Module in a patient presenting with AF and atypical AFL after a previous AF cryoablation procedure.

Case Presentation

A 64-year-old female with a history of symptomatic, drug-refractory AF presented for cryoablation. During the initial procedure, all four pulmonary veins were isolated with a 28 mm balloon. No pulmonary vein activity was seen, and exit and entrance block were demonstrated. No other ablation lesions were delivered during the index procedure. After the three-month blanking period, the patient had recurrent AF as well as an atypical AFL. The patient chose to undergo a repeat procedure for both arrhythmias with radiofrequency ablation.  

During the repeat procedure, the patient presented in normal sinus rhythm. General anesthesia was induced and groin access was obtained. Heparin was infused with a target activated clotting time of 300-350 s. Using intracardiac ultrasound guidance, a double transseptal puncture was then performed. An SL-1 sheath and an Agilis steerable introducer (Abbott) were advanced into the left atrium. A 15 mm Advisor FL Circular Mapping Catheter, Sensor Enabled (Abbott) was advanced through these sheaths. In addition, a 4 mm TactiCath Quartz Contact Force Ablation Catheter (Abbott) was placed in the left atrium (LA).  

High-density mapping of the left atrium was then performed using the EnSite Precision Cardiac Mapping System with the AutoMap Module (Abbott) primarily with the circular mapping catheter. Based on previous experience with the mapping system, settings were customized to maximize accuracy and efficiency with this type of case (Table 1). A total of 5122 points were obtained in 5.8 minutes of mapping time. The data was interpreted to show a voltage map. Values between 0.15 mV and 2.0 mV were set. All voltage values below 0.15 mV were shown with the color grey and interpreted as scar. Based on this map, the left-sided veins remained isolated from the prior ablation. In addition, no electrical activity was noted inside the left pulmonary veins (Figure 1). However, significant activity was noted in the right-sided veins. An antral ablation lesion set was placed on the anterior portion of the right-sided veins, which led to isolation (Figure 2). 

With isolation of the right-sided veins, the patient spontaneously converted to an atypical AFL with a left-to-right pattern in the coronary sinus; cycle length was 220 ms (Figures 3 and 4). A second voltage map was then made with the circular mapping catheter. A total of 5574 points was obtained in 7 minutes. Using a method previously described,^5,6 the mapping system was then set to display all of the mapping points using only 8 isochronal color bands using the following activation pattern: whiteredorangeyellowgreenlight bluedark bluepurple. Interpretation of the map is simplified using this limited color palate. Each color band represents equally spaced timing. Therefore, large and wide color bands represent fast conduction, while tightly spaced color bands represent slow conduction. Interpretation of the map demonstrated an atypical flutter traveling counterclockwise around the mitral valve (Figure 5).

The contact force ablation catheter was then advanced into the targeted location. The narrowest part of the circuit was located between the left atrial appendage and the anterior portion of the mitral valve (Figure 6). As obtaining adequate catheter contact was difficult in this area, an area slightly more anterior was targeted. A series of ablation lesions were delivered.  Energy was titrated to achieve an LS (lesion size index) of 5.5 in each location. With the fifth ablation lesion, the tachycardia terminated. No further arrhythmias were induced with isoproterenol infusion and pacing challenge. The total procedure time was 112 minutes, and the fluoroscopy time was 4 minutes. The patient was discharged receiving no antiarrhythmic medical therapy. At 3 months, she wore a 1-month continuous monitor, which showed no evidence of arrhythmia. At 6 months, she reported no further arrhythmias.

Discussion

In this case, high-density activation sequence mapping with voltage gradient mapping overlay was used to identify critical zones of conduction and to ablate an atypical AFL that developed subsequent to cryoablation for AF. Use of the EnSite Precision Cardiac Mapping System for mapping and data collection enabled collection of a large number of points in an expedient timeframe, allowing for accurate characterization and ablation in a challenging case. Altering the nominal settings on cardiac mapping system was intuitive, enabling optimization on a patient-by-patient basis. Use of a simplified color scheme of 8 colors, in combination with the voltage map, provided the clarity needed to easily differentiate between active and passive tissue channels. The color sequence can be used in real time during the case. If an area of tissue is identified that does not have all of the colors in the spectrum, or if the colors are out of sequence, this must be via passively activating tissue or with two passive wavefronts colliding. Therefore, these areas were not an area of interest and were not targeted for ablation. Ablation catheter choice was important due to the amount of scar tissue. Use of a contact force catheter helped ensure successful lesion placement. Targeting the high-voltage area within the slow zone enabled termination of the arrhythmia with a minimal number of lesions. The total procedure time in this case, including high-density map creation, represents a dramatic reduction over the time needed using traditional mapping procedures.

The results obtained in this case are consistent with those in a sequence of 21 patients presenting with 26 different atypical atrial flutter circuits after a previous catheter or surgical AF ablation.⁶ Patients in this series were treated using the same protocols and techniques for mapping, data collection protocol, and ablation, but with an earlier generation mapping system. An average of 2996 ± 690 points was collected in 12.39 ± 4.71 min (including analysis time). The mean total procedure time was 135 ± 46 min; the mean fluoroscopy time was 8.5 ± 3.7 min. In contrast, the historical control group of 21 consecutive patients had a mean total procedure time of 210 ± 41 min and a mean fluoroscopy time of 17.7 ± 7.7 min. 

Although direct comparison is not possible, the technical advancements in the mapping system as well as operator experience have contributed to ongoing improvements. It is now possible to expediently and accurately gather even larger amounts of data with reduced fluoroscopic exposure. This case illustrates how the EnSite Precision Cardiac Mapping System, in combination with the AutoMap Module, can be used to create high-density maps to quickly and efficiently locate voltage areas in the LA. Additionally, the system can be used to identify the critical isthmus in an atypical AFL in a routine and predictable manner.

Disclosures. Drs. William Choe and Sri Sundaram are consultants and recipients of an investigator-initiated research grant from Abbott. Dr. Sundaram also discloses he is a consultant for Medtronic, and is chief medical officer with equity interest in North American Interconnect. Charles Boorman and Nate Mullins are employees of Abbott.

References

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