Feasibility of transthoracic echocardiographic guidance for multicatheter electrophysiological mapping studies in horses.

BACKGROUND: Improved characterization of arrhythmias is based on minimally invasive catheterizations. However, these catheterizations have been poorly explored in horses because apart from 3-dimensional (3D) mapping systems, continuous guidance of the catheter's position with adequate detail is difficult using current imaging modalities. HYPOTHESIS: Position multiple electrophysiology catheters simultaneously at predetermined strategical positions in the heart using transthoracic echocardiographic guidance. ANIMALS: Eight adult healthy horses. METHODS: Observational study. Two electrophysiological studies were performed: 1 procedure with catheters positioned in the right heart in the standing sedated horse and 1 procedure under general anesthesia with catheters positioned in the left heart. Except for the coronary sinus catheter, each catheter positioning was simultaneously guided by right-parasternal transthoracic echocardiography and 3D electro-anatomical mapping. RESULTS: For each catheter position, a central imaging plane was taken as the starting point, after which the imaging probe was shifted, rotated, and angulated to visualize the catheter over its entire length, including its distal electrode. Catheter positionings in the right heart and left ventricle were successfully guided in the majority of the horses whereas catheter positionings in the left atrium, and especially the pulmonary veins, were challenging to guide echocardiographically. CONCLUSIONS AND CLINICAL IMPORTANCE: Ultrasound guidance of catheters to specific positions useful for electrophysiological mapping was feasible in the right heart and left ventricle but challenging for the left atrium. This approach creates a perspective for minimally invasive arrhythmia diagnosis without the need for a 3D mapping system. Left parasternal views and intracardiac echocardiography might provide better guidance for left atrial positions.

Accuracy of a Single-Lead ECG Device for Diagnosis of Cardiac Arrhythmias Compared Against Cardiac Electrophysiology Study.

BACKGROUND: Single-lead electrocardiogram (ECG) devices may allow detection and diagnosis of cardiac rhythms. However, data on their accuracy for detecting cardiac arrhythmias beyond atrial fibrillation are limited. We aimed to determine the accuracy of the AliveCor KardiaMobile (AC) (AliveCor Inc, Mountain View, CA, USA) for the diagnosis of arrhythmias against gold standard cardiac electrophysiology study (EPS). METHOD: Patients undergoing clinically indicated EPS underwent simultaneous rhythm recording with an AC, standard 12-lead ECG, and EP catheters for intracardiac electrograms. Rhythms recorded during EPS were classified based on electrogram, 12-lead ECG, and clinical findings. Blinded reviewers provided differential diagnoses for the single-lead AC tracings; a separate reviewer compared diagnoses made between the AC tracings and EPS findings. RESULTS: In 49 patients, 843 cardiac rhythms were captured during 502 AC recordings. Analysis of tracings containing sinus rhythm (n=273) returned an overall accuracy of 92%, with sensitivity and specificity values of 93% and 92%, respectively. Accuracy for tracings per rhythm was atrial fibrillation 91% (n=51); supraventricular tachycardia accuracy was 89% (n=191), ventricular tachycardia 91% (n=198), ventricular fibrillation 98% (n=11), and asystole 100% (n=5). Accuracy for supraventricular ectopy was 93% (n=28) and for premature ventricular complexes was 91% (n=86). Overall accuracy was 94% for solitary rhythms and 93% in tracings from patients with baseline bundle branch block. CONCLUSIONS: When compared against the gold standard EPS diagnosis, the interpretation of arrhythmias recorded by an AliveCor single-lead ECG device had reasonable diagnostic accuracy.

Multipolar Electrograms: A New Configuration That Increases the Measurement Accuracy of Intracardiac Signals.

