Heart-on-a-Chip Model with Integrated Extra- and Intracellular Bioelectronics for Monitoring Cardiac Electrophysiology under Acute Hypoxia

We demonstrated a bioelectronic heart-on-a-chip model for studying the effects of acute hypoxia on cardiac function. A microfluidic channel enabled rapid modulation of medium oxygenation, which mimicked the regimes induced by a temporary coronary occlusion and reversibly activated hypoxia-related transduction pathways in HL-1 cardiac model cells. Extracellular bioelectronics provided continuous readouts demonstrating that hypoxic cells experienced an initial period of tachycardia followed by a reduction in beat rate and eventually arrhythmia. Intracellular bioelectronics consisting of Pt nanopillars temporarily entered the cytosol following electroporation, yielding action potential (AP)-like readouts. We found that APs narrowed during hypoxia, consistent with proposed mechanisms by which oxygen deficits activate ATP-dependent K⁺ channels that promote membrane repolarization. Significantly, both extra- and intracellular devices could be multiplexed, enabling mapping capabilities unachievable by other electrophysiological tools. Our platform represents a significant advance toward understanding electrophysiological responses to hypoxia and could be applicable to disease modeling and drug development.

Balance Between Rapid Delayed Rectifier K+ Current and Late Na+ Current on Ventricular Repolarization: An Effective Antiarrhythmic Target?

BACKGROUND

Rapid delayed rectifier K+ current (IKr) and late Na+ current (INaL) significantly shape the cardiac action potential (AP). Changes in their magnitudes can cause either long or short QT syndromes associated with malignant ventricular arrhythmias and sudden cardiac death.

METHODS

Physiological self AP-clamp was used to measure INaL and IKr during the AP in rabbit and porcine ventricular cardiomyocytes to test our hypothesis that the balance between IKr and INaL affects repolarization stability in health and disease conditions.

RESULTS

We found comparable amount of net charge carried by IKr and INaL during the physiological AP, suggesting that outward K+ current via IKr and inward Na+ current via INaL are in balance during physiological repolarization. Remarkably, IKr and INaL integrals in each control myocyte were highly correlated in both healthy rabbit and pig myocytes, despite high overall cell-to-cell variability. This close correlation was lost in heart failure myocytes from both species. Pretreatment with E-4031 to block IKr (mimicking long QT syndrome 2) or with sea anemone toxin II to impair Na+ channel inactivation (mimicking long QT syndrome 3) prolonged AP duration (APD); however, using GS-967 to inhibit INaL sufficiently restored APD to control in both cases. Importantly, INaL inhibition significantly reduced the beat-to-beat and short-term variabilities of APD. Moreover, INaL inhibition also restored APD and repolarization stability in heart failure. Conversely, pretreatment with GS-967 shortened APD (mimicking short QT syndrome), and E-4031 reverted APD shortening. Furthermore, the amplitude of AP alternans occurring at high pacing frequency was decreased by INaL inhibition, increased by IKr inhibition, and restored by combined INaL and IKr inhibitions.

CONCLUSIONS

Our data demonstrate that IKr and INaL are counterbalancing currents during the physiological ventricular AP and their integrals covary in individual myocytes. Targeting these ionic currents to normalize their balance may have significant therapeutic potential in heart diseases with repolarization abnormalities. Visual Overview: A visual overview is available for this article.

Effectiveness of Implanted Cardiac Rhythm Recorders With Electrocardiographic Monitoring for Detecting Arrhythmias in Pregnant Women With Symptomatic Arrhythmia and/or Structural Heart Disease: A Randomized Clinical Trial

Importance

Arrhythmias are an important cause of maternal morbidity and mortality but remain difficult to diagnose.

Objective

To compare implantable loop recorder (ILR) plus 24-hour Holter electrocardiographic (ECG) monitoring with standard 24-hour Holter ECG monitoring alone in terms of acceptability, ability to identify significant arrythmias, and effect on management and pregnancy outcome in women who were symptomatic or at high risk of arrythmia because of underlying structural heart disease.

Design, Setting, and Participants

This single-center, prospective randomized clinical trial recruited 40 consecutive patients from the Cardiac Disease and Maternity Clinic at Groote Schuur Hospital in Cape Town, South Africa. Pregnant patients with symptoms of arrhythmia and/or structural heart disease at risk of arrhythmia were included.

Intervention

Patients were randomized to standard care (SC; 24-hour Holter ECG monitoring [n = 20]) or standard care plus ILR (SC-ILR; 24-hour Holter ECG monitoring plus ILR [n = 20]). Only 17 consented to ILR insertion, and the 3 who declined ILR were allocated to the SC group.

Main Outcomes and Measures

Arrhythmias considered included atrial fibrillation, atrial flutter, premature ventricular complexes, supraventricular tachycardia, ventricular tachycardia, or ventricular fibrillation.

Results

Among the 40 women in this trial, the mean (SD) age was 28.4 (5.5) years. Holter monitoring detected arrhythmias in 3 of 23 patients (13%) in the SC group and 4 of 17 patients (24%) in the SC-ILR group compared with 9 of 17 patients (53%) patients who had arrhythmias detected by ILR. Seven patients (4 with supraventricular tachycardia, 1 with premature ventricular complexes, and 2 with paroxysmal atrial fibrillation recorded by ILR) did not have arrhythmias detected by 24-hour Holter monitoring. Three of these 7 patients (43%) had a change in management as a result of their ILR recordings. There were no maternal deaths. However, the SC group had a significantly lower mean (SD) gestational stage at delivery (35 [5] weeks vs 38 [2], P = .04).

Conclusions and Relevance

The ILR was better than 24-hour Holter monitoring in detecting arrhythmias, which led to a change in management for a significant proportion of patients. Our findings suggest that ILR may be beneficial for pregnant women at risk of arrhythmia.

Trial Registration

ClinicalTrials.gov Identifier: NCT02249195.

Audiovisual telesupport system for cardiovascular catheter interventions: A preliminary report on the clinical implications

OBJECTIVES

This study aimed to validate the clinical implications of audiovisual telesupport system use.

BACKGROUND

An audiovisual telesupport system with supervisors has been effective in guiding procedures when surgeons have limited experience with the technique. However, cardiovascular catheter interventions using an audiovisual telesupport system has not been previously reported.

METHODS

Starting in September 2017, two cardiologists in Kamisu Saiseikai Hospital (Kamisu, Japan, with limited cardiologists) began performing cardiovascular catheter interventions using an audiovisual telesupport system. This system enabled them to perform catheter interventions with the support of advisors in the University of Tsukuba (Tsukuba, Japan). We retrospectively assessed procedure time and complications of percutaneous coronary intervention (PCI) and catheter ablation (CA).

RESULTS

In the first 10 months, 21 patients with coronary artery disease underwent PCI using this system. The mean procedure duration of PCI was 42 ± 10 min. Nine patients with tachyarrhythmia including supraventricular tachycardia (SVT), ventricular premature contraction (VPC), common atrial flutter, and paroxysmal atrial fibrillation (AF) underwent CA using this system. The mean CA procedure time was 134 ± 31 min for SVT, 100 ± 14 min for VPC, and 200 min for AF. All PCI and CA procedures were successfully performed without any complications.

CONCLUSIONS

The audiovisual telesupport system enabled cardiologists with limited human resources to provide safe and high-quality catheter interventions.

Conditions for the genesis of early afterdepolarization in a model of a ventricular myocyte

Early afterdepolarization (EAD) is a major arrhythmogenic factor in the long QT syndrome (LQTS), whose conditions for genesis have puzzled people for several decades. Here, we employ the phase I Luo-Rudy ventricular myocyte model to investigate EAD using methods from nonlinear dynamics and provide valuable insights into EAD genesis from a physical perspective. Two major results are obtained: (i) Sufficient parametric conditions for EAD are analytically determined and then used to analyze in detail the effects of the physiological parameters. (ii) The normal form of the Hopf bifurcation that leads to EAD is derived and then used to determine whether the Hopf bifurcation is subcritical or supercritical for EAD genesis and the corresponding amplitude and period of the EAD oscillation. Our work here paves the way for further studies of more complicated multi-scale dynamics of EAD and may lead to effective treatments for LQTS arrhythmias.

