Effect of adaptation to short-term stress exposure on the fibrillation threshold and ectopic activity of the heart in experimental myocardial infarct

Preliminary adaptation to short-term stress was shown to prevent the decrease in the heart fibrillation threshold and an increase in ectopic activity which is usually observed in experimental myocardial infarction. This protective effect involves an enhanced activity of the antioxidant system. Therefore, a synthetic antioxidant ionol was applied to prevent disturbances of the heart electrical stability in infarction. It was established that ionol completely prevents the decrease in the electrical threshold and the increase in ectopic activity of the heart in experimental infarction. Thus, it can be concluded that ionol possesses an antiarrhythmic effect.     

Prevention of disorders of the electric stability of the heart in experimental infarct using adaptation to hypoxia

It has been shown on rats preadapted to hypoxia in an altitude chamber that myocardial infarction induced by ligation of the coronary artery was accompanied by less disturbances in the electrical stability of the heart, namely by a twofold decrease in ventricular fibrillation threshold and a considerable decrease in the heart ectopic activity. Preliminary adaptation provided the maintenance of myocardial contractility in infarction.     

Heart tissue viability monitoring in vivo by using combined fluorescence, thermography and electrical activity measurements.

A prototype system for in vivo monitoring of the heart tissue viability by using combined measurements of fluorescence, thermography and electrical activity has been elaborated for cardiac surgery. The fluorescence imaging of nicotinamide adenine dinucleotide NAD(P)H in the blue light range (lambda=467 nm) by using UV light (lambda=347 nm) excitation was used to detect metabolic disturbances. The method of the principal component analysis was used for the processing of the fluorescence image sequences. Far infrared (lambda=7.5-13 microm) imaging was used to evaluate temperature dynamics of the tissue surface during circulation disturbances. Evaluation of the epicardial electrogram shape by using continuous wavelet transform was used to detect and evaluate ischemia-caused disturbances of the electrical activity of the tissue. The combination of temperature, fluorescence and electrical activity estimates obtained from synchronically registered parameters during the experiments on model systems and experimental animals yielded qualitatively new results for the evaluation of cardiac tissue viability and enabled to achieve a versatile evaluation of the heart tissue viability.     

Different Profile of mRNA Expression in Sinoatrial Node from Streptozotocin-Induced Diabetic Rat

BackgroundExperiments in isolated perfused heart have shown that heart rate is lower and sinoatrial node (SAN) action potential duration is longer in streptozotocin (STZ)–induced diabetic rat compared to controls. In sino-atrial preparations the pacemaker cycle length and sino-atrial conduction time are prolonged in STZ heart. To further clarify the molecular basis of electrical disturbances in the diabetic heart the profile of mRNA encoding a wide variety of proteins associated with the generation and transmission of electrical activity has been evaluated in the SAN of STZ-induced diabetic rat heart.Conclusions/SignificanceCollectively, this study has demonstrated differences in the profile of mRNA encoding a variety of proteins that are associated with the generation, conduction and regulation of electrical signals in the SAN of STZ-induced diabetic rat heart. Data from this study will provide a basis for a substantial range of future studies to investigate whether these changes in mRNA translate into changes in electrophysiological function.     

Effect of emotional stress on the cardiac rhythm variability in rats

A degree of irregularities of the heart rhythm was studied by two methods: chaos-analysis and the HRV (heart rate variability) analysis. Our study shows an individual response in 3 groups of animals: 1--animals with low initial level of chaos (correlation dimension (PD2 < 2); 2--animals with high level of chaos (PD2 > 4); and animals with middle level of chaos (2 < PD2 < 4). The first two groups proved to be more sensitive to stress than the third group. Moreover we found that the electrical stability of the heart as measured by the fibrillation threshold, was higher for the chaos third group. The animals of the first two groups had low cardiac stability and high risk of stress-induced cardiac disturbances.     

Mechanisms of electromechanical function disturbances in cardiomyocytes overloaded with calcium. The theoretical study

Arrhythmias and mechanical disturbances are simulated in a mathematical model of cardiomyocyte electromechanical activity. The simulated pattern is similar to that observed for acute heart failure associated with calcium overloading of myocardium cells. Special attention was paid to the calcium overloading resulting from the reduced Na+,K+ pump activity. In the framework of the model, it was shown that mechanical factors could promote arrhythmia initiation when the pump activity reduced. Different approaches to electrical and mechanical function restoration during acute heart failure associated with calcium overloading were suggested and analyzed in the model.     

