The circle of reentry: Characteristics of trigger-substrate interaction leading to sudden cardiac arrest

Sudden cardiac death is often caused by ventricular arrhythmias driven by reentry. Comprehensive characterization of the potential triggers and substrate in survivors of sudden cardiac arrest has provided insights into the trigger-substrate interaction leading to reentry. Previously, a “Triangle of Arrhythmogenesis”, reflecting interactions between substrate, trigger and modulating factors, has been proposed to reason about arrhythmia initiation. Here, we expand upon this concept by separating the trigger and substrate characteristics in their spatial and temporal components. This yields four key elements that are required for the initiation of reentry: local dispersion of excitability (e.g., the presence of steep repolarization time gradients), a critical relative size of the region of excitability and the region of inexcitability (e.g., a sufficiently large region with early repolarization), a trigger that originates at a time when some tissue is excitable and other tissue is inexcitable (e.g., an early premature complex), and which occurs from an excitable region (e.g., from a region with early repolarization). We discuss how these findings yield a new mechanistic framework for reasoning about reentry initiation, the “Circle of Reentry.” In a patient case of unexplained ventricular fibrillation, we then illustrate how a comprehensive clinical investigation of these trigger-substrate characteristics may help to understand the associated arrhythmia mechanism. We will also discuss how this reentry initiation concept may help to identify patients at risk, and how similar reasoning may apply to other reentrant arrhythmias

A Framework for Assessing the Effect of Cardiac and Respiratory Motion for Stereotactic Arrhythmia Radioablation Using a Digital Phantom With a 17-Segment Model: A STOPSTORM.eu Consortium Study

PURPOSE: The optimal motion management strategy for patients receiving stereotactic arrhythmia radioablation (STAR) for the treatment of ventricular tachycardia (VT) is not fully known. We developed a framework using a digital phantom to simulate cardiorespiratory motion in combination with different motion management strategies to gain insight into the effect of cardiorespiratory motion on STAR. METHODS AND MATERIALS: The 4-dimensional (4D) extended cardiac-torso (XCAT) phantom was expanded with the 17-segment left ventricular (LV) model, which allowed placement of STAR targets in standardized ventricular regions. Cardiac- and respiratory-binned 4D computed tomography (CT) scans were simulated for free-breathing, reduced free-breathing, respiratory-gating, and breath-hold scenarios. Respiratory motion of the heart was set to population-averaged values of patients with VT: 6, 2, and 1 mm in the superior-inferior, posterior-anterior, and left-right direction, respectively. Cardiac contraction was adjusted by reducing LV ejection fraction to 35%. Target displacement was evaluated for all segments using envelopes encompassing the cardiorespiratory motion. Envelopes incorporating only the diastole plus respiratory motion were created to simulate the scenario where cardiac motion is not fully captured on 4D respiratory CT scans used for radiation therapy planning. RESULTS: The average volume of the 17 segments was 6 cm 3 (1-9 cm 3). Cardiac contraction-relaxation resulted in maximum segment (centroid) motion of 4, 6, and 3.5 mm in the superior-inferior, posterior-anterior, and left-right direction, respectively. Cardiac contraction-relaxation resulted in a motion envelope increase of 49% (24%-79%) compared with individual segment volumes, whereas envelopes increased by 126% (79%-167%) if respiratory motion also was considered. Envelopes incorporating only the diastole and respiration motion covered on average 68% to 75% of the motion envelope. CONCLUSIONS: The developed LV-segmental XCAT framework showed that free-wall regions display the most cardiorespiratory displacement. Our framework supports the optimization of STAR by evaluating the effect of (cardio)respiratory motion and motion management strategies for patients with VT

Datasheet1_The circle of reentry: Characteristics of trigger-substrate interaction leading to sudden cardiac arrest.docx

