High-resolution Mapping in Patients with Persistent AF

High-density and high coverage composite mapping of repetitive atrial activation patterns

BACKGROUND

Repetitive atrial activation patterns (RAAPs) during atrial fibrillation (AF) may be associated with localized mechanisms that maintain AF. Current electro-anatomical mapping systems are unsuitable for analyzing RAAPs due to the trade-off between spatial coverage and electrode density in clinical catheters. This work proposes a technique to overcome this trade-off by constructing composite maps from spatially overlapping sequential recordings.

METHODS

High-density epicardial contact mapping was performed during open-chest surgery in goats (n=16, left and right atria) with 3 or 22 weeks of sustained AF (249-electrode array, electrode distance 2.4 mm). A dataset mimicking sequential recordings was generated by segmenting the grid into four spatially overlapping regions (each region 6.5 cm², 48±10% overlap) without temporal overlap. RAAPs were detected in each region using recurrence plots of activation times. RAAPs in two different regions were joined in case of RAAP cross-recurrence between overlapping electrodes. We quantified the reconstruction success rate and quality of the composite maps.

RESULTS

Of 1021 RAAPs found in the full mapping array (32±13 per recording), 328 spatiotemporally stable RAAPs were analyzed. 247 composite maps were generated (75% success) with a quality of 0.86±0.21 (Pearson correlation). Success was significantly affected by the RAAP area. Quality was weakly correlated with the number of repetitions of RAAPs (r=0.13, p<0.05) and not affected by the atrial side (left or right) or AF duration (3 or 22 weeks of AF).

CONCLUSIONS

Constructing composite maps by combining spatially overlapping sequential recordings is feasible. Interpretation of these maps can play a central role in ablation planning.

High-resolution mapping as an alternative for exit block testing in the presence of entrance block after high-power short-duration pulmonary vein isolation

BACKGROUND

After pulmonary vein isolation (PVI) for atrial fibrillation (AF), it is common as an endpoint to demonstrate an exit block from the pulmonary veins (PVs) in addition to an entrance block into them. By using high-resolution mapping catheters, even very small signals can be detected.

OBJECTIVES

We investigated whether additional exit block testing is still necessary when using high-resolution mapping catheters after ablation in high-power short-duration (HPSD) techniques.

MATERIALS AND METHODS

Overall, 114 patients with AF (average age, 65.14 ± 11.3 years; 65.8% male) undergoing radiofrequency PVI were included in the study. Ablation was performed with the HPSD technique using a fixed protocol for energy delivery of 50 W (contact force 3-20 g). Entrance and exit block were tested with a high-resolution mapping catheter. Isolation of the PVs was achieved in all patients.

RESULTS

Capture of local PV tissue was demonstrated in all patients after PVI and exit block was present in all patients after entrance block was detected using a high-resolution mapping catheter.

CONCLUSION

Exit block testing in addition to the demonstration of an entrance block as an endpoint of PVI seems to have no additional benefit and might no longer be necessary when a high-resolution mapping catheter is used in HPSD ablation for PVI of AF.

Atrial conduction velocity mapping: clinical tools, algorithms and approaches for understanding the arrhythmogenic substrate

Characterizing patient-specific atrial conduction properties is important for understanding arrhythmia drivers, for predicting potential arrhythmia pathways, and for personalising treatment approaches. One metric that characterizes the health of the myocardial substrate is atrial conduction velocity, which describes the speed and direction of propagation of the electrical wavefront through the myocardium. Atrial conduction velocity mapping algorithms are under continuous development in research laboratories and in industry. In this review article, we give a broad overview of different categories of currently published methods for calculating CV, and give insight into their different advantages and disadvantages overall. We classify techniques into local, global, and inverse methods, and discuss these techniques with respect to their faithfulness to the biophysics, incorporation of uncertainty quantification, and their ability to take account of the atrial manifold.

