Epicardial Activation Research Articles

Epicardial slices: an innovative 3D organotypic model to study epicardial cell physiology and activation

The epicardium constitutes an untapped reservoir for cardiac regeneration. Upon heart injury, the adult epicardium re-activates, leading to epithelial-to-mesenchymal transition (EMT), migration, and differentiation. While interesting mechanistic and therapeutic findings arose from lower vertebrates and rodent models, the introduction of an experimental system representative of large mammals would undoubtedly facilitate translational advancements. Here, we apply innovative protocols to obtain living 3D organotypic epicardial slices from porcine hearts, encompassing the epicardial/myocardial interface. In culture, our slices preserve the in vivo architecture and functionality, presenting a continuous epicardium overlaying a healthy and connected myocardium. Upon thymosin β4 treatment of the slices, the epicardial cells become activated, upregulating epicardial and EMT genes, resulting in epicardial cell mobilization and differentiation into epicardial-derived mesenchymal cells. Our 3D organotypic model enables to investigate the reparative potential of the adult epicardium, offering an advanced tool to explore ex vivo the complex 3D interactions occurring within the native heart environment.

CineECG: A novel method to image the average activation sequence in the heart from the 12-lead ECG

The standard 12-lead electrocardiogram (ECG) is a diagnostic tool to asses cardiac electrical activity. The vectorcardiogram is a related tool that represents that activity as the direction of a vector. In this work we investigate CineECG, a new 12-lead ECG based analysis method designed to directly estimate the average cardiac anatomical location of activation over time.We describe CineECG calculation and a novel comparison parameter, the average isochrone position (AIP). In a model study, fourteen different activation sequences were simulated and corresponding 12-lead ECGs were computed. The CineECG was compared to AIP in terms of location and direction. In addition, 67-lead body surface potential maps from ten patients were used to study the sensitivity of CineECG to electrode mispositioning and anatomical model selection. Epicardial activation maps from four patients were used for further evaluation.The average distance between CineECG and AIP across the fourteen sequences was 23.7 ± 2.4 mm, with significantly better agreement in the terminal (27.3 ± 5.7 mm) versus the initial QRS segment (34.2 ± 6.1 mm). Up to four cm variation in electrode positioning produced an average distance of 6.5 ± 4.5 mm between CineECG trajectories, while substituting a generic heart/torso model for a patient-specific one produced an average difference of 6.1 ± 4.8 mm. Dominant epicardial activation map features were recovered.Qualitatively, CineECG captured significant features of activation sequences and was robust to electrode misplacement. CineECG provides a realistic representation of the average cardiac activation in normal and diseased hearts. In particular, the terminal segment of the CineECG might be useful to detect pathology.

Abstract 11481: Non-Invasive Electrocardiographic Mapping of the Human Heart Through a Novel 'Cardiac Magnetic Resonance-Electrocardiographic Imaging' Solution for High Throughput Use

Background: Electrocardiographic imaging (ECGI) non-invasively maps the heart’s electrical activity through multiple leads on the body surface. Cardiologists need a safe, quick, affordable and re-usable ECGI method to apply to patients undergoing cardiovascular magnetic resonance (CMR), but current solutions are not suitable for high-throughput use. We developed a CMR-ECGI vest for high-throughput use and report the first in vivo results. Methods: We designed and fabricated the CMR-ECGI vest from cotton, containing 256 square (2x2cm) dry textile electrodes each tagged with a localisation marker ( Fig 1 ). Body surface potentials were recorded and co-registered with heart-torso geometries obtained from CMR ( Fig 2 ). Epicardial unipolar potentials were reconstructed using state-of-the-art ECGI algorithms (YR Lab) and local activation and repolarization times were computed using standard methods. Results: Ten healthy volunteers with normal resting ECGs were recruited (34±10years; 60% male). A recumbent 5-minute ECGI recording was performed (preparation time ~15 minutes for montage and doffing). 3 Tesla CMR provided baseline parameters (left ventricular ejection fraction [LVEF] 75±5%, right ventricular [RV] EF 57±5%, native T1 1275±23ms, T2 42±1ms) and showed no clinically significant late gadolinium enhancement. ECGI showed that the sites of earliest and latest activation were the basal RV ( Fig 3A ) and basal-lateral LV respectively ( Fig 3B ). Total duration of epicardial activation and repolarization was 73.3±8.9ms and 195±35.2ms, respectively. These epicardial activation patterns in health are in line with previously described ECGI data. Conclusions: We have developed a re-usable and high-throughput CMR-ECGI solution that is safe and well-tolerated in vivo . This technology is now available for large-scale clinical research use to provide deeper insights into the pathophysiology of arrhythmogenesis, through seamless integration with CMR.