Electrocardiographic changes following intracranial haemorrhage: a retrospective cohort study

OBJECTIVE

To improve the understanding of the association between electrocardiographic (ECG) abnormalities and clinical outcomes of patients with all types of intracranial hemorrhage (ICH).

METHODS

A retrospective cohort study was conducted in a tertiary healthcare hospital on patients with ICH without cardiac disease or renal disease requiring dialysis. Demographic and clinical data were collected from hospital records. ECG record were obtained within 24 hours of presentation and prior to treatment. Records were interpreted for this study by a cardiologist blinded to other data.

RESULTS

Assessment of 291 patients (228 adults and 63 children) showed that subdural hemorrhage was the most common type of ICH (31.6%) followed by intraparenchymal hemorrhage (23.0%). ECG records were available for 98 patients. ECG abnormalities were most commonly nonspecific ST-segment changes (32.6%). In adults, history of neurological disease was associated with atrioventricular block (p=.004) and QTc prolongation (p=.041). Pediatric patients exhibited associations between ST-segment changes (p=.045) and sinus tachycardia (p=.027) and type of ICH. However, ECG changes were not statistically associated with clinical outcomes in adults or children.

CONCLUSION

Significant ECG changes frequently occurred in patients with all types of ICH but did not consistently predict the outcome in this study. Close observation of patients is still recommended to detect ECG changes that could affect the treatment.

Interleukin-33/suppression of tumorigenicity 2 (IL-33/ST2) axis in idiopathic inflammatory myopathies and its association with laboratory and clinical parameters: a pilot study

Idiopathic inflammatory myopathies (IIM) are rare connective tissue diseases, which can lead to internal organ involvement. IL-33/ST2 pathway is involved in the pathogenesis of numerous diseases including autoimmune disorders. IL-33 fulfils cardioprotective function, while soluble ST2 (sST2) is a decoy receptor that reduces protective impact of IL-33. The aim of the study was to evaluate the concentrations of sST2 and IL-33 in sera of patients with IIM and evaluate its associations with the clinical course of the disease. Patients with IIM as well as age- and sex-matched healthy controls were recruited. Concentrations of sST2 and IL-33 were assessed with ELISA in sera of both patients and controls. Patients were asked to fill in the questionnaires concerning clinical symptoms and physical functioning. Concentrations of sST2 and IL-33 were correlated with the results of laboratory tests and clinical symptoms. Concentrations of sST2 were significantly higher in IIM group than in healthy subjects (median sST2 in IIM 26.51 vs in healthy controls 21.39; p = 0.03). In the majority of patients, IL-33 concentrations did not exceed the detection limit. Anti-SRP-positive patients presented significantly higher concentrations of sST2 as compared to anti-SRP-negative patients (p = 0.04). In patients with anti-Ro52 antibodies, sST2 concentrations were significantly lower than in anti-Ro52-negative patients (p = 0.02). Concentrations of sST2 correlated with the degree of disability evaluated with Health Assessment Questionnaire. sST2 is increased in patients with IIM and its concentration correlates with the degree of disability. In patients with anti-SRP antibodies, levels of sST2 are exceptionally high.

Cardiac Mapping Systems: Rhythmia, Topera, EnSite Precision, and CARTO

Novel cardiac mapping systems allow a safe and highly accurate 3-D reconstruction of cardiac structures as well as fast and accurate visualization of cardiac arrhythmias. In addition, they are increasingly reducing the need for fluoroscopy in these procedures. The current state of the art, as well as the presentation of possible uses of individual systems and their limitations, is presented in this article. Cardiac mapping systems can significantly contribute to an optimal therapeutic decision making in invasive electrophysiology. This article introduces new developments of Rhythmia, Topera, EnSite Precision, and CARTO systems and provides a look ahead to the future.

A human embryonic stem cell reporter line for monitoring chemical-induced cardiotoxicity

AIMS

Human embryonic stem cells (hESCs) can be used to generate scalable numbers of cardiomyocytes (CMs) for studying cardiac biology, disease modelling, drug screens, and potentially for regenerative therapies. A fluorescence-based reporter line will significantly enhance our capacities to visualize the derivation, survival, and function of hESC-derived CMs. Our goal was to develop a reporter cell line for real-time monitoring of live hESC-derived CMs.

METHODS AND RESULTS

We used CRISPR/Cas9 to knock a mCherry reporter gene into the MYH6 locus of hESC lines, H1 and H9, enabling real-time monitoring of the generation of CMs. MYH6:mCherry+ cells express atrial or ventricular markers and display a range of cardiomyocyte action potential morphologies. At 20 days of differentiation, MYH6:mCherry+ cells show features characteristic of human CMs and can be used successfully to monitor drug-induced cardiotoxicity and oleic acid-induced cardiac arrhythmia.

CONCLUSION

We created two MYH6:mCherry hESC reporter lines and documented the application of these lines for disease modelling relevant to cardiomyocyte biology.

Electrocardiographic markers for the prediction of ventricular arrhythmias in patients with systemic sclerosis

SSc is an autoimmune disease characterized by microvascular damage, endothelial dysfunction and fibrosis of the skin and the internal organs. Cardiac manifestation in patients with SSc is one of the major organ involvements. Approximately 20% of SSc patients suffer from primary cardiovascular disease and another 20% may have secondary cardiac involvement. Although cardiac arrhythmias are mostly linked to myocardial fibrosis, atrioventricular conduction abnormalities are secondary to the fibrosis of the pulse conduction system. Despite the severe consequences of ventricular rhythm disturbances in patients with SSc, the exact role of electrocardiographic markers in the prediction of these arrhythmias has not yet been clearly elucidated. Therefore, the question is whether certain ECG parameters reflecting ventricular repolarization may help to recognize scleroderma patients with increased risk for ventricular arrhythmias and sudden cardiac death.

Reactive oxygen species and nitric oxide imbalances lead to in vivo and in vitro arrhythmogenic phenotype in acute phase of experimental Chagas disease

Chagas Disease (CD) is one of the leading causes of heart failure and sudden death in Latin America. Treatments with antioxidants have provided promising alternatives to ameliorate CD. However, the specific roles of major reactive oxygen species (ROS) sources, including NADPH-oxidase 2 (NOX2), mitochondrial-derived ROS and nitric oxide (NO) in the progression or resolution of CD are yet to be elucidated. We used C57BL/6 (WT) and a gp91PHOX knockout mice (PHOX-/-), lacking functional NOX2, to investigate the effects of ablation of NOX2-derived ROS production on the outcome of acute chagasic cardiomyopathy. Infected PHOX-/- cardiomyocytes displayed an overall pro-arrhythmic phenotype, notably with higher arrhythmia incidence on ECG that was followed by higher number of early afterdepolarizations (EAD) and 2.5-fold increase in action potential (AP) duration alternans, compared to AP from infected WT mice. Furthermore, infected PHOX-/- cardiomyocytes display increased diastolic [Ca2+], aberrant Ca2+ transient and reduced Ca2+ transient amplitude. Cardiomyocyte contraction is reduced in infected WT and PHOX-/- mice, to a similar extent. Nevertheless, only infected PHOX-/- isolated cardiomyocytes displayed significant increase in non-triggered extra contractions (appearing in ~75% of cells). Electro-mechanical remodeling of infected PHOX-/-cardiomyocytes is associated with increase in NO and mitochondria-derived ROS production. Notably, EADs, AP duration alternans and in vivo arrhythmias were reverted by pre-incubation with nitric oxide synthase inhibitor L-NAME. Overall our data show for the first time that lack of NOX2-derived ROS promoted a pro-arrhythmic phenotype in the heart, in which the crosstalk between ROS and NO could play an important role in regulating cardiomyocyte electro-mechanical function during acute CD. Future studies designed to evaluate the potential role of NOX2-derived ROS in the chronic phase of CD could open new and more specific therapeutic strategies to treat CD and prevent deaths due to heart complications.

