Electroanatomical Mapping (CARTO) of ectopic atrial tachycardia: impact of bipolar and unipolar local electrogram annotation for localization the focal origin

Limitations of Unipolar Signals in Guiding Successful Outflow Tract Premature Ventricular Contraction Ablation

OBJECTIVES

The authors sought to compare bipolar electrograms (BiEGMs) vs unipolar electrograms (UniEGMs) in guiding successful ablation of right ventricular outflow tract (RVOT) vs intramural outflow tract (OT) premature ventricular contractions (PVCs). The authors hypothesized that: 1) earliest bipolar local activation time (LAT_Bi) would better guide mapping and ablation, vs UniEGM dV/dt (LAT_Uni) or QS morphology; and 2) LAT differences using bipolar vs unipolar EGMs (ΔLAT_Bi-Uni) would be greater for intramural OT than RVOT PVCs.

BACKGROUND

UniEGMs are commonly used to annotate earliest local activation of focal arrhythmias. However, their utility in guiding PVC ablation may be limited when the PVC source is less superficial.

METHODS

Consecutive patients undergoing successful PVC ablation 2017 to2020 requiring only RVOT or RVOT+left ventricular OT (RVOT+LVOT) ablation were retrospectively analyzed. BiEGMs and UniEGMs at successful ablation sites were compared.

RESULTS

Of 70 patients, 50 required RVOT-only, and 20 required RVOT+LVOT ablation for acute and long-term PVC suppression. Mean ΔLAT_Bi-Uni was lower for RVOT vs RVOT+LVOT groups (9.3 ± 6.4 ms vs 17.4 ± 9.9 ms; P < 0.01). QS UniEGM was seen in 78% of RVOT, compared with 53% of RVOT+LVOT patients (P < 0.016). RVOT+LVOT sites most frequently included the posteroseptal RVOT and adjacent LVOT (73%), and 43% lacked a QS unipolar EGM. ΔLAT_Bi-Uni ≥15 ms best distinguished sites in which RVOT-only vs RVOT+LVOT ablation achieved acute PVC suppression (area under the curve: 0.77).

CONCLUSIONS

Earliest BiEGM activation guides successful ablation of OT PVCs better than UniEGM-guided analysis, especially when an intramural PVC source is present.

Cardiac Conduction Velocity, Remodeling and Arrhythmogenesis

Cardiac electrophysiological disorders, in particular arrhythmias, are a key cause of morbidity and mortality throughout the world. There are two basic requirements for arrhythmogenesis: an underlying substrate and a trigger. Altered conduction velocity (CV) provides a key substrate for arrhythmogenesis, with slowed CV increasing the probability of re-entrant arrhythmias by reducing the length scale over which re-entry can occur. In this review, we examine methods to measure cardiac CV in vivo and ex vivo, discuss underlying determinants of CV, and address how pathological variations alter CV, potentially increasing arrhythmogenic risk. Finally, we will highlight future directions both for methodologies to measure CV and for possible treatments to restore normal CV.

Reinserting Physiology into Cardiac Mapping Using Omnipolar Electrograms

Omnipolar electrograms (EGMs) make use of biophysical electric fields that accompany activation along the surface of the myocardium. A grid-like electrode array provides bipolar signals in orthogonal directions to deliver catheter-orientation-independent assessments of cardiac electrophysiology. Studies with myocyte monolayers, isolated animal and human hearts, and anesthetized animals validated the tenets of omnipolar EGMs. The combination of information from omnipolar-based activation vectors and voltages may aid in localizing areas of scar, lesion gaps, wavefront disorganization, and fractionation or collision during arrhythmias. The goal of omnipolar EGMs is to better characterize myocardium through reintroducing electrogram direction related fundamentals of cardiac electrophysiology.

Focal atrial tachycardia ablation: Highly successful with conventional mapping

BACKGROUND/OBJECTIVE

Radiofrequency catheter ablation (RFCA) of focal atrial tachycardia (FAT) traditionally is guided by conventional endocardial mapping of earliest atrial activation; however, more recently electro-anatomical mapping is heralded as a more effective, albeit more expensive, tool to guide ablation. Herein we present the results of conventional mapping-guided RFCA. Apropos, we conducted a literature search of studies reporting > 10 FAT patients submitted to RFCA.

