Monophasic Action Potentials Research Articles

Abstract 4136983: Estimating Atrial Fibrillation Rate in Patients Using Artificial Intelligence Referenced to Tissue Action Potentials

Background: Ablation by pulmonary vein isolation (PVI) is the most effective approach to treat atrial fibrillation (AF), but 30-40% of patients may not respond. Studies including the CAPLA trial suggest that ablating sites of rapid activation on the posterior left atrial wall or elsewhere may improve success. However, AF rate is rarely calibrated and, since electrograms often include noise or far field activity, may overestimate rate (underestimate cycle length) at many sites. Hypothesis: We hypothesized that artificial intelligence (AI) algorithms may more accurately indicate local AF rate, by excluding spurious activations referenced to simultaneous monophasic action potential (MAP) recordings, compared to conventional measurements. Methods: We studied N=303 AF patients at ablation (68.2±8.0 years, 17.8% females, 72.9% non-paroxysmal AF). Patients were matched N=229 into development and one quarter (N=74) into hold-out test cohorts. Patients underwent AF mapping using multipolar catheters, and a subset with MAP catheters (MedFact, GmbH). We used the development set to train an AI algorithm to reliably detect AF activations, which we compared in the test cohort to a standard dV/dt approach referenced to adjacent MAPs within 2 mm (N=20 patients) and manually annotated activations (N=64 patients). Results: Fig A shows AF in a 66 year old woman, where dV/dt often marked non-physiological activations within repolarization shown in the adjacent MAP. Conversely, the AI system excluded spurious deflections and better correlated with experts (black). In summary, Fig. B shows that AI provided a higher F1 score than dV/dt compared to MAPs (median[IQR]: 0.86 [0.5 - 1] vs. 0.67 [0.40 - 0.73], p<0.01) and experts (0.89 [0.73 - 1] vs. 0.72 [0.60 - 0.89]], p<0.01). Fig C shows that the AI approach better identified AF cycle length (rate; blue) than standard approaches (green) that substantially underestimate cycle length (p<0.05). Conclusions: In this large registry, a novel AI-based approach more accurately detected AF rates in clinical electrograms, referenced to experts and action potential recordings, than standard approaches which overestimated rate. AI may improve characterization of AF activity within the atria.

Neuron circuit made of a single locally-active memristor

Neuromorphic computing, inspired by the human brain’s architecture, is expected to break the physical limits of transistors and von Neumann bottleneck. The multiple internal state variables of higher-order memristors (second-order or above) possess dynamic complexity and adaptability, enabling them to mimick the characteristics of biological neurons, which are very important building blocks for neuromorphic computing. This paper presents a simple neuron circuit containing a single second-order current-controlled locally-active memristor (LAM). The pinched hysteresis loop and DC V–I curve of the proposed second-order LAM show good odd symmetry. Applying small signal analysis method, we obtain the small-signal equivalent circuit of the neuron circuit, showing a [Formula: see text] parallel structure and an edge of chaos kernel in its locally-active domain. Also, we draw a parameter classification of the neuron circuit, showing four symmetrical edge of chaos domains, which plays an important role in biphasic action potentials. Finally, we demonstrate that the simple neuron circuit can produce monophasic action potentials, biphasic action potentials and co-existing neuromorphic phenomena via subcritical Hopf bifurcation with different input, verifying the simple circuit is suitable as artificial neurons.

Beneficial normalization of cardiac repolarization by carnitine in transgenic short QT syndrome type 1 rabbit models.

Short QT syndrome type 1 (SQT1) is a genetic channelopathy caused by gain-of-function variants in human-ether-a-go-go (HERG) underlying the rapid delayed-rectifier K+ current (IKr), leading to QT-shortening, ventricular arrhythmias, and sudden cardiac death. Data on efficient pharmacotherapy for SQT1 are scarce. In patients with primary carnitine-deficiency, acquired-short QT syndrome (SQTS) has been observed and rescued by carnitine supplementation. Here, we assessed whether carnitine exerts direct beneficial (prolonging) effects on cardiac repolarization in genetic SQTS. Adult wild-type (WT) and transgenic SQT1 rabbits (HERG-N588K, gain of IKr) were used. In vivo electrocardiograms (ECGs), ex vivo monophasic action potentials (APs) in Langendorff-perfused hearts, and cellular ventricular APs and ion currents were assessed at baseline and during L-Carnitine/C16-Carnitine-perfusion. Two-dimensional computer simulations were performed to assess re-entry-based ventricular tachycardia-inducibility. L-Carnitine/C16-Carnitine prolonged QT-intervals in WT and SQT1, leading to QT-normalization in SQT1. Similarly, monophasic and cellular AP duration (APD) was prolonged by L-Carnitine/C16-Carnitine in WT and SQT1. As underlying mechanisms, we identified acute effects on the main repolarizing ion currents: IKr-steady, which is pathologically increased in SQT1, was reduced by L-Carnitine/C16-Carnitine and deactivation kinetics were accelerated. Moreover, L-Carnitine/C16-Carnitine decreased IKs-steady and IK1. In silico modelling identified IKr changes as the main factor for L-Carnitine/C16-Carnitine-induced APD-prolongation. 2D simulations revealed increased sustained re-entry-based arrhythmia formation in SQT1 compared to WT, which was decreased to the WT-level when adding carnitine-induced ion current changes. L-Carnitine/C16-Carnitine prolong/normalize QT and whole-heart/cellular APD in SQT1 rabbits. These beneficial effects are mediated by acute effects on IKr. L-Carnitine may serve as a potential future QT-normalizing, anti-arrhythmic therapy in SQT1.

