[Electrocardiographic image of myocardial ischemia: real measurements and biophysical models. Part II]

By means of biophysical models of the heart electrical activity some alterations of the ST-T interval of an electrocardiogram were considered under changes of electrophysiological parameters of the cardiac muscle, characteristic for ischemia development. A computer program "The model of electrical activity of ischemic heart" developed in our Lab was used as a "Generator" for selection of model electrocardiosignals (ECS) when changing parameters of the transmembrane action potential (TAP) in "ischemic" area which was characterized in the model terms by its location and extent. The obvious development of ischemia was triggered by the deflection of TAP parameters from the reference values accepted for "conventional norm". For trapezoidal approximation of the TAP form chosen at the first stage of the work the following changed TAP parameters were used: (a) modification of duration of the horizontal plateau phase at the constant phase 3 slope; (b) a change in the amplitude of the plateau phase at the constant duration of this phase and all TAP; (c) modification in the slope of the fast repolarization phase at the constant duration of the plateau phase (in this case, the total duration of TAP also changes); (d) reduction in the duration of phase 2 at constant TAP duration, that, naturally, entails modification of the slope for the fast repolarization phase. We studied (out-of-scenarios developed before) separate effects of these parameters on changes of the T wave shape and the ST segment level. A number of new parameters for description of the changes observed in the ST-T interval pattern are offered and investigated. Computer experiments were performed using a system for 3D-modeling of the cardiac electrical activity. With the selected real and simulated ECSs a comparative study for diagnostic possibilities of some electrocardiographic criteria for detecting myocardial ischemia is carried out. The results obtained at this stage of work are of interest for identification and prediction of an electrophysiological state of the heart.