BACKGROUND:Catheter ablation of ventricular tachycardia (VT) is characterized by long procedures and frequent recurrence. Personalized image-based computational models may provide noninvasive ablation target guidance but are computationally demanding and cannot localize focal arrhythmias. OBJECTIVE:This study aims to clinically validate our near real-time in silico pace mapping (InSPM) approach, which rapidly localizes both focal and re-entrant arrhythmia site of origins within personalized image-based models. METHODS:Personalized models incorporating scar were reconstructed from imaging data in 18 patients with structural heart disease; 12-lead electrocardiogram (ECGs) were obtained during clinical pace mapping and pacing site locations defined as ground truth. ECG templates of induced monomorphic VT were obtained. Virtual pacing was conducted in models and simulated ECGs correlated with clinical templates to produce high-resolution virtual pace-maps. Distance (d) between clinical ground truth sites and simulation predicted target areas with highest correlation quantitatively assessed InSPM accuracy for localizing focal activations. For re-entrant VT, predicted targets were compared with surrogates of VT site of origin and mapped VT circuits. RESULTS:Intrinsic resolution of clinical pace mapping was approximately 4 mm for similarly correlated ECGs (mean correlation coefficient >0.99). Across 270 clinical pace-mapping locations, d was 8.2 mm (6.9‒12 mm), relatively insensitive to cardiomyopathy, but with increased accuracy in right vs left ventricles. Patient-specific ECG electrodes alongside accurate scar representation, particularly in patients with ischemia, were important for optimizing InSPM accuracy. InSPM created from clinical ECG VT templates reliably identified re-entrant VT exit sites. CONCLUSION:InSPM provides a rapid and validated personalized computational modeling ablation technology to accurately localize both focal and re-entrant VTs, which may be practically integrated into clinical workflows.

Background Extrastimulus pacing may identify ventricular tachycardia substrate by exposing decremental conduction, a proarrhythmic myocardial property. Functional conduction block may also occur during extrastimulus pacing but its relevance as a marker of arrhythmogenicity is unknown. Objectives This study sought to establish the differences in ventricular tachycardia substrate identification between steady-state (S1) and single extrastimulus (S2) pacing using isochronal late activation mapping deceleration zones (DZs). Methods S1 and S2 (ventricular effective refractory period +20 ms) maps were collected during right ventricular pacing. DZs were identified for all maps. Annotation delta (ΔS1S2), the difference in last deflection between S1 and S2, was calculated to identify regions demonstrating decremental conduction and functional conduction block. Changes in DZ location and ΔS1S2 were analyzed to identify altered substrate behavior evoked by the extrastimulus. Results Eleven patients (age 66 ± 10 years, 9 male) were included. DZ location was significantly different between S1 and S2 maps. Extrastimulus pacing revealed 5 DZs not identified during steady-state pacing, but functional conduction block masked 4 DZs on the S2 maps that were present on their corresponding S1 map. Regions of significant ΔS1S2 colocalized to the primary DZ in 19 of 22 maps, with no significant difference between the proportion of positive and negative delta observed (P = 0.898). Conclusions Extrastimulus pacing may change the location of DZs identified on isochronal late activation mapping maps and can reveal additional substrate; functional block can mask DZs on S2 maps. Analysis of both S1 and S2 maps facilitates more comprehensive substrate characterization, and regions demonstrating significant ΔS1S2 may represent important ablation targets.

