Novel ECG and Intracardiac Electrograms Signal Processing Schemes for Predicting the Outcome of Atrial Fibrillation Catheter Ablation

Atrial fibrillation (AF) is the most common encountered cardiac rhythm disorder (arrhythmia) in clinical practice. It is responsible for about one third of arrhythmia-related hospitalizations. This arrhythmia, which increases in prevalence with age, leads to severe complications and subsequently decreases the quality of life for the affected patients. Lifetime risks for developing AF are ~25% in subjects older than 40 years old. Currently, this arrhythmia is considered as a major public health concern. AF is a progressive disease, starting by short and rare episodes which further develop into longer and more frequent occurrences. When the arrhythmia becomes sustained for more than one year, it is labelled as long-standing persistent. AF advancement gives rise to an electrical of the atria (the upper chambers of the heart) resulting from abnormal high frequency atrial activations. The main goals of therapeutic management for patients with AF are to prevent severe complications associated with this arrhythmia, and ultimately to restore a normal rhythm. Currently, the cornerstone of non-pharmacological therapy is the radiofrequency catheter ablation of AF, which consists in delivering at strategic locations within the atria high-frequency electrical impulses. However, catheter ablation for patients with long-standing persistent AF involves extensive ablation of the atria and the success rate reported in various publications is associated with conflicting results. Over the last twenty years, an important effort has been made by the scientific community to develop signal processing algorithms to quantify the complexity of temporal or spectral characteristics of AF dynamics in terms of organization. As such, multiple approaches have been proposed to quantify AF organization either based on time-domain or frequency-domain analysis. All these methods shared one common goal: the development of organization indices which are interpretable from an electrophyisiological viewpoint. In the context of catheter ablation of patients with long-standing persistent AF, the success rate appears limited as the "classical" organization indices are not performant in assessing the amount of ablation required to achieve AF termination. Thus, there is a strong interest in predicting the procedural outcome from the surface electrocardiogram (ECG) recorded at baseline, i.e., prior to ablation. The main objective of this thesis was to derive novel organization indices from surface ECG and intracardiac signals acquired at baseline which could discriminate patients in whom AF was terminated from patients in whom AF persisted during catheter ablation within the left atrium. As the standard surface ECG is not appropriate for measuring the atrial activity, we aimed at adapting the placement of at least one ECG lead such that additional electrical information from the atria was provided. In our ECG signals study, we hypothesized that a quantification of the harmonic structure of AF signals brings more insight into AF complexity. Time-invariant and time-varying approaches were used to derive the ECG organization indices, and their performance for predicting the acute outcome of catheter ablation were compared. In the first scheme, the harmonic components of AF waves were extracted using linear time-invariant filters. In the second one, the components were extracted using an adaptive harmonic frequency tracking algorithm. [...

Mechano-electrical contribution of ventricular contractions to the complexity of atrial fibrillation electrograms

Purpose: Intracardiac organization indices (OI) have been used to track the efficiency of stepwise radiofrequency catheter ablation (step-CA) of persistent atrial fibrillation (pers-AF). A better understanding of the components and complexity of AF electrograms (EGMs) is fundamental for tracking the organization of AF. It remains unknown whether ventricular contractions affect the complexity of AF EGMs by means of mechano-eletrical feedback. Our study is aimed at developing new methods to quantify the potential mechano-electrical contribution of ventricular contractions on AF complexity. Methods: During step-CA, a quadripolar catheter was placed into the right atrial appendage (RAA). Robust maximum positive peak detection was applied. The time difference between two adjacent peaks was regularly resampled resulting in the intra-cardiac variability (ICV) signal. ICV reflects the intrinsic atrial activation time variability as well as the potential mechano-electrical feedback of ventricular contractions (VC). A lowpass version impulses series of R wave locations was used as input to an adaptive interference canceller in order to suppress the VC contribution to ICV (VC-ICV). Results: Step-CA (including PVI, CFAE, roof and mitral isthmus lines) terminated 2/3 pers-AF into flutter. The mean contribution of the mechano-electrical feedback on AF complexity achieved 37%. The figure shows a representative example where the VC component (2.03 Hz) has been removed from the ICV, resulting in the atrial-ICV. All other components have been preserved. Conclusions: Our preliminary findings suggest that by means of mechano-electrical feedback, VC contribute up to 37% of the atrial complexity during pers-AF. It is also a first step in the elaboration of new organization indices free of ventricular contribution

Morphological Study of Intracardiac Signals as a New Tool to Track the Efficiency of Stepwise Ablation of Persistent Atrial Fibrillation

