Background Conductivity Research Articles

Anisotropic induced polarization modeling with neural networks and effective medium theory

Interpreting three-dimensional induced polarization (IP) data requires rock physics models that reflect the omnipresent anisotropy of the Earth’s crust. The Generalized Effective Medium Theory of Induced Polarization (GEMTIP) can model the IP signatures of rocks with polarizable mineral inclusions. However, it is computationally demanding because it requires numerically solving the depolarization tensors of each inclusion. We aim to streamline GEMTIP simulations by (1) integrating anisotropic background conductivity and triaxial ellipsoidal inclusions in the model and (2) estimating the depolarization tensors with a neural network. We validate the neural network predictions against known solutions for spherical and spheroidal inclusions, and we test our method using data from an actual rock sample. The neural network shows a relative sensitivity of 56% to inclusion shape and 44% to host rock anisotropy and is up to 100,000 times faster than numerical integration. We release the pre-trained neural network implementation as an open-source Python package, thereby providing a new method to interpret the IP signatures of anisotropic rocks.

Real-world evidence of implanting leadless pacemakers after transcatheter aortic valve implantation procedures

Abstract Background Conduction disturbances can be a complication of Transcatheter Aortic Valve Implantation (TAVI) procedures, for which transvenous pacemakers (TVPs) are recommended. Leadless pacemakers (LPs) are a safe alternative to TVPs in a pacemaker-indicated population, but little is known about their use for TAVI-related conduction disturbances. Purpose To examine rates of pacemaker implantation post-TAVI, compare complications, all-cause mortality, and ventricular pacing rates in LP vs. TVP patients, and assess pacemaker deactivations/upgrades in LP patients. Methods Data from Optum’s de-identified Clinformatics Data Mart Database linked to a device registry between 2016 and 2021 were used to identify patients with TAVI procedures that are subsequently implanted with an LP or a TVP. Claims data were used to assess complications and all-cause mortality; device-reported parameters were used to calculate VP rates and deactivations. Complication rates, all-cause mortality, ventricular pacing rates, and device deactivations were calculated for patients with a pacemaker implant between 7 days before and 90 days after TAVI. Chronic complication rates, defined as complications with the potential to occur outside the acute peri- or post-procedural period, were assessed at 1 year. Regressions were used to compare complications and all-cause mortality, adjusting for patient characteristics. Results In a cohort of 18,073 patients with a TAVI procedure, 11.7% were implanted with a pacemaker at 1 year post-TAVI; 76.7% of implants occurred within 7 days. LPs comprised 7.2% of the total pacemaker implants observed. Of those LPs in the registry, around 25% have VDD capability. LP patients were older (avg. 84 LP, 82 TVP, p=0.02) and were more likely to have atrial fibrillation, end-stage or chronic kidney disease, and ventricular arrhythmias. Of patients implanted with a pacemaker within 90 days post-TAVI (LP N=122, TVP N=1,779), there were no differences in 30-day complication rates (12.3% LP, 15.6% TVP, unadj. p=0.33, adj. p=0.27). LP had fewer chronic complications than TVP (0.8% LP, 9.4% TVP, unadj. p=0.02, adj p=0.02) though the sample size was small. LP patients had higher unadjusted 30-day all-cause mortality (4.1% LP, 1.0% TVP, unadj. p=0.01, adj. p=0.06), reflecting the higher acuity of LP patients. At both 30 days and 1 year post-implant, most patients (85.3% LP, 72.7% TVP) continued to receive pacing support (ventricular pacing >10%). TVP patients were more likely than LP patients to be pacing dependent (ventricular pacing ≥90%) at both 30 days (53.8% vs. 29.4%) and 1 year (44.7% vs. 35.7%) post-implant. There were no observed deactivations/upgrades in LP patients at 1 year. Conclusion LPs, when used concomitantly with TAVI procedures, show similar acute and lower chronic complication rates compared to patients treated with TVPs implanted with TAVI. Most patients who received a pacemaker post-TAVI continue to receive pacing support.Acute and Chronic complicationsVentricular pacing

Utilizing unsupervised machine learning to uncover novel phenogroups within the broad QRS complex