Hypokalemia-induced ultrastructural, histochemical and connexin-43 alterations resulting in atrial and ventricular fibrillations

Perfusion of the isolated guinea pig heart with hypokalemic solution provide simple model for examination of the molecular mechanisms involved in the incidence of atrial and/or ventricular fibrillations. The results point out that dispersion of the metabolic and subcellular alterations and heterogenously impaired intercellular coupling might account for electrical disturbances and desynchronization of the myocardium thus facilitate occurrence of fibrillation.     

Electrical Inhomogeneity in Left Ventricular Hypertrophy

Recent studies designed to assess the relationship between aortic compliance and heterogeneity of heart electrical activity has shown that hypertrophy aggravates repolarization disturbances in the myocardium. Numerous mechanisms of electrical instability and inhomogeneity associated with left ventricular hypertrophy are now under investigation. Most of the studies have been found to be focused on ventricular Gradient, QT dispersion, amplitudes of isointegral maps during ventricular repolarization, abnormally low-QRST areas, dispersion of the QT interval, and spatial QRS-T _angle. These studies point to marked repolarization abnormalities in left ventricular hypertrophy and the dispersion of the QT interval as a valuable index for inhomogeneity of repolarization and the subsequent heart rate variability. The heart rate-corrected QT dispersion and QT apex dispersion seem to be significantly longer in the patients with left ventricular hypertrophy than in normal individuals. The review study has also identified QRST isointegral map as a valuable technique in assessment of the electro-cardiac events in LVH.     

Electrophysiological heart rate regulation in patients with the Wolff-Parkinson-White phenomenon and syndrome

The article presents the results of electrocardiography, echocardiography, heart rate variability, and nonlinear dynamics in patients with Wolff-Parkinson-White phenomenon and syndrome (WPW). Fifty-four patients were enrolled in the study; they were divided into three groups: the WPW phenomenon group, the WPW syndrome group, and the group of healthy subject. Using the mathematical models based on correlation analysis, the role of the main pathophysiological mechanisms of the formation of cardiac pathology in WPW syndrome—the disturbances of regulatory mechanisms, as well as the electrical and mechanical remodeling of the myocardium—was proven.     

Aspects of cardiomyopathy in Copper-deficient pigs

Pigs were made copper(Cu)-deficient to evaluate cardiac function and pathology, and electrocardiography. Fifteen-day-old pigs were fed a Cu-restricted diet over an 8 wk period and compared to Cu-adequate diet-fed pigs. Cardiac effects were examined concerning gross morphometry and ultrastructure, echocardiography, and electrocardiography, as well as serum cholesterol levels. The Cu-restricted diet-fed pigs exhibited a marked deceleration of growth and lower hematocrit, hemoglobin, and liver and serum Cu concentrations compared to the Cu-adequate diet-fed pigs. The Cu-restricted diet-fed pigs developed a significantly greater heart weight:body weight ratio, along with greater diastolic measures of ventricular wall and internal dimension relative to body weight. Electrocardiography in the Cu-restricted diet-fed pigs revealed one instance of electrical alternans and an intraventricular conduction disturbance and several instances of T-wave inversion. The Cu-restricted pigs also displayed a prolonged QT interval at the closure of study. Increased mitochondrial volume density and mitochondria: myofibril volume density ratio were observed in the Cu-restricted pig electron micrographs along with excessive lipid and glycogen inclusion and focal degradation of Z-lines, intercalated disk, and sarcomeres. Copper-restriction in young pigs results in cardiac pathology and electrical disturbances. These alterations are similar to those reported for young Cu-restricted rodents. Given then that many cardiac manifestations of developed Cu-deficiency appear conserved across specie lines, the potential for human disturbances in response to severe Cu-deficiency may be plausible.     

Soliton-Like Regimes and Excitation Pulse Reflection (Echo) in Homogeneous Cardiac Purkinje Fibers: Results of Numerical Simulations

On the basis of numerical simulations of the partial McAllister-Noble-Tsien equations quantitatively describing the dynamics of electrical processes in conductive cardiac Purkinje fibers we reveal unusual – soliton-like – regimes of interaction of nonlinear excitation pulses governing the heart contraction rhythm: reflection of colliding pulses instead of their annihilation. The phenomenological mechanism of the reflection effects is that in a narrow (but finite) range of the system parameters the traveling pulse presents a doublet consisting of a high-amplitude leader followed by a low-amplitude subthreshold wave. Upon collisions of pulses the leaders are annihilated, but subthreshold waves summarize becoming superthreshold and initiating two novel echo-pulses traveling in opposite directions. The phenomenon revealed presents an analogy to the effect of reflection of colliding nerve pulses, predicted recently, and can be of use in getting insight into the mechanisms of heart rhythm disturbances.     