Sudden cardiac death is often caused by ventricular arrhythmias driven by reentry. Comprehensive characterization of the potential triggers and substrate in survivors of sudden cardiac arrest has provided insights into the trigger-substrate interaction leading to reentry. Previously, a “Triangle of Arrhythmogenesis”, reflecting interactions between substrate, trigger and modulating factors, has been proposed to reason about arrhythmia initiation. Here, we expand upon this concept by separating the trigger and substrate characteristics in their spatial and temporal components. This yields four key elements that are required for the initiation of reentry: local dispersion of excitability (e.g., the presence of steep repolarization time gradients), a critical relative size of the region of excitability and the region of inexcitability (e.g., a sufficiently large region with early repolarization), a trigger that originates at a time when some tissue is excitable and other tissue is inexcitable (e.g., an early premature complex), and which occurs from an excitable region (e.g., from a region with early repolarization). We discuss how these findings yield a new mechanistic framework for reasoning about reentry initiation, the “Circle of Reentry.” In a patient case of unexplained ventricular fibrillation, we then illustrate how a comprehensive clinical investigation of these trigger-substrate characteristics may help to understand the associated arrhythmia mechanism. We will also discuss how this reentry initiation concept may help to identify patients at risk, and how similar reasoning may apply to other reentrant arrhythmias.</p

Catheter ablation in highly symptomatic Brugada patients: a Dutch case series

Aims: In the past few years, promising results were described in targeting the arrhythmogenic substrate of the epicardial right ventricular outflow tract (RVOT) region in patients with Brugada syndrome (BrS). In this report, we describe our experience with endo- and epicardial substrate mapping and ablation in a series of highly symptomatic BrS patients. Methods: This case series consists of seven patients with clinical BrS diagnosis who underwent catheter ablation in two Dutch hospitals (Isala hospital Zwolle; and Amsterdam University Medical Centre, location AMC, Amsterdam) and Hamad Heart Hospital in Qatar between 2013 and 2017. All patients had an ICD and recurrent ventricular arrhythmia (VA) episodes. All patients underwent endo-and epicardial mapping of the RVOT region. Elimination of all abnormal potentials and disappearance of BrS ECG pattern during the ablation procedure was the aimed endpoint. Results: The study group consisted of seven patients with mean age 45.6 ± 16.9 years. Five patients had SCN5A mutations. One patient was excluded from analysis, since ablation could not be performed due to a very large low-voltage area and was later diagnosed with arrhythmogenic right ventricular cardiomyopathy, associated with an SCN5A mutation. One patient underwent both endo- and epicardial ablation to eliminate VA. During a mean follow-up of 3.6 ± 1.5 years, 5/6 patients remained VA free with two patients continuing quinidine. Conclusion: In patients with BrS and drug-refractory VA, ablation of the arrhythmogenic substrate in the RVOT region was associated with excellent long-term VA-free survival. The majority of these highly symptomatic BrS patients had an SCN5A mutation and also low-voltage areas epicardially. Graphic abstract: [Figure not available: see fulltext.]

Juvenile-onset multifocal atrial arrhythmias, atrial standstill and compound heterozygosity of genetic variants in TAF1A:sentinel event for evolving dilated cardiomyopathy-a case report

Background Juvenile onset of extensive atrial electromechanical failure, including atrial standstill, is a rare disease entity that may precede ventricular cardiomyopathy. Genetic variants associated with early-onset atrioventricular (AV) cardiomyopathy are increasingly recognized.Case summary A 16-year-old patient presented with atrial brady- and tachyarrhythmias and concomitant impaired atrial electromechanical function (atrial standstill). The atrial phenotype preceded the development of a predominantly right-sided AV dilated cardiomyopathy with pronounced myocardial fibrosis. A His-bundle pacemaker was installed for high-degree AV conduction block and sinus arrest. Using familial-based whole-exome sequencing, a missense mutation and a copy number variant deletion (compound heterozygosity) of the TAF1A gene (involved in ribosomal RNA synthesis) were identified.Discussion Juvenile onset of severe atrial electromechanical failure with atrial arrhythmias should prompt deep pheno- and genotyping and calls for vigilance for downstream cardiomyopathic deterioration

A framework for assessing the impact of cardiac and respiratory motion for STereotactic Arrhythmia Radioablation (STAR) using a digital phantom with a 17-segment model - A STOPSTORM.eu consortium study