Isochronal late activation mapping (ILAM) is an electrogram annotation and display strategy in which conduction slowing is visually represented by isochronal crowding (IC). Areas of IC have been shown to effectively identify substrate for reentrant VT, which have been called deceleration zones (DZ). Extra-stimulus (ES) mapping is a strategy to unmask arrhythmic substrate by introducing premature complexes. The impact of ES pacing on the location of DZ identified using ILAM is unknown. To compare ILAM maps created during ES pacing, created using the S1 and S2 stimuli, to consider the impact of S2 on activation patterns and the location of DZ. A cohort of seven patients, four with ischaemic and three with non-ischaemic cardiomyopathy, were analysed using the electro-anatomical mapping data collected during a clinical ablation procedure. Electrograms were processed using a custom filtering algorithm based on automated pacing artefact annotation to exclude bipolar electrograms (bip-EGMs) that do not match the specified S2 coupling interval, defined by the operator during the ablation procedure. The last deflection (LD) of the selected bip-EGMs, marking the end of local ventricular activity, was automatically annotated. Bip-EGM selection and annotation was manually verified. LD maps were visualised using eight equally spaced isochrones, reflecting the ILAM strategy. A delta-S1S2 map was generated, displaying the difference between S1 and S2 LD time at corresponding locations during ES mapping, computed as S2-S1. Areas of isochronal crowding, defined as >3 isochrones within a 1cm radius, were classified as primary DZ or other DZ and compared between the S1 and S2 ILAM maps. 23.79±8.37% of the chamber mapped demonstrated earlier activation during S2 mapping, indicating conduction block proximal to the site, 56.99±9.32% of the chamber demonstrated no significant change (<±20ms), and 19.21±6.48% of the chamber mapped demonstrated later activation during S2 mapping, indicating conduction delay. An average of 1.71 DZ were identified on S1 maps, and 2.14 DZ identified on S2 maps. Primary DZ were localised to a different area in 6/7 patients when comparing S1 and S2 ILAM maps. The delta-S1S2 map visualises areas with differences in LD time between the S1 and S2 stimulus, with areas activated later following S2 displayed as blue, and areas activated earlier following S2 displayed in red. A representative example is shown demonstrating isochronal crowding only evident during S2 pacing that localises to the interface between low and normal range bipolar voltage. ILAM identifies different DZ when applied to ES pacing. ES pacing effectively induces decrement in some regions, however functional conduction block may obscure or reveal substrate. A novel method is presented for aggregation of data collected during ES pacing to help visualise global LV activation differences during S1 and S2 mapping.

Computational models of atrial electrophysiology (EP) are increasingly utilized for applications such as the development of advanced mapping systems, personalized clinical therapy planning, and the generation of virtual cohorts and digital twins. These models have the potential to establish robust causal links between simulated in silico behaviors and observed human atrial EP, enabling safer, cost-effective, and comprehensive exploration of atrial dynamics. However, current state-of-the-art approaches lack the fidelity and scalability required for regulatory-grade applications, particularly in creating high-quality virtual cohorts or patient-specific digital twins. Challenges include anatomically accurate model generation, calibration to sparse and uncertain clinical data, and computational efficiency within a streamlined workflow. This study addresses these limitations by introducing novel methodologies integrated into an automated end-to-end workflow for generating high-fidelity digital twin snapshots and virtual cohorts of atrial EP. These innovations include: (i) automated multi-scale generation of volumetric biatrial models with detailed anatomical structures and fiber architecture; (ii) a robust method for defining space-varying atrial parameter fields; (iii) a parametric approach for modeling inter-atrial conduction pathways; and (iv) an efficient forward EP model for high-fidelity electrocardiogram computation. We evaluated this workflow on a cohort of 50 atrial fibrillation patients, producing high-quality meshes suitable for reaction-eikonal and reaction-diffusion models and demonstrating the ability to simulate atrial ECGs under parametrically controlled conditions. These advancements represent a critical step toward scalable, precise, and clinically applicable digital twin models and virtual cohorts, enabling enhanced patient-specific predictions and therapeutic planning.

Background and Objective: Data from electro-anatomical mapping (EAM) systems are playing an increasingly important role in computational modeling studies for the patient-specific calibration of digital twin models. However, data exported from commercial EAM systems are challenging to access and parse. Converting to data formats that are easily amenable to be viewed and analyzed with commonly used cardiac simulation software tools such as openCARP remains challenging. We therefore developed an open-source platform, pyCEPS, for parsing and converting clinical EAM data conveniently to standard formats widely adopted within the cardiac modeling community. Methods and Results: pyCEPS is an open-source Python-based platform providing the following functions: (i) access and interrogate the EAM data exported from clinical mapping systems; (ii) efficient browsing of EAM data to preview mapping procedures, electrograms (EGMs), and electro-cardiograms (ECGs); (iii) conversion to modeling formats according to the openCARP standard, to be amenable to analysis with standard tools and advanced workflows as used for in silico EAM data. Documentation and training material to facilitate access to this complementary research tool for new users is provided. We describe the technological underpinnings and demonstrate the capabilities of pyCEPS first, and showcase its use in an exemplary modeling application where we use clinical imaging data to build a patient-specific anatomical model. Conclusion: With pyCEPS we offer an open-source framework for accessing EAM data, and converting these to cardiac modeling standard formats. pyCEPS provides the core functionality needed to integrate EAM data in cardiac modeling research. We detail how pyCEPS could be integrated into model calibration workflows facilitating the calibration of a computational model based on EAM data.