Interplay between ephaptic coupling and complex geometry of border zone during acute myocardial ischemia: Effect on arrhythmogeneity

Acute myocardial ischemia is an imbalance between myocardial blood supply and demand, which is caused by the cessation of blood flow within the heart resulting from an obstruction in one of the major coronary arteries. A severe blockage may result in a region of nonperfused tissue known as ischemic core (IC). As a result, a border zone (BZ) between perfused and nonperfused regions is created due to differences in blood and oxygen supplies. Recent experimental findings reveal a complex "finger-like" geometry in BZ; however, its effect on arrhythmogenicity is not clear. Ephaptic coupling, which relies on the intercalated disk between cell ends, has been suggested to play an active role in mediating intercellular electrical communication when gap junctions are impaired. In this paper, we explored the interplay between ephaptic coupling and the geometry of BZ on action potential propagation across the ischemic region. Our study shows that ephaptic coupling can greatly suppress the occurrence of a conduction block, which points to its beneficial effect. The beneficial effect of ephaptic coupling is more evident in BZ with the "finger-like" geometry. In addition, the complex geometry of BZ, i.e., more frequent, deeper, and wider "fingers," promotes the conduction through the ischemic region. In contrast, the larger size of IC impedes the cardiac conduction across the ischemic region. Our results also show that ephaptic coupling promotes the impact of the complex geometry of BZ on signal propagation; however, it inhibits the impact of IC size.

Factors affecting the electrocardiographic QT interval in malaria: A systematic review and meta-analysis of individual patient data

BACKGROUND

Electrocardiographic QT interval prolongation is the most widely used risk marker for ventricular arrhythmia potential and thus an important component of drug cardiotoxicity assessments. Several antimalarial medicines are associated with QT interval prolongation. However, interpretation of electrocardiographic changes is confounded by the coincidence of peak antimalarial drug concentrations with recovery from malaria. We therefore reviewed all available data to characterise the effects of malaria disease and demographic factors on the QT interval in order to improve assessment of electrocardiographic changes in the treatment and prevention of malaria.

METHODS AND FINDINGS

We conducted a systematic review and meta-analysis of individual patient data. We searched clinical bibliographic databases (last on August 21, 2017) for studies of the quinoline and structurally related antimalarials for malaria-related indications in human participants in which electrocardiograms were systematically recorded. Unpublished studies were identified by the World Health Organization (WHO) Evidence Review Group (ERG) on the Cardiotoxicity of Antimalarials. Risk of bias was assessed using the Pharmacoepidemiological Research on Outcomes of Therapeutics by a European Consortium (PROTECT) checklist for adverse drug events. Bayesian hierarchical multivariable regression with generalised additive models was used to investigate the effects of malaria and demographic factors on the pretreatment QT interval. The meta-analysis included 10,452 individuals (9,778 malaria patients, including 343 with severe disease, and 674 healthy participants) from 43 studies. 7,170 (68.6%) had fever (body temperature ≥ 37.5°C), and none developed ventricular arrhythmia after antimalarial treatment. Compared to healthy participants, patients with uncomplicated falciparum malaria had shorter QT intervals (-61.77 milliseconds; 95% credible interval [CI]: -80.71 to -42.83) and increased sensitivity of the QT interval to heart rate changes. These effects were greater in severe malaria (-110.89 milliseconds; 95% CI: -140.38 to -81.25). Body temperature was associated independently with clinically significant QT shortening of 2.80 milliseconds (95% CI: -3.17 to -2.42) per 1°C increase. Study limitations include that it was not possible to assess the effect of other factors that may affect the QT interval but are not consistently collected in malaria clinical trials.

CONCLUSIONS

Adjustment for malaria and fever-recovery-related QT lengthening is necessary to avoid misattributing malaria-disease-related QT changes to antimalarial drug effects. This would improve risk assessments of antimalarial-related cardiotoxicity in clinical research and practice. Similar adjustments may be indicated for other febrile illnesses for which QT-interval-prolonging medications are important therapeutic options.

Effect of puerarin on action potential and sodium channel activation in human hypertrophic cardiomyocytes

OBJECTIVE

To study the effect of puerarin on electrophysiology using a hypertrophic cardiomyocyte (HC) model.

MATERIALS AND METHODS

Human urine epithelial cells were used to generate the HC model (hiPSC-CM). Cardiomyocyte hypertrophy was induced by applying 10 nM endothelin-1 (ET-1). Effects of puerarin pre-treatment (PPr) and post-treatment (PPo) on action potential, sodium current (INa) activation and inactivation, and recovery following INa inactivation were tested using patch clamp electrophysiology.

RESULTS

Depolarization to repolarization 50% time (APD50) and repolarization 30% time (APD30) were significantly prolonged in the PPo and PPr groups compared with the controls. However, there were no significant differences in the action potential depolarization amplitude (APA) or the maximum depolarization velocity (Vmax) in phase 0. The PPr group had a slightly shortened APD90, and an extended APD50 and APD30, but did not exhibit any significant changes in stage A of APA and Vmax. The PPo group did not exhibit any significant changes in INa, while 12 h of PPr improved INa. However, puerarin did not significantly affect the activation, inactivation, or recovery of the sodium channel.

CONCLUSIONS

Cardiomyocyte hypertrophy significantly decreased the Vmax of the action potential and the peak density of INa. PPr inhibited the decrease in Vmax and increased the peak density of INa. Thus, puerarin could be used to stabilize the electrophysiological properties of hypertrophic cardiomyocytes and reduce arrhythmias.

Ventricular divergence correlates with epicardial wavebreaks and predicts ventricular arrhythmia in isolated rabbit hearts during therapeutic hypothermia

INTRODUCTION

High beat-to-beat morphological variation (divergence) on the ventricular electrogram during programmed ventricular stimulation (PVS) is associated with increased risk of ventricular fibrillation (VF), with unclear mechanisms. We hypothesized that ventricular divergence is associated with epicardial wavebreaks during PVS, and that it predicts VF occurrence.

METHOD AND RESULTS

Langendorff-perfused rabbit hearts (n = 10) underwent 30-min therapeutic hypothermia (TH, 30°C), followed by a 20-min treatment with rotigaptide (300 nM), a gap junction modifier. VF inducibility was tested using burst ventricular pacing at the shortest pacing cycle length achieving 1:1 ventricular capture. Pseudo-ECG (p-ECG) and epicardial activation maps were simultaneously recorded for divergence and wavebreaks analysis, respectively. A total of 112 optical and p-ECG recordings (62 at TH, 50 at TH treated with rotigaptide) were analyzed. Adding rotigaptide reduced ventricular divergence, from 0.13±0.10 at TH to 0.09±0.07 (p = 0.018). Similarly, rotigaptide reduced the number of epicardial wavebreaks, from 0.59±0.73 at TH to 0.30±0.49 (p = 0.036). VF inducibility decreased, from 48±31% at TH to 22±32% after rotigaptide infusion (p = 0.032). Linear regression models showed that ventricular divergence correlated with epicardial wavebreaks during TH (p<0.001).

CONCLUSION

Ventricular divergence correlated with, and might be predictive of epicardial wavebreaks during PVS at TH. Rotigaptide decreased both the ventricular divergence and epicardial wavebreaks, and reduced the probability of pacing-induced VF during TH.