Abstract 11266: Murine Adult Epicardium Requires Hypoxia for Progenitor and Multipotency Ability

Introduction: The epicardium is a source of the coronary vasculature and stroma during heart development. Although quiescent in the physiological adult heart, increasing evidences indicate the potential epicardium activation and differentiation into its progeny after cardiac injury; however, this remains debated. Hypothesis: We hypothesize that in vivo hypoxia exposure can mimic the embryonic cardiac profile and prime the adult epicardial progenitor cell to a more immature profile. Methods: Perinatal and adult BL6 and Pw1 nLacz hearts were used to track the expression of PW1 - progenitor cell marker - together with cell surface proteins. In vivo hypoxia (10% O 2 ) exposure was used to stimulate the adult heart. Histology, protein expression profiles and single cell analysis were assessed. Freshly FACS isolated Gp38 + PW1 + epicardial cells were cultured to determine their progenitor cell potential (clonogenicity, self-renewal and cell fate potential). Results: Here, we report that PW1 expression decreases during postnatal life, but is maintained in the cardiac hypoxic niche epicardium and subepicardium. Adult mice exhibit increased PW1 expression in epicardial/subepicardial cells and endothelial cells in response to hypoxia. The epicardium and subepicardium are activated to undergo cell proliferation and re-express a subset of embryonic genes in response to hypoxia. We established a new in vitro model to study purified PW1 + /Gp38 + epicardial cells, and we found properties of clonogenicity, self-renewal and multipotency (fibroblast, smooth muscle and endothelial cells) at single cell level in the developing epicardial cells. Cell fate potential towards an endothelial profile is dependent upon low levels of oxygen, and the in vitro ability to grow in culture is restore after in vivo priming of the adult heart. Conclusions: In conclusion our data support that the resident PW1 + /Gp38 + epicardial cells are a reminiscent progenitor population in adult mammalian heart that can be reactivated by exposure to hypoxia, highlighting the potential therapeutic role of hypoxia in regenerative medicine.

An improved procedure for isolating adult mouse cardiomyocytes for epicardial activation mapping.

Cardiovascular disease is a leading cause of death and disability worldwide. Although genetically modified mouse models offer great potential for robust research in vivo, in vitro studies using isolated cardiomyocytes also provide an important approach for investigating the mechanisms underlying cardiovascular disease pathogenesis and drug actions. Currently, isolation of mouse adult cardiomyocytes often relies on aortic retrograde intubation under a stereoscopic microscope, which poses considerable technical barriers and requires extensive training. Although a simplified, Langendorff‐free method has been used to isolate viable cardiomyocytes from the adult mouse heart, the system requires enzymatic digestions and continuous manual technical operation. This study established an optimized approach that allows isolation of adult mouse cardiomyocytes and epicardial activation mapping of mouse hearts using a Langendorff device. We used retrograde puncture through the abdominal aorta in vivo and enzymatic digestion on the Langendorff perfusion device to isolate adult mouse cardiomyocytes without using a microscope. The yields of isolated cardiomyocytes were amenable to patch clamp techniques. Furthermore, this approach allowed epicardial activation mapping. We used a novel, simplified method to isolate viable cardiomyocytes from adult mouse hearts and to map epicardial activation. This novel approach could be beneficial in more extensive research in the cardiac field.

Ex vivo Validation of Noninvasive Epicardial and Endocardial Repolarization Mapping.