Loss of protein phosphatase 2A regulatory subunit PPP2R5A is associated with increased incidence of stress-induced proarrhythmia.

Protein phosphatase 2A (PP2A) is a serine/threonine-selective holoenzyme that controls Ca2+ homeostasis and contractility of the heart via dephosphorylation of regulatory proteins. In some genetically modified mouse models with increased arrhythmogenicity, a reduced expression of the regulatory subunit B56α of PP2A was found as a concomitant effect. Whether there is a general correlation between the abundance of B56α and the promotion of cardiac arrhythmogenesis remains unclear. The aim of this study was therefore to investigate the role of PP2A-B56α in the propensity for arrhythmic activity in the heart. The experimental analysis of this question has been addressed by using a mouse model with deletion of the PP2A-B56α gene, PPP2R5A (KO), in comparison to wild-type animals (WT). Evidence for arrhythmogenicity was investigated in whole animal, isolated heart and cardiomyocytes by ECG, recording of monophasic action potential (MAP) induced by programmed electrical stimulation (PES), measurement of Ca2+ transients under increased pacing frequencies and determination of total K+ channel currents (I K). ECG measurements showed a prolongation of QT time in KO vs. WT. KO mice exhibited a higher rate of premature ventricular contractions in the ECG. MAP measurements in Langendorff-perfused KO hearts showed increased episodes of ventricular tachyarrhythmia induced by PES. However, the KO hearts showed values for MAP duration that were similar to those in WT hearts. In contrast, KO showed more myocardial cells with spontaneous arrhythmogenic Ca2+ transient events compared to WT. The whole-cell patch-clamp technique applied to ventricular cardiomyocytes revealed comparable peak potassium channel current densities between KO and WT. These findings support the assumption that a decrease or even the loss of PP2A-B56α leads to an increased propensity of triggered arrhythmias. This could be based on the increased spontaneous Ca2+ tansients observed.

Optical mapping of cardiac electromechanics in beating in vivo hearts

Optical mapping has been widely used in the study of cardiac electrophysiology in motion-arrested, ex vivo heart preparations. Recent developments in motion artifact mitigation techniques have made it possible to optically map beating ex vivo hearts, enabling the study of cardiac electromechanics using optical mapping. However, the ex vivo setting imposes limitations on optical mapping such as altered metabolic states, oversimplified mechanical loads, and the absence of neurohormonal regulation. In this study, we demonstrate optical electromechanical mapping in an in vivo heart preparation. Swine hearts were exposed via median sternotomy. Voltage-sensitive dye, either di-4-ANEQ(F)PTEA or di-5-ANEQ(F)PTEA, was injected into the left anterior descending artery. Fluorescence was excited by alternating green and amber light for excitation ratiometry. Cardiac motion during sinus and paced rhythm was tracked using a marker-based method. Motion tracking and excitation ratiometry successfully corrected most motion artifact in the membrane potential signal. Marker-based motion tracking also allowed simultaneous measurement of epicardial deformation. Reconstructed membrane potential and mechanical deformation measurements were validated using monophasic action potentials and sonomicrometry, respectively. Di-5-ANEQ(F)PTEA produced longer working time and higher signal/noise ratio than di-4-ANEQ(F)PTEA. In addition, we demonstrate potential applications of the new optical mapping system including electromechanical mapping during vagal nerve stimulation, fibrillation/defibrillation. and acute regional ischemia. In conclusion, although some technical limitations remain, optical mapping experiments that simultaneously image electrical and mechanical function can be conducted in beating, in vivo hearts.

The Antiarrhythmic Action of the Na+/Ca2+ Exchanger Inhibitor SEA0400 on Drug-Induced Long QT Syndrome Depends on the Severity of Proarrhythmic Conditions in Anesthetized Atrioventricular Block Rabbits.

To clarify the pharmacological properties of the Na+/Ca2+ exchanger (NCX) inhibitor SEA0400 as an antiarrhythmic agent, we assessed its effects on rapid component of delayed rectifier K+ current (IKr) blocker-induced torsade de pointes (TdP) in isoflurane-anesthetized rabbits. Atrioventricular block was induced in rabbits using a catheter ablation technique, and the monophasic action potential (MAP) of the right ventricle was measured under electrical pacing at 60 beats/min. In non-treated control animals, intravenous administration of low-dose (0.3 mg/kg) or high-dose nifekalant (3 mg/kg) prolonged the MAP duration (MAP90) by 113 ± 11 ms (n = 5) and 237 ± 39 ms (n = 5), respectively, where TdP was induced in 1/5 animals treated with a low dose and in 3/5 animals treated with a high dose of nifekalant. In SEA0400-treated animals, low- and high-dose nifekalant prolonged the MAP90 by 65 ± 13 ms (n = 5) and 230 ± 20 ms (n = 5), respectively. No TdP was induced by the low dose but 1/5 animals treated with a high dose of nifekalant developed TdP. In verapamil-treated animals, low-dose and high-dose nifekalant prolonged MAP90 by 50 ± 12 ms (n = 5) and 147 ± 30 ms (n = 5), respectively, without inducing TdP. These results suggest that SEA0400 has the potential to inhibit low-dose nifekalant-induced TdP by suppressing the MAP-prolonging action of nifekalant, whereas the drug inhibited high-dose nifekalant-induced TdP without affecting the MAP-prolonging action of nifekalant. This may reveal that, in contrast to verapamil, the antiarrhythmic effects of SEA0400 on IKr blocker-induced TdP may be multifaceted, depending on the severity of the proarrhythmogenic conditions present.