Inhibition of NaV1.8 prevents atrial arrhythmogenesis in human and mice

Pharmacologic approaches for the treatment of atrial arrhythmias are limited due to side effects and low efficacy. Thus, the identification of new antiarrhythmic targets is of clinical interest. Recent genome studies suggested an involvement of SCN10A sodium channels (Na_V1.8) in atrial electrophysiology. This study investigated the role and involvement of Na_V1.8 (SCN10A) in arrhythmia generation in the human atria and in mice lacking Na_V1.8. Na_V1.8 mRNA and protein were detected in human atrial myocardium at a significant higher level compared to ventricular myocardium. Expression of Na_V1.8 and Na_V1.5 did not differ between myocardium from patients with atrial fibrillation and sinus rhythm. To determine the electrophysiological role of Na_V1.8, we investigated isolated human atrial cardiomyocytes from patients with sinus rhythm stimulated with isoproterenol. Inhibition of Na_V1.8 by A-803467 or PF-01247324 showed no effects on the human atrial action potential. However, we found that Na_V1.8 significantly contributes to late Na⁺ current and consequently to an increased proarrhythmogenic diastolic sarcoplasmic reticulum Ca²⁺ leak in human atrial cardiomyocytes. Selective pharmacological inhibition of Na_V1.8 potently reduced late Na⁺ current, proarrhythmic diastolic Ca²⁺ release, delayed afterdepolarizations as well as spontaneous action potentials. These findings could be confirmed in murine atrial cardiomyocytes from wild-type mice and also compared to SCN10A^-/- mice (genetic ablation of Na_V1.8). Pharmacological Na_V1.8 inhibition showed no effects in SCN10A^-/- mice. Importantly, in vivo experiments in SCN10A^-/- mice showed that genetic ablation of Na_V1.8 protects against atrial fibrillation induction. This study demonstrates that Na_V1.8 is expressed in the murine and human atria and contributes to late Na⁺ current generation and cellular arrhythmogenesis. Blocking Na_V1.8 selectively counteracts this pathomechanism and protects against atrial arrhythmias. Thus, our translational study reveals a new selective therapeutic target for treating atrial arrhythmias.

Hypokalemia Promotes Arrhythmia by Distinct Mechanisms in Atrial and Ventricular Myocytes

RATIONALE

Hypokalemia occurs in up to 20% of hospitalized patients and is associated with increased incidence of ventricular and atrial fibrillation. It is unclear whether these differing types of arrhythmia result from direct and perhaps distinct effects of hypokalemia on cardiomyocytes.

OBJECTIVE

To investigate proarrhythmic mechanisms of hypokalemia in ventricular and atrial myocytes.

METHODS AND RESULTS

Experiments were performed in isolated rat myocytes exposed to simulated hypokalemia conditions (reduction of extracellular [K⁺] from 5.0 to 2.7 mmol/L) and supported by mathematical modeling studies. Ventricular cells subjected to hypokalemia exhibited Ca²⁺ overload and increased generation of both spontaneous Ca²⁺ waves and delayed afterdepolarizations. However, similar Ca²⁺-dependent spontaneous activity during hypokalemia was only observed in a minority of atrial cells that were observed to contain t-tubules. This effect was attributed to close functional pairing of the Na⁺-K⁺ ATPase and Na⁺-Ca²⁺ exchanger proteins within these structures, as reduction in Na⁺ pump activity locally inhibited Ca²⁺ extrusion. Ventricular myocytes and tubulated atrial myocytes additionally exhibited early afterdepolarizations during hypokalemia, associated with Ca²⁺ overload. However, early afterdepolarizations also occurred in untubulated atrial cells, despite Ca²⁺ quiescence. These phase-3 early afterdepolarizations were rather linked to reactivation of nonequilibrium Na⁺ current, as they were rapidly blocked by tetrodotoxin. Na⁺ current-driven early afterdepolarizations in untubulated atrial cells were enabled by membrane hyperpolarization during hypokalemia and short action potential configurations. Brief action potentials were in turn maintained by ultra-rapid K⁺ current (I_Kur); a current which was found to be absent in tubulated atrial myocytes and ventricular myocytes.

CONCLUSIONS

Distinct mechanisms underlie hypokalemia-induced arrhythmia in the ventricle and atrium but also vary between atrial myocytes depending on subcellular structure and electrophysiology.

Bringing Critical Race Praxis Into the Study of Electrophysiological Substrate of Sudden Cardiac Death: The ARIC Study

Background Race is an established risk factor for sudden cardiac death (SCD). We sought to determine whether the association of electrophysiological substrate with SCD varies between black and white individuals. Methods and Results Participants from the ARIC (Atherosclerosis Risk in Communities) study with analyzable ECGs (n=14 408; age, 54±6 years; 74% white) were included. Electrophysiological substrate was characterized by ECG metrics. Two competing outcomes were adjudicated: SCD and non-SCD. Interaction of ECG metrics with race was studied in Cox proportional hazards and Fine-Gray competing risk models, adjusted for prevalent cardiovascular disease, risk factors, and incident nonfatal cardiovascular disease. At the baseline visit, adjusted for age, sex, and study center, blacks had larger spatial ventricular gradient magnitude (0.30 mV; 95% CI, 0.25-0.34 mV), sum absolute QRST integral (18.4 mV*ms; 95% CI, 13.7-23.0 mV*ms), and Cornell voltage (0.30 mV; 95% CI, 0.25-0.35 mV) than whites. Over a median follow-up of 24.4 years, SCD incidence was higher in blacks (2.86 per 1000 person-years; 95% CI, 2.50-3.28 per 1000 person-years) than whites (1.37 per 1000 person-years; 95% CI, 1.22-1.53 per 1000 person-years). Blacks with hypertension had the highest rate of SCD: 4.26 (95% CI, 3.66-4.96) per 1000 person-years. Race did not modify an association of ECG variables with SCD, except QRS-T angle. Spatial QRS-T angle was associated with SCD in whites (hazard ratio, 1.38; 95% CI, 1.25-1.53) and hypertension-free blacks (hazard ratio, 1.52; 95% CI, 1.09-2.12), but not in blacks with hypertension (hazard ratio, 1.15; 95% CI, 0.99-1.32) (P-interaction=0.004). Conclusions Race did not modify associations of electrophysiological substrate with SCD and non-SCD. Electrophysiological substrate does not explain racial disparities in SCD rate.

Acute interaction between human epicardial adipose tissue and human atrial myocardium induces arrhythmic susceptibility

Epicardial adipose tissue (EAT) deposition has a strong clinical association with atrial arrhythmias; however, whether a direct functional interaction exists between EAT and the myocardium to induce atrial arrhythmias is unknown. Therefore, we aimed to determine whether human EAT can be an acute trigger for arrhythmias in human atrial myocardium. Human trabeculae were obtained from right atrial appendages of patients who have had cardiac surgery (n = 89). The propensity of spontaneous contractions (SCs) in the trabeculae (proxy for arrhythmias) was determined under physiological conditions and during known triggers of SCs (high Ca²⁺, β-adrenergic stimulation). To determine whether EAT could trigger SCs, trabeculae were exposed to superfusate of fresh human EAT, and medium of 24 h-cultured human EAT treated with β_1/2 (isoproterenol) or β₃ (BRL37344) adrenergic agonists. Without exposure to EAT, high Ca²⁺ and β_1/2-adrenergic stimulation acutely triggered SCs in, respectively, 47% and 55% of the trabeculae that previously were not spontaneously active. Acute β₃-adrenergic stimulation did not trigger SCs. Exposure of trabeculae to either superfusate of fresh human EAT or untreated medium of 24 h-cultured human EAT did not induce SCs; however, specific β₃-adrenergic stimulation of EAT did trigger SCs in the trabeculae, either when applied to fresh (31%) or cultured (50%) EAT. Additionally, fresh EAT increased trabecular contraction and relaxation, whereas media of cultured EAT only increased function when treated with the β₃-adrenergic agonist. An acute functional interaction between human EAT and human atrial myocardium exists that increases the propensity for atrial arrhythmias, which depends on β₃-adrenergic rather than β_1/2-adrenergic stimulation of EAT.

High Frame Rate Ultrasound for Electromechanical Wave Imaging to Differentiate Endocardial From Epicardial Myocardial Activation

Differentiation between epicardial and endocardial ventricular activation remains a challenge despite the latest technologies available. The aim of the present study was to develop a new tool method, based on electromechanical wave imaging (EWI), to improve arrhythmogenic substrate activation analysis. Experiments were conducted on left ventricles (LVs) of four isolated working mode swine hearts. The protocol aimed at demonstrating that different patterns of mechanical activation could be observed whether the ventricle was in sinus rhythm, paced from the epicardium or from the endocardium. A total of 72 EWI acquisitions were recorded on the anterior, lateral and posterior segments of the LV. A total of 54 loop records were blindly assigned to two readers. EWI sequences interpretations were correct in 89% of cases. The overall agreement rate between the two readers was 83%. When in a paced ventricle, the origin of the wave front was focal and originated from the endocardium or the epicardium. In sinus rhythm, wave front was global and activated within the entire endocardium toward the epicardium at a speed of 1.7 ± 0.28 m·s^-1. Wave front speeds were respectively measured when the endocardium or the epicardium were paced at a speed of 1.1 ± 0.35 m·s^-1 versus 1.3 ± 0.34 m·s^-1 (p = NS). EWI activation mapping allows activation localization within the LV wall and calculation of the wave front propagation speed through the muscle. In the future, this technology could help localize activation within the LV thickness during complex ablation procedures.

