Internal nutrients dominate load and drive hypoxia in a eutrophic estuary.

The hypothesis that local hypoxia and chlorophyll concentration are spatially tethered to local, sediment-driven nutrient release was examined in a small, nutrient-impacted estuary in the Southern Gulf of St. Lawrence, Canada. Sediment reactor core samples were taken at 10 locations between 0.

Quantifying arrhythmic long QT effects of hydroxychloroquine and azithromycin with whole-heart optical mapping and simulations.

Background: In March 2020, hydroxychloroquine (HCQ) alone or combined with azithromycin (AZM) was authorized as a treatment for COVID-19 in many countries. The therapy proved ineffective with long QT and deadly cardiac arrhythmia risks, illustrating challenges to determine the new safety profile of repurposed drugs.

Objective: To investigate proarrhythmic effects and mechanism of HCQ and AZM (combined and alone) with high doses of HCQ as in the COVID-19 clinical trials.

Discordant Alternans as a Mechanism for Initiation of Ventricular Fibrillation In Vitro.

Background Ventricular tachyarrhythmias are often preceded by short sequences of premature ventricular complexes. In a previous study, a restitution-based computational model predicted which sequences of stimulated premature complexes were most likely to induce ventricular fibrillation in canines in vivo. However, the underlying mechanism, based on discordant-alternans dynamics, could not be verified in that study.

Extravasation injury in a paediatric population.

Background: Extravasation occurs when a drug is inadvertently administered outside of the vein. Depending on the substance involved, this may lead to tissue necrosis with significant long-term morbidity. Children, particularly neonates, are particularly susceptible to extravasation with up to 70% of children in neonatal intensive care unit having some form of extravasation injury.

Synchronization as a mechanism for low-energy anti-fibrillation pacing.

Background: Low-energy anti-fibrillation pacing (LEAP) has been suggested as an alternative treatment in symptomatic fibrillation patients. It significantly lowers the energy required compared with standard 1-shock defibrillation.

Objective: In this study, we investigated the mechanism of arrhythmia termination by LEAP and systematically analyzed the influence of shock period and timing on the success rate of LEAP.

Shock-induced termination of reentrant cardiac arrhythmias: comparing monophasic and biphasic shock protocols.

In this article, we compare quantitatively the efficiency of three different protocols commonly used in commercial defibrillators. These are based on monophasic and both symmetric and asymmetric biphasic shocks. A numerical one-dimensional model of cardiac tissue using the bidomain formulation is used in order to test the different protocols.

Effects of pacing site and stimulation history on alternans dynamics and the development of complex spatiotemporal patterns in cardiac tissue.

Alternans of action potential duration has been associated with T wave alternans and the development of arrhythmias because it produces large gradients of repolarization. However, little is known about alternans dynamics in large mammalian hearts. Using optical mapping to record electrical activations simultaneously from the epicardium and endocardium of 9 canine right ventricles, we demonstrate novel arrhythmogenic complex spatiotemporal dynamics.

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.

The arterialized saphenous venous flow-through flap with dual venous drainage.

Background: Venous flow-through flaps are well-described options for small defects where donor site morbidity is undesirable or in areas where useful local veins are in close proximity to the defect, particularly in the extremities. However, higher rates of flap loss have limited their utility. The saphenous venous flap in particular has been widely sought as a useful flap, and while arterialization of this flap improved survival rates, congestion has remained a limiting feature.

Teaching cardiac electrophysiology modeling to undergraduate students: laboratory exercises and GPU programming for the study of arrhythmias and spiral wave dynamics.

As part of a 3-wk intersession workshop funded by a National Science Foundation Expeditions in Computing award, 15 undergraduate students from the City University of New York(1) collaborated on a study aimed at characterizing the voltage dynamics and arrhythmogenic behavior of cardiac cells for a broad range of physiologically relevant conditions using an in silico model. The primary goal of the workshop was to cultivate student interest in computational modeling and analysis of complex systems by introducing them through lectures and laboratory activities to current research in cardiac modeling and by engaging them in a hands-on research experience. The success of the workshop lay in the exposure of the students to active researchers and experts in their fields, the use of hands-on activities to communicate important concepts, active engagement of the students in research, and explanations of the significance of results as the students generated them.

Low-energy control of electrical turbulence in the heart.

Controlling the complex spatio-temporal dynamics underlying life-threatening cardiac arrhythmias such as fibrillation is extremely difficult, because of the nonlinear interaction of excitation waves in a heterogeneous anatomical substrate. In the absence of a better strategy, strong, globally resetting electrical shocks remain the only reliable treatment for cardiac fibrillation. Here we establish the relationship between the response of the tissue to an electric field and the spatial distribution of heterogeneities in the scale-free coronary vascular structure.

In vivo electrochemical characterization of tissue-electrode interface during metamorphic growth.

The domestication of insect locomotion has been recently investigated through microelectrode based systems implanted in the insect to tap into its neuromuscular system. Benefiting from developmental changes, the idea of performing such surgical implantation during metamorphic development enabled the fusion of engineered constructs to these living biological organisms. This study uses electrochemical analysis to provide a preliminary quantitative comparison of tissue-electrode coupling over the course of metamorphic development and after eclosion, where PEDOT:PSS coated gold electrodes are implanted in the insect during the early pupal stages and right after emergence.

