Limitations and Pitfalls of Substrate Mapping for Ventricular Tachycardia

Significance of coherent mapping in unveiling slow conduction zones of ventricular tachycardia substrate in ischemic cardiomyopathy

BACKGROUND

Identifying slow conduction zones (SCZs) within the ventricular tachycardia (VT) substrate remains a major challenge in ischemic cardiomyopathy (ICM). We aimed to evaluate the role of coherent mapping (CM) in identifying SCZs within low-voltage areas (LVAs) in VT substrate mapping and assess its impact on VT ablation outcomes.

METHODS

This retrospective study included 32 patients with ICM who underwent ablation for recurrent VT. CM-SCZs were compared with traditional substrate markers, including late potentials (LPs), local abnormal ventricular activities (LAVAs), and ILAM-based deceleration zones (DZs). Ablation strategies targeting CM-SCZs were analyzed in relation to procedural and clinical outcomes, including VT recurrence and total radiofrequency (RF) ablation time.

RESULTS

CM-SCZs were consistently identified adjacent to LVAs in all cases, with a mean area of 5.2 ± 2.3 cm2. CM-SCZs colocalized with ILAM-based DZs in 56.3% of cases and overlapped with LPs and LAVAs in selected patients. Among patients who remained free from VT recurrence, total RF ablation time was significantly longer (938 ± 354 vs. 380 ± 448 s, p = 0.03), suggesting that more extensive substrate modification played a role in arrhythmia suppression. Furthermore, patients with VT recurrence had lower post-ablation non-inducibility rates (50% vs. 91.6%, p = 0.02).

CONCLUSION

CM improves the identification of SCZ within the VT substrate and enhances substrate-based ablation strategies. Incorporating CM-SCZs into VT ablation protocols may improve procedural success and reduce arrhythmia recurrence. Future studies should validate these findings and explore role of CM in broader patient populations.

Ventricular tachycardia substrate mapping: What's been done and what needs to be done

Substrate mapping is an important component of electrophysiological (EP) study for the treatment of reentrant ventricular tachycardia (VT). It is used to detect characteristics of the electrical circuit and, in particular, the location and properties of the central common pathway, aka the isthmus, where multiple circuit loops can coincide. Typically, reentrant circuits are single or double loop, but as the common pathway size increases, 4-loop patterns may emerge, consisting of 2 parallel isthmuses or a single isthmus with 4 loops. Arrhythmogenic substrate contains a mixture of scar, calcification, and fibrofatty regions blended with viable ventricular myocytes, which can slow conduction. It is identified in the EP laboratory in part by the presence of low-amplitude electrograms and a zone of uniform slow conduction resulting from a sparsity of remaining viable myocytes and molecular-level remodeling. The electrograms recorded near isthmus boundaries frequently exhibit an abnormal morphology, such as fractionation and late or split deflections, due to the separation of muscle fiber bundles by fibroadipose tissue or calcification, and due to other conduction impediments such as source-sink mismatch, wherein topographic changes to the viable myocardial structure occur. Substrate mapping facilitates the identification of arrhythmogenic regions during sinus rhythm, whereas inducible VT with periods of ongoing reentry, when recordable, can be used for further assessment. Substrate modeling augments substrate mapping by seeking to predict electrogram morphology and mapped features and properties to be encountered during EP study based on an accurate depiction of arrhythmogenic tissue. Herein, we elaborate on the details of VT substrate mapping and modeling to the present time.

Stepwise ablation strategy in radiofrequency ablation improves acute and long-term outcomes of scar-related ventricular tachycardias

BACKGROUND

The optimal intervention procedures for scar-related ventricular tachycardia (VT) is still unclear.

OBJECTIVE

This study aimed to compare the acute and long-term outcomes of a stepwise ablation approach targeting critical sites identified through activation mapping during VT or pace mapping followed by substrate ablation with substrate modification alone in patients with scar-related VT.

METHODS

Data of 41 patients with scar-related VTs treated with stepwise ablation (Group 1, n = 29) or substrate modification alone during sinus rhythm (Group 2, n = 12) were retrospectively reviewed. The procedure acute success and long-term success during follow-up were compared.