Effects of white-coat, masked and sustained hypertension on coronary artery stenosis and cardiac arrhythmia

This study aimed to investigate whether hypertension phenotypes such as white-coat hypertension (WCHT), diagnosed with the addition of nighttime blood pressure (BP) criteria, are related to coronary artery stenosis (CAS) and cardiac arrhythmia. In this cross-sectional observational study, 844 participants who did not use antihypertensive, lipid-lowering, and antiplatelet drugs were selected. The subjects were divided into normotensive (NT), WCHT, masked hypertension (MHT), and sustained hypertension (SHT) groups based on the results of clinic BP measurement and ambulatory BP monitoring. Coronary angiography and ambulatory electrocardiography were performed to determine the participants' CAS and cardiac arrhythmia status. Coronary angiography revealed 556 patients with CAS and 288 participants with normal coronary arteries. The chi-squared test showed that the incidence of CAS was higher in the MHT and SHT groups than in the NT group, while no significant change was found in the WCHT group (P = 0.003, P < 0.001, P = 0.119). The logarithm of the Gensini score was used to compare the degree of CAS between the groups. Multiple linear regression analysis showed that the degree of CAS was higher in the WCHT, MHT, and SHT groups than in the NT group (P < 0.05). The incidences of frequent atrial premature beats, atrial tachycardia, and ventricular cardiac arrhythmia were significantly higher in the WCHT and SHT groups than in the NT group, while only ventricular cardiac arrhythmia changes were observed in the MHT group. This study found that hypertension phenotypes such as WCHT were closely associated with CAS and cardiac arrhythmia.

STIM1-Ca2+ signaling in coronary sinus cardiomyocytes contributes to interatrial conduction

Pacemaker action potentials emerge from the sinoatrial node (SAN) and rapidly propagate through the atria to the AV node via preferential conduction pathways, including one associated with the coronary sinus. However, few distinguishing features of these tracts are known. Identifying specific molecular markers to distinguish among these conduction pathways will have important implications for understanding atrial conduction and atrial arrhythmogenesis. Using a Stim1 reporter mouse, we discovered stromal interaction molecule 1 (STIM1)-expressing coronary sinus cardiomyocytes (CSC)s in a tract from the SAN to the coronary sinus. Our studies here establish that STIM1 is a molecular marker of CSCs and we propose a role for STIM1-CSCs in interatrial conduction. Deletion of Stim1 from the CSCs slowed interatrial conduction and increased susceptibility to atrial arrhythmias. Store-operated Ca²⁺ currents (I_soc) in response to Ca²⁺ store depletion were markedly reduced in CSCs and their action potentials showed electrical remodeling. Our studies identify STIM1 as a molecular marker for a coronary sinus interatrial conduction pathway. We propose a role for SOCE in Ca²⁺ signaling of CSCs and implicate STIM1 in atrial arrhythmogenesis.

The Emergence of Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes (hiPSC-CMs) as a Platform to Model Arrhythmogenic Diseases

There is a need for improved in vitro models of inherited cardiac diseases to better understand basic cellular and molecular mechanisms and advance drug development. Most of these diseases are associated with arrhythmias, as a result of mutations in ion channel or ion channel-modulatory proteins. Thus far, the electrophysiological phenotype of these mutations has been typically studied using transgenic animal models and heterologous expression systems. Although they have played a major role in advancing the understanding of the pathophysiology of arrhythmogenesis, more physiological and predictive preclinical models are necessary to optimize the treatment strategy for individual patients. Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have generated much interest as an alternative tool to model arrhythmogenic diseases. They provide a unique opportunity to recapitulate the native-like environment required for mutated proteins to reproduce the human cellular disease phenotype. However, it is also important to recognize the limitations of this technology, specifically their fetal electrophysiological phenotype, which differentiates them from adult human myocytes. In this review, we provide an overview of the major inherited arrhythmogenic cardiac diseases modeled using hiPSC-CMs and for which the cellular disease phenotype has been somewhat characterized.

Identification of Target Genes of Antiarrhythmic Traditional Chinese Medicine Wenxin Keli

Wenxin Keli (WXKL) is a traditional Chinese medicine drug approved for the treatment of cardiovascular diseases. This study aimed to identify WXKL-targeting genes involved in antiarrhythmic efficacy of WXKL. The Traditional Chinese Medicine Systems Pharmacology (TCMSP) technology platform was used to screen active compounds of WXKL and WXKL-targeting arrhythmia-related genes. A pig model of myocardial ischemia (MI) was established by balloon-expanding the endothelium of the left coronary artery. Pigs were divided into the model group and WXKL group (n = 6). MI, QT interval, heart rate, and arrhythmia were recorded, and the mRNA expression of target genes in myocardial tissues was detected by PCR. Eleven active ingredients of WXKL and eight WXKL-targeting arrhythmia-related genes were screened. Five pathways were enriched, and an "ingredient-gene-path" network was constructed. WXKL markedly decreased the incidence of arrhythmia in the MI pig model (P < 0.05). The QT interval was significantly shortened, and the heart rate was slowed down in the WXKL group compared with the model group (P < 0.05). In addition, the expression of sodium channel protein type 5 subunit alpha (SCN5A) and beta-2 adrenergic receptor (ADRB2) was downregulated, while muscarinic acetylcholine receptor M2 (CHRM2) was upregulated in the WXKL group (P < 0.05). In conclusion, WXKL may shorten the QT interval and slow down the heart rate by downregulating SCN5A and ADRB2 and upregulating CHRM2 during MI. These findings provide novel insight into molecular mechanisms of WXKL in reducing the incidence of ventricular arrhythmia.

Missing Link between Molecular Aspects of Ventricular Arrhythmias and QRS Complex Morphology in Left Ventricular Hypertrophy

The aim of this opinion paper is to point out the knowledge gap between evidence on the molecular level and clinical diagnostic possibilities in left ventricular hypertrophy (LVH) regarding the prediction of ventricular arrhythmias and monitoring the effect of therapy. LVH is defined as an increase in left ventricular size and is associated with increased occurrence of ventricular arrhythmia. Hypertrophic rebuilding of myocardium comprises interrelated processes on molecular, subcellular, cellular, tissue, and organ levels affecting electrogenesis, creating a substrate for triggering and maintaining arrhythmias. The knowledge of these processes serves as a basis for developing targeted therapy to prevent and treat arrhythmias. In the clinical practice, the method for recording electrical phenomena of the heart is electrocardiography. The recognized clinical electrocardiogram (ECG) predictors of ventricular arrhythmias are related to alterations in electrical impulse propagation, such as QRS complex duration, QT interval, early repolarization, late potentials, and fragmented QRS, and they are not specific for LVH. However, the simulation studies have shown that the QRS complex patterns documented in patients with LVH are also conditioned remarkably by the alterations in impulse propagation. These QRS complex patterns in LVH could be potentially recognized for predicting ventricular arrhythmia and for monitoring the effect of therapy.

