Mechanisms Of Arrhythmias Research Articles

Generation of an iPSC cell line (VANYHHi001-A) from a patient with cardiac arrythmias carrying CACNA1D, SCN5A, and DSP variants

Progressive cardiac conduction defect often associated with variants in sodium voltage-gated channel SCN5A gene and variants in the L-type calcium voltage-gated channel CACNA1D gene are implicated in sinoatrial node dysfunction. We generated an induced pluripotent stem cell line (iPSC) from a 13-year-old patient with history of conduction system disease and ventricular tachycardia, carrying variants in SCN5A (c.2618C > G), CACNA1D (c.3786G > T), and DSP (c.1582C > G). The generated iPSC line exhibited pluripotency markers, differentiated into the three embryonic germ layers, and maintained a normal karyotype. This iPSC line offers insights into the pathophysiological mechanisms of cardiac arrhythmias and personalized therapies development.

Epidemiology, clinical characteristics and potential mechanism of ibrutinib-induced ventricular arrhythmias.

The Bruton's Tyrosine Kinase Inhibitor, ibrutinib, has been widely employed due to its significant efficacy in B-cell lymphoma. However, the subsequent cardiac complications, notably atrial fibrillation (AF) and ventricular arrhythmias (VAs),associated with ibrutinib treatment have emerged as a major concern in cardio-oncology and hematology. Ibrutinib-induced AF has been well described, whereas mechanisms of ibrutinib-induced VAs are still under-investigation. The incidence of ibrutinib-induced VAs can vary vastly due to under-recognition and limitations of the retrospective studies. Recent investigations, including our previous work, have proposed several potential mechanisms contributing to this adverse event, necessitating further validation. The development of effective strategies for the prevention and treatment of ibrutinib-induced VAs still requires in-depth exploration. This review aims to establish a comprehensive framework encompassing the epidemiology, mechanistic insights, and clinical considerations related to ibrutinib-induced VAs. This article outlines potential strategies for the clinical management of patients undergoing ibrutinib therapy based on suggested mechanisms.

Mechanisms and Implications of Electrical Heterogeneity in Cardiac Function in Ischemic Heart Disease.

A healthy heart shows intrinsic electrical heterogeneities that play a significant role in cardiac activation and repolarization. However, cardiac diseases may perturb the baseline electrical properties of the healthy cardiac tissue, leading to increased arrhythmic risk and compromised cardiac functions. Moreover, biological variability among patients produces a wide range of clinical symptoms, which complicates the treatment and diagnosis of cardiac diseases. Ischemic heart disease is usually caused by a partial or complete blockage of a coronary artery. The onset of the disease begins with myocardial ischemia, which can develop into myocardial infarction if it persists for an extended period. The progressive regional tissue remodeling leads to increased electrical heterogeneities, with adverse consequences on arrhythmic risk, cardiac mechanics, and mortality. This review aims to summarize the key role of electrical heterogeneities in the heart on cardiac function and diseases. Ischemic heart disease has been chosen as an example to show how adverse electrical remodeling at different stages may lead to variable manifestations in patients. For this, we have reviewed the dynamic electrophysiological and structural remodeling from the onset of acute myocardial ischemia and reperfusion to acute and chronic stages post-myocardial infarction. The arrhythmic mechanisms, patient phenotypes, risk stratification at different stages, and patient management strategies are also discussed. Finally, we provide a brief review on how computational approaches incorporate human electrophysiological heterogeneity to facilitate basic and translational research.

Gain-of-Function and Loss-of-Function Mutations in the RyR2-Expressing Gene Are Responsible for the CPVT1-Related Arrhythmogenic Activities in the Heart.

