Ablation of Reentry-Vulnerable Zones Determined by Left Ventricular Activation From Multiple Directions: A Novel Approach for Ventricular Tachycardia Ablation: A Multicenter Study (PHYSIO-VT)

Impact of Multidirectional Pacing on Activation and Repolarization Parameters to Localize Ischemic Ventricular Tachycardia Circuits

BACKGROUND

In ventricular tachycardia (VT), optimal substrate mapping strategies identifying arrhythmogenic sites are not established.

OBJECTIVES

This study sought to evaluate multidirectional pacing on the distribution of specific conduction and repolarization metrics to localize re-entrant VT sites in a porcine infarct model.

METHODS

Substrate maps were created in 13 pigs with chronic myocardial infarction using the Advisor HD Grid (Abbott) during right ventricular (RV), left ventricular, biventricular pacing (BIV), and sinus rhythm (SR). Critical VT sites of early-, mid-, and late-diastolic signals were delineated. Vulnerable sites to re-entry were defined as sites of latest activation timing within and post-QRS complex, largest activation and activation-recovery interval gradients. Distances between the 20 most vulnerable sites and diastolic VT points were measured, and identification of VT points was assessed using the area under the receiver-operating characteristic curve.

RESULTS

A total of 34 VTs were mapped, and 48 sinus and pacing maps were obtained (10 BIV, 13 left ventricular, 13 RV, 12 SR). Late potential mapping in SR was taken as the established clinical standard for comparison. Latest activation time with BIV pacing provided the closest localization for VT isthmus (median 5.5 mm; IQR: 7.15 mm; P < 0.005). The gradient of activation-recovery interval using RV pacing had closest localization for VT exit and entrance (median 10.6 mm; IQR: 5.0 mm; P < 0.005 and 9.4 mm; IQR: 8.0 mm; P < 0.05). Global sensitivity and specificity analysis showed that gradient of activation-recovery interval in SR achieved the highest area under the receiver-operating characteristic curve, with similar results from the gradient of activation timing.

CONCLUSIONS

Multidirectional pacing in combination with conduction and repolarization parameters enables better localization of VT diastolic critical sites vs SR late potentials.

Optimal cardiac rhythm during substrate mapping in scar-related ventricular tachycardia: Significance of wavefront direction on identifying critical sites

BACKGROUND

A rotational activation pattern (RAP) around the localized line of a conduction block often correlates with sites specific to the critical zones of ventricular tachycardia (VT). The wavefront direction during substrate mapping affects manifestation of the RAP and line of block.

OBJECTIVE

The purpose of this study was to investigate the most optimal cardiac rhythm for identifying RAP and line of block in substrate mapping.

METHODS

We retrospectively evaluated 71 maps (median 3205 points/map) in 46 patients (65 ± 15 years; 33% with ischemic cardiomyopathy) who underwent high-density substrate mapping and ablation of scar-related VT. Appearance of a RAP during sinus, right ventricular (RV)-paced, left ventricular (LV)-paced, and biventricular-paced rhythms was investigated.

RESULTS

RAP was identified in 24 of 71 maps (34%) in the region where wavefronts from a single direction reached but not in the region where wavefronts from multiple directions centripetally collided. The probability of identifying the RAP depended on scar location; that is, anteroseptal and inferoseptal, inferior and apical, and basal lateral RAPs were likely to be identified during sinus/atrial, RV-paced, and LV-paced rhythms, respectively. In 13 patients, the RAP was not evident in the baseline map but became apparent during remapping in the other rhythm, in which the wavefront reached the site earlier within the entire activation time.

CONCLUSION

The optimal rhythm for substrate mapping depends on the spatial distribution of the area of interest. A paced rhythm with pacing sites near the scar may facilitate the identification of critical VT zones.

Substrate Mapping for Ventricular Tachycardia Ablation Through High-Density Whole-Chamber Double Extra Stimuli: The S3 Protocol

BACKGROUND

A partial delineation of targets for ablation of ventricular tachycardia (VT) during a stable rhythm is likely responsible for a suboptimal success rate. The abnormal low-voltage near-field functional components may be hidden within the high-amplitude far-field signal.

OBJECTIVES

The aim of this study was to evaluate the benefit and feasibility of functional substrate mapping using a full-ventricle S3 protocol and to assess its colocalization with arrhythmogenic conducting channels (CCs) on late gadolinium enhancement cardiac magnetic resonance.

METHODS

An S3 mapping protocol with a drive train of S1 followed by S2 (effective refractory period + 30 ms) and S3 (effective refractory period + 50 ms) from the right ventricular apex was performed in 40 consecutive patients undergoing scar-related VT ablation. Deceleration zones (DZs) and areas of late potentials (LPs) were identified for all maps. A preprocedural noninvasive substrate assessment was done using late gadolinium enhancement cardiac magnetic resonance and postprocessing with automated CC identification.