Association of Abnormal P-Wave Indices With Dementia and Cognitive Decline Over 25 Years: ARIC-NCS (The Atherosclerosis Risk in Communities Neurocognitive Study)

Background Abnormal P-wave indices (PWIs)-reflecting underlying left atrial abnormality-are associated with increased risk of stroke independent of atrial fibrillation. We assessed whether abnormal PWIs are associated with incident dementia and greater cognitive decline, independent of atrial fibrillation and ischemic stroke. Methods and Results We included 13 714 participants (mean age, 57±6 years; 56% women; 23% black) who were followed for dementia through the end of 2015. (Abnormal P-wave terminal force in lead V1, ≥4000 μV×ms), abnormal P-wave axis (>75° or <0°), prolonged P-wave duration (>120 ms), and advanced interatrial block were determined from ECGs at visits 2 to 4. Dementia was adjudicated by an expert panel using data from cognitive tests and hospitalization International Classification of Diseases codes. Cognitive function was measured longitudinally using 3 neuropsychological tests. Cox proportional hazards models were used to assess the association between time-dependent abnormal PWIs with incident dementia. Linear regression models were used to evaluate PWIs with cognitive function over time. At the conclusion of the study, 19%, 16%, 28%, and 1.9% of participants had abnormal P-wave terminal force in lead V1, abnormal P-wave axis, prolonged P-wave duration, and advanced interatrial block, respectively. During mean follow-up of 18 years, there were 1390 (10%) dementia cases. All abnormal PWIs except advanced interatrial block were associated with an increased risk of dementia even after adjustment for incident atrial fibrillation and stroke: multivariable hazard ratio of abnormal P wave terminal force in lead V1=1.60, 95% CI, 1.41 to 2.83; abnormal P-wave axis, hazard ratio =1.36, 95% CI, 1.17 to 2.57; prolonged P-wave duration, hazard ratio=1.60, 95% CI, 1.42 to 1.80. Only abnormal P-wave terminal force in lead V1 was associated with greater decline in global cognition. Conclusions Abnormal PWIs are independently associated with an increased risk of dementia. This novel finding should be replicated in other cohorts and the underlying mechanisms should be evaluated.

Cardiac complications in systemic sclerosis: early diagnosis and treatment

OBJECTIVE

Systemic sclerosis (SSc) is a remarkably systemic heterogeneous connective tissue disease with many organs involved. The heart is one of the major organs involved, carrying the threat of sudden cardiac death, especially in diffuse cutaneous SSc. This review summarizes the pathophysiology, types, new diagnostic approaches, and imaging and novel therapies of primary cardiac complications while underlining the effects of recently developed non-contrast cardiovascular magnetic resonance (CMR) in early diagnosis.

DATA SOURCES

Medline and Embase were searched for articles published up to July 2019. A combination of Medical Subject Headings (MeSH) terms and keywords pertaining to SSc ("Scleroderma, Systemic" OR "Systemic sclerosis" OR' SSc"), AND cardiology ("cardiology" OR "heart" OR "cardiac") were applied to the search strategies.

STUDY SELECTION

Literature was mainly printed in English and Chinese about cardiac complications in systemic sclerosis. After selected simply on the title and abstract, the articles were included for the full text. Article type was not limited.

RESULTS

Relevant cardiac manifestations are complex, including arrhythmias, pericardial effusion, myocardial dysfunction, and valvular diseases. Even though the symptoms of cardiac complications are well known, unfortunately, they appear to be poor prognostic factors. As systemic sclerosis with cardiac complications has a high mortality rate and patients might have a poor quality of life, it is essential to promote early diagnosis and treatment. With the advent of non-invasive imaging techniques, such as CMR, early diagnosis of cardiac complications in SSc is becoming more effective.

CONCLUSIONS

Cardiac complications play an essential role in SSc and carry the threat of sudden cardiac death. More basic and clinical studies are warranted to develop better management of cardiac involvement in patients with SSc.

Combination Formulation of Tetrodotoxin and Lidocaine as a Potential Therapy for Severe Arrhythmias

Severe arrhythmias-such as ventricular arrhythmias-can be fatal, but treatment options are limited. The effects of a combined formulation of tetrodotoxin (TTX) and lidocaine (LID) on severe arrhythmias were studied. Patch clamp recording data showed that the combination of LID and TTX had a stronger inhibitory effect on voltage-gated sodium channel 1.5 (Nav1.5) than that of either TTX or LID alone. LID + TTX formulations were prepared with optimal stability containing 1 μg of TTX, 5 mg of LID, 6 mg of mannitol, and 4 mg of dextran-40 and then freeze dried. This formulation significantly delayed the onset and shortened the duration of arrhythmia induced by aconitine in rats. Arrhythmia-originated death was avoided by the combined formulation, with a decrease in the mortality rate from 64% to 0%. The data also suggests that the anti-arrhythmic effect of the combination was greater than that of either TTX or LID alone. This paper offers new approaches to develop effective medications against arrhythmias.

Modulating Perioperative Ventricular Excitability

Ventricular arrhythmias are associated with significant morbidity and mortality. In the perioperative period, more than 10% of patients undergoing a general anesthetic have an abnormal heart rhythm. Arrhythmia development is a dynamic interplay between an arrhythmogenic substrate, myocardial electrophysiologic properties, modifying factors, and triggering factors. Imbalances in the autonomic nervous system can lead to increased myocardial excitability, which is a major contributor to the pathophysiology of ventricular tachyarrhythmias. Myocardial excitability and ventricular arrhythmogenesis is modulated perioperatively through hemodynamic management, electrolyte balance, anesthetic agents, or regional anesthetic and surgical techniques.

Spanish Catheter Ablation Registry. 18th Official Report of the Spanish Society of Cardiology Working Group on Electrophysiology and Arrhythmias (2018)

INTRODUCTION AND OBJECTIVES

This report presents the findings of the 2018 Spanish Catheter Ablation Registry.

METHODS

Data collection was retrospective. A standardized questionnaire was completed by each of the participating centers.

RESULTS

Data sent by 100 centers were analyzed, with a total number of 16566 ablation procedures performed (the highest historically reported in this registry) for a mean of 165.5±127.9 and a median of 119 procedures per center. The ablation targets most frequently treated were atrial fibrillation (n=4234; 25.6%), atrioventricular nodal re-entrant tachycardia (n=3525; 21.3%) and cavotricuspid isthmus (n=3425; 20.7%). A new peak was observed in the ablation of atrial fibrillation, increasing the distance from the other substrates. The overall success rate was 91%. The rate of major complications was 2.2%, and the mortality rate was 0.04%. A total of 2.1% of the ablations were performed in pediatric patients.

CONCLUSIONS

The Spanish Catheter Ablation Registry enrolls systematically and continuously enrolls the ablation procedures performed in Spain, showing a progressive increasing in the number of ablations over the years, with a high success rate and low percentage of complications.

Dynamic predictive accuracy of electrocardiographic biomarkers of sudden cardiac death within a survival framework: the Atherosclerosis Risk in Communities (ARIC) study

BACKGROUND

The risk of sudden cardiac death (SCD) is known to be dynamic. However, the accuracy of a dynamic SCD prediction is unknown. We aimed to measure the dynamic predictive accuracy of ECG biomarkers of SCD and competing non-sudden cardiac death (non-SCD).

METHODS

Atherosclerosis Risk In Community study participants with analyzable ECGs in sinus rhythm were included (n = 15,716; 55% female, 73% white, age 54.2 ± 5.8 y). ECGs of 5 follow-up visits were analyzed. Global electrical heterogeneity and traditional ECG metrics (heart rate, QRS, QTc) were measured. Adjudicated SCD was the primary outcome; non-SCD was the competing outcome. Time-dependent area under the receiver operating characteristic curve (ROC(t) AUC) analysis was performed to assess the prediction accuracy of a continuous biomarker in a period of 3,6,9 months, and 1,2,3,5,10, and 15 years using a survival analysis framework. Reclassification improvement as compared to clinical risk factors (age, sex, race, diabetes, hypertension, coronary heart disease, stroke) was measured.