Sepsis has emerged as a global health burden associated with multiple organ dysfunction and 20% mortality rate in patients. Numerous clinical studies over the past two decades have correlated the disease severity and mortality in septic patients with impaired heart rate variability (HRV), as a consequence of impaired chronotropic response of sinoatrial node (SAN) pacemaker activity to vagal/parasympathetic stimulation. However, the molecular mechanism(s) downstream to parasympathetic inputs have not been investigated yet in sepsis, particularly in the SAN. Based on electrocardiography, fluorescence Ca2+ imaging, electrophysiology, and protein assays from organ to subcellular level, we report that impaired muscarinic receptor subtype 2-G protein-activated inwardly-rectifying potassium channel (M2R-GIRK) signaling in a lipopolysaccharide-induced proxy septic mouse model plays a critical role in SAN pacemaking and HRV. The parasympathetic responses to a muscarinic agonist, namely IKACh activation in SAN cells, reduction in Ca2+ mobilization of SAN tissues, lowering of heart rate and increase in HRV, were profoundly attenuated upon lipopolysaccharide-induced sepsis. These functional alterations manifested as a direct consequence of reduced expression of key ion-channel components (GIRK1, GIRK4, and M2R) in the mouse SAN tissues and cells, which was further evident in the human right atrial appendages of septic patients and likely not mediated by the common proinflammatory cytokines elevated in sepsis.

The aim of this study was to describe the morphology of the cavotricuspid isthmus (CTI) in detail and introduce a comprehensive scheme to describe the topology of this region based on functional considerations. This may lead to a better understanding of isthmus-dependent flutter and fibrillation and to improved intervention strategies. We used images of the cavotricuspid isthmus from 52 rabbits of both sexes with a median weight of 3.40 ± 0.93 kg. The area of the CTI was 124.25 ± 42.14 mm2 with 53.28 ± 21.13 mm2 covered by pectinate muscles connecting the terminal crest and the vestibule. Isthmus length decreased from inferolateral (13.09 ±2.14 mm) to central (9.85 ± 2.14 mm) to paraseptal (4.88 ± 1.96 mm) resembling the overall human geometry. Ramification sites of pectinate muscles were identified and six levels dividing the CTI from posterior to anterior were introduced. This allowed the classification of pectinate muscle segments based on the connected ramification level. To account for the high inter-individual variations in size and shape, the CTI was projected onto a normalized reference frame using bilinear transformation. Furthermore, two measures of complexity were introduced: (i) the ramification index, which reflects the total number of muscle segments connected to a ramification site and (ii) the complexity index, which reflects the type of ramification (branching or merging site). Topological analysis showed that the complexity of the pectinate muscle network decreases from inferolateral to paraseptal and that the number of electrically uncoupled parallel pathways increases in the central section between the terminal crest and the vestibule which introduces potential reentry pathways.

BACKGROUND:Identification of targets for ablation of post-infarction ventricular tachycardias (VTs) remains challenging, often requiring arrhythmia induction to delineate the reentrant circuit. This carries a risk for the patient and may not be feasible. Substrate mapping has emerged as a safer strategy to uncover arrhythmogenic regions. However, VT recurrence remains common.GOAL:To use computer simulations to assess the ability of different substrate mapping approaches to identify VT exit sites.METHODS:A 3D computational model of the porcine post-infarction heart was constructed to simulate VT and paced rhythm. Electroanatomical maps were constructed based on endocardial electrogram features and the reentry vulnerability index (RVI - a metric combining activation (AT) and repolarization timings to identify tissue susceptibility to reentry). Since scar transmurality in our model was not homogeneous, parameters derived from all signals (including dense scar regions) were used in the analysis. Potential ablation targets obtained from each electroanatomical map during pacing were compared to the exit site detected during VT mapping.RESULTS:Simulation data showed that voltage cut-offs applied to bipolar electrograms could delineate the scar, but not the VT circuit. Electrogram fractionation had the highest correlation with scar transmurality. The RVI identified regions closest to VT exit site but was outperformed by AT gradients combined with voltage cut-offs. The performance of all metrics was affected by pacing location.CONCLUSIONS:Substrate mapping could provide information about the infarct, but the directional dependency on activation should be considered. Activation-repolarization metrics have utility in safely identifying VT targets, even with non-transmural scars.