RESULTS

The S3 protocol was completed in 34 of the 40 procedures (85.0%). The S3 protocol enhanced the identification of VT isthmus on the basis of DZ (89% vs 62%; P < 0.01) and LP (93% vs 78%; P = 0.04) assessment. The percentage of CCs unmasked by DZs and LPs using S3 maps was significantly higher than the ones using S2 and S1 maps (78%, 65%, and 48% [P < 0.001] and 88%, 81%, and 68% [P < 0.01], respectively). The functional substrate identified during S3 activation mapping was significantly more extensive than the one identified using S2 and S1, including a greater number of DZs (2.94, 2.47, and 1.82, respectively; P < 0.001) and a wider area of LPs (44.1, 38.2, and 29.4 cm2, respectively; P < 0.001). After VT ablation, 77.9% of patients have been VT free during a median follow-up period of 13.6 months.

CONCLUSIONS

The S3 protocol was feasible in 85% of patients, allows a better identification of targets for ablation, and might improve VT ablation results.

Targeting Wavefront Discontinuity Lines for Scar-Related Ventricular Tachycardia Ablation: A Novel Functional Substrate Ablation Approach

BACKGROUND

The boundaries of critical isthmuses for re-entrant ventricular tachycardia (VT) are formed by wavefront discontinuities (fixed lines of block, slow propagation, and rotational propagation) seen during baseline rhythm. It is unknown whether wavefront discontinuities can be automatically identified and targeted for ablation using electroanatomic mapping systems.

OBJECTIVES

The purpose of this study was to assess the electrophysiologic characteristics of automatically projected wavefront discontinuity lines (WADLs) and outcomes of an ablation strategy targeting WADLs in a mixed cohort of VT patients.

METHODS

Late activation substrate maps were analyzed from 1 or more baseline rhythm wavefronts. WADLs were identified using the Carto Extended Early Meets Late module. Number, total length, and distance to critical VT sites were measured. VT recurrence and VT-free survival were followed.

RESULTS

In total, 49 patients underwent 52 ablations with 71 unique substrate maps analyzed (18.8% epicardial; 62.0% right ventricular paced, 28.2% sinus rhythm, 9.9% left ventricular paced). A total of 28 VT critical sites were identified in 24 patients. WADLs were present in 49 of 71 (69.0%) maps. WADLs were present regardless of cardiomyopathy etiology, mapping wavefront, or surface. At a WADL threshold of 30%, 73.9% of critical VT sites were in close proximity (≤15 mm) to a WADL. VT-free survival was 62% at 1 year, with a competing risk model estimating a 1-year risk of VT recurrence of 23%.

CONCLUSIONS

WADLs can be automatically projected in a majority of patients in a mixed cohort of cardiomyopathy etiology, mapped wavefronts, and myocardial surfaces mapped. Targeting WADLs results in low rate of VT recurrence at 1 year.

RIPPLE-VT study: Multicenter prospective evaluation of ventricular tachycardia substrate ablation by targeting scar channels to eliminate latest scar potentials without direct ablation

BACKGROUND

Recurrent ventricular tachycardia (VT) can be treated by substrate modification of the myocardial scar by catheter ablation during sinus rhythm without VT induction. Better defining this arrhythmic substrate could help improve outcome and reduce ablation burden.

OBJECTIVE

The study aimed to limit ablation within postinfarction scar to conduction channels within the scar to reduce VT recurrence.

METHODS

Patients undergoing catheter ablation for recurrent implantable cardioverter-defibrillator therapy for postinfarction VT were recruited at 5 centers. Left ventricular maps were collected on CARTO using a Pentaray catheter. Ripple mapping was used to categorize infarct scar potentials (SPs) by timing. Earliest SPs were ablated sequentially until there was loss of the terminal SPs without their direct ablation. The primary outcome measure was sustained VT episodes as documented by device interrogations at 1 year, which was compared with VT episodes in the year before ablation.

RESULTS

The study recruited 50 patients (mean left ventricular ejection fraction, 33% ± 9%), and 37 patients (74%) met the channel ablation end point with successful loss of latest SPs without direct ablation. There were 16 recurrences during 1-year follow-up. There was a 90% reduction in VT burden from 30.2 ± 53.9 to 3.1 ± 7.5 (P < .01) per patient, with a concomitant 88% reduction in appropriate shocks from 2.1 ± 2.7 to 0.2 ± 0.9 (P < .01). There were 8 deaths during follow-up. Those who met the channel ablation end point had no significant difference in mortality, recurrence, or VT burden but had a significantly lower ablation burden of 25.7 ± 4.2 minutes vs 39.9 ± 6.1 minutes (P = .001).

CONCLUSION

Scar channel ablation is feasible by ripple mapping and can be an alternative to more extensive substrate modification techniques.

An annotation-independent algorithm based on electrogram characteristics to guide the identification of ventricular tachycardia isthmuses in patients with structural heart disease

BACKGROUND

Criteria such as electrograms voltage or late potentials have been largely utilized in the past to help identify areas of substrate maps that are within the ventricular tachycardia (VT) isthmus; yet their specificity and positive predictive value are quite low. The Lumipoint fractionation tool of the Rhythmia system illuminates regions with fractionated electrograms irrespective of their timing and annotation. We aimed to ascertain whether the use of this tool can rapidly identify areas within VT isthmuses from substrate maps.

METHODS

Thirty patients with structural cardiomyopathy in whom a complete right ventricular-paced substrate map and a full reconstruction of the diastolic isthmus during VT could be obtained were enrolled. The VT isthmus border was projected on each substrate map to verify whether the areas illuminated by Lumipoint fell within those borders. The behavior of the electrograms detected at the illuminated areas of the substrate maps was studied during a right ventricular drive train and extra stimulus protocol: if the near field potentials showed a delayed conduction after a single extra stimulus, defined as a minimum of 10 ms increase of the time interval between the far field and the near field activation measured during the drive train, the electrogram was said to have a "decremental" behavior.

