Etiology-Specific Remodeling in Ventricular Tissue of Heart Failure Patients and Its Implications for Computational Modeling of Electrical Conduction

With an estimated 64.3 million cases worldwide, heart failure (HF) imposes an enormous burden on healthcare systems. Sudden death from arrhythmia is the major cause of mortality in HF patients. Computational modeling of the failing heart provides insights into mechanisms of arrhythmogenesis, risk stratification of patients, and clinical treatment. However, the lack of a clinically informed approach to model cardiac tissues in HF hinders progress in developing patient-specific strategies. Here, we provide a microscopy-based foundation for modeling conduction in HF tissues. We acquired 2D images of left ventricular tissues from HF patients (n = 16) and donors (n = 5). The composition and heterogeneity of fibrosis were quantified at a sub-micrometer resolution over an area of 1 mm². From the images, we constructed computational bidomain models of tissue electrophysiology. We computed local upstroke velocities of the membrane voltage and anisotropic conduction velocities (CV). The non-myocyte volume fraction was higher in HF than donors (39.68 ± 14.23 vs. 22.09 ± 2.72%, p < 0.01), and higher in ischemic (IC) than nonischemic (NIC) cardiomyopathy (47.2 ± 16.18 vs. 32.16 ± 6.55%, p < 0.05). The heterogeneity of fibrosis within each subject was highest for IC (27.1 ± 6.03%) and lowest for donors (7.47 ± 1.37%) with NIC (15.69 ± 5.76%) in between. K-means clustering of this heterogeneity discriminated IC and NIC with an accuracy of 81.25%. The heterogeneity in CV increased from donor to NIC to IC tissues. CV decreased with increasing fibrosis for longitudinal (R ² = 0.28, p < 0.05) and transverse conduction (R ² = 0.46, p < 0.01). The tilt angle of the CV vectors increased 2.1° for longitudinal and 0.91° for transverse conduction per 1% increase in fibrosis. Our study suggests that conduction fundamentally differs in the two etiologies due to the characteristics of fibrosis. Our study highlights the importance of the etiology-specific modeling of HF tissues and integration of medical history into electrophysiology models for personalized risk stratification and treatment planning.

Catheter ablation of ventricular tachycardia in nonischemic cardiomyopathy with near-normal left ventricular ejection fraction

BACKGROUND

Patients with idiopathic nonischemic cardiomyopathy (NICM) and near-normal left ventricular ejection fraction (LVEF) may develop ventricular tachycardia (VT).

OBJECTIVE

The purpose of this study was to describe procedural characteristics and outcomes in patients requiring ablation for NICM-related VT with near-normal LVEF compared to impaired LVEF.

METHODS

Over 8 years, 77 consecutive patients with NICM-related VT underwent catheter ablation. Of these patients, 47 had idiopathic NICM (20 near-normal LVEF, 27 impaired LVEF). Procedural characteristics and outcomes were compared.

RESULTS

Mean age was 64 ± 12years, mean LVEF was 40% ± 14%, and 75% were male. In the near-normal LVEF group compared to the impaired LVEF group, LVEF was higher (54% ± 5% vs 30 ± 8%; P <.001), scar was predominantly located in the perivalvular left ventricle (LV) and basal septum (15/20 [75%]), was smaller in size [bipolar: 9.7 (6.2-32.4) cm² vs 30.4 (21.1-37.6) cm², P = .03; unipolar: 23.3 (6.6-39.9) cm² vs 57.2 (42.2-74.9) cm², P = .009], and required smaller areas of ablation [7.0 (5.9-14.2) cm² vs 11.4 (8.5-16.7) cm², P = .06]. Both groups experienced comparable procedure times, fluoroscopy doses, ablation times, VT cycle lengths, and acute success rates. After final ablation, VA-free survival was comparable between both groups (65% vs 63%; P = .63) at 12 months.

CONCLUSION

Idiopathic NICM-related VT with near-normal LVEF was associated with discrete areas of arrhythmogenic, predominantly intramural, scar in the perivalvular LV and basal septum. Despite smaller scar, patients required similar ablation amounts and experienced comparable long-term outcomes compared to patients with idiopathic NICM-related VT and impaired LVEF. These findings underscore the "three-dimensionality" of substrate, whereby the intramural basal septum forms the third dimension and impacts ablation outcomes.

Strain by speckle tracking echocardiography correlates with electroanatomic scar location and burden in ischaemic cardiomyopathy

AIMS

Ventricular tachycardia (VT) in ischaemic cardiomyopathy (ICM) originates from scar, identified as low-voltage areas with invasive high-density electroanatomic mapping (EAM). Abnormal myocardial deformation on speckle tracking strain echocardiography can non-invasively identify scar. We examined if regional and global longitudinal strain (GLS) can localize and quantify low-voltage scar identified with high-density EAM.

METHODS AND RESULTS

We recruited 60 patients, 40 ICM patients undergoing VT ablation and 20 patients undergoing ablation for other arrhythmias as controls. All patients underwent an echocardiogram prior to high-density left ventricular (LV) EAM. Endocardial bipolar and unipolar scar location and percentage were correlated with regional and multilayer GLS. Controls had normal GLS and normal bipolar and unipolar voltages. There was a strong correlation between endocardial and mid-myocardial longitudinal strain and endocardial bipolar scar percentage for all 17 LV segments (r = 0.76-0.87, P < 0.001) in ICM patients. Additionally, indices of myocardial contraction heterogeneity, myocardial dispersion (MD), and delta contraction duration (DCD) correlated with bipolar scar percentage. Endocardial and mid-myocardial GLS correlated with total LV bipolar scar percentage (r = 0.83; 0.82, P < 0.001 respectively), whereas epicardial GLS correlated with epicardial bipolar scar percentage (r = 0.78, P < 0.001). Endocardial GLS -9.3% or worse had 93% sensitivity and 82% specificity for predicting endocardial bipolar scar >46% of LV surface area.

CONCLUSIONS

Multilayer strain analysis demonstrated good linear correlations with low-voltage scar by invasive EAM. Validation studies are needed to establish the utility of strain as a non-invasive tool for quantifying scar location and burden, thereby facilitating mapping and ablation of VT.

Unipolar electrogram-based voltage mapping with far-field cancellation to improve detection of abnormal atrial substrate during atrial fibrillation

INTRODUCTION

An important substrate for atrial fibrillation (AF) is fibrotic atrial myopathy. Identifying low voltage, myopathic regions during AF using traditional bipolar voltage mapping is limited by the directional dependency of wave propagation. Our objective was to evaluate directionally independent unipolar voltage mapping, but with far-field cancellation, to identify low-voltage regions during AF.

