Type Of Reentry Research Articles

Context and perspectives of sub-orbital activities and transit through airspace/ground support activities

This paper provides some considerations on the current context and perspectives concerning the sub-orbital activities and transit through airspace/ground support activities issued in the frame of the IAF-IAA-IISL Working Group on Space Traffic Management (STM). The group brought together experts from different backgrounds and countries in order to analyze the different aspects of these activities, namely, technically, programmatically, and legally.The rise in space activities, both orbital and suborbital, increases the number of possible interactions with national airspace, inducing potential problems of traffic management. Spacecraft transiting through airspace (both international and national) involve different objects (satellites, launch vehicles, rocket bodies, suborbital vehicles, aircraft …) and missions with varied associated risks. These risks can be generally characterized by the time in airspace, the velocity of spacecraft, and its altitude. Despite the increase in space activities, there are currently no binding international rules specific for spacecraft traversing through airspace. However, there are guidelines, national frameworks, recommendations from organizations (e.g. UN-COPUOS, OSI) covering part of the interaction of space activities and transit through airspace. Additionally, some may argue customary international law exists in the current practice of preventing fallout during launch/re-entry activity into sovereign airspace.The rising number of spaceports, both for orbital and suborbital missions, contribute to increase of space traffic in terms of location of the launch sites and of widespread type of launch and re-entry missions.The working group focused on the identification of the objects to be considered for this interaction, the current available rules and guidelines, the recommendations issued by specific organizations on the subject, and the experts’ advice in order to have a global view of the context and summarize some general recommendations for future operations.

Scar-related atrial macroreentries: Different arrhymogenic basis generates different reentry type.

Catheter ablation is an established therapeutic strategy to treat scar-related macroreentry atrial tachycardia (MAT). However, the scar properties and arrhythmogenicity and the reentry type have not been clearly defined. A total of 122 patients with scar-related MAT were enrolled in this study. The atrial scars were classified into two categories: spontaneous scars (Group A: n=28) and iatrogenic scars (Group B: n=94). According to the relationship between scar location and the reentry circuit, MAT was described as scar pro-flutter MAT, scar-dependent MAT, and scar-mediated MAT. The reentry type of MAT was significantly different between Groups A and B: pro-flutter (40.5%vs. 62.0%, p=0.02), scar-dependent AT (40.5%vs. 13.0%, p<0.001), and scar-mediated AT (19.0%vs. 25.0%, p=0.42). After a median follow-up of 25 months, 21 patients with AT recurrence were observed. Compared with the spontaneous group, there was a lower recurrence rate of MAT in the iatrogenic group (28.6%vs. 10.6%, p=0.03). Scar-related MAT has three reentry types, and the proportion of each type varies with the scar properties and its arrhythmogenic basis. Optimization of the ablation strategy based on the scar properties to improve the long-term outcome of catheter ablation of MAT is necessary.

Comparison between Different Re-Entry Technologies for Debris Mitigation in LEO

The population of satellites in Low Earth Orbit is predicted to growth exponentially in the next decade due to the proliferation of small-sat constellations. Consequently, the probability of collision is expected to increase dramatically, possibly leading to a potential Kessler syndrome situation. It is therefore necessary to strengthen all the technologies required for collision avoidance and end-of-life disposal of new satellites, together with active debris removal of current and potential future dead satellites. Both situations require the lowering of the altitude of a satellite up to re-entry. In this paper several de-orbiting technologies are evaluated: natural decay, chemical propulsion (solid and liquid), electric propulsion, drag sail, electrodynamic tether, and combinations of the previous ones. The comparison considers the initial altitude, system mass, de-orbiting time, collision probability during descent, reliability, and technological limits. Differences between active debris removal and satellite end-of-life self-disposal are taken into account. Moreover, the different types of re-entry, controlled vs. non-controlled, expendable vs. reusable system, demisable vs. non-demisable system are also discussed. Finally, the possibility to operate the satellite in Very Low Earth Orbits with a propulsion system for drag compensation and passive re-entry at end of life is investigated.