RESULTS

Over a median 24.4 y follow-up, there were 577 SCDs (incidence 1.76 (95%CI 1.63-1.91)/1000 person-years), and 829 non-SCDs [2.55 (95%CI 2.37-2.71)]. No ECG biomarkers predicted SCD within 3 months after ECG recording. Within 6 months, spatial ventricular gradient (SVG) elevation predicted SCD (AUC 0.706; 95%CI 0.526-0.886), but not a non-SCD (AUC 0.527; 95%CI 0.303-0.75). SVG elevation more accurately predicted SCD if the ECG was recorded 6 months before SCD (AUC 0.706; 95%CI 0.526-0.886) than 2 years before SCD (AUC 0.608; 95%CI 0.515-0.701). Within the first 3 months after ECG recording, only SVG azimuth improved reclassification of the risk beyond clinical risk factors: 18% of SCD events were reclassified from low or intermediate risk to a high-risk category. QRS-T angle was the strongest long-term predictor of SCD (AUC 0.710; 95%CI 0.668-0.753 for ECG recorded within 10 years before SCD).

CONCLUSION

Short-term and long-term predictive accuracy of ECG biomarkers of SCD differed, reflecting differences in transient vs. persistent SCD substrates. The dynamic predictive accuracy of ECG biomarkers should be considered for competing SCD risk scores. The distinction between markers predicting short-term and long-term events may represent the difference between markers heralding SCD (triggers or transient substrates) versus markers identifying persistent substrate.

Arrhythmogenicity of scuba diving: Holter monitoring in a hyperbaric environment

INTRODUCTION

About 26% of diving-related fatalities are caused by cardiac disease, part of which might be associated with fatal arrhythmias. This raises the question as to whether fatal arrhythmias are being provoked by hyperbaric conditions themselves or if exercise or stress provokes the fatal arrhythmias in cases of underlying (ischemic) cardiac disease.

OBJECTIVE

To measure the influence of hyperbaric conditions (50 msw) on cardiac conduction and arrhythmias in professional divers by means of ECG.

METHODS

This is a prospective study on military divers in a hyperbaric chamber with continuous ECG monitoring using Holter registrations. Supraventricular and ventricular ectopy was registered during hyperbaric conditions. RR, PR, QRS, QT and QTc intervals were calculated at 50 msw and compared with ECGs at rest.

RESULTS

Included were 17 male military divers who made 20 dives. A total of 10 PVCs, 45 PACs, four atrial runs and four atrial pairs were seen. Significant prolongation of the PR interval was seen and a decrease of in QRS duration at 50 msw. There was no significant change in the RR, QT and QTc intervals.

CONCLUSION

In these divers, no clinically relevant arrhythmias were observed during wet dives in a recompression chamber at 50 msw. We observed a small prolongation of PR interval that is probably not clinically relevant in divers without any known conduction disorders.

Mapping and Ablation of Arrhythmias from Uncommon Sites (Aortic Cusp, Pulmonary Artery, and Left Ventricular Summit)

Despite advances in our understanding of the relevant anatomy and mapping and catheter ablation techniques of idiopathic outflow tract ventricular arrhythmias, challenging sites for catheter ablation remain the aortic cusps, pulmonary artery, and notably the left ventricular summit. A systematic approach should be used to direct mapping efforts efficiently between endocardial, coronary venous, and epicardial sites. Foci at the left ventricular summit, particularly intraseptal and at the inaccessible epicardial region, remain difficult to reach and when percutaneous techniques fail, surgical ablation remains an option but with risk of late coronary artery stenosis.

X-Linked Emery-Dreifuss Muscular Dystrophy: Study Of X-Chromosome Inactivation and Its Relation with Clinical Phenotypes in Female Carriers

X-linked Emery–Dreifuss muscular dystrophy (EDMD1) affects approximately 1:100,000 male births. Female carriers are usually asymptomatic but, in some cases, they may present clinical symptoms after age 50 at cardiac level, especially in the form of conduction tissue anomalies. The aim of this study was to evaluate the relation between heart involvement in symptomatic EDMD1 carriers and the X-chromosome inactivation (XCI) pattern. The XCI pattern was determined on the lymphocytes of 30 symptomatic and asymptomatic EDMD1 female carriers—25 familial and 5 sporadic cases—seeking genetic advice using the androgen receptor (AR) methylation-based assay. Carriers were subdivided according to whether they were above or below 50 years of age. A variance analysis was performed to compare the XCI pattern between symptomatic and asymptomatic carriers. The results show that 20% of EDMD1 carriers had cardiac symptoms, and that 50% of these were ≥50 years of age. The XCI pattern was similar in both symptomatic and asymptomatic carriers. Conclusions: Arrhythmias in EDMD1 carriers poorly correlate on lymphocytes to a skewed XCI, probably due to (a) the different embryological origin of cardiac conduction tissue compared to lymphocytes or (b) the preferential loss of atrial cells replaced by fibrous tissue.

Severe Hypoglycemia-Induced Fatal Cardiac Arrhythmias Are Mediated by the Parasympathetic Nervous System in Rats

The contribution of the sympathetic nervous system (SNS) versus the parasympathetic nervous system (PSNS) in mediating fatal cardiac arrhythmias during insulin-induced severe hypoglycemia is not well understood. Therefore, experimental protocols were performed in nondiabetic Sprague-Dawley rats to test the SNS with 1) adrenal demedullation and 2) chemical sympathectomy, and to test the PSNS with 3) surgical vagotomy, 4) nicotinic receptor (mecamylamine) and muscarinic receptor (AQ-RA 741) blockade, and 5) ex vivo heart perfusions with normal or low glucose, acetylcholine (ACh), and/or mecamylamine. In protocols 1-4, 3-h hyperinsulinemic (0.2 units/kg/min) and hypoglycemic (10-15 mg/dL) clamps were performed. Adrenal demedullation and chemical sympathectomy had no effect on mortality or arrhythmias during severe hypoglycemia compared with controls. Vagotomy led to a 6.9-fold decrease in mortality; reduced first- and second-degree heart block 4.6- and 4-fold, respectively; and prevented third-degree heart block compared with controls. Pharmacological blockade of nicotinic receptors, but not muscarinic receptors, prevented heart block and mortality versus controls. Ex vivo heart perfusions demonstrated that neither low glucose nor ACh alone caused arrhythmias, but their combination induced heart block that could be abrogated by nicotinic receptor blockade. Taken together, ACh activation of nicotinic receptors via the vagus nerve is the primary mediator of severe hypoglycemia-induced fatal cardiac arrhythmias.

[The subcutaneous implantable cardioverter-defibrillator in clinical practice]

Overcoming lead-related complications, the subcutaneous implantable cardioverter-defibrillator (S-ICD) represents the greatest advancement in the management of patients with ventricular arrhythmias and the prevention of sudden cardiac death. Due to the absence of leads within the body, the S-ICD requires an innovative approach for sensing of subcutaneous signals and defibrillation. The aim of this review is to analyze the current evidence regarding patient selection, technical aspects such as the implant technique, programming and follow-up, as well as complications and troubleshooting of this innovative technology.

Muscarinic receptors promote pacemaker fate at the expense of secondary conduction system tissue in zebrafish

Deterioration or inborn malformations of the cardiac conduction system (CCS) interfere with proper impulse propagation in the heart and may lead to sudden cardiac death or heart failure. Patients afflicted with arrhythmia depend on antiarrhythmic medication or invasive therapy, such as pacemaker implantation. An ideal way to treat these patients would be CCS tissue restoration. This, however, requires precise knowledge regarding the molecular mechanisms underlying CCS development. Here, we aimed to identify regulators of CCS development. We performed a compound screen in zebrafish embryos and identified tolterodine, a muscarinic receptor antagonist, as a modifier of CCS development. Tolterodine provoked a lower heart rate, pericardiac edema, and arrhythmia. Blockade of muscarinic M3, but not M2, receptors induced transcriptional changes leading to amplification of sinoatrial cells and loss of atrioventricular identity. Transcriptome data from an engineered human heart muscle model provided additional evidence for the contribution of muscarinic M3 receptors during cardiac progenitor specification and differentiation. Taken together, we found that muscarinic M3 receptors control the CCS already before the heart becomes innervated. Our data indicate that muscarinic receptors maintain a delicate balance between the developing sinoatrial node and the atrioventricular canal, which is probably required to prevent the development of arrhythmia.

Decreased heart rate variability as a predictor for diabetes-A prospective study of the Brazilian longitudinal study of adult health

AIM

To investigate whether heart rate variability (HRV) is a predictor for the incidence of diabetes in a 4-year follow-up.

