Assessment of pericardial adhesions by means of the EpiCO2 technique: Brighton Adhesion Classification.

BACKGROUND: Epicardial ablation complications are more frequent in patients with preexisting pericardial adhesions. As opposed to the dry puncture technique, the coronary vein exit and carbon dioxide (CO2) insufflation (EpiCO2) technique allows diagnosing pericardial adhesions before subxiphoid puncture. OBJECTIVE: This study aimed to evaluate the efficacy of the EpiCO2 technique in diagnosing pericardial adhesions prior to subxiphoid puncture. METHODS: Following coronary vein exit, contrast was injected in the pericardial space, and adhesions classified using our novel Brighton Adhesion Classification (BAC) into BAC-0 (no adhesions), BAC-1 (dispersed adhesions), and BAC-2 (dense adhesions extending to the entire assessed area). CO2 insufflation allowed subclassification of BAC-1 adhesions into BAC-1a (not preventing epicardial access or restricting catheter movement) and BAC-1b (either preventing epicardial access or significantly limiting catheter movement). RESULTS: Intentional coronary vein exit (right atrial appendage exit in 1 case) was achieved in all 235 consecutive epicardial ablation procedures undertaken at our center. A diagnosis of BAC-0 was made in 219 cases (93.2%), BAC-1a in 9 cases (3.8%), BAC-1b in 2 cases (0.9%), and BAC-2 in 5 cases (2.1%). This led to not attempting subxiphoid puncture in 6 cases (2.6%) and abandoning epicardial mapping because of limited catheter movement in 1 case (0.4%). Access-related complications occurred in 7 cases (3%) only in the BAC-0 group. CONCLUSION: The EpiCO2 technique allows assessment of the presence of pericardial adhesions prior to attempting subxiphoid puncture for epicardial access, which may lead to a reduction in the procedural complications within this subset of patients.

RETRO-mapping: A novel algorithm automating wavefront categorization using activation mapping during persistent atrial fibrillation demonstrates a reduction in wavefront collisions following pulmonary vein isolation.

RETRO-mapping was developed to automate activation mapping of atrial fibrillation (AF). We used the algorithm to study the effect of pulmonary vein isolation (PVI) on the frequency of focal, planar, and colliding wavefronts in persistent AF. An AFocusII catheter was placed on the left atrial endocardium to record 3 s of AF at six sites pre and post-PVI in patients undergoing wide circumferential PVI for persistent AF. RETRO-mapping analyzed each segment in 2 ms time windows for evidence of focal, planar, and colliding waveforms and the automated categorizations manually validated. Ten patients were recruited. A total of 360 s of data in 120 segments of 3 s from 60 left atrial locations were analyzed. RETRO-map was highly effective at identifying focal waves and collisions during AF. PVI significantly reduced collision frequency but not focal and planar activation frequency. However, there was a significant reduction in the dispersion of activation directions. Larger studies may help determine factors associated with successful clinical outcome.

How to ablate the septo-pulmonary bundle: a case-based review of percutaneous ablation strategies to achieve roof line block.

Electrical conduction through cardiac muscle fibres separated from the main myocardial wall by layers of interposed adipose tissue are notoriously difficult to target by endocardial ablation alone. They are a recognised important cause for procedural failure due to the difficulties of delivering sufficient energy via the endocardial radiofrequency catheter to reach the outer epicardial layer without risking adverse events of the otherwise thin walled atria. Left atrial ablations for atrial fibrillation (AF) and tachycardia are commonly affected by the presence of several epicardial structures, with the septo-pulmonary bundle (SPB), Bachmann's bundle, and the ligament of Marshall all posing substantial challenges for endocardial procedures. Delivery of a transmural lesion set is essential for sustained pulmonary vein isolation and for conduction block across linear atrial lines which in turn has been described to translate into a reduced AF/atrial tachycardia recurrence rate. To overcome the limitations of endocardial-only approaches, surgical ablation techniques for epicardial or combined hybrid endo-epicardial ablations have been described to successfully target these connections. Yet, these techniques confer an increase in procedure complexity, duration, cost, and morbidity. Alternatively, coronary venous system ethanol ablation has been successfully employed by sub-selecting the vein of Marshall to facilitate mitral isthmus line block, although this approach is naturally limited to this area by the coronary venous anatomy. Increased awareness of the pathophysiological relevance of these epicardial structures and their intracardiac conduction patterns in the era of high-resolution 3D electro-anatomical mapping technology has allowed greater understanding of their contribution to the persistence of AF as well as failure to achieve transmural block by traditional ablation approaches. This might translate into novel catheter ablation strategies with procedural success rates comparable to surgical 'cut-and-sew' techniques. This review aims to give an overview of percutaneous catheter ablation strategies to target the SPB, an important cause of failed block across the roof line and isolation of the left atrial posterior wall and/or the pulmonary veins. Existing and investigational technologies will be discussed and an outlook of future approaches provided.