Tailoring the Ablative Strategy for Atrial Fibrillation: A State-of-the-Art Review

In spite of technological progress and the improving skills of operators, atrial fibrillation (AF) ablation results appear to date to be at a plateau. In any case, the superiority of ablation over pharmacological therapy in terms of effectiveness, reduction of hospitalizations, and improvement has been well demonstrated in recent randomized trials. Triggers, substrate, and modulating factors (elements of Coumel's triangle) play different roles in paroxysmal and persistent AF, so induction and perpetuation mechanisms of arrhythmia may be different in each patient. Although effective ablative strategies are available for the treatment of paroxysmal AF triggers and persistent AF substrates, an adequate clinical evaluation of the patient is crucial in order to increase the chances of success. Recognizing triggers allows not only performing an effective ablation but also to avoid unnecessary lesions and at the same time reducing the risk of complications. AF beginning and triggers could be recorded by 12-lead ECG, continuous Holter monitoring, or implantable devices. In case of an unsuccessful noninvasive evaluation, nonpulmonary vein triggers should be investigated with an electrophysiological study. Persistent AF needs more effort to perform an accurate substrate characterization. Among the many methods proposed, recently the use of high-density mapping and multipolar catheters seems of particular benefit in order to clarify the arrhythmia mechanisms. Surgical and hybrid techniques allow to treat regions such as the posterior wall or Bachmann's bundle, which is fundamental for an ablative strategy that goes beyond just pulmonary vein isolation. Too often, patients are referred to electrophysiology laboratories without adequate preprocedural screening and planning in order to submit them to a standard "ready-made" procedure. The accurate search for triggers in paroxysmal AF and the correct recognition of the link between a possible underlying heart disease and the substrate in persistent AF could allow us to tailor the interventional approach in order to overcome the current plateau, increasing ablative procedure success and minimizing complications.

Analyzing the effect of electrode size on electrogram and activation map properties

BACKGROUND

Atrial electrograms recorded from the epicardium provide an important tool for studying the initiation, perpetuation, and treatment of AF. However, the properties of these electrograms depend largely on the properties of the electrode arrays that are used for recording these signals.

METHOD

In this study, we use the electrode's transfer function to model and analyze the effect of electrode size on the properties of measured electrograms. To do so, we use both simulated as well as clinical data. To simulate electrogram arrays we use a two-dimensional (2D) electrogram model as well as an action propagation model. For clinical data, however, we first estimate the trans-membrane current for a higher resolution 2D modeled cell grid and later use these values to interpolate and model electrograms with different electrode sizes.

RESULTS

We simulate electrogram arrays for 2D tissues with 3 different levels of heterogeneity in the conduction and stimulation pattern to model the inhomogeneous wave propagation observed during atrial fibrillation. Four measures are used to characterize the properties of the simulated electrogram arrays of different electrode sizes. The results show that increasing the electrode size increases the error in LAT estimation and decreases the length of conduction block lines. Moreover, visual inspection also shows that the activation maps generated by larger electrodes are more homogeneous with a lower number of observed wavelets. The increase in electrode size also increases the low voltage areas in the tissue while decreasing the slopes and the number of detected deflections. The effect is more pronounced for a tissue with a higher level of heterogeneity in the conduction pattern. Similar conclusions hold for the measurements performed on clinical data.

CONCLUSION

The electrode size affects the properties of recorded electrogram arrays which can respectively complicate our understanding of atrial fibrillation. This needs to be considered while performing any analysis on the electrograms or comparing the results of different electrogram arrays.

A new interpretation of nonpulmonary vein substrates of the left atrium in patients with atrial fibrillation

BACKGROUND

Substrate analysis of the left atrium in patients undergoing atrial fibrillation ablation has limitations when performed by means of simple bipolar acquisition.

OBJECTIVE

To evaluate the incidence of low-voltage zones (LVZs) through maps constructed by means of various catheters: multipolar (MC), omnipolar (OC), and circular catheters (CMCs) with the 3D electro-anatomical systems (3d-S) CARTO3 and EnSite Precision.

METHODS

To assess LVZs, we acquired maps by means of CMC and MC in the voltage range 0.05-0.5 mV in 70 consecutive patients in sinus rhythm. In the case of OC only, we made an intra-patient comparison of bipolar maps constructed by means of the along and across, and HD-Wave configurations of the EnSite 3d-S in the ranges of 0.05-0.5 and 0.5-1.0 mV. On the basis of this comparison, we chose the range that best identified LVZs as a set of different colors (SDC) compatible with patchy fibrosis (qualitative analysis). Subsequently, we detected the voltage values corresponding to purple and gray points, close to SDC, and the value inside corresponding to blue, green, and red colors, and we evaluated the color change in other voltage ranges. Finally, we performed a quantitative analysis of LVZs by applying the qualitative characteristics described above.