Late sodium current in synergism with Ca2+/calmodulin-dependent protein kinase II contributes to β-adrenergic activation-induced atrial fibrillation.

Atrial fibrillation (AF) is frequently associated with β-adrenergic stimulation, especially in patients with structural heart diseases. The objective of this study was to determine the synergism of late sodium current (late INa) and Ca2+/calmodulin-dependent protein kinase (CaMKII)-mediated arrhythmogenic activities in β-adrenergic overactivation-associated AF. Monophasic action potential, conduction properties, protein phosphorylation, ion currents and cellular trigger activities were measured from rabbit-isolated hearts, atrial tissue and atrial myocytes, respectively. Isoproterenol (ISO, 1-15 nM) increased atrial conduction inhomogeneity index, phospho-Nav1.5 and phospho-CaMKII protein levels and late INa by 108%, 65%, 135% and 87%, respectively, and induced triggered activities and episodes of AF in all hearts studied (p < 0.05). Sea anemone toxin II (ATX-II, 2 nM) was insufficient to induce any atrial arrhythmias, whereas the propensities of AF were greater in hearts treated with a combination of ATX-II and ISO. Ranolazine, eleclazine and KN-93 abolished ISO-induced AF, attenuated the phosphorylation of Nav1.5 and CaMKII, and reversed the increase of late INa (p < 0.05) in a synergistic mode. Overall, late INa in association with the activation of CaMKII potentiates β-adrenergic stimulation-induced AF and the inhibition of both late INa and CaMKII exerted synergistic anti-arrhythmic effects to suppress atrial arrhythmic activities associated with catecholaminergic activation. This article is part of the theme issue 'The heartbeat: its molecular basis and physiological mechanisms'.

Electric Field-Based Spatial Analysis of Noncontact Unipolar Electrograms to Map Regional Activation-Repolarization Intervals

BackgroundSpatial heterogeneity in repolarization plays an important role in generating and sustaining cardiac arrhythmias. Reliable determination of repolarization times remains challenging. ObjectivesThe goal of this study was to improve processing of densely sampled noncontact unipolar electrograms to yield reliable high-resolution activation and repolarization maps. MethodsEndocardial noncontact unipolar electrograms were both simulated and recorded in pig left ventricle. Electrical activity on the endocardial surface was processed in terms of a pseudo-electric field. Activation and repolarization times were calculated by using an amplitude-weighted average on QRS and T waves (ie, the E-field method). This was compared vs the conventional Wyatt method on unipolar electrograms. Timing maps were validated against timing on endocardial action potentials in a simulation study. In vivo, activation and repolarization times determined by using this alternative E-field method were validated against simultaneously recorded endocardial monophasic action potentials (MAPs). ResultsSimulation showed that the E-field method provides viable measurements of local endocardial action potential activation and repolarization times. In vivo, correlation of E-field activation times with MAP activation times (rE = 0.76; P < 0.001) was similar to those of Wyatt (rWyatt = 0.80, P < 0.001; P[h1:rE > rWyatt] = 0.82); for repolarization times, correlation improved significantly (rE = 0.96, P < 0.001; rWyatt = 0.82, P < 0.001; P[h1:rE > rWyatt] < 0.00001). This resulted in improved correlations of activation-repolarization intervals to endocardial action potential duration on MAP (rE = 0.96, P < 0.001; rWyatt = 0.86, P < 0.001; P[h1:rE > rWyatt] < 0.00001). Spatial beat-to-beat variation of repolarization could only be calculated by using the E-field methodology and correlated well with the MAP beat-to-beat variation of repolarization (rE = 0.76; P = 0.001). ConclusionsThe E-field method substantially enhances information from endocardial noncontact electrogram data, allowing for dense maps of activation and repolarization times and derived parameters.

Biphasic action potential and chaos in a symmetrical Chua Corsage Memristor-based circuit.

Neuromorphic computing provides unique computing and memory capabilities that could break the limitation of conventional von Neumann computing. Toward realizing neuromorphic computing, fabrication and synthetization of hardware elements and circuits to emulate biological neurons are crucial. Despite the striking progress in exploring neuron circuits, the existing circuits can only reproduce monophasic action potentials, and no studies report on circuits that could emulate biphasic action potentials, limiting the development of neuromorphic devices. Here, we present a simple third-order memristive circuit built with a classical symmetrical Chua Corsage Memristor (SCCM) to accurately emulate biological neurons and show that the circuit can reproduce monophasic action potentials, biphasic action potentials, and chaos. Applying the edge of chaos criterion, we calculate that the SCCM and the proposed circuit have the symmetrical edge of chaos domains with respect to the origin, which plays an important role in generating biphasic action potentials. Also, we draw a parameter classification map of the proposed circuit, showing the edge of chaos domain (EOCD), the locally active domain, and the locally passive domain. Near the calculated EOCD, the third-order circuit generates monophasic action potentials, biphasic action potentials, chaos, and ten types of symmetrical bi-directional neuromorphic phenomena by only tuning the input voltage, showing a resemblance to biological neurons. Finally, a physical SCCM circuit and some experimentally measured neuromorphic waveforms are exhibited. The experimental results agree with the numerical simulations, verifying that the proposed circuit is suitable as artificial neurons.