METHODS AND RESULTS

Conventional mapping-guided RFCA, performed in 63 FAT patients (aged 42.4 + 17.3 years; 14 with incessant tachycardia and 12 with tachycardiomyopathy (TCM)), was successful in 61 (96.8%) patients, applied for single foci in 59 (93.7%) and two foci in 4 patients, right (n = 46) or left sided (n = 17). The earliest atrial activation time at the ablation site was 41.3 ± 16.2 ms. Fluoroscopy time averaged 27.3 + 18.7 min, and procedure lasted 2.6 + 1.7 h. Complications occurred in two patients (sinus pauses in one needing a pacemaker and a large inguinal hematoma in one). Over 29.0 + 22.9 months, four patients (6.5%) had recurrences, of whom three were successfully re-ablated. All patients with TCM showed gradual improvement to normalization over 4-6 months. Literature search showed that RFCA success is equally high when guided with either conventional (88.5%) or electro-anatomical mapping (90%) with similar recurrences (9.6% vs. 9.5%).

CONCLUSION

Conventional mapping-guided RFCA of FAT had high success (96.8%) with low complication (3.2%) and recurrence rates (6.5%). TCM was fully reversible. These results are comparable to those achieved with the more expensive electro-anatomical mapping, which may be reserved for more complex cases or for those failing the conventional approach.

Predictive value of unipolar and bipolar electrograms in idiopathic outflow tract ventricular arrhythmia mapping and ablation

INTRODUCTION

Radiofrequency catheter ablation is an effective therapy for focal idiopathic outflow tract ventricular arrhythmia (OTVA). However, visual inspection of the unipolar electrogram (EGM) QS morphology is subjective with a poor specificity for predicting successful ablation sites. This study aims to evaluate the predictive value of unipolar and bipolar EGMs in OTVA mapping and ablation.

METHODS AND RESULTS

Twenty-two patients scheduled for idiopathic OTVA ablation were prospectively enrolled. During the procedure, unipolar and bipolar EGMs were recorded simultaneously and visually inspected by the operator to identify their values for predicting arrhythmogenic sites. Quantitative features of the unipolar EGM including the ratio of amplitude of the first positive peak versus the nadir (R-ratio), the maximum descending slope (MaxSlope), and the time interval between the initial deflection point to the MaxSlope (D-Max) were calculated for each target site in offline analysis. EGMs from 100 sites were collected in 20 patients and analyzed. The bipolar reverse polarity characteristic was not as practical for identifying successful ablation site as the unipolar QS characteristic. Successful ablation sites demonstrated smaller R-ratio and shorter D-Max than unsuccessful sites, but no significant difference in MaxSlope. A unipolar EGM-derived quantitative criterion provided significantly better specificity (0.70) than visual inspection (0.37) without compromising on the sensitivity (0.83 vs. 0.89).

CONCLUSION

The bipolar reverse polarity characteristic was not a practical method for identifying target in idiopathic OTVA ablation. The unipolar EGM-derived quantitative criteria have better predictive performance than visual inspection of the QS characteristic and are likely to reduce unnecessary ablation sites.

Automatic activation mapping and origin identification of idiopathic outflow tract ventricular arrhythmias

PURPOSE

Activation mapping is used to guide ablation of idiopathic outflow tract ventricular arrhythmias (OTVAs). Isochronal activation maps help to predict the site of origin (SOO): left vs right outflow tract (OT). We evaluate an algorithm for automatic activation mapping based on the onset of the bipolar electrogram (EGM) signal for predicting the SOO and the effective ablation site in OTVAs.

METHODS

Eighteen patients undergoing ablation due to idiopathic OTVAs were studied (12 with left ventricle OT origin). Right ventricle activation maps were obtained offline with an automatic algorithm and compared with manual annotation maps obtained during the intervention. Local activation time (LAT) accuracy was assessed, as well as the performance of the 10ms earliest activation site (EAS) isochronal area in predicting the SOO.

RESULTS

High correlation was observed between manual and automatic LATs (Spearman's: 0.86 and Lin's: 0.85, both p<0.01). The EAS isochronal area were closely located in both map modalities (5.55 ± 3.56mm) and at a similar distance from the effective ablation site (0.15±2.08mm difference, p=0.859). The 10ms isochronal area longitudinal/perpendicular diameter ratio measured from automatic maps showed slightly superior SOO identification (67% sensitivity, 100% specificity) compared with manual maps (67% sensitivity, 83% specificity).

CONCLUSIONS

Automatic activation mapping based on the bipolar EGM onset allows fast, accurate and observer-independent identification of the SOO and characterization of the spreading of the activation wavefront in OTVAs.