Background: The detection and localization of electrophysiological substrates currently involve invasive cardiac mapping. Electrocardiographic imaging (ECGI) using the equivalent dipole layer (EDL) method allows the noninvasive estimation of endocardial and epicardial activation and repolarization times (AT and RT), but the RT validation is limited to in silico studies. We aimed to assess the temporal and spatial accuracy of the EDL method in reconstructing the RTs from the surface ECG under physiological circumstances and situations with artificially induced increased repolarization heterogeneity.Methods: In four Langendorff-perfused pig hearts, we simultaneously recorded unipolar electrograms from plunge needles and pseudo-ECGs from a volume-conducting container equipped with 61 electrodes. The RTs were computed from the ECGs during atrial and ventricular pacing and compared with those measured from the local unipolar electrograms. Regional RT prolongation (cooling) or shortening (pinacidil) was achieved by selective perfusion of the left anterior descending artery (LAD) region.Results: The differences between the computed and measured RTs were 19.0 ± 17.8 and 18.6 ± 13.7 ms for atrial and ventricular paced beats, respectively. The region of artificially delayed or shortened repolarization was correctly identified, with minimum/maximum RT roughly in the center of the region in three hearts. In one heart, the reconstructed region was shifted by ~2.5 cm. The total absolute difference between the measured and calculated RTs for all analyzed patterns in selectively perfused hearts (n = 5) was 39.6 ± 27.1 ms.Conclusion: The noninvasive ECG repolarization imaging using the EDL method of atrial and ventricular paced beats allows adequate quantitative reconstruction of regions of altered repolarization.

Single-cell RNA sequencing of human fetal epicardium reveals novel markers and regulators of EMT

Abstract Background The heart is covered by the epicardium, consisting of epithelial cells and a mesenchymal layer. The epicardium has been shown to be essential during cardiac development by contributing cells through epithelial-to-mesenchymal transition (EMT) and the secretion of paracrine factors. In the adult, the epicardium conveys a cardioprotective response after myocardial infarction, albeit suboptimal compared to the epicardial contribution to heart development. Although the developing epicardium has been characterised in mice and zebrafish, knowledge on the human fetal epicardium derives mostly from cell culture models. Therefore, direct analysis of the human fetal epicardium is vital as it provides new insights into the cellular and biochemical interactions within the developing heart, which can potentially contribute to enhancing the post-injury response. Aim To study the human fetal epicardium using single-cell RNA sequencing (scRNA seq) in order to determine its cellular composition. The data are further explored to e.g. identify regulators of epicardial EMT. Methods Epicardial layers were isolated from four fetal human hearts (14–15 weeks gestation, obtained under informed consent and according to local ethical approval). Tissue was digested, and single live cells were sorted into 384-wells plates and sequenced. Data analysis was performed using R-packages RaceID3 and StemID2. Findings were validated using qPCR and immunohistochemistry. Results Analysis of 2073 cells reveals a clear clustering of the epicardial epithelium and the mesenchymal population. Importantly, we found that “classical” markers, such as Wilms' Tumor 1 and T-box transcription factor 18, are not specific enough to reliably identify the epicardium, but our analysis has provided markers that do allow for robust identification of the epicardium. Additionally, we were able to identify epicardial subpopulations based on their expression profile and validated these using immunohistochemistry in human fetal and adult heart tissue sections. To establish the regulation of epicardial activation we are focussing on the process of EMT within our dataset using RaceID2. From our analysis, several regulators of epicardial EMT are proposed that will be followed up on in vitro. Conclusions We identify various novel markers of the fetal epithelial epicardium, as well as characterizing markers of the mesenchymal layer. We also identified novel factors involved in epicardial EMT, and these are currently being validated in our cell-culture model. These data can provide new insights into the post-injury response in the adult heart. Funding Acknowledgement Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Dutch Heart Foundation

Atrial slow conduction develops and dynamically expands during premature stimulation in an animal model of persistent atrial fibrillation.