MATERIALS AND METHODS

The HRV of 9192 participants free of diabetes was analysed in time and frequency domains and stratified based on the reference values presented in the literature. The participants were then allocated to one of three groups, according to age-specific value distributions for each HRV domain: lower than the 25^th percentile, between the 25^th and 75^th percentiles, and higher than the 75^th percentile. The association between HRV and diabetes incidence at 4-year follow-up was analysed using Poisson regression models with robust estimator.

RESULTS

Six hundred thirty-four participants (6.90%) developed diabetes within 4 years and five out of six HRV analysed indices showed increased relative risk of developing diabetes associated with low HRV: SDNN (RR = 1.29; 95% CI, 1.09-1.52; .003), pNN50 (RR = 1.33; 95% CI, 1.11-1.58; .001), RMSSD (RR = 1.29; 95% CI, 1.09-1.53; .004), LF (RR = 1.25; 95% CI, 1.05-1.48; .012), and HF (RR = 1.39; 95% CI, 1.16-1.63; .001).

CONCLUSIONS

This study suggests that both overall variability and changes in parasympathetic modulation precede the incidence of diabetes. For four HRV indices below the 25^th percentile, the risk for incident diabetes was 68% higher than for those participants who presented none. We concluded that HRV is an independent risk predictor of diabetes in a 4-year period.

Energy-Efficient Intelligent ECG Monitoring for Wearable Devices

Wearable intelligent ECG monitoring devices can perform automatic ECG diagnosis in real time and send out alert signal together with abnormal ECG signal for doctor's further analysis. This provides a means for the patient to identify their heart problem as early as possible and go to doctors for medical treatment. For such system the key requirements include high accuracy and low power consumption. However, the existing wearable intelligent ECG monitoring schemes suffer from high power consumption in both ECG diagnosis and transmission in order to achieve high accuracy. In this work, we have proposed an energy-efficient wearable intelligent ECG monitor scheme with two-stage end-to-end neural network and diagnosis-based adaptive compression. Compared to the state-of-the-art schemes, it significantly reduces the power consumption in ECG diagnosis and transmission while maintaining high accuracy.

Fibrosis and Ventricular Arrhythmogenesis: Role of Cardiac MRI

Cardiac fibrosis is a significant increase in collagen volume fraction of myocardial tissue. It plays an important role in the pathophysiology of many cardiovascular abnormalities. Electrophysiologically, myocardial fibrosis produces anisotropic conduction, inhomogeneity, and conduction delay. Several markers are available to detect myocardial fibrosis. CMRI is the most common imaging technique; late gadolinium enhancement cardiac magnetic resonance (LGE-CMR) provides markers for tissue characterization, disease progression and arrhythmic events. LGE-CMR can be used as risk marker of occurrence of pathologic conditions. LGE-CMR demonstrates specific patterns related to different pathologic substrates. We discuss the role of CMRI in ventricular arrhythmogenesis.

Generation of a cohort of whole-torso cardiac models for assessing the utility of a novel computed shock vector efficiency metric for ICD optimisation

Implanted cardiac defibrillators (ICDs) seek to automatically detect and terminate potentially lethal ventricular arrhythmias by applying strong internal electric shocks across the heart. However, the optimisation of the specific electrode design and configurations represents an intensive area of research in the pursuit of reduced shock strengths and fewer device complications and risks. Computational whole-torso simulations play an important role in this endeavour, although knowing which specific metric should be used to assess configuration efficacy and assessing the impact of different patient anatomies and pathologies, and the corresponding effect this may have on different metrics has not been investigated. We constructed a cohort of CT-derived high-resolution whole torso-cardiac computational models, including variants of cardiomyopathies and patients with differing torso dimensions. Simulations of electric shock application between electrode configurations corresponding to transveneous (TV-ICD) and subcutaneous (S-ICD) ICDs were modelled and conventional metrics such as defibrillation threshold (DFT) and impedance computed. In addition, we computed a novel metric termed the shock vector efficiency (η), which quantifies the fraction of electrical energy dissipated in the heart relative to the rest of the torso. Across the cohort, S-ICD configurations showed higher DFTs and impedances than TV-ICDs, as expected, although little consistent difference was seen between healthy and cardiomyopathy variants. η was consistently <2% for S-ICD configurations, becoming as high as 13% for TV-ICD setups. Simulations also suggested that a total torso height of approximately 20 cm is required for convergence in η. Overall, η was seen to be approximately negatively correlated with both DFT and impedance. However, important scenarios were identified in which certain values of DFT (or impedance) were associated with a range of η values, and vice-versa, highlighting the heterogeneity introduced by the different torsos and pathologies modelled. In conclusion, the shock vector efficiency represents a useful additional metric to be considered alongside DFT and impedance in the optimisation of ICD electrode configurations, particularly in the context of differing torso anatomies and cardiac pathologies, which can induce significant heterogeneity in conventional metrics of ICD efficacy.

Noninvasive Mapping and Electrocardiographic Imaging in Atrial and Ventricular Arrhythmias (CardioInsight)

Electrocardiographic imaging is a mapping technique aiming to noninvasively characterize cardiac electrical activity using signals collected from the torso to reconstruct epicardial potentials. Its efficacy has been demonstrated clinically, from mapping premature ventricular complexes and accessory pathways to of complex arrhythmias. Electrocardiographic imaging uses a standardized workflow. Signals should be checked manually to avoid automatic processing errors. Reentry is confirmed in the presence of local activation covering the arrhythmia cycle length. Focal breakthroughs demonstrate a QS pattern associated with centrifugal activation. Electrocardiographic imaging offers a unique opportunity to better understand the mechanism of cardiac arrhythmias and guide ablation.

Noninvasive Cardioablation

Stereotactic body radiotherapy uses the principle of 3-dimensional localization of a target to deliver a high dose of radiation to a precise location. The aim of this technique is to ablate tissue noninvasively. Because of its high precision and target conformity, it can deliver a high dose of radiation to a specific area in a tissue without significantly affecting nearby tissues. It is being actively studied and even used in therapy for atrial fibrillation and ventricular tachycardia.

Loss of MD1 increases vulnerability to ventricular arrhythmia in diet-induced obesity mice via enhanced activation of the TLR4/MyD88/CaMKII signaling pathway

BACKGROUND AND AIM

Obesity is an important risk factor for ventricular arrhythmia (VA), and myeloid differentiation protein 1 (MD1) has been reported to decrease in obese hearts. Nevertheless, underlying mechanisms linking MD1 and VA have not been fully studied. This study aims to investigate the regulatory role of MD1 in VA caused by diet-induced obesity.

METHODS AND RESULTS

MD1 knock-out (KO) and wild type (WT) mice from experimental groups were fed with a high-fat diet (HFD) since the age of six weeks for 20 weeks. The body weight gain, fast glucose and serum lipid levels were measured and recorded. In addition, pathological analysis, echocardiography, electrocardiography, langendorff-perfused heart and molecular analysis were performed to detect HFD-induced vulnerability to VA and its underlying mechanisms. After a 20-week HFD feeding, the mice showed an increase in body weight, glycemic, lipid levels, QTc interval, LVEDd, LVEDs and LVFS. HFD feeding also increased vulnerability to VA, as shown by the prolonged action potential duration (APD), enhanced APD alternans threshold and greater incidence of VA. Moreover, HFD feeding caused LV hypertrophy and fibrosis, and decreased the protein expressions of Kv4.2, Kv4.3, Kv1.5, Kv2.1 and Cav1.2 channels. At last, the above-mentioned HFD-induced adverse effects were further exacerbated in KO mice compared with WT mice. Mechanistically, MD1 deletion markedly enhanced the activation of TLR4/MyD88/CaMKII signaling pathway in HFD-fed mice.

CONCLUSION

MD1 deficiency increased HFD-induced vulnerability to VA. This is mainly caused by the aggravated maladaptive LV hypertrophy, fibrosis and decreased protein expressions of ion channels, which are induced by the enhanced activation of the TLR4/MyD88/CaMKII signaling pathway.