RESULTS

The logistic analysis showed that areas with fractionated electrograms illuminated by the Lumipoint software and showing the greatest decremental behavior fell within the VT isthmus borders (OR = 1.66, CI: 1.41-1.75, p<0.001; OR=1.57 CI: 1.32-1.72, p<0.001, respectively) with a sensitivity, specificity, and positive predictive value of 87%, 96%, and 97%, respectively.

CONCLUSIONS

Fractionated electrograms illuminated by the automated Lumipoint software on right ventricular-paced substrate maps showing the greatest decremental behavior fall within the VT isthmus borders with a probability of 0.97, irrespective of their timing, annotation, or voltage, without any need for subjective assessment of their involvement in slow conduction areas.

Ventricular Tachycardia Ablation Endpoints: Moving Beyond Noninducibility

In patients with structural heart disease and ventricular tachycardia (VT) undergoing catheter ablation, the response to programmed electrical stimulation (PES) at the end of the procedure has been traditionally used to evaluate the acute success and predict long-term outcomes. Although noninducibility at PES has been extensively investigated and validated in clinical trials and large multicenter registries, its performance in predicting long-term freedom from VT is suboptimal. In addition, PES has inherent limitations related to the influence of background antiarrhythmic drug therapy, periprocedural use of anesthesia, and the heterogeneity in PES protocols. The increased utilization of substrate-based ablation approaches that focus on ablation of abnormal electrograms identified with mapping in sinus or paced rhythm has been paralleled by a need for additional procedural endpoints beyond VT noninducibility at PES. This article critically appraises the relative merits and limitations of different procedural endpoints according to different ablation techniques for catheter ablation of scar-related VT.

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.

Non-invasive detection of slow conduction with cardiac magnetic resonance imaging for ventricular tachycardia ablation

AIMS

Non-invasive myocardial scar characterization with cardiac magnetic resonance (CMR) has been shown to accurately identify conduction channels and can be an important aid for ventricular tachycardia (VT) ablation. A new mapping method based on targeting deceleration zones (DZs) has become one of the most commonly used strategies for VT ablation procedures. The aim of the study was to analyse the capability of CMR to identify DZs and to find predictors of arrhythmogenicity in CMR channels.

METHODS AND RESULTS

Forty-four consecutive patients with structural heart disease and VT undergoing ablation after CMR at a single centre (October 2018 to July 2021) were included (mean age, 64.8 ± 11.6 years; 95.5% male; 70.5% with ischaemic heart disease; a mean ejection fraction of 32.3 ± 7.8%). The characteristics of CMR channels were analysed, and correlations with DZs detected during isochronal late activation mapping in both baseline maps and remaps were determined. Overall, 109 automatically detected CMR channels were analysed (2.48 ± 1.15 per patient; length, 57.91 ± 63.07 mm; conducting channel mass, 2.06 ± 2.67 g; protectedness, 21.44 ± 25.39 mm). Overall, 76.1% of CMR channels were associated with a DZ. A univariate analysis showed that channels associated with DZs were longer [67.81 ± 68.45 vs. 26.31 ± 21.25 mm, odds ratio (OR) 1.03, P = 0.010], with a higher border zone (BZ) mass (2.41 ± 2.91 vs. 0.87 ± 0.86 g, OR 2.46, P = 0.011) and greater protectedness (24.97 ± 27.72 vs. 10.19 ± 9.52 mm, OR 1.08, P = 0.021).

CONCLUSION

Non-invasive detection of targets for VT ablation is possible with CMR. Deceleration zones found during electroanatomical mapping accurately correlate with CMR channels, especially those with increased length, BZ mass, and protectedness.

Identification of Human Ventricular Tachycardia Demarcated by Fixed Lines of Conduction Block in a 3-Dimensional Hyperboloid Circuit

BACKGROUND

The circuit boundaries for reentrant ventricular tachycardia (VT) have been historically conceptualized within a 2-dimensional (2D) construct, with their fixed or functional nature unresolved. This study aimed to examine the correlation between localized lines of conduction block (LOB) evident during baseline rhythm with lateral isthmus boundaries that 3-dimensionally constrain the VT isthmus as a hyperboloid structure.

METHODS

A total of 175 VT activation maps were correlated with isochronal late activation maps during baseline rhythm in 106 patients who underwent catheter ablation for scar-related VT from 3 centers (42% nonischemic cardiomyopathy). An overt LOB was defined by a deceleration zone with split potentials (≥20 ms isoelectric segment) during baseline rhythm. A novel application of pacing within deceleration zone (≥600 ms) was implemented to unmask a concealed LOB not evident during baseline rhythm. LOB identified during baseline rhythm or pacing were correlated with isthmus boundaries during VT.