BACKGROUND: Accurate measurements of intracardiac electrograms (EGMs) remain a clinical challenge because of the suboptimal attenuation of far-field potentials. Multielectrode mapping catheters provide an opportunity to construct multipolar instead of bipolar EGMs for rejecting common far-field potentials recorded from a multivectorial space. OBJECTIVES: The purpose of this study was to develop a multipolar EGM and compare its characteristics to those of bipolar EGMs METHODS: Using a 36-electrode array catheter (Optrell-36, Biosense Webster), a far-field component was mathematically constructed from clusters of electrodes surrounding each inspected electrode. This component was subtracted from the unipolar waveform to produce a local unipolar, referred to as a "multipolar EGM." The performance of multipolar EGMs was evaluated in 7 swine with healed anteroseptal infarction. RESULTS: Multipolar EGMs proved superior in attenuating far-field potentials in infarct border zones, increasing the near-field to far-field ratio from 0.92 ± 0.2 to 2.25 ± 0.3 (P < 0.001). Removal of far-field components reduced the voltage amplitude (P < 0.001) and enlarged the infarct surface area (P = 0.02), aligning more closely with histological findings. Of 379 EGMs with ≥20 ms activation time difference between bipolar and multipolar EGMs, 95.3% (361 of 379) were accurately annotated using multipolar EGMs, while annotation based on bipolar EGM was predominantly made on far-field components. CONCLUSIONS: Multielectrode array catheters provide a unique platform for constructing multipolar EGMs. This new EGM may be beneficial for "purifying" local potentials within a complex electrical field, resulting in more accurate voltage and activation maps.

Use of three-dimensional electroanatomic mapping for epicardial access: needle tracking, electrographic characteristics, and clinical application.

AIMS: Pericardiocentesis is usually completed under fluoroscopy. The electroanatomic mapping (EAM) system allows visualizing puncture needle tip (NT) while displaying the electrogram recorded from NT, making it possible to obtain epicardial access (EA) independent of fluoroscopy. This study was designed to establish and validate a technique by which EA is obtained under guidance of three-dimensional (3D) EAM combined with NT electrogram. METHODS AND RESULTS: 3D shell of the heart was generated, and the NT was made trackable in the EAM system. Unipolar NT electrogram was continuously monitored. Penetration into pericardial sac was determined by an increase in NT potential amplitude and an injury current. A long guidewire of which the tip was also visible in the EAM system was advanced to confirm EA. Epicardial access was successfully obtained without complication in 13 pigs and 22 patients. In the animals, NT potential amplitude was 3.2 ± 1.0 mV when it was located in mediastinum, 5.2 ± 1.6 mV when in contact with fibrous pericardium, and 9.8 ± 2.8 mV after penetrating into pericardial sac (all P ≤ 0.001). In human subjects, it measured 1.54 ± 0.40 mV, 3.61 ± 1.08 mV, and 7.15 ± 2.88 mV, respectively (all P < 0.001). Fluoroscopy time decreased in every 4-5 cases (64 ± 15, 23 ± 17, and 0 s for animals 1-4, 5-8, 9-13, respectively, P = 0.01; 44 ± 23, 31 ± 18, 4±7 s for patients 1-7, 8-14, 15-22, respectively, P < 0.001). In five pigs and seven patients, EA was obtained without X-ray exposure. CONCLUSION: By tracking NT in the 3D EAM system and continuously monitoring the NT electrogram, it is feasible and safe to obtain EA with minimum or no fluoroscopic guidance.

Multisize Electrode Field-of-View: Validation by High Resolution Gadolinium-Enhanced Cardiac Magnetic Resonance.

BACKGROUND: Voltage mapping to detect ventricular scar is important for guiding catheter ablation, but the field-of-view of unipolar, bipolar, conventional, and microelectrodes as it relates to the extent of viable myocardium (VM) is not well defined. OBJECTIVES: The purpose of this study was to evaluate electroanatomic voltage-mapping (EAVM) with different-size electrodes for identifying VM, validated against high-resolution ex-vivo cardiac magnetic resonance (HR-LGE-CMR). METHODS: A total of 9 swine with early-reperfusion myocardial infarction were mapped with the QDOT microcatheter. HR-LGE-CMR (0.3-mm slices) were merged with EAVM. At each EAVM point, the underlying VM in multisize transmural cylinders and spheres was quantified from ex vivo CMR and related to unipolar and bipolar voltages recorded from conventional and microelectrodes. RESULTS: In each swine, 220 mapping points (Q1, Q3: 216, 260 mapping points) were collected. Infarcts were heterogeneous and nontransmural. Unipolar and bipolar voltage increased with VM volumes from >175 mm3 up to >525 mm3 (equivalent to a 5-mm radius cylinder with height >6.69 mm). VM volumes in subendocardial cylinders with 1- or 3-mm depth correlated poorly with all voltages. Unipolar voltages recorded with conventional and microelectrodes were similar (difference 0.17 ± 2.66 mV) and correlated best to VM within a sphere of radius 10 and 8 mm, respectively. Distance-weighting did not improve the correlation. CONCLUSIONS: Voltage increases with transmural volume of VM but correlates poorly with small amounts of VM, which limits EAVM in defining heterogeneous scar. Microelectrodes cannot distinguish thin from thick areas of subendocardial VM. The field-of-view for unipolar recordings for microelectrodes and conventional electrodes appears to be 8 to 10 mm, respectively, and unexpectedly similar.