Abstract Background Conduction disease can manifest as a broad QRS complex on the ECG. Broad QRS is conventionally categorised as left bundle branch block (LBBB) and right bundle branch block (RBBB) or non-specific intraventricular conduction delay (IVCD), based on QRS morphology. These subgroups were coined over a century ago and have been relevant for heart failure with reduced ejection fraction and cardiac resynchronization therapy (CRT). However, there may be more precise phenogroups underlying broad QRS complexes. Purpose Using unsupervised machine learning to define novel broad QRS phenogroups and characterise them using clinical variables and disease outcomes. Methods We extracted 51 relevant features using a Variational Autoencoder from 47,456 median-beat ECGs with broad QRS intervals (QRS ≥ 130ms) from a secondary care cohort. These were input into Discriminative Dimensionality Reduction via Learning a Tree (DDRTree), a clustering method that models the continuum of heterogeneity by projecting the underlying distribution as a tree structure in a low-dimensional space, while assigning distinct branch/cluster labels. Results Six distinct phenogroups were identified within broad QRS morphologies (Figure-1). Two branches were RBBB dominant (Branch 1: more males, high-comorbidity; Branch 6: low-comorbidity/healthy-RBBB). Two branches were LBBB dominant (Branch 4: mixed IVCD with CHB burden; Branch 5: more females, CRT responders). Two branches were IVCD/mixed-phenotype (Branch 2: IVCD-dominant, high risk of future cardiovascular events; Branch 3: average/core branch). Within LBBB, Branch 4 and 5 showed similar trends with improving echocardiography profiles and CRT response when adjusted for covariates, each compared against the core branch. Branch 5 was distinct due its high risk of future HF (HR 1.19 [1.07-1.33] p < 0.01), cardiovascular death (HR 1.35 [1.20-1.50] p < 0.0001), all-cause mortality (HR 1.08 [1.01-1.16] p < 0.05) and CHB (HR 1.35 [1.16-1.56] p < 0.0001) (Figure-2). Conversely within RBBB, Branch 1 and 6 showed stark differences across various traits. Branch 1 captured a high-risk profile associated to higher risk of cardiovascular death (HR 1.37 [1.24-1.52] p < 0.0001), all-cause mortality (HR 1.20 [1.12-1.29] p < 0.0001) and CHB (HR 1.15 [1.01-1.32] p < 0.05) (Figure-2), while Branch 6 retained a low-risk phenotype. The tree dimensions also revealed relevant trends in cardiac anatomy and valvular dysfunction; the top-left region in Figure-1 associated with higher left ventricular ejection fraction and lower left ventricular end-diastolic dimension, lower left ventricular end-systolic dimension and a greater CRT response. Conclusion Through unsupervised methods we have identified conduction disease phenogroups with additive value for disease prognosis and CRT response prediction beyond traditional LBBB and RBBB labels. These novel phenogroups may help guide precision care for patients with a broad QRS complex.Figure-1Figure-2

Multifunctional polymeric stationary phases with enhanced hydrophilicity grafted with polyethyleneimine and polyglycidol

Two methods for increasing the degree of hydrophilization and screening of the sorbent matrix based on a copolymer of styrene and divinylbenzene grafted with polyethyleneimine quaternized with glycidol are proposed. The first method involves the polymerization of glycidol in the functional layer by varying the pH of the reaction medium, and the second method involves modifying the matrix by oxidizing the double bonds on its surface to obtain anchor epoxy groups. It was demonstrated that in the first method, the optimal approach is the twofold addition of glycidol before and after the addition of alkali, as in this case, the first addition of glycidol is consumed for the quaternization of polyamine, and the second for polymerization in ion-exchange centers. The new method of matrix modification, combined with the developed method of creating hydrophilic layers, significantly reduced the retention of oxyhalides, haloacetic acids, and polarizable anions in ion chromatography with suppressed background conductivity and amino acids in hydrophilic chromatography up to the point of changing the elution order. The obtained stationary phases are suitable for the simultaneous determination of standard inorganic anions, oxyhalides, and anions of haloacetic or alkylphosphonic acids in ion chromatography, as well as for the separation of amino acids, sugars, and vitamins in hydrophilic chromatography.