RESULTS

Among 202 deceleration zones analyzed during baseline rhythm, an overt LOB was evident in 47%. When differential pacing was performed in 38 deceleration zones without overt LOB, an underlying concealed LOB was exposed in 84%. In 152 VT activation maps (2D=53, 3-dimensional [3D]=99), 69% of lateral boundaries colocalized with an LOB in 2D activation patterns, and the depth boundary during 3D VT colocalized with an LOB in 79%. In VT circuits with isthmus regions that colocalized with a U-shaped LOB (n=28), the boundary invariably served as both lateral boundaries in 2D and 3D. Overall, 74% of isthmus boundaries were identifiable as fixed LOB during baseline rhythm or differential pacing.

CONCLUSIONS

The majority of VT circuit boundaries can be identified as fixed LOB from intrinsic or paced activation during sinus rhythm. Analysis of activation while pacing within the scar substrate is a novel technique that may unmask concealed LOB, previously interpreted to be functional in nature. An LOB from the perspective of a myocardial surface is frequently associated with intramural conduction, supporting the existence of a 3D hyperboloid VT circuit structure. Catheter ablation may be simplified to targeting both sides around an identified LOB during sinus rhythm.

Association of Sinus Wavefront Activation and Ventricular Extrastimuli Mapping With Ventricular Tachycardia Re-Entrant Circuits

BACKGROUND

Substrate-based ablation targets areas of delayed and fractionated electrograms during sinus rhythm, which are sensitive for identifying the ventricular tachycardia (VT) isthmus but is influenced by the activation wavefront direction and decremental pacing.

OBJECTIVES

The aim of this study was to correlate the areas of latest activation during varying wavefront activation mapping and decremental pacing mapping with sites critical to the VT isthmus.

METHODS

Three high-density electroanatomical substrate maps were created in patients presenting for ablation of monomorphic VT: 1) native sinus rhythm; 2) right ventricular (RV) apical pacing; and 3) an RV apical S2 map following the S1 drive train at 20 ms above the ventricular effective refractory period. Areas corresponding to the latest activation were compared with the VT isthmus identified by conventional mapping.

RESULTS

Twenty patients with structural heart disease with a mean age of 55.6 ± 16.9 years were included. The majority of the cohort consisted of patients with ischemic heart disease (50%) and arrhythmogenic RV cardiomyopathy (35%). Epicardial ablation was performed in 45% of patients. The concordance of the site of latest activation in sinus rhythm with the VT isthmus was 75%. The location of the latest activation during RV apical pacing corresponded with the VT isthmus in 85% of cases. However, in 95% of cases, the site of the latest activation following the S2 stimulus colocalized to the VT isthmus.

CONCLUSIONS

In a mix of underlying myocardial substrates, regions of conduction slowing during decremental pacing colocalize with the VT isthmus more frequently than sinus rhythm activation mapping and may have a role in substrate-based ablation where VT induction is undesirable.

Wavefront directionality and decremental stimuli synergistically improve identification of ventricular tachycardia substrate: insights from personalized computational heart models

AIMS

Multiple wavefront pacing (MWP) and decremental pacing (DP) are two electroanatomic mapping (EAM) strategies that have emerged to better characterize the ventricular tachycardia (VT) substrate. The aim of this study was to assess how well MWP, DP, and their combination improve identification of electrophysiological abnormalities on EAM that reflect infarct remodelling and critical VT sites.

METHODS AND RESULTS

Forty-eight personalized computational heart models were reconstructed using images from post-infarct patients undergoing VT ablation. Paced rhythms were simulated by delivering an initial (S1) and an extra-stimulus (S2) from one of 100 locations throughout each heart model. For each pacing, unipolar signals were computed along the myocardial surface to simulate substrate EAM. Six EAM features were extracted and compared with the infarct remodelling and critical VT sites. Concordance of S1 EAM features between different maps was lower in hearts with smaller amounts of remodelling. Incorporating S1 EAM features from multiple maps greatly improved the detection of remodelling, especially in hearts with less remodelling. Adding S2 EAM features from multiple maps decreased the number of maps required to achieve the same detection accuracy. S1 EAM features from multiple maps poorly identified critical VT sites. However, combining S1 and S2 EAM features from multiple maps paced near VT circuits greatly improved identification of critical VT sites.

CONCLUSION

Electroanatomic mapping with MWP is more advantageous for characterization of substrate in hearts with less remodelling. During substrate EAM, MWP and DP should be combined and delivered from locations proximal to a suspected VT circuit to optimize identification of the critical VT site.

Substrate Mapping Alters Ventricular Tachycardia Inducibility

BACKGROUND

Initiation of ventricular tachycardia (VT) by programmed electrical stimulation (PES) has an important role to allow mapping and assess ablation end points. We hypothesized that substrate mapping may alter VT inducibility by mechanical bumping of critical sites.

METHODS

Subjects with left ventricular scar-related VT that was inducible by PES who were undergoing ablation were included. PES was repeated after substrate mapping (Group I) or after time under sedation/anesthesia during which additional imaging and transeptal puncture were performed without substrate mapping (Group II). The response to the second PES was categorized as type I if the same VT was induced, type II if a different VT was induced, and type III if VT was not inducible.