METHODS

In 12 patients undergoing pulmonary vein isolation for AF, high-resolution voltage mapping was performed in the left atrium during sinus rhythm and AF using a roving 20-pole circular catheter. Bipolar electrograms (EGMs) (Bi) < 0.5 mV in sinus rhythm identified low-voltage regions. During AF, bipolar voltage and unipolar voltage maps were created, the latter with (uni-res) and without (uni-orig) far-field cancellation using a novel, validated least-squares algorithm.

RESULTS

Uni-res voltage was ~25% lower than uni-orig for both low voltage and normal atrial regions. Far-field EGM had a dominant frequency (DF) of 4.5-6.0 Hz, and its removal resulted in a lower DF for uni-orig compared with uni-res (5.1 ± 1.5 vs. 4.8 ± 1.5 Hz; p < .001). Compared with Bi, uni-res had a significantly greater area under the receiver operator curve (0.80 vs. 0.77; p < .05), specificity (86% vs. 76%; p < .001), and positive predictive value (43% vs. 30%; p < .001) for detecting low-voltage during AF. Similar improvements in specificity and positive predictive value were evident for uni-res versus uni-orig.

CONCLUSION

Far-field EGM can be reliably removed from uni-orig using our novel, least-squares algorithm. Compared with Bi and uni-orig, uni-res is more accurate in detecting low-voltage regions during AF. This approach may improve substrate mapping and ablation during AF, and merits further study.

The role of imaging in catheter ablation of ventricular arrhythmias

Late gadolinium enhancement cardiac magnetic resonance (LGE-CMR) and multidetector cardiac computed tomography (MDCT) have emerged as novel, fascinating imaging tools for arrhythmogenic substrate identification and characterization. The role of these techniques for aiding and guiding the catheter ablation of ventricular tachycardia, either as a complement or a surrogate of the electroanatomic map, has been rising in recent years. Integrating pixel signal intensity maps or wall thickness maps delivered from LGE-CMR or MDCT, respectively, into the navigation system has become a cornerstone for VT ablation procedures in a few centers of excellence around the world. The pre-procedure scar characterization offers some advantages, helping decide for the best procedure planning and approach; complete substrate identification and characterization, helping to focus electroanatomical mapping in regions of interest and also has a positive impact in procedure efficiency and outcomes. In the present article, we perform a review of the most practical aspects for using LGE-CMR or MDCT when a VT ablation procedure is planned, from the image acquisition to the integration into the navigation system, analyzing the current role of the LGE-CMR and MDCT for arrhythmogenic substrate characterization as well as for guiding VT ablation.

Electrical Substrate Ablation for Refractory Ventricular Fibrillation: Results of the AVATAR Study

[Figure: see text].

Late-Gadolinium Enhancement Interface Area and Electrophysiological Simulations Predict Arrhythmic Events in Patients With Nonischemic Dilated Cardiomyopathy

OBJECTIVES

This study sought to investigate whether shape-based late gadolinium enhancement (LGE) metrics and simulations of re-entrant electrical activity are associated with arrhythmic events in patients with nonischemic dilated cardiomyopathy (NIDCM).

BACKGROUND

The presence of LGE predicts life-threatening ventricular arrhythmias in NIDCM; however, risk stratification remains imprecise. LGE shape and simulations of electrical activity may be able to provide additional prognostic information.

METHODS

Cardiac magnetic resonance (CMR)-LGE shape metrics were computed for a cohort of 156 patients with NIDCM and visible LGE and tested retrospectively for an association with an arrhythmic composite endpoint of sudden cardiac death and ventricular tachycardia. Computational models were created from images and used in conjunction with simulated stimulation protocols to assess the potential for re-entry induction in each patient's scar morphology. A mechanistic analysis of the simulations was carried out to explain the associations.

RESULTS

During a median follow-up of 1,611 (interquartile range: 881 to 2,341) days, 16 patients (10.3%) met the primary endpoint. In an inverse probability weighted Cox regression, the LGE-myocardial interface area (hazard ratio [HR]: 1.75; 95% confidence interval [CI]: 1.24 to 2.47; p = 0.001), number of simulated re-entries (HR: 1.40; 95% CI: 1.23 to 1.59; p < 0.01) and LGE volume (HR: 1.44; 95% CI: 1.07 to 1.94; p = 0.02) were associated with arrhythmic events. Computational modeling revealed repolarization heterogeneity and rate-dependent block of electrical wavefronts at the LGE-myocardial interface as putative arrhythmogenic mechanisms directly related to the LGE interface area.

CONCLUSIONS

The area of interface between scar and surviving myocardium, as well as simulated re-entrant activity, are associated with an elevated risk of major arrhythmic events in patients with NIDCM and LGE and represent novel risk predictors.

Myocardial Substrate Characterization by CMR T1 Mapping in Patients With NICM and No LGE Undergoing Catheter Ablation of VT

OBJECTIVES

The goal of this study was to characterize the relationship between DF, the electroanatomic mapping (EAM) substrate, and outcomes of catheter ablation of VT in NICM.

BACKGROUND

A substantial proportion of patients with nonischemic dilated cardiomyopathy (NICM) and ventricular tachycardia (VT) do not have scar detectable by cardiac magnetic resonance late gadolinium enhancement (LGE) imaging. In these patients, the significance of diffuse fibrosis (DF) detected with T₁ mapping has not been previously investigated.

METHODS

This study included 51 patients with NICM and VT undergoing catheter ablation (median age 55 years; 77% male subjects) who had no evidence of LGE on pre-procedural cardiac magnetic resonance. Post-contrast T₁ relaxation time determined on the septum was assessed as a surrogate of DF burden. The extent of endocardial low-voltage areas (LVAs) at EAM was correlated with T₁ mapping data.

RESULTS

Bipolar LVAs were present in 22 (43%) patients (median extent 15 cm² [8 to 29 cm²]) and unipolar LVA in all patients (median extent 48 cm² [26 to 120 cm²]). A significant inverse correlation was found between T₁ values and both unipolar-LVA (R² = 0.64; β = -0.85; p < 0.01) and bipolar-LVA (R² = 0.16; β = -1.63; p < 0.01). After a median follow-up of 45 months (22 to 57 months), 2 (4%) patients died, 3 (6%) underwent heart transplantation, and 8 (16%) experienced VT recurrence. Shorter post-contrast T₁ time was associated with an increased risk of VT recurrence (hazard ratio: 1.16; 95% confidence interval: 1.03 to 1.33 per 10 ms decrease; p = 0.02).

