Vulnerability during short-term memory induced response in canine ventricle.

Cardiac short-term memory is an intrinsic property which can make the action potential duration produce a transient response after a sudden change in heart rate. The change of vulnerability was investigated by using computer simulation method during the transient period which was created by abruptly shortening the cycle length from 800ms to 300ms. The study was performed on a heterogeneous fiber consisting of endo-, mid-, and epi-cardiac canine myocytes.

Effects of electrical heterogeneity on transmural reentry during acute global ischemia.

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.

Vulnerability to unidirectional conduction block and reentry in rabbit left ventricular wedge preparation: effects of stimulation sequence and location.

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.

[An optical mapping system based on spectral shift of voltage-sensitive dyes].

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.

Study for relevance of the acute myocardial ischemia to arrhythmia by the optical mapping method.

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.

Mechanisms of the acute ischemia-induced arrhythmogenesis--a simulation study.

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.

Computer simulation of the reentrant cardiac arrhythmias in ischemic myocardium.

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.