Intracardiac electrogram envelope detection during atrial fibrillation using fast orthogonal search

The performance of any intracardiac electrogram processing method is limited by the accuracy of its activation detection approach. The most common activation detection approaches in the literature aim to find the highest peak in the activation envelope disregarding the start and end points. However, the duration of the activation can be used to extract useful information such as wave collisions. In this work, we propose a novel orthogonal based approach for fast and accurate estimation of the start and end of the activations (activation envelope) in intracardiac recordings during atrial fibrillation. Wavelet decomposition of the signals was used to create a pool of basis functions for the proposed modeling method. The database included 24 recordings of approximate length of 6s obtained from atrial endocardium of 5 patients who underwent catheter ablation therapy. The start and end of activations in each electrogram was manually annotated by an expert electrophysiologist and the annotations were used as a gold standard to calculate the performance of our envelope detection method. The results show promising performance and excellent robustness to training data for our proposed method with respect to envelope estimation error.

Reversed polarity of bipolar electrograms for predicting a successful ablation site in focal idiopathic right ventricular outflow tract arrhythmias

BACKGROUND

Radiofrequency catheter ablation (RFCA) for idiopathic right ventricular outflow tract (RVOT) arrhythmias is typically guided by local activation time (LAT) mapping and unipolar electrogram morphology (QS configuration). However, LAT mapping is limited by the large variation among patients, and the area demonstrating a QS configuration of the unipolar electrogram may be larger than the focal source. Reversed polarity has been proposed as a criterion for guiding RFCA.

OBJECTIVE

The purpose of this study was to investigate the value of reversed polarity of adjacent bipolar electrograms for predicting a successful ablation site in idiopathic RVOT arrhythmias.

METHODS

Twenty-five consecutive patients (12 men [48%], age 43 ± 15 years) undergoing RFCA for RVOT arrhythmia were studied. Electrograms of ablation sites and of points within a 15-mm radius to the successful site were evaluated for LAT, unipolar electrogram morphology, and the presence of reversed polarity of adjacent bipolar electrograms. Electrogram characteristics of successful ablation sites were compared to those of nonsuccessful ablation sites. The spatial distribution of each electrogram characteristic was studied.

RESULTS

Successful ablation sites more often demonstrated reversed polarity and had an earlier LAT than nonsuccessful sites. A wide spatial distribution was observed for unipolar electrograms with a QS configuration around the successful ablation site. Mapping based on LAT and reversed polarity had a higher predictive value for a successful ablation site than mapping based on LAT and QS configuration.

CONCLUSION

The presence of reversed polarity has a high predictive value for successful ablation sites in focal idiopathic RVOT arrhythmias and is likely to reduce the number of RFCA applications.

Non-invasive detection of conduction pathways to left atrium using magnetocardiography: validation by intra-cardiac electroanatomic mapping

AIMS

Alteration in conduction from right to left atrium (LA) is linked to susceptibility to atrial fibrillation (AF). We examined whether different inter-atrial conduction pathways can be identified non-invasively by magnetocardiographic mapping (MCG).

METHODS AND RESULTS

In 27 patients undergoing catheter ablation of paroxysmal AF, LA activation sequence was determined during sinus rhythm using invasive electroanatomic mapping. Before this, 99-channel magnetocardiography was recorded over anterior chest. The orientation of the magnetic fields during the early (40-70 ms from P onset) and later part (last 50%) of LA depolarization was determined using pseudocurrent conversion. Breakthrough of electrical activation to LA occurred through Bachmann bundle (BB) in 14, margin of fossa ovalis (FO) in 3, coronary sinus ostial region (CS) in 2, and their combinations in 10 cases by invasive reference in total of 29 different P-waves. Based on the combination of pseudocurrent angles over early and late parts of LA activation, the MCG maps were divided to three types. These types correctly identified the LA breakthrough sites to BB, CS, FO, or their combinations in 27 of 29 (93%) cases.

CONCLUSION

Magnetocardiographic mapping seems capable of distinguishing inter-atrial conduction pathways. Recognizing the inter-atrial conduction pattern may assist in understanding the pathogenesis of AF and identifying the subgroups for patient-tailored therapy.

Fragmented, Long-Duration, Low-Amplitude Electrograms Characterize the Origin of Focal Atrial Tachycardia

BACKGROUND

Focal atrial tachycardias (FAT) originate from areas with poor cell-to-cell coupling. Due to cellular uncoupling extracellular potentials become fractionated. The degree of fragmentation may be used to identify the site of origin of FAT prior to catheter ablation. We studied electrical fragmentation in relation to the distance to the site of earliest activity during FAT.

METHODS

Three-dimensional (3-D) electroanatomical activation/voltage maps obtained from patients (n = 15: 6 male, age 40 +/- 14 (19-72) years) referred for catheter ablation of FAT were analyzed. Bipolar atrial potentials (BP) were categorized according to the number of deflections. The peak-to-peak amplitude and the time interval between the first and last deflection (fractionation duration) of each BP were measured.