CONCLUSIONS

In patients with NICM and no evidence of LGE undergoing catheter ablation of VT, DF estimated by using post-contrast T₁ mapping correlates with the voltage abnormality at EAM and seems to affect post-ablation outcomes.

Assessing the ability of substrate mapping techniques to guide ventricular tachycardia ablation using computational modelling

BACKGROUND

Identification of targets for ablation of post-infarction ventricular tachycardias (VTs) remains challenging, often requiring arrhythmia induction to delineate the reentrant circuit. This carries a risk for the patient and may not be feasible. Substrate mapping has emerged as a safer strategy to uncover arrhythmogenic regions. However, VT recurrence remains common.

GOAL

To use computer simulations to assess the ability of different substrate mapping approaches to identify VT exit sites.

METHODS

A 3D computational model of the porcine post-infarction heart was constructed to simulate VT and paced rhythm. Electroanatomical maps were constructed based on endocardial electrogram features and the reentry vulnerability index (RVI - a metric combining activation (AT) and repolarization timings to identify tissue susceptibility to reentry). Since scar transmurality in our model was not homogeneous, parameters derived from all signals (including dense scar regions) were used in the analysis. Potential ablation targets obtained from each electroanatomical map during pacing were compared to the exit site detected during VT mapping.

RESULTS

Simulation data showed that voltage cut-offs applied to bipolar electrograms could delineate the scar, but not the VT circuit. Electrogram fractionation had the highest correlation with scar transmurality. The RVI identified regions closest to VT exit site but was outperformed by AT gradients combined with voltage cut-offs. The performance of all metrics was affected by pacing location.

CONCLUSIONS

Substrate mapping could provide information about the infarct, but the directional dependency on activation should be considered. Activation-repolarization metrics have utility in safely identifying VT targets, even with non-transmural scars.

2019 HRS/EHRA/APHRS/LAHRS expert consensus statement on catheter ablation of ventricular arrhythmias

Ventricular arrhythmias are an important cause of morbidity and mortality and come in a variety of forms, from single premature ventricular complexes to sustained ventricular tachycardia and fibrillation. Rapid developments have taken place over the past decade in our understanding of these arrhythmias and in our ability to diagnose and treat them. The field of catheter ablation has progressed with the development of new methods and tools, and with the publication of large clinical trials. Therefore, global cardiac electrophysiology professional societies undertook to outline recommendations and best practices for these procedures in a document that will update and replace the 2009 EHRA/HRS Expert Consensus on Catheter Ablation of Ventricular Arrhythmias. An expert writing group, after reviewing and discussing the literature, including a systematic review and meta-analysis published in conjunction with this document, and drawing on their own experience, drafted and voted on recommendations and summarized current knowledge and practice in the field. Each recommendation is presented in knowledge byte format and is accompanied by supportive text and references. Further sections provide a practical synopsis of the various techniques and of the specific ventricular arrhythmia sites and substrates encountered in the electrophysiology lab. The purpose of this document is to help electrophysiologists around the world to appropriately select patients for catheter ablation, to perform procedures in a safe and efficacious manner, and to provide follow-up and adjunctive care in order to obtain the best possible outcomes for patients with ventricular arrhythmias.

Improved Procedural Efficiency of Atrial Fibrillation Ablation Using a Dedicated Ablation Protocol and Lean Management

OBJECTIVES

In this study the authors hypothesized that "Lean management" within a dedicated ablation protocol could standardize the pulmonary vein isolation (PVI) procedure and improve quality.

BACKGROUND

There is a large variability in safety, effectiveness, and efficiency of PVI.

METHODS

This was a single-center prospective study with inclusion of all consecutive PVI procedures from 2017 to 2019. A 3-step intervention was introduced based on Lean management: step 1) simplification (CLOSE protocol); step 2) waste elimination (higher power shorter duration); and step 3) improved standardization (Lab Optimization Tool [LOT]). PVI was divided into steps that were tracked (in minutes) using LOT. Parameters were compared in 6-month intervals.

RESULTS

Overall, 295 patients (146 patients with LOT) were analyzed. Step 1 reduced skin-to-skin procedure duration (2017: 119 ± 21 min vs. 2018: 77 ± 15 min; p < 0.001) and variance (from 2018 to 2019 p = 0.024). Step 2 reduced the radiofrequency time (2017: 38 ± 6 min vs. 2018: 20 ± 3 min; p < 0.001) and variance (from 2018 to 2019 p < 0.001). Analysis of step 3 demonstrated that only 53% of the entire procedure length (143 ± 22 min) was used for treatment (skin-to-skin time 77 ± 16 min), the remaining time being devoted for setup (42 ± 12 min, 29%); left atrial access (16 ± 7 min, 12%); respiratory gating, left atrial map, and pseudo-circle annotation (10 ± 6 min, 7%); ablation (39 ± 10 min, 27%); and bilateral block validation (10 ± 8 min, 7%).

CONCLUSIONS

Standardization of PVI using a dedicated ablation protocol and Lean management can help to reduce procedure and radiofrequency ablation duration and variance, and increase procedural efficiency without compromising safety. To improve health care utilization, increased efficiency should become an accepted goal in addition to procedural safety and effectiveness.

Impact of Micro-, Mini- and Multi-Electrode Mapping on Ventricular Substrate Characterisation

Accurate substrate characterisation may improve the evolving understanding and treatment of cardiac arrhythmias. During substrate-based ablation techniques, wide practice variations exist with mapping via dedicated multi-electrode catheter or conventional ablation catheters. Recently, newer ablation catheter technology with embedded mapping electrodes have been introduced. This article focuses on the general misconceptions of voltage mapping and more specific differences in unipolar and bipolar signal morphology, field of view, signal-to-noise ratio, mapping capabilities (density and resolution), catheter-specific voltage thresholds and impact of micro-, mini- and multi-electrodes for substrate mapping. Efficiency and cost-effectiveness of different catheter types are discussed. Increasing sampling density with smaller electrodes allows for higher resolution with a greater likelihood to record near-field electrical information. These advances may help to further improve our mechanistic understanding of the correlation between substrate and ventricular tachycardia, as well as macro-reentry arrhythmia in humans.

3D Electrophysiological Modeling of Interstitial Fibrosis Networks and Their Role in Ventricular Arrhythmias in Non-Ischemic Cardiomyopathy

OBJECTIVE

Interstitial fibrosis is a pathological expansion of the heart's inter-cellular collagen matrix. It is a potential complication of nonischemic cardiomyopathy (NICM), a class of diseases involving electrical and or mechanical dysfunction of cardiac tissue not caused by atherosclerosis. Patients with NICM and interstitial fibrosis often suffer from life threatening arrhythmias, which we aim to simulate in this study.