RESULTS

Twenty-eight patients (median age 66 years, 61% ischemic cardiomyopathy), 14 in Group I and 14 in Group II, were included. Age, time between initial and second PES, type of cardiomyopathy, ejection fraction, and anesthesia methods were not different between the 2 groups. Initial VT cycle length, however, was shorter in Group I (305 millisecond [range, 235-600] versus 350 millisecond [range, 235-600], P=0.016). Also, Group I required more extrastimuli to induce VT in PES 1 (2 [1-4] versus 2 [1-3], P=0.022). In Group I, following substrate mapping, the second PES induced the same VT in 3 patients (21%), a different VT in 9 (64%), and no VT in 2 (14%) patients. In contrast, in Group II the same VT was induced in 10 (71%) patients, a different VT in 3 (21%) and no VT in 1 (7%) patient (P=0.017).

CONCLUSIONS

Mechanical effects of substrate mapping commonly alter inducibility of VT. This has important implications for catheter ablation procedure planning and acute assessment of outcome and can potentially account for some recurrent VTs that are not recognized at the time of the procedure.

Impact of different activation wavefronts on ischemic myocardial scar electrophysiological properties during high-density ventricular tachycardia mapping and ablation

INTRODUCTION

Scar-related ventricular tachycardia (VT) usually results from an underlying reentrant circuit facilitated by anatomical and functional barriers. The later are sensitive to the direction of ventricular activation wavefronts. We aim to evaluate the impact of different ventricular activation wavefronts on the functional electrophysiological properties of myocardial tissue.

METHODS

Patients with ischemic heart disease referred for VT ablation underwent high-density mapping using Carto®3 (Biosense Webster). Maps were generated during sinus rhythm, right and left ventricular pacing, and analyzed using a new late potential map software, which allows to assess local conduction velocities and facilitates the delineation of intra-scar conduction corridors (ISCC); and for all stable VTs.

RESULTS

In 16 patients, 31 high-resolution substrate maps from different ventricular activation wavefronts and 7 VT activation maps were obtained. Local abnormal ventricular activities (LAVAs) were found in VT isthmus, but also in noncritical areas. The VT isthmus was localized in areas of LAVAs overlapping surface between the different activation wavefronts. The deceleration zone location differed depending on activation wavefronts. Sixty-six percent of ISCCs were similarly identified in all activating wavefronts, but the one acting as VT isthmus was simultaneously identified in all activation wavefronts in all cases.

CONCLUSION

Functional based substrate mapping may improve the specificity to localize the most arrhythmogenic regions within the scar, making the use of different activation wavefronts unnecessary in most cases.

Retrospective Window of Interest Annotation Provides New Insights Into Functional Channels in Ventricular Tachycardia Substrate

BACKGROUND

Accurate annotation of local activation time is crucial in the functional assessment of ventricular tachycardia (VT) substrate. A major limitation of modern mapping systems is the standard prospective window of interest (sWOI) is limited to 490 to 500 milliseconds, preventing annotation of very late potentials (LPs). A novel retrospective window of interest (rWOI), which allows annotation of all diastolic potentials, was used to assess the functional VT substrate.

OBJECTIVES

This study sought to investigate the utility of a novel rWOI, which allows accurate visualization and annotation of all LPs during VT substrate mapping.

METHODS

Patients with high-density VT substrate maps and a defined isthmus were included. All electrograms were manually annotated to latest activation using a novel rWOI. Reannotated substrate maps were correlated to critical sites, with areas of late activation examined. Propagation patterns were examined to assess the functional aspects of the VT substrate.

RESULTS

Forty-eight cases were identified with 1,820 ± 826 points per map. Using the novel rWOI, 31 maps (65%) demonstrated LPs beyond the sWOI limit. Two distinct patterns of channel activation were seen during substrate mapping: 1) functional block with unidirectional conduction into the channel (76%); and 2) wave front collision within the channel (24%). In addition, a novel marker termed the zone of early and late crowding was studied in the rWOI substrate maps and found to have a higher positive predictive value (85%) than traditional deceleration zones (69%) for detecting critical sites of re-entry.

CONCLUSIONS

The standard WOI of contemporary mapping systems is arbitrarily limited and results in important very late potentials being excluded from annotation. Future versions of electroanatomical mapping systems should provide longer WOIs for accurate local activation time annotation.

Intracardiac Electrogram Targets for Ventricular Tachycardia Ablation

The pathogenesis of ventricular tachycardia (VT) in most patients with a prior myocardial scarring is reentry involving compartmentalized muscle fibers protected within the scar. Often the 12-lead ECG morphology of the VT itself is not available when treated with a defibrillator. Consequently, VT ablation takes on an interesting challenge of finding critical targets in sinus rhythm. High-density recordings are essential to evaluate a substrate based on whole electrogram voltage and activation delay, supplemented with substrate perturbation through alternate site pacing or introducing an extra stimulation. In this article, we discuss contemporary intracardiac electrogram targets for VT ablation, with explanation on each of their specific fundamental physiology.

Automated conduction velocity estimation based on isochronal activation of heart chambers

BACKGROUND

Spatial differences in conduction velocity (CV) are critical for cardiac arrhythmias induction. We propose a method for an automated CV calculation to identify areas of slower conduction during cardiac arrhythmias and sinus rhythm.

METHODS

Color-coded representations of the isochronal activation map using data coming from the RHYTHMIA™ Mapping System were reproduced by applying a temporal isochronal window at 20 ms. Geodesic distances of the 3D mesh were calculated using an algorithm selecting the minimum distance pathway (MDP). The CV estimation was performed considering points on the boundary of two spatially and temporally adjacent isochrones. For each of the boundary points of a given isochrone, the nearest boundary point of the consecutive isochrone was chosen, the MDP was evaluated, and a map of CV was created. The proposed method has been applied to a population of 29 patients.