The optimal motion management strategy for patients receiving stereotactic arrhythmia radioablation (STAR) for the treatment of ventricular tachycardia (VT) is not fully known. We developed a framework using a digital phantom to simulate cardiorespiratory motion in combination with different motion management strategies to gain insight into the impact of cardiorespiratory motion on STAR. The 4D XCAT phantom was expanded with the 17-segment left ventricular (LV) model which allowed placement of STAR targets in standardized ventricular regions. Cardiac- and respiratory-binned 4D-CT scans were simulated for free-breathing, reduced free-breathing, respiratory-gating, and breath-hold scenarios. Respiratory motion of the heart was set to population-averaged values of VT patients: 6, 2, and 1 mm in the Superior-Inferior, Posterior-Anterior, and Left-Right direction, respectively. Cardiac contraction was adjusted by reducing LV ejection fraction to 35%. Target displacement was evaluated for all segments using envelopes encompassing the cardiorespiratory motion. Envelopes incorporating only the diastole plus respiratory motion were created to simulate the scenario where cardiac motion is not fully captured on 4D-respiratory CT scans used for radiotherapy planning. The average volume of the 17 segments was 6 cm (1-9 cm ). Cardiac contraction-relaxation resulted in maximum segment (centroid) motion of 4, 6, and 3.5 mm in Superior-Inferior, Posterior-Anterior, and Left-Right direction, respectively. Cardiac contraction-relaxation resulted in a motion envelope increase of 49% (24-79%) compared to individual segment volumes, whereas envelopes increased by 126% (79-167%) if also respiratory motion was considered. Envelopes incorporating only the diastole and respiration motion covered on average 68-75% of the motion envelope. The developed LV-segmental XCAT framework showed that free-wall regions display the most cardiorespiratory displacement. Our framework supports the optimization of STAR by evaluating the impact of (cardio)respiratory motion and motion management strategies for VT patients

Noninvasive detection of spatiotemporal activation-repolarization interactions that prime idiopathic ventricular fibrillation

A comprehensive understanding of the interaction between triggers and electrical substrates leading to ventricular fibrillation (VF) and sudden cardiac arrest is lacking, and electrical substrates are difficult to detect and localize with current clinical tools. Here, we created repolarization time (RT) dispersion by regional drug infusion in perfused explanted human (n = 1) and porcine (n = 6) hearts and in a computational model of the human ventricle. Arrhythmia induction was tested with a single ventricular extrastimulus applied at the early or late RT region. Arrhythmias could only be induced from early RT regions. Vulnerability to VF increased with RT gradient steepness and with larger areas of early RT, but not with markers on the body-surface electrocardiogram. Noninvasive electrocardiographic imaging was performed in survivors of idiopathic VF (n = 11), patients with frequent premature ventricular complexes (PVCs) but no history of sudden cardiac arrest (n = 7), and controls (n = 10). In survivors of idiopathic VF, RT gradients were steeper than in controls, without differences in the clinical electrocardiogram, consistent with the ex vivo results. Patients with idiopathic VF also showed local myocardial regions with distinctly early-versus-late RT that were more balanced in size than in controls. Premature beats originated more often from the early RT regions in idiopathic VF survivors than in patients with frequent PVCs only. Thus, idiopathic VF emerges from the spatiotemporal interaction of a premature beat from an early-repolarization region with critical repolarization dispersion in that region. Electrocardiographic imaging can uncover the co-occurrence of these abnormalities

Rationale and Design of the ISOLATION Study:: A Multicenter Prospective Cohort Study Identifying Predictors for Successful Atrial Fibrillation Ablation in an Integrated Clinical Care and Research Pathway

Introduction: Continuous progress in atrial fibrillation (AF) ablation techniques has led to an increasing number of procedures with improved outcome. However, about 30-50% of patients still experience recurrences within 1 year after their ablation. Comprehensive translational research approaches integrated in clinical care pathways may improve our understanding of the complex pathophysiology of AF and improve patient selection for AF ablation. Objectives: Within the "IntenSive mOlecular and eLectropathological chAracterization of patienTs undergoIng atrial fibrillatiOn ablatioN " (ISOLATION) study, we aim to identify predictors of successful AF ablation in the following domains: (1) clinical factors, (2) AF patterns, (3) anatomical characteristics, (4) electrophysiological characteristics, (5) circulating biomarkers, and (6) genetic background. Herein, the design of the ISOLATION study and the integration of all study procedures into a standardized pathway for patients undergoing AF ablation are described. Methods: ISOLATION (NCT04342312) is a two-center prospective cohort study including 650 patients undergoing AF ablation. Clinical characteristics and routine clinical test results will be collected, as well as results from the following additional diagnostics: determination of body composition, pre-procedural rhythm monitoring, extended surface electrocardiogram, biomarker testing, genetic analysis, and questionnaires. A multimodality model including a combination of established predictors and novel techniques will be developed to predict ablation success. Discussion: In this study, several domains will be examined to identify predictors of successful AF ablation. The results may be used to improve patient selection for invasive AF management and to tailor treatment decisions to individual patient