Dg-mapping as a tool to determine the spatial distribution of the focal sources and the number of reentries during torsade de pointes in the cavb dog model

Abstract Funding Acknowledgements Type of funding sources: None. Background Torsade de Pointes (TdP) is a ventricular tachycardia that is still incompletely understood. While the origin of the arrhythmia is generally accepted to be caused by triggered activity, the perpetuation of such an episode is still under debate. Purpose We compare the difference in reentrant activity between self- and non-terminating(ST and NT) TdP episodes. In addition, we analyzed the distribution of the triggered activity for preferred locations. Methods A total of 5 dogs with Chronic Atrioventricular Block developed 54 episodes of TdP. These episodes were examined for reentry loops and focal sources. First, to detect loops, we used Directed Graph Mapping, a novel mapping technique based on principles from network theory. Subsequently, the number of simultaneous loops and the presence of (bi-)ventricular reentry was compared between the ST and NT groups. Second, focal sources were accumulated into heatmaps. The distribution of sources was compared to a randomly distributed model for the detection of preferred locations. Results Concerning reentry, during the time at which loops are present, a typical ST episode shows an average of 1.33(±0.66) reentry loops present at one time compared to an average of 2.72(±1.48) for a typical NT episode. Looking at the (bi-)ventricular reentry, only 1 of the 4 ST episodes (25%) shows the presence of this type of reentry and only 7.12 % of the total reentry duration, while all 9 NT episodes (100%) develop (bi-)ventricular reentry to a greater degree than in the one ST episode (Between 10.10% and 69.62% of their total reentry duration). Regarding the triggered activity, we see locations in the heatmaps containing up to 23% of all detected focal sources in the entire system. Compared to a random distribution of focal sources, the chances to get as many sources in one location as shown in the data are close to 0%. Conclusion Reentry in NT TdP differentiates itself from the reentry in ST cases on the basis of the number of simultaneous loops in the system and the presence of (bi-)ventricular reentry. Triggered activity in CAVB dogs occurs at preferred locations in the ventricles. Therefore, ablating these preferred regions could be a possible strategy to prevent TdP.

DG-Mapping: a novel software package for the analysis of any type of reentry and focal activation of simulated, experimental or clinical data of cardiac arrhythmia.

In this work, we present the release of a novel easy to use software package called DGM or Directed-Graph-Mapping. DGM can automatically analyze any type of arrhythmia to find reentry or focal sources if the measurements are synchronized in time. Currently, DGM requires the local activation times (LAT) and the spatial coordinates of the measured electrodes. However, there is no requirement for any spatial organization of the electrodes, allowing to analyze clinical, experimental or computational data. DGM creates directed networks of the activation, which are analyzed with fast algorithms to search for reentry (cycles in the network) and focal sources (nodes with outgoing arrows). DGM has been mainly optimized to analyze atrial tachycardia, but we also discuss other applications of DGM demonstrating its wide applicability. The goal is to release a free software package which can allow researchers to save time in the analysis of cardiac data. An academic license is attached to the software, allowing only non-commercial use of the software. All updates of the software, user and installation guide will be published on a dedicated website www.dgmapping.com . Graphical Abstract Direct-Graph-Mapping is a method to automatically analyze a given arrhythmia by converting measured data of the electrodes in a directed network. DGM requires the local activation times (LAT) and the spatial coordinates of the measured electrodes. There is no requirement for any spatial organization of the electrodes, allowing to analyze clinical, experimental or computational data (see left). An example could be the LATs and coordinates from a CARTO file. DGM creates a directed network of the activation by (1) determining the neighbors of each node, 2 (2) allowing a directed arrow between two neighbors if propagation of the electrical wave is possible, (3) repeating this process for all nodes, (4) if necessary, redistributing the nodes more uniformly and repeating step (1)-(3). Two possible steps are (5) to visualize the wavefront by creating an average graph or (6) find the cycles in the network which represent the reentry loops. Focal sources are nodes with only outgoing arrows.

Ablation of Left Atrial Tachycardia following Catheter Ablation of Atrial Fibrillation: 12-Month Success Rates.