Mapping and ablation of left atrial roof-dependent tachycardias using an ultra-high resolution mapping system.

BACKGROUND: Left atrial roof-dependent tachycardias (LARTs) are common macroreentrant atrial tachycardias (ATs). We sought to characterize clinical LARTs using an ultra-high resolution mapping system. METHODS: This study included 22 consecutive LARTs in 21 patients who underwent AT mapping/ablation using Rhythmia systems. RESULTS: Three, 13, 4, and 2 LART patients were cardiac intervention naïve (Group-A), post-roof line ablation (Group-B), post-atrial fibrillation ablation without linear ablation (Group-C), and post-cardiac surgery (Group-D), respectively. The mean AT cycle length was 244 ± 43 ms. Coronary sinus activation was proximal-to-distal or distal-to-proximal in 16 (72.7%) ATs. The activation map revealed 13 (59.1%) clockwise and 9 (40.9%) counter-clockwise LARTs. A 12-lead synchronous isoelectric interval was observed in 10/19 (52.6%) LARTs. The slow conduction area was identified on the LA roof, anterior/septal wall, and posterior wall in 18, 6, and 2 ATs, respectively. Twenty concomitant ATs among 13 procedures were also eliminated, and peri-mitral AT coexisted in 7 of 9 non-group-B patients. In group-B, the conduction gap was predominantly located on the mid-roof. Sustained LARTs were terminated by a single application and linear ablation in 6 (27.3%) and 9 (40.9%), while converting to other ATs in 7 (31.8%) LARTs. Complete linear block was created without any complications in all, however, ablation at the mid-posterior wall was required to achieve block in 4 (18.2%) procedures. During 14.0 (6.5-28.5) months of follow-up, 17 (81.0%) and 19 (90.5%) patients were free from any atrial tachyarrhythmias after single and last procedures. CONCLUSIONS: The LART mechanisms were distinct in individual patients, and elimination of all concomitant ATs was required for the management.

Effect of electrode size and spacing on electrograms: Optimized electrode configuration for near-field electrogram characterization.

BACKGROUND: Detailed effects of electrode size on electrograms (EGMs) have not been systematically examined. OBJECTIVES: We aimed to elucidate the effect of electrode size on EGMs and investigate an optimal configuration of electrode size and interelectrode spacing for gap detection and far-field reduction. METHODS: This study included 8 sheep in which probes with different electrode size and interelectrode spacing were epicardially placed on healthy, fatty, and lesion tissues for measurements. Between 3 electrode sizes (0.1 mm/0.2 mm/0.5 mm) with 3 mm spacing. As indices of capability in gap detection and far-field reduction, in different electrode sizes (0.1 mm/0.2 mm/0.5 mm) and interelectrode spacing (0.1 mm/0.2 mm/0.3 mm/0.5 mm/3 mm) and the optimized electrode size and interelectrode spacing were determined. Compared between PentaRay and the optimal probe determined in study 2. RESULTS: Study 1 demonstrated that unipolar voltage and the duration of EGMs increased as the electrode size increased in any tissue (P < .001). Bipolar EGMs had the same tendency in healthy/fat tissues, but not in lesions. Study 2 showed that significantly higher gap to lesion volume ratio and healthy to fat tissue voltage ratio were provided by a smaller electrode (0.2 mm or 0.3 mm electrode) and smaller spacing (0.1 mm spacing), but 0.3 mm electrode/0.1 mm spacing provided a larger bipolar voltage (P < .05). Study 3 demonstrated that 0.3 mm electrode/0.1 mm spacing provided less deflection with more discrete EGMs (P < .0001) with longer and more reproducible AF cycle length (P < .0001) compared to PentaRay. CONCLUSION: Electrode size affects both unipolar and bipolar EGMs. Catheters with microelectrodes and very small interelectrode spacing may be superior in gap detection and far-field reduction. Importantly, this electrode configuration could dramatically reduce artifactual complex fractionated atrial electrograms and may open a new era for AF mapping.