Nonlinear analysis of beat-to-beat variability of action potential time series data identifies dynamic re-entrant substrates in a hypokalaemic mouse model of acquired long QT syndrome

BackgroundPrevious studies have quantified repolarization variability using time-domain, frequency-domain and nonlinear analysis in mouse hearts. Here, we investigated the relationship between these parameters and ventricular arrhythmogenicity in a hypokalaemia model of acquired long QT syndrome.MethodsLeft ventricular monophasic action potentials (MAPs) were recorded during right ventricular regular 8 Hz pacing during normokalaemia (5.2 mM [K+]), hypokalaemia modeling LQTS (3 mM [K+]) or hypokalaemia with 0.1 mM heptanol in Langendorff-perfused mouse hearts.ResultsDuring normokalaemia, mean APD was 33.5 ± 3.7 ms. Standard deviation (SD) of APDs was 0.63 ± 0.33 ms, coefficient of variation was 1.9 ± 1.0% and the root mean square (RMS) of successive differences in APDs was 0.3 ± 0.1 ms. Low- and high-frequency peaks were 0.6 ± 0.5 and 2.3 ± 0.7 Hz, respectively, with percentage powers of 38 ± 22 and 61 ± 23%. Poincaré plots of APDn+1 against APDn revealed ellipsoid morphologies with SD along the line-of-identity (SD2) to SD perpendicular to the line-of-identity (SD1) ratio of 4.6 ± 1.1. Approximate and sample entropy were 0.49 ± 0.12 and 0.64 ± 0.29, respectively. Detrended fluctuation analysis revealed short- and long-term fluctuation slopes of 1.62 ± 0.27 and 0.60 ± 0.18, respectively. Hypokalaemia provoked ventricular tachycardia in six of seven hearts, prolonged APDs (51.2 ± 7.9 ms), decreased SD2/SD1 ratio (3.1 ± 1.0), increased approximate and sample entropy (0.68 ± 0.08 and 1.02 ± 0.33) and decreased short-term fluctuation slope (1.23 ± 0.20) (ANOVA, P < 0.05). Heptanol prevented VT in all hearts studied without further altering the above repolarization parameters observed during hypokalaemia.ConclusionReduced SD2/SD1, increased entropy and decreased short-term fluctuation slope may reflect arrhythmic risk in hypokalaemia. Heptanol exerts anti-arrhythmic effects without affecting repolarization variability.

Abstract 11651: Machine Learning of Action Potential Shape to Define Refractory Periods in Ischemiccardiomyopathy

Introduction: The effective refractory period (ERP) can characterize arrhythmic risk. To measure it clinically, a pacing protocol with 8-10 beats is required, preventing beat to beat analysis. Monophasic action potentials (MAP) can indicate ERP on every single beat (Fig A), but are often difficult to annotate due to a wandering baseline (Fig B). Hypothesis: We hypothesized that machine learning of ventricular MAPs could help identify instantaneous repolarization, without requiring manual measurement and without measuring time to drop to a specific repolarization voltage. Methods: We analyzed 5706 MAPs from 42 patients (age 65±13 Y) with ischemic cardiomyopathy in pacing. A multilayer perceptron (MLP) was developed to input MAP shapes and output action potential duration at 30, 60, 90% (MAPD 30,60,90) repolarization, indicating ERP. We used 60% of data in training, 20% in validation, 20% in testing. Results were compared to manual measurement. To identify which MAP regions were key to machine learning, we systematically perturbed MAP regions with white noise and assessed the drop in performance. Results: Errors between APD 30,60 and 90 from MLP and manual marking were 9.3(2.0), 5.8 (1.1) and 5.8 (0.7) ms respectively (fig. C). Fig D shows that MAP phases 0 and 3 were used by MLP to predict APD, as seen in the significant increase in error with perturbations in those MAP regions ( P &lt;0.05). Conclusions: Machine learning can directly indicate effective refractory periods by learning the electrogram shape of single beats, without extrastimuli or manual measurement. Explainability studies confirm that machines learn physiological data. This approach can be used to assess beat-to-beat characterization of atrial fibrillation patients.

Reduction of artifacts and noise in small electrogram datasets without manual annotation using transfer machine learning

