The effect of psychoemotional load on ventricular repolarization reflected in integral body surface potential maps.

The aim of the present study was to investigate the reflection of psychoemotional stress in the body surface potential distribution as documented by isointegral maps of cardiac activation and recovery. In 72 young men (18.3+/- 7.3 y.) with no cardiovascular history body surface potential maps (BSPMs) at rest and during the test of mental arithmetic were recorded. The digitalized data for each point of the QRS, STT and QRST integral maps, for each subject in both situations, were processed and evaluated by methods of univariate as well as spatial mathematical and statistical modeling. The results showed during MA a significant decrease of repolarization integral values over the sternum and right precordium, which contributed to analogically localized decrements also in the QRST BSM. The decrease occurred in more than 2/3 of lead points. The most pronounced changes were observed in the right precordial area, where potentials decreased in more than in 70 % of subjects. In conclusion, the discriminative power of the difference STT and QRST integral maps was strong enough to distinguish the mental arithmetic induced changes in the superficial cardiac electric field. These adrenergic transient alterations in ventricular recovery may be of importance in subjects at risk for ventricular arrhythmias.

Computer simulation of propagated activation in different types of left ventricular enlargement.

An increase of the left ventricular mass does not always have an unambiguous effect on the electro- or vectorcardiographic image of ventricular activation. To analyse this phenomenon, three types of left ventricular enlargement were simulated by a computer model of propagated activation in cardiac ventricles. These were obtained from the reference (normal) left ventricle by an increase of its wall thickness either centripetally or centrifugally, as well as by increase of the ventricular cavity dimensions (dilatation). Two different degrees of mentioned changes, corresponding to an increase of the value of the respective parameters by 50% or 100% of reference left ventricular wall thickness, were analysed. In the case of a centrifugal increase of left ventricular wall thickness, the magnitude of instantaneous cardiac vectors increased only during the last two-thirds of ventricular activation time. A centripetal increase of the wall thickness resulted in a decrease of the resultant cardiac vector magnitudes during the first half of ventricular activation followed by their slight increase. In dilatation of the left ventricle the cardiac vectors were enhanced during the whole activation time.

Information on heart repolarization changes obtained from body surface ECG potentials.

Possibility to obtain information about local changes of heart repolarization from body surface potentials was studied on a model. Activation-recovery intervals (ARI) in surface ECG leads were tested as indicators of changed repolarization in the underlying myocardium. ECG signals corresponding to activation of myocardium with normal and changed action potential duration were simulated on the surface of a realistic inhomogeneous torso. ARI intervals were derived from all ECG signals and displayed as surface ARI maps. Results suggest that shortening and prolongation of action potentials in anterior myocardial regions can be visible in corresponding areas on surface ARI maps while only prolongation in postero-lateral regions can be observed. Reproducibility of ARI maps was checked on real measurements using 63 and 192 surface ECG leads. Obtained ARI maps exhibited acceptable reproducibility with correlation of 0.73 to 0.87. Based on the model and experimental results it is hoped that ARI maps can give some insight into the myocardium repolarization and help to recognize tissue with changed properties, primarily in heart regions underlying the anterior chest.

[New results in computer simulation of the spread of excitation in the myocardium]. / Nové výsledky pocítacovej simulácie sírenia sa podrázdenia v myokarde.

The paper presents the results from three series of simulation experiments performed by means of a realistic computer model of activation propagation in the myocardium. Simulation of two types of hypertrophy showed that hypertrophy of the ventricles without their simultaneous dilatation leaves the parameters of the cardioelectric field virtually unchanged. Change in the activation rate in the layer of elements formed by the intraventricular surface of the cavities, compared to the rate in the other elements of the heart, considerably affects the magnitude and orientation of cardiac vectors during the middle and terminal phase of activation. Rotation of the model heart around its longitudinal axis induces similar changes in the time course of the cardiac vector as are observed in some types of hypertrophy and in volume load of the ventricles.

Modelling developmental changes of human cardiac electric field in early postnatal period.

In early postnatal life, human cardiac electric field undergoes dramatic changes resulting from the adaptation of the heart to new hemodynamic conditions. For the study of the effect of changes in ventricular geometry as well as in spatial orientation of the heart occurring in this period of life, on the resultant heart vectors, our computer model of propagated activation was used. This model allows to change both mentioned characteristics of ventricles so that they reflect the developmental changes in the human heart. The pattern of activation of the model of newborn heart, characterized by equal thicknesses of the left and right ventricular walls as well as by the planar shape of the septum, showed that the resulting electrical forces were oriented anteriorly, slightly to the right, with clockwise rotation of the cardiac vectorgram in the horizontal plane projection. The gradual increase of the left ventricular wall thickness shifted the cardiac vector loop gradually to the left and anteriorly. When the ratio of the left to right ventricular wall thickness was the same as in adult human heart, the cardiac vector loop was oriented posteriorly, to the left and inferiorly. The left orientation of the initial cardiac vectors, commonly observed in 50% of full-term babies until 24 hrs of life, could be achieved only by the rotation of the heart around its long axis and/or by change of the azimuth of this axis. The simulated cardiac vectorgrams followed the typical early postnatal evolution of the vectorcardiograms of human newborns. (Fig. 4, Ref. 9.)

[Vectorcardiography of variations in localization of specific conduction systems in the left ventricle]. / Vektorokardiografický obraz variácie polohy zakoncení specifického vodivého systému v l'avej komore srdca.

A realistic computer model of propagation of ventricular activation was used to study the effects of varying the position of specific conduction system terminations in the left ventricle and the septum, representing the sites of initial activation, on the resulting simulated spatial heart vectors. Three differently localized foci of initial activation, each of them represented by one model element, were considered: in the central part of the left septal surface, posteriorly at about one third of the distance from the apex to the base, and in the upper part of the anterior free wall. During the model experiments, the positions of the initial activation were shifted +/- 5 model units (ca 5 mm) in the vertical and lateral direction either separately or in different mutual combinations. Small variations of the initial activation site in the basal parts of the left ventricle led to significantly smaller changes of the vectorcardiographic loop than variations of the same extent with the initial activation site located more apically.

Spontaneous variability and reactive postural beat-to-beat changes of integral ECG body surface potential maps.

There is virtually no information on spontaneous variability of ECG body surface potential maps (BSPMs) and on dynamics of their reactive changes in healthy subjects. This study evaluated quantitatively the depolarization (QRS) and repolarization (QRST) parameters derived from the respective integral BSPMs, constructed