The treatment of atrial tachycardia following catheter ablation of atrial fibrillation is often challenging. Electrophysiological studies using high-resolution 3D mapping systems have contributed significantly to their understanding, and new ablation approaches have shown high rates of acute terminations with low recurrences for the clinical AT. However, patient populations are very heterogeneous, and long-term data of the freedom from any atrial tachycardia or any arrhythmia are still sparse. To evaluate long-term success, a unified patient population and predefined ablation strategies are preferred. In this study, we present 12-month success and mean 30 month follow-up data of catheter ablation of left atrial tachycardia. All 35 patients had a history of pulmonary vein isolation (PVI), 71% of which had a previous substrate modification. A total of 54 ATs, with a mean cycle length 297 ± 86 ms, 31 macro-reentries, and 4 localized reentries, were targeted. The ablation strategy to be used was given by the study protocol, depending on the type of reentry and the number of critical isthmuses. All available ablation strategies were included: standard (anatomical) lines, individual lines, critical isthmuses, and focal ablation. All ATs were terminated by ablation. A total of 91% terminated upon the first ablation strategy. Freedom from any AT after 12 months was 82%, and from any arrhythmia, it was 77%. The multi-procedure success after 30 months was 65% for any AT and 55% for any arrhythmia. In conclusion, individual ablation strategies based on the reentry mechanism and the number of critical isthmuses seems promising and demonstrates a high long-term clinical success. Tachycardia comprising a single critical isthmus can be ablated by critical isthmus ablation only. These patients present with the highest 12-month and long-term success rates.

Dissecting the ecosystems’ determinants of entrepreneurial re-entry after a business failure

Purpose This study aims to evaluate the role of entrepreneurial ecosystems conditions (formal, informal and social capital) on different types of entrepreneurial re-entry at a global scale. Design/methodology/approach Given this phenomenon’s nature, this study builds a panel of data of 54 economies covering different (advanced and emerging) countries across the globe during the period 2004–2017 by mixing multiples sources of information (e.g. Global Entrepreneurship Monitor, the World Economic Forum, the World Bank and the International Monetary Fund). The statistical analysis consisted of the fixed-effect dynamic generalized method of moments (GMM) estimation for panel data. Findings Three empirical insights emerge from the study. First, the entrepreneurial ecosystem’s formal conditions are mainly configured to support high-growth entrepreneurship ignoring re-entrepreneurs. Consequently, the formal conditions’ contribution is very limited in emerging economies. Second, the analysis of informal conditions revealed social media’s critical contribution for legitimizing entrepreneurship and supporting those entrepreneurs who want to re-enter the domestic or international market after a business failure. Third, social networks built during previous business angels or entrepreneurial experiences or with other entrepreneurs also play a crucial role for re-entrepreneurs to overcome the weaknesses in the entrepreneurial ecosystems’ conditions. Originality/value The study contributes to two ongoing academic debates among entrepreneurship scholars. The first is related to how the entrepreneurial ecosystem supports entrepreneurial activity in different economic contexts. The second is related to the study of the contextual determinants of entrepreneurial re-entry after a business failure.

Paradigm shifts in electrophysiological mechanisms of atrial fibrillation

AbstractDetermining the sequence of activation is a major source of information for understanding the electrophysiological mechanism(s) of atrial fibrillation (AF). However, the complex morphology of the electrograms hampers their analysis, and has stimulated generations of electrophysiologists to develop a large variety of technologies for recording, pre-processing, and analysis of fibrillation electrograms. This variability of approaches is mirrored by a large variability in the interpretation of fibrillation electrograms and, thereby, opinions regarding the basic electrophysiological mechanism(s) of AF vary widely. Multiple wavelets, different types of re-entry including rotors, double layers, multiple focal activation patterns all have been advocated, and a comprehensive and commonly accepted paradigm for the fundamental mechanisms of AF is still lacking. Here, we summarize the Maastricht perspective and Cleveland perspective regarding AF mechanism(s). We also describe some of the key observations in mapping of AF reported over the past decades, and how they changed over the years, often as results of new techniques introduced in the experimental field of AF research.

The Mechanism of Reflection Type Reentry: A Simulation Study.

