In this feature interview, EP Lab Digest speaks with Dr. Xunzhang Wang, electrophysiologist and Director of the Complex Ablation Laboratory at Cedars-Sinai Medical Center in Los Angeles, California, about his experience using a new ultra-high resolution 3D imaging and mapping system that offers instant remapping (AcQMap® High Resolution Imaging and Mapping System, Acutus Medical), which received FDA approval in October 2017.
Tell us about your program at Cedars-Sinai.
In 2018, the Smidt Heart Institute at Cedars-Sinai was ranked #3 in the field of adult cardiology and heart surgery hospitals by U.S. News & World Report. We are a national referral center, accepting patients with complex arrhythmias, many of whom have had multiple, previously failed cardiac catheter ablations.
How long have you been using the AcQMap System? In approximately how many cases have you used AcQMap?
We have used the AcQMap System (Figure 1) in over 40 cases in the last 4 months.
What prompted you to use the AcQMap system? What do you find unique about the system?
Recent publications of clinical trials have shown conflicting outcomes on the best ablation strategy for producing optimal clinical results in patients with persistent AF. Which strategy is the best? Should we include pulmonary vein isolation (PVI) either by cryo or radiofrequency (RF) ablation plus additional ablation of complex fragmented potentials? Or should we perform linear left atrial ablation of substrate scar for persistent AF? We were looking for a system that could help us define a better ablation strategy, and having the ability to use an advanced high-resolution tool to see dipole density mapping instead of just voltage mapping does just that. Dipole density has a 5x higher resolution capability than voltage-based mapping, and allows me to see things in real time that I never could have seen with conventional systems.
AcQMap is a novel non-contact mapping system that allows us to map unstable complex arrhythmias such as atrial fibrillation (AFib) by recording electrical activation within the left or right atrium. These maps can be generated in just minutes, and can display activation wavefronts across the chamber and waveforms at any single location. Activation can be displayed through time, or can be fixed at any given time point during the ablation procedure. Given that a map can be created in just minutes, repeat mapping throughout the procedure to assess my ablation strategy is finally possible and isn’t burdensome.
How has the AcQMap System assisted you in the treatment of your patients with complex arrhythmias, and how does this differ from other available mapping systems? What types of cases do you use the system for, and what methods were you using previously?
In our lab, we use the AcQMap System for paroxysmal AFib, persistent AFib, and complex atrial flutter s/p catheter or surgical ablation. For patients with persistent AFib, we can determine an ablation strategy based on clinical information, CT or MRI data, combined with substrate mapping of the left atrium by AcQMap.
We have also found it useful to use AcQMap for recurrent AFib in patients who have undergone previous ablation attempts. We have performed mapping and ablation guided by AcQMap in nine cases with recurrent AFib (not including atypical atrial flutter alone). In all cases, there were relatively large reentry circuits around scar or anatomic boundaries with coexisting fibrillatory activity elsewhere that was revealed by mapping with AcQMap. Current contact mapping systems are not able to map activation of such unstable arrhythmias. This advancement in mapping capabilities is encouraging, as patients who undergo repeat ablations have usually been referred for a surgical MAZE procedure. We feel that identification of unique dipole density activation patterns gives us an additional option for ablative treatment of AFib that may limit surgical referrals and thereby minimize patient morbidity.
Please describe an example case in which the AcQMap System was used.
Our first experience with the AcQMap System was in a patient referred to our center after his own physicians refused to consider ablation therapy to treat his persistent AFib. The patient entered the lab in sinus rhythm, and we used the AcQMap ultrasound capability to reconstruct the left atrium. We created maps in sinus rhythm, during proximal and distal CS pacing, before inducing and mapping AFib. Two areas of interest were identified that coincided with similar regions that also displayed delayed conduction and block during sinus and paced rhythms. The anterior target was more complex and broad, while the posterior target was more compact and organized (Figure 2). After isolating the pulmonary veins, we decided to ablate the posterior target first, and then remap. Our strategy was to ablate the core region and anchor the ablation with a line to the LIPV isolation line. As we completed the final ablations, the rhythm converted to what appeared to be a typical RA flutter. We subsequently mapped the flutter from the LA, and found passive conduction entering at the low septum and sweeping around with collision on the lateral wall, thus supporting typical flutter in the RA. Prior to moving to the right side, the anterior target was ablated and tied to the RSPV isolation line and mitral valve annulus. Ultrasound was used to create the RA anatomy, and mapping revealed the typical counterclockwise pattern of conduction, with significant slowing in the region of Koch’s triangle. Successful ablation terminated the flutter to sinus rhythm. The patient has done well since the ablation procedure and remains in sinus rhythm.
To date, we have treated 40 patients with the AcQMap System. In our persistent AFib cases, we are using cryoablation for PVI with additional RF substrate ablation guided by the AcQMap System. Cryoablation makes for a fast PVI, which gives me time to use AcQMap to map the non-PV targets. We have been successful in terminating AFib during RF application of non-PV targets in patients who demonstrate a more organized fibrillatory conduction pattern (see the four panels in Figure 3A showing different stages of activation during AFib; Figure 3B shows where RF lesions were applied). In patients who had significantly more chaotic patterns of fibrillatory conduction in the left atrium, we have been able to successfully cardiovert these patients following ablation of the identified areas of interest. Our hope is to be able to stage persistent AFib based on left atrial AcQMap dipole density maps combined with clinical information, including left atrial volume on CT, to help guide individual ablation strategies.
We have also found an interesting observation with paroxysmal AFib. In several patients, AFib and left atrial flutter could not be induced by burst atrial pacing following PVI with cryoablation (CS pace at 200 ms for 30 to 50 times). One case had evidence of LSPV firing, one case had an unclear etiology, and four cases had rotational activation in the left atrium adjacent to the PV, which may help explain why AFib can be eliminated by PVI alone. We have noted that the regions with rotational activation during AFib are very similar to the locations of abnormal slow conduction during sinus rhythm and/or coronary sinus pacing. A few focal RF ablation applications delivered to the region of rotational activation often terminated the atrial fibrillation without further inducibility of AFib or flutter.
Would you recommend the use of the AcQMap System to other physicians? Have you been happy with the results of the system?
Absolutely. In only a short amount of time using this system, we have been able to document activation patterns that have not been evident with other systems. This is exciting, and we plan to continue to expand our use of the AcQMap System.
Is there anything else you would like to add?
With continued use, we are expanding our clinical database to address a very broad range of research, including: 1) assessment of pacing induction for paroxysmal AFib after PVI; 2) assessment of the percent of AFib or LA flutter recurrence with and without ablation using the AcQMap System for paroxysmal AFib; and 3) investigation of optimal pacing induction protocols that will be reliable for evaluation and prediction of the recurrence of AFib.
We believe that AcQMap can have a significant impact on guiding ablation and understanding possible mechanisms in paroxysmal and persistent AFib. We plan to continue using AcQMap in patients with AFib and complex atrial flutter. We anticipate future generations of AcQMap, with the addition of LA wall motion evaluation, mechanical function assessment, and esophageal imaging for added safety when ablating the posterior wall, will further enhance our ability to terminate atrial fibrillation.
Disclosure: The author has no conflicts of interest to report regarding the content herein.
This article is published with support from Acutus Medical.