Optimised electrical resistance tomography performance for coarse-particle suspensions with a settled bed

Electrical Resistance Tomography (ERT) offers a non-intrusive method to visualise the dynamic distribution of internal solids in suspension flows. While ERT can produce good qualitative images, quantitative analysis faces challenges due to low spatial resolution, sensitivity to electric noise, and the ill-posed nature of the inverse problem. This study aims to enhance ERT's performance for coarse-particle suspensions by considering system configuration, injection current, background conductivity and reconstruction techniques. Validation is performed on both static and dynamic suspensions with physically sensible flow scenarios. To ensure high-quality ERT data acquisition, the background conductivity must allow a range of injection current while maintaining a favourable signal-to-noise ratio. A more conductive carrier is needed for effective current injection in densely packed beds or larger-scale pipes. Reconstruction based on current and voltage measurements following Ohm's law is essential. The commonly adopted Linear Back Projection (LBP) algorithm in a commercial ERT system exhibits limited information in the bed-occupied area, leading to underestimations of integrated concentration. ERT predictions of chord-averaged concentration profiles in a dynamic suspension display similar trends as those from the one-dimensional Eskin model. When compared to experimental measurements, ERT results generally underestimate the integrated concentration by approximately 15 % v/v in a dynamic suspension.

Hysteresis, Rectification, and Relaxation Times of Nanofluidic Pores for Neuromorphic Circuit Applications

AbstractBased on the emergence of iontronic fluidic components for brain‐inspired computation, the general dynamical behavior of nanopore channels is discussed. The main memory effects of fluidic nanopores are obtained by the combination of rectification and hysteresis. Rectification is imparted by an intrinsic charge asymmetry that affects the ionic current across the nanopores. It is accurately described by a background conductivity and a higher conduction branch that is activated by a state variable. Hysteresis produces self‐crossing diagrams, in which the high current side shows inductive hysteresis, and the low current side presents capacitive hysteresis. These properties are well captured by measurements of impedance spectroscopy that show the correspondent spectra in each voltage wing. The detailed properties of hysteresis and transient response are determined by the relaxation time of the gating variable, that is inspired in the Hodgkin‐Huxley neuron model. The classification of effects based on simple models provides a general guidance of the prospective application of artificial nanopore channels in neuromorphic computation according to the measurement of complementary techniques.

Development of chronic thresholds in His bundle pacing: single-center experience over 7 years in 426 patients

Abstract Background Conduction system pacing (CSP), e. g. by His bundle pacing (HBP) has the potential to perform highly synchronized ventricular pacing in patients with AV block and narrow QRS complex or right bundle branch block. Therefore, CSP is recommended in these patients to prevent pacing-induced cardioomyopathy. However, there have been reports about an acute and chronic threshold increase in HBP that may cause asystole in pacemaker-dependent patients. Purpose We checked the development of chronic pacing thresholds, the incidence of dislodgements and of consecutive asystole in patients with HBP. Methods All consecutive patients with HBP attempted in our center between 6/2016 and 11/2023 were enrolled. Pacing and sensing parameters over 36 months together with the follwing events were collected and analyzed: His bundle lead dislodgement, loss of capture, threshold increase to ≥3.0V/1.0 ms, emergency admission due to syncope with loss of HBP and asystole. Results In 426 patients (78±11 years, 38% female, 90% AV block, left ventricular ejection fraction 54±10%), HBP was attempted and in 388 patients successful (47% non-selective, 53% selective HBP), 16 patients were converted to left bundle branch area pacing, 22 implantations attemps were unsuccessful. Pacing and sensing performance during follow-up are listed in the Fig. There were 3 lead dislodgements (2 patients with Twiddler syndrome), 1 loss of capture (patient with sinus node disease), and 13 increases of pacing thresholds to ≥3.0V/1.0 ms, summing up to 17 events over 3 years (4.3%). No patient had a clinical event due to threshold increase or loss of HBP capture. All His bundle threshold increases were clinically silent because patients were not pacemaker-dependent, had non-selective HBP with myocardial capture serving as a "back-up" or due to a previously implanted right ventricular back-up lead. Conclusions There is a modest pacing threshold increase in His bundle thresholds from 1.1 to 1.8V@1.0 ms over a period of 3 years. However, this did not cause clinically relevant events in our patient cohort.Chronic pacing and sensing parameters

Safety and feasibility of left bundle branch pacing for pediatric and congenital heart disease patients

