Adrian Luca

Nonlinear analysis of right atrial electrograms predicts termination of persistent atrial fibrillation within the left atrium by catheter ablation

The termination of long-standing persistent atrial fibrillation (LS-pAF) can be achieved by stepwise catheter ablation (step-CA) within the left atrium (LA). Our study aims to applying complexity measures derived from nonlinear time series analysis in order to characterize LS-pAF in terms of organization and to identify patients in whom AF can be terminated from those in whom AF cannot be terminated by step-CA within the LA. A total of 33 consecutive patients (age 61  ±  7 years, sustained AF duration 19  ±  11 months) with LS-pAF underwent step-CA. The organization of right bipolar electrograms before and during the ablation procedure was assessed using the coarse-grained correlation dimension. LS-pAF was terminated into sinus rhythm or atrial tachycardia in 22 patients during step-CA within the LA (left terminated patients-LT). In 11 patients the ablation procedure failed to terminate AF within LA (not left terminated patients-NLT). The statistical analysis of the estimated coarse-grained correlation dimension revealed that a higher right atrial (RA) organization before step-CA was associated to AF termination within the LA. During the ablation procedure, the level of RA organization displayed distinctive evolution between LT and NLT patients with a significant organization increase before AF termination for the LT patients.

Influence of right and left atrial tissue heterogeneity on atrial fibrillation perpetuation

We propose a biophysical modelling approach to separately investigate the impact of right and left atrial (RA/LA) electrical heterogeneity on atrial fibrillation (AF) perpetuation. The baseline AF substrate was based on a 4:1 anisotropy ratio and uniform membrane properties. AF was initiated by a ramp-pacing protocol applied in the pulmonary veins region. Once AF was observed, random patchy heterogeneities in action potential duration (shorter duration inside the patches) were introduced in the cellular model for the subsequent simulation of AF. The effect of tissue heterogeneity on AF perpetuation was quantified by the duration of AF episodes (an AF episode lasting more than 50 s was considered as sustained). For high percentages of heterogeneities, the mean AF episode duration and the number of non-terminated AF episodes were significantly higher for the RA compared to the LA. This could be indicative of a very probable involvement of the RA substrate into the persistent AF process in this model. A direct link between the spatial localization of tissue heterogeneity and AF duration was also observed.

Concealed abnormal atrial phenotype in patients with Brugada syndrome and no history of atrial fibrillation

OBJECTIVES The electrocardiogram (ECG) of patients with BrS in sinus rhythm might reflect intrinsic atrial electrical abnormalities independent from any previous atrial fibrillation (AF). Aim of this study is to investigate the presence of P-wave abnormalities in patients with BrS and no history of AF, and to compare them with those displayed by patients with documented paroxysmal AF and by healthy subjects. METHODS Continuous 5-min 16-lead ECG recordings in sinus rhythm were obtained from 72 participants: 32 patients with a type 1 Brugada ECG, 20 patients with a history of paroxysmal AF and 20 age-matched healthy subjects. Different ECG-based features were computed on the P-wave first principal component representing the predominant morphology across leads and containing the maximal information on atrial depolarization: duration, full width half maximum (FWHM), area under the curve and number of peaks in the wave. RESULTS Patients with BrS and no history of AF (mean age: 53±12years; males: 28 pts., spontaneous type 1 ECG: 20 pts., SCN5A mutation: 10 pts) presented with longer P-wave duration, higher FWHM and wider area under the curve in comparison with the other two groups. Although P-wave features were abnormal in BrS patients, no significant difference was found between patients with spontaneous type 1 ECG and ajmaline-induced type 1 ECG, symptomatic and asymptomatic ones, and between patients with a pathogenic SCNA5 mutation and patients without a known gene mutation. CONCLUSIONS Patients with BrS without previous occurrence of AF present with a concealed abnormal atrial phenotype. In these patients atrial electrical abnormalities can be detected even in the absence of an overt ECG ventricular phenotype, symptoms and a SCN5A mutation.

Divergent patterns of atrial ECG organization during catheter ablation of persistent atrial fibrillation revealed by adaptive harmonic frequency schemes

Introduction: We hypothesized that organization indices based on the analysis of atrial ECG harmonic components may help identify patients (pts) with persistent AF (pAF) unresponsive to pulmonary vein isolation (PVI) and left atrial (LA) ablation. Using adaptive harmonic frequency tracking schemes, we computed on the atrial ECG: 1) the variance of the phase difference (aPD) between the dominant frequency (DF) and the 1st harmonic (H1), and 2) the organization index (AOI) defined as the ratio of the power of the DF and H1 over the total power of the unprocessed atrial signal as measures of AF regularity. Methods: In 34 consecutive pts (61±7 y, pAF duration: 19±11 m), PVI and LA ablation were performed until AF termination. 40-sec ECG time series devoid of QRST were recorded at baseline (BL), after PVI (end_PVI) and at the end of LA ablation (end_ABL). APD and AOI were estimated on leads V1 and V6b (placed on the pts back). Results: pAF was terminated within the LA in 68% (23/34 LT - left terminated) of the pts, while 32% (11/34 NLT - not left terminated) did not. The figure shows that: 1) LT pts displayed higher AOI values at BL indicative of greater atrial ECG organization that increased significantly (p<0.05 for V1 and V6b) during LA ablation as opposed to NLT pts, and 2) NLT pts displayed higher APD values at BL indicative of greater atrial ECG disorganization that decreased during LA ablation, but did not reach LT pts values. Conclusion: Estimation of the level of organization of atrial ECG based on adaptive harmonic schemes appears as promising tools for the measure of pAF complexity and prediction of procedural outcome.

Atrial fibrillation septal pacing: translation of modelling results

AIMS Atrial fibrillation (AF) septal pacing consists of rapid pacing from a ring of electrodes around the atrial septum, leading to local capture of both atria during AF. The present model-based study evaluated the impact of the number of stimulation electrodes in the septal ring on AF capture for different types of sustained AF dynamics. METHODS AND RESULTS Using a biophysical model of AF based on CT scans from an AF patient, models with different AF substrates (Cholinergic AF and Meandering Wavelets) were created by varying the atrial membrane kinetics. Rapid pacing was applied from the septum area with a ring of 1, 2, 3, 4, 6, 8, or 12 electrodes during 20 seconds at a pacing cycle lengths (PCLs) in the range 60-100% of AF cycle length (AFCL), in 4% steps. Percentage of captured tissue during rapid pacing was determined using 24 sensing electrode pairs evenly distributed on the atrial surface. Results were averaged over 10 AF simulations. For Cholinergic AF, the number of stimulation electrodes on the septal ring had no significant impact on AF capture independently of AF dynamics. For Meandering Wavelets, more electrodes were needed to achieve AF capture in the presence of complex AF. CONCLUSION Changes in AF substrate significantly impacted septal pacing outcomes and response to rapid AF pacing may similarly vary patient-to-patient. The number of stimulation electrodes had a lesser impact, suggesting that the design of a ring with 3-4 electrodes around the septum would be sufficient for most AF dynamics.