Local abnormal ventricular activity detection in scar-related VT: Microelectrode versus conventional bipolar electrode.

BACKGROUND: Conventional bipolar electrodes (CBE) may be suboptimal to detect local abnormal ventricular activities (LAVAs). Microelectrodes (ME) may improve the detection of LAVAs. This study sought to elucidate the detectability of LAVAs using ME compared with CBE in patients with scar-related ventricular tachycardia (VT). METHODS: We included consecutive patients with structural heart disease who underwent radiofrequency catheter ablation for scar-related VT using either of the following catheters equipped with ME: QDOTTM or IntellaTip MIFITM. Detection field of LAVA potentials were classified as three types: Type 1 (both CBE and ME detected LAVA), Type 2 (CBE did not detect LAVA while ME did), and Type 3 (CBE detected LAVA while ME did not). RESULTS: In 16 patients (68 ± 16 years; 14 males), 260 LAVAs electrograms (QDOT = 72; MIFI = 188) were analyzed. Type 1, type 2, and type 3 detections were 70.8% (QDOT, 69.4%; MIFI, 71.3%), 20.0% (QDOT, 23.6%; MIFI, 18.6%) and 9.2% (QDOT, 6.9%; MIFI, 10.1%), respectively. The LAVAs amplitudes detected by ME were higher than those detected by CBE in both catheters (QDOT: ME 0.79 ± 0.50 mV vs. CBE 0.41 ± 0.42 mV, p = .001; MIFI: ME 0.73 ± 0.64 mV vs. CBE 0.38 ± 0.36 mV, p < .001). CONCLUSIONS: ME allow to identify 20% of LAVAs missed by CBE. ME showed higher amplitude LAVAs than CBE. However, 9.2% of LAVAs can still be missed by ME.

A new implantable tool for repeated assessment of supraventricular electrophysiology and atrial fibrillation susceptibility in freely moving rats.

The complex pathophysiology of atrial fibrillation (AF) is governed by multiple risk factors in ways that are still elusive. Basic electrophysiological properties, including atrial effective refractory period (AERP) and conduction velocity, are major factors determining the susceptibility of the atrial myocardium to AF. Although there is a great need for affordable animal models in this field of research, in vivo rodent studies are limited by technical challenges. Recently, we introduced an implantable system for long-term assessment of AF susceptibility in ambulatory rats. However, technical considerations did not allow us to perform concomitant supraventricular electrophysiology measurements. Here, we designed a novel quadripolar electrode specifically adapted for comprehensive atrial studies in ambulatory rats. Electrodes were fabricated from medical-grade silicone, four platinum-iridium poles, and stainless-steel fixating pins. Initial quality validation was performed ex vivo, followed by implantation in adult rats and repeated electrophysiological studies 1, 4, and 8 wk postimplantation. Capture threshold was stable. Baseline AERP values (38.1 ± 2.3 and 39.5 ± 2.0 using 70-ms and 120-ms S1-S1 cycle lengths, respectively) confirmed the expected absence of rate adaptation in the unanesthetized state and validated our prediction that markedly higher values reported under anesthesia are nonphysiological. Evaluation of AF substrate in parallel with electrophysiological parameters validated our recent finding of a gradual increase in AF susceptibility over time and demonstrated that this phenomenon is associated with an electrical remodeling process characterized by AERP shortening. Our findings indicate that the miniature quadripolar electrode is a potent new tool, which opens a window of opportunities for better utilization of rats in AF research.NEW & NOTEWORTHY Rodents are increasingly used in AF research. However, technical challenges restrict long-term supraventricular electrophysiology studies in these species. Here, we developed an implantable electrode adapted for such studies in the rat. Our findings indicate that this new tool is effective for long-term follow-up of critical parameters such as atrial refractoriness. Obtained data shed light on the normal electrophysiology and on the increased AF susceptibility that develops in rats with implanted atrial electrodes over time.

Digital Health and the Care of the Patient With Arrhythmia: What Every Electrophysiologist Needs to Know.