RESULTS

Eighteen different atrial tachycardias (AT) (CL 346 +/- 109 [190-550]) msec were analyzed. The incidence of single potentials ranged from 30 to 81 (59 +/- 16)%. The occurrence of double and fractionated potentials < or = 2 cm of the site of earliest activity ("focal area") was higher compared to the remainder of the atria (67 +/- 22% vs 34 +/- 14%, P < 0.001). Focal area potentials were characterized by a longer duration (49 +/- 22 msec vs 34 +/- 17 msec, P < 0.001) and a lower peak-to-peak amplitude (0.51 +/- 0.43 [0.12-1.7] mV vs 0.94 +/- 0.69 [0.22-2.58] mV, P = 0.03). Fractionation was not associated with FAT cycle length (r =-0.26, P = 0.29) or left atrial diameter (r = 0.47, P = 0.30).

CONCLUSION

Significant differences in fractionation, fractionation duration, and peak-to-peak-amplitude of atrial potentials between the focal area and the remainder of the atria exist. Fractionation and voltage mapping can be used, besides activation mapping, to identify the site of origin of FAT during catheter ablation.

[Right atrial ablation of ectopic atrial tachycardia using a 20-pole mapping catheter]

INTRODUCTION

Ectopic atrial tachycardia (EAT) are frequently unresponsive to pharmacological antiarrhythmic therapy. Radiofrequency ablation seems to be a safe approach to treat those arrhythmias. In the present study we report our results of radiofrequency ablation of EAT with a new mapping system (Stablemapr, Medtronic).

METHODS

Thirty consecutive patients with right atrial tachycardia were included in the study. In 15 patients (G1) the 20-polar Stablemapr was used for localization of the arrhythmia foci. Data were compared with a control group (G2, n=15), in which mapping was performed conventionally. The demographic characteristics and the distribution of the different cardiac diseases were comparable in both groups. In group 1 the identification of the EAT was facilitated by the placement of the 20-pole mapping catheter in the right atrium. In group 2 point by point measurements were performed to find the earliest local atrial activation compared to a reference electrode in the high right atrium (activation mapping), or foci were identified by analysis of the P-wave morphology during stimulation (pacemapping).

RESULTS

It was possible to successfully ablate all atrial tachycardias. The distribution of the foci was similar in both groups (G1/G2): near to the superior (3/5) and inferior (1/0) caval vene ostium, on the free wall (3/3), at the coronary sinus ostium (3/3) and on the interatrial septum (5/4). The mean procedure (G1: 88+/-33 vs G2: 151+/-61 min; p= or <0.05) and fluoroscopic times (G1: 19+/-9 vs G2: 38+/-28 min; p= or <0.05) were significantly shorter in group 1. Moreover, the mean number of radiofrequency applications was reduced significantly by using the new mapping system (G1: 10+/-10 vs G2: 16+/-13; p= or <0.05).

CONCLUSION

Radiofrequency ablation of EAT with right atrial focus can be performed safely and successfully using a 20-pole mapping catheter. The greatest advantages compared to conventional mapping and ablation strategies lies in the shortened investigation and fluoroscopic time.

Focal Atrial Tachycardia II: Management

Over the last decade there have been significant changes in the treatment of focal atrial tachycardia (AT). This review concentrates on the different approaches to the treatment of focal AT. Initial therapies included antiarrhythmic medications and surgery. However, with the advent of radiofrequency ablation, and the poor efficacy of pharmacological therapy, there has been a shift toward a primary ablative approach. Several different mapping techniques have been proposed. The different techniques, including P-wave morphology and advanced three-dimensional mapping, are discussed in this review.

Ablation of focal atrial arrhythmia in patients with congenital heart defects after surgery: role of circumscribed areas with heterogeneous conduction

BACKGROUND

In patients late after surgical repair of congenital heart disease (CHD), areas with abnormal electrophysiologic properties may serve as slow conducting pathways within a macroreentrant circuit or may be the source of focal atrial tachycardia.

OBJECTIVES

The purpose of this study was to evaluate the role of abnormal areas during focal atrial tachycardia prior to ablation.

METHODS

Electroanatomic activation mapping of 62 atrial tachycardias was performed in 43 consecutive patients (37 +/- 12 years) after surgical repair of CHD. The mechanism of atrial tachycardia was scar related intra-atrial reentry (n = 27), cavotricuspid-related atrial flutter (n = 21), atrial fibrillation (n = 2), or focal atrial tachycardia (n = 10). During intra-atrial reentry, channels of slow conduction could be identified in all patients. Subsequent ablation was directed toward connecting two nonconductive borders. The site of origin during focal atrial tachycardia showed fractionated potentials and/or continuous electrical activity.

