Advanced mapping capabilities 2018—summary: are we working towards more personalized ablation strategies?

We started our journey on high-density mapping (HDM) with an insight on how to identify conduction gaps in previously applied pulmonary vein (PV) isolation. A substantial number of atrial fibrillation (AF) patients have to represent themselves for ‘touch-up’ procedures as PV reconnection is still the prevailing problem of after any type of ablation energy including balloons [e.g. cryo, laser, or radiofrequency (RF) current]. Bolao and colleagues shared their approach to gap identification and furthered our knowledge on gap dimensions.1 Using the HDM system, fast acquisition and automatic annotation of the electrical information has been demonstrated. Having more information of the antral PV activation allows differentiation of both atrial and PV potentials. Using the basket mapping catheter, activation during different pacing manoeuvres can be easily and quasi-simultaneously tested, which facilitates ultimately to locate conduction patterns. This information let to a significantly shorter overall RF delivery time and also shortened the overall procedure time. There was also a trend to significantly better outcome, albeit non-statistically significant despite the use of non-contact force equipped ablation catheters in the treatment arm as compared to a historic control of the same operator. Larger, multicentre trials are clearly necessary with accurate patient sample sizes to confirm this finding. In the second manuscript, two experienced electrophysiologists debated the role of the atrial myocardium as the substrate for maintenance of AF vs. trigger initiation from the PVs.2 Their dialogue was illustrated by deliberations on the various studies from conventional mapping and ablation techniques. Using the HDM, identification of the individual myocardial substrate should be facilitated and thereby truly allowing to personalize the AF ablation strategy. This may be especially important in patients with persistent or longstanding-persistent AF or patients with significantly enlarged atria. However, the step from individual substrate identification to delivery of the ‘winning’ ablation strategy is obviously still a challenge, but due to the small electrode sizes low-amplitude voltage areas should be much easier to identify. Whether this level of detail provides an incremental benefit for strategies involving scar ablation is an area of future investigation and has to date not been demonstrated. Latcu and colleagues reported very insightful and instructive on how to take advantage of the high resolution mapping capabilities in identifying atrial tachycardia substrates mostly after extensive AF ablation.3 As substrate modification by linear lesions and other non-PV isolation techniques are applied in many non-paroxysmal AF patients, the incidence of iatrogenic atrial tachycardia has risen exponentially. Mapping of these atrial tachycardias can be a great challenge and identification of micro-reentry and bystander areas can be difficult if lower resolution systems are employed. Bourier and colleagues demonstrated that the HDM system could successfully be applied to ventricular arrhythmia.4 This information is compared to the information obtained from the gold standards of CARTO or ENSITE sequential mapping systems. They carefully reviewed the published evidence for catheter ablation of ventricular tachycardia using high resolution mapping techniques and highlighted the different electrcardiogram characteristics when mapping is performed using small mapping electrodes in comparison to the standard mapping and ablation tip. In addition, they emphasized the advantage of 3D image integration to identify ‘anatomical’ substrates rather than only ‘functional’ substrates. All HDM-guided procedures listed the lack of appropriate lesion assessment as one of the leading problems in ablation for both atrial and ventricular arrhythmias. Gunawardene and colleagues reported on their single centre pilot experience with local impedance (LI) measurements from a novel ablation catheter and compared the results to the conventional impedance displayed at the RF generator (GI).5 The catheter tip is equipped with three additional electrodes that allow recording of nearfield impedance, which changes characteristically once RF energy is delivered into the myocardium. Depending on baseline LI, an appropriate drop in LI of about 13 Ω seems to predict good lesion formation, whilst fluctuating LI is characteristic for poor catheter stability and thereby poorer lesion formation. In both settings, the changes in LI are more pronounced then in GI. However, due to the overall small sample size and the explorative nature of a pilot trial, no final claim of improved effectiveness especially in low voltage areas can be made at this point in time. The authors point out that the multicentre LOCALIZE trial has already been initiated, which will address this issue in greater detail. Catheter ablation of atrial tachycardia in patients with congenital heart disease poses a number of challenges including the identification of previously acquired surgical scars and/or previous ablation attempts. Another challenge is the sheer size of the atrial chambers which makes any sequential mapping attempt more difficult. With the multitude of potential substrates, these patients are typically plagued by multiple atrial tachycardias which Ernst et al. attempted to address in a sequential fashion.6 Recommendations for scar settings and 3D image integration are reviewed, cautioning the expectations at least for the present. We hope this variety of contributions from several groups will provide further insights into contemporary HDM and ablation in order to improve our understanding of complex tachyarrhythmias and help to overcome hurdles still preventing us from successful treatment of these entities. Thus, this supplement may represent a small step towards more personalized strategies in this setting. Conflict of interest: S.E. received honoraria from Boston Scientific, Stereotaxis and Biosense Webster and has research collaborations with Baylis Medical, Medilumics and Catheter Precision. S.W.: none declared.