Reflection is a special type of reentry in which an electrical wave front travels in a forward direction through tissue that is then re-excited by a wave front that propagates backward. This type of reentry has been studied computationally in 1-dimensional fibers and verified experimentally. Different hypotheses explaining reflected reentry have been proposed based on the structure and heterogeneity of the tissue properties, but the mechanism remains uncertain. We used the bidomain model to represent cardiac tissue and the Luo-Rudy model to describe the active membrane properties. We consider an ischemic region in a volume of ventricular myocardium. Our results show that a slow depolarization in the ischemic border zone caused by electrotonic coupling to depolarized tissue in the normal region creates a delay between proximal and distal regions that produces enough electrotonic current in the distal region to re-excite the proximal region. Our simulation shows that an early afterdepolarization (EAD) is not the source of the reflection. It depends on the pacing interval and stimulus strength necessary to maintain enough time delay between proximal and distal regions.

82 * Ablation of ventricular tachycardia in the very elderly with cardiomyopathy

Introduction: Ablation procedures for ventricular tachycardia (VT) have become the state-of-the-art treatment for patients with refractory symptomatic VT in the context of ischaemic or non-ischaemic cardiomyopathy. Some studies have suggested this procedure is feasible, safe and effective in the elderly population. We aim at evaluating the acute and post-acute effectiveness and safety of VT ablation in very elderly patients with ischaemic or non-ischaemic cardiomyopathy. Methods: All patients 80 years of age or older with previously known ischaemic or non-ischaemic cardiomyopathy admitted for VT ablation from January 1st 2008 to December 31st 2013 were included and followed for an average of 12 months (range 1-30 months). The following data were collected: demographic characteristics, medication, clinical and procedural information and follow-up data. Study endpoints were all-cause mortality and the occurrence of any significant VT, defined as the occurrence of any ICD therapy or any symptomatic VT regardless of ICD therapy. Results: Fourteen VT ablations in 13 patients with ischaemic or non-ischaemic cardiomyopathy were performed during the above-mentioned time period (mean age 84.2, range 80-92, 30.8% females, all but one with ischaemic cardiomyopathy, 46.1% with severe left ventricular dysfunction, 77% on either amiodarone or sotalol). All patients had the procedure due to either recurrent symptomatic VT and/or ICD shocks. Voltage mapping and late potentials were used to guide the ablation in all cases except one where the VT was of a bundle branch re-entry type. Complete success was achieved in 11 procedures, while in 2 cases the clinical VT was still inducible albeit with much more aggressive pacing protocols. The ablation failed in one case. No direct complications of any of the 14 procedures were reported. Seven patients died during follow-up: their mean and median additional months of life after VT ablation were 15.3 and 21, respectively. The remaining 6 patients are still alive (average follow-up of 6 months). Five patients had ventricular arrhythmia after the ablation procedure: 4 patients had ICD therapy delivered once (ATP in 3 cases, ATP plus shock in the remaining one), but only 2 had symptoms; an additional patient had one symptomatic VT that did not trigger ICD therapy, as the VT rate was below the programmed tachycardia zone. Conclusions: VT ablation is feasible and safe in very elderly patients with ischaemic or non-ischaemic cardiomyopathy. Acute and post-acute success rates seem similar to those described in the literature for their younger counterparts.

Computational Analysis of Radiative Heat Loading on Hypervelocity Reentry Vehicles

Space exploration missions may include atmospheric entries at very high velocities (for example, sample return or entries from hyperbolic orbits) or into an atmosphere with highly radiative constituents (for example, Mars or Titan). The effects of gas radiation in the shock layer and wake flows may become significant at such flight conditions; hence, an accurate computational fluid dynamics analysis of these flows requires adequate modeling of the local absorption and emission properties and the energy transport by radiation. The wide range of numerical techniques for the integration of radiation in entry vehicle simulations includes Monte Carlo models, which enable accurate and computationally efficient predictions of radiative energy transport in participating (absorbing and emitting) media for complex geometries. Reentry type flow properties are characterized by a large variation of local absorption and emission properties in the spectral range. Therefore, and due to the absence of general averaging rules, a fine spectral discretization is needed for practical computations. Here, binning methods offer the potential to reduce the required resolution while maintaining a high level of accuracy. The application of a Monte Carlo radiation transport code using high spectral resolution and a loose coupling approach with the applied flow solver was found to give good agreement with the available heating rate measurements of the Second Flight Investigation of Reentry Environment flight experiment.