RESULTS

There was no statistical difference between the two groups on basic characteristics. Group 1 demonstrated shorter ablation time (P = 0.02), longer VT-free survival rates at a median follow-up of 24.0 months (P = 0.02) and a lower VT recurrence rate (hazard ratio: 0.17, 95% confidence interval: [0.03, 0.93], P = 0.04) compared to Group 2. The acute success and ratio of ablation area to scar area were comparable between the two groups (P ≥ 0.05).

CONCLUSION

The stepwise ablation strategy shows promise for improving acute and long-term outcomes and reducing the recurrence risk in patients with scar-related VT.

State of the Art: Mapping Strategies to Guide Ablation in Ischemic Heart Disease

Catheter ablation to prevent ventricular tachycardia (VT) that emerges late after a myocardial infarction aims to interrupt the re-entry substrate. Interruption of potential channels and regions of slow conduction that can be identified during stable sinus or paced rhythm is often effective and a number of substrate markers for guiding this approach have been described. While there is substantial agreement with different markers in some patients, the different markers select different regions for ablation in others. Mapping during VT to identify critical re-entry circuit isthmuses is likely more specific, and most useful when VT is incessant or frequent during the procedure or when sinus rhythm substrate ablation fails. Both approaches are often combined. These methods for identifying and characterizing post-infarct-related arrhythmia substrate and the re-entry circuits are reviewed.

Dynamic Voltage Mapping of the Post-infarct Ventricular Tachycardia Substrate: A Practical Technique to Help Differentiate Scar from Borderzone Tissue

During catheter ablation of post-infarct ventricular tachycardia (VT), substrate mapping is used when VT is non-inducible or poorly tolerated. Substrate mapping aims to identify regions of slowly conducting myocardium (borderzone) within and surrounding myocardial scar for ablation. Historically, these tissue types have been identified using bipolar voltage mapping, with areas of low bipolar voltage (<0.50 mV) defined as scar, and areas with voltages between 0.50 mV and 1.50 mV as borderzone. In the era of high-density mapping, studies have demonstrated slow conduction within areas of bipolar voltage <0.50 mV, suggesting that this historical cut-off is outdated. While electrophysiologists often adapt voltage cut-offs to account for this, the optimal scar-borderzone threshold is not known. In this review, we discuss dynamic voltage mapping, a novel substrate mapping technique we have developed, which superimposes data from both activation and voltage maps, to help delineate the post-infarct VT circuit through identification of the optimal scar-borderzone voltage threshold.

Multipolar Electrograms: A New Configuration That Increases the Measurement Accuracy of Intracardiac Signals

BACKGROUND

Accurate measurements of intracardiac electrograms (EGMs) remain a clinical challenge because of the suboptimal attenuation of far-field potentials. Multielectrode mapping catheters provide an opportunity to construct multipolar instead of bipolar EGMs for rejecting common far-field potentials recorded from a multivectorial space.

OBJECTIVES

The purpose of this study was to develop a multipolar EGM and compare its characteristics to those of bipolar EGMs METHODS: Using a 36-electrode array catheter (Optrell-36, Biosense Webster), a far-field component was mathematically constructed from clusters of electrodes surrounding each inspected electrode. This component was subtracted from the unipolar waveform to produce a local unipolar, referred to as a "multipolar EGM." The performance of multipolar EGMs was evaluated in 7 swine with healed anteroseptal infarction.

RESULTS

Multipolar EGMs proved superior in attenuating far-field potentials in infarct border zones, increasing the near-field to far-field ratio from 0.92 ± 0.2 to 2.25 ± 0.3 (P < 0.001). Removal of far-field components reduced the voltage amplitude (P < 0.001) and enlarged the infarct surface area (P = 0.02), aligning more closely with histological findings. Of 379 EGMs with ≥20 ms activation time difference between bipolar and multipolar EGMs, 95.3% (361 of 379) were accurately annotated using multipolar EGMs, while annotation based on bipolar EGM was predominantly made on far-field components.

