Cardiac Conduction Velocity, Remodeling and Arrhythmogenesis

Omnipolar conduction velocity mapping for ventricular substrate characterization: Impact of CV estimation method and EGM type on in vivo conduction velocity measurements

BACKGROUND

Areas of abnormal or heterogeneous conduction velocity (CV) are important ablation targets for ventricular tachycardias, yet precise assessment of CV in clinical contact mapping remains challenging. Numerous different CV estimation methods have been proposed.

OBJECTIVE

This study aimed to compare the automated local activation time (LAT)-independent omnipolar-based CV estimation method termed wave speed (WS) with 4 established LAT-based methods to formally establish the quantitative differences between them.

METHODS

High-density contact maps in patients with structurally normal hearts during sinus rhythm (SR) and ventricular ectopy (VE) were retrospectively analyzed. CV was assessed and compared by 5 methods: omnipolar WS, gradient method, planar wavefront fitting, circular wavefront fitting, and radial basis function. CV variations based on electrogram (EGM) type (unipolar, bipolar, and omnipolar), catheter movement, and surrogate markers for catheter contact were analyzed.

RESULTS

The study included 23 patients (47.8% male; 45.7 ± 17.3 years) with 22 SR maps (11 left ventricle, 11 right ventricle) and 16 VE maps (9 left ventricle, 7 right ventricle). The WS algorithm yielded statistically significant higher CV estimates in SR (mean, 1.41 ± 0.18 m/s) and VE (mean, 1.23 ± 0.18 m/s) maps compared with all LAT-based estimation methods, with absolute differences ranging from 0.1 m/s to 0.81 m/s. Median pointwise differences in SR and VE between WS and LAT-based methods were high, ranging from 0.55 ± 0.15 m/s (WS vs planar wavefront fitting) to 0.67 ± 0.16 m/s (WS vs radial basis function). For LAT-based methods, use of unipolar EGMs yielded significantly higher CV estimates than bipolar or omnipolar EGMs in SR.

CONCLUSION

The CV estimation method has an important, statistically significant impact on ventricular CV measurements. Future work will focus on how these differences affect identification of pathologic conduction slowing in scar-related substrate.

Improved algorithm for generating evenly-spaced streamlines from an orientation field on a triangulated surface

BACKGROUND

Vector fields such as cardiac fiber orientation can be visualized on a surface using streamlines. The application of evenly-spaced streamline generation to the construction of interconnected cable structure for cardiac propagation models has more stringent requirements imperfectly fulfilled by current algorithms.

METHOD

We developed an open-source C++/python package for the placement of evenly-spaced streamlines on a triangulated surface. The new algorithm improves upon previous works by more accurately handling streamline extremities, U-turns and limit cycles, by providing stronger geometrical guarantees on inter-streamline minimal distance, particularly when a high density of streamlines (up to 10μm spacing) is desired, and by making a more efficient parallel implementation available. The approach requires finding intersections between geometrical capsules and triangles to update an occupancy mask defined on the triangles. This enables fast streamline integration from thousands of seed points to identify optimal streamline placement.

RESULTS

The algorithm was assessed qualitatively on different left atrial models of fiber orientation with varying mesh resolutions (up to 375k triangles) and quantitatively by measuring streamline lengths and distribution of inter-streamline minimal distance. The complexity and the computational performance of the algorithm were studied as a function of streamline spacing in relation to triangular mesh resolution.

CONCLUSION

More accurate geometrical computations, attention to details and fine-tuning led to an algorithm more amenable to applications that require precise positioning of streamlines.

A Review of Personalised Cardiac Computational Modelling Using Electroanatomical Mapping Data

Computational models of cardiac electrophysiology have gradually matured during the past few decades and are now being personalised to provide patient-specific therapy guidance for improving suboptimal treatment outcomes. The predictive features of these personalised electrophysiology models hold the promise of providing optimal treatment planning, which is currently limited in the clinic owing to reliance on a population-based or average patient approach. The generation of a personalised electrophysiology model entails a sequence of steps for which a range of activation mapping, calibration methods and therapy simulation pipelines have been suggested. However, the optimal methods that can potentially constitute a clinically relevant in silico treatment are still being investigated and face limitations, such as uncertainty of electroanatomical data recordings, generation and calibration of models within clinical timelines and requirements to validate or benchmark the recovered tissue parameters. This paper is aimed at reporting techniques on the personalisation of cardiac computational models, with a focus on calibrating cardiac tissue conductivity based on electroanatomical mapping data.