RESULTS

In all cases of perimitral atrial flutter (16 pts out of 29 (55%)), areas with significantly low CV (< 30 cm/s) were found. Half of the cases present regions with low CV located in the anterior wall. No case with low CV at the so-called LA isthmus was observed. Right atrial maps during common atrial flutters showed low CV areas mainly located in the inferior inter-atrial septum. No areas of low CV were observed in subjects without a history of atrial arrhythmia while pts affected by paroxysmal AF showed areas with a limited extension of low CV.

CONCLUSIONS

The proposed software for automated CV estimation allows the identification of low CV areas, potentially helping electrophysiologists to plan the ablation strategy.

Ventricular Tachycardia Ablation Guided by Functional Substrate Mapping: Practices and Outcomes

Catheter ablation of ventricular tachycardia has demonstrated its important role in the treatment of ventricular tachycardia in patients with structural cardiomyopathy. Conventional mapping techniques used to define the critical isthmus, such as activation mapping and entrainment, are limited by the non-inducibility of the clinical tachycardia or its poor hemodynamic tolerance. To overcome these limitations, a voltage mapping strategy based on bipolar electrograms peak to peak analysis was developed, but a low specificity (30%) for VT isthmus has been described with this approach. Functional mapping strategy relies on the analysis of the characteristics of the electrograms but also their propagation patterns and their response to extra-stimulus or alternative pacing wavefronts to define the targets for ablation. With this review, we aim to summarize the different functional mapping strategies described to date to identify ventricular arrhythmic substrate in patients with structural heart disease.

Substrate-based approaches in ventricular tachycardia ablation

Catheter ablation for ventricular tachycardia (VT) in patients with structural heart disease is now part of standard care. Mapping and ablation of the clinical VT is often limited when the VT is noninducible, nonsustained or not haemodynamically tolerated. Substrate-based ablation strategies have been developed in an aim to treat VT in this setting and, subsequently, have been shown to improve outcomes in VT ablation when compared to focused ablation of mapped VTs. Since the initial description of linear ablation lines targeting ventricular scar, many different approaches to substrate-based VT ablation have been developed. Strategies can broadly be divided into three categories: 1) targeting abnormal electrograms, 2) anatomical targeting of conduction channels between areas of myocardial scar, and 3) targeting areas of slow and/or decremental conduction, identified with “functional” substrate mapping techniques. This review summarises contemporary substrate-based ablation strategies, along with their strengths and weaknesses.

Thermal ablation effects on rotors that characterize functional re-entry cardiac arrhythmia

Thermal ablation is a well-established successful treatment for cardiac arrhythmia, but it still presents limitations that require further studies and developments. In the rotor-driven functional re-entry arrhythmia, tissue heterogeneity results on the generation of spiral/scroll waves and wave break dynamics that may cause dangerous sustainable fibrillation. The selection of the target region to perform thermal ablation to mitigate this type of arrhythmia is challenging, since it considerably affects the local electrophysiology dynamics. This work deals with the numerical simulation of the thermal ablation of a cardiac muscle tissue and its effects on the dynamics of rotor-driven functional re-entry arrhythmia. A non-homogeneous two-dimensional rectangular region is used in the present numerical analysis, where radiofrequency ablation is performed. The electrophysiology problem for the propagation of the action potential in the cardiac tissue is simulated with the Fenton-Karma model. Thermal damage caused to the tissue by the radiofrequency heating is modeled by the Arrhenius equation. The effects of size and position of a heterogeneous region in the original muscle tissue were first analyzed, in order to verify the possible existence of the functional re-entry arrhythmia during the time period considered in the simulations. For each case that exhibited re-entry arrhythmia, six different ablation procedures were analyzed, depending on the position of the radiofrequency electrode and heating time. The obtained results revealed the effects of different model parameters on the existence and possible mitigation of the functional re-entry arrhythmia.

High Density Pace-Mapping for Scar-related Ventricular Tachycardia Ablation

Despite advances in medical and interventional therapies, ventricular tachycardia (VT) due to reentrant activity within complex regions of myocardial scar remains a common late complication of myocardial infarction This article is protected by copyright. All rights reserved.

NOVEL "LATE POTENTIAL MAP" ALGORITHM: ABNORMAL POTENTIALS AND SCAR CHANNELS DETECTION FOR VENTRICULAR TACHYCARDIA ABLATION

BACKGROUND

Automated systems for substrate mapping in context of ventricular tachycardia (VT) ablation may annotate far-field rather than near-field signals, rendering the resulting maps hard to interpret. Additionally, quantitative assessment of local conduction velocity (LCV) remains an unmet need in clinical practice. We evaluate whether a new Late Potential Map (LPM) algorithm can provide an automatic and reliable annotation and localized bipolar voltage measurement of ventricular electrograms, and if LCV analysis allows to recognize intra-scar conduction corridors acting as VT isthmuses.