Abstract Background/Introduction Mapping AF is challenging. Monophasic action potentials (MAPs) show that most of the recorded signals are not representing the atrial activity, and arise from far-field or other artifacts. Thus, reducing noise in electrophysiological signals is essential, yet it can be difficult for cross-talk from other chambers and pacing. Strategies to reduce noise include template matching, averaging, and smoothing, but all of them have major limitations. Furthermore, expert interpretation requires knowledge to discriminate signals from noise, but is subjective. Purpose We hypothesised a) that atrial and ventricular electrograms with varying artifact and noise can be denoised using autoencoder neural networks (NNs) without requiring manual annotation and in a reproducible manner, and b) we could train these NNs on a large available dataset ventricular signals, then apply transfer learning to the original smaller atrial dataset. We applied this approach to MAPs, which have interpretable shapes and would help identifying local from far-field signals helping in diagnosis, mapping and ablation. Methods We first trained with 5706 left and right ventricular MAPs from 42 patients with ischemic cardiomyopathy (age 65±13y; Fig. 1A), with 60% for training, 20% (validation) and 20% (testing). Transfer learning and parameter-tuning were then used to apply this NN to a smaller sample of atrial MAPs (N=641 from 21 patients, 67±5y, 13 women; Fig. 2B, D, F). The autoencoder was used to eliminate pacing artifacts in ventricular MAPs (Fig. 1B, C) and denoise atrial MAPs (Fig. 2C, E, G) by reconstructing key learned features. The accuracy of the reconstruction was evaluated using Pearson Correlation Coefficient (PCC) and a novel similarity coefficient (SC). No manual annotation was required to identify noisy signals. Results The trained NN encoder learned key features of ventricular MAPs and reconstructed these clean signals with a SC=0.91±0.16 and PCC=0.99±0.01 (Fig. 1A). With this training, the NN was able to denoise ventricular MAPs with pacing artifact (Fig. 1B, C). After fine-tuning, the NN learned key signal features (upstroke, triangular descent, terminus) and thus reduced diverse noise without specific training or manual annotation. Namely, it was able to reconstruct atrial MAPs eliminating ventricular noise, high frequency noise and truncated signals (Fig. 2). Conclusions Machine learned encoder-decoders are powerful tools that can learn essential features of atrial and ventricular signals and hence isolate noise. Transfer learning is effective when large datasets are unavailable for training. This approach can separate atrial beats from far-field ventricular beats and other sources of noise. The ability to eliminate a diverse range of noise improves this approach over existing techniques and may have far-reaching applications in electrophysiology, such as mapping and ablation. Funding Acknowledgement Type of funding sources: Public grant(s) – National budget only. Main funding source(s): NIH

Artificial intelligence to reduce artifact in cardiac electrophysiological signals

Abstract Background/Introduction Signals in Electrophysiology cases are often noisy despite laboratory shielding and filtering, and current noise-reduction methods are suboptimal. Template matching can identify a “nearest type” of electrogram, but libraries of signal shapes may be unavailable. Beat averaging can reduce noise but obscures beat-to-beat variations and is not optimal to analyze dynamically changing signals, such as when moving a catheter in the heart. Smoothing reduces noise yet blurs high frequency components. Purpose We set out to test if machine learned autoencoders could reduce noise in single beats without requiring massive training data or beat libraries. Specifically, we hypothesised that noisy electrograms in small datasets of atrial signals could be de-noised using an encoder-decoder neural network (NN) using transfer learning of machines trained to recognize key features in larger datasets of related signals. Methods We applied NN to monophasic action potentials (MAPs), because they have visually verifiable shapes. The NN was first trained to reconstruct 5706 left and right ventricular MAPs in 42 patients (67±13y; Fig. 1A). Transfer learning was then used to apply the NN to a much smaller dataset of 641 atrial MAPs in 21 patients (67±5y, 13 women; Fig. 1B, D, F). Results NN reconstructed atrial MAPs with a Pearson correlation of 0.87±0.11. After fine-tuning, NN reconstruction accuracy improved dramatically (Pearson 0.99±0.01; p&amp;lt;0.001). In Fig. 1B–G the NN learned key MAP features (upstroke, triangular descent, terminus) and thus could eliminate ventricular artifact and electrical circuit noise without specific training or manual annotation. Conclusion Machine learned autoencoders are a novel and powerful approach to de-noise electrophysiological signals in a dynamic, beat-to-beat fashion. The ability to learn fundamental signal features from models trained in large datasets, and apply them via transfer learning to small datasets in different heart chambers may have wide ranging applications for automated signal annotation, mapping and ablation. Funding Acknowledgement Type of funding sources: Public grant(s) – National budget only. Main funding source(s): NIH

Feasibility of simultaneous multichannel magnetocardiographic mapping, multiple monophasic action potential recording and laser photocoagulation of isolated and perfused rabbit ventricular myocardium

Abstract Background Multichannel magnetocardiographic mapping (MCG) has been validated as an accurate non-invasive method for 3D localization of arrhythmogenic substrates suitable for ablation treatment and of intracardiac electrophysiology catheters (1,2). High resolution (HR) MCG-guided multiple simultaneous monophasic action potential (multi-MAP) recording and pacing with a single patented amagnetic catheter (AC) detects local arrhythmogenic mechanisms (3). Laser photocoagulation (LP) providing more controlled and homogeneous myocardial lesions (4), may be an alternative to radiofrequency (RF) ablation, without unwanted electromagnetic noise effect during real-time MCG. Purpose This study aimed to experimentally test the feasibility of simultaneous multi-MAP recording and LP guided by real-time MCG. Methods An unshielded 36 channels SQUID system (sensitivity of 30 fT/Hz1/2, at 1 Hz) (CMI, USA) was used to study Langendorff-perfused isolated rabbit heart with MCG (Figure 1A). Four epicardial MAPs were simultaneously recorded (inter MAP distance: 1 mm) with a single multi-MAP AC (bandpass: DC-500 Hz; sampling frequency: 2 kHz) (GE-Prucka Cardiolab). LP was performed with a NdYAG laser (Dornier Medilas 5100) and a catheter system for safe myocardium LP (5). The study was carried out according to NIH guidelines for animal care and use. Results MCG imaging of rabbit ventricular magnetic field distribution and inverse source localization with the magnetic dipole model are shown in Figure 1B. The difference in morphology of local HR ventricular multi-MAP signals was compatible with myocardial anisotropy (Figure 1C). With appropriate cooling of the optic fiber-tissue interface, no epicardial damage was induced by LP, whereas deeper well defined intramural myocardial lesions were appreciable, of different size as a function of the energy delivered (Figure 1D). Multi-MAP recording was not significantly disturbed by LP. Keeping the Medilas unit at least 5 meters away from the MCG sensors, no electromagnetic artifacts were observed during MCG. Conclusion MCG, single catheter multi-MAP recording and well-defined LP lesions of ventricular myocardium were simultaneously feasible on Langendorff-perfused isolated rabbit heart, without major electromagnetic interferences, in an unshielded catheterization laboratory. With appropriate technological developments, safe MCG-guided single-catheter laser ablation of focal arrhythmogenic substrates is foreseen as a possible minimally invasive alternative to current interventional approaches. Funding Acknowledgement Type of funding sources: None.