Novel 2D/3D Hybrid Organoid System for High-Throughput Drug Screening in iPSC Cardiomyocytes

Human induced pluripotent stem cell cardiomyocytes (hiPSC-CMs) allow for high-throughput evaluation of cardiomyocyte (CM) physiology in health and disease. While multimodality testing provides a large breadth of information related to electrophysiology, contractility, and intracellular signaling in small populations of iPSC-CMs, current technologies for analyzing these parameters are expensive and resource-intensive. We sought to design a 2D/3D hybrid organoid system and harness optical imaging techniques to assess electromechanical properties, calcium dynamics, and signal propagation across CMs in a high-throughput manner. We validated our methods using a doxorubicin-based system, as the drug has well-characterized cardiotoxic, pro-arrhythmic effects. hiPSCs were differentiated into CMs, assembled into organoids, and thereafter treated with doxorubicin. The organoids were then replated to form a hybrid 2D/3D iPSC-CM construct where the 3D cardiac organoids acted as the source of electromechanical activity which propagated outwards into a 2D iPSC-CM sheet. The organoid recapitulated cardiac structure and connectivity, while 2D CMs facilitated analysis at an individual cellular level which recreated numerous doxorubicin-induced electrophysiologic and propagation abnormalities. Thus, we have developed a novel 2D/3D hybrid organoid model that employs an integrated optical analysis platform to provide a reliable high-throughput method for studying cardiotoxicity, providing valuable data on calcium, contractility, and signal propagation.

[Developments of ex vivo cardiac electrical mapping and intelligent labeling of atrial fibrillation substrates]

Cardiac three-dimensional electrophysiological labeling technology is the prerequisite and foundation of atrial fibrillation (AF) ablation surgery, and invasive labeling is the current clinical method, but there are many shortcomings such as large trauma, long procedure duration, and low success rate. In recent years, because of its non-invasive and convenient characteristics, ex vivo labeling has become a new direction for the development of electrophysiological labeling technology. With the rapid development of computer hardware and software as well as the accumulation of clinical database, the application of deep learning technology in electrocardiogram (ECG) data is becoming more extensive and has made great progress, which provides new ideas for the research of ex vivo cardiac mapping and intelligent labeling of AF substrates. This paper reviewed the research progress in the fields of ECG forward problem, ECG inverse problem, and the application of deep learning in AF labeling, discussed the problems of ex vivo intelligent labeling of AF substrates and the possible approaches to solve them, prospected the challenges and future directions for ex vivo cardiac electrophysiology labeling.

Ventricular fibrillation/ventricular tachycardia within 72 h of VA-ECMO: incidence, outcomes, risk factors, and management

AIMS

Veno-arterial extracorporeal membrane oxygenation (VA-ECMO) is an important technique for the treatment of refractory cardiogenic shock and cardiac arrest; however, the early management of ventricular fibrillation/ventricular tachycardia (VF/VT), within 72 h of VA-ECMO, and its effects on patient prognosis remain unclear.

METHODS AND RESULTS

We retrospectively analysed patients at the First Affiliated Hospital of Nanjing Medical University who underwent VA-ECMO between January 2017 and March 2022. The patients were divided into two groups, VF/VT and nVF/VT, based on whether or not VF/VT occurred within 72 h after the initiation of VA-ECMO. We utilized logistic regression analysis to evaluate the independent risk factors for VF/VT in patients undergoing VA-ECMO and to ascertain whether the onset of VF/VT affected 28 day survival rate, length of intensive care unit stay, and/or other clinical prognostic factors. Subgroup analysis was performed for the VF/VT group to determine whether defibrillation affected prognosis. In the present study, 126 patients were included, 65.87% of whom were males (83/126), with a mean age of 46.89 ± 16.23, a 28 day survival rate of 57.14% (72/126), an incidence rate of VF/VT within 72 h of VA-ECMO initiation of 27.78% (35/126), and 80% of whom (28/35) received extracorporeal cardiopulmonary resuscitation. The incidence of VF/VT resulting from cardiac arrest at an early stage was significantly higher than that of refractory cardiogenic shock (80% vs. 20%; P = 0.022). The restricted cubic spline model revealed a U-shaped relationship between VF/VT incidence and initial heart rate (iHR), and multivariate logistic regression analysis showed that an iHR > 120 b.p.m. [odds ratio (OR) 6.117; 95% confidence interval (CI) 1.672-22.376; P = 0.006] and hyperlactataemia (OR 1.125; 95% CI 1.016-1.246; P = 0.023) within 1 h of VA-ECMO initiation were independent risk factors for the occurrence of VF/VT. VF/VT was not found to be associated with the 28 day survival of patients undergoing VA-ECMO support, nor did it affect other secondary endpoints. Defibrillation did not alter the overall prognosis in patients with VF/VT during VA-ECMO.