METHODS

In 16 patients referred for scar-related VT ablation, 8 VT activation maps and 29 high-resolution substrate maps from different activation wavefronts were obtained. In offline analysis, the LPM algorithm was compared to manually annotated substrate maps. Locations of the VT isthmuses were compared with the corresponding substrate maps in regard to LCV.

RESULTS

The LPM algorithm had an overall/local abnormal ventricular activity (LAVA) annotation accuracy of 94.5%/81.1%, which compares to 83.7%/23.9% for the previous Wavefront algorithm. The resultant maps presented a spatial concordance of 88.1% in delineating regions displaying local abnormal ventricular activity (LAVA). LAVA median localized bipolar voltage was 0.22 mV, but voltage amplitude assessment had modest accuracy in distinguishing LAVA from other abnormal electrograms (AUC:0.676; p<0.001). LCV analysis in high-density substrate maps identified a median of 2 intra-scar conduction corridors per patient (IQR: 2-3), including the one acting as VT isthmus in all cases.

CONCLUSION

The new LPM algorithm and LCV analysis may enhance substrate characterization in scar-related VT. This article is protected by copyright. All rights reserved.

Structure and function of the ventricular tachycardia isthmus

Catheter ablation of postinfarction reentrant ventricular tachycardia (VT) has received renewed interest owing to the increased availability of high-resolution electroanatomic mapping systems that can describe the VT circuits in greater detail, and the emergence and need to target noninvasive external beam radioablation. These recent advancements provide optimism for improving the clinical outcome of VT ablation in patients with postinfarction and potentially other scar-related VTs. The combination of analyses gleaned from studies in swine and canine models of postinfarction reentrant VT, and in human studies, suggests the existence of common electroanatomic properties for reentrant VT circuits. Characterizing these properties may be useful for increasing the specificity of substrate mapping techniques and for noninvasive identification to guide ablation. Herein, we describe properties of reentrant VT circuits that may assist in elucidating the mechanisms of onset and maintenance, as well as a means to localize and delineate optimal catheter ablation targets.

Rotational Activation Pattern During Functional Substrate Mapping: Novel Target for Catheter Ablation of Scar-Related Ventricular Tachycardia

BACKGROUND

Recent advancements in a 3-dimensional mapping system allow for the assessment of detailed conduction properties during sinus rhythm and thus the establishment of a strategy targeting functionally abnormal regions in scar-related ventricular tachycardia (VT). We hypothesized that a rotational activation pattern (RAP) observed in maps during baseline rhythm was associated with the critical location of VT.

METHODS

We retrospectively examined the pattern of wavefront propagation during sinus rhythm in patients with scar-related VT. The prevalence and features of the RAP on critical VT circuits were analyzed. RAP was defined as >90° of inward curvature directly above or at the edge of the slow conductive areas.

RESULTS

Forty-five VTs in 37 patients (66±15 years old, 89% male, 27% ischemic heart disease) were evaluated. High-density substrate mapping during sinus rhythm (median, 2524 points) was performed using the CARTO3 system before VT induction. Critical sites for reentry were identified by direct termination by radiofrequency catheter ablation in 21 VTs or by pace mapping in 12 VTs. Among them, RAP was present in 70% of the 33 VTs. Four VTs had no RAP at the critical sites during sinus rhythm, but it became visible in the mappings with different wavefront directions. Six VTs, in which intramural or epicardial isthmus was suspected, were rendered noninducible by radiofrequency catheter ablation to the endocardial surface without RAP. RAP had a sensitivity and specificity of 70% and 89%, respectively, for predicting the elements in the critical zone for VT.

CONCLUSIONS

The critical zone of VT appears to correspond to an area characterized by the RAP with slow conduction during sinus rhythm, which facilitates targeting areas specific for reentry. However, this may not be applicable to intramural VT substrates and might be affected by the direction of wavefront propagation to the scar during mapping.

Analyzing the Role of Repolarization Gradients in Post-infarct Ventricular Tachycardia Dynamics Using Patient-Specific Computational Heart Models

Aims: Disease-induced repolarization heterogeneity in infarcted myocardium contributes to VT arrhythmogenesis but how apicobasal and transmural (AB-TM) repolarization gradients additionally affect post-infarct VT dynamics is unknown. The goal of this study is to assess how AB-TM repolarization gradients impact post-infarct VT dynamics using patient-specific heart models.

Method: 3D late gadolinium-enhanced cardiac magnetic resonance images were acquired from seven post-infarct patients. Models representing the patient-specific scar and infarct border zone distributions were reconstructed without (baseline) and with repolarization gradients along both the AB-TM axes. AB only and TM only models were created to assess the effects of each ventricular gradient on VT dynamics. VTs were induced in all models via rapid pacing.

Results: Ten baseline VTs were induced. VT inducibility in AB-TM models was not significantly different from baseline (p>0.05). Reentry pathways in AB-TM models were different than baseline pathways due to alterations in the location of conduction block (p<0.05). VT exit sites in AB-TM models were different than baseline VT exit sites (p<0.05). VT inducibility of AB only and TM only models were not significantly different than that of baseline (p>0.05) or AB-TM models (p>0.05). Reentry pathways and VT exit sites in AB only and TM only models were different than in baseline (p<0.05). Lastly, repolarization gradients uncovered multiple VT morphologies with different reentrant pathways and exit sites within the same structural, conducting channels.