METHODS

Our methodology builds on an efficient discrete finite element (DFE) method which allows for the representation of fibrosis as infinitesimal splits in a mesh. We update the DFE method with a local connectivity analysis which creates a consistent topology in the fibrosis network. This is particularly important in nonischemic disease due to the potential presence of large and contiguous fibrotic regions and therefore potentially complex fibrosis networks.

RESULTS

In experiments with an image-based model, we demonstrate that our methodology is able to simulate reentrant electrical events associated with cardiac arrhythmias. These reentries depended crucially upon sufficient fibrosis density, which was marked by conduction slowing at high pacing rates. We also created a 2D test-case which demonstrated that fibrosis topologies can modulate transient conduction block, and thereby reentrant activations.

CONCLUSION

Ventricular arrhythmias due to interstitial fibrosis in NICM can be efficiently simulated using our methods in medical image based geometries. Furthermore, fibrosis topology modulates transient conduction block, and should be accounted for in electrophysiological simulations with interstitial fibrosis.

SIGNIFICANCE

Our study provides methodology which has the potential to predict arrhythmias and to optimize treatments non-invasively for nonischemic cardiomyopathies.

Role of cardiac imaging in patients undergoing catheter ablation of ventricular tachycardia

Ventricular tachycardia is a major health issue in patients with structural heart disease (SHD). Implantable cardioverter defibrillator (ICD) therapy has significantly reduced the risk of sudden cardiac death (SCD) in such patients, but on the other hand, it has led to frequent ICD shocks as an emerging problem, being associated with poor quality of life, frequent hospitalizations and increased mortality. Myocardial scar plays a central role in the genesis and maintenance of re-entrant arrhythmias, as the coexistence of surviving myocardial fibres within fibrotic tissue leads to the formation of slow conduction pathways and to a dispersion of activation and refractoriness that constitutes the milieu for ventricular tachycardia circuits. Catheter ablation has repeatedly proven to be well tolerated and highly effective in treating VT and in the last two decades has benefited from continuous efforts to determine ventricular tachycardia mechanisms by integration with a wide range of invasive and noninvasive imaging techniques such as intracardiac echocardiography, cardiac magnetic resonance, multidetector computed tomography and nuclear imaging. Cardiovascular imaging has become a fundamental aid in planning and guiding catheter ablation procedures by integrating structural and electrophysiological information, enabling the ventricular tachycardia arrhythmogenic substrate to be characterized and effective ablation targets to be identified with increasing precision, and allowing the development of new ablation strategies with improved outcomes. In this review, we provide an overview of the role of cardiac imaging in patients undergoing catheter ablation of ventricular tachycardia.

Mini-, Micro-, and Conventional Electrodes: An in Vivo Electrophysiology and Ex Vivo Histology Head-to-Head Comparison

OBJECTIVES

This study sought to assess the relative effect of catheter, tissue, and catheter-tissue parameters, on the ability to determine the amount of viable myocardium in vivo.

BACKGROUND

Although multiple variables impact bipolar voltages (BVs), electrode size, interelectrode spacing, and directional dependency are of particular interest with the development of catheters incorporating mini and microelectrodes.

METHODS

Nine swine with early reperfusion myocardial infarctions were mapped using the QDot catheter and then remapped using a Pentaray catheter. All QDot points were matched with Pentaray points within 5 mm. The swine were sacrificed, and mapping data projected onto the heart. Transmural biopsies corresponding to mapping points were obtained, allowing a comparison of electrograms recorded by mini, micro-, and conventional electrodes with histology.

RESULTS

The conventional BV of 2,322 QDot points was 1.9 ± 1.3 mV. The largest of the 3 microelectrode BVs (BV_µMax) average 4.8 ± 3.1 mV. The difference between the largest (BV_μMax) and smallest (BV_μMin) at a given location was 53.7 ± 18.1%. The relationships between both BV_μMax and BV_μMin and between the conventional BV and BV_μMax were positively related but with a significant spread in data, which was more pronounced for the latter. Pentaray points positively related to the BV_μMax with poor fit. On histology, increasing viable myocardium increased voltage, but both the slope coefficient and fit were best for BV_μMax.

CONCLUSIONS

Using histology, we could demonstrate that BV_μMax is superior to identify viable myocardium compared with BV_C and BV using the Pentaray catheter. The ability to simultaneously record 3 BV_μs with different orientations, for the same beat, with controllable contact and selecting BV_μMax for local BV may partially compensate for wave front direction.

Association of septal late gadolinium enhancement on cardiac magnetic resonance with ventricular tachycardia ablation targets in nonischemic cardiomyopathy

BACKGROUND

Ablation of septal substrate-associated ventricular tachycardia (VT) in patients with nonischemic cardiomyopathy (NICM) is challenging. We sought to standardize the characterization of septal substrates on late gadolinium enhancement (LGE) cardiac magnetic resonance (CMR) and to examine the association of that substrate with VT exit and isthmus sites on invasive mapping.

METHODS

LGE-CMR was performed before electroanatomic mapping and ablation for VT in 20 NICM patients. LGE extent and distribution were quantified using myocardial signal-intensity Z scores (SI-Z). The SI-Z thresholds correlating to previously validated voltage thresholds, for abnormal tissue and dense scar were defined.

RESULTS

Bipolar and unipolar (electrogram) voltage amplitude measurements from the LV and RV were negatively associated with SI-Z from LGE-CMR imaging (p < .05). SI-Z thresholds for appropriate CMR identification of septal substrates were determined to be greater than -.15 for border zone and greater than .03 for a dense scar. Among all patients, 34 critical VT sites were identified with SI-Z distribution in the range of -.97 to .06. Thirty (88.2%) critical sites were located in the dense LGE, 1 (2.9%) in the border zone, and 3 (8.9%) in healthy tissue but within 7 mm of LGE. Of note, critical VT sites were all located at the basal septum close to valves (distance to aortic valve: 17.5 ± 31.2 mm, mitral valve: 21.2 ± 8.7 mm) in nonsarcoidosis cases.

CONCLUSIONS

Critical sites of septal VT in NICM patients are predominantly in the CMR defined dense scar when using standardized signal-intensity thresholds.

