Case Study

Initial Experience with the EnSite Precision Cardiac Mapping System

Gregory Harris, MD, PhD and Anil K. Gehi, MD, FHRS, Medical Director of Cardiac Electrophysiology and Program Director, Fellowship in Clinical Cardiac Electrophysiology

University of North Carolina (UNC) School of Medicine, 

Division of Cardiology

Chapel Hill, North Carolina

Gregory Harris, MD, PhD and Anil K. Gehi, MD, FHRS, Medical Director of Cardiac Electrophysiology and Program Director, Fellowship in Clinical Cardiac Electrophysiology

University of North Carolina (UNC) School of Medicine, 

Division of Cardiology

Chapel Hill, North Carolina

Three-dimensional electroanatomic mapping is a cornerstone to effective treatment of complex arrhythmias in the modern era. Over the last 10 years, there has been rapid technological advancement in this field that has resulted in faster data acquisition, more precise geometric mapping, improved point annotation, and in turn, better patient care. One such advancement is the EnSite Precision Cardiac Mapping System (Abbott), which builds on the previous generation EnSite Velocity System. With the inclusion of both impedance measurements as well as magnetic catheter tracking, we find the EnSite Precision Cardiac Mapping System provides improved map stability, while the AutoMap feature provides fast and accurate automated acquisition of a multitude of mapping parameters.

Our lab at the University of North Carolina at Chapel Hill upgraded to the EnSite Precision Cardiac Mapping System in 2017. To better illustrate how using this upgraded system has enhanced the workflow of our lab, we present several cases below.

Features of the New System

Catheter location and navigation with this system have conventionally been impedance based. With an impedance-based system, an 8 kHz signal is emitted through each pair of surface patches to create a voltage gradient along each axis. Once an electrophysiologic catheter is introduced into this transthoracic field, the system calculates the three-dimensional position of the catheter electrodes, enabling the creation of 3D electroanatomic models. However, an electroanatomic map created solely with an impedance-based system can lose precision during a case due to changes in impedance with ablation, fluid shifts, patient motion, etc. The new EnSite Precision Cardiac Mapping System includes the addition of magnetic field data in sensor-enabled catheters, which allows for dynamic optimization of the model. This allows for a much more stable model that is not influenced by tissue changes due to ablation or minor movements of the patient, such as a result of cardioversion, which may have previously required manual realignment. 

While the integration of both impedance mapping as well as magnetic geometry has increased the accuracy and stability of the maps, magnet-enabled catheters are not required to utilize key features of the EnSite Precision Cardiac Mapping System. This translates into a huge advantage, as specific cases such as right-sided SVTs and typical flutters may not require the use of magnet-enabled catheters. At one time or another in a busy, high-throughput lab, a specific catheter may not be in stock, resulting in delays or even postponement of the case. Finally, there is no requirement to register an ablation catheter with the system before mapping can occur. This is a great cost-saving benefit in the event that an EP study is negative and ablation is not needed. 

With the new updated system, detailed activation and voltage maps can be generated concurrently with the generation of geometry. Although this was also performed with previous generations, the addition of new filters has resulted in faster map generation due to improved automated functionality and decreased need for manual point annotation. Automated annotation is accomplished by accepting annotated points only meeting certain criteria, including: surface P or QRS morphology match, cycle length tolerance, mapping catheter movement, distance from the surface, and contact force (if a contact force catheter is used for mapping). With rapid acquisition of points, less interpolation is necessary. A new Sparkle map feature provides a novel way to depict propagation maps. We find that the ease in generating maps with improved resolution translates to more rapid identification of complex circuits and overall better patient care.

Case #1

A 65-year-old male, with a history of persistent atrial fibrillation, underwent ablation with pulmonary vein isolation (PVI) in 2015. During that procedure, after PVI, he developed organized atrial flutter with distal to proximal activation in the coronary sinus (CS). Entrainment and activation mapping suggested a mitral annular flutter. A mitral annular line from the left inferior pulmonary vein (LIPV) to the mitral valve was performed. During ablation, the activation of the tachycardia shifted to a proximal to distal activation in the CS. Mapping suggested a septal flutter; a septal line was then made, which slowed but did not alter the activation. A new activation map was made, localizing the source to the medial base of the left atrial appendage (LAA). A lesion at the base of the appendage terminated the tachycardia to sinus rhythm. Tachyarrhythmia was not inducible at the end of the case, but atrial tachyarrhythmia returned approximately one month later despite administration of dofetilide and repeated cardioversions. He presented for repeat ablation.