Slow conduction areas and conduction block in the atria are considered pro-arrhythmic conditions. Studies examining the size and distribution of slow conduction regions in the context of persistent atrial fibrillation (AF) may help to develop improved therapeutic strategies for patients with AF. In this work, we studied the differences of size and number in slow conduction areas between control and persistent AF goats and the influence of propagation direction on the development of these pathological conduction areas. Epicardial atrial electrical activations from the left atrial roof were optically mapped with physiological pacing cycle lengths and for the shortest captured cycle lengths. The recordings were converted to local activation times and conduction velocity measures. Regions with slow conduction velocity (less than ) were identified. The size of the connected regions and the number of non-connected regions were counted for propagation from different orthogonal directions. We found that regions of slow conduction significantly increases in our 15 persistent AF goat recordings in response to premature stimulation (24.4±4.3% increase to 36.6±4.4%, p < 0.001). This increase is driven by an increase of size from (3.70±0.89[mm2] to 6.36±0.91[mm2], p = 0.014) for already existing regions and not by generation of new slow conduction regions (11.6±1.8 vs. 13±1.9, p = 0.242). In 12 control goat recordings, no increase from baseline pacing to premature pacing was found. Similarly, size of the slow conduction areas and the count did not change significantly in control animals.

Comparing Non-invasive Inverse Electrocardiography With Invasive Endocardial and Epicardial Electroanatomical Mapping During Sinus Rhythm.

This study presents a novel non-invasive equivalent dipole layer (EDL) based inverse electrocardiography (iECG) technique which estimates both endocardial and epicardial ventricular activation sequences. We aimed to quantitatively compare our iECG approach with invasive electro-anatomical mapping (EAM) during sinus rhythm with the objective of enabling functional substrate imaging and sudden cardiac death risk stratification in patients with cardiomyopathy. Thirteen patients (77% males, 48 ± 20 years old) referred for endocardial and epicardial EAM underwent 67-electrode body surface potential mapping and CT imaging. The EDL-based iECG approach was improved by mimicking the effects of the His-Purkinje system on ventricular activation. EAM local activation timing (LAT) maps were compared with iECG-LAT maps using absolute differences and Pearson’s correlation coefficient, reported as mean ± standard deviation [95% confidence interval]. The correlation coefficient between iECG-LAT maps and EAM was 0.54 ± 0.19 [0.49–0.59] for epicardial activation, 0.50 ± 0.27 [0.41–0.58] for right ventricular endocardial activation and 0.44 ± 0.29 [0.32–0.56] for left ventricular endocardial activation. The absolute difference in timing between iECG maps and EAM was 17.4 ± 7.2 ms for epicardial maps, 19.5 ± 7.7 ms for right ventricular endocardial maps, 27.9 ± 8.7 ms for left ventricular endocardial maps. The absolute distance between right ventricular endocardial breakthrough sites was 30 ± 16 mm and 31 ± 17 mm for the left ventricle. The absolute distance for latest epicardial activation was median 12.8 [IQR: 2.9–29.3] mm. This first in-human quantitative comparison of iECG and invasive LAT-maps on both the endocardial and epicardial surface during sinus rhythm showed improved agreement, although with considerable absolute difference and moderate correlation coefficient. Non-invasive iECG requires further refinements to facilitate clinical implementation and risk stratification.

Combining endocardial mapping and electrocardiographic imaging (ECGI) for improving PVC localization: A feasibility study

IntroductionAccurate reconstruction of cardiac activation wavefronts is crucial for clinical diagnosis, management, and treatment of cardiac arrhythmias. Furthermore, reconstruction of activation profiles within the intramural myocardium has long been impossible because electrical mapping was only performed on the endocardial surface. Recent advancements in electrocardiographic imaging (ECGI) have made endocardial and epicardial activation mapping possible. We propose a novel approach to use both endocardial and epicardial mapping in a combined approach to reconstruct intramural activation times. ObjectiveTo implement and validate a combined epicardial/endocardial intramural activation time reconstruction technique. MethodsWe used 11 simulations of ventricular activation paced from sites throughout myocardial wall and extracted endocardial and epicardial activation maps at approximate clinical resolution. From these maps, we interpolated the activation times through the myocardium using thin-plate-spline radial basis functions. We evaluated activation time reconstruction accuracy using root-mean-squared error (RMSE) of activation times and the percent of nodes within 1 ms of the ground truth. ResultsReconstructed intramural activation times showed an RMSE and percentage of nodes within 1 ms of the ground truth simulations of 3 ms and 70%, respectively. In the worst case, the RMSE and percentage of nodes were 4 ms and 60%, respectively. ConclusionWe showed that a simple, yet effective combination of clinical endocardial and epicardial activation maps can accurately reconstruct intramural wavefronts. Furthermore, we showed that this approach provided robust reconstructions across multiple intramural stimulation sites.

