Wavefront direction and cycle length affect left atrial electrogram amplitude

Influence of Heart Rate and Change in Wavefront Direction through Pacing on Conduction Velocity and Voltage Amplitude in a Porcine Model: A High-Density Mapping Study

BACKGROUND

Understanding the dynamics of conduction velocity (CV) and voltage amplitude (VA) is crucial in cardiac electrophysiology, particularly for substrate-based catheter ablations targeting slow conduction zones and low voltage areas. This study utilizes ultra-high-density mapping to investigate the impact of heart rate and pacing location on changes in the wavefront direction, CV, and VA of healthy pig hearts.

METHODS

We conducted in vivo electrophysiological studies on four healthy juvenile pigs, involving various pacing locations and heart rates. High-resolution electroanatomic mapping was performed during intrinsic normal sinus rhythm (NSR) and electrical pacing. The study encompassed detailed analyses at three levels: entire heart cavities, subregions, and localized 5-mm-diameter circular areas. Linear mixed-effects models were used to analyze the influence of heart rate and pacing location on CV and VA in different regions.

RESULTS

An increase in heart rate correlated with an increase in conduction velocity and a decrease in voltage amplitude. Pacing influenced conduction velocity and voltage amplitude. Pacing also influenced conduction velocity and voltage amplitude, with varying effects observed based on the pacing location within different heart cavities. Pacing from the right atrium (RA) decreased CV in all heart cavities. The overall CV and VA changes in the whole heart cavities were not uniformly reflected in all subregions and subregional CV and VA changes were not always reflected in the overall analysis. Overall, there was a notable variability in absolute CV and VA changes attributed to pacing.

CONCLUSIONS

Heart rate and pacing location influence CV and VA within healthy juvenile pig hearts. Subregion analysis suggests that specific regions of the heart cavities are more susceptible to pacing. High-resolution mapping aids in detecting regional changes, emphasizing the substantial physiological variations in CV and VA.

Initial experience of the High-Density Grid catheter in patients undergoing catheter ablation for atrial fibrillation

PURPOSE

A significant proportion of patients undergoing catheter ablation for atrial fibrillation (AF) experience arrhythmia recurrence. This is mostly due to pulmonary vein reconnection (PVR). Whether mapping using High-Density Wave (HDW) technology is superior to standard bipolar (SB) configuration at detecting PVR is unknown. We aimed to evaluate the efficacy of HDW technology compared to SB mapping in identifying PVR.

METHODS

High-Density (HD) multipolar Grid catheters were used to create left atrial geometries and voltage maps in 36 patients undergoing catheter ablation for AF (either due to recurrence of an atrial arrhythmia from previous AF ablation or de novo AF ablation). Nineteen SB maps were also created and compared. Ablation was performed until pulmonary vein isolation was achieved.

RESULTS

Median time of mapping with HDW was 22.3 [IQR: 8.2] min. The number of points collected with HDW (13299.6±1362.8 vs 6952.8±841.9, p<0.001) and used (2337.3±158.0 vs 1727.5±163.8, p<0.001) was significantly higher compared to SB. Moreover, HDW was able to identify more sleeves (16 for right and 8 for left veins), where these were confirmed electrically silent by SB, with significantly increased PVR sleeve size as identified by HDW (p<0.001 for both right and left veins). Importantly, with the use of HDW, the ablation strategy changed in 23 patients (64% of targeted veins) with a significantly increased number of lesions required as compared to SB for right (p=0.005) and left veins (p=0.003).

CONCLUSION

HDW technology is superior to SB in detecting pulmonary vein reconnections. This could potentially result into a significant change in ablation strategy and possibly to increased success rate following pulmonary vein isolation.

Substrate mapping of the left atrium in persistent atrial fibrillation: spatial correlation of localized complex conduction patterns in global charge-density maps to low-voltage areas in 3D contact bipolar voltage maps

Purpose

This study aimed to investigate the spatial relationship between low-voltage areas (LVAs) in bipolar voltage mapping (BVM) and localized complex conduction (LCC)-cores in a global, non-contact, charge-density-based imaging, and mapping system (AcM).

Methods

Patients with history of index PVI for PsAF and scheduled for a repeat ablation procedure for recurrence of the same arrhythmia were enrolled between August 2018 and February 2020. All patients underwent both substrate mappings of the left atrium (LA) with the CARTO 3D map-ping system and with AcM.

Results

Ten patients where included in our analysis. All presented with persistency of PVI in all veins at the moment of repeat procedure. There was no linear relationship in BVM maps between SR and CSd (correlation coefficient 0.31 ± 0.15), SR and CSp (0.36 ± 0.12) and CSd and CSp (0.43 ± 0.10). The % overlap of localized irregular activation (LIA), localized rotational activation (LRA) and Focal (F) regions with LVA was lower at 0.2 mV compared to 0.5 mV (4.97 ± 7.39%, 3.27 ± 5.25%, 1.09 ± 1.92% and 12.59 ± 11.81%, 7.8 ± 9.20%, 4.62 ± 5.27%). Sensitivity and specificity are not significantly different when comparing composite maps with different LVA cut-offs. AURC was 0.46, 0.48, and 0.39 for LIA, LRA, and Focal, respectively.

