Case Study

Use of the FlexAbility Ablation Catheter, Sensor Enabled at MUSC Health

Jeffrey Winterfield, MD 
Director, Ventricular Arrhythmia Service 
MUSC Health
Charleston, South Carolina

Jeffrey Winterfield, MD 
Director, Ventricular Arrhythmia Service 
MUSC Health
Charleston, South Carolina

On March 1, 2017, Abbott announced U.S. Food and Drug Administration (FDA) approval of the FlexAbility™ Ablation Catheter, Sensor Enabled™ (Abbott) for cardiac ablation procedures to treat atrial flutter. It is a second-generation catheter in the FlexAbility platform, and the introduction of this catheter closely follows FDA clearance of EnSite Precision™ Cardiac Mapping System (Abbott) in December 2016. The EnSite Precision Cardiac Mapping System weds magnetic sensing with impedance-based geometry creation for improved dimensional accuracy in map creation. Approval of the FlexAbility Ablation Catheter, Sensor Enabled expands the magnetic sensor-enabled catheter toolset compatible with the EnSite Precision Cardiac Mapping System. At the time of the launch of the mapping system in December 2016, concomitant launch of the Advisor™ FL Circular Mapping Catheter, Sensor Enabled™ (Abbott) provided the only sensor-enabled tool for creation of atrial and pulmonary vein anatomy for atrial fibrillation and atrial flutter cases. 
 
In March 2017, Dr. John Day provided the first in the U.S. report of his experience with the EnSite Precision Cardiac Mapping System for ablation of atrial fibrillation in a case that took place on December 19, 2016.1 Since then, multiple labs have obtained this system for mapping a variety of arrhythmias, including ventricular tachycardia (VT). However, magnetically enabled geometry creation had been feasible only if the operator chose to use the Advisor FL Circular Mapping Catheter. Mapping ventricular chambers would not be safe or feasible with the Advisor due to risk of entrapment of the atrioventricular valve chordal apparatus, so geometry creation for VT cases was limited to the legacy EnSite system for impedance-based mapping with a roving catheter devoid of a magnetic sensor.
 
Although the FlexAbility Ablation Catheter, Sensor Enabled has FDA approval, our lab and others already had significant experience with the first-generation FlexAbility Ablation Catheter in VT cases, since that catheter received approval by the FDA in January 2015. A flexible tip on the FlexAbility catheter results in reduced irrigation and directs flow towards the site of tissue contact, resulting in a potentially lower risk of steam pops without compromised lesion sizes.2 The now-canceled STAR-VT trial, which launched in early 2015, was an investigational device exemption (IDE) study evaluating the first-generation FlexAbility catheter for use in early VT ablation vs routine care in patients with ICDs. Despite low enrollment in the trial, many operators continued to use the first-generation FlexAbility catheter for off-label VT ablation with good success. However, given the complexity of ventricular geometries and variability in impedance fields within typically enlarged cardiac chambers, EnSite’s impedance-based 3D maps provided less desirable dimensional accuracy compared with Biosense Webster’s magnetically enabled CARTO system. 
 
The new FlexAbility Ablation Catheter, Sensor Enabled, in concert with the EnSite Precision Cardiac Mapping System, has substantially improved the quality and dimensional accuracy of ventricular maps for VT cases. Additionally, the impedance drifts observed during prolonged VT ablations in an impedance-only mapping environment have largely been eliminated. Since the launch of the EnSite Precision Cardiac Mapping System at our center in January 2017, we have performed over 40 VT ablations (excluding PVC cases) in patients with advanced structural heart disease using the FlexAbility Ablation Catheter, Sensor Enabled and other nonmagnetic-enabled mapping catheters.
 

However, even before the launch of the EnSite Precision Cardiac Mapping System, we had been early adopters of the use of high-density mapping catheters for creation of ventricular endocardial and epicardial geometries and for detection of late potentials (LPs) and local abnormal ventricular activities (LAVA).3,4 Our workflow includes use of both a duodecapolar Livewire™ steerable diagnostic catheter (Abbott) for initial mapping of the ventricular chamber, followed by use of a FlexAbility Ablation Catheter, Sensor Enabled, for ablation as well as for magnetic sensor-based automatic field scaling of the map geometry to better approximate the true dimensionality of the structures. A case study below details use of both catheters in a patient with recurrent VT following ablation several years prior in the setting of ischemic cardiomyopathy with remote coronary artery bypass grafting (CABG) in 2006. 