Heart rate variability describes the variation in time intervals between consecutive heart beats and serves as a prognostic marker in cardiac and non-cardiac diseases. The experimental setup used for this study enables electrical as well as optical studie

As progressive organ shortage in cardiac transplantation demands extension of donor criteria, effort is needed to optimize graft survival. Reactive oxygen and nitrogen species, generated during organ procurement, transplantation, and reperfusion, contribute to acute and late graft dysfunction. The combined application of diverse substances acting via different molecular pathways appears to be a reasonable approach to face the complex mechanism of ischemia reperfusion injury. Thus, an antioxidant solution containing α -ketoglutaric acid, 5-hydroxymethylfurfural, N -acetyl-L-methionine, and N -acetyl-selenium-L-methionine was combined with endogenous angiotensin-(1-7). Its capacity of myocardial protection was investigated in isolated Langendorff-perfused rat hearts subjected to warm and cold ischemia. The physiological cardiac parameters were assessed throughout the experiments. Effects were evaluated via determination of the oxidative stress parameters malondialdehyde and carbonyl proteins as well as immunohistochemical and ultrastructural tissue analyses. It was shown that a combination of 20% (v/v) antioxidant solution and 220 pM angiotensin-(1-7) led to the best results with a preservation of heart tissue against oxidative stress and morphological alteration. Additionally, immediate cardiac recovery (after warm ischemia) and normal physiological performance (after cold ischemia) were recorded. Overall, the results of this study indicate substantial cardioprotection of the novel combination with promising prospective for future clinical use.

Beat to beat variability of cardiac tissue or isolated cells is frequently investigated by determining time intervals from electrode measurements in order to compute scale dependent or scale independent parameters. In this study, we utilize high-speed video camera recordings to investigate the variability of intervals as well as mechanical contraction strengths and relative contraction strengths with nonlinear analyses. Additionally, the video setup allowed us simultaneous electrode registrations of extracellular potentials. Sinoatrial node tissue under control and acetylcholine treated conditions was used to perform variability analyses by computing sample entropies and Higuchi dimensions. Beat to beat interval variabilities measured by the two recording techniques correlated very well, and therefore, validated the video analyses for this purpose. Acetylcholine treatment induced a reduction of beating rate and contraction strength, but the impact on interval variability was negligible. Nevertheless, the variability analyses of contraction strengths revealed significant differences in sample entropies and Higuchi dimensions between control and acetylcholine treated tissue. Therefore, the proposed high-speed video camera technique might represent a non-invasive tool that allows long-lasting recordings for detecting variations in beating behavior over a large range of scales.

Hyperthermia during radiofrequency ablation causes reversible and irreversible changes of the electrophysiological properties of cardiac tissue. However, the mechanisms are incompletely understood. We studied changes of conduction velocity (CV) in rat myocardium under hyperthermic conditions from macroscopic to microscopic scale by using simultaneous optical mapping and a miniaturized electrode array. Atrial preparations from five rats were superfused at tissue bath temperatures between 36.7°C and 43.8°C. Optical mapping data showed an elevated median CV by 21% when increasing the temperature from 36.7°C to 42.0°C. CV did not increase above 42.0°C. Electrical measurements revealed a similar temperature dependence of CV between 36.7°C and 42.0°C, i.e. an increase of median CV by 26%. The consolidation of optical and electrical data in this study allowed investigation of excitation during global hyperthermia. Macroscopic optical mapping and microscopic electrical measurements demonstrated that hyperthermia strongly influenced electrical propagation at a microscopic scale.

Heart rate (HR) constantly changes on a beat-to-beat basis due to autonomic influences on the pacemaker process of the sinoatrial node. These changes can be quantified as heart rate variability (HRV). In principle, HRV is caused by complex nonlinear interactions between sinoatrial node cells and the autonomic nervous system. Intracellular recordings of spontaneous action potentials were performed with glass micropipettes. Microelectrodes were connected to a battery-operated amplifier. The reference electrode for potential measurements was a chlorided silver wire immersed into the experiment chamber. Microscopic techniques are commonly used in order to visualize biological tissues or cells. Beside aspects of magnification, illumination, and resolution, the most important parameter in order to visualize beating single cells is contrast. The microscope's field of view depends on the magnification as well as additional optical elements such as mirrors or lenses in the optical path.

