Mapping Complex Atypical Atrial Flutters Using a Dynamic Window of Interest

Introduction

Atypical flutters are a common occurrence that are found post cardiac surgeries and/or ablations, and account for a significant percentage of repeat procedures. The term ‘atypical’ has been applied to rapid atrial tachycardias with ECG patterns differing from the typical and reverse typical flutter, as well as to re-entrant tachycardias with circuit configuration different from the typical right atrial flutter circuit.¹ Atypical flutters often have critical isthmuses and complex circuitry that are often difficult to reproduce with current mapping techniques. In this article, we discuss two cases in which we were able to successfully map and terminate two complex atypical flutters using a coronary sinus-based dynamic window of interest with customized mapping settings.

About the Technique

The most common mapping technique for atrial flutters is to set one’s window of interest with a 50/50 timing allocation, encompassing 90-95% of the tachycardia’s cycle length.² Although this technique works, it often fails to show the arrhythmia’s whole circuitry due to points either falling out of the window of interest or falling in the wrong cycle of the set window of interest. The mapping information displayed is often difficult to interpret, requiring time to individually correct points collected or even create an entirely new map.

Given this problem, we tried various mapping settings and adjustments in the window of interest. This resulted in a method of mapping these complex atypical flutters using a dynamic window of interest based on the tachycardia’s coronary sinus activation with customized mapping settings to suit the arrhythmia.

Our technique involves the use of a duodecapolar coronary sinus catheter with 2-8-2(60)2-8-2 spacing. The distal portion of the catheter is positioned in the coronary sinus, while the proximal portion of the catheter is in the lateral wall of the right atrium; this provides a global overview of the tachycardia in both the left and right atrium. The tachycardia’s activation can then be observed, and a window of interest is set based on the earliest signal in the coronary sinus catheter. With the earliest signal being set as the reference, the left and right curtains are based on the activation of the tachycardia. For example, if the reference is set to CS 1-2 and the activation is from distal to proximal, the right curtain will be set to CS 9-10 (latest electrogram) and the left curtain will be the rest of the tachycardia’s cycle length. This will force the timing sequence to have an early and late pattern, thus revealing the entire circuitry of the tachycardia (Figure 1).

We used the AutoMap feature of the EnSite Precision Cardiac Mapping System (Abbott) for its customizable and dynamic point collection settings along with its best duplicate algorithm.³ The mapping catheter that we primarily use is the Advisor^™ HD Grid Mapping Catheter, Sensor Enabled^™ (Abbott) because of its ability to accurately collect points regardless of wavefront directionality (both parallel and perpendicular points). With the best duplicate algorithm, the catheter displays the highest orthogonal signals and can uncover substrates that are otherwise invisible to traditionally spaced bipole-oriented catheters.

The following cases demonstrate our technique for mapping two different complex atypical flutters in the left atrium.

Case #1

A 74-year-old female presented with an atypical flutter with a cycle length of 240-250 ms. She had a history of persistent atrial flutter and atrial fibrillation, despite previous treatment with amiodarone and multiple cardioversions. Her ejection fraction was 65%. By transesophagheal echocardiogram (TEE), measurement of the right atrium was 29 cm² and the left atrium was 37 cm².

The coronary sinus catheter was positioned and transseptal access was obtained. We then proceeded to map the tachycardia with the mapping catheter. Right and left curtains were set based on the activation of the tachycardia on the coronary sinus catheter. Our reference was set to CS 1-2 based on the tachycardia having a distal to proximal activation pattern. The right curtain covered 99 ms of the cycle length, and the left curtain covered 155 ms of the cycle length (Figure 2). For mapping settings, we used a cycle length tolerance of ± 10 ms, speed limit of 25 mm/s, and signal-to-noise ratio of 2.0 (Figure 3). Furthermore, with the tachycardia conducting in a 4:1 fashion, we took advantage of the Independent Scoring Interval to blank out the QRS, thus excluding any ventricular points on our map; this accounts for the score value of 70 in our mapping settings.

We collected over 11,000 points in just over five minutes, revealing a mitral isthmus flutter with slow conduction located in the anterior wall of the left atrium. This area had fractionated signals, and interestingly, where an early-meets-late pattern was present (Figure 4). Very few points needed editing after mapping was completed.