The field of cardiac electrophysiology has been on the cutting edge of advanced digital technologies for many years. More recently, medical device development through traditional clinical trials has been supplemented by direct to consumer products with advancement of wearables and health care apps. The rapid growth of innovation along with the mega-data generated has created challenges and opportunities. This review summarizes the regulatory landscape, applications to clinical practice, opportunities for virtual clinical trials, the use of artificial intelligence to streamline and interpret data, and integration into the electronic medical records and medical practice. Preparation of the new generation of physicians, guidance and promotion by professional societies, and advancement of research in the interpretation and application of big data and the impact of digital technologies on health outcomes will help to advance the adoption and the future of digital health care.

Prospective STAR-Guided Ablation in Persistent Atrial Fibrillation Using Sequential Mapping With Multipolar Catheters.

BACKGROUND: A novel stochastic trajectory analysis of ranked signals (STAR) mapping approach to guide atrial fibrillation (AF) ablation using basket catheters recently showed high rates of AF termination and subsequent freedom from AF. METHODS: This study aimed to determine whether STAR mapping using sequential recordings from conventional pulmonary vein mapping catheters could achieve similar results. Patients with persistent AF<2 years were included. Following pulmonary vein isolation AF drivers (AFDs) were identified on sequential STAR maps created with PentaRay, IntellaMap Orion, or Advisor HD Grid catheters. Patients had a minimum of 10 multipolar recordings of 30 seconds each. These were processed in real-time and AFDs were targeted with ablation. An ablation response was defined as AF termination or cycle length slowing ≥30 ms. RESULTS: Thirty patients were included (62.4±7.8 years old, AF duration 14.1±4.3 months) of which 3 had AF terminated on pulmonary vein isolation, leaving 27 patients that underwent STAR-guided AFD ablation. Eighty-three potential AFDs were identified (3.1±1.1 per patient) of which 70 were targeted with ablation (2.6±1.2 per patient). An ablation response was seen at 54 AFDs (77.1% of AFDs; 21 AF termination and 33 cycle length slowing) and occurred in all 27 patients. No complications occurred. At 17.3±10.1 months, 22 out of 27 (81.5%) patients undergoing STAR-guided ablation were free from AF/atrial tachycardia off antiarrhythmic drugs. CONCLUSIONS: STAR-guided AFD ablation through sequential mapping with a multipolar catheter effectively achieved an ablation response in all patients. AF terminated in a majority of patients, with a high freedom from AF/atrial tachycardia off antiarrhythmic drugs at long-term follow-up. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT02950844.

Complete Electroanatomic Imaging of the Diastolic Pathway Is Associated With Improved Freedom From Ventricular Tachycardia Recurrence.

BACKGROUND: The development of multielectrode mapping catheters has expanded the spectrum of mappable ventricular tachycardias (VTs). Full diastolic pathway recording has been associated with a high rate of VT termination during radiofrequency ablation as well as noninducibility at study end. However, the role of diastolic pathway mapping on VT recurrence has yet to be clearly elucidated. We aimed to explore the role of complete diastolic pathway activation mapping on VT recurrence. METHODS: Eighty-five consecutive patients who underwent VT ablation guided by high-density mapping were enrolled. During activation mapping, the presence of electrical activity in all segments of diastole defined the evidence of having had recorded the whole diastolic interval. Patients were categorized as having recorded the full diastolic pathway, partial diastolic pathway, or no diastolic pathway map performed. Recurrences of VT were defined as appropriate implantable cardioverter defibrillator therapies or on the basis of ECG-documented arrhythmia. RESULTS: Eighty-five patients were included. Complete recording of the diastolic pathway was achieved in 36/85 (42.4%) patients. Partial recording of the diastolic pathway of the clinical VT was achieved in 24/85 (28.2%) patients. No recording of the diastolic pathway of the clinical VT was feasible in 25/85 patients (29.4%). At a mean of 12.8 months, freedom from VT recurrence was 67% in the overall cohort. At a mean of 12.8 months, freedom from VT recurrence was 88%, 50%, and 55% in patients who had full diastolic activity recorded, partial diastolic activity recorded, or underwent substrate modification, respectively; the observed differences were statistically significant (P=0.02). CONCLUSIONS: Mapping of the entire diastolic pathway was associated with a higher freedom from VT recurrence as compared with partial diastolic pathway recording and substrate modification. The use of multielectrode mapping catheters in recording diastolic activity may help predict those VTs employing intramural circuits and further optimize ablation strategies.