CONCLUSIONS

Multielectrode array catheters provide a unique platform for constructing multipolar EGMs. This new EGM may be beneficial for "purifying" local potentials within a complex electrical field, resulting in more accurate voltage and activation maps.

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.

Guiding ablation strategies for ventricular tachycardia in patients with structural heart disease by analyzing links and conversion patterns of traceable abnormal late potential zone

BACKGROUND

Substrate-based ablation can treat uninducible or hemodynamically instability scar-related ventricular tachycardia (VT). However, whether a correlation exists between the critical VT isthmus and late activation zone (LAZ) during sinus rhythm (SR) is unknown.

OBJECTIVE

To demonstrate the structural and functional properties of abnormal substrates and analyze the link between the VT circuit and abnormal activity during SR.

METHODS

Thirty-six patients with scar-related VT (age, 50.0 ± 13.7 years and 86.1% men) who underwent VT ablation were reviewed. The automatic rhythmia ultrahigh resolution mapping system was used for electroanatomic substrate mapping. The clinical characteristics and mapping findings, particularly the LAZ characteristics during SR and VT, were analyzed. To determine the association between the LAZ during the SR and VT circuits, the LAZ was defined as five activation patterns: entrance, exit, core, blind alley, and conduction barrier.

RESULTS

Forty-five VTs were induced in 36 patients, 91.1% of which were monomorphic. The LAZ of all patients was mapped during the SR and VT circuits, and the consistency of the anatomical locations of the LAZ and VT circuits was analyzed. Using the ultrahigh resolution mapping system, interconversion patterns, including the bridge, T, puzzle, maze, and multilayer types, were identified. VT ablation enabled precise ablation of abnormal late potential conduction channels.

CONCLUSION

Five interconversion patterns of the LAZ during the SR and VT circuits were summarized. These findings may help formulate more precise substrate-based ablation strategies for scar-related VT and shorter procedure times.

Ventricular Electrograms Duration Map to Detect Ventricular Arrhythmia Substrate: the VEDUM Project Study

BACKGROUND

The analysis of the wave-front activation patterns is crucial for the comprehension and treatment of ventricular tachycardia (VT). The ventricular electrograms duration map (VEDUM) is a potential method to identify areas (VEDUM area) with slow and inhomogeneous activation. There is no available data on the characteristics and the arrhythmogenic role of VEDUM areas identified during sinus/paced rhythm.

METHODS

Patients referred for VT ablation were enrolled at 3 different centers. VEDUM maps during sinus/paced rhythm as well as substrate and functional maps were created; activation mapping was performed for all hemodynamically tolerated VT.

RESULTS

Thirty-two patients (mean age:70.1±9.4 years; males 93.8%) were enrolled. The VEDUM approach was achieved in all patients and the mean size of the VEDUM area was 12.1±6.9 cm2 (interquartile range, 7.8-14.9 cm2). A significative difference was observed between the electrogram duration in the VEDUM area and the normal tissue (163.7 ms [interquartile range, 142.3-199.2 ms]; versus 65.5 ms [interquartile range, 59.5-76.2 ms]; P<0.001). The VEDUM area was visualized in a dense scar (<0.5 mV) in 19 (59.4%) patients. A deceleration zone and late potentials were recorded inside the VEDUM area in 56.3% and 81.3%, respectively. When a complete VT activation mapping was available, the isthmus projected in the VEDUM area in 93.5% of patients; 8 of them had multiple VTs mapped and in the 87.5% all VT isthmuses were included in the VEDUM area.

CONCLUSIONS

VEDUM maps allow the identification of discrete areas of inhomogeneous and slow conduction. They represent a potential target for VT ablation, including patients with multiple morphologies.

Advanced Imaging Integration for Catheter Ablation of Ventricular Tachycardia

PURPOSE OF REVIEW

Imaging plays a crucial role in the therapy of ventricular tachycardia (VT). We offer an overview of the different methods and provide information on their use in a clinical setting.