CONCLUSIONS

An iHR > 120 b.p.m. and hyperlactataemia were independent risk factors for the occurrence of VF/VT within 72 h of VA-ECMO initiation. The occurrence of VF/VT does not affect, nor does defibrillation in these patients improve the overall patient prognosis.

TRIAL REGISTRATION

ChiCTR1900026105.

Vericiguat alleviates ventricular remodeling and arrhythmias in mouse models of myocardial infarction via CaMKII signaling

AIMS

Maladaptive ventricular remodeling is a major cause of ventricular arrhythmias following myocardial infarction (MI) and adversely impacts the quality of life of affected patients. Vericiguat is a new soluble guanylate cyclase (sGC) activator with cardioprotective properties. However, its effects on MI-induced ventricular remodeling and arrhythmias are not fully comprehended; hence, our research evaluated the effect of vericiguat on mice post-MI.

MATERIALS AND METHODS

Mice were divided into four treatment groups: Sham, Sham+Veri, MI, and MI + Veri. For the MI groups and MI + Veri groups, the left anterior descending (LAD) coronary artery was occluded to induce MI. Conversely, the Sham group underwent mock surgery. Vericiguat was administered orally daily for 28 days to the Sham+Veri and MI + Veri groups. Additionally, H9c2 cells were cultured for further mechanistic studies. Assessment methods included echocardiography, pathological analysis, electrophysiological analysis, and Western blotting.

KEY FINDINGS

Vericiguat reduced cardiac dysfunction and infarct size after MI. It also mitigated MI-induced left ventricular fibrosis and cardiomyocyte apoptosis. Vericiguat normalized the expression of ion channel proteins (Kv4.3, Kv4.2, Kv2.1, Kv1.5, Kv7.1, KCNH2, Cav1.2) and the gap junction protein connexin 43, reducing the susceptibility to ventricular arrhythmia. Vericiguat significantly inhibited MI-induced calcium/calmodulin-dependent protein kinase II (CaMKII) pathway activation in mice.

SIGNIFICANCE

Vericiguat alleviated MI-induced left ventricular adverse remodeling and arrhythmias through modulation of the CamkII signaling pathway.

Localized cardiomyocyte lipid accumulation is associated with slowed epicardial conduction in rats

Transmural action potential duration differences and transmural conduction gradients aid the synchronization of left ventricular repolarization, reducing vulnerability to transmural reentry and arrhythmias. A high-fat diet and the associated accumulation of pericardial adipose tissue are linked with conduction slowing and greater arrhythmia vulnerability. It is predicted that cardiac adiposity may more readily influence epicardial conduction (versus endocardial) and disrupt normal transmural activation/repolarization gradients. The aim of this investigation was to determine whether transmural conduction gradients are modified in a rat model of pericardial adiposity. Adult Sprague-Dawley rats were fed control/high-fat diets for 15 wk. Left ventricular 300 µm tangential slices were generated from the endocardium to the epicardium, and conduction was mapped using microelectrode arrays. Slices were then histologically processed to assess fibrosis and cardiomyocyte lipid status. Conduction velocity was significantly greater in epicardial versus endocardial slices in control rats, supporting the concept of a transmural conduction gradient. High-fat diet feeding increased pericardial adiposity and abolished the transmural conduction gradient. Slowed epicardial conduction in epicardial slices strongly correlated with an increase in cardiomyocyte lipid content, but not fibrosis. The positive transmural conduction gradient reported here represents a physiological property of the ventricular activation sequence that likely protects against reentry. The absence of this gradient, secondary to conduction slowing and cardiomyocyte lipid accumulation, specifically in the epicardium, indicates a novel mechanism by which pericardial adiposity may exacerbate ventricular arrhythmias.