The Role of Myocardial Fiber Direction in Epicardial Activation Patterns via Uncertainty Quantification.

Fiber structure governs the spread of excitation in the heart; however, little is known about the effects of physiological variability in fiber orientation on epicardial activation. To investigate these effects, we implemented ventricular simulations of activation using rule-based fiber orientations, and robust uncertainty quantification algorithms to capture detailed maps of model sensitivity. Specifically, we implemented polynomial chaos expansion, which allows for robust exploration with reduced computational demand through an emulator function to approximate the underlying forward model. We applied these techniques to examine the activation sequence of the heart in response to both epicardial and endocardial stimuli within the left ventricular free wall and variations in fiber orientation. Our results showed that physiological variation in fiber orientation does not significantly impact the location of activation features, but it does impact the overall spread of activation. Future studies will investigate under which circumstances physiological changes in fiber orientation might alter electrical propagation such that the resulting simulations produce misleading outcomes.

Effect of age and sex on the incidence of ventricular arrhythmia in a rat model of acute ischemia

BackgroundThe impact of sex and age on the arrhythmic susceptibility within the setting of acute ischemia is masked by the fact that acute coronary events result from coronary artery disease appearing with age much earlier among men than among women. Methods and resultsLAD ligation or sham operations were performed in rats of both sexes at the age 3 and 24 months. An ECG was recorded continuously for 6 h after the operation. The number of early and late premature ventricular beats (PVBs), episodes of ventricular tachycardia (VT) and fibrillation (VF), heart rate, QRS, QT and Tpeak-Tend duration were analysed. Epicardial action potentials were recorded in vivo, Ca2+ signaling was evaluated in isolated cardiomyocytes, fibrosis and connexin-43 expression and localization were measured in the septum. PVBs, VT and VF episodes are much more common in older males than in young males and females independently from their age. Fibrosis with varying intensity in different muscle layers, hypertrophy of cardiomyocytes, reduced number of gap junctions and their appearance on the lateral myocyte membrane, QT prolongation, increase transmural dispersion of repolarisation and a decreased function of SERCA2a may increase the propensity to arrhythmia within the setting of acute ischemia. ConclusionWe show that the male sex, especially in case of older individuals is a strong predictor of increased arrhythmic susceptibility within the acute ischemia setting regardless of its impact on the occurrence of cardiovascular diseases. A personalized sex-dependent prevention treatment is needed to reduce the mortality in acute phases of myocardial infarction.

GEASI: Geodesic-based earliest activation sites identification in cardiac models.

The identification of the initial ventricular activation sequence is a critical step for the correct personalization of patient‐specific cardiac models. In healthy conditions, the Purkinje network is the main source of the electrical activation, but under pathological conditions the so‐called earliest activation sites (EASs) are possibly sparser and more localized. Yet, their number, location and timing may not be easily inferred from remote recordings, such as the epicardial activation or the 12‐lead electrocardiogram (ECG), due to the underlying complexity of the model. In this work, we introduce GEASI (Geodesic‐based Earliest Activation Sites Identification) as a novel approach to simultaneously identify all EASs. To this end, we start from the anisotropic eikonal equation modeling cardiac electrical activation and exploit its Hamilton–Jacobi formulation to minimize a given objective function, for example, the quadratic mismatch to given activation measurements. This versatile approach can be extended to estimate the number of activation sites by means of the topological gradient, or fitting a given ECG. We conducted various experiments in 2D and 3D for in‐silico models and an in‐vivo intracardiac recording collected from a patient undergoing cardiac resynchronization therapy. The results demonstrate the clinical applicability of GEASI for potential future personalized models and clinical intervention.