2019 HRS/EHRA/APHRS/LAHRS expert consensus statement on catheter ablation of ventricular arrhythmias

Ventricular arrhythmias are an important cause of morbidity and mortality and come in a variety of forms, from single premature ventricular complexes to sustained ventricular tachycardia and fibrillation. Rapid developments have taken place over the past decade in our understanding of these arrhythmias and in our ability to diagnose and treat them. The field of catheter ablation has progressed with the development of new methods and tools, and with the publication of large clinical trials. Therefore, global cardiac electrophysiology professional societies undertook to outline recommendations and best practices for these procedures in a document that will update and replace the 2009 EHRA/HRS Expert Consensus on Catheter Ablation of Ventricular Arrhythmias. An expert writing group, after reviewing and discussing the literature, including a systematic review and meta-analysis published in conjunction with this document, and drawing on their own experience, drafted and voted on recommendations and summarized current knowledge and practice in the field. Each recommendation is presented in knowledge byte format and is accompanied by supportive text and references. Further sections provide a practical synopsis of the various techniques and of the specific ventricular arrhythmia sites and substrates encountered in the electrophysiology lab. The purpose of this document is to help electrophysiologists around the world to appropriately select patients for catheter ablation, to perform procedures in a safe and efficacious manner, and to provide follow-up and adjunctive care in order to obtain the best possible outcomes for patients with ventricular arrhythmias.

Prevalence and Prognostic Impact of Pathogenic Variants in Patients With Dilated Cardiomyopathy Referred for Ventricular Tachycardia Ablation

OBJECTIVES

This study aimed to assess the frequency of (likely) pathogenic variants (LP/Pv) among dilated cardiomyopathy (DCM) ventricular tachycardia (VT) patients referred for CA and their impact on procedural outcome and long-term prognosis.

BACKGROUND

The prevalence of genetic variants associated with monomorphic VT among DCM is unknown.

METHODS

Ninety-eight consecutive patients (age 56 ± 15 years; 84% men, left ventricular ejection fraction [LVEF] 39 ± 12%) referred for DCM-VT ablation were included. Patients underwent electroanatomical mapping and testing of ≥55 cardiomyopathy-related genes. Mapping data were analyzed for low-voltage areas and abnormal potentials. LP/Pv-positive (LP/Pv+) patients were compared with LP/Pv-negative (LP/Pv-) patients and followed for VT recurrence and mortality.

RESULTS

In 37 (38%) patients, LP/Pv were identified, most frequently LMNA (n = 11 of 37, [30%]), TTN (n = 6 of 37, [16%]), PLN (n = 6 of 37, [16%]), SCN5A (n = 3 of 37, [8%]), RBM20 (n = 2 of 37, [5%]) and DSP (n = 2 of 37, [5%]). LP/Pv+ carriers had lower LVEF (35 ± 13% vs. LP/Pv-: 42 ± 11%; p = 0.005) and were less often men (n = 27 [73%] vs. n = 55 [90%]; p = 0.03). After a median follow-up of 2.4 years (interquartile range: 0.9 to 4.4 years), 63 (64%) patients had VT recurrence (LP/Pv+: 30 of 37 [81%] vs. LP/Pv-: 33 of 61 [54%]; p = 0.007). Twenty-eight patients (29%) died (LP/Pv+: 19 of 37 [51%] vs. LP/Pv-: 9 of 61 [15%]; p < 0.001). The cumulative 2-year VT-free survival was 41% in the total cohort (LP/Pv+: 16% vs. LP/Pv-: 54%; p = 0.001). The presence of LP/Pv (hazard ratio: 1.9; 95% confidence interval: 1.1 to 3.4; p = 0.02) and unipolar low-voltage area size/cm² increase (hazard ratio: 2.5; 95% confidence interval: 1.6 to 4.0; p < 0.001) were associated with a decreased 2-year VT-free survival.

CONCLUSIONS

In patients with DCM-VT, a genetic cause is frequently identified. LP/Pv+ patients have a lower LVEF and more extensive VT substrates, which, in combination with disease progression, may contribute to the poor prognosis. Genetic testing in patients with DCM-VT should therefore be recommended.

Myocardial Fibrosis in a 3D Model: Effect of Texture on Wave Propagation

Non-linear electrical waves propagate through the heart and control cardiac contraction. Abnormal wave propagation causes various forms of the heart disease and can be lethal. One of the main causes of abnormality is a condition of cardiac fibrosis, which, from mathematical point of view, is the presence of multiple non-conducting obstacles for wave propagation. The fibrosis can have different texture which varies from diffuse (e.g., small randomly distributed obstacles), patchy (e.g., elongated interstitional stria), and focal (e.g., post-infarct scars) forms. Recently, Nezlobinsky et al. (2020) used 2D biophysical models to quantify the effects of elongation of obstacles (fibrosis texture) and showed that longitudinal and transversal propagation differently depends on the obstacle length resulting in anisotropy for wave propagation. In this paper, we extend these studies to 3D tissue models. We show that 3D consideration brings essential new effects; for the same obstacle length in 3D systems, anisotropy is about two times smaller compared to 2D, however, wave propagation is more stable with percolation threshold of about 60% (compared to 35% in 2D). The percolation threshold increases with the obstacle length for the longitudinal propagation, while it decreases for the transversal propagation. Further, in 3D, the dependency of velocity on the obstacle length for the transversal propagation disappears.

A computational investigation into rate-dependant vectorcardiogram changes due to specific fibrosis patterns in non-ischæmic dilated cardiomyopathy

Patients with scar-associated fibrotic tissue remodelling are at greater risk of ventricular arrhythmic events, but current methods to detect the presence of such remodelling require invasive procedures. We present here a potential method to detect the presence, location and dimensions of scar using pacing-dependent changes in the vectorcardiogram (VCG). Using a clinically-derived whole-torso computational model, simulations were conducted at both slow and rapid pacing for a variety of scar patterns within the myocardium, with various VCG-derived metrics being calculated, with changes in these metrics being assessed for their ability to discern the presence and size of scar. Our results indicate that differences in the dipole angle at the end of the QRS complex and differences in the QRS area and duration may be used to predict scar properties. Using machine learning techniques, we were also able to predict the location of the scar to high accuracy, using only these VCG-derived rate-dependent changes as input. Such a non-invasive predictive tool for the presence of scar represents a potentially useful clinical tool for identifying patients at arrhythmic risk.

Long-Term Arrhythmic Risk Assessment in Biopsy-Proven Myocarditis

OBJECTIVES

This study sought to assess long-term arrhythmic risk in patients with myocarditis who received an implantable cardioverter-defibrillator (ICD).

BACKGROUND

The arrhythmic risk of patients with myocarditis overtime remains poorly known.