The fungicide tebuconazole modulates the sodium current of human NaV1.5 channels expressed in HEK293 cells

The fungicide Tebuconazole is a widely used pesticide in agriculture and may cause cardiotoxicity. In our present investigation the effect of Tebuconazole on the sodium current (INa) of human cardiac sodium channels (NaV1.5) was studied using a heterologous expression system and whole-cell patch-clamp techniques. Tebuconazole reduced the amplitude of the peak INa in a concentration- and voltage-dependent manner. At the holding potential of -120 mV the IC50 was estimated at 204.1 ± 34.3 μM, while at -80 mV the IC50 was 0.3 ± 0.1 μM. The effect of the fungicide is more pronounced at more depolarized potentials, indicating a state-dependent interaction. Tebuconazole caused a negative shift in the half-maximal inactivation voltage and delayed recovery from fast inactivation of INa. Also, it enhanced closed-state inactivation, exhibited use-dependent block in a voltage-dependent manner. Furthermore, Tebuconazole reduced the increase in late sodium current induced by the pyrethroid insecticide β-Cyfluthrin. These results suggest that Tebuconazole can interact with NaV1.5 channels and modulate INa. The observed effects may lead to decreased cardiac excitability through reduced INa availability, which could be a new mechanism of cardiotoxicity to be attributed to the fungicide.

Impact of Impaired Kidney Function on Arrhythmia-Promoting Cardiac Ion Channel Regulation

Chronic kidney disease (CKD) is associated with a significantly increased risk of cardiovascular events and sudden cardiac death. Although arrhythmias are one of the most common causes of sudden cardiac death in CKD patients, the molecular mechanisms involved in the development of arrhythmias are still poorly understood. In this narrative review, therefore, we summarize the current knowledge on the regulation of cardiac ion channels that contribute to arrhythmia in CKD. We do this by first explaining the excitation-contraction coupling, outlining current translational research approaches, then explaining the main characteristics in CKD patients, such as abnormalities in electrolytes and pH, activation of the autonomic nervous system, and the renin-angiotensin-aldosterone system, as well as current evidence for proarrhythmic properties of uremic toxins. Finally, we discuss the substance class of sodium-glucose co-transporter 2 inhibitors (SGLT2i) on their potential to modify cardiac channel regulation in CKD and, therefore, as a treatment option for arrhythmias.

A simple approach for image-based modelling of the heart that enables robust simulation of highly heterogeneous electrical excitation

Remodelling of cardiac tissue structure, including intercellular electrical coupling, is a major determinant of the complex and heterogeneous excitation patterns associated with cardiac arrhythmias. Evaluation of the precise mechanisms by which local tissue structure determines global arrhythmic excitation patterns is a major challenge that may be critically important for the development of effective treatment strategies. Computational modelling is a key tool in the study of cardiac arrhythmias, yet the established approaches for organ-scale modelling are unsuitable to capture the impact of local conduction heterogeneities; a novel approach is required to provide this multi-scale mechanistic insight. We present a fundamentally simple yet powerful approach to simulate electrical excitation in highly heterogeneous whole-heart models that exploits the underlying discreteness of the myocardium. Preliminary simulations demonstrate that this approach can capture lower conduction velocities and reproduce wave breakdown and the development of re-entry in a range of conditions.

Optical Mapping of Cardiomyocytes in Monolayer Derived from Induced Pluripotent Stem Cells

Optical mapping is a powerful imaging technique widely adopted to measure membrane potential changes and intracellular Ca2+ variations in excitable tissues using voltage-sensitive dyes and Ca2+ indicators, respectively. This powerful tool has rapidly become indispensable in the field of cardiac electrophysiology for studying depolarization wave propagation, estimating the conduction velocity of electrical impulses, and measuring Ca2+ dynamics in cardiac cells and tissues. In addition, mapping these electrophysiological parameters is important for understanding cardiac arrhythmia mechanisms. In this review, we delve into the fundamentals of cardiac optical mapping technology and its applications when applied to hiPSC-derived cardiomyocytes and discuss related advantages and challenges. We also provide a detailed description of the processing and analysis of optical mapping data, which is a crucial step in the study of cardiac diseases and arrhythmia mechanisms for extracting and comparing relevant electrophysiological parameters.