Mutations in the ryanodine receptor (RyR2) gene have been linked to arrhythmia and possibly sudden cardiac death (SCD) during acute emotional stress, physical activities, or catecholamine perfusion. The most prevalent disorder is catecholaminergic polymorphic ventricular tachycardia (CPVT1). Four primary mechanisms have been proposed to describe CPVT1 with a RyR2 mutation: (a) gain-of-function, (b) destabilization of binding proteins, (c) store-overload-induced Ca2+ release (SOICR), and (d) loss of function. The goal of this study was to use computational models to understand these four mechanisms and how they might contribute to arrhythmia. To this end, we have developed a local control stochastic model of a ventricular cardiac myocyte and used it to investigate how the Ca2+ dynamics in the mutant RyR2 are responsible for the development of an arrhythmogenic episode under the condition of β-adrenergic (β-AR) stimulation or pauses afterward. Into the model, we have incorporated 20,000 distinct cardiac dyads consisting of stochastically gated L-type Ca2+ channels (LCCs) and ryanodine receptors (RyR2s) and the intervening dyadic cleft to analyze the alterations in Ca2+ dynamics. Recent experimental findings were incorporated into the model parameters to test these proposed mechanisms and their role in triggering arrhythmias. The model could not find any connection between SOICR and the destabilization of binding proteins as the arrhythmic mechanisms in the mutant myocyte. On the other hand, the model was able to observe loss-of-function and gain-of-function mutations resulting in EADs (Early Afterdepolarizations) and variations in action potential amplitudes and durations as the precursors to generate arrhythmia, respectively. These computational studies demonstrate how GOF and LOF mutations can lead to arrhythmia and cast doubt on the feasibility of SOICR as a mechanism of arrhythmia.

Abstract 4137177: A pharmacovigilance investigation from the FAERS database on patients using pembrolizumab and its association with cardiac arrhythmias

Background: Arrhythmia is always a concern in oncological treatments. The advent of immune checkpoint inhibitors (ICIs) has revolutionized cancer treatment, enhancing the immune system's ability to combat malignancies. They are being more frequently used, revealing a range of immune-related adverse events (irAEs). This study aims to investigate the incidence of cardiac arrhythmias in patients receiving Pembrolizumab. Methods: We conducted a retrospective analysis of the FDA Adverse Event Reporting System (FAERS) database, focusing on reports submitted between 2006 to 2024. Cases involving patients treated with ICs were identified, and information related to cardiac arrhythmias was extracted using the Medical Dictionary for Regulatory Activities (MedDRA). Patients ≥ 18 years of age treated with ICIs were included in this study. A disproportionality analysis was conducted to identify arrhythmia events associated with pembrolizumab by comparing it with other immune checkpoint inhibitors (nivolumab, ipilimumab, and atezolizumab) and the entire FAERS database using the reporting odds ratio (ROR) and information component (IC). Results: A comprehensive analysis of 61,236 reported cases of pembrolizumab use revealed a total of 3,901 cases with cardiac complications. Among these, 672 cases (17.22 %) of arrhythmias were reported, with 452 individuals (67.26%) requiring hospitalization and 172 cases (25.59%) resulting in fatalities. Atrial fibrillation emerged as the most prevalent arrhythmia (49.7%). The occurrence of ventricular tachycardia with an ROR of 1.67 (1.18–2.35) and an IC of 0.44 (0.01–1.46) and complete atrio-ventricular block with an ROR of 1.57 (1.19–2.08) and an IC of 0.40 (0.04–1.24) were statistically significant. The reported arrhythmias associated with pembrolizumab are tabulated in Table 1 . The majority of events were reported in males, as shown in Figure 1 . Conclusion: This research offers significant insights into the connection between ICIs and cardiac arrhythmias, utilizing real-world data from the FAERS database. Healthcare providers should monitor cardiac events in patients receiving ICIs and aim to achieve a balance between anticancer effectiveness and cardiovascular safety. Further investigation is necessary to better understand the underlying mechanisms of arrhythmia and enhance risk stratification strategies for this specific patient group.

Desmin-related myopathy manifested by various types of arrhythmias: a case report and literature review.