Precise Signals with a High-Density Grid Mapping Catheter Are Useful for an Entrainment Study.

Complex atrial tachycardias (ATs) after catheter ablation or a MAZE procedure is sometimes difficult to determine the circuits of the tachycardia. A high-density, grid-shapes mapping catheter has been launched, which can be useful for detecting the detail circuits of tachycardias on three-dimensional mapping systems. The signal quality is also important for performing electrophysiological studies (EPSs), such as entrainment mapping, to identify the circuit. This unique mapping catheter has 1 mm electrodes on 2.5 Fr shafts, which improve the signal quality. The high-quality intracardiac electrograms facilitate differentiating small critical potentials, which allows us to perform detailed entrainment mapping in targeted narrow areas. Here, we describe a patient with a perimetral AT with epi-endocardium breakthrough after a MAZE surgery and catheter ablation, which was treated successfully along with detailed entrainment mapping using the HD Grid. This catheter with high-quality signals could be a significant diagnostic tool for a classic EPS as well as for the construction of 3D mapping.

Intrinsically stretchable electrode array enabled in vivo electrophysiological mapping of atrial fibrillation at cellular resolution.

Electrophysiological mapping of chronic atrial fibrillation (AF) at high throughput and high resolution is critical for understanding its underlying mechanism and guiding definitive treatment such as cardiac ablation, but current electrophysiological tools are limited by either low spatial resolution or electromechanical uncoupling of the beating heart. To overcome this limitation, we herein introduce a scalable method for fabricating a tissue-like, high-density, fully elastic electrode (elastrode) array capable of achieving real-time, stable, cellular level-resolution electrophysiological mapping in vivo. Testing with acute rabbit and porcine models, the device is proven to have robust and intimate tissue coupling while maintaining its chemical, mechanical, and electrical properties during the cardiac cycle. The elastrode array records epicardial atrial signals with comparable efficacy to currently available endocardial-mapping techniques but with 2 times higher atrial-to-ventricular signal ratio and >100 times higher spatial resolution and can reliably identify electrical local heterogeneity within an area of simultaneously identified rotor-like electrical patterns in a porcine model of chronic AF.

Loop Recorder Implantation on a Telemetry Ward.

The implantable loop recorder (ILR) is a valuable tool used in the evaluation of syncope, arrhythmia, and cryptogenic stroke. In the inpatient setting, ILRs are routinely implanted in the electrophysiology (EP) lab despite the low complication rate. The purpose of this study was to evaluate the safety, feasibility, and cost of implanting ILRs at the patient's bedside by both electrophysiologists and advanced practice providers (APPs). This was a single center, retrospective study of consecutive ILR implantations performed from February 2018 to May 2019. We examined 3 groups: implantations in the EP lab by electrophysiologists (EP Lab/MD), implantations at the bedside by electrophysiologists (Floor/MD), and implantations at the bedside by APPs (Floor/APP). Over 15 months, 152 patients underwent ILR implantation: 48 in the EP Lab/MD group, 57 in the Floor/MD group, and 47 in the Floor/APP group. The procedure duration was longer in the Floor/APP group (14.2 ± 5.9 minutes) compared with the EP Lab/MD and Floor/MD groups (6.8 ± 4.3 minutes, 9.1 ± 4.9 minutes, p <0.001). The overall complication rate was low (2.6%) with no differences between the groups (p = 0.83). The calculated costs per implant for the EP Lab/MD group, Floor/MD group, and Floor/APP group were $482.05, $162.82, and $73.08, respectively.

Electrogram morphology discriminators in implantable cardioverter defibrillators: A comparative evaluation.