METHODS

The study enrolled 56 patients with biopsy-proven myocarditis who received an ICD for either primary (57%) or secondary prevention (43%) according to current guidelines. Clinical characteristics, biopsy findings, electrophysiological data from endocardial 3-dimensional electroanatomic voltage mapping, and device interrogation data were analyzed to detect arrhythmic events overtime. Coronary angiography excluded significant coronary artery disease in all patients.

RESULTS

At a mean follow-up of 74 ± 60 months (median 65 months), 25 (45%) patients had major ventricular arrhythmias treated by ICD intervention (76% being terminated by ICD shock and 24% by antitachyarrhythmia burst pacing). At multivariable analysis, the presence of sustained ventricular tachycardia on admission (hazard ratio: 13.0; 95% confidence interval: 2.0 to 35.0; p = 0.032) and the extension of the areas of low potentials at the bipolar endocardial mapping (hazard ratio: 1.19; 95% confidence interval: 1.04 to 1.37; p = 0.013) were the only independent predictors of appropriate ICD interventions. A cutoff value of 10% of abnormal bipolar area at electroanatomical ventricular mapping discriminated patients with appropriate ICD interventions with a sensitivity of 89% and a specificity of 85%.

CONCLUSIONS

The study demonstrates that the prevalence of life-threatening ventricular arrhythmias in patients with myocarditis receiving an ICD according to current guidelines is high and the arrhythmic risk persists late overtime. Electroanatomical ventricular mapping may be a useful tool to identify patients at greater arrhythmic risk.

Multimodality Imaging to Guide Ventricular Tachycardia Ablation in Patients with Non-ischaemic Cardiomyopathy

Catheter ablation is an effective treatment option for ventricular tachycardia (VT) in patients with non-ischaemic cardiomyopathy (NICM). The heterogeneous nature of NICM aetiologies and VT substrate in patients with NICM play a role in long-term ablation outcomes in this population. Over the past decades, more precise identification of NICM aetiologies and better characterisation of various substrates have been made. Application of multimodal imaging has greatly contributed to the accurate diagnosis of NICM subtypes and improved VT ablation strategies. This article summarises the current knowledge of multimodal imaging used in the characterisation of non-ischaemic NICM substrates, procedural planning and image integration for the optimisation of VT ablation.

Anisotropic conduction in the myocardium due to fibrosis: the effect of texture on wave propagation

Cardiac fibrosis occurs in many forms of heart disease. It is well established that the spatial pattern of fibrosis, its texture, substantially affects the onset of arrhythmia. However, in most modelling studies fibrosis is represented by multiple randomly distributed short obstacles that mimic only one possible texture, diffuse fibrosis. An important characteristic feature of other fibrosis textures, such as interstitial and patchy textures, is that fibrotic inclusions have substantial length, which is suggested to have a pronounced effect on wave propagation. In this paper, we study the effect of the elongation of inexcitable inclusions (obstacles) on wave propagation in a 2D model of cardiac tissue described by the TP06 model for human ventricular cells. We study in detail how the elongation of obstacles affects various characteristics of the waves. We quantify the anisotropy induced by the textures, its dependency on the obstacle length and the effects of the texture on the shape of the propagating wave. Because such anisotropy is a result of zig-zag propagation we show, for the first time, quantification of the effects of geometry and source-sink relationship, on the zig-zag nature of the pathway of electrical conduction. We also study the effect of fibrosis in the case of pre-existing anisotropy and introduce a procedure for scaling of the fibrosis texture. We show that fibrosis can decrease or increase the preexisting anisotropy depending on its scaled texture.

Ventricular Tachycardia Ablation in Non-ischemic Cardiomyopathy

Non-ischemic cardiomyopathies are a heterogeneous group of diseases of the myocardium that have a distinct proclivity to ventricular arrhythmias. Of these, ventricular tachycardias pose significant management challenges with the risk of sudden cardiac death and morbidity from multiple causes. Catheter ablation of ventricular tachycardias is becoming an increasingly utilised intervention that has been found to have significant benefits with improving symptoms, reducing anti-arrhythmic drug burden and debilitating device therapies, thereby improving quality of life. Nonetheless, the approach to the ablation of ventricular tachycardias in non-ischemic cardiomyopathies is governed heavily by the disease process, with several distinct differences from ischemic cardiomyopathy including a preponderance to epicardial and deep intramural substrate. This contemporary review aims to present the various disease processes within non-ischemic cardiomyopathies, catheter ablation techniques which have been developed to target ventricular tachycardia and more novel adjunctive therapeutic measures.

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

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

Mapping and Ablation of Ventricular Arrhythmias in Cardiomyopathies

Mapping and ablation of ventricular arrhythmias in patients with nonischemic cardiomyopathies remain a major challenge. The electroanatomic abnormalities are frequently inaccessible to conventional endocardial ablations. Diagnostic diligence with a thorough understanding of the potential mechanisms/substrate, coupled with detailed electroanatomic mapping, is essential. Careful procedural planning, advanced imaging, and unipolar recordings help to formulate ablation strategy, facilitate work flow, and improve outcomes. Inaccessibility of arrhythmogenic substrate and disease progression are important causes of ablation failure. Early intervention may help to improve outcome and minimize complications. Several novel adjunctive ablation techniques are capable of serving as alternative options in refractory cases.

Sustained Monomorphic Ventricular Tachycardia in Nonischemic Heart Disease

As the population of patients with implanted defibrillators has grown, an increasing number of patients nonischemic cardiomyopathies are requiring therapy to reduce ventricular arrhythmias. Most of these arrhythmias are related to areas of ventricular scar. Although the pathophysiology of scar development is not well understood in these diseases, advances in cardiac imaging and mapping are better characterizing the scar locations that give rise to the arrhythmias. Here, we review the pathophysiologic and electrocardiographic correlations that inform ablation strategies for ventricular tachycardia in these diseases.

Scar shape analysis and simulated electrical instabilities in a non-ischemic dilated cardiomyopathy patient cohort

This paper presents a morphological analysis of fibrotic scarring in non-ischemic dilated cardiomyopathy, and its relationship to electrical instabilities which underlie reentrant arrhythmias. Two dimensional electrophysiological simulation models were constructed from a set of 699 late gadolinium enhanced cardiac magnetic resonance images originating from 157 patients. Areas of late gadolinium enhancement (LGE) in each image were assigned one of 10 possible microstructures, which modelled the details of fibrotic scarring an order of magnitude below the MRI scan resolution. A simulated programmed electrical stimulation protocol tested each model for the possibility of generating either a transmural block or a transmural reentry. The outcomes of the simulations were compared against morphological LGE features extracted from the images. Models which blocked or reentered, grouped by microstructure, were significantly different from one another in myocardial-LGE interface length, number of components and entropy, but not in relative area and transmurality. With an unknown microstructure, transmurality alone was the best predictor of block, whereas a combination of interface length, transmurality and number of components was the best predictor of reentry in linear discriminant analysis.