Safe electrophysiologic profile of the neprilysin-inhibitor sacubitril in combination with different antiarrhythmic drugs

Abstract Background Observational clinical data suggest a direct effect of sacubitril on cardiac electrophysiology. However, data concerning the impact of combination of sacubitril with antiarrhythmic drug therapy is sparse. Purpose We aimed at characterizing the electrophysiologic effects of a combination therapy of sacubitril with the class III-drug sotalol and the class IB-agent mexiletine in a sensitive, experimental whole-heart model. Methods and results 25 isolated rabbit hearts were retrogradely perfused. Hearts were treated with mexiletine (25 μM, 13 hearts) or sotalol (100 μM, 12 hearts) after generating baseline data. Eight endo- and epicardial monophasic action potentials and ECG recordings demonstrated an abbreviation of action potential duration (APD90, −21 ms, p&amp;lt;0.01) and no significant changes of QT interval (+10ms, p=ns) after administration of mexiletine. Spatial dispersion of repolarization (SDR) remained stable after mexiletine treatment (+6 ms, p=ns) whereas effective refractory periods (ERP) were significantly prolonged (+80 ms, p&amp;lt;0.01). Sotalol prolonged cardiac repolarization (APD90: +1 ms, p=ns; QT: +24 ms, p&amp;lt;0.01) and amplified spatial dispersion (+19 ms, p&amp;lt;0.01) without changing ERP (+8 ms, p=ns). Additional treatment with sacubitril (5 μM) led to a significant reduction of APD90 (−12 ms, p&amp;lt;0.01), QT interval (−20 ms, p&amp;lt;0.01) and ERP (−23 ms, p&amp;lt;0.01) in the presence of a stable SDR (−4 ms, p=ns) in the mexiletine group. In the sotalol group, additional administration of sacubitril abbreviated APD90 (−9 ms, p&amp;lt;0.05) and QT interval (−13 ms, p&amp;lt;0.01) and reduced ERP (−18 ms, p&amp;lt;0.01) without affecting SDR (−3 ms, p=ns). Ventricular vulnerability was assessed by a predefined pacing protocol employing premature extra stimuli and burst stimulation. After lowering the potassium concentration, 30 episodes of torsade de pointes tachycardia were observed after sotalol treatment (vs. 0 episodes under baseline, p&amp;lt;0.05). Additional sacubitril treatment significantly suppressed torsade de pointes tachycardia (8 episodes, p&amp;lt;0.05) in the sotalol-group. No proarrhythmic effect was observed after mexiletine treatment (8 episodes vs. 3 episodes under baseline conditions, p=ns). Additional sacubitril treatment did not increase ventricular vulnerability (32 episods, p=ns). Conclusion Sacubitril in combination with antiarrhythmic drugs demonstrates a safe electrophysiologic profile. In class IB- and class III-pretreated hearts, sacubitril abbreviates cardiac repolarization duration and effective refractory periods without changing spatial dispersion of repolarization. Thereby, sacubitril reduces the occurrence of torsade de pointes-tachycardia in antiarrhythmic pretreated hearts. Funding Acknowledgement Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): Deutsche Stiftung für Herzforschung (to G.F.)

Dapagliflozin but not empagliflozin prevents atrial fibrillation in an experimental whole-heart model

