Formation of a border ischemic zone depends on plasma potassium concentration.

Extracellular potassium concentration might modify electrophysiological properties in the border zone of ischemic myocardium. We evaluated the depolarization and repolarization characteristics across the ischemic-normal border under [K] variation. Sixty-four-lead epicardial mapping was performed in 26 rats ([K] 2.

Blockade of Melatonin Receptors Abolishes Its Antiarrhythmic Effect and Slows Ventricular Conduction in Rat Hearts.

Melatonin has been reported to cause myocardial electrophysiological changes and prevent ventricular tachycardia or fibrillation (VT/VF) in ischemia and reperfusion. We sought to identify electrophysiological targets responsible for the melatonin antiarrhythmic action and to explore whether melatonin receptor-dependent pathways or its antioxidative properties are essential for these effects. Ischemia was induced in anesthetized rats given a placebo, melatonin, and/or luzindole (MT1/MT2 melatonin receptor blocker), and epicardial mapping with reperfusion VT/VFs assessment was performed.

ECG Markers of Acute Melatonin Treatment in a Porcine Model of Acute Myocardial Ischemia.

In myocardial ischemia, melatonin confers antiarrhythmic action, but its electrocardiographic expression is unclear. We aimed to evaluate the effects of melatonin treatment on electrocardiogram (ECG) parameters reflecting major arrhythmogenic factors and to test the association of these parameters with ventricular fibrillation (VF) incidence. Myocardial ischemia was induced by 40 min coronary artery occlusion in 25 anesthetized pigs.

Melatonin treatment improves ventricular conduction via upregulation of Nav1.5 channel proteins and sodium current in the normal rat heart.

Melatonin treatment was reported to reduce the risk of cardiac arrhythmias, and crucial for this antiarrhythmic action was the effect of melatonin on activation spread. The aim of the present study was evaluation of the mechanisms of this activation enhancement. Experiments were performed in a total of 123 control and melatonin-treated (10 mg/kg, daily, for 7 days) male Wistar rats.

Determinants of reperfusion arrhythmias: action potential duration versus dispersion of repolarization.

The role of a border zone in arrhythmogenesis is not fully understood. In this study we evaluated independent contributions of action potential duration (APD) and dispersion of repolarization (DOR) across the normal/ischemic border to the development of ventricular tachycardia and/or fibrillation (VT/VF). Ischemia-reperfusion episodes were induced in anesthetized rats by transient coronary occlusion.

Terminal T-wave inversion predicts reperfusion tachyarrhythmias in STEMI.

Introduction: A reliable electrocardiographic predictor of ventricular fibrillation (VF) in patients with ST elevation myocardial infarction (STEMI) is lacking so far. Previous experimental/simulation study suggested a terminal T-wave inversion (TTWI) in ischemia-related ECG leads corresponding to anterior infarct localization as an independent predictor of reperfusion VF (rVF). This T-wave characteristic has never been tested as a rVF predictor in clinical settings.

Melatonin pretreatment does not modify extrasystolic burden in the rat ischemia-reperfusion model.

The mechanism of reentrant ventricular tachyarrhythmias complicating acute myocardial ischemia is largely based on the interaction between an arrhythmogenic substrate and triggers. Melatonin was proposed as an antiarrhythmic medication and was shown to ameliorate the arrhythmogenic substrate. Also, melatonin provides a sympatholytic effect in different settings and might attenuate ectopic activity, which provides reentry triggers.

Prolongation of experimental diabetes mellitus increased susceptibility to reperfusion ventricular tachyarrhythmias.

Diabetes mellitus (DM) is associated with increased risk of sudden cardiac death, but its role in arrhythmogenesis is not clear. We evaluated contributions of DM duration and hyperglycemia level to development of proarrhythmic electrophysiological changes in the experimental ischemia/reperfusion model. Ventricular epicardial 64-lead mapping and arrhythmia susceptibility burst-pacing testing were performed in 43 healthy and 55 diabetic (alloxan model) anesthetized rabbits undergoing 15 min left anterior descending coronary artery occlusion, followed by 15 min reperfusion.

Melatonin Prevents Early but Not Delayed Ventricular Fibrillation in the Experimental Porcine Model of Acute Ischemia.

Antiarrhythmic effects of melatonin have been demonstrated ex vivo and in rodent models, but its action in a clinically relevant large mammalian model remains largely unknown. Objectives of the present study were to evaluate electrophysiological and antiarrhythmic effects of melatonin in a porcine model of acute myocardial infarction. Myocardial ischemia was induced by 40-min coronary occlusion in 25 anesthetized pigs.

Entropy-Based Approach for the Detection of Changes in Arabic Newspapers' Content.

A new method for the recognition of meaningful changes in social state based on transformations of the linguistic content in Arabic newspapers is suggested. The detected alterations of the linguistic material in Arabic newspapers play an indicator role. The currently proposed approach acts in an "online" fashion and uses pre-trained vector representations of Arabic words.

Contribution of Depolarization and Repolarization Changes to J-Wave Generation and Ventricular Fibrillation in Ischemia.

: Activation delay in ischemic myocardium has been found to contribute to J-wave appearance and to predict ventricular fibrillation (VF) in experimental myocardial infarction. However, the role of ischemia-related repolarization abnormalities in J-wave generation remains unclear. : The objective of our study was to assess a contribution of myocardial repolarization changes to J-wave generation in the body surface ECG and VF in a porcine acute myocardial infarction model.