Computer simulation turns out to be beneficial when clinical data lack spatio-temporal resolution or parameters cannot be measured at all. To derive trustworthy results, these in-silico models have to thoroughly parameterized and validated. In this work we present data from a simplified in-vitro setup for characterizing ventricular electromechanics. Right ventricular papillary muscles from New Zealand rabbits were isolated and stretched from slack length to lmax, i.e. the muscle length at maximum active force development. Active stress development showed an almost linear increase for moderate strain (90–100% of lmax) and a significant decrease for larger strain (100–105% of lmax). Passive strain development showed a nonlinear increase. Conduction velocity CV showed an increase of ≈10% between low and moderate strain and no significant decrease beyond. Fitting active active stress-strain relationship using a 5th-order polynomial yielded adequate results for moderate and high strain values, whereas fitting using a logistic function yielded more reasonable results for low strain values. Passive stress-strain relationship was satisfactorily fitted using an exponential function.

Radiofrequency ablation (RFA) is a standard clinical procedure for treating many cardiac arrhythmias. In order to increase the success rate of this treatment, the evaluation of lesion development with the help of intracardiac electrogram (EGM) criteria has to be improved further. We are investigating in-vitro the electrophysiological characteristics of cardiac tissue by using fluorescence-optical and electrical techniques. In this project, it is intended to create ablation lesions under defined conditions in rat atria or ventricle and to determine the electrical activity in the myocardium surrounding these lesions less than 1 s after the ablation. Therefore, we developed a semi-automatic RFA procedure, which was integrated into an existing experimental setup. Firstly, a controllable protection circuit board was designed to galvanically isolate the sensitive amplifiers for measuring extracellular potentials during the ablation. Secondly, a real-time system was implemented to control and to autonomously monitor the RFA procedure. We verified each component as well as the different sequences of the RFA procedure. In conclusion, the expanded setup will be used in future in-vitro experiments to determine new EGM criteria to assess lesion formation during the RFA procedure.

Computer simulation turns out to be beneficial when clinical data lack spatio-temporal resolution or parameters cannot be measured at all. To derive trustworthy results, these in-silico models have to thoroughly parameterized and validated. In this work we present data from a simplified in-vitro setup for characterizing ventricular electromechanics. Right ventricular papillary muscles from New Zealand rabbits were isolated and stretched from slack length to lmax, i.e. the muscle length at maximum active force development. Active stress development showed an almost linear increase formoderate strain (90– 100% of lmax) and a significant decrease for larger strain (100–105% of lmax). Passive strain development showed a nonlinear increase. Conduction velocity CV showed an increase of ≈10% between low and moderate strain and no significant decrease beyond. Fitting active active stressstrain relationship using a 5th-order polynomial yielded adequate results for moderate and high strain values, whereas fitting using a logistic function yielded more reasonable results for low strain values. Passive stress-strain relationship was satisfactorily fitted using an exponential function.

Extracardiac factors of heart rate variability have commonly been investigated using linear and nonlinear methods for a long time. Recently, intracardiac mechanisms on an electrophysiological basis have been found to be also important. This work is focused on the evaluation of complex measures of temporal signals gained with microelectrode measurements of embryonic chick heart aggregates. Septic conditions were mimicked in vitro by lipopolysaccharide (LPS) administration in order to investigate the influence on beat to beat variability. Surrogate data analysis revealed high statistical significances for normalized complexity measures.

Intracellular measurement of action potential duration (APD) restitution is challenging in beating heart tissue preparations because of the risk of loosing impalement of glass microelectrodes during pacing. Therefore short-time pacing protocols are beneficial. In this work we show results from two short lasting pacing protocols applied on a guinea pig papillary muscle which could enhance APD restitution measurements in beating tissue preparations. Furthermore measurements at a large number of recording sites could be promoted by minimizing experiment duration and therefore prevent superfused tissue from suffering ischemia. Simultaneously measured extracellular parameters show large beat-to-beat variations prior to conduction block in one type of protocol (ramp-like). This could provide a basis for conduction block forecasting.