Ablation versus anti-arrhythmic therapy for reducing all hospital episodes from recurrent atrial fibrillation: a prospective, randomized, multi-centre, open label trial.

AIMS: There is rising healthcare utilization related to the increasing incidence and prevalence of atrial fibrillation (AF) worldwide. Simplifying therapy and reducing hospital episodes would be a valuable development. The efficacy of a streamlined AF ablation approach was compared to drug therapy and a conventional catheter ablation technique for symptom control in paroxysmal AF. METHODS AND RESULTS: We recruited 321 patients with symptomatic paroxysmal AF to a prospective randomized, multi-centre, open label trial at 13 UK hospitals. Patients were randomized 1:1:1 to cryo-balloon ablation without electrical mapping with patients discharged same day [Ablation Versus Anti-arrhythmic Therapy for Reducing All Hospital Episodes from Recurrent (AVATAR) protocol]; optimization of drug therapy; or cryo-balloon ablation with confirmation of pulmonary vein isolation and overnight hospitalization. The primary endpoint was time to any hospital episode related to treatment for atrial arrhythmia. Secondary endpoints included complications of treatment and quality-of-life measures. The hazard ratio (HR) for a primary endpoint event occurring when comparing AVATAR protocol arm to drug therapy was 0.156 (95% CI, 0.097-0.250; P < 0.0001 by Cox regression). Twenty-three patients (21%) recorded an endpoint event in the AVATAR arm compared to 76 patients (74%) within the drug therapy arm. Comparing AVATAR and conventional ablation arms resulted in a non-significant HR of 1.173 (95% CI, 0.639-2.154; P = 0.61 by Cox regression) with 23 patients (21%) and 19 patients (18%), respectively, recording primary endpoint events (P = 0.61 by log-rank test). CONCLUSION: The AVATAR protocol was superior to drug therapy for avoiding hospital episodes related to AF treatment, but conventional cryoablation was not superior to the AVATAR protocol. This could have wide-ranging implications on how demand for AF symptom control is met. TRIAL REGISTRATION: Clinical Trials Registration: NCT02459574.

Localized mesospheric ozone destruction corresponding to isolated proton aurora coming from Earth's radiation belt.

Relativistic electron precipitation (REP) from the Earth's radiation belt plays an important role in mesospheric ozone loss as a connection between space weather and the climate system. However, the rapid (tens of minutes) destruction of mesospheric ozone directly caused by REP has remained poorly understood due to the difficulty of recognizing its location and duration. Here we show a compelling rapid correspondence between localized REP and ozone destruction during a specific auroral phenomenon, the called an isolated proton aurora (IPA). The IPA from the Earth's radiation belt becomes an important spatial and temporal proxy of REP, distinct from other auroral phenomena, and allowing visualizing micro-ozone holes. We found ozone destruction of as much as 10-60% within 1.5 h of the initiation of IPA. Electromagnetic ion cyclotron waves in the oxygen ion band observed as the driver of REP likely affect through resonance with mainly ultra-relativistic (> 2 mega-electron-volts) energy electrons. The rapid REP impact demonstrates its crucial role and direct effect on regulating the atmospheric chemical balance.

Cycle Length Evaluation in Persistent Atrial Fibrillation Using Kernel Density Estimation to Identify Transient and Stable Rapid Atrial Activity.