Agreement between gadolinium-enhanced cardiac magnetic resonance and electro-anatomical maps in patients with non-ischaemic dilated cardiomyopathy and ventricular arrhythmias

AIMS

We sought to investigate the overlap between late gadolinium enhancement (LGE) in cardiac magnetic resonance (CMR) and electro-anatomical maps (EAM) of patients with non-ischaemic dilated cardiomyopathy (NIDCM) and how it relates with the outcomes after catheter ablation of ventricular arrhythmias (VA).

METHODS AND RESULTS

We identified 50 patients with NIDCM who received CMR and ablation for VA. Late gadolinium enhancement was detected in 16 (32%) patients, mostly in those presenting with sustained ventricular tachycardia (VT): 15 patients. Low-voltage areas (<1.5 mV) were observed in 23 (46%) cases; in 7 (14%) cases without evidence of LGE. Using a threshold of 1.5 mV, a good and partially good agreement between the bipolar EAM and LGE-CMR was observed in only 4 (8%) and 9 (18%) patients, respectively. With further adjustments of EAM to match the LGE, we defined new cut-off limits of median 1.5 and 5 mV for bipolar and unipolar maps, respectively. Most VT exits (12 out of 16 patients) were found in areas with LGE. VT exits were found in segments without LGE in two patients with VT recurrence as well as in two patients without recurrence, P = 0.77. In patients with VT recurrence, the LGE volume was significantly larger than in those without recurrence: 12% ± 5.8% vs. 6.9% ± 3.4%; P = 0.049.

CONCLUSIONS

In NIDCM, the agreement between LGE and bipolar EAM was fairly poor but can be improved with adjustment of the thresholds for EAM according to the amount of LGE. The outcomes were related to the volume of LGE.

Myofibrillolysis and fibrosis predicts myocardial insufficiency

Introduction

Cardiocyte myofibrillolysis and interstitial fibrosis belong to histopathological changes in cardiomyopathies, leading to heart failure.

Aim

To evaluate these changes in apical resection during left ventricular assist device (LVAD) implantation.

Material and methods

The studied group consisted of 40 patients with cardiomyopathy, and apical samples excised during left ventricular assist device implantation were studied (CM/VAD group, mean: 48.1 ±10 y/o). A control group consisted of 6 apical samples from healthy heart graft donors (mean: 29 ±2.3 years old). Area fraction (AF) was calculated for: fibrosis, cardiocytes with myofibrillolysis (MFL), non-myofibrillolytic cardiocytes (non-MFL).

Results

Single lymphocytes were seen in 18 (45%) cases in the CM/VAD group. Cardiomyopathy grade evaluated semiquantitatively in CM/VAD was: slight (25% of a group), moderate (35.5%), advanced (35.5%). CM/VAD cases showed nearly ten times higher fibrosis than the control group. The MFL cells occupied nearly a five times larger area in CM/VAD than in the control group, whereas non-MFL cells were found in the control group, as a predominant pattern. The linear regression calculated between fibrosis AF and types of cardiocytes indicated the depletion of cardiomyocytes with fibrosis increase. The control group presented insignificant dependency between fibrosis and MFL cells, suggesting the lack of replacement fibrosis. Significant negative dependence between fibrosis and non-MFL cardiocytes suggested remodeling in controls. Correlation analysis showed a strong relation between depletion of normal cardiocytes and progression of fibrosis.

Conclusions

Progression of cardiomyopathy and fibrosis depends on the loss of cardiocytes rather than degeneration of these cells.

The Role of Cardiac MRI in the Management of Ventricular Arrhythmias in Ischaemic and Non-ischaemic Dilated Cardiomyopathy

Ventricular tachycardia (VT) and VF account for the majority of sudden cardiac deaths worldwide. Treatments for VT/VF include anti-arrhythmic drugs, ICDs and catheter ablation, but these treatments vary in effectiveness and carry substantial risks and/or expense. Current methods of selecting patients for ICD implantation are imprecise and fail to identify some at-risk patients, while leading to others being overtreated. In this article, the authors discuss the current role and future direction of cardiac MRI (CMRI) in refining diagnosis and personalising ventricular arrhythmia management. The capability of CMRI with gadolinium contrast delayed-enhancement patterns and, more recently, T1 mapping to determine the aetiology of patients presenting with heart failure is well established. Although CMRI imaging in patients with ICDs can be challenging, recent technical developments have started to overcome this. CMRI can contribute to risk stratification, with precise and reproducible assessment of ejection fraction, quantification of scar and 'border zone' volumes, and other indices. Detailed tissue characterisation has begun to enable creation of personalised computer models to predict an individual patient's arrhythmia risk. When patients require VT ablation, a substrate-based approach is frequently employed as haemodynamic instability may limit electrophysiological activation mapping. Beyond accurate localisation of substrate, CMRI could be used to predict the location of re-entrant circuits within the scar to guide ablation.

2019 HRS/EHRA/APHRS/LAHRS expert consensus statement on catheter ablation of ventricular arrhythmias

Ventricular arrhythmias are an important cause of morbidity and mortality and come in a variety of forms, from single premature ventricular complexes to sustained ventricular tachycardia and fibrillation. Rapid developments have taken place over the past decade in our understanding of these arrhythmias and in our ability to diagnose and treat them. The field of catheter ablation has progressed with the development of new methods and tools, and with the publication of large clinical trials. Therefore, global cardiac electrophysiology professional societies undertook to outline recommendations and best practices for these procedures in a document that will update and replace the 2009 EHRA/HRS Expert Consensus on Catheter Ablation of Ventricular Arrhythmias. An expert writing group, after reviewing and discussing the literature, including a systematic review and meta-analysis published in conjunction with this document, and drawing on their own experience, drafted and voted on recommendations and summarized current knowledge and practice in the field. Each recommendation is presented in knowledge byte format and is accompanied by supportive text and references. Further sections provide a practical synopsis of the various techniques and of the specific ventricular arrhythmia sites and substrates encountered in the electrophysiology lab. The purpose of this document is to help electrophysiologists around the world to appropriately select patients for catheter ablation, to perform procedures in a safe and efficacious manner, and to provide follow-up and adjunctive care in order to obtain the best possible outcomes for patients with ventricular arrhythmias.