Preventive Administration of Melatonin Attenuates Electrophysiological Consequences of Myocardial Ischemia.

The effect of preventive administration of melatonin on the arrhythmogenic substrate in the myocardium was studied in the rabbit model of acute ischemia/reperfusion in vivo. The animals treated with melatonin 60 min before ischemia induction had shorter median activation time compared to the control group (p=0.039), less pronounced shortening of repolarization durations in the ischemic zone during coronary occlusion (p=0.

Managing of ventricular reperfusion tachyarrhythmias - focus on a perfused myocardium.

In this study we tested a hypothesis that reperfusion ventricular tachyarrhythmias can be modified by direct control of repolarization duration in the perfused myocardium during ischemic exposure. After induction of coronary occlusion, three groups of rats were given agencies affecting repolarization duration tetraethylammonium (TEA) 4 mg/kg, n = 9; pinacidil (Pin) 0.3 mg/kg, n = 11, and saline as placebo (control) n = 10.

Association Between Antiarrhythmic, Electrophysiological, and Antioxidative Effects of Melatonin in Ischemia/Reperfusion.

Melatonin is assumed to confer cardioprotective action via antioxidative properties. We evaluated the association between ventricular tachycardia and/or ventricular fibrillation (VT/VF) incidence, oxidative stress, and myocardial electrophysiological parameters in experimental ischemia/reperfusion under melatonin treatment. Melatonin was given to 28 rats (10 mg/kg/day, orally, for 7 days) and 13 animals received placebo.

Multi-lead vs single-lead T -T interval measurements for prediction of reperfusion ventricular tachyarrhythmias.

Introduction: Electrocardiographic T -T interval (Tp-Te) is a promising marker for the prediction of ventricular tachycardia and/or ventricular fibrillation (VT/VF). The study was aimed to compare single-lead vs multilead Tp-Te variables as VT/VF predictors in experimental ischemia/reperfusion model.

Methods And Results: Computer simulations were done using the ECGSIM model with an ischemic region set in anterior left ventricular apex.

Effect of Water-Soluble Echinochrome Analog on Arrhythmia Severity in Experimental Model of Acute Myocardial Ischemia.

The effects of therapeutic or preventive-therapeutic administration of water-soluble echinochrome analog U-441 on arrhythmia severity assessed by a set of myocardial spatio-temporal depolarization and repolarization parameters were examined on the model of acute myocardial ischemia in cats. Coronary occlusion increased activation time and decreased repolarization time in the ischemic zone; in addition, it increased both global and borderline (local) dispersions of repolarization. The linear regression model showed that only activation time values measured at the initial state and at termination of occlusion were associated with total arrhythmia score during ischemia (regression coefficient β=0.

Repolarization in perfused myocardium predicts reperfusion ventricular tachyarrhythmias.

Background: Aim of the study was to find out which myocardial repolarization parameters predict reperfusion ventricular tachycardia and fibrillation (VT/VF) and determine how these parameters express in ECG.

Methods: Coronary occlusion and reperfusion (30/30min) was induced in 24 cats. Local activation and end of repolarization times (RT) were measured in 88 intramyocardial leads.

Mechanism of electrocardiographic T-wave flattening in diabetes mellitus: experimental and simulation study.

In the present study we investigated the contribution of ventricular repolarization time (RT) dispersion (the maximal difference in RT) and RT gradients (the differences in RT in apicobasal, anteroposterior and interventricular directions) to T-wave flattening in a setting of experimental diabetes mellitus. In 9 healthy and 11 diabetic (alloxan model) open-chest rabbits, we measured RT in ventricular epicardial electrograms. To specify the contributions of apicobasal, interventricular and anteroposterior RT gradients and RT dispersion to the body surface potentials we determined T-wave voltage differences between modified upper- and lower-chest precordial leads (T-wave amplitude dispersions, TWAD).

Ventricular electrical heterogeneity in experimental diabetes mellitus: effect of myocardial ischemia.

Aims of the study were to compare the development of electrocardiographic responses of the ischemia-induced heterogeneities of activation and repolarization in the ventricular myocardium of normal and diabetic animals. Body surface ECGs and unipolar electrograms in 64 epicardial leads were recorded before and during 20 min after the ligation of the left anterior descending artery in diabetic (alloxan model, 4 weeks, n=8) and control (n=8) rabbits. Activation times (ATs), end of repolarization times (RTs) and repolarization durations (activation-recovery intervals, ARIs) were determined in ischemic and periischemic zones.

Effects of echinochrome on ventricular repolarization in acute ischemia.

Background: Myocardial ischemic electrophysiological alterations are associated with the generation of reactive oxygen species. However, electrophysiological effects of antioxidants are unclear. Our objective was to determine the effects of the antioxidant echinochrome on ventricular repolarization in a feline model of 30-min ischemia.

What does the T(peak)-T(end) interval reflect? An experimental and model study.

Background: It is unclear whether the Tpeak-Tend interval is an index of the transmural or the total dispersion of repolarization.

Methods: We examined the Tpeak-Tend interval using a computer model of the rabbit heart ventricles based on experimentally measured transmural, apicobasal, and interventricular gradients of action potential duration.

Results: Experimentally measured activation-recovery intervals increased from apex to base, from the left ventricle to the right ventricle, and in the apical portion of the left ventricle from epicardium to endocardium and from the right side of septum to the left side.