PURPOSE: Left atrial (LA) rapid AF activity has been shown to co-localise with areas of successful atrial fibrillation termination by catheter ablation. We describe a technique that identifies rapid and regular activity. METHODS: Eight-second AF electrograms were recorded from LA regions during ablation for psAF. Local activation was annotated manually on bipolar signals and where these were of poor quality, we inspected unipolar signals. Dominant cycle length (DCL) was calculated from annotation pairs representing a single activation interval, using a probability density function (PDF) with kernel density estimation. Cumulative annotation duration compared to total segment length defined electrogram quality. DCL results were compared to dominant frequency (DF) and averaging. RESULTS: In total 507 8 s AF segments were analysed from 7 patients. Spearman's correlation coefficient was 0.758 between independent annotators (P < 0.001), 0.837-0.94 between 8 s and ≥ 4 s segments (P < 0.001), 0.541 between DCL and DF (P < 0.001), and 0.79 between DCL and averaging (P < 0.001). Poorer segment organization gave greater errors between DCL and DF. CONCLUSION: DCL identifies rapid atrial activity that may represent psAF drivers. This study uses DCL as a tool to evaluate the dynamic, patient specific properties of psAF by identifying rapid and regular activity. If automated, this technique could rapidly identify areas for ablation in psAF.

RETRO-MAPPING: A New Approach to Activation Mapping in Persistent Atrial Fibrillation Reveals Evidence of Spatiotemporal Stability.

[Figure: see text].

A New Era in Epicardial Access for the Ablation of Ventricular Arrhythmias: The Epi-Co2 Registry.

OBJECTIVES: This multicenter registry aimed to assess the reproducibility and safety of intentional coronary vein exit and carbon dioxide insufflation to facilitate subxiphoid epicardial access in the setting of ventricular tachycardia ablation. BACKGROUND: Epicardial ablation for ventricular tachycardia is not a widespread technique due to the significant potential complications associated with subxiphoid puncture. The first experience in 12 patients showed that intentional coronary vein exit and carbon dioxide insufflation was technically feasible. METHODS: A branch of the coronary sinus was cannulated by means of a diagnostic JR4 coronary catheter. Intentional perforation at the distal portion of that branch was performed with a high tip load 0.014-inch angioplasty wire. A microcatheter was advanced over the wire into the pericardial space. Carbon dioxide was then insufflated into the pericardial space, allowing direct visualization of the anterior pericardial space to facilitate subxiphoid puncture. RESULTS: Intentional coronary vein exit was attempted in 102 consecutive patients in 16 different centers and successfully completed in 101 patients. Significant pericardial adhesions were confirmed in 3 patients, preventing carbon dioxide insufflation and epicardial ablation. None of the punctures were complicated with inadvertent right ventricular puncture or damage to a coronary artery. Significant bleeding (>80 ml) due to coronary vein exit occurred in 5 patients, without hemodynamic compromise. None of the patients required surgery. CONCLUSIONS: Coronary vein exit and carbon dioxide insufflation can be safely and reproducibly achieved to facilitate subxiphoid pericardial access in the setting of ventricular tachycardia ablation.

Optimizing Assessment of Surgical Knot Tying Skill.

OBJECTIVES: Knot tying is a fundamental surgical skill. Existing knot tying models assess tying efficiency and errors but do not address respect for tissue. Development of a model that assesses tissue displacement during knot tying may provide a good surrogate for respect for tissue, allow detection of expertise, and offer an improved training platform for skill acquisition. This study aimed to develop a novel, low-cost, knot tying board (KTB) that collects objective, automated metrics of knot displacement, and assesses knot displacement by level of surgical expertise. DESIGN: The novel KTB was developed in collaboration between engineering students and surgical educators. Joystick potentiometers were incorporated on 2 parallel rubber tubes to measure vertical and horizontal displacement while tying. Participants used a standardized technique to tie 1- and 2-handed knots. Differences in time and tubing displacement were compared among junior residents (postgraduate year 1-2), senior residents (postgraduate year 3-5), and attending surgeons; p < 0.05 was considered statistically significant. SETTING: This study was conducted at the Indiana University Surgical Skills Center in Indianapolis, IN. PARTICIPANTS: Forty-seven residents and faculty participated in the study (26 juniors, 14 seniors, 7 attendings). RESULTS: KTB development required 100 hours and $70.00. The attending surgeons tied 2-handed knots faster and with significantly more vertical tubing displacement than residents. Senior residents tied knots significantly faster but with similar tubing displacement as juniors. Similar trends were found for 1-handed knots. CONCLUSIONS: A novel, low-cost KTB was developed to measure knot displacement as a surrogate for tissue handling. The new performance metric of vertical knot displacement proved more sensitive in detecting performance differences among groups compared with horizontal knot displacement. This board and its novel metrics may promote the development of robust knot tying skill by residents.