Arrhythmias in the gut

In recent years, it has become possible to record, from a large number of extracellular electrodes, the electrical activities of smooth muscle organs. These recordings, after proper processing and analysis, may reveal origin and propagation of normal and abnormal electrical activities in these organs. Several publications have appeared in the past 5 years describing origin and propagation of slow waves in the stomach of experimental animals and in humans. Furthermore, publications are now starting to appear that describe pathophysiological patterns of propagation and these studies provide us with novel concepts regarding potential mechanisms of arrhythmias in the gut, crucial information if we are ever going to successfully treat patients suffering from such arrhythmias. In this issue of Neurogastroenterology & Motility, Angeli et al. have mapped the slow wave propagation in the porcine small intestine and discovered two types of reentry; functional reentry and circumferential reentry. Next to the descriptions of arrhythmias in the stomach, the fact that reentrant arrhythmias may also occur in the small intestine further extends this new emerging field of gastrointestinal (GI) arrhythmias. In this viewpoint, the relevance of these arrhythmias is further discussed and a few ideas for future research in this field, not necessarily constrained to the GI system, proposed.

Mechanisms of ventricular arrhythmias: a dynamical systems-based perspective.

Defining the cellular electrophysiological mechanisms for ventricular tachyarrhythmias is difficult, given the wide array of potential mechanisms, ranging from abnormal automaticity to various types of reentry and kk activity. The degree of difficulty is increased further by the fact that any particular mechanism may be influenced by the evolving ionic and anatomic environments associated with many forms of heart disease. Consequently, static measures of a single electrophysiological characteristic are unlikely to be useful in establishing mechanisms. Rather, the dynamics of the electrophysiological triggers and substrates that predispose to arrhythmia development need to be considered. Moreover, the dynamics need to be considered in the context of a system, one that displays certain predictable behaviors, but also one that may contain seemingly stochastic elements. It also is essential to recognize that even the predictable behaviors of this complex nonlinear system are subject to small changes in the state of the system at any given time. Here we briefly review some of the short-, medium-, and long-term alterations of the electrophysiological substrate that accompany myocardial disease and their potential impact on the initiation and maintenance of ventricular arrhythmias. We also provide examples of cases in which small changes in the electrophysiological substrate can result in rather large differences in arrhythmia outcome. These results suggest that an interrogation of cardiac electrical dynamics is required to provide a meaningful assessment of the immediate risk for arrhythmia development and for evaluating the effects of putative antiarrhythmic interventions.

Pulsed Thermography and Ultrasonic Non-Destructive Evaluation of Corrugated Metallic Thermal Protection System (MTPS) Panel

Space vehicles that re-enter earth’s atmosphere require thermal protection system (TPS) to safeguard them from intense aerodynamic heating. Depending on the type of re-entry (lifting/ballistic), trajectory, duration of flight in atmospheric regime etc., the heat flux may vary from 40kW/m2to 180kW/m2. In our studies on metallic TPS (MTPS), corrugated core is joined to either side of the skins by brazing. The brazed joint is evaluated using both pulsed thermography (PT) and ultrasonic testing. PT images show clear visualization of joint and defects. Also it is faster and easier. Ultrasonic testing is done using pitch-catch and pulse-echo techniques, which shows many limitations. In literature, it is reported that for brazed joints using ultrasonic testing, defect location can be identified by faster decay pattern of multiple echoes (compared to that of good location). In case of PM 2000 panel, reversal of the patterns is observed. This new phenomenon is verified with the support of PT. It is also found that for inconel panel, the decay patterns are as reported in literature.