Electroanatomical Conduction Characteristics of Pig Myocardial Tissue Derived from High-Density Mapping

BACKGROUND

Ultra-high-density mapping systems allow more precise measurement of the heart chambers at corresponding conduction velocities (CVs) and voltage amplitudes (VAs). Our aim for this study was to define and compare a basic value set for unipolar CV and VA in all four heart chambers and their separate walls in healthy, juvenile porcine hearts using ultra-high-density mapping.

METHODS

We used the Rhythmia Mapping System to create electroanatomical maps of four pig hearts in sinus rhythm. CVs and VAs were calculated for chambers and wall segments with overlapping circular areas (radius of 5 mm).

RESULTS

We analysed 21 maps with a resolution of 1.4 points/mm2. CVs were highest in the left atrium (LA), followed by the left ventricle (LV), right ventricle (RV), and right atrium (RA). As for VA, LV was highest, followed by RV, LA, and RA. The left chambers had a higher overall CV and VA than the right. Within the chambers, CV varied more in the right than in the left chambers, and VA varied in the ventricles but not in the atria. There was a slightly positive correlation between CVs and VAs at velocity values of <1.5 m/s.

CONCLUSIONS

In healthy porcine hearts, the left chambers showed higher VAs and CVs than the right. CV differs mainly within the right chambers and VA differs only within the ventricles. A slightly positive linear correlation was found between slow CVs and low VAs.

Biomimetic Approaches in Cardiac Tissue Engineering: Replicating the Native Heart Microenvironment

Cardiovascular diseases, including heart failure, pose significant challenges in medical practice, necessitating innovative approaches for cardiac repair and regeneration. Cardiac tissue engineering has emerged as a promising solution, aiming to develop functional and physiologically relevant cardiac tissue constructs. Replicating the native heart microenvironment, with its complex and dynamic milieu necessary for cardiac tissue growth and function, is crucial in tissue engineering. Biomimetic strategies that closely mimic the natural heart microenvironment have gained significant interest due to their potential to enhance synthetic cardiac tissue functionality and therapeutic applicability. Biomimetic approaches focus on mimicking biochemical cues, mechanical stimuli, coordinated electrical signaling, and cell-cell/cell-matrix interactions of cardiac tissue. By combining bioactive ligands, controlled delivery systems, appropriate biomaterial characteristics, electrical signals, and strategies to enhance cell interactions, biomimetic approaches provide a more physiologically relevant environment for tissue growth. The replication of the native cardiac microenvironment enables precise regulation of cellular responses, tissue remodeling, and the development of functional cardiac tissue constructs. Challenges and future directions include refining complex biochemical signaling networks, paracrine signaling, synchronized electrical networks, and cell-cell/cell-matrix interactions. Advancements in biomimetic approaches hold great promise for cardiovascular regenerative medicine, offering potential therapeutic strategies and revolutionizing cardiac disease modeling. These approaches contribute to the development of more effective treatments, personalized medicine, and improved patient outcomes. Ongoing research and innovation in biomimetic approaches have the potential to revolutionize regenerative medicine and cardiac disease modeling by replicating the native heart microenvironment, advancing functional cardiac tissue engineering, and improving patient outcomes.

Sevoflurane Improves Ventricular Conduction by Exosomes Derived from Rat Cardiac Fibroblasts After Hypothermic Global Ischemia-Reperfusion Injury

Purpose

This study investigated the effect of exosomes derived from sevoflurane-treated cardiac fibroblasts (Sev-CFs-Exo) on reperfusion arrhythmias (RA), ventricular conduction, and myocardial ischemia-reperfusion injury (MIRI).

Methods

Primary cardiac fibroblasts (CFs) were isolated from the hearts of neonatal rats and identified by morphology and immunofluorescence. Exosomes were isolated from CFs at passages 2-3 after they had been treated with 2.5% sevoflurane for an hour and cultivated for 24-48 hours. The control group was CFs that did not receive any treatment. The hypothermic global ischemia-reperfusion injury model was established using the Langendorff perfusion technique following injection with exosomes through the caudal vein. Multi-electrode array (MEA) mapping was used to investigate the changes in RA and ventricular conduction in isolated hearts. Western blots and immunofluorescence were used to examine the relative expression and location of connexin 43 (Cx43). In addition, the MIRI was evaluated with triphenyl tetrazolium chloride and Hematoxylin-Eosin staining.