Granger Causality-Based Analysis for Classification of Fibrillation Mechanisms and Localization of Rotational Drivers.

BACKGROUND: The mechanisms sustaining myocardial fibrillation remain disputed, partly due to a lack of mapping tools that can accurately identify the mechanism with low spatial resolution clinical recordings. Granger causality (GC) analysis, an econometric tool for quantifying causal relationships between complex time-series, was developed as a novel fibrillation mapping tool and adapted to low spatial resolution sequentially acquired data. METHODS: Ventricular fibrillation (VF) optical mapping was performed in Langendorff-perfused Sprague-Dawley rat hearts (n=18), where novel algorithms were developed using GC-based analysis to (1) quantify causal dependence of neighboring signals and plot GC vectors, (2) quantify global organization with the causality pairing index, a measure of neighboring causal signal pairs, and (3) localize rotational drivers (RDs) by quantifying the circular interdependence of neighboring signals with the circular interdependence value. GC-based mapping tools were optimized for low spatial resolution from downsampled optical mapping data, validated against high-resolution phase analysis and further tested in previous VF optical mapping recordings of coronary perfused donor heart left ventricular wedge preparations (n=12), and adapted for sequentially acquired intracardiac electrograms during human persistent atrial fibrillation mapping (n=16). RESULTS: Global VF organization quantified by causality pairing index showed a negative correlation at progressively lower resolutions (50% resolution: P=0.006, R2=0.38, 12.5% resolution, P=0.004, R2=0.41) with a phase analysis derived measure of disorganization, locations occupied by phase singularities. In organized VF with high causality pairing index values, GC vector mapping characterized dominant propagating patterns and localized stable RDs, with the circular interdependence value showing a significant difference in driver versus nondriver regions (0.91±0.05 versus 0.35±0.06, P=0.0002). These findings were further confirmed in human VF. In persistent atrial fibrillation, a positive correlation was found between the causality pairing index and presence of stable RDs (P=0.0005,R2=0.56). Fifty percent of patients had RDs, with a low incidence of 0.9±0.3 RDs per patient. CONCLUSIONS: GC-based fibrillation analysis can measure global fibrillation organization, characterize dominant propagating patterns, and map RDs using low spatial resolution sequentially acquired data.

Evaluation of a new algorithm for tracking activation during atrial fibrillation using multipolar catheters in humans.

BACKGROUND: Conventional mapping techniques during atrial fibrillation (AF) are difficult to apply because of cycle length irregularity. Mapping studies are usually restricted to short durations of AF in limited regions because of the laborious manual annotation of local activation time (LAT). The purpose of this study was to test an automated algorithm to map activation during AF, with comparable accuracy to manual annotation. METHODS: Left atrial (LA) mapping was performed using a 20-pole double loop catheter (AFocusII) in 30-second data segments from 16 patients. The new algorithm (RETRO-Mapping) was designed to detect wavefront propagation between electrodes, and display activating wavefronts on a two-dimensional representation of the catheter. Activation patterns were validated against their bipolar electrograms and with isochronal maps. The mapping protocol was approved by the research ethics committee (13/LO1169 and 14/LO1367). RESULTS: During AF, uniform wavefront activation direction (mean ± SD, degrees) from manually constructed isochronal maps was comparable to RETRO-Propagation Map (RETRO-PM) and RETRO-Automated Direction (RETRO-AD): 1 ± 6.9 for RETRO-PM; and 2 ± 6.6 for RETRO-AD. There was no significant difference in activation direction assigned to 1373 uniform wavefronts during AF when comparing RETRO-PM with RETRO-AD (Bland-Altman mean difference: -0.1 degrees; limits of agreement: -8.0 to 8.3; 95% CI -0.4 to 0.2; (r = 0.01) R2 = < 0.005; P = .77). CONCLUSION: We have developed and validated a new technique to map activation during AF. This technique shows comparable accuracy to that of conventional isochronal mapping with careful manual adjustment of LAT.