RESULTS

On the basis of our settings, for OC, the optimal range identifying LVZs was 0.3-0.6 mV. OC revealed smaller LVZs than MC (P < .05 or P < .001), except in the lateral wall. No significant differences were observed between CMCs.

CONCLUSIONS

In our experience, OC does not present the limits of bipolar HD maps, though further studies are needed in order to confirm that 0.3-0.6 mV is the optimal voltage range within which to identify LVZs.

Evaluation of left atrial remodeling by 2D-speckle-tracking echocardiography versus by high-density voltage mapping in patients with atrial fibrillation

BACKGROUND

Strain imaging during left atrial (LA) reservoir phase (LASr) is used as a surrogate for LA structural remodeling and fibrosis. Atrial fibrillation (AF) patients with >5% low-voltage zones (LVZs) obtained by 3D-electro-anatomical-mapping have higher recurrence rate post-ablation. We investigated the relationship between LA remodeling using two-dimensional-speckle-tracking echocardiography (2D-STE) and high-density voltage mapping in AF patients.

METHODS

A prospective study of 42 consecutive patients undergoing AF ablation. 2D-echo, 2D-STE, and high-density contact LA bipolar voltage maps were constructed before ablation. LVZs were determined with different bipolar amplitudes and their ratio per patient's LA area were investigated for correlation with LASr. We compared 2D-LASr results in patients with LVZs ≥ 5% (LVZs group) versus those with LVZ < 5% (non-LVZs group).

RESULTS

Compared with non-LVZs group (n = 15), LVZs group (n = 27) included significantly older patients, more women, more persistent AF, higher CHA₂ DS₂ -VASc score, higher E/A ratio and higher LA volume index (p < .05). LVZs group had lower %LASr values (12.4 ± 5.9% vs. 21.1 ± 6.3, respectively; p<.001). LVZs% in different amplitudes (<0.1 mV, <0.2 mV, and <0.5 mV) were negatively correlated with %LASr (r = -.63, r = -.68, and r = -.72, respectively; p< .001). Atrial strain thresholds for LVZs ≥ 5% in amplitudes <0.1 mV, <0.2 mV, and <0.5 mV were associated with %LASr 12.98, 16.16 and 19.55, respectively; p< .05). In a multivariate analysis, %LASr was the only independent indicator of LVZs (OR, 0.8; 95% CI, 0.6-0.9; p= .04).

CONCLUSIONS

LVZs ≥ 5% has a negative association with atrial %LASr. Thus, a simple 2D-STE measurement of %LASr can be used as a noninvasive method to evaluate significant LA remodeling and fibrosis in AF patients.

Atrial Fibrillation Structural Substrates: Aetiology, Identification and Implications

Atrial remodelling in AF underlines the electrical, structural and mechanical changes in the atria of patients with AF. Several risk factors for AF contribute to the development of the atrial substrate, with some evidence that atrial remodelling reversal is possible with targeted intervention. In this article, the authors review the electrophysiological changes that characterise the atrial substrate in patients with AF risk factors. They also discuss the pitfalls of mapping the atrial substrate and the implications for developing tailored ablation strategies to improve outcomes in patients with AF.

Dynamic Local Activation Time Mapping in Heavily Scarred Left Atrium and Persistent Atrial Fibrillation: A proof of concept case report

We report the case of a 68-year-old male, presenting with persistent atrial fibrillation (Pe AF) refractory to anti arrhythmic medications and cardioversion, on a background history of ischaemic heart disease. Pre and post standard pulmonary vein isolation (PVI), left atrial (LA) voltageanalyses wereperformed, followed by dynamic local activation time (DLAT) mapping in addition to focal activity identification.Thisdemonstrated a heavily scarred LA, and a number ofareas of focal activity. The patient remained in atrial fibrillation (AF) post rotor (focal activity) targeting,howevernotable changes in AF cycle length (CL)werenotedandslowed by an average of 25.3 milliseconds. Comparison between DLAT mappingpre and post PVI were anatomically similar but not identical. The anatomical distribution of heavy scar areas in the LA did not correspond to the DLAT areas of interest. The patient subsequentlyremained in normal sinus rhythm (SR) for 6 monthson a low dose Beta blockade in a short follow up period. DLAT mapping and its characteristics in heavily scarred LA are reported in this case.