Results

The primary CFs had a variety of morphologies, no spontaneous pulsation, and were vimentin-positive, which confirmed their successful isolation. Sev-CFs-Exo increased the heart rate (HR) at reperfusion for 15 minutes (T₂) and 30 minutes (T₃) and lowered the score and duration of RA and the time for restoration of heartbeat in reperfusion. Meanwhile, Sev-CFs-Exo increased conduction velocity (CV), decreased absolute inhomogeneity (P_5-95) and inhomogeneity index (P_5-95/P₅₀) at T₂ and T₃, as well as promoted the recovery of HR, CV, P_5-95 and P_5-95/P₅₀ after hypothermic global ischemia-reperfusion injury. Furthermore, Sev-CFs-Exo raised expression and reduced lateralization of Cx43, and improved myocardial infarct sizes and cellular necrosis. However, while cardiac fibroblast-derived exosomes (CFs-Exo) showed similar cardioprotective effects, the outcomes were not as significant.

Conclusion

Sevoflurane reduces the risk of RA and improves ventricular conduction and MIRI by CFs-Exo, and this may be driven by the expression and location of Cx43.

KairoSight-3.0 : A Validated Optical Mapping Software to Characterize Cardiac Electrophysiology, Excitation-Contraction Coupling, and Alternans

Background

Cardiac optical mapping is an imaging technique that measures fluorescent signals across a cardiac preparation. Dual optical mapping of voltage-sensitive and calcium-sensitive probes allow for simultaneous recordings of cardiac action potentials and intracellular calcium transients with high spatiotemporal resolution. The analysis of these complex optical datasets is both time intensive and technically challenging; as such, we have developed a software package for semi-automated image processing and analysis. Herein, we report an updated version of our software package ( KairoSight-3 . 0 ) with features to enhance characterization of cardiac parameters using optical signals.

Methods

To test software validity and applicability, we used Langendorff-perfused heart preparations to record transmembrane voltage and intracellular calcium signals from the epicardial surface. Isolated hearts from guinea pigs and rats were loaded with a potentiometric dye (RH237) and/or calcium indicator dye (Rhod-2AM) and fluorescent signals were acquired. We used Python 3.8.5 programming language to develop the KairoSight-3 . 0 software. Cardiac maps were validated with a user-specified manual mapping approach.

Results

Manual maps of action potential duration (30 or 80% repolarization), calcium transient duration (30 or 80% reuptake), action potential and calcium transient alternans were constituted to validate the accuracy of software-generated maps. Manual and software maps had high accuracy, with >97% of manual and software values falling within 10 ms of each other and >75% within 5 ms for action potential duration and calcium transient duration measurements (n=1000-2000 pixels). Further, our software package includes additional cardiac metric measurement tools to analyze signal-to-noise ratio, conduction velocity, action potential and calcium transient alternans, and action potential-calcium transient coupling time to produce physiologically meaningful optical maps.

Conclusions

KairoSight-3 . 0 has enhanced capabilities to perform measurements of cardiac electrophysiology, calcium handling, and the excitation-contraction coupling with satisfactory accuracy.

Graphical Abstract Demonstrating Experimental and Data Analysis Workflow

Created with Biorender.com.

Modulation of cardiac ventricular conduction: Impact on QRS duration, amplitude and dispersion

Alterations in cardiac impulse conduction may exert both beneficial and detrimental effects. The assessment of ventricular conduction properties is of paramount importance both in clinical and in experimental settings. Currently the duration of the QRS complex is regarded as hallmark of in-vivo assessment of global ventricular conduction time. In addition, the amplitude of the QRS complex has been suggested to reflect ventricular conduction time in man and in rats. Here, for the first time, we systematically investigated the relationship between QRS duration ("QRS") and QRS amplitude ("RS-height"; RSh) in the murine ECG obtained during anesthesia. In mice harbouring a homozygous knockout of the transmembrane protein podoplanin (PDPN-/-; n = 10) we found both a shorter QRS and a greater RSh than in wild-type animals (n = 13). In both genotypes cumulative i.p. administration of 5 mg/kg and 10 mg/kg of the Na channel blocker flecainide resulted in dose-dependent QRS increase and RSh decrease, whereby the drug-induced changes in RSh were greater than in QRS. In both genotypes the flecainide-induced changes in QRS and in RSh were significantly correlated with each other (R = -0.56, P = 0.004). Whereas dispersion of QRS and RSh was similar between genotypes, dispersion of the ratio QRS/RSh was significantly smaller in PDPN-/- than in wild-types. We conclude that in the murine ECG QRS is inversely related to RSh. We suggest that both parameters should be considered in the analysis of ventricular conduction time in the murine ECG.

