AF Ablation: Challenging the Current Paradigm

Complex electrophysiology procedures, including atrial fibrillation (AF) ablation, can account for a large percentage of cases being performed in many EP labs worldwide. Since the inception of the original procedure, evolutionary changes have matured the current practice of AF ablation to be quicker, safer, and most importantly, more effective. While no one would disagree that success in AF ablation would be the primary objective, I would argue that speed and efficiency are also deeply intermixed within the primary objective. Longer procedures incur more complications, extensive general anesthesia times, and more difficult patient recovery. Additionally, there is the inherent risk of radiation exposure due to excessive fluoroscopy times from a long procedure such as AF ablation.¹

As three-dimensional electroanatomic mapping and ultrasound technologies develop, so do our processes as electrophysiologists to adapt to the tools at hand. From an ablation standpoint, it has become common practice for me to perform the majority of my AF ablation procedures without the use of fluoroscopy in those patients without intracardiac devices. The frequency in which ablations require x-ray is minimal. Personal experience has suggested that in cases where uncertainty loomed and x-ray was utilized, no additional benefit was conferred from fluoroscopy, except some personal reassurance about catheter positioning. The need for CT or MRI image integration has also become unnecessary in this era of fast image acquisition by multipolar electrode catheters and the CARTOSOUND^® Module (Biosense Webster, Inc., a Johnson & Johnson company).

Workflows vary when ablation procedures are compared between electrophysiologists. As stated previously, my goals are closely intertwined with the objectives of being safe and achieving a successful result. Rooted in those goals is speed and efficiency. Following endotracheal intubation and pre-procedure TEE, I will pass an ESOPHASTAR^® Catheter (Biosense Webster, Inc., a Johnson & Johnson company) via the oropharynx and generate a 3D map of the esophagus. The patient is then prepped and when venous access is obtained, I will use a force sensing catheter (in this case, Biosense Webster’s THERMOCOOL SMARTTOUCH^® Catheter) and guide it up to the superior vena cava. I generate a quick 3D map of the RA, SVC, IVC, and CS for purposes of orientation. I will then place a decapolar catheter in the CS and a SOUNDSTAR^® eco Catheter in the RA with direct visualization of the interatrial septum. I then exchange a short sheath for a longer transseptal sheath, typically an Agilis sheath (St. Jude Medical). Once in the IVC, I remove the wire and dilator, and reinsert the ablation catheter, which then guides the long sheath up to the SVC. Confirmation of sheath position is made by observing the proximal pole of the ablation catheter turning black on the CARTO^® 3 System (Figure 1). I then reinsert the wire and dilator, and subsequently exchange the wire for a BRK-1 needle (St. Jude Medical). While observing under ICE, I then withdraw the apparatus until it drops along the fossa ovalis and tenting is observed along the septum with the needle posteriorly directed towards the left-sided pulmonary veins. I then push the needle across into the LA and remove the needle so that I can place an exchange length guidewire into the LSPV. This allows me to guide my sheath safely across by solely using ICE. Once the outer sheath is across, and the dilator and wire are removed, I will do a second puncture in the same manner. Once in the LA, I will use a multipolar catheter, either a 20-pole Lasso or PENTARAY^® Catheter (Biosense Webster, Inc., a Johnson & Johnson company), as well as a THERMOCOOL SMARTTOUCH^® Catheter. 

The complement of ICE, intracardiac electrograms, and 3D mapping (fast activation mapping) are utilized to generate a complete map of the LA to include the pulmonary veins and ostia, LAA, and mitral valve annulus. At this point, divergent opinions appear about how to proceed with AF ablation. Most agree that when it comes to paroxysmal AF, PV isolation is the cornerstone of the procedure. In this setting, I will place the multipolar catheter in the LSPV and proceed with wide area circumferential ablation (WACA). Once complete, I will then identify and perform the same ablation on the right-sided veins. In the past, I relied solely on electrogram-guided ablation from within the vein to help identify potential sites of connectivity. This, at times, is slow and arduous. Typically, areas of PV connection do not necessarily correlate with electrograms that are present on the adjacent multipolar catheter. 