Abstract Background Conduction system pacing (CSP) has evolved and validated in adults. Due to technical challenges, pediatric and congenital heart disease (CHD) patients were excluded from original trials in this field. We report the safety and feasibility results of our initial experience with pediatric and CHD patients undergoing LBBAP (Left bundle branch area pacing). Purpose To analyze the indications, intraoperative outcomes, electrocardiographic and clinical data from the initial follow-up of pediatric and CHD patients who underwent LBBAP. Methods Indications, intraoperative technical issues, electronic parameters of the implant and early complications of consecutive pediatric and CAD patients submitted to stimulation of the conduction system were evaluated. Results This study was performed between February 2022 and November 2023 and recruited 11 consecutive patients with complete AV block (age: 15-43 years; 7 women) who underwent LBBAP. Four patients had congenital heart disease repaired surgically and two patients with congenitally corrected transposition of the great arteries. Upgrading from VVIR to LBBAP underwent in four patients. Right ventricle (RV) leads were extracted in three patients before CSP. DDD pacemakers with Lumneless 3830 pacing leads were implanted in all patients. The pre-implant QRS duration was 146 (104- 200) ms and 120 (110-130) ms after the procedure. The mean left ventricle activation time was 72 (50-90) ms. The R-wave amplitude was 10.00 (6-29) mV, with a stimulation threshold of 0.8 (0.4-1) V x 0.4 ms and impedance of 676 (534-780) ohms. Transition from non-selective to either myocardial or selective capture and fixation beats were respectively demonstrated in five and three patients. The procedure duration was 125 (70-130) min, and the fluoroscopy time was 15.2 (4-23.6) min. LBBAP substantially shortened the QRS duration and improved LV dyssynchrony echocardiographic parameters in four patients with prior epicardial or endocardial pacing. The LBBAP was successful in all patients with no early complications occured. At mean three months follow-up, QRS duration showed no significant changes compared with baseline. Conclusion Our initial experience on cardiac stimulation of the His-Purkinje conduction system through the stimulation of the left bundle branch is a safe and feasible technique in pediatric and CHD patients. The widespread use of this pacing technique is very useful and cost-effective to prevent heart failure in this vulnerable population.

Conduction velocity-based functional substrate mapping during atrial fibrillation (AF) enhances identification of AF drivers compared to mapping during sinus rhythm

Abstract Background Conduction velocity (CV) heterogeneity is known to play a role in the initiation and maintenance of atrial fibrillation (AF) [1,2]. CV has been shown to decrease with cycle lengths (CLs) <600ms in low voltage areas (LVAs) [3,4], and with CLs <300ms in non-LVAs [4]. Yet, the impact of rhythm and CL on voltage-independent, CV-based atrial substrate mapping remains uncertain. Purpose This study evaluates CV differences based on mapping protocol and explores the relationship between CV and AF pathologic conduction patterns (PCPs) identified through global, non-contact, charge density mapping (CDM) [5]. Methods CDM was performed in twelve patients with persistent AF, presenting for de novo ablation. All mapping was performed prior to any ablation. Sinus rhythm (SR) CV was assessed during atrial pacing at two CLs (380ms and 800ms). To mitigate the impact of wavefront direction, pacing was performed at three sites: mid coronary sinus, left atrial appendage, and right atrial appendage. AF CV was determined from a 20-second continuous recording of global propagation. PCPs were identified as: focal firing (FF), rotational propagation (Localised Rotational Activation [LRA]), and pivoting propagation (Localised Irregular Activity [LIA]) [5]. Patients’ left atrial geometries consisted of approximately 3000 vertices, facilitating paired comparisons of spatial data. At each vertex, values for median CV dependent on mapping protocol and frequency of PCPs were utilised for analysis. Variables are presented as mean±standard deviation, median (interquartile range), and count (percentage) as appropriate. All analyses were performed using R (version 4.1.2). CV distributions were compared using the Analysis of Variance test. Results Mean age was 64±12 years, eight (67%) were male, median time since AF diagnosis was 3.1 (2-3.5) years, and median CHA2DS2-VASc score was 2 (2-4). Median CV across our cohort was significantly lower during AF than SR with either long or short CL pacing (0.37mm/ms vs 0.66mm/ms vs 0.61mm/ms, p<0.001). Histograms of CV vs left atrial surface area demonstrated similar distributions for both CLs. However, there was poor overlap with AF, which was prominently skewed towards slower CVs (Figure 1). Slower CVs during AF were associated with an increased frequency of PCPs (Figure 2), particularly FF with CVs <0.2mm/ms, and LRA and LIA with CVs <0.4mm/ms. This association was absent during SR. Conclusions Rhythm has a significant impact on CV-based functional substrate mapping. Slower CVs observed during AF likely result from the presence of CLs shorter than 300ms, which impact both LVA and non-LVA areas. Crucially, areas of slow CV during AF were associated with the location of PCPs. Mapping performed during AF may improve identification of areas where functional remodelling has preceded structural. Such areas, characterised by CV heterogeneity, may serve as promising targets for catheter ablation.Figure 1.Figure 2.

