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ABSTRACT: Ventricular arrhythmias are commonly observed in patients with ischemia. It is reported that the electrophysiological changes evoked by ischemia are greater in the epicardium than in the endocardium. To investigate the effects of this heterogeneity on transmural reentry, the computer simulation method is used. A two-dimensional model which can reproduce the endocardial, epicardial and middle cell types, approximate the ischemic characteristics and distribution of the ischemic severity is developed by setting different ratios of the maximum conductance of the rapid and slow inward rectifier potassium currents and considering the three major component conditions of acute ischemia at the ionic level. The results demonstrate that action potentials of the ischemic cells have elevated resting potential, shortened duration, slowed upstroke and declined amplitude. Conduction velocity is much more depressed in the epicardium because of the ischemia-induced transmural gradient of excitability. The epicardially initiated activation has wider vulnerable window and more possibility to cause unidirectional propagation even reentry. Dispersion of the excitability is proposed to be the underlying mechanism.
General Physiology and Biophysics 03/2010; 29(1):12-22. · 1.19 Impact Factor
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ABSTRACT: Many factors influence the initiation of unidirectional conduction block and reentry. To explore the influential factors on the temporal vulnerable window of the unidirectional conduction block, we investigated the effect of stimulation sequence and location on the temporal vulnerability in epicardial and endocardial sites in an arterially perfused rabbit left ventricular wedge preparation at three basic cycle lengths (BCL) of 2,000, 1,000 and 500 ms. An extrastimulus (S2) was introduced at coupling intervals incremented by 1 ms to scan the entire diastolic interval. The results showed that the vulnerable window increased with the lengthening of BCL, which ranged from 48.55 +/- 18.04 ms at BCL of 500 ms to 92.50 +/- 25.59 ms at BCL of 2,000 ms for endocardial, and is a similar style for epicardial from 21.00 +/- 14.02 ms at BCL of 500 ms to 75.71 +/- 16.34 ms at BCL of 2,000 ms (P < 0.05). The vulnerable window of endocardial was wider than that of epicardial (P < 0.05). Furthermore, the window size for reentry was about 39% smaller than that for unidirectional conduction block. Meanwhile, we found that increasing the number of premature beats enlarged the vulnerable window markedly due to enhanced transmural dispersion of repolarization (TDR) of ventricle. The vulnerable window is an effective index to evaluate the increased risk for unidirectional conduction block. Therefore, the factors that increase the vulnerable window are associated with the higher incidence of ventricular arrhythmias.
The Chinese journal of physiology 02/2009; 52(1):16-22. · 0.56 Impact Factor
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Proceedings of the 2nd International Conference on BioMedical Engineering and Informatics, BMEI 2009, October 17-19, 2009, Tianjin, China; 01/2009
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ABSTRACT: Recently, non-invasive optical methods to monitor transmembrane electrical potential using voltage sensitive dyes have been applied widely in the studies of normal and pathological heart rhythms and defibrillation. In the present paper, the authors measured the excitation and the emission spectra of the voltage-sensitive dyes di-4-ANEPPS bound to phospholipid bilayer membranes. And according to the spectral shift of di-4-ANEPPS, the authors presented an optical mapping system combining a DALSA CCD camera and a LED light source. Using this optical mapping system, the authors could record the action potential duration of the heart cells with high spatial and temporal resolutions. It can be a powerful tool in the study of cardiac arrhythmia mechanisms.
Guang pu xue yu guang pu fen xi = Guang pu 04/2008; 28(3):617-20. · 0.84 Impact Factor
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ABSTRACT: Ventricular arrhythmias are commonly observed in patients with acute coronary occlusion and ischemia. The purpose of the present study is to determine ischemic electrophysiological effects and their role in ischemia-induced arrhythmia. Optical mapping of the membrane potential with voltage-sensitive dyes was used in the study. The mapping was performed with di-4-ANEPPS in Langendorff-perfused rabbit hearts. The excitation-contraction decoupler 2,3-butanedione monoxime was used to suppress motion artifacts caused by contraction of the heart. The acute global ischemia was developed by a rapid reduction of the flow rate. The experiments revealed that ischemic tissues were characterized by an obvious reduction in action potential duration and action potential upstroke, slower conduction velocity (CV) and the property of post-repolarization refractoriness. Moreover, the magnitude of CV reduced both in control and ischemia when the pacing cycle length was short. CV reduction was even early in ischemia, resulting in a broader curve during ischemia. Moreover, the dominant frequency of ventricular tachycardia/ventricular fibrillation (VT/VF) in ischemia was less than that in control, implying a decreasing tendency of VT/VF frequency for low excitability. Therefore, combined with our previous simulation study, the dynamic changes of CV and longer refractory period were suggested to play an important role in the ischemia-related arrhythmia. Low excitability in ischemic tissue was the fundamental mechanism in it.