Desmin is a type III intermediate filament protein specifically expressed in muscle cells, which is encoded by the DES gene. Defects in the desmin protein and cytoskeletal instability may interfere with cardiac muscle conduction signals, a fundamental mechanism for arrhythmias in patients with desmin-related myopathy. This current case report presents a female patient in her early 20s who presented with early-onset complete atrioventricular block and complete left bundle branch block over the previous decade. More recently, she had developed ventricular tachycardia, ventricular fibrillation, atrial fibrillation and other arrhythmias. Echocardiography revealed non-compaction of the ventricular myocardium and pulmonary hypertension. Whole-exome sequencing analysis identified a heterozygous missense mutation in the DES gene: c.1216C>T (p.Arg406Trp). She was eventually diagnosed with arrhythmias due to desmin-related myopathy. A literature review of international databases was undertaken to summarise the clinical characteristics of the cardiac involvement associated with this DES gene mutation.

Concealed cardiomyopathy as an emerging cause of sudden cardiac arrest and sudden cardiac death.

The inherited cardiomyopathies exhibit a broad spectrum of disease, with some patients remaining asymptomatic throughout life, while, for others, the first symptom of disease is sudden cardiac death at a young age. The risk of malignant ventricular arrhythmia in these conditions has traditionally been linked to the degree of structural myocardial abnormalities and functional impairment. However, recent advances in genetic testing and knowledge of the genetic basis of the diseases have led to the identification of concealed cardiomyopathy, in which sudden cardiac arrest or sudden cardiac death occurs in the absence of observable clinical features of cardiomyopathy, with a diagnosis being made only after the identification of a causative genetic variant. Increased awareness of concealed cardiomyopathy, a better understanding of mechanisms of arrhythmia and identification of risk modulators will be vital to improve care for families with concealed cardiomyopathy.

Aborted coumel sign: a novel diagnostic marker for arrhythmia mechanism recognition.

Aborted coumel sign: a novel diagnostic marker for arrhythmia mechanism recognition.

Biventricular modelling for investigating ventricular arrhythmias in silico

Abstract Background Ventricular arrhythmias have a significant incidence rate worldwide and may potentially lead to sudden cardiac death in severe cases. Despite therapeutic advancements, the intricate mechanisms dictating these arrhythmias remain elusive. Biventricular modelling and deep learning provide a way to investigate the complex electrophysiological substrates underlying cardiac arrhythmogenesis. Purpose This study aims to develop and validate a patient-specific biventricular computational modelling pipeline for simulating ventricular arrhythmias in silico. We provide a comprehensive platform for understanding the initiation, propagation, and treatment response of various ventricular arrhythmias. Methods To facilitate large-scale computational experiments and personalised model predictions within clinical timeframes, it is imperative to establish a rapid and reproducible modelling framework. First, we constructed biventricular volumetric models derived from late gadolinium-enhanced magnetic resonance imaging (LGE-MRI) data from the Cardiac Atlas Project (2018 Atria Segmentation Challenge), and then we calculate biventricular coordinates to facilitate data registration between measures, and fibre and fibrosis inclusion. We also apply the pipeline to cardiac magnetic resonance (CMR) data and electrocardiogram recordings from UK Biobank. Results We have successfully developed a pipeline for constructing biventricular volumetric models and efficiently processed biventricular coordinates (Figure). By systematically exploring interactions between ventricular regions, the model may identify critical factors contributing to arrhythmia susceptibility and guide personalised therapeutic strategies. Furthermore, the model may provide insights into the efficacy of antiarrhythmic interventions, ablation techniques, and device therapies, facilitating the development of precision medicine approaches. Conclusions We demonstrate a pipeline for constructing patient-specific biventricular computational models at scale from imaging data and apply this to LGE-MRI data and UK Biobank CMR data. These biventricular models enable investigation of the complex mechanisms of ventricular arrhythmias, providing novel insights for clinical decision-making and treatment strategies.

Macrophage-mediated interleukin-6 signaling drives ryanodine receptor-2 calcium leak in postoperative atrial fibrillation