Single-center experience with His bundle lead implantation: success rate, implantation method optimization, and lessons learned in 426 patients

Abstract Background Conduction system pacing (CSP) is increasingly used to avoid the development of pacing-induced cardiomyopathy in patients who require a high amount of ventricular pacing. His bundle pacing (HBP) is considered as ideal to achieve the narrowest paced QRS and optimal synchronization in patients with intrinsic narrow QRS or right bundle branch block but also as difficult at implantation. Purpose We analyzed our experience with HBP in terms of time and effort, pacing and sensing results, success rate, and lessons learned for optimization over a time period of 7 years. Methods All consecutive patients in whom HBP was attempted between 6/2016 and 11/2023 were included in this analysis. Implantations were performed using a pacing system analyzer (PSA) with high-resolution electrograms (EGMs). Data on implantation success [selective or non-selective HBP, left bundle branch area pacing (LBBAP)], sensing and pacing parameters, achievement of His bundle current of injury (coi), duration of implantation and fluoroscopy were collected prospectively. These results were compared for the 1st, 2nd, 3rd and 4th quartile of implantations and reasons for improvement or deterioration were analyzed. Results HBP was attempted in 426 patients (78±11 years, 38% female, 90% AV block, left ventricular ejection fraction 54±10 %, 81 single-, 286 dual-, 46 triple-chamber pacemakers, 2 dual- and 11 triple-chamber ICDs) and was successful in 404 patients (95%): 182 non-selective HBP, 206 selective HBP, and 16 LBBAP. R wave amplitude was 4.5±3.5 mV, pacing threshold 1.1 ± 0.6V/1.0 ms. In 16% of patients, a ventricular back-up lead was implanted. A His bundle coi was achieved in 61% of patients. The implantation duration was 92±43 min, fluoroscopy duration 10±8 min. Success rate increased from 89% in the 1st to 99% in the 4th quartile. Improved implantation success was associated with using a stiff 3D steerable sheath, implantation site at the distal His bundle, and an increased number of screw-in turns until a His bundle coi was visible. Conclusions Establishing an implantation routine with 1) a PSA and high-resolution EGMs, 2) use of a stiff 3D steerable sheath, 3) implantation at the distal His bundle with myocardial capture (non-selective HBP) as a back-up, and 4) an increased number of screw-in turns of the lead tip until a His bundle coi is achieved, HBP implantation can be facilitated and results optimized to a highly acceptable implantation effort and a success rate >95%.

Conduction system pacing: procedural success and failures over the years

Abstract Background Conduction system pacing (CSP) ensures physiological ventricular activation and avoids the dyssynchrony. New tools (sheaths and leads) can better assist the implant thus increasing procedural successes. Objective Retrospective analysis of CSP implants from the last 4 years, analyzing procedural success and failures. Methods From 2019 to 2022, 820 CSP implant were performed, being 66% of the overall implants (excluding SR and DR ICDs). 89% were PMs and 11% were ICDs. 32.6% were styled-driven leads while 67.4% were lumenless. Pacing indications were standard with prevalence of AV block (53.6%); AF with slow ventricular rate 14.8%; sinus node disease 12.9%; ablate&pace 3.7%; heart failure 12.8%, re-interventions after malfunction of a previous implant 2.2%. Mean age was 78±9 years; 61.8% were males. Results From 2019 to 2022, CSP was successfully achieved in 756 cases (92.2%) considering all indications. In 64 (7.8%) cases, CSP lead implant failed (17 lumenless leads; 47 stylet driven leads) and the lead was then implanted in RV septum or coronary sinus. Reasons for failure were: 2.7% suboptimal electrical parameters (mainly high threshold); 1.1% uncorrected BBB; 0.9% intraprocedural lead dislodgement; 1.4% impossibility to penetrate the septum; 1.4% severe right atrial enlargement; 0.3% unavailable venous access. Heart failure and left ventricular dysfunction (EF<45%) were found more frequently in the failed implant subgroup. Procedural failures were more frequently associated with more than 1 sheath and more than 1 lead utilization during the procedure. Interestingly, in 12.8 % of successful procedures the sheath was changed intraprocedurally; and in the 5.4% of successful procedures the lead was changed (from lumenless to styled-driven or viceversa). No predictors of procedural failure were found in the logistic regression analysis. IInterestingly, failed implants have not decreased over the years. Conclusions conduction system pacing is feasible in daily clinical practice. Both lumenless and stylet-driven lead can be utilized. Different sheaths allow to customize the procedure based on the anatomy. During a 4-year experience, the overall procedural success rate was 92.2% while 7.8% of the procedures failed. Interestingly the failure rate has not decreased over the years, likely being related to increasingly complex cardiac conditions where CSP has been attempted.CSP implant success and failures