BACKGROUND: Morphology algorithms are currently recommended as a standalone discriminator in single-chamber implantable cardioverter defibrillators (ICDs). However, these proprietary algorithms differ in both design and nominal programming. OBJECTIVE: To compare three different algorithms with nominal versus advanced programming in their ability to discriminate between ventricular (VT) and supraventricular tachycardia (SVT). METHODS: In nine European centers, VT and SVTs were collected from Abbott, Boston Scientific, and Medtronic dual- and triple-chamber ICDs via their respective remote monitoring portals. Percentage morphology matches were recorded for selected episodes which were classified as VT or SVT by means of atrioventricular comparison. The sensitivity and related specificity of each manufacturer discriminator was determined at various values of template match percentage from receiving operating characteristics (ROC) curve analysis. RESULTS: A total of 534 episodes were retained for the analysis. In ROC analyses, Abbott Far Field MD (area under the curve [AUC]: 0.91; P < .001) and Boston Scientific RhythmID (AUC: 0.95; P < .001) show higher AUC than Medtronic Wavelet (AUC: 0.81; P < .001) when tested for their ability to discriminate VT from SVT. At nominal % match threshold all devices provided high sensitivity in VT identification, (91%, 100%, and 90%, respectively, for Abbott, Boston Scientific, and Medtronic) but contrasted specificities in SVT discrimination (85%, 41%, and 62%, respectively). Abbott and Medtronic's nominal thresholds were similar to the optimal thresholds. Optimization of the % match threshold improved the Boston Scientific specificity to 79% without compromising the sensitivity. CONCLUSION: Proprietary morphology discriminators show important differences in their ability to discriminate SVT. How much this impact the overall discrimination process remains to be investigated.

Fast in vivo detection of myocardial norepinephrine levels in the beating porcine heart.

The sympathetic nervous system modulates cardiac function by controlling key parameters such as chronotropy and inotropy. Sympathetic control of ventricular function occurs through extrinsic innervation arising from the stellate ganglia and thoracic sympathetic chain. In the healthy heart, sympathetic release of norepinephrine (NE) results in positive modulation of chronotropy, inotropy, and dromotropy, significantly increasing cardiac output. However, in the setting of myocardial infarction or injury, sympathetic activation persists, contributing to heart failure and increasing the risk of arrhythmias, including sudden cardiac death. Methodologies for detection of norepinephrine in cardiac tissue are limited. Present techniques rely on microdialysis for analysis by high-performance liquid chromatography coupled to electrochemical detection (HPLC-ED), radioimmunoassay, or other immunoassays, such as enzyme-linked immunosorbent assay (ELISA). Although significant information about the release and action of norepinephrine has been obtained with these methodologies, they are limited in temporal resolution, require large sample volumes, and provide results with a significant delay after sample collection (hours to weeks). In this study, we report a novel approach for measurement of interstitial cardiac norepinephrine, using minimally invasive, electrode-based, fast-scanning cyclic voltammetry (FSCV) applied in a beating porcine heart. The first multispatial and high temporal resolution, multichannel measurements of NE release in vivo are provided. Our data demonstrate rapid changes in interstitial NE profiles with regional differences in response to coronary ischemia, sympathetic nerve stimulation, and alterations in preload/afterload.NEW & NOTEWORTHY Pharmacological, electrical, or surgical regulation of sympathetic neuronal control can be used to modulate cardiac function and treat arrhythmias. However, present methods for monitoring sympathetic release of norepinephrine in the heart are limited in spatial and temporal resolution. Here, we provide for the first time a methodology and demonstration of practice and rapid measures of individualized regional autonomic neurotransmitter levels in a beating heart. We show dynamic, spatially resolved release profiles under normal and pathological conditions.

Heart-on-a-Chip Model with Integrated Extra- and Intracellular Bioelectronics for Monitoring Cardiac Electrophysiology under Acute Hypoxia.

We demonstrated a bioelectronic heart-on-a-chip model for studying the effects of acute hypoxia on cardiac function. A microfluidic channel enabled rapid modulation of medium oxygenation, which mimicked the regimes induced by a temporary coronary occlusion and reversibly activated hypoxia-related transduction pathways in HL-1 cardiac model cells. Extracellular bioelectronics provided continuous readouts demonstrating that hypoxic cells experienced an initial period of tachycardia followed by a reduction in beat rate and eventually arrhythmia. Intracellular bioelectronics consisting of Pt nanopillars temporarily entered the cytosol following electroporation, yielding action potential (AP)-like readouts. We found that APs narrowed during hypoxia, consistent with proposed mechanisms by which oxygen deficits activate ATP-dependent K+ channels that promote membrane repolarization. Significantly, both extra- and intracellular devices could be multiplexed, enabling mapping capabilities unachievable by other electrophysiological tools. Our platform represents a significant advance toward understanding electrophysiological responses to hypoxia and could be applicable to disease modeling and drug development.