Abstract Background The SGLT2 inhibitors dapagliflozin and empagliflozin have an evolving role in heart failure therapy. Observational data suggest a lower risk of atrial fibrillation (AF) for patients on SGLT2 inhibitors. So far, it is unclear whether this is related to a direct antiarrhythmic potential of SGLT2 inhibitors or just a marker of improved heart function. Experimental data on the impact of SGTL2 inhibitors on atrial electrophysiology is scarce. Purpose This study aimed at evaluating the effects of the two SGLT2 inhibitors dapagliflozin and empagliflozin on atrial electrophysiology. Methods 25 rabbit hearts were explanted and retrogradely perfused employing the Langendorff-setup. Two catheters were placed on both atria to record monophasic action potentials. Hearts were paced at three different cycle lengths (350ms, 250ms, 150ms), thereby obtaining cycle-length dependent atrial action potential durations (aAPD90) and effective refractory periods (aERP). Atrial post-repolarization (aPRR) refractoriness was determined by the difference between aERP and aAPD90. AF was induced in the presence of acetylcholine (ACh, 1μM) and isoproterenol (Iso, 1μM). Thereafter, hearts were treated with dapagliflozin (n=13, 3 μM) or empagliflozin (n=12, 3 μM). Results Ach/Iso abbreviated aAPD90, aERP and prolonged aPRR in both groups (dapagliflozin group: aAPD90: −49 ms, p&amp;lt;0.01; aERP: −33 ms, p&amp;lt;0.01; aPRR: +18 ms, p=0.06; empagliflozin group: aAPD90: −40 ms, p&amp;lt;0.01; aERP: −25 ms, p&amp;lt;0.05; aPRR: +18 ms, p=0.05). Further treatment with dapagliflozin increased aAPD90 (+13 ms, p&amp;lt;0.01), aERP (+34 ms, p&amp;lt;0.05) and aPRR (+6 ms, p=ns). Additional administration of empagliflozin had no significant effect on aAPD90 (−8 ms, p=ns), aERP (−1 ms, p=ns) or aPRR (+9 ms, p=ns). Vulnerability to AF was assessed by a standardized protocol consisting of several trains of burst pacing. Ach/Iso increased the vulnerability to AF episodes in both groups (dapagliflozin group: 71 episodes vs. 1 under baseline conditions, p&amp;lt;0.01; empagliflozin group: 27 episodes vs. 2 under baseline conditions, p=0.08). Additional perfusion of dapagliflozin significantly reduced the occurrence of AF (to 30 episodes, p&amp;lt;0.05) while additional empagliflozin treatment had no significant antiarrhythmic effect (32 episodes, p=ns). Conclusion Dapagliflozin and empagliflozin had opposing effects on atrial electrophysiology. Dapagliflozin prolonged aAPD90 and aERP, thereby preventing AF. In contrast, empagliflozin did not change aAPD90 or aERP, resulting in no antiarrhythmic effect. Our findings hint at a potential antiarrhythmic benefit of dapagliflozin. Funding Acknowledgement Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): Hans and Gertie Fischer-Foundation (to C.E.)

Effects and pharmacological mechanism of Zhigancao Decoction on electrical and structural remodeling of the atrium of rabbits induced by rapid atrial pacing.

Zhigancao decoction (ZD) has a long history in China as a traditional Chinese medicine compound for the treatment of tachyarrhythmias. This study mainly explored the pharmacological mechanism of Zhigancao Decoction in preventing atrial fibrillation by altering the electrical and structural remodeling of the atrial in rabbits. In total, 30 male New Zealand white rabbits were randomly divided into 3 groups (ten rabbits for each). The first group was sham-operated (control group). The second group was intervened by the rapid right atrium pacing (RAP) to induce atrial fibrillation (AF group), while the third group was given ZD gavage and RAP (AF + ZD group). All rabbits were anesthetized before two monophasic action potential (MAP) catheters were sequentially inserted into the right atrium. After 8h of rapid right atrial pacing, the electrophysiological indexes and the induction rate of atrial fibrillation were observed in the three groups of rabbits, and the left atrial myocardium samples were taken to observe the ultrastructure. Single atrial myocytes were separated by enzymolysis, and the L-type calcium current (ICa-L) of atrial myocytes in different experimental groups was observed by whole-cell patch clamp technique. The fluorescence intensity of Ca2+ in atrial myocytes was observed after Fluo-3/AM fluorescent staining. The main components of ZD were identified by liquid chromatography-mass spectrometry-mass spectrometry (LC-MS/MS) method. Compared with the AF group, the maximum ascent rate (Max dV/dt) and plateau potential were significantly reduced in the ZD group, the action potential duration at 10% and 20% (APD10, APD20) were significantly shortened (P < 0.01), action potential duration at 50%, 70%, and 90% (APD50, APD70, APD90) were significantly prolonged, and atrial effective refractory period (AERP) was significantly prolonged (P < 0.01) in the ZD group. In the ZD group, the ICa-L amplitudes of rabbit atrial myocytes under each clamping voltage were significantly smaller than those in the AF group (P < 0.01) and the control group (P < 0.05). The Ca2+ fluorescence intensity in the rabbit atrial myocytes in the ZD group was significantly weaker than that in the AF group (P < 0.01) and the control group (P < 0.05). Electron microscopy displayed that the control group had neatly arranged atrial tissue myofilaments and intact mitochondria. However, the ultrastructural damage of the AF group was severe compared with that of the ZD group. LC-MS/MS analysis confirmed that ZD contained several antiarrhythmic compounds including ginsenoside, isoliensinine, catalpol, glycyrrhizinate and hesperetin. Rapid atrial pacing (RAP) could cause the electrical and structural remodeling of rabbit atrial myocytes. ZD might reverse the atrial electrical remodeling but could have little effect on structural remodeling, which might be the mechanism of ZD treatment on atrial fibrillation.