Simulation of Conducted Responses in Microvascular Networks: Role of Current Rectification by Endothelial Cell Gap Junctions

Neuronal activity in the brain stimulates local increases in blood flow. Such flow increases require dilation of feeding arterioles, which can be initiated by upstream conducted responses in the form of electrical currents transmitted along the endothelial lining of the vessels. One potential trigger for this response is hyperpolarization of capillary endothelial cells in active regions resulting from local elevation of extracellular K+ concentration. The conducted hyperpolarization causes arteriolar dilation. For this mechanism to be effective in delivering increased flow to a specific location, the conducted response must travel in the upstream direction only, without reentry into adjacent parallel flow pathways. Such specificity in the response to activation has been observed in skeletal muscle, and may result from partial rectification of current in gap junctions connecting adjacent endothelial cells. The goal of this work is to simulate the spread of hyperpolarizing currents along vessel walls in microvascular networks of the cerebral circulation, including the effects of rectification in gap junctions. A theoretical model was developed for the spread of electrical current in the endothelial cells of a network of microvessels in response to local K+- induced hyperpolarization. Transmembrane currents are represented in the model by a KIR-channel conductance, a non-voltage-dependent K+ conductance, and a background conductance. Currents along vessel walls are represented assuming asymmetric gap junction conductance between adjacent endothelial cells, with higher conductance for downstream currents (causing upstream hyperpolarization) than for upstream currents. The model was applied to a synthetic network of 45 segments, assuming 20 nS conductance for upstream propagation, while a range of values was used for downstream propagation. The model shows effective upstream propagation of conducted responses when the gap junction conductance for downstream propagation is 1 nS or less. This result was confirmed in a simulation of a reconstructed murine cerebral cortex network with 4881 segments. In conclusion, partial current rectification by endothelial gap junctions can result in preferential upstream propagation of conducted responses, consistent with experimental observations of local flow regulation. Supported by NIH grant U01 HL133362. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Conduction system disease management in patients candidate and/or treated for the aortic valve disease: an Italian Survey promoted by Italian Association of Arrhythmology and Cardiac Pacing (AIAC)

Background Conduction system disorders represent a frequent complication in patients undergoing surgical (surgical aortic valve replacement, SAVR) or percutaneous (transcatheter aortic valve implantation, TAVI) aortic valve replacement. The purpose of this survey was to evaluate experienced operators approach in this clinical condition. Methods This survey was independently conducted by the Italian Association of Arrhythmology and Cardiac Pacing (AIAC) and it consisted of 24 questions regarding the respondents’ profile, the characteristics of participating centres, and conduction disease management in different scenarios. Results Fifty-five physicians from 55 Italian arrhythmia centres took part in the survey. Prophylactic pacemaker implantation is rare. In case of persistent complete atrioventricular block (AVB), 49% and 73% respondents wait less than one week before implanting a definitive pacemaker after SAVR and TAVI, respectively. In case of second degree AVB, the respondents wait some days more for definitive implantation. Respondents consider bundle branch blocks, in particular pre-existing left bundle branch block (LBBB), the worst prognostic factors for pacemaker implantation after TAVI. The implanted valve type is considered a relevant element to evaluate. In patients with new-onset LBBB and severe/moderate left ventricular systolic dysfunction, respondents would implant a biventricular pacemaker in 100/55% of cases, respectively. Conclusions Waiting time before a definitive pacemaker implantation after aortic valve replacement has reduced compared to the past, and it is anticipated in TAVI vs. SAVR. Bundle branch blocks are considered the worse prognostic factor for pacemaker implantation after TAVI. The type of pacemaker implanted in new-onset LBBB patients without severe left ventricular systolic dysfunction is heterogeneous.

Optoelectronic Synapse Based on 2D Electron Gas in Stoichiometry-Controlled Oxide Heterostructures.