Activation mapping revealed isolated right-sided PVs, reconnected left-sided PVs, and a focal source of tachycardia on the ridge between the left pulmonary vein ostia and the base of the LAA (Figure 2). A TactiCath Quartz Contact Force Ablation Catheter (Abbott) was advanced to the site of earliest atrial activation, which also showed significant fractionation of the electrogram suggestive of micro-reentry. During administration of the initial radiofrequency lesion, the flutter terminated to sinus rhythm (Figure 3). The left-sided PVs were again isolated and confirmed with administration of adenosine. 

In this case, the rapid acquisition of both the voltage and activation map using the EnSite Precision Cardiac Mapping System facilitated the identification of the clinical atrial tachycardia as well as demonstrated that the pulmonary veins were reconnected. The time between transseptal puncture and the first lesion being delivered (which terminated the tachycardia) was approximately 20 minutes. 

Case #2

A 76-year-old female presented for ablation of symptomatic persistent atrial fibrillation despite being on dofetilide. On presentation to the EP lab, she was found to be in an atypical atrial flutter with a distal to proximal activation sequence on the CS catheter. Initial voltage mapping with a decapolar Lasso catheter (Biosense Webster, Inc., a Johnson & Johnson company) demonstrated severe fibrosis of the left atrium (Figure 4) with complex diastolic potentials on the left pulmonary vein ridge, posterior left atrium, and left atrial roof (scar cutoff 0.1 mV). Activation mapping was performed (Figure 5, Video 1). This map suggested a figure-of-8 flutter rotating clockwise around the mitral annulus as well as around the left-sided PVs. The left and right pulmonary veins were isolated. The posterior left atrium was also isolated with roof and inferior wall lines connecting the superior and inferior pulmonary veins, respectively. During the course of ablation, the rhythm slowed to a stable slower flutter. A new activation map suggested clockwise mitral flutter, which was confirmed by entrainment mapping (Video 2). A line of lesions was then created between the LIPV and the mitral annulus. The flutter slowed further. Additional lesions performed on the epicardial side of the mitral isthmus via the CS terminated the tachycardia.

Multiple complex atrial tachyarrhythmias were found in this case, requiring multiple rounds of activation mapping. The rapid creation of high-resolution maps was integral to the treatment of this patient’s arrhythmias. 

Case #3

A 72-year-old male who had failed medical therapy presented for ablation of paroxysmal atrial fibrillation as well as atypical flutter. The patient was in sinus rhythm on presentation to the EP lab. Initial baseline voltage maps demonstrated minimal atrial fibrosis. After baseline measurements were made, atrial fibrillation was initiated with rapid atrial pacing. Bilateral antral PVI was performed. Atrial fibrillation terminated during isolation, but transitioned to a regular atrial tachyarrhythmia with distal to proximal activation in the CS.

Activation mapping of the left atrium demonstrated earliest activation at a focal area at the base of the LAA (Figure 6, Video 3). Ablation lesions placed in this area of earliest activation resulted in restoration of sinus rhythm.

Pacing performed from all four PVs demonstrated entry and exit block, and there was no latent pulmonary vein conduction with administration of adenosine. Repeated inductions of atrial fibrillation terminated spontaneously in <5 minutes. 

The Sparkle map highlighted in this case provided excellent visualization of the origin of the left atrial tachycardia as well as its course. Because of this visualization, it was apparent this was a focal origin and a series of tightly grouped lesions were sufficient to terminate the tachycardia. 

Case #4

A 45-year-old female presented with complaints of recurrent atrial tachycardia. She had a history of open surgical ASD closure as a child and prior ablation for typical atrial flutter. The patient was in ongoing atrial flutter on arrival to the EP lab. Although initial appearance of activation on a multipolar right atrial catheter suggested counterclockwise typical flutter, entrainment form the CS ostium resulted in a long post-pacing interval. The post-pacing interval was best in the lateral right atrium. Activation mapping demonstrated scar-related lateral right atrial flutter (Figure 7, Video 4). Additional mapping identified a line of double potentials in the lateral right atrium with breakthrough below the line. 

A series of radiofrequency lesions were made from the double potentials to the inferior vena cava (Figure 8). During one of these lesions, the atrial flutter abruptly terminated. Block was confirmed by differential pacing.

Conclusions

As demonstrated in the above cases, the EnSite Precision Cardiac Mapping System has become an invaluable tool for reliable and accurate map generation at the University of North Carolina at Chapel Hill. The addition of magnetic field data provides map stability and precision. Through the course of a single case, new maps often need to be generated as activation sequences change. This upgraded system allows for rapid generation of these maps, which is essential in a busy lab environment. The open platform provides flexibility in catheter use, and the high resolution allows precise localization of arrhythmia foci. 

Disclosures: Dr. Harris has no conflicts of interest to report regarding the content herein. Dr. Gehi reports personal fees from Abbott, as a symposium director for fellows education.

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