Ablation versus Anti-Arrhythmic Therapy for Reducing All Hospital Episodes from Recurrent Atrial Fibrillation (AVATAR-AF): Design and rationale.

Atrial Fibrillation (AF) ablation using the cryoballoon is effective at reducing symptomatic AF episodes. The prevalence of AF is increasing with the aging population and access to such treatment would be enhanced by reducing the resource requirements. Relinquishing electrical mapping of the pulmonary veins (PV) removes the need for PV catheters, electrical recording equipment and staff trained in using this equipment. Moreover, the majority of complications are peri-procedural so overnight hospitalization maybe unnecessary. We tested this streamlined approach to AF ablation against medical therapy using the endpoint of time to all hospital episodes. METHODS: The AVATAR-AF study is a prospective, multicenter, randomized controlled trial testing the primary hypothesis that AF ablation done without PV mapping or overnight hospitalization is more effective than anti-arrhythmic drugs at reducing all hospital episodes related to recurrent atrial arrhythmias. We included a third arm to test a secondary hypothesis that confirming PV entrance block as per consensus guidelines can improve outcomes. Three hundred twenty-one patients with documented paroxysmal AF will be randomized in a 1:1:1 manner to one of three investigation arms: (1) AVATAR protocol cryoballoon ablation without assessment of acute PV isolation or overnight hospitalization; (2) medical therapy with anti-arrhythmic drugs; or (3) conventional cryoballoon ablation with assessment of acute PV isolation. The primary endpoint is defined as the time to all hospital episodes (including outpatient consultation) related to treatment for atrial arrhythmia. CONCLUSION: The AVATAR-AF study will determine whether the resource utilization for AF ablation can be reduced whilst maintaining superiority over medical therapy.

Explaining the apparent impenetrable barrier to ultra-relativistic electrons in the outer Van Allen belt.

Recent observations have shown the existence of an apparent impenetrable barrier at the inner edge of the ultra-relativistic outer electron radiation belt. This apparent impenetrable barrier has not been explained. However, recent studies have suggested that fast loss, such as associated with scattering into the atmosphere from man-made very-low frequency transmissions, is required to limit the Earthward extent of the belt. Here we show that the steep flux gradient at the implied barrier location is instead explained as a natural consequence of ultra-low frequency wave radial diffusion. Contrary to earlier claims, sharp boundaries in fast loss processes at the barrier are not needed. Moreover, we show that penetration to the barrier can occur on the timescale of days rather than years as previously reported, with the Earthward extent of the belt being limited by the finite duration of strong solar wind driving, which can encompass only a single geomagnetic storm.

Drivers of Atrial Fibrillation: Theoretical Considerations and Practical Concerns.

Understanding the mechanisms responsible for driving AF is key to improving the procedural success for AF ablation. In this review, we look at some of the proposed drivers of AF, the disagreement between experts and the challenges confronted in attempting to map AF. Defining a 'driver' is also controversial, but for the purposes of this review we will consider an AF driver to be either a focal or localised source demonstrating fast, repetitive activity that propagates outward from this source, breaking down in to disorganisation further away from its origin.

Using ultra-low frequency waves and their characteristics to diagnose key physics of substorm onset.

Substorm onset is marked in the ionosphere by the sudden brightening of an existing auroral arc or the creation of a new auroral arc. Also present is the formation of auroral beads, proposed to play a key role in the detonation of the substorm, as well as the development of the large-scale substorm current wedge (SCW), invoked to carry the current diversion. Both these phenomena, auroral beads and the SCW, have been intimately related to ultra-low frequency (ULF) waves of specific frequencies as observed by ground-based magnetometers. We present a case study of the absolute and relative timing of Pi1 and Pi2 ULF wave bands with regard to a small substorm expansion phase onset. We find that there is both a location and frequency dependence for the onset of ULF waves. A clear epicentre is observed in specific wave frequencies concurrent with the brightening of the substorm onset arc and the presence of "auroral beads". At higher and lower wave frequencies, different epicentre patterns are revealed, which we conclude demonstrate different characteristics of the onset process; at higher frequencies, this epicentre may demonstrate phase mixing, and at intermediate and lower frequencies these epicentres are characteristic of auroral beads and cold plasma approximation of the "Tamao travel time" from near-earth neutral line reconnection and formation of the SCW.