Emulating synaptic functionalities in optoelectronic devices is significant in developing artificial visual-perception systems and neuromorphic photonic computing. Persistent photoconductivity (PPC) in metal oxides provides a facile way to realize the optoelectronic synaptic devices, but the PPC performance is often limited due to the oxygen vacancy defects that release excess conduction electrons without external stimuli. Herein, a high-performance optoelectronic synapse based on the stoichiometry-controlled LaAlO3/SrTiO3 (LAO/STO) heterostructure is developed. By increasing La/Al ratio up to 1.057:1, the PPC is effectively enhanced but suppressed the background conductivity at the LAO/STO interface, achieving strong synaptic behaviors. The spectral noise analyses reveal that the synaptic behaviors are attributed to the cation-related point defects and their charge compensation mechanism near the LAO/STO interface. The short-term and long-term plasticity is demonstrated, including the paired-pulse facilitation, in the La-rich LAO/STO device upon exposure to UV light pulses. As proof of concepts, two essential synaptic functionalities, the pulse-number-dependent plasticity and the self-noise cancellation, are emulated using the 5×5 array of La-rich LAO/STO synapses. Beyond the typical oxygen deficiency control, the results show how harnessing the cation stoichiometry can be used to design oxide heterostructures for advanced optoelectronic synapses and neuromorphic applications.

Tricuspid regurgitation burden following transcatheter aortic valve replacement requiring early pacemaker implantation

Background Conduction abnormality requiring the implantation of a permanent pacemaker (PPM) is a well-known and clinically important complication of transcatheter aortic valve replacement (TAVR). However, PPM implantation may result in lead-associated tricuspid valve regurgitation (TR). This study sought to determine the incidence and progression of TR following PPM implantation after TAVR. Methods This was a retrospective review of all echocardiograms of patients who underwent PPM following TAVR at the Baylor Scott & White hospitals from 2012 to 2021. The primary endpoint was TR progression at 30 days and 1 year. A subanalysis comparing the change in TR progression between small and large TAVR devices was also conducted. Secondary outcomes included all-cause death at 30 days and 1 year. Results Out of the 2744 patients who underwent TAVR between April 2012 and August 2021, 177 patients (6.5%) subsequently received a new PPM. There was a statistically significant progression of TR at 1-year follow-up (McNemar’s P value = 0.02). TR progression rates were comparable between the small and large valve groups at 1-year follow-up (4% vs 11%, P = 0.09, respectively). Conclusion In this single healthcare system study, we demonstrated a significant progression of TR in patients with PPM post TAVR at 1 year.

Evaluation of the applicability of a metal oxide semiconductor gas sensor for methane emissions from agriculture

This work investigated the potential of metal oxide semiconductor (MOS) gas sensors for environmental monitoring of methane. Calibrations were performed under controlled conditions in the lab, and under semi-controlled conditions in the field, using a modified head space chamber set-up. Concentrations up to ±300 ppm methane were tested. The relationship between sensor conductance and methane concentrations could be very well described using principles from adsorption theory. The adjustable parameters were background conductance G0, a sensitivity constant S and a non-ideality coefficient n, where n has a non-rational value between 0 and 1. Sensor behaviour was very different in dry air than in humid air, with the background conductance increasing approximately tenfold and sensitivity decreasing between 20 fold and 80 fold, while the non-ideality coefficient increased from ±0.4 to ±0.6. Nevertheless, at high methane concentrations comparable conductance values were recorded in dry and humid air. The standard deviation of predicted values was 1.6 μS.for the least well described dataset. Using the corresponding calibration curve, a detection limit of 11 ppm is calculated for humid ambient air. This values suggests that MOS sensor are adequately sensitive to be used for methane detection in an agricultural context.

Fractional Calderón problems and Poincaré inequalities on unbounded domains

We generalize many recent uniqueness results on the fractional Calderón problem to cover the cases of all domains with nonempty exterior. The highlight of our work is the characterization of uniqueness and nonuniqueness of partial data inverse problems for the fractional conductivity equation on domains that are bounded in one direction for conductivities supported in the whole Euclidean space and decaying to a constant background conductivity at infinity. We generalize the uniqueness proof for the fractional Calderón problem by Ghosh, Salo and Uhlmann to a general abstract setting in order to use the full strength of their argument. This allows us to observe that there are also uniqueness results for many inverse problems for higher order local perturbations of a lower order fractional Laplacian. We give concrete example models to illustrate these curious situations and prove Poincaré inequalities for the fractional Laplacians of any order on domains that are bounded in one direction. We establish Runge approximation results in these general settings, improve regularity assumptions also in the cases of bounded sets and prove general exterior determination results. Counterexamples to uniqueness in the inverse fractional conductivity problem with partial data are constructed in another companion work.