Dexmedetomidine: A Novel Drug for the Treatment of Atrial and Junctional Tachyarrhythmias During the Perioperative Period for Congenital Cardiac Surgery: A Preliminary Study

Atrial and junctional tachyarrhythmias occur frequently during the perioperative period for congenital cardiac surgery and can be a cause of increased morbidity and mortality. These rhythm disturbances that may be well tolerated in a normal heart can cause significant hemodynamic instability in patients with congenital heart defects, particularly during the postcardiopulmonary bypass period. Management of these arrhythmias presents more of a challenge, since currently available antiarrhythmic drugs can be ineffective and poorly tolerated. In this study, we examined the possible effect of dexmedetomidine, a primarily sedative drug, on atrial and junctional tachyarrhythmias. Though some animal data have shown that it can prevent certain types of ventricular tachycardia, its therapeutic role during these types of arrhythmias has not been studied. This was a retrospective, nonrandomized, noncontrolled study. Fourteen patients admitted to the cardiac intensive care unit and who received dexmedetomidine for both, sedation/analgesia and for junctional ectopic tachycardia (JET), atrial ectopic tachycardia (AET), reentry type supraventricular tachycardia (Re-SVT), atrial flutter (AF) or junctional accelerated rhythm (JAR) were included. Dexmedetomidine was used as a primary drug or as a rescue if other antiarrhythmics had been used. Our primary end-points were (a) conversion to normal sinus rhythm (NSR) within 3 min for Re-SVT, and 2 h for all other arrhythmias or (b) heart rate (HR) reduction to improve hemodynamics; JET < or =170 bpm, AET > or =20%, AF < or =150 bpm and for JAR prevention of progression to JET. The mean age and weight were 2 +/- 3 mo and 4 +/- 1.5 kg, respectively. Most of the arrhythmias (79%) occurred during the postoperative period. Dexmedetomidine was used as a primary treatment in nine and as a rescue in five patients. Ten patients (71%) received an initial loading dose of 1.1 +/- 0.5 microg/kg. A continuous infusion, 0.9 +/- 0.3 microg x kg(-1) x h(-1) was administered in 12 patients. Thirteen patients' lungs were mechanically ventilated. Adverse effects were seen in four patients (28%). Three had hypotension that responded to fluid administration and one had a possible brief complete atrioventricular (AV) block. Nine of the 14 patients were transiently paced with atrial (seven) or AV sequential (two) pacing to improve AV synchrony. The primary outcome with rhythm and/or HR control was achieved in 13 patients (93%). JET rate decreased from 197 +/- 22 to 165 +/- 17 bpm within 67 +/- 75 min of dexmedetomidine administration. Five of these patients converted to NSR in 39 +/- 31 h and one remained in JAR. All four patients with Re-SVT had resolution of their tachyarrhythmia. Three converted to NSR and one to JAR. One patient with AET (220-270 bpm) responded well with decreasing HR to 120 bpm within 35 min and to NSR in 85 min. One patient with AF failed to respond. In two patients with JAR, neither progressed to JET and HR decreased from 158 +/- 11 to 129 +/- 1 bpm. This preliminary, observational report suggests that dexmedetomidine may have a potential therapeutic role in the acute phase of perioperative atrial and junctional tachyarrhythmias for either HR control or conversion to NSR.

Mechanical, Thermal and Oxidation Behaviour of Zirconium Diboride Based Ultra-High Temperature Ceramic Composites

A comparative study has been carried out on the mechanical properties at room temperature, thermal shock and ablation resistance as well as oxidation behaviour of ZrB2-20SiC, ZrB2-20SiC-5Si3N4 and ZrB2-20ZrC-20SiC-5Si3N4 (amounts represent volume percent) composites. Fracture toughness has been determined using either three-point bend tests on single edge notch bend specimens, or by indentation technique. Addition of Si3N4 as sintering aid leads to enhancement in flexural strength and fracture toughness in the composite without ZrC. The specimens were subjected to thermal shock by quenching from temperatures in the range of 800o- 1200oC to ice cold water, and to ablation by exposure to oxy-acetylene flame at 2200oC. The composite having ZrC as constituent, exhibits the highest resistance to damage due to thermal shock and ablation, while the ZrB2-SiC composite shows the least change in mass during ablation. On the other hand, thermogravimetric experiments from room temperature to 1300oC have shown that the presence of ZrC is detrimental for oxidation resistance. Hence, the constituents of the composites need to be selected on the basis of the nature of application. The results of this study show that the investigated ZrB2 based composites bear the potential for multiple use thermal protection of reentry type space vehicles.