Three-dimensional myocardial scar characterization from the endocardium: Usefulness of endocardial unipolar electroanatomic mapping

Epicardial ablation may be required to eliminate ventricular tachycardia (VT) in patients with underlying structural heart disease. The decision to gain epicardial access is frequently based on the suspicion of an epicardial origin for the VT and/or presence of an arrhythmogenic substrate. Epicardial pathology and VT is frequently present in patients with nonischemic right and/or left cardiomyopathies even in the setting of modest or no endocardial bipolar voltage substrate. In this setting, unipolar voltage mapping from the endocardium serves to help identify midmyocardial and/or epicardial VT substrate. The additional value of endocardial unipolar mapping includes its usefulness to predict the clinical outcome after VT ablation, to determine the irreversibility of myocardial disease, and to guide endomyocardial biopsy procedures to specific areas of intramural scarring. In this review, we aim to provide a guide to the use of endocardial unipolar mapping and its appropriate interpretation in a variety of clinical situations.

Information theory to tachycardia therapy: electrogram entropy predicts diastolic microstructure of reentrant ventricular tachycardia

There is no known strategy to differentiate which multicomponent electrograms in sinus rhythm maintain reentrant ventricular tachycardia (VT). Low entropy in the voltage breakdown of a multicomponent electrogram can localize conditions suitable for reentry but has not been validated against the classic VT activation mapping. We examined whether low entropy in a late and diversely activated ventricular scar region characterizes and differentiates the diastolic path of VT and represents protected tissue channels devoid of side branches. Intraoperative bipolar electrogram (BiEGM) activation and entropy maps were obtained during sinus rhythm in 17 patients with ischemic cardiomyopathy and compared with diastolic activation paths of VT (total of 39 VTs). Mathematical modeling of a zigzag main channel with side branches was also used to further validate structural representation of low entropy in the ventricular scar. A median of one region per patient (range: 1–2 regions) was identified in sinus rhythm, in which BiEGMwith the latest mean activation time and adjacent minimum entropy were assembled together in a high-activation dispersion region. These regions accurately recognized diastolic paths of 34 VTs, often to multiple inducible VTs within a single individual arrhythmogenic region. In mathematical modeling, side branching from the main channel had a strong influence on the BiEGMcomposition along the main channel. The BiEGMobtained from a long unbranched channel had the lowest entropy compared with those with multiple side branches. In conclusion, among a population of multicomponent sinus electrograms, those that demonstrate low entropy and are delayed colocalize to critical long-protected channels of VT. This information is pertinent for planning VT ablation in sinus rhythm.

NEW & NOTEWORTHY Entropy is a measure to quantify breakdown in information. Electrograms from a protected tissue channel can only possess a few states in their voltage and thus less information. In contrast, current-load interactions from side branches in unprotected channels introduce a number of dissimilar voltage deflections and thus high information. We compare here a mapping approach based on entropy against a rigorous reference standard of activation mapping during VT and entropy was assessed in sinus rhythm.

Dynamical anchoring of distant arrhythmia sources by fibrotic regions via restructuring of the activation pattern

Rotors are functional reentry sources identified in clinically relevant cardiac arrhythmias, such as ventricular and atrial fibrillation. Ablation targeting rotor sites has resulted in arrhythmia termination. Recent clinical, experimental and modelling studies demonstrate that rotors are often anchored around fibrotic scars or regions with increased fibrosis. However, the mechanisms leading to abundance of rotors at these locations are not clear. The current study explores the hypothesis whether fibrotic scars just serve as anchoring sites for the rotors or whether there are other active processes which drive the rotors to these fibrotic regions. Rotors were induced at different distances from fibrotic scars of various sizes and degree of fibrosis. Simulations were performed in a 2D model of human ventricular tissue and in a patient-specific model of the left ventricle of a patient with remote myocardial infarction. In both the 2D and the patient-specific model we found that without fibrotic scars, the rotors were stable at the site of their initiation. However, in the presence of a scar, rotors were eventually dynamically anchored from large distances by the fibrotic scar via a process of dynamical reorganization of the excitation pattern. This process coalesces with a change from polymorphic to monomorphic ventricular tachycardia.

Rotors are waves of cardiac excitation like a tornado causing cardiac arrhythmia. Recent research shows that they are found in ventricular and atrial fibrillation. Burning (via ablation) the site of a rotor can result in the termination of the arrhythmia. Recent studies showed that rotors are often anchored to regions surrounding scar tissue, where part of the tissue still survived called fibrotic tissue. However, it is unclear why these rotors anchor to these locations. Therefore, in this work, we investigated why rotors are so abundant in fibrotic tissue with the help of computer simulations. We performed simulations in a 2D model of human ventricular tissue and in a patient-specific model of a patient with an infarction. We found that even when rotors are initially at large distances from the fibrotic region, they are attracted by this region, to finally end up at the fibrotic tissue. We called this process dynamical anchoring and explained how the process works.

Fibrosis Microstructure Modulates Reentry in Non-ischemic Dilated Cardiomyopathy: Insights From Imaged Guided 2D Computational Modeling

Aims: Patients who present with non-ischemic dilated cardiomyopathy (NIDCM) and enhancement on late gadolinium magnetic resonance imaging (LGE-CMR), are at high risk of sudden cardiac death (SCD). Further risk stratification of these patients based on LGE-CMR may be improved through better understanding of fibrosis microstructure. Our aim is to examine variations in fibrosis microstructure based on LGE imaging, and quantify the effect on reentry inducibility and mechanism. Furthermore, we examine the relationship between transmural activation time differences and reentry. Methods and Results: 2D Computational models were created from a single short axis LGE-CMR image, with 401 variations in fibrosis type (interstitial, replacement) and density, as well as presence or absence of reduced conductivity (RC). Transmural activation times (TAT) were measured, as well as reentry incidence and mechanism. Reentries were inducible above specific density thresholds (0.8, 0.6 for interstitial, replacement fibrosis). RC reduced these thresholds (0.3, 0.4 for interstitial, replacement fibrosis) and increased reentry incidence (48 no RC vs. 133 with RC). Reentries were classified as rotor, micro-reentry, or macro-reentry and depended on fibrosis micro-structure. Differences in TAT at coupling intervals 210 and 500ms predicted reentry in the models (sensitivity 89%, specificity 93%). A sensitivity analysis of TAT and reentry incidence showed that these quantities were robust to small changes in the pacing location. Conclusion: Computational models of fibrosis micro-structure underlying areas of LGE in NIDCM provide insight into the mechanisms and inducibility of reentry, and their dependence upon the type and density of fibrosis. Transmural activation times, measured at the central extent of the scar, can potentially differentiate microstructures which support reentry.