Accurately characterizing the importance of wave-particle interactions in radiation belt dynamics: The pitfalls of statistical wave representations.

Wave-particle interactions play a crucial role in energetic particle dynamics in the Earth's radiation belts. However, the relative importance of different wave modes in these dynamics is poorly understood. Typically, this is assessed during geomagnetic storms using statistically averaged empirical wave models as a function of geomagnetic activity in advanced radiation belt simulations. However, statistical averages poorly characterize extreme events such as geomagnetic storms in that storm-time ultralow frequency wave power is typically larger than that derived over a solar cycle and Kp is a poor proxy for storm-time wave power.

Catheter ablation of atrial fibrillation in patients with heart failure: impact of maintaining sinus rhythm on heart failure status and long-term rates of stroke and death.

AIMS: Catheter ablation of atrial fibrillation (AF) in patients with heart failure (HF) can improve left ventricular (LV) function and HF symptoms. We aimed to investigate whether long-term maintenance of sinus rhythm impacts on hard outcomes such as stroke and death. METHODS AND RESULTS: An international multicentre registry was compiled from seven centres for consecutive patients undergoing catheter ablation of AF. Long-term freedom from AF was examined in patients with and without HF. The impact of maintaining sinus rhythm on rates of stroke and death was also examined. A total of 1273 patients were included: 171 with HF and 1102 without. Median follow-up was 3.1 years (IQR 2.0-4.3). The final procedure success rate was no different for paroxysmal AF (PAF) (78.7 vs. 85.7%, P = 0.186), but significantly different for persistent AF (57.3 vs. 75.8%, P < 0.001). Multivariate analysis showed that HF independently predicted recurrent arrhythmia [hazard ratio (HR) 1.7, 95% confidence interval (CI) 1.2-2.4, P = 0.002]. New York Heart Association class decreased from 2.3 ± 0.7 at baseline to 1.5 ± 0.8 at follow-up (P < 0.001). Left ventricular ejection fraction (LVEF) increased from 34.3 ± 9.0 to 45.8 ± 12.8% (P < 0.001). Recurrent AF was strongly predictive of stroke or death in HF patients (HR 8.33, 95% CI 1.86-37.7, P = 0.001). CONCLUSION: Long-term success rates for persistent (but not paroxysmal) AF ablation are significantly lower in HF patients. Left ventricular function and HF symptoms were improved following ablation. In HF patients, recurrent arrhythmia strongly predicted stroke and death during follow-up.

Analytic expressions for ULF wave radiation belt radial diffusion coefficients.

We present analytic expressions for ULF wave-derived radiation belt radial diffusion coefficients, as a function of L and Kp, which can easily be incorporated into global radiation belt transport models. The diffusion coefficients are derived from statistical representations of ULF wave power, electric field power mapped from ground magnetometer data, and compressional magnetic field power from in situ measurements. We show that the overall electric and magnetic diffusion coefficients are to a good approximation both independent of energy. We present example 1-D radial diffusion results from simulations driven by CRRES-observed time-dependent energy spectra at the outer boundary, under the action of radial diffusion driven by the new ULF wave radial diffusion coefficients and with empirical chorus wave loss terms (as a function of energy, Kp and L). There is excellent agreement between the differential flux produced by the 1-D, Kp-driven, radial diffusion model and CRRES observations of differential electron flux at 0.976 MeV-even though the model does not include the effects of local internal acceleration sources. Our results highlight not only the importance of correct specification of radial diffusion coefficients for developing accurate models but also show significant promise for belt specification based on relatively simple models driven by solar wind parameters such as solar wind speed or geomagnetic indices such as Kp. KEY POINTS: Analytic expressions for the radial diffusion coefficients are presentedThe coefficients do not dependent on energy or wave m valueThe electric field diffusion coefficient dominates over the magnetic.