Abstract Background Postoperative atrial fibrillation (poAF) is self-limited AF that occurs within days after cardiac surgery in one-third of patients. Clinical and preclinical studies have demonstrated that the magnitude of the perioperative increase in systemic inflammation, in particular mediated by interleukin (IL)-6, correlates with poAF risk. However, no studies to-date have mechanistically linked IL-6 signaling to fundamental arrhythmia mechanisms or identified the specific cell types driving postoperative atrial IL-6 signaling. Methods We performed single-cell RNA sequencing (scRNAseq), followed by pseudotime trajectory and cell-cell communication analyses on atrial non-myocytes comparing mice with and without poAF. We followed up our scRNAseq findings with pharmacologic and genetic approaches in mice to validate pathways related to macrophage-mediated IL-6 signaling. We used confocal imaging to assess calcium-signaling mechanisms at the single atrial cardiomyocyte (ACM) level and performed parallel patch-clamp studies in isolated human ACMs as well as biochemical analyses of human atrial tissue to assess the translational relevance of our findings. Results Our scRNAseq results demonstrated macrophages to be the most prominently altered cell type in the atria of mice with poAF. Pseudotime trajectory analyses revealed IL-6 to be one of the top inflammatory pathways implicated in macrophage transcriptional state. Indeed, both macrophage depletion and conditional knockout of IL-6 receptors in macrophages were sufficient to prevent poAF. We found that inhibition of STAT3, which is downstream of the IL-6Ra, with FDA-approved phospho-STAT3 inhibitor TTI-101 prevented poAF in mice. Lastly, we demonstrate that enhanced STAT3 activity in poAF promotes arrhythmogenic Ca2+ sparks and waves through ryanodine receptor-2 dysfunction, and that CaMKII inhibition is sufficient to ameliorate Ca2+ mishandling at the single atrial myocyte level. Conclusions Taken together, we use an integrated approach incorporating mouse and human biochemical, functional, and single-cell sequencing data to demonstrate that infiltrating atrial macrophages are fundamentally required for poAF. IL-6 was found to be a critical pathway upregulated in poAF leading to downstream ryanodine receptor-2 dysfunction and atrial arrhythmogenesis. Our findings portend significant therapeutic utility by providing robust mechanistic evidence that targeting the IL-6 axis may be used for poAF prevention and treatment in a clinically amenable timeframe.

Development and implementation of a guideline-based decision support system for etiological diagnosis of Sustained Monomorphic Ventricular Tachycardia (SMVT)

Abstract Background Guideline (GL)-based decision support systems (DSSs) play a significant role in supporting physicians in their decision-making processes by providing structured clinical guidance. While these systems have shown significant success in enhancing practitioner performance and patient outcomes in general practice, their application in the context of ventricular arrhythmias remains limited. Moreover, the clinical etiological diagnosis of ventricular arrhythmias presents various challenges for healthcare professionals, such as adherence to updated diagnostic criteria and understanding of complex arrhythmia mechanisms. Purpose In this study, we aim to design, implement, and evaluate a guideline-based decision support systems for etiological diagnosis of sustained monomorphic ventricular tachycardia (SMVT), which could potentially address critical challenges associated with the disease diagnosis and management. Methods To comprehensively capture the semantics embedded in clinical guidelines, we first developed a dedicated knowledge graph tailored to the clinical decision-making. This involved extracting entities and relationships pertinent to key decision procedures from ESC guidelines for ventricular arrhythmias, clinical textbooks or literatures. Subsequently, we translated instances within the knowledge graph into archetypes within openEHR, amplifying the interoperability of clinical information. To enhance the interpretability of the DSS, we established executable diagnostic and treatment processes to offer visual representation of clinical steps in diagnosis and treatment. Ultimately, we constructed a decision support engine to implement the GL-DSS, and its effectiveness was evaluated with anonymous real-world data. Results The proposed GL-DSS was found to be quite feasible and could provide etiological diagnosis for SMVT. The knowledge base for the constructed GL-DDS included more than 2000 entities and relations, which played a vital role in representing disease pathogenesis. The proposed system can map the clinical entities to a set of openEHR archetypes, thus mitigate the interoperability issues of the hospital information systems and CDSS data integration. Also, this module improved system usability and ensured that guidelines could be easily translated and updated into decision support tools. Real-word medical records from 20 patient were collected for model evaluation, the results showed that the GL-DSS covered most of the entities and relations between diseases and diagnostic evidence recorded in clinical texts and achieved a diagnosis accuracy of 80%. Conclusions The results demonstrated that our proposed GL-DSS could completely and accurately capture the diagnostic information under the concrete EHR data. Thus, the implement decision support system could have the potential to improve clinical decision-making, patient care, and outcomes in this specialized medical domain.