Data from Kapa et al provide a framework for what we can consider left atrial scar.² They concluded that bipolar voltage cutoff values of 0.20 to 0.45 mV in the LA help delineate areas of scar, which is quite different from what we know about VT ablation. This is not surprising, as bipolar voltage cutoff criteria for endocardial and epicardial VT ablation are quite different as well. Once the initial WACA is complete, I will take my multipolar catheter and, within a couple of minutes, create an accurate bipolar voltage map of the LA using Biosense Webster’s CONFIDENSE™ Module (Video available on www.eplabdigest.com). This feature on the CARTO^® 3 System allows for quick and accurate multipoint data acquisition. Achieving durable PV isolation can be quicker and more efficient by targeting healthy tissue around the veins that have bipolar voltage above 0.45 mV. More often than not, I will notice gaps between areas of low voltage that are adjacent to healthy, viable tissue. I then direct my ablation focus at these interspersed sites. Entrance and exit block are then confirmed by differential pacing maneuvers and high-output pacing along my ablation line confirming inexcitable dense scar (IDS). Recently published data from Squara et al supports this approach and challenges commonly accepted practices to PV isolation using a traditional electrogram-guided technique.³ In their study, they delineate criteria for first-time and redo ablation for IDS. Different cutoff values for IDS help create a construct in which we can prove durable PV isolation (Figure 2).

Perhaps even more helpful is employing this strategy in persistent AF patients. I will typically follow WACA of the PVs with posterior wall isolation. At this time, a 3D mesh map of the esophagus created at the onset of the procedure is superimposed over the LA posterior wall. Visual confirmation of the esophagus helps me avoid prolonged ablation directly over adjacent posterior wall sites. While the patient is in AF, I will ablate the LA roof from LSPV to RSPV, and follow this up with a floor line from LIPV to RIPV. If the patient is still in AF, I will then cardiovert the patient to sinus, and immediately create a bipolar voltage map in NSR of the PVs and posterior wall. Data from Kapa et al only applies to patients in sinus rhythm. As with most people, I always become concerned with linear ablation. Potential for gaps is greater, and there is always concern for perforation, fistula formation, and downstream atrial arrhythmias. I have noticed increased success in isolating the posterior wall and shorter ablation times by again targeting sites of healthy, viable tissue that appear to break through my linear lesions. I am not amiss to remapping using the CONFIDENSE™ Module multiple times during a case until I am comfortable that the lines are intact using bipolar voltage criteria. Typically, once this is complete, I will confirm isolation by directly pacing along the posterior wall. Once these areas are confirmed and reconfirmed to be isolated, the procedure is done (Figures 3 and 4). 

Adapting new methods can be difficult and challenging. As fellows, we were largely taught through repetitious memory. Doing a procedure over and over again in the same manner helps minimize deviations from practice, and helps create muscle and mental memory. As technologies and our understanding of AF evolve, we need to accept the new information and integrate them into our everyday practices.

Disclosure: The author has no conflicts of interest to report regarding the content herein.   

References

1. Lickfett L, Mahesh M, Vasamreddy C, et al. Radiation exposure during catheter ablation of atrial fibrillation. Circulation. 2004;110:3003-3010.
2. Kapa S, Desjardins B, Callans DJ, Marchlinski FE, Dixit S. Contact electroanatomic mapping derived voltage criteria for characterizing left atrial scar in patients undergoing ablation for atrial fibrillation. J Cardiovasc Electrophysiol. 2014;25:1044-1052.
3. Squara F, Frankel DS, Schaller R, et al. Voltage mapping for delineating inexcitable dense scar in patients undergoing atrial fibrillation ablation: A new end point for enhancing pulmonary vein isolation. Heart Rhythm. 2014;11(11):1904-1911.