Conclusion

Due to wave front direction dependency, LVAs mapped with BVM in sinus rhythm and during coronary sinus pacing only partially overlap in patients with PsAF. LCC-cores mapped during PsAF partially co-localize with LVAs.

Electrogram recording and analyzing techniques to optimize selection of target sites for ablation of cardiac arrhythmias

The extracellular electrogram is caused by transmembrane currents that flow into extracellular space during propagation of the electrical impulse. Electrograms are usually recorded in unipolar or bipolar mode that have different characteristics, but provide complementary information. Both recording modes have specific advantages, but also suffer from disadvantages. Techniques to circumvent some of the weaknesses are reviewed. The origin of remote and fractionated deflections and their relation with electrode characteristics are discussed. Epicardial and endocardial sites of origin and breakthrough sites as well as the effect of fatty tissue on extracellular electrograms are presented. Induction of tachycardia to assess the arrhythmogenic area is not always possible because of hemodynamic instability of the patient. Techniques to assess sites with high reentry vulnerability without induction of arrhythmias are outlined such as activation‐repolarization mapping and decremental stimulation. Pitfalls of substrate mapping and techniques to avoid them as omnipolar mapping and characterization of complex electrograms by entropy are presented. Technical aspects that influence electrogram morphology as electrode size, filtering, contact force, and catheter position are delineated. Data from the various publications suggest that a combination of unipolar and bipolar electrogram analysis techniques is helpful to optimize determination of target sites for ablation.

Voltage during atrial fibrillation is superior to voltage during sinus rhythm in localizing areas of delayed enhancement on magnetic resonance imaging: An assessment of the posterior left atrium in patients with persistent atrial fibrillation

BACKGROUND

Bipolar electrogram voltage during sinus rhythm (VSR) has been used as a surrogate for atrial fibrosis in guiding catheter ablation of persistent atrial fibrillation (AF), but the fixed rate and wavefront characteristics present during sinus rhythm may not accurately reflect underlying functional vulnerabilities responsible for AF maintenance.

OBJECTIVE

The purpose of this study was determine whether, given adequate temporal sampling, the spatial distribution of mean AF voltage (VmAF) better correlates with delayed-enhancement magnetic resonance imaging (MRI-DE)-detected atrial fibrosis than VSR.

METHODS

AF was mapped (8 seconds) during index ablation for persistent AF (20 patients) using a 20-pole catheter (660 ± 28 points/map). After cardioversion, VSR was mapped (557 ± 326 points/map). Electroanatomic and MRI-DE maps were co-registered in 14 patients.

RESULTS

The time course of VmAF was assessed from 1-40 AF cycles (∼8 seconds) at 1113 locations. VmAF stabilized with sampling >4 seconds (mean voltage error 0.05 mV). Paired point analysis of VmAF from segments acquired 30 seconds apart (3667 sites; 15 patients) showed strong correlation (r = 0.95; P <.001). Delayed enhancement (DE) was assessed across the posterior left atrial (LA) wall, occupying 33% ± 13%. VmAF distributions were (median [IQR]) 0.21 [0.14-0.35] mV in DE vs 0.52 [0.34-0.77] mV in non-DE regions. VSR distributions were 1.34 [0.65-2.48] mV in DE vs 2.37 [1.27-3.97] mV in non-DE. VmAF threshold of 0.35 mV yielded sensitivity of 75% and specificity of 79% in detecting MRI-DE compared with 63% and 67%, respectively, for VSR (1.8-mV threshold). CONCLUSION: The correlation between low-voltage and posterior LA MRI-DE is significantly improved when acquired during AF vs sinus rhythm. With adequate sampling, mean AF voltage is a reproducible marker reflecting the functional response to the underlying persistent AF substrate.

Left atrial voltage mapping: defining and targeting the atrial fibrillation substrate

Low atrial endocardial bipolar voltage, measured during catheter ablation for atrial fibrillation (AF), is a commonly used surrogate marker for the presence of atrial fibrosis. Low voltage shows many useful associations with clinical outcomes, comorbidities and has links to trigger sites for AF. Several contemporary trials have shown promise in targeting low voltage areas as the substrate for AF ablation; however, the results have been mixed. In order to understand these results, a thorough understanding of voltage mapping techniques, the relationship between low voltage and the pathophysiology of AF, as well as the inherent limitations in voltage measurement are needed. Two key questions must be answered in order to optimally apply voltage mapping as the road map for ablation. First, are the inherent limitations of voltage mapping small enough as to be ignored when targeting specific tissue based on voltage? Second, can conventional criteria, using a binary threshold for voltage amplitude, truly define the extent of the atrial fibrotic substrate? Here, we review the latest clinical evidence with regard to voltage-based ablation procedures before analysing the utility and limitations of voltage mapping. Finally, we discuss omnipole mapping and dynamic voltage attenuation as two possible approaches to resolving these issues.