Electrical Remodelling in Cardiac Disease

The human heart responds to various diseases with structural, mechanical, and electrical remodelling processes [...].

Assessment of Tissue Viability by Functional Imaging of Membrane Potential

Electrical activity plays a key role in physiology, in particular for signaling and coordination. Cellular electrophysiology is often studied with micropipette-based techniques such as patch clamp and sharp electrodes, but for measurements at the tissue or organ scale, more integrated approaches are needed. Epifluorescence imaging of voltage-sensitive dyes ("optical mapping") is a tissue non-destructive approach to obtain insight into electrophysiology with high spatiotemporal resolution. Optical mapping has primarily been applied to excitable organs, especially the heart and brain. Action potential durations, conduction patterns, and conduction velocities can be determined from the recordings, providing information about electrophysiological mechanisms, including factors such as effects of pharmacological interventions, ion channel mutations, or tissue remodeling. Here, we describe the process for optical mapping of Langendorff-perfused mouse hearts, highlighting potential issues and key considerations.

Guidelines for assessment of cardiac electrophysiology and arrhythmias in small animals

Cardiac arrhythmias are a major cause of morbidity and mortality worldwide. Although recent advances in cell-based models, including human-induced pluripotent stem cell-derived cardiomyocytes (iPSC-CM), are contributing to our understanding of electrophysiology and arrhythmia mechanisms, preclinical animal studies of cardiovascular disease remain a mainstay. Over the past several decades, animal models of cardiovascular disease have advanced our understanding of pathological remodeling, arrhythmia mechanisms, and drug effects and have led to major improvements in pacing and defibrillation therapies. There exist a variety of methodological approaches for the assessment of cardiac electrophysiology and a plethora of parameters may be assessed with each approach. This guidelines article will provide an overview of the strengths and limitations of several common techniques used to assess electrophysiology and arrhythmia mechanisms at the whole animal, whole heart, and tissue level with a focus on small animal models. We also define key electrophysiological parameters that should be assessed, along with their physiological underpinnings, and the best methods with which to assess these parameters.

Atrial conduction velocity mapping: clinical tools, algorithms and approaches for understanding the arrhythmogenic substrate

Characterizing patient-specific atrial conduction properties is important for understanding arrhythmia drivers, for predicting potential arrhythmia pathways, and for personalising treatment approaches. One metric that characterizes the health of the myocardial substrate is atrial conduction velocity, which describes the speed and direction of propagation of the electrical wavefront through the myocardium. Atrial conduction velocity mapping algorithms are under continuous development in research laboratories and in industry. In this review article, we give a broad overview of different categories of currently published methods for calculating CV, and give insight into their different advantages and disadvantages overall. We classify techniques into local, global, and inverse methods, and discuss these techniques with respect to their faithfulness to the biophysics, incorporation of uncertainty quantification, and their ability to take account of the atrial manifold.

Insight into the Role of the PI3K/Akt Pathway in Ischemic Injury and Post-Infarct Left Ventricular Remodeling in Normal and Diabetic Heart

Despite the significant decline in mortality, cardiovascular diseases are still the leading cause of death worldwide. Among them, myocardial infarction (MI) seems to be the most important. A further decline in the death rate may be achieved by the introduction of molecularly targeted drugs. It seems that the components of the PI3K/Akt signaling pathway are good candidates for this. The PI3K/Akt pathway plays a key role in the regulation of the growth and survival of cells, such as cardiomyocytes. In addition, it has been shown that the activation of the PI3K/Akt pathway results in the alleviation of the negative post-infarct changes in the myocardium and is impaired in the state of diabetes. In this article, the role of this pathway was described in each step of ischemia and subsequent left ventricular remodeling. In addition, we point out the most promising substances which need more investigation before introduction into clinical practice. Moreover, we present the impact of diabetes and widely used cardiac and antidiabetic drugs on the PI3K/Akt pathway and discuss the molecular mechanism of its effects on myocardial ischemia and left ventricular remodeling.