An endogenous cholinergic system controls electrical conduction in the heart.

The cholinergic system is distributed in the nervous system, mediating electrical conduction through acetylcholine (ACh). This study aims to identify whether the heart possesses an intact endogenous cholinergic system and to explore its electrophysiological functions and relationship with arrhythmias in both humans and animals. The components of the heart's endogenous cholinergic system were identified by a combination of multiple molecular cell biology techniques. The relationship of this system with cardiac electrical conduction and arrhythmias was analysed through electrophysiological techniques. An intact cholinergic system including ACh, ACh transmitter vesicles, ACh transporters, ACh metabolic enzymes, and ACh receptors was identified in both human and mouse ventricular cardiomyocytes (VCs). The key components of the system significantly regulated the conductivity of electrical excitation among VCs. The influence of this system on electrical excitation conduction was further confirmed both in the mice with α4 or α7 nicotinic ACh receptors (nAChRs) knockouts and in the monolayers of human induced pluripotent stem cell-derived cardiomyocytes. Mechanistically, ACh induced an inward current through nAChRs to reduce the minimum threshold current required to generate an action potential in VCs, thereby enhancing the excitability that acts as a prerequisite for electrical conduction. Importantly, defects in this system were associated with fatal ventricular arrhythmias in both patients and mice. This study identifies an integrated cholinergic system inherent to the heart, rather than external nerves that can effectively control cardiac electrical conduction. The discovery reveals arrhythmia mechanisms beyond classical theories and opens new directions for arrhythmia research.

Arrhythmias in adult patients after Rastelli surgery: a single-centre experience.

Rastelli surgery is used for the correction of several CHDs. Although late-onset cardiac arrhythmias have emerged as a major complication after corrective surgeries, there is a paucity of data on arrhythmias after Rastelli surgery. This retrospective cohort study was conducted on patients who had undergone Rastelli surgery and have been followed at the adult CHD clinic at our hospital. A total of 55 patients (36.4% female, age 22.2 ± 6.4 years) were followed for a median period of 24.2 (20.6-31.0) years. Tachyarrhythmias occurred in 21 (38.4 %) patients (n = 15 for atrial tachycardia, 5 for ventricular tachycardia, and 1 for both atrial and ventricular tachycardia). Older age at surgery was significantly associated with the risk of tachyarrhythmias (P = 0.022). Bradyarrhythmia occurred in 12 (21.8%) patients and consisted of perioperative AV block (n = 5), late AV block (n = 1), and sinus node dysfunction (n = 6). Nine (16.4%) patients underwent catheter ablation. The mechanisms of atrial arrhythmias include cavotricuspid isthmus-dependent and surgical scar-dependent intra-atrial reentrant tachycardias. Among the three patients who underwent ablation for ventricular tachycardia, all circuits were dependent on the scar at the base of the right ventricle to pulmonary artery conduit. Median survival free from any event (arrhythmia, death, or heart failure) was 31.6 (28.1-35.1) years after Rastelli surgery. The prevalence of arrhythmias late after Rastelli surgery is substantial and increases in the second decade after surgery. Older age at surgery is associated with a higher prevalence of arrhythmias.

Interstitial fibrosis and arrhythmic mitral valve prolapse: Unraveling sex-based differences