Illicit drugs and cardiac arrhythmias in athletes

The current management of athletes with cardiac arrhythmias has become complicated by the widespread use of illicit drugs, which can be arrhythmogenic. The World Anti-Doping Agency annually updates a list of prohibited substances and methods banned by the International Olympic Committee that includes different classes of substances namely, anabolic androgenic steroids, hormones and related substances, beta2-agonists, diuretics, stimulants, narcotics, cannabinoids, glucocorticosteroids, alcohol, beta-blockers and others. Almost all illicit drugs may cause, through a direct or indirect arrhythmogenic effect, a wide range of cardiac arrhythmias (focal or reentry type, supraventricular and/or ventricular) that can even be lethal and which are frequently sport activity related. A large use of illicit drugs has been documented in competitive athletes, but the arrhythmogenic effect of specific substances is not precisely known. Precipitation of cardiac arrhythmias, particularly in the presence of a latent electrophysiologic substrate including some inherited cardiomyopathies, at risk of sudden death or due to long-term consumption of the substances, should raise the suspicion that illicit drugs may be a possible cause and lead cardiologists to investigate carefully this relationship and appropriately prevent the clinical consequences.

Modes of Initiation of Two Types of Atrial Reentry in a Patient with Typical Atrial Flutter: Isthmus-dependent Micro-reentry versus Macro-reentry

We studied the modes of initiation of two types of atria] reentrant tachycardias (i.e., microreentry isthmus tachycardia and counterclockwise atrial flutter) in a 39‐year‐old male with typical atrial flutter. Rapid atrial pacing from proximal coronary sinus at a cycle length of 220 msec initiated micro‐reentry isthmus tachycardia (non‐sustained), while rapid atrial pacing at a cycle length of 210 msec initiated sustained atrial flutter circulating counterclockwise around the tricuspid annulus. It was suggested that initiation of the counterclockwise atrial flutter was associated with a pacing‐induced conduction block in the entire width of the isthmus, whereas initiation of the micro‐reentry isthmus tachycardia was associated with a pacing‐induced conduction block in a limited segment of the isthmus (i.e., partial isthmus block).

Differences between left and right ventricular anatomy determine the types of reentrant circuits induced by an external electric shock. A rabbit heart simulation study

Despite the fact that elucidating the mechanisms of cardiac vulnerability to electric shocks is crucial to understanding why defibrillation shocks fail, important aspects of cardiac vulnerability remain unknown. This research utilizes a novel anatomically based bidomain finite-element model of the rabbit ventricles to investigate the effect of shock polarity reversal on the reentrant activity induced by an external defibrillation-strength shock in the paced ventricles. The specific goal of the study is to examine how differences between left and right ventricular chamber anatomy result in differences in the types of reentrant circuits established by the shock. Truncated exponential monophasic shocks of duration 8 ms were delivered via two external electrodes at various timings. Vulnerability grids were constructed for shocks of reversed polarity (referred to as RV− or LV− when either the RV or the LV electrode is a cathode). Our results demonstrate that reversing electrode polarity from RV− to LV− changes the dominant type of post-shock reentry: it is figure-of-eight for RV− and quatrefoil for LV− shocks. Differences in secondary types of post-shock arrhythmia also occur following shock polarity reversal. These effects of polarity reversal are primarily due to the fact that the LV wall is thicker than the RV, resulting in a post-shock excitable gap that is predominantly within the LV wall for RV− shocks and in the septum for LV− shocks.

Modes of Initiation of Two Types of Atrial Reentry in a Patient with Typical Atrial Flutter: Isthmus-dependent Micro-reentry versus Macro-reentry

We studied the modes of initiation of two types of atria] reentrant tachycardias (i.e., microreentry isthmus tachycardia and counterclockwise atrial flutter) in a 39-year-old male with typical atrial flutter. Rapid atrial pacing from proximal coronary sinus at a cycle length of 220 msec initiated micro-reentry isthmus tachycardia (non-sustained), while rapid atrial pacing at a cycle length of 210 msec initiated sustained atrial flutter circulating counterclockwise around the tricuspid annulus. It was suggested that initiation of the counterclockwise atrial flutter was associated with a pacing-induced conduction block in the entire width of the isthmus, whereas initiation of the micro-reentry isthmus tachycardia was associated with a pacing-induced conduction block in a limited segment of the isthmus (i.e., partial isthmus block).