Adaptive Cardiac Resynchronization Therapy Effect on Electrical Dyssynchrony (aCRT-ELSYNC): A randomized controlled trial.

BackgroundAdaptive cardiac resynchronization therapy (aCRT) is known to have clinical benefits over conventional CRT, but the mechanisms are unclear.ObjectiveCompare effects of aCRT and conventional CRT on electrical dyssynchrony.MethodsA prospective, double-blind, 1:1 parallel-group assignment randomized controlled trial in patients receiving CRT for routine clinical indications. Participants underwent cardiac computed tomography and 128-electrode body surface mapping. The primary outcome was change in electrical dyssynchrony measured on the epicardial surface using noninvasive electrocardiographic imaging before and 6 months post-CRT. Ventricular electrical uncoupling (VEU) was calculated as the difference between the mean left ventricular (LV) and right ventricular (RV) activation times. An electrical dyssynchrony index (EDI) was computed as the standard deviation of local epicardial activation times.ResultsWe randomized 27 participants (aged 64 ± 12 years; 34% female; 53% ischemic cardiomyopathy; LV ejection fraction 28% ± 8%; QRS duration 155 ± 21 ms; typical left bundle branch block [LBBB] in 13%) to conventional CRT (n = 15) vs aCRT (n = 12). In atypical LBBB (n = 11; 41%) with S waves in V5-V6, conduction block occurred in the anterior RV, as opposed to the interventricular groove in strict LBBB. As compared to baseline, VEU reduced post-CRT in the aCRT (median reduction 18.9 [interquartile range 4.3–29.2 ms; P = .034]), but not in the conventional CRT (21.4 [-30.0 to 49.9 ms; P = .525]) group. There were no differences in the degree of change in VEU and EDI indices between treatment groups.ConclusionThe effect of aCRT and conventional CRT on electrical dyssynchrony is largely similar, but only aCRT harmoniously reduced interventricular dyssynchrony by reducing RV uncoupling.

Inference of ventricular activation properties from non-invasive electrocardiography

The realisation of precision cardiology requires novel techniques for the non-invasive characterisation of individual patients’ cardiac function to inform therapeutic and diagnostic decision-making. Both electrocardiography and imaging are used for the clinical diagnosis of cardiac disease. The integration of multi-modal datasets through advanced computational methods could enable the development of the cardiac ‘digital twin’, a comprehensive virtual tool that mechanistically reveals a patient's heart condition from clinical data and simulates treatment outcomes. The adoption of cardiac digital twins requires the non-invasive efficient personalisation of the electrophysiological properties in cardiac models. This study develops new computational techniques to estimate key ventricular activation properties for individual subjects by exploiting the synergy between non-invasive electrocardiography, cardiac magnetic resonance (CMR) imaging and modelling and simulation. More precisely, we present an efficient sequential Monte Carlo approximate Bayesian computation-based inference method, integrated with Eikonal simulations and torso-biventricular models constructed based on clinical CMR imaging. The method also includes a novel strategy to treat combined continuous (conduction speeds) and discrete (earliest activation sites) parameter spaces and an efficient dynamic time warping-based ECG comparison algorithm. We demonstrate results from our inference method on a cohort of twenty virtual subjects with cardiac ventricular myocardial-mass volumes ranging from 74 cm3 to 171 cm3 and considering low versus high resolution for the endocardial discretisation (which determines possible locations of the earliest activation sites). Results show that our method can successfully infer the ventricular activation properties in sinus rhythm from non-invasive epicardial activation time maps and ECG recordings, achieving higher accuracy for the endocardial speed and sheet (transmural) speed than for the fibre or sheet-normal directed speeds.