RESULTS

Ablation directed at isolating the source area resulted in termination of focal atrial tachycardia in all cases. In two patients, ablation of an area showing continuous electrical activity giving rise to fibrillatory conduction resulted in termination of atrial fibrillation. Ablation of intra-atrial reentry was successful in 70%. Atrial flutter and focal atrial tachycardia were successfully ablated in all patients. No complications were observed.

CONCLUSION

In patients with surgically corrected CHD, atrial tachycardia most often is caused by a macroreentrant mechanism but in some is the result of a focal mechanism. Areas of abnormal conduction may serve not only as a zone of slow conduction within a macroreentrant circuit but also as the site of origin of a focal atrial arrhythmia. Catheter ablation directed at "source isolation" is effective in eliminating focal atrial tachycardia in patients with CHD.

Novel use of postpacing interval mapping to guide radiofrequency ablation of focal atrial tachycardia with long intra-atrial conduction time

If the intra-atrial conduction time of a focal tachycardia is prolonged and exceeds the tachycardia cycle length, isochronal electroanatomical maps may be confusing by not showing the classical centrifugal pattern of focal activation. In addressing the hypothesis that by mapping post pacing intervals (PPI), the shortest PPI (ideally identical to tachycardia cycle length) would clearly display the site of origin of a focal tachycardia; this technique was used successfully to identify the origin and ablate the atrial tachycardia of a patient with previously corrected Tetralogy of Fallot.

Influence of High-Pass Filtering on Noncontact Mapping and Ablation of Atrial Tachycardias

The aim of the study was to define the impact of different high-pass filter settings (HPF) on the accuracy of mapping of ectopic atrial tachycardias (EAT) using a noncontact mapping (NCM) system. In 20 patients with 22 EAT a noncontact probe was deployed in the right (n = 19) or in the left atrium (n = 3). The device enables interpolation and analysis of unipolar electrograms. It provides information on focus localization and signal morphology. These parameters were compared in different HPF of 0.5 Hz, 2 Hz, 8 Hz, and 16 Hz. The NCM signal morphology was preserved at all HPF. An initial negative deflection recorded by NCM system showed a positive predictive value of 93% regarding the ablation success. The deviation (spatial disparity) between visualized focus origin and successful ablation site was 6.9 +/- 5.4 mm. Between two consecutive filter settings, the focus shift was more pronounced between 0.5 and 2 Hz (5.4 +/- 4.5 mm) compared to a setting between 8 and 16 Hz (2.9 +/- 2.9 mm; P < 0.05). Successful ablation was achieved in 15/18 right atrial tachycardias (83%) and in 2/3 left atrial arrhythmias. Different HPF influence NCM spatial analysis of EAT. However, a small variability in foci localization does not impact final ablation results.

Voltage and Activation Mapping

BACKGROUND

Endocardial mapping is mandatory before radiofrequency catheter ablation (RFCA). Mapping can be performed with either unipolar or bipolar recordings. Impact of the recording technique used was studied in patients with and without structural heart disease using the 3D electroanatomic CARTO mapping system.

METHODS AND RESULTS

Patients (n=44; 16 males; age 43+/-16 years) referred for RFCA of atrial flutter (AFL, n=18), focal atrial tachycardia (FAT, n=4), AV nodal reentrant tachycardia (AVNRT, n=5), or scar-related atrial reentrant tachycardia (IART, n=17) were studied. Voltage and activation maps were constructed. Unipolar and bipolar voltage distribution in the different groups was studied to establish a cutoff voltage value to facilitate delineation of scar tissue. Electrograms were recorded during tachycardia (FAT: n=246, cycle length [CL]=449+/-35 ms; AVNRT: n=182, CL=359+/-47 ms; AFL: n=1164, CL=255+/-56 ms; IART: n=2431, CL=280+/-74 ms). Unipolar voltages were greater than bipolar voltages (P<0.001). Unipolar voltages < or =1.0 mV were equally distributed in both AFL and IART patients. Bipolar voltages < or =0.1 mV were only found in patients with IART, and subsequently 0.1 mV was used as the cutoff value to delineate scar tissue. No unipolar cutoff value could be established. Timing of unipolar and bipolar local activation was correlated in all patient groups.

CONCLUSIONS

The recording technique used has considerable impact on reconstruction of reentrant pathways and on the outcome of RFCA. In general, unipolar and bipolar recordings provide complementary information; however, only bipolar recordings allow voltage-based scar tissue delineation in patients with congenital heart disease.