Ablation in this area with high-power short-duration lesions using a contact force catheter resulted in termination of the tachycardia. We were not able to reinduce the tachycardia, despite aggressive burst pacing with high doses of isoproterenol. In addition, we performed pulmonary vein isolation and a cavotricuspid isthmus line ablation.

Case #2

A 74-year-old male presented with an atypical flutter with a cycle length of 250 ms. His history included atrial fibrillation and atrial flutter after mitral valve replacement and coronary artery bypass surgery. Ejection fraction was 25%. By TEE, measurement of the right atrium was 23 cm² and the left atrium was 24.5 cm². The left atrial appendage had been ligated at the time of surgery.

Again, once the coronary sinus catheter was positioned and transseptal access was obtained, we began to map the tachycardia with the mapping catheter. Right and left curtains were set based on the activation of the tachycardia on the coronary sinus catheter. Our reference was set to CS 1-2 with the tachycardia having a distal to proximal activation pattern. The right curtain covered 97 ms of the cycle length and the left curtain covered 160 ms of the cycle length (Figure 5). For mapping settings, we used a cycle length tolerance of ± 10 ms, speed limit of 20 mm/s, distance of 0.5 mm, and signal-to-noise ratio of 2.0 (Figure 6). However, this tachycardia had variable conduction. Thus, we had to be careful and diligent in collecting points at the vicinity of the mitral valve.

We were able to collect over 40,000 points in a little over nine minutes, revealing a macroreentrant tachycardia propagating at the roof of the left atrium. The Advisor HD Grid revealed an area of slow conduction with fractionated electrograms in this area. (Figure 7)

Ablation in this area of slow conduction with high-power short-duration lesions using a contact force catheter resulted in termination of the tachycardia (Figure 8). We were not able to reinduce the tachycardia despite aggressive burst pacing with high doses of isoproterenol. In addition, we performed pulmonary vein isolation.

Discussion

Use of this technique has allowed us to successfully map multiple complex atypical flutters in both the right and left atrium. This technique works with either a duodecapolar or decapolar coronary sinus catheter. Our experience has shown that since every complex flutter is unique, the mapping technique should be tailored to suit the arrhythmia. For example, with a flutter stable conduction, the QRS can be blanked using the Independent Scoring Interval feature, resulting in a very accurate map up to the valve level. However, this technique is just the tip of the proverbial iceberg, there are still more novel techniques to be developed for mapping these complex atypical flutters with current and future technologies.

The settings for mapping using an AutoMap feature should also be tailored for the arrhythmia. For example, cycle length variability should be kept in mind to ensure points that are collected are consistent with the primary arrhythmia being mapped. We usually keep our cycle length tolerance at a value of ± 10.

Although advances in mapping technology and techniques allow maps to be more accurate and reproducible, we should never forget the cornerstones of electrophysiology. Entrainment maneuvers should always be performed to confirm and define the circuit’s location.

Conclusion

In summary, the use of a coronary sinus activation-based dynamic window of interest with customizable mapping settings has changed the way we map complex atypical flutters. This technique has allowed us to quickly and accurately map these complex arrhythmias, resulting in successful termination. We look forward to further evolving this mapping technique to better map and understand complex atypical flutters. 

Acknowledgements: Dr. Diaz would like to thank Bryan Makalintal from Abbott for his assistance with the article.

Disclosures: Dr. Diaz has no conflicts of interest to report regarding the content herein. Outside the submitted work, he reports consulting and research honoraria from Boston Scientific and Abbott.

1. Cosio FG. Atrial Flutter, typical and atypical: a review. Arrhythmia & Electrophysiology Review. 2017;6(2):55-62.
2. Bhakta D, Miller JM. Principles of electroanatomic mapping. Indian Pacing Electrophysiol J. 2008;8(1):32-50.
3. Sommer P, Albenque JP, van Driel V, et al. Arrhythmia‐specific settings for automated high‐density mapping: a multicenter experience. J Cardiovasc Electrophysiol. 2018;29:1210-1220.