Control of action potential duration alternans in canine ventricular tissue.

Cardiac action potential duration alternans is characterized by a beat-to-beat alternation in action potential waveform. Its presence has been putatively linked to the onset of lethal cardiac arrhythmias. Previous studies, which have been limited to cardiac Purkinje fibers, have shown that closed-loop alternans control techniques, which apply a succession of externally administered cycle perturbations, provide ineffectual spatial alternans elimination.

Wireless transmission of cardiac action potentials with ultrasonically guided insertion of silicon probes.

This paper reports on the coupling of ultrasonically guided cardiac probes with wireless transmission of cardiac action potentials for applications in monitoring the 3D electrical onset of ventricular fibrillation. An application specific integrated circuit has been designed with a 40 dB amplifying stage and a frequency modulating oscillator to wirelessly transmit the recorded action potentials. Combined with the ultrasonically inserted cardiac probe that reduces penetration force, this system demonstrates the initial results in wireless monitoring of 3D action potential propagation.

Control of action potential duration alternans in canine cardiac ventricular tissue.

Cardiac electrical alternans, characterized by a beat-to-beat alternation in action potential waveform, is a naturally occurring phenomenon, which can occur at sufficiently fast pacing rates. Its presence has been putatively linked to the onset of cardiac reentry, which is a precursor to ventricular fibrillation. Previous studies have shown that closed-loop alternans control techniques that apply a succession of externally administered cycle perturbations at a single site provide limited spatially-extended alternans elimination in sufficiently large cardiac substrates.

Transmural ultrasound-based visualization of patterns of action potential wave propagation in cardiac tissue.

The pattern of action potential propagation during various tachyarrhythmias is strongly suspected to be composed of multiple re-entrant waves, but has never been imaged in detail deep within myocardial tissue. An understanding of the nature and dynamics of these waves is important in the development of appropriate electrical or pharmacological treatments for these pathological conditions. We propose a new imaging modality that uses ultrasound to visualize the patterns of propagation of these waves through the mechanical deformations they induce.

Off-site control of repolarization alternans in cardiac fibers.

Repolarization alternans, a beat-to-beat alternation in action potential duration, has been putatively linked to the onset of cardiac reentry. Anti-alternans control strategies can eliminate alternans in individual cells by exploiting the rate dependence of action potential duration. The same approach, when applied to a common measuring/stimulating site at one end of a cardiac fiber, has been shown to have limited spatial efficacy.

Effects of hypocalcemia on electrical restitution and ventricular fibrillation.

We have shown previously that verapamil reduces the slope of the action potential duration (APD) restitution relation, suppresses APD alternans and converts ventricular fibrillation (VF) into a periodic rhythm. To determine whether these effects result primarily from reduction of the APD restitution slope, as opposed to alteration of calcium dynamics unrelated to restitution, we tested the effects of hypocalcemia ([CaCl2]=31-125 microM) in canine ventricle. At normal [CaCl2] (2.

Balloon-assisted flight of radio-controlled insect biobots.

We report on radio-controlled insect biobots by directing the flight of Manduca sexta through neuromuscular activation. Early metamorphosis insertion technology was used to implant metal wire probes into the insect brain and thorax tissue. Inserted probes were adopted by the developing tissue as a result of the metamorphic growth.

Termination of atrial fibrillation using pulsed low-energy far-field stimulation.

Background: Electrically based therapies for terminating atrial fibrillation (AF) currently fall into 2 categories: antitachycardia pacing and cardioversion. Antitachycardia pacing uses low-intensity pacing stimuli delivered via a single electrode and is effective for terminating slower tachycardias but is less effective for treating AF. In contrast, cardioversion uses a single high-voltage shock to terminate AF reliably, but the voltages required produce undesirable side effects, including tissue damage and pain.

Orbital floor reconstruction: a case for silicone. A 12 year experience.

Introduction: Controversy still exists regarding the choice of implant material for orbital floor reconstructions, in particular the use of silicone. We aimed to evaluate the long-term outcomes of orbital floor reconstructions with silicone versus other non-silicone implants.

Patients And Methods: We conducted a 12 year retrospective review of patients who had orbital floor reconstructions for fractures at the Royal Hobart Hospital, Tasmania, Australia, from 1995 to 2007.

Insect-machine interface based neurocybernetics.

We present details of a novel bioelectric interface formed by placing microfabricated probes into insect during metamorphic growth cycles. The inserted microprobes emerge with the insect where the development of tissue around the electronics during the pupal development allows mechanically stable and electrically reliable structures coupled to the insect. Remarkably, the insects do not react adversely or otherwise to the inserted electronics in the pupae stage, as is true when the electrodes are inserted in adult stages.

Evaluation of atrial fibrillation induced during anesthesia with fentanyl and pentobarbital in German Shepherd Dogs with inherited arrhythmias.

Objective: To determine the type of atrial fibrillation induced by use of 2 pacing protocols during fentanyl and pentobarbital anesthesia before and after administration of atropine and to determine the organization of electrical activity in the left and right atria during atrial fibrillation in German Shepherd Dogs.

Animals: 7 German Shepherd Dogs.

Procedures: Extrastimulus and pacedown protocols were performed before and after atropine administration.