Molecular Mechanisms of Inherited Arrhythmias

Inherited arrhythmias and conduction system diseases are known causes of sudden cardiac death and are responsible for significant mortality and morbidity in patients with congenital heart disease and electrical disorders. Knowledge derived from human genetics and studies in animal models have led to the discovery of multiple molecular defects responsible for arrhythmogenesis. This review summarizes the molecular basis of inherited arrhythmias in structurally normal and altered hearts.On the cellular and molecular levels, minor disturbances can provoke severe arrhythmias. Ion channels are responsible for the initiation and propagation of the action potential within the cardiomyocyte. Structural heart diseases, such as hypertrophic or dilated cardiomyopathies, increase the likelihood of cardiac electrical abnormalities. Ion channels can also be up- or down-regulated in congenital heart disease, altering action potential cellular properties and therefore triggering arrhythmias. Conduction velocities may be inhomogeneously altered if connexin function, density or distribution changes. Another important group of electrophysiologic diseases is the heterogeneous category of inherited arrhythmias in the structurally normal heart, with a propensity to sudden cardiac death. There have been many recent relevant discoveries that help explain the molecular and functional mechanisms of long QT syndrome, Brugada syndrome, catecholaminergic polymorphic ventricular tachycardia, and other electrical myopathies. Identification of molecular pathways allows the identification of new therapeutic targets, for both disease palliation and cure. As more disease-causing mutations are identified and genotypic-phenotypic correlation is defined, families can be screened prior to symptom-onset and patients may potentially be treated in a genotype-specific manner, opening the doors of cardiac electrophysiology to the emerging field of pharmacogenomics.     

Nature of the relation between contractile activity indices of the left and right heart ventricles in normal and pathological conditions

Positive correlations were established between contractile activity of left and right rabbit ventricles in normal conditions, reflecting synchronous activity of both heart ventricles. These correlations could be broken in case of pathology due to disturbances of adaptation mechanisms resulting in the impairment of heart functioning.     

Noninvasive detection of epicardial and endocardial activity of the heart

Determining electrical activation of the heart in a noninvasive way is one of the challenges in cardiac electrophysiology. The ECG provides some, but limited information about the electrical status of the heart. This article describes a method to determine both endocardial and epicardial activation of the heart of an individual patient from 64 electrograms recorded from the body surface. Information obtained in this way might be helpful for the treatment of arrhythmias, to assess the effect of drugs on conduction in the heart and to assess electrical stability of the heart.     

Effects of clinical death and pre-administered inderal on adrenoreactivity of the heart in post-resuscitation period

Acute lethal blood loss followed by resuscitation was found to decrease noradrenaline and increase epinephrine levels in heart muscle in experiments on mongrel male rats which significantly increase heart beta-adreno-receptors sensitivity to exogenous noradrenaline. Preliminary inderal injection prevents excessive heart beta-adreno-receptors stimulation by catecholamines, considerably reduces post-resuscitation rhythmic disturbances and prevents ventricular fibrillation which significantly decreases early post-resuscitation lethality.     

ATPase activity of the smooth and rough microsomal subfractions of the heart and liver in rabbits with a short-term microcirculatory disorder]

Short-time disturbances of the microcirculation in rabbits had a different influence on the ATP-ase activity of smooth and rough microsomes of the liver and heart. Mg+2ATP-ase activity in the liver decreased in both microsome fractions; as in the heart, the enzyme activity increased only in the smooth (light) microsomes.     

Age-related characteristics of the electrical activity of the cardiac fibers in the human embryo

Transmembrane action potential and intercellular electric coupling have been studied in isolated heart during various stages of intrauterine growth of human embryos as well as in heart preparations of human adults. Formation of electrical properties of ventricular myocardium was slower than that of atrial fibres and was found to be fully completed in the first 14 weeks of intrauterine growth. Intercellular electrical coupling enhanced in the course of the embryonic development as indicated by a drop in the input resistance and an increase in electronic length.     

Slow excitation waves and mechanisms of polymorphic ventricular tachycardia in an experimental model: isolated walls of the right ventricle from rabbit and squirrel

The mechanism of polymorphic disturbances of the heart rhythm is studied on an experimental model, isolated ventricular preparations of ground squirrel and rabbit. Polymorphic arrhythmias are identified from habitus of the isolated preparation pseudoECGs mathematically derived from electrograms registered simultaneously at 32 endocardial and 32 epicardial points. The same electrograms allow one to visualize the excitation wave propagation along each of the preparation surfaces. The comparison of excitation wave pictures and corresponding pseudoECGs enabled us to reveal the conditions necessary and sufficient for polymorphism in heart rhythm disturbances. Polymorphic arrhythmias are due to changes in wave pictures in the regions of retarded excitation propagation.