Implicit Solutions of the Electrical Impedance Tomography Inverse Problem in the Continuous Domain with Deep Neural Networks.

Electrical impedance tomography (EIT) is a non-invasive imaging modality used for estimating the conductivity of an object Ω from boundary electrode measurements. In recent years, researchers achieved substantial progress in analytical and numerical methods for the EIT inverse problem. Despite the success, numerical instability is still a major hurdle due to many factors, including the discretization error of the problem. Furthermore, most algorithms with good performance are relatively time consuming and do not allow real-time applications. In our approach, the goal is to separate the unknown conductivity into two regions, namely the region of homogeneous background conductivity and the region of non-homogeneous conductivity. Therefore, we pose and solve the problem of shape reconstruction using machine learning. We propose a novel and simple jet intriguing neural network architecture capable of solving the EIT inverse problem. It addresses previous difficulties, including instability, and is easily adaptable to other ill-posed coefficient inverse problems. That is, the proposed model estimates the probability for a point of whether the conductivity belongs to the background region or to the non-homogeneous region on the continuous space Rd∩Ω with d∈{2,3}. The proposed model does not make assumptions about the forward model and allows for solving the inverse problem in real time. The proposed machine learning approach for shape reconstruction is also used to improve gradient-based methods for estimating the unknown conductivity. In this paper, we propose a piece-wise constant reconstruction method that is novel in the inverse problem setting but inspired by recent approaches from the 3D vision community. We also extend this method into a novel constrained reconstruction method. We present extensive numerical experiments to show the performance of the architecture and compare the proposed method with previous analytic algorithms, mainly the monotonicity-based shape reconstruction algorithm and iteratively regularized Gauss-Newton method.

An efficient one-step proximal method for EIT sparse reconstruction based on nonstationary iterated Tikhonov regularization

ABSTRACT Image reconstruction of EIT mathematically is a seriously ill-posed inverse problem, which is easily affected by measurement noise. This fact leads to a relatively low spatial resolution, particularly in the accuracy of identifying object boundaries. This paper concerns with reconstructing a finite number of simple and small inclusions equipped with the homogeneous background conductivity. The sparsity with respect to the inclusions in the spacial representation domain is apriori assumed. We try to reexamine the multi-parameter constraints on mixing between -norm and -norm for attaining the sparse reconstruction as well as simultaneously enhancing the stability. On the basis of the reference approximation reconstructed by nonstationary iterated Tikhonov regularization (NITR) method, we propose a novel one-step proximal sparsity-promoting approach by one induced proximal shrink operator, abbreviated as one-step PNITR method. The proposed one-step PNITR method consists of twofold: one first performs NITR with mth iteration to generate the reference approximation, and then performs one-step proximal shrinkage processing and one forcing constraint function on it to obtain the final sparsity-promoting reconstruction. For the latter, the former aims to not only enhance higher reliability but also guarantee the sparsity. The proposed method can benefit from the double regularization effect. It is supposed to further improve the imaging quality in terms of sharpening the edges and reducing the artefacts. To validate the advantage of the proposed method, numerical simulations with synthetic data have been carried out. Also, qualitative and quantitative comparisons are conducted. Results indicate that the proposed approach can lead to substantial improvements in EIT image resolution. The performed numerical simulations show that our method is promising.

Signal-to-noise ratio variance impact on the image reconstruction of electrical resistance tomography in solutions with high background conductivity.

Electrical Resistance Tomography (ERT) has the potentialities of non-intrusive techniques and high temporal resolution which are essential characteristics for multiphase flow measurements. However, high background conductivities, such as saline water in oil extraction, impose a limitation in ERT image reconstruction. Focusing on the operational limits of an ERT tomography system operating in different conductivity backgrounds from 0.010 to 4.584 S/m, the impact on the image reconstruction was assessed via signal-to-noise variance. The signal-to-noise ratio (SNR) variance had a strong correlation (p-value = 5.40 × 10-15) with the image reconstruction quality at the threshold of 30 dB, reaching a correlation value of r = -0.92 in the range of 0.010-0.246 S/m. Regarding the position error of the phantom, p-value = 1.30 × 10-5 and r = -0.66 were attained. The global results revealed that the correlation of the mean of the SNR (p-value = 5 × 10-4 and r = 0.55) was kept unaltered through the whole conductivity range, showing that such a statistical index can induce bias in establishing the operational limits of the hardware.