Atypical Atrial Flutter Ablation: The Clinical Impact of High-Density MappingBahjat Z. Ghazzal MD1, Marwan M. Refaat, MD21 Division of Cardiology, Department of Internal Medicine, University of Massachusetts Chan Medical School , Worcester, Massachusetts, USA2 Division of Cardiology, Department of Internal Medicine, American University of Beirut Medical Center, Beirut, LebanonRunning Title: Atypical Atrial Flutter Ablation: The Clinical Impact of High-Density MappingWords: 700 (excluding the title page and references)Keywords: cardiac arrhythmias, heart diseases, cardiovascular diseases, catheter ablation, atrial flutter, high density mappingFunding: NoneDisclosures: NoneCorresponding Author:Marwan M. Refaat, MD, FACC, FAHA, FHRS, FASE, FESC, FACP, FRCPTenured Professor of MedicineTenured Professor of Biochemistry and Molecular GeneticsMember, Division of Cardiology/ Section of Cardiac ElectrophysiologyDirector, Cardiovascular Fellowship Program American University of Beirut Faculty of Medicine and Medical CenterPO Box 11-0236, Riad El-Solh 1107 2020- Beirut, LebanonUS Address: 3 Dag Hammarskjold Plaza, 8th Floor, New York, NY 10017, USAOffice: +961-1-350000/+961-1-374374 Extension 5353 or Extension 5366 (Direct)Atypical atrial flutter (AAFL) is an arrhythmia that is distinct from typical atrial flutter (AFL) due to its non-isthmus-dependent reentrant circuit, and often arises in patients with a history of cardiac surgery or ablation, where the resulting iatrogenic scar provides the basis for re-entry circuits.1 Catheter ablation for AAFL is an effective treatment option, associated with lower rates of thromboembolic events, transfusions, and shorter hospital stays compared to typical AFL.2 However, the complexity of AAFL circuits requires precise mapping, and traditional techniques often lack the resolution to accurately delineate these pathways. High-density (HD) mapping technology has emerged as a significant advancement in this regard, offering detailed electroanatomic maps that enhance procedural success.3 In this issue of the Journal of Cardiovascular Electrophysiology, the study by Sink et al. investigates the impact of HD mapping on AAFL ablation outcomes and healthcare utilization, providing valuable insights into its clinical benefits.4In this retrospective analysis, Sink et al. examined 108 patients who underwent AAFL ablation at a single academic center from 2005 to 2022. The cohort was divided into two groups: those who received HD mapping with a 16-electrode HD Grid catheter and Precision mapping system, and those who underwent non-HD mapping using traditional spiral catheters and the Velocity system. Primary outcomes included procedural success, defined as non-inducibility of the arrhythmia after ablation, and AFL recurrence. Secondary outcomes included emergency department (ED) visits, hospitalizations, and overall healthcare utilization within one-year post-procedure. The study revealed that HD mapping significantly improved both the delineation of AAFL circuits (92.5% vs. 76%; p=0.014) and procedural success rates (91% vs. 71%; p=0.006). Additionally, patients in the HD mapping group experienced significantly fewer ED visits (aIRR 0.32; p=0.007) and hospitalizations (aIRR 0.32; p=0.004) for AF/AFL/HF within the first year. While there was a trend towards lower AFL recurrence in the HD mapping group (aHR 0.60; p=0.13), this difference did not reach statistical significance. This study highlights the significant advantages of HD mapping in AAFL ablation. The enhanced resolution provided by HD mapping allows for more precise identification and targeting of arrhythmogenic substrates, leading to improved clinical outcomes.Though this study was well-conducted, minor limitations must be noted. The study’s retrospective design and single-center setting introduce potential biases and limit the generalizability of the results. The non-randomized nature of the study also raises the possibility of selection bias. Furthermore, the higher use of contact force-sensing catheters in the HD mapping group may have contributed to the observed differences in outcomes. A larger sample size would have likely allowed the study to achieve statistical significance when comparing recurrent AAFL rates between groups. Despite these limitations however, this study provides strong support for the clinical utility of HD mapping in AAFL ablation. Future multi-center, randomized trials should validate these findings and examine factors not studied here, such as procedure fluoroscopy time and complication rates between groups. Long-term benefits should also be further investigated, as some prior studies for example have shown no significant decrease in anti-arrhythmic drug use at 1-year follow-up5 and significantly decreased rates of sinus rhythm maintenance for repeat ablations compared with single ablations6. Research on HD mapping in patients with specific comorbidities could also provide insights into its broader applicability. For instance, one study showed a greater chance of acute procedural failure in patients with a history of surgical correction for congenital heart disease.7 Though HD-mapping-guided ablation demonstrates higher acute procedural success, several studies have shown long-term recurrence rates remain significant.8, 9 Hence, further research is needed to identify strategies to reduce these rates. In this context, the development of new mapping tools, such as the Octaray TM system (Biosense Webster Inc., Irvine, CA, USA)10 and the Ensite TM Omnipolar Technology (OT) (Abbott, Chicago, IL, USA)11, may offer improved outcomes. Further research is also needed to assess the clinical outcomes, healthcare utilization and biomarker response for ablation of AAFL with HD mapping in the setting of heart failure with reduced ejection fraction.12 To the best of our knowledge, this is the first such study to demonstrate that ablation with HD mapping for AAFL results in reduced re-hospitalization and ED visits. Future research should attempt to expand on these findings to evaluate potential cost-benefit and impact on patient quality of life.References:1. Cherian Tharian S, Supple G, Smietana J, Santangeli P, Nazarian S, Lin D, Hyman Matthew C, Walsh K, Marchlinski F and Arkles J. Idiopathic Atypical Atrial Flutter Is Associated With a Distinct Atriopathy.JACC: Clinical Electrophysiology . 2021;7:1193-1195.2. Ko Ko NL, Sriramoju A, Khetarpal BK and Srivathsan K. Atypical atrial flutter: review of mechanisms, advances in mapping and ablation outcomes.Curr Opin Cardiol . 2022;37:36-45.3. Raymond-Paquin A, Pillai A, Myadam R, Mankad P, Lovejoy S, Koneru JN and Ellenbogen KA. Atypical atrial flutter catheter ablation in the era of high-density mapping.J Interv Card Electrophysiol . 2023;66:1807-1815.4. Sink JC, Kasen; Uppalapati, Lakshmi; Lancki, Nicola; Peigh, Graham; Lohrmann, Graham; Elsayed, Mahmoud; Carneiro, Herman; Baman, Jayson; Pfenniger, Anna; Patil, Kaustubha D.; Verma, Nishant; Arora, Rishi; Kim, Susan S.; Chicos, Alexandru B.; Lin, Albert C.; Knight, Bradley P.; Passman, Rod S. Association Between High-Density Mapping of Atypical Atrial Flutter, Clinical Outcomes and Healthcare Utilization. Journal of Cardiovascular Electrophysiology . 2024.5. 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