Physiological Measurement 06/2007; 28(5):481-8. · 1.68 Impact Factor
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ABSTRACT: The underlying ionic mechanisms of ischemic-induced arrhythmia were studied by the computer simulation method. To approximate the real situation, ischemic cells were simulated by considering the three major component conditions of acute ischemia (elevated extracellular K(+) concentration, acidosis and anoxia) at the level of ionic currents and ionic concentrations, and a round ischemic zone was introduced into a homogeneous healthy sheet to avoid sharp angle of the ischemic tissue. The constructed models were solved using the operator splitting and adaptive time step methods, and the perturbation finite difference (PFD) scheme was first used to integrate the partial differential equations (PDEs) in the model. The numerical experiments showed that the action potential durations (APDs) of ischemic cells did not exhibited rate adaptation characteristic, resulting in flattening of the APD restitution curve. With reduction of sodium channel availability and long recovery of excitability, refractory period of the ischemic tissue was significantly prolonged, and could no longer be considered as same as APD. Slope of the conduction velocity (CV) restitution curve increased both in normal and ischemic region when pacing cycle length (PCL) was short, and refractory period dispersion increased with shortening of PCL as well. Therefore, dynamic changes of CV and dispersion of refractory period rather than APD were suggested to be the fundamental mechanisms of arrhythmia in regional ischemic myocardium.
Mathematical Biosciences 10/2006; 203(1):1-18. · 1.54 Impact Factor
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ABSTRACT: Computer simulation was performed to determine how reentrant activity could occur due to the spatial heterogeneity in refractoriness induced by the regional ischemia. Two regional ischemic models were developed by decreasing the intracellular ATP concentration, reducing conductance of the inward Na+ current and increasing the extracellular K+ concentration on the two-dimensional sheet. Operator splitting method was used to integrate the models. The vulnerability to reentry was estimated from the timings of premature stimuli on the constructed models, which could result in unidirectionally propagating action potentials. Two kinds of sustained spiral waves and their Pseudo-Electroscardiograms were observed in numerical simulation. The results showed that the dispersion of refractory period increased with ischemic aggravation, and led to augment of the vulnerable window. A permature stimulation within the vulnerable window could easily induce spiral reentry. The Pseudo-Electrocardiograms of the spiral waves exhibited monomorphic tachycardiac waveforms. Thus, the spatial heterogeneity in refractoriness could be a substrate for reentrant ventricular tachyarrhythmias on the regional ischemic tissue.
The Chinese journal of physiology 10/2005; 48(3):155-9. · 0.56 Impact Factor
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ABSTRACT: Simulated regional ischemic models with abrupt transition between normal and ischemic region are often used to study mechanisms of arrhythmia. Whether the simplified models could better approximate the real ischemic myocardium was our concern in this paper. Two kinds of regional ischemic fibers were constructed in our simulation research. One had abrupt change between normal and ischemic region. The other transition was gradual with linear change. The ischemic cells were developed by decreasing the intracellular ATP concentration, reducing conductance of the inward Na<sup>+</sup> current and increasing the extracellular K<sup>+</sup> concentration. The operator splitting method was used to integrate the models. The duration, resting potential, and amplitude of the cellular action potential along gradually changed fiber were in between the corresponding value of the normal and severely ischemic cell in sudden transitional fiber. The conduction velocity of the wave slowed while the width of the vulnerable window increased with the ischemic aggravation. It proved that due to electrotonic interaction the transitional portion actually existed even if the change between different tissues was assumed to be abrupt. The two constructed models had the similar properties. Therefore, the simplified regional ischemic models with abrupt transition could not influence the qualitative results of the simulation study.
Mechatronics and Automation, 2005 IEEE International Conference; 02/2005