Interstitial fibrosis as quantified by cardiovascular magnetic resonance (CMR) has been demonstrated in arrhythmic mitral valve prolapse (AMVP), a condition with known female predominance. Prior studies of interstitial fibrosis in AMVP have only included cases with significant mitral regurgitation (MR) or mitral annular disjunction (MAD), limiting our understanding of alternative arrhythmic mechanisms in mitral valve prolapse (MVP). We sought to evaluate the association between interstitial fibrosis and AMVP, regardless of MAD and without severe MR, while also investigating the contribution of sex to this association. We performed research-based contrast CMR in consecutive individuals with MVP between 2019 and 2022. Extracellular volume fraction (ECV%), a surrogate marker for interstitial fibrosis, was quantified using T1 mapping in the basal and mid-left ventricular slices. Replacement fibrosis was assessed using late gadolinium enhancement (LGE). AMVP was defined as MVP with frequent premature ventricular contractions and/or non-sustained/sustained ventricular tachycardia (VT) or fibrillation (VF). We identified 65 MVP cases without severe MR (30 [46%] women, 22 [34%] no/trace, 30 [44%] mild, and 13 [21%] moderate MR) and with adequate ECV% measurement. Among these, 38% were classified as AMVP, including two cases of aborted VF arrest, both in premenopausal females. Global ECV% was significantly higher in AMVP vs non-AMVP (31% [27-33] vs 27% [23-30], p=0.002). In the AMVP group, higher segmental ECV% was not limited to the inferolateral/inferior walls, typically subject to myocardial traction by the prolapsing leaflets/MAD but was more diffuse and involved atypical segments such as the anterior/anterolateral walls (p<0.05). The association between AMVP and global ECV% was driven by female sex (32% [30-34] vs 27% [25-30], p=0.002 in females; 28% [23-32] vs 26% [23-30], p=0.41 in males). ECV% remained independently associated with an increased risk of arrhythmic events, including VT/VF (p<0.01), even after adjustment for cardiovascular risk factors, MAD, and LGE (p<0.01). In MVP without significant MR, interstitial fibrosis by CMR is associated with an increased risk of arrhythmic events, suggesting a primary myopathic process. The selective association between interstitial fibrosis and AMVP in females may explain why severe arrhythmic complications are more prevalent among women.

Sinoatrial node function and the role of sinoatrial conduction in the typical atrial flutter substrate

BackgroundSinoatrial node (SAN) activation and sinoatrial conduction pathways (SACPs) have been assessed in animals but not in humans. ObjectivesWe used ultrahigh-density mapping and simulated models to characterize the SAN and to investigate whether slowed SAN conduction may contribute to the atrial flutter (AFL) substrate. MethodsTwenty-seven patients undergoing electrophysiologic procedures had right atrial mapping. SAN activation patterns and conduction block were analyzed. The interaction between the SAN and the intercaval line of block (LOB) was analyzed, and right atrial simulations with different degrees of block were created to investigate arrhythmia mechanisms. ResultsFifteen AFL patients and 12 reference patients were enrolled. SACPs were identified in all patients with sinus rhythm maps. An SAN-adjacent LOB was observed in AFL patients. SAN conduction velocity was slower in AFL vs reference (0.60 m/s [0.56–0.78 m/s] vs 1.13 m/s [1.00–1.21 m/s]; P = .0021). Coronary sinus paced maps displayed an intercaval LOB in AFL patients but not in reference patients, which was completed superiorly by the SAN-adjacent LOB. Corrected sinus node recovery time was longer in AFL patients (552.3 ± 182.9 ms vs 325.4 ± 138.3 ms; P < .006) and correlated with degree of intercaval block (r = 0.7236; P = .0003). Computer modeling supported an important role of SAN-associated block in the flutter substrate. ConclusionUltrahigh-density mapping accurately identifies SAN activation and SACPs. The LOB important for typical AFL was longer in AFL patients, and when partial, it was always present inferiorly and completed superiorly because of slowed conduction across the SAN. Corrected sinus node recovery time correlated with intercaval block, suggesting a role for SAN disease in the genesis of the typical AFL substrate.

Efficacy and safety of early postoperative ablation in patients with congenital heart disease