3-Dimensional ventricular electrical activation pattern assessed from a novel high-frequency electrocardiographic imaging technique: principles and clinical importance

The study introduces and validates a novel high-frequency (100–400 Hz bandwidth, 2 kHz sampling frequency) electrocardiographic imaging (HFECGI) technique that measures intramural ventricular electrical activation. Ex-vivo experiments and clinical measurements were employed. Ex-vivo, two pig hearts were suspended in a human-torso shaped tank using surface tank electrodes, epicardial electrode sock, and plunge electrodes. We compared conventional epicardial electrocardiographic imaging (ECGI) with intramural activation by HFECGI and verified with sock and plunge electrodes. Clinical importance of HFECGI measurements was performed on 14 patients with variable conduction abnormalities. From 3 × 4 needle and 108 sock electrodes, 256 torso or 184 body surface electrodes records, transmural activation times, sock epicardial activation times, ECGI-derived activation times, and high-frequency activation times were computed. The ex-vivo transmural measurements showed that HFECGI measures intramural electrical activation, and ECGI-HFECGI activation times differences indicate endo-to-epi or epi-to-endo conduction direction. HFECGI-derived volumetric dyssynchrony was significantly lower than epicardial ECGI dyssynchrony. HFECGI dyssynchrony was able to distinguish between intraventricular conduction disturbance and bundle branch block patients.

Prolonged alloxan diabetes mellitus in rabbits, an experimental model associated with increased susceptibility to reperfusion ventricular tachyarrhythmias

Introduction Diabetes mellitus (DM) increases the risk of ventricular arrhythmias and sudden cardiac death in patients with coronary artery disease. However, experimental studies often yield inconsistent results concerning arrhythmic outcomes in DM. Moreover, some studies reported that DM confers antiarrhythmic protection. We hypothesized that the duration of experimental diabetic conditions might be crucial in the DM-related arrhythmogenesis and evaluated myocardial electrical remodeling and susceptibility to ventricular tachyarrhythmias in rabbits with DM of different duration in the experimental ischemia/reperfusion model. Methods Ventricular epicardial contact potential 64-lead mapping and arrhythmia susceptibility burst-pacing testing were performed in 43 healthy and 55 diabetic (alloxan model) anesthetized rabbits undergoing 15-min left anterior descending coronary artery occlusion, followed by 15-min reperfusion. DM duration was from 28 to 76 days (median 42 days, interquartile range (IQR) 36-54 days). Results During ischemia, arrhythmia inducibility did not differ between the groups (14 out of 55 vs 7 out of 43 in the DM and control groups, respectively, p=0.272), but the number of reperfusion ventricular tachycardias and/or ventricular fibrillations (VT/VFs) was higher in the DM group (14 out of 55) as compared to control (3 out of 43, p=0.017). In the diabetic animals, the DM duration was an independent predictor of reperfusion VT/VF in logistic regression analysis adjusted for glucose concentration (OR 1.060; 95% CI 1.006-1.117; p = 0.029). We compared preischemic electrophysiological parameters in the control group, and groups with short and prolonged DM (cut-point 42 days of DM). The groups did not differ in dispersion of repolarization, time of epicardial activation breakthrough, duration of epicardial and total ventricular activation. Only duration of activation-repolarization intervals (ARIs, a surrogate for action potential duration) differed between the groups being increased in the prolonged DM group (Figure). Among the mapping parameters, DM duration was associated with the prolongation of total ventricular activation duration (B 0.152; 95% CI 0.049-0.255; p=0.005) and activation-repolarization intervals (ARIs) (B 0.900; 95% CI 0.315-1.484; p=0.003). The prolonged ARI was the only mapping characteristic predicting reperfusion VT/VF development in logistic regression analysis (OR 1.028; 95% CI 1.009-1.048; p = 0.004) and ROC curve analysis (AUC 0.781, p=0.001) with the optimal cut-off value ARI > 120 ms (sensitivity 0.80, specificity 0.75). Conclusions Prolongation of alloxan DM leads to the progressive lengthening of repolarization and increase in the reperfusion VT/VF inducibility.

Exploring the cause of conduction delays in patients with repaired Tetralogy of Fallot.