Role of cardiac α1-adrenoreceptors for the torsadogenic action of IKr blocker nifekalant in the anesthetized atrioventricular block rabbit

We analyzed role of cardiac α1-adrenoreceptors for the torsadogenic action of IKr blocker nifekalant in isoflurane-anesthetized atrioventricular block rabbits. Bradycardia was induced by atrioventricular node ablation, and the ventricle was electrically driven at a constant rate of 60 beats/min throughout the experiments to prevent rate-dependent modification by the IKr blocker in ventricular repolarization phase. Nifekalant (3 mg/kg per 10 min, n = 5) prolonged the duration of monophasic action potential (MAP90) by +178 ± 43 ms, increased the short-term variability of repolarization (STV) to 4.2 ± 1.2 ms, and induced torsade de pointes (TdP) in 1 animal. In the presence of methoxamine (n = 5), nifekalant prolonged the MAP90 by +328 ± 32 ms, increased the STV to 8.0 ± 1.0 ms, and induced TdP in 2 animals. In the presence of prazosin and methoxamine (n = 5), nifekalant prolonged the MAP90 by +267 ± 22 ms, increased the STV to 9.2 ± 3.6 ms, and induced no TdP. These results suggest that cardiac α1-adrenoreceptor activation by methoxamine essentially sensitizes the rabbit heart to nifekalant-induced QT interval prolongation, leading to the onset of TdP.

Aging-associated susceptibility to stress-induced ventricular arrhythmogenesis is attenuated by tetrodotoxin

Aging is associated with increased prevalence of life-threatening ventricular arrhythmias, but mechanisms underlying higher susceptibility to arrhythmogenesis and means to prevent such arrhythmias under stress are not fully defined. We aimed to define differences in aging-associated susceptibility to ventricular fibrillation (VF) induction between young and aged hearts. VF induction was attempted in isolated perfused hearts of young (6-month) and aged (24-month-old) male Fischer-344 rats by rapid pacing before and following isoproterenol (1 μM) or global ischemia and reperfusion (I/R) injury with or without pretreatment with low-dose tetrodotoxin, a late sodium current blocker. At baseline, VF could not be induced; however, the susceptibility to inducible VF after isoproterenol and spontaneous VF following I/R was 6-fold and 3-fold higher, respectively, in old hearts (P < 0.05). Old animals had longer epicardial monophasic action potential at 90% repolarization (APD90; P < 0.05) and displayed a loss of isoproterenol-induced shortening of APD90 present in the young. In isolated ventricular cardiomyocytes from older but not younger animals, 4-aminopyridine prolonged APD and induced early afterdepolarizations (EADs) and triggered activity with isoproterenol. Low-dose tetrodotoxin (0.5 μM) significantly shortened APD without altering action potential upstroke and prevented 4-aminopyridine-mediated APD prolongation, EADs, and triggered activity. Tetrodotoxin pretreatment prevented VF induction by pacing in isoproterenol-challenged hearts. Vulnerability to VF following I/R or catecholamine challenge is significantly increased in old hearts that display reduced repolarization reserve and increased propensity to EADs, triggered activity, and ventricular arrhythmogenesis that can be suppressed by low-dose tetrodotoxin, suggesting a role of slow sodium current in promoting arrhythmogenesis with aging.

Effects of different dosages esketamine on cardiac conduction and heterogeneity of Cx43: the epicardial mapping in guinea pigs.

BackgroundEsketamine is favored in clinical settings. Relative to other anesthetics it preserves protective airway reflexes, maintains spontaneous respiration, stabilizes hemodynamics, and alleviates neuropathic pain. This study sought to evaluate the cardiac safety of esketamine at 3 sub-anesthetic gradient concentrations.MethodsWe examined the cardiac electrophysiological effects of esketamine with infusion rates of 0.125, 0.25, and 0.5 mg·kg−1·h−1. Short-term studies were performed in ventricular myocytes using patch-clamp techniques and optically mapped Langendorff-perfused guinea-pig hearts. Long-term studies were performed using Langendorff-perfused guinea-pig hearts and electrically mapping the receipt of the infusion for 3 hours.ResultsEsketamine changed the action potential (AP) morphology of cardiomyocytes. Notably, it increased the resting membrane potential (RMP), attenuated the amplitude of action potential (APA), reduced the maximum upstroke velocity (Vmax), and shortened the action potential duration (APD) at 30% to 70%, which led to relatively prolonged monophasic action potentials (MAP) triangulation in G0.25 and G0.5. All the effects were partially eluted. Optical mapping demonstrated almost equal and heterogeneous conduction. G0.125 resulted in an increased heart rate (HR) accompanied by a shortened APD. No detectable arrhythmia was observed at the cycle lengths (CLs) used. Long-term electrical mapping demonstrated the dose-dependent deceleration of the Vmax and APA, but only prolonged the AP parameters in G0.5. Left-ventricular isochronal conduction maps revealed the conduction heterogeneities at G0.5, and conduction velocity (CV) was increased in G0.125 and G0.25. None of these effects were reversed on drug washout. Electrocardiogram (ECG) traces revealed an accelerated HR with the associated curtailment of QT intervals in G0.125; HRs were decreased in G0.25 and G0.5; the PR intervals and QRS duration differed between G0.125 and G0.25, G0.5, which elicited electrical alternans. Connexin43 (Cx43) expression were significantly decreased in G0.125, G0.25 and G0.5.ConclusionsThese data provide a basic electrophysiology for esketamine. Specifically, we found that (I) various methods of esketamine infusion had different effects on cardiac conduction at different dosages; (II) the heterogeneous expression of Cx43 is associated with spatially dispersed conduction; and (III) potential cardiac risks should be considered for high-risk patients receiving continuous esketamine infusions of high dosages.