BackgroundPostoperative arrhythmias are most often transient and medically treated, but some patients may require electrophysiology study (EPS) and ablation. ObjectiveThe purpose of this study was to describe the efficacy and safety of early postoperative ablation. MethodsThis study presents a retrospective series of patients who underwent EPS within 12 months of surgery for congenital heart disease between 2000 and 2021. The procedural outcome included complete or partial success, empirical ablation or failure, and complications. The long-term outcome included arrhythmia recurrence and burden according to a 12-point clinical arrhythmia severity score (documented arrhythmia, arrhythmia severity, cardioversion, and antiarrhythmic medication). ResultsAmong 28,902 operations during the study period, 24 patients (0.1%) underwent EPS within 3 months of surgery and 26 (0.1%) 3–12 months after surgery. Most patients had great (n = 27 [50%]) or moderate (n = 21 [42%]) congenital heart disease complexity. Mechanisms of arrhythmias included intra-atrial reentrant tachycardia (n = 23 [46%]), ectopic atrial tachycardia (n = 13 [26%]), accessory pathway (n = 6 [12%]), atrioventricular nodal reentrant tachycardia (n = 7 [14%]), twin atrioventricular node (n = 1 [2%]), atrial fibrillation (n = 1 [2%]), junctional ectopic tachycardia (n = 1 [2%]), and ventricular tachycardia (n = 2 [4%]). The procedure was acutely successful in 41 patients (82%), empirical in 5 (10%), and unsuccessful in 4 (8%). Complications occurred in 4 (8%) patients (major in 1, moderate in 1, and minor in 2). The recurrence of arrhythmia was documented in 27 patients (54%), although the burden of arrhythmia was significantly reduced. ConclusionA minority of patients require early postoperative EPS and ablation. For those, the procedure can be performed with reasonable acute success and manageable morbidity even in critically ill patients with complex surgical anatomy.

Modeling Idiopathic Ventricular Fibrillation Using iPSC Cardiomyocytes and Computational Approaches: A Proof-of-Concept Study.

Idiopathic ventricular fibrillation (IVF) is an unrefined diagnosis representing a heterogeneous patient group without a structural or genetic definition. IVF treatment is not mechanistic-based due to the lack of experimental patient-models. We sought to create a methodology to assess cellular arrhythmia mechanisms for IVF as a proof-of-concept study. Using IVF patient-specific induced pluripotent stem cell-derived cardiomyocytes, we integrate electrophysiological optical mapping with computational modeling to characterize the cellular phenotype. This approach flips the traditional paradigm using a biophysically detailed computational model to solve the problem inversely. Insight into the cellular mechanisms of this patient's IVF phenotype could also serve as a therapeutic testbed.

Abstract We112: Volumetric imaging to recapitulate cardiac injury and arrhythmias

Advanced understanding of cardiac structure and function is crucial for uncovering the underlying mechanism of injury and arrhythmias. To explore cues to structural and functional abnormalities in extensively established animal models, we have developed optical imaging and computational methods tailored to investigate intact hearts of zebrafish and rodents at cellular resolution. Our cardiac light-field microscopy allows us to capture instantaneous dynamics such as calcium transients, irregular contraction, and blood flow at 200 volumes per second in zebrafish larvae 1 . To improve the spatial resolution and enable the study of rodent models, we have customized two light-sheet imaging systems. One system is empowered by the retrospective synchronization and machine learning for the study of contractile function and focal myocardial mechanics from end-systole to end-diastole 2 , while the other integrates tissue clearing and axially scanning approaches for the exploration of ventricular trabeculation and myocardial compaction 3 . These methods aim to overcome the trade-off in spatial resolution, imaging speed, field of view across the atria and ventricles with minimal photo-damage and maximal penetration depth, enabling long-term investigation of cardiac development and regenerative processes. To further interpret the large volume of datasets, we have customized a successive subspace learning and virtual reality-based platform for interactive image analysis 4 . Collectively, our multi-scale strategy has opened up new landscapes for exploring the cardiac micro-structure and contractile function, both in health and disease.

Abstract Or102: Macrophage-Mediated Interleukin-6 Signaling Drives Ryanodine Receptor-2 Calcium Leak in Postoperative Atrial Fibrillation