RECENT FINDINGS

The use of imaging in VT has progressed recently. Intracardiac echography facilitates catheter navigation and the targeting of moving intracardiac structures. Integration of pre-procedural CT or MRI allows for targeting the VT substrate, with major expected impact on VT ablation efficacy and efficiency. Advances in computational modeling may further enhance the performance of imaging, giving access to pre-operative simulation of VT. These advances in non-invasive diagnosis are increasingly being coupled with non-invasive approaches for therapy delivery. This review highlights the latest research on the use of imaging in VT procedures. Image-based strategies are progressively shifting from using images as an adjunct tool to electrophysiological techniques, to an integration of imaging as a central element of the treatment strategy.

Best Practices for the Catheter Ablation of Ventricular Arrhythmias

Techniques for catheter ablation have evolved to effectively treat a range of ventricular arrhythmias. Pre-operative electrocardiographic and cardiac imaging data are very useful in understanding the arrhythmogenic substrate and can guide mapping and ablation. In this review, we focus on best practices for catheter ablation, with emphasis on tailoring ablation strategies, based on the presence or absence of structural heart disease, underlying clinical status, and hemodynamic stability of the ventricular arrhythmia. We discuss steps to make ablation safe and prevent complications, and techniques to improve the efficacy of ablation, including optimal use of electroanatomical mapping algorithms, energy delivery, intracardiac echocardiography, and selective use of mechanical circulatory support.

Fat infiltration in the infarcted heart as a paradigm for ventricular arrhythmias

Infiltrating adipose tissue (inFAT) has been recently found to co-localize with scar in infarcted hearts and may contribute to ventricular arrhythmias (VAs), a life-threatening heart rhythm disorder. However, the contribution of inFAT to VA has not been well-established. We investigated the role of inFAT versus scar in VA through a combined prospective clinical and mechanistic computational study. Using personalized computational heart models and comparing the results from simulations of VA dynamics with measured electrophysiological abnormalities during the clinical procedure, we demonstrate that inFAT, rather than scar, is a primary driver of arrhythmogenic propensity and is frequently present in critical regions of the VA circuit. We determined that, within the VA circuitry, inFAT, as opposed to scar, is primarily responsible for conduction slowing in critical sites, mechanistically promoting VA. Our findings implicate inFAT as a dominant player in infarct-related VA, challenging existing paradigms and opening the door for unexplored anti-arrhythmic strategies.

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.

On the Electrophysiology and Mapping of Intramural Arrhythmic Focus

BACKGROUND

Conventional mapping of focal ventricular arrhythmias relies on unipolar electrogram characteristics and early local activation times. Deep intramural foci are common and associated with high recurrence rates following catheter-based radiofrequency ablation. We assessed the accuracy of unipolar morphological patterns and mapping surface indices to predict the site and depth of ventricular arrhythmogenic focal sources.

METHODS

An experimental beating-heart model used Langendorff-perfused, healthy swine hearts. A custom 56-pole electrode array catheter was positioned on the left ventricle. A plunge needle was placed perpendicular in the center of the grid to simulate arrhythmic foci at variable depths. Unipolar electrograms and local activation times were generated. Simulation models from 2 human hearts were also included with grids positioned simultaneously on the endocardium-epicardium from multiple left ventricular, septal, and outflow tract sites.

RESULTS

A unipolar Q or QS complex lacks specificity for superficial arrhythmic foci, as this morphology pattern occupies a large surface area and is the predominant pattern as intramural depth increases without developing a R component. There is progressive displacement from the arrhythmic focus to the surface exit as intramural focus depth increases. A shorter total activation time over the overlying electrode array, larger surface area within initial 20 ms activation, and a dual surface breakout pattern all indicate a deep focus.

CONCLUSIONS

Displacement from the focal intramural origin to the exit site on the mapping surface could lead to erroneous lesion delivery strategies. Traditional unipolar electrogram features lack specificity to predict the intramural arrhythmic source; however, novel endocardial-epicardial mapping surface indices can be used to determine the depth of arrhythmic foci.

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.