Cardiac dyssynchrony in patients with repaired Tetralogy of Fallot (rToF) has been attributed to right bundle branch block (RBBB), fibrosis and/or the patches that are inserted during repair surgery. We aimed to investigate the basis of abnormal activation in rToF patients by mapping the electrical activation sequence during sinus rhythm (SR) and right ventricular (RV) pacing. A total of 17 patients were studied [13 with rToF, 2 with left bundle branch block (LBBB), and 2 without RBBB or LBBB (non-BBB)] during medically indicated cardiac surgery. During SR and RV pacing, measurements were performed using 112-electrode RV endocardial balloons (rToF only) and biventricular epicardial sock arrays (four of the rToF and all non-rToF patients). During SR, functional lines of block occurred in five rToF patients, while RV pacing caused functional blocks in four rToF patients. The line of block persisted during both SR and RV pacing in only 2 out of 13 rToF patients. Compared to SR, RV pacing increased dispersion of septal activation, but not dispersion of endocardial and epicardial activation of the RV free wall. During pacing, RV and left ventricular activation dispersion in rToF patients were comparable to that of the non-rToF patients. The results of the present study indicate that the delayed activation in the right ventricle of rToF patients is predominantly due to block(s) in the Purkinje system and that conduction in RV tissue is fairly normal.

Gap Junctional Communication via Connexin43 between Purkinje Fibers and Working Myocytes Explains the Epicardial Activation Pattern in the Postnatal Mouse Left Ventricle.

The mammalian ventricular myocardium forms a functional syncytium due to flow of electrical current mediated in part by gap junctions localized within intercalated disks. The connexin (Cx) subunit of gap junctions have direct and indirect roles in conduction of electrical impulse from the cardiac pacemaker via the cardiac conduction system (CCS) to working myocytes. Cx43 is the dominant isoform in these channels. We have studied the distribution of Cx43 junctions between the CCS and working myocytes in a transgenic mouse model, which had the His-Purkinje portion of the CCS labeled with green fluorescence protein. The highest number of such connections was found in a region about one-third of ventricular length above the apex, and it correlated with the peak proportion of Purkinje fibers (PFs) to the ventricular myocardium. At this location, on the septal surface of the left ventricle, the insulated left bundle branch split into the uninsulated network of PFs that continued to the free wall anteriorly and posteriorly. The second peak of PF abundance was present in the ventricular apex. Epicardial activation maps correspondingly placed the site of the first activation in the apical region, while some hearts presented more highly located breakthrough sites. Taken together, these results increase our understanding of the physiological pattern of ventricular activation and its morphological underpinning through detailed CCS anatomy and distribution of its gap junctional coupling to the working myocardium.

Electrophysiological properties and involvement of anatomical factors for the prediction of intramural origin in patients with ventricular tachyarrhythmia arising from the left ventricular outflow tract.

To elucidate the electrophysiological predictors of the intramural origins of left ventricular outflow tract-ventricular tachyarrhythmias (LVOT-VAs), and to clarify the involvement of anatomical factors. Twenty-nine successfully ablated LVOT-VAs patients with origins in the aortomitral continuity (AMC) (n = 8), aortic sinus of valsalva (ASV) (n = 9), great cardiac vein (GCV) (n = 5), and intramural myocardium (n = 7) were enrolled. Intramural origins were defined as when effective ablation from AMC and epicardium (ASV and/or GCV) was needed. The local activation time difference (LATD) was calculated as follows: (earliest AMC activation) - (earliest epicardial activation), and was presented as an absolute value. Electrophysiological parameters and anatomical factors predisposing the intramural origins were investigated. LATD of intramural origins was significantly shorter than that of AMC and GCV (4.5 ± 2.6 vs. 12.1 ± 7.4 vs. 17.4 ± 4.7, P < 0.05), respectively. In multivariate logistic regression analysis, LATD was associated with intramural origins (odds ratio: 0.711, confidence interval: 0.514-0.985, P = 0.040). ROC analysis revealed LATD of 7 ms as cut-off value. In computed tomography analysis, some patients who had thick fat tissue below the GCV, and an unusual GCV running pattern might be misdiagnosed as intramural origins. LATD ≤ 7 ms was associated with intramural origins, but with some anatomical limitations.