Postoperative atrial fibrillation (poAF) is self-limited AF that occurs days after cardiac surgery in one-third of patients. The degree of perioperative increase in systemic inflammation, particularly involving interleukin (IL)-6, correlates with poAF risk. However, no studies to-date have identified the cell types involved nor mechanistically linked IL-6 signaling to fundamental arrhythmia mechanisms. To study poAF, we developed a mouse model consisting of atrial pericardiectomy and transient aortic cross-clamping followed by intracardiac burst pacing on postoperative day three to assess poAF inducibility. Single-cell RNA sequencing of atrial non-myocytes revealed macrophages to be the most prominently altered atrial cell type – increased 2.4-fold ( P &lt;0.001) in mice with versus without poAF. Pseudotime trajectory analyses revealed IL-6 to be the top cytokine altered in macrophages, which we confirmed by western blot demonstrating a 1.7-fold ( P =0.012) increase in atrial IL-6 protein in mice with versus without poAF. Indeed, both macrophage depletion and conditional knockout of IL-6Ra in macrophages decreased poAF inducibility by 5.2-fold ( P =0.048) and 5.5-fold ( P =0.027), respectively. Downstream inhibition using an FDA-approved STAT3 inhibitor also rescued poAF (6.0-fold decrease, P =0.022). At the single atrial cardiomyocyte (ACM) level, IL-6 challenge led to a 6.3-fold ( P &lt;0.001) increase in calcium (Ca 2+ ) spark frequency after normalization to sarcoplasmic reticulum Ca 2+ load, indicative of ryanodine receptor-2 (RyR2) dysfunction. Indeed, RyR2 phosphorylation at Ser2814, the target of Ca 2+ /calmodulin-dependent protein kinase II (CaMKII), was increased in the atria of mice with poAF, and CaMKII inhibition was sufficient to rescue arrhythmogenic Ca 2+ sparks in ACMs from mice with poAF. We corroborated our findings in human ACMs and atrial tissue to demonstrate translational relevance. Taken together, we use an integrated approach incorporating mouse and human biochemical, functional, and single-cell sequencing data to demonstrate that infiltrating atrial macrophages, specifically IL-6Ra from macrophages, are fundamentally required for poAF development ( Fig. 1 ). Molecularly, enhanced atrial IL-6 signaling led to arrhythmogenic RyR2 dysfunction through CaMKII. Our findings portend therapeutic utility by providing mechanistic evidence that targeting the IL-6 axis may be used for poAF prevention and treatment in a clinically amenable timeframe.

Abstract Mo125: Translating ECG responses to drugs across sexes: model development and validation in the clinic

Background: Sex-based differences in cardiac electrophysiology and their potential to impact susceptibility to cardiac arrhythmia and response to treatment are widely recognized. For example, female sex is an independent risk factor for drug-induced Long QT syndrome, Torsade de Pointes, and sudden cardiac death. However, arrhythmia studies have been predominantly performed in males, thus limiting our understanding of sex-specific arrhythmia mechanisms and the development of sex-specific metrics for arrhythmia risk. Computational tools are a powerful approach for integrating sex differences across scales and studying such multi-level phenomena, accelerating challenging and costly human and animal experiments. Aim: To develop a quantitative tool that predicts drug-induced responses in female electrocardiogram (ECG) features based on ECG data collected in males (and vice versa). Methods: Male and female 1D cable models of ventricular cardiomyocytes were constructed by incorporating transmural heterogeneity and sex-specific parameterizations. We constructed populations of male and female models by randomly perturbing baseline parameters, and derived pseudo-ECGs from computed extracellular potentials. We then utilized lasso regression to map ECG features (QRS duration, QT interval, T-peak-end duration, and T-wave amplitude) extracted from the male pseudo-ECG onto the female ECG features (and vice versa) ( Fig 1 ). Results: Our simulated data-driven translator accurately predicted female pseudo-ECG features from male data in an independent simulated test set (R 2 &gt;0.95). This predictive capability was further assessed in an independent dataset simulating the effects of 95 drugs at different concentrations ( Fig 2A ), exhibiting an average translation error &lt;1% for the QT interval ( Fig 2B ). Proof-of-concept application to ECG data sourced from publicly available FDA-approved datasets, in patients of both sexes under various anti-arrhythmic drugs and drug combinations, demonstrates high accuracy ( Fig 3 ) and validates the translator's applicability to the clinic. Conclusions: Our findings underscore the translator's potential in conducting sex-specific cardiac safety and efficacy assessments, enhancing the precision of evaluations in females. We plan to expand our translator capability to predict sex-specific effects of perturbations, including physiological and pathophysiological stressors.