Value of fRagmented Atrial electrOgrams, Computed Tomography and Intracardiac Echocardiography for Identification of optiMal Sites for Radio-frequency Delivery During cArdioneuroablation for Asystolic Reflex syNcope

Cardioneuroablation (CNA) is a new method for the treatment of asystolic reflex syncope. Although the procedure is becoming more and more popular, many important issues remain unresolved. One such a problem is the optimal method for identification of presumed sites of ganglionated plexi (GP) which are located in the epicardial fat surrounding myocardium and are the target for CNA. Several methods have been used, including anatomical approach using computed tomography (CT), intracardiac echocardiography (ICE) and 3D electro-anatomical mapping (EAM) as well as electrophysiological methods which include high-frequency stimulation and recording of fragmented atrial potentials (FP).

Areas of FAP are sought to represent nerve fibers endings, extending from GPs to myocardium. The technique was first described by in 2004 and spectral analysis with fast Fourier transformation was used to identify these areas. Next, the time-domain quantification of FAP characteristics was performed. It was found that a high number of deflections (at least 4) identified the presumed areas of GPs. Later on, this method was further developed and it has been shown that FAP-guided CNA was associated with shorter procedure and fluoroscopy times. The currently advocated approach is to evaluate FAP for the number of deflections at filter settings of 200-500 Hz or 100-500 Hz. If ≥3 deflections are present, these sites are tagged as ablation targets.

However, the role of FAP for the identification of optimal sites for GPs ablation is still debatable. Reproducibility of the results of spectral analysis of GPs areas has not been well established. Also, sensitivity and specificity of both spectral and time-domain analysis of FAP have not been established. The sensitivity of 72% and specificity of 91% values were calculated for patients undergoing ablation for atrial fibrillation and not CNA, were based on reflex bradycardia/asystole during RF delivery, mainly at posterior left atrial (LA) wall and not by extra cardiac vagal stimulation (ECVS) after ablation at typical sites for septal GPs. In fact, specificity may be limited because FAP may represent areas of scarred atrial tissue, pulmonary vein (PV) potentials or fragmented electrograms at such areas in the right atrium (RA) as slow pathway region, coronary sinus (CS) os or RA-superior vena cava (SVC) junction. Moreover, the adipose tissue surrounding the heart can infiltrate the atrial myocardium, causing heterogeneous activation resulting in the presence of FAP. In addition, the sensitivity may also be limited since effective RF applications, which cause total vagal denervation confirmed by ECVS, can be sometimes performed at the areas with no FAP. To date, no study examined prospectively and blindly characteristics of FAP in effective and non-effective sites, confirmed by ECVS, in patients undergoing CNA due to reflex asystolic syncope.

Intracardiac echocardiography. This is another tool used for anatomical localisation of presumed GP areas. With ICE, areas of epicardial fat in the so-called pyramidal space, containing paraseptal inferior GP, as well as space between right superior PV (RSPV) and SVC, containing superior paraseptal GP, can be visualised. The correlation between ICE-identified areas of GPs and other tools like CT or FAP has not yet been established.

Computed tomography. Lastly, CT can be used during anatomical approach to identify target sites for CNA. Current techniques enable visualisation of pericardial fat. Also, density of the epicardial fat which may correspond to the density of GPs, can be quantified using CT.