Case Description

The patient was a 75-year-old male with known ischemic cardiomyopathy, a dual-chamber ICD, and a large inferior left ventricular (LV) wall scar at the time of his index VT ablation in 2013. He developed recurrent VT within a year post ablation and, following sotalol initiation, remained electrically stable for several years until recurrent VT in summer 2017 necessitated repeat ablation. He had a total of 24 pace-terminated and highly symptomatic VT episodes over the span of one month. All VTs demonstrated a similar cycle length of approximately 380 ms. At time of the lab procedure, we easily and reproducibly induced the clinical VT (by cycle length) with single extrastimuli (600/360 ms) from the RV apex. The induced VT demonstrated a RBBB V1 morphology with a rightward inferior axis and positive precordial concordance suggestive of a mitral annular origin. 
 

Using a transseptal approach, we began with mapping of the LV endocardium in sinus rhythm using the Livewire duodecapolar mapping catheter (Figure 1). We utilized the AutoMap feature of the software to automatically detect and annotate local activation timing of the “latest late potentials” in sinus rhythm. We did not initially display voltage, though a separate voltage map (Figure 2) was generated concurrently and in the background of the late potential mapping. Our interest has been to map sites of isochronal crowding of late potentials, as has been described by Dr. Roderick Tung and colleagues.5 We identified a site of isochronal crowding along the lateral mitral valve annulus (Figure 3, Video 1). 
 
We exchanged the duodecapolar catheter for the FlexAbility Ablation Catheter, Sensor Enabled, to continue with mapping and ablation. During manipulation of the FlexAbility Ablation Catheter, Sensor Enabled in the LV, we typically observed adjustment of the impedance-based maps with auto field scaling to better approximate the true dimensions of the ventricular chamber. Pace mapping with the FlexAbility Ablation Catheter, Sensor Enabled from the site of isochronal crowding on the lateral mitral valve annulus appeared to be an excellent match for the target VT, and demonstrated a long stimulation to QRS consistent with a zone of slow conduction or a protected corridor. Following VT induction, we confirmed that this site appeared compatible with an isthmus, and RF application promptly terminated VT (Video 2, plays after Video 1 clip). Following ablation transecting the line of interest, we were no longer able to induce VT. A remap of the ventricle with the steerable diagnostic catheter demonstrated an absence of further isochronal crowding, and we deferred additional ablation. 

Conclusion

Overall, we have been pleased with the opportunities to create rapid and high-density maps of ventricular surfaces for VT cases. A workflow with the FlexAbility Ablation Catheter, Sensor Enabled as an ablation tool, coupled with the steerable diagnostic catheter, has enabled us to explore more mechanistic concepts in VT substrates without relying as much on voltage alone. The use of multipolar catheters with tighter electrode spacing raises many questions about how best to adjudicate voltage in diseased myocardial and arrhythmogenic substrates, though this remains an interesting avenue of investigation.
 
Disclosure: Dr. Winterfield has no conflicts of interest to report regarding the content herein. Outside the submitted work, he reports consultancy with St. Jude Medical/Abbott.   

References

  1. Day J. User Review: The New EnSite Precision Cardiac Mapping System. EP Lab Digest. Published March 2017. Available at http://bit.ly/2ps6tEv. Accessed August 21, 2017.
  2. Winterfield JR, Jensen J, Gilbert T, et al. Lesion Size and Safety Comparison Between the Novel Flex Tip on the FlexAbility Ablation Catheter and the Solid Tips on the ThermoCool and ThermoCool SF Ablation Catheters. J Cardiovasc Electrophysiol. 2016;27:102-109. 
  3. Vergara P, Trevisi N, Ricco A, et al. Late potentials abolition as an additional technique for reduction of arrhythmia recurrence in scar related ventricular tachycardia ablation. J Cardiovasc Electrophysiol. 2012;23:621-627.
  4. Jaïs P, Maury P, Khairy P, et al. Elimination of local abnormal ventricular activities: a new end point for substrate modification in patients with scar-related ventricular tachycardia. Circulation. 2012;125:2184-2196.
  5. Irie T, Yu Y, Bradfield JS, et al. Relationship Between Sinus Rhythm Late Activation Zones and Critical Sites for Scar-Related Ventricular Tachycardia: A Systematic Analysis of Isochronal Late Activation Mapping. Circ Arrhythm Electrophysiol. 2015;8:390-399.