Conclusion: VT inducibility was not impacted by the addition of AB-TM repolarization gradients, but the VT reentrant pathway and exit sites were greatly affected due to modulation of conduction block. Thus, during ablation procedures, physiological and pharmacological factors that impact the ventricular repolarization gradient might need to be considered when targeting the VTs.

A novel Ventricular map of Electrograms DUration as a Method to identify areas of slow conduction for ventricular tachycardia ablation: The VEDUM pilot study

BACKGROUND

Bipolar electrogram (EGM) duration is indicative of local activation property and, if prolonged, is useful to discover areas of slow conduction favoring arrhythmias.

OBJECTIVE

The present study aimed to create a map of EGM duration during the ventricular tachycardia (VT) (Ventricular Electrograms DUration as a Method map [VEDUM map]) to verify if the slowest activation area is crucial for reentry and could represent a suitable target for rapid VT interruption during ablation.

METHODS

Prospectively 30 patients were enrolled for this study. Twenty-one patients were selected, and 24 VT maps with complete circuit delineation (>90% tachycardia cycle length) were analyzed. Activation and VEDUM maps during VT as well as voltage maps during sinus rhythm were created.

RESULTS

Twenty-two of 24 VTs (88%) were interrupted during the first radiofrequency delivery (mean time 7.3 ± 5.4 seconds; range 3-25 seconds) at the area with the longest EGM duration (212 ± 47 ms; range 113-330 ms). The mean percentage of the cycle length of VT covered by the EGM with the longest duration was 58% ± 12%. In 9 patients (37%), the longest EGM was located at the isthmus entrance, at the exit in 7 maps (30%), and the mid-isthmuses in 8 maps (33%). In 6 patients (25%), the EGM covered the full diastolic phase. The mean isthmus width was 28 ± 11 mm (range 16-48 mm; median 25 mm).

CONCLUSION

A VEDUM map is highly accurate in defining a conductive vulnerable zone of the VT circuit. The longest EGM duration within the isthmus is highly predictive of rapid VT termination at the first radiofrequency delivery even in the case of large isthmuses.

Multi-Modality Imaging for the Identification of Arrhythmogenic Substrates Prior to Electrophysiology Studies

Noninvasive cardiac imaging is crucial for the characterization of patients who are candidates for cardiac ablations, for both procedure planning and long-term management. Multimodality cardiac imaging can provide not only anatomical parameters but even more importantly functional information that may allow a better risk stratification of cardiac patients. Moreover, fusion of anatomical and functional data derived from noninvasive cardiac imaging with the results of endocavitary mapping may possibly allow a better identification of the ablation substrate and also avoid peri-procedural complications. As a result, imaging-guided electrophysiological procedures are associated with an improved outcome than traditional ablation procedures, with a consistently lower recurrence rate.

Decrement Evoked Potential Mapping to Guide Ventricular Tachycardia Ablation: Elucidating the Functional Substrate

Empirical approaches to targeting the ventricular tachycardia (VT) substrate include mapping of late potentials, local abnormal electrogram, pace-mapping and homogenisation of the abnormal signals. These approaches do not try to differentiate between the passive or active role of local signals as the critical components of the VT circuit. By not considering the functional components, these approaches often view the substrate as a fixed anatomical barrier. Strategies to improve the success of VT ablation need to include the identification of critical functional substrate. Decrement-evoked potential (DeEP) mapping has been developed to elucidate this using an extra-stimulus added to a pacing drive train. With knowledge translation in mind, the authors detail the evolution of the DeEP concept by way of a study of simultaneous panoramic endocardial mapping in VT ablation; an in silico modelling study to demonstrate the factors influencing DeEPs; a multicentre VT ablation validation study; a practical approach to DeEP mapping; the potential utility of DeEPs to identify arrhythmogenic atrial substrate; and, finally, other functional mapping strategies.

Functional Activation Mapping of Scar-Related Ventricular Tachycardia Substrate

The optimal method to identify the arrhythmogenic substrate of scar-related ventricular tachycardia (VT) is unknown. Sites of activation slowing during sinus rhythm (SR) often co-localize with the VT circuit. This is a report of two scar related VT substrate mapping using a strategy of voltage-independent approach.

Signature signal strategy: Electrogram-based ventricular tachycardia mapping

Multiple decades of work have recognized complexities of substrates responsible for ventricular tachycardia (VT). There is sufficient evidence that 3 critical components of a re-entrant VT circuit, namely, region of slow conduction, zone of unidirectional block, and exit site, are located in spatial vicinity to each other in the ventricular scar. Each of these components expresses characteristic electrograms in sinus rhythm, at initiation of VT, and during VT, respectively. Despite this, abnormal electrograms are widely targeted without appreciation of these signature electrograms during contemporary VT ablation. Our aim is to stimulate physiology-based VT mapping and a targeted ablation of VT. In this article, we focus on these 3 underappreciated aspects of the physiology of ischemic scar-related VT circuits that have practical applications during a VT ablation procedure. We explore the anatomic and functional elements underlying these distinctive bipolar electrograms, specifically the contribution of tissue branching, conduction restitution, and wave curvature to the substrate, as they pertain to initiation and maintenance of VT. We propose a VT ablation approach based on these 3 electrogram features that can be a potential practical means to recognize critical elements of a VT circuit and target ablation.