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Mapping and Ablation of Challenging Atypical Atrial Flutters

Senthil Thambidorai, MD, FHRS; Regional Director of Cardiac Electrophysiology, HCA North Texas; Associate Professor of Medicine, Texas Christian University (TCU), UNTHSC School of Medicine; Fort Worth, Texas

Senthil Thambidorai, MD, FHRS; Regional Director of Cardiac Electrophysiology, HCA North Texas; Associate Professor of Medicine, Texas Christian University (TCU), UNTHSC School of Medicine; Fort Worth, Texas

Introduction

Terminating atypical flutters is one of the great challenges of being an ablationist. Substantial consideration must be made to precisely locate the area of conduction block before delivering radiofrequency therapy. Mapping scar-mediated atrial flutters can be problematic without intuitive data to localize a zone of slow conduction. 

Mapping technology is advancing at a rapid pace, delivering a much more accurate representation of anatomy and critical areas of interest.1 There are many mapping modalities that can be used when dealing with these cases. In this article, we present our experience with the Coherent module and CARTO 3 V7 (Biosense Webster, Inc., a Johnson & Johnson company), which has allowed us to rapidly collect accurate high-density maps of complex arrhythmias.2-3

Case Description

The patient is a 62-year-female with sustained atrial flutter refractory to optimal drug therapy as well as multiple failed cardioversion. Past medical history includes atrial myxoma resection in 1998, nonobstructive coronary artery disease, type 2 diabetes, hypertension, and hyperlipidemia. Before initial consultation, the patient was experiencing recurrent episodes of palpitations that led to shortness of breath and lightheadedness. Review of the system was otherwise negative. The patient has failed rate control therapy with the maximum dose of beta-blockers, as well as failed a rhythm control strategy with cardioversion and dronedarone. 

Physical examination was suggestive of an irregular rhythm and a systolic ejection murmur best heard in the right parasternal region. The 12-lead ECG is shown in Figure 1.

Due to the inefficacy of non-invasive intervention, a plan was made to treat the arrhythmia with radiofrequency catheter ablation. 

Bilateral groin access was obtained with a modified Seldinger technique under ultrasound guidance. Catheters in the left femoral vein included the CARTO SOUNDSTAR and Webster CS Catheter (Biosense Webster, Inc.). The right femoral vein access was reserved for sequential mapping and ablation. Coronary sinus activation was concentric, and the tachycardia conducted at an atrial cycle length of 300 ms with slight variability. Right atrial contours of interest were drawn with a CARTO SOUNDSTAR for initial demarcation of right atrial anatomy. Subsequently, a PENTARAY (D-curve) catheter with 2-6-2 electrode spacing was utilized for mapping with the CONFIDENSE Module. Simultaneous local activation time (LAT) and bipolar mapping were performed with a 50/50 window of interest and custom voltage setting of 0.1 mV to 0.3 mV, respectively. The entire right atrium was mapped, with extra attention to the lateral wall as scar borders began to delineate. The timing laterally spanned much of the cycle length and complex fractionated signals were noted.

Once the entire cycle length was acquired, the LAT map was analyzed with propagation and an extended early meets late (EEML) feature (Figure 2). The LAT map revealed a possible channel on the lateral wall displaying propagation from a low to high fashion with a superior breakout. 

Ripple mapping was then simultaneously displayed over LAT and the bipolar voltage maps, revealing slow breakthrough conduction in an area suspected to be the atriotomy site on the lateral wall (Figure 3). (Ripple voltage setting was decreased to 0.03 mV to ensure low-level signals would not be excluded.) Incorrectly annotated points can skew the LAT map, but Ripple confirmed that data displaying LAT propagation was accurate. 

Coherent mapping illuminated a clear critical isthmus with the intuitive display of conduction vectors. As we theorized, the slow zone of the circuit was contained in the lateral atriotomy scar. Areas of slow or no conduction (termed “SNO zones”) were illustrated with a copper color and very clearly aligned to scar areas on the bipolar voltage map (Figure 4).

Feeling confident that the critical isthmus was accurately identified, our strategy was then to ablate across the isthmus and connect the lateral atriotomy scar to prevent any future atypical flutters. A bidirectional THERMOCOOL SMARTTOUCH SF ablation catheter (Biosense Webster, Inc.) was utilized at a setting of 35 watts to terminate the tachycardia at the anticipated critical isthmus site. The lateral scar sites were connected to create a complete line of block, and post-ablation testing to reinduce the tachycardia produced no evidence of any arrhythmia. 

Discussion

As with all the complexities faced in the EP lab, the first step is to control the constants. A detailed look at this patient’s history revealed a higher probability of scar-related tachycardia. Based on this finding, a mapping strategy was made to simultaneously display LAT and bipolar voltage maps. Detailed visualization of anatomy with intracardiac echo guidance mitigated the need for fluoroscopy and gave insight to structural intricacies.4 Taking time during the map creation process with a tightly spaced 2-6-2 PENTARAY was essential, as there were many discrete fractionated EGMs.3

Mapping scar-mediated atrial flutters can be difficult without important data to localize a zone of slow conduction. Traditionally available modalities such as entrainment and activation mapping can be helpful when a correlation is found in the data set, but this is not always the case. LAT mapping alone can lead to uninterpretable maps due to the timing of low-level signals as well as multiple areas with similar timing. Novel modalities that use precise propagation vectors will likely reduce empirical ablations by not only defining the tachycardia mechanism, but also distinguishing the critical isthmus for an effective ablation strategy.2 

Disclosures: Dr. Thambidorai has no conflicts of interest to report regarding the content herein.  

References
  1. Huang S, Miller J. Catheter Ablation of Cardiac Arrhythmias (3rd edition). Saunders; 2014.
  2. Anter E, Duytschaever M, Shen C, et al. Activation mapping with integration of vector and velocity information improves the ability to identify the mechanism and location of complex scar-related atrial tachycardias. Circ Arrhythm Electrophysiol. 2018;11:e006536.
  3. Anter E, Tschabrunn CM, Josephson ME. High-resolution mapping of scar-related atrial arrhythmias using smaller electrodes with closer interelectrode spacing. Circ Arrhythm Electrophysiol. 2015;8(3):537-545. 
  4. Issa ZF, Miller J. Clinical Arrhythmology and Electrophysiology: A Companion to Braunwald’s Heart Disease (2nd edition). Saunders; 2012.
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