Intracardiac organization indices such as atrial fibrillation (AF) cycle length (AFCL) have been used to track the efficiency of stepwise catheter ablation (step-CA) of longstanding persistent AF, however with limited success. The morphology of AF activation waves reflects the underlying activation patterns. Its temporal evolution is a local organization indicator that could be potentially used for tracking the efficiency of step-CA. We report a new method for characterizing the structure of the temporal evolution of activation wave morphology. Using recurrence plots, novel organization indices are proposed. By computing their relative evolution during the first step of ablation vs baseline, we found that these new parameters are superior to AFCL to track the effect of step-CA “en route” to AF termination

Contribution of Left and Right Atrial Appendage Activities to ECG Fibrillation Waves

It was recently shown that atrial fibrillation (AF) waves on chest lead V1 adequately reflect right atrial appendage (RAA) activity during long standing persistent AF (pers-AF). The contribution of the left atrial (LA) activity to chest leads AF waves, however, remains unknown. Our study is aimed at evaluating the respective contribution of the RA and LA depolarization to ECG chest leads AF waves during pers-AF. Methods: Catheters (CAT) were introduced in 10 consecutive patients (60±5 y, AF duration 22±14 m) prior to ablation: 1) a quadripolar CAT in the RAA, 2) a decapolar CAT in the coronary sinus (CS) and 3) a duodecapolar CAT in the LA appendage (LAA). Local activation times were extracted from bipolar recordings using sliding windows. Chest lead V6 was placed in the back (V6b). Mean AF cycle length (AFCL) of leads V1 to V6b were computed as the inverse of the dominant frequency of ECG spectra after QRST cancellation, and compared to intracardiac RAA, LAA and CS AFCL using Pearson’s correlation coefficient. Results: The figure shows that the correlation between RAA and chest leads AFCL was maximal for V1 and progressively dropped till V5, with a moderate rise for V6b. LAA AFCL showed the opposite pattern with the highest correlation in V6B and the lowest one in V2. The correlation of CS AFCL was similar to the LAA one, but of lower magnitude. Conclusion: Our preliminary results suggest that the respective contribution of RAA and LAA activities can be estimated using a modified surface ECG. Whether this technique has the potential to guide ablation of LA and RA drivers in pers-AF needs further validation

Measures of Right Atrial Organization as a Mean to Select Candidates for Sinus Rhythm Restoration by Catheter Ablation

Stepwise catheter ablation (step-CA) can terminate long-standing persistent atrial fibrillation (LS-pAF) within the left atrium (LA) or may require additional right atrial (RA) ablation. Intracardiac organization indices such as AF cycle length (AFCL) have been used to track the efficiency of step-CA, but predictive parameters of procedural success are lacking. In this study, we hypothesized that the oscillations of time intervals between consecutive AF wavefronts reflect the underlying AF dynamic. We report a new method for quantifying the temporal variability of atrial activation wavefronts (VAW). Our results suggest that the mean and variance of the oscillations around the mean AFCL computed before any ablation can identify patients whose LS-pAF will terminate within the left atrium. These findings are indicative of a higher baseline organization in AF terminated within the left atrium

Adaptive harmonic frequency schemes of atrial ECG reveal divergent patterns of organization during catheter ablation of persistent atrial fibrillation

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

ECG periodic components as a promising tool for complexity assessment during stepwise ablation of atrial fibrillation

Introduction: Stepwise radiofrequency catheter ablation (step-CA) has become a treatment of choice for the restoration of sinus rhythm (SR) in patients (pts) with long-standing persistent atrial fibrillation (pers-AF). Its success rate appears limited as the amount of ablation to achieve long term SR is unknown. Recently, intracardiac organization indices (OI) of AF have been used to track the efficiency of step-CA, with limited success. Our study is aimed at developing new OIs based on the relationships between harmonic components of atrial activity from the surface ECG as a global assessment of AF complexity and organization during step-CA. Methods: 3 pts with pers-AF (age 62, AF duration 17 months) underwent a step-CA. An adaptive tracking algorithm was developed for estimating the instantaneous frequency of atrial activity on chest lead V1 (after QRST subtraction) and for extracting its fundamental and harmonic components. An adaptive organization index (AOI) was computed as the ratio between the power of the extracted components and the total power of the signal to evaluate the temporal evolution of AF oscillations. The variance of the phase difference (PD) between the fundamental and harmonic components was used for measuring AF regularity. Results: Step-CA terminated 2/3 pers-AF into flutter. Importantly, in the 2 terminated pts, the AOI did not show any significant change during the step-CA (from pre-ablation to CFAE), while the PD showed a gradual reduction suggestive of increased coupling between the fundamental and the 1st harmonic. See figure. Conclusions: The PD and the AOI as measurements of complexity from the surface ECG appear as promising methods for tracking the effect of step-CA on global AF organization. This, however, needs to be validated on a larger population

Tracking of Stepwise Ablation of Persistent Atrial Fibrillation using Synchronization of nearby Electrograms

Purpose: The timing of bipolar intracardiac electrograms (EGMs) during atrial fibrillation (AF) reflects the dynamics of AF wavelets. The extent of synchronization between EGMs is an indirect measure of AF spatial organization. Our study intends to determine whether the synchronization of nearby electrodes can track the gradual organization produced by stepwise catheter ablation (step-CA) “en route” to AF termination (AF-term, i.e. restoration of sinus rhythm (SR)/conversion to atrial tachycardia). Methods: 5 patients (mean age 60±4) with long-standing persistent AF (per-AF) (mean duration 16±10 months) successfully underwent AF step-CA consisting of pulmonary veins isolation, ablation of fragmented potentials and left atrial lines until AF-term. Bipolar EGMs from a quadripolar catheter placed into the right atrial appendage were continuously recorded and split into 10-sec epochs. Windows (whose size corresponded to the mean AF cycle length – AFCL) centered on each maximum positive activation potential of the source (distal electrode) were computed on the target (proximal electrode). These windows were summed to form a vector, the sparseness (SPAR) of which quantified the synchronization between proximal and distal dipoles. Differences in SPAR and AFCL values (in %) were compared during the last two steps preceding AF-term. Results: Before AF-term, SPAR and AFCL both increased. However, SPAR increased by 31% while AFCL by 3%. SPAR performed considerably better than AFCL. Conclusion: Our preliminary results suggest that our index based on the synchronization of nearby electrodes was able to track the evolution of organization before AF-term. SPAR is a promising parameter that might help to titrate the amount of ablation required to restore long term SR

A New Method for ECG Tracking of Persistent Atrial Fibrillation Termination during Stepwise Ablation

Stepwise radiofrequency catheter ablation (step-CA) has become the treatment of choice for the restoration of sinus rhythm (SR) in patients with long-standing persistent atrial fibrillation (pers-AF). Its success rate appears limited as the amount of ablation to achieve long term SR is unknown. Multiple organization indexes (OIs) have been previously developed to track the organization of AF during step-CA, however, with limited success. We report an adaptive method for tracking AF termination (AF-term) based on OIs characterizing the relationship between harmonic components of atrial activity from the surface ECG of AF activity. By computing their relative evolution during the last two steps preceding AF-term, we found that the performance of our OIs was superior to classical indices to track the efficiency of step-CA “en route” to AF-term. Our preliminary results suggest that the gradual synchronization between the fundamental and its first harmonic of AF activity appears as a promising parameter for predicting AF-term during step-CA

A Non-linear Filter to Detect Atrial Activation from Intracardiac Electrograms

Atrial activation (AA) detection during atrial fibrillation (AF) can be considered as a first step in estimating AF characteristics such as the AF cycle length. The detection of AA from intracardiac electrograms (EGM) remains challenging due to the constant variation in amplitude and duration of atrial EGM. This study is aimed at developing a robust detection of AA based on a novel non-linear filtering technique. Three consecutive patients (62-64 yrs.) with persistent AF (sustained AF duration 9-25 months) underwent catheter ablation (CA). Before CA, multipolar catheters were sequentially placed within the four pulmonary veins and the left atrial appendage for a duration of one minute. Sliding shortand long-term signal energies were measured for each sample in the EGM. A coefficient signal was then created as the ratio between the corresponding short- and long-term energies. Filtering was carried out by multiplying the coefficient signal to the EGM. Since AA have relatively higher amplitude than that of the noise and other EGM activities, the coefficient signal values are close to one where AA take place, while insignificant otherwise. Performance of the algorithm was measured with respect to activations manually annotated by a clinical expert. For a total of 5216 annotated activations, our method achieved a 99.6% detection rate, 99.8% specificity and 99.8% positive prediction value (PPV), against a state-of-theart approach [1] with 93.6%, 94.6% and 98.9% of detection rate, specificity and PPV respectively. These preliminary results indicate that the non-linear filter efficiently detects AA. This method is implementable by using two simple filters, avoids excessive use of arbitrary thresholds while incorporating physiological constraints. It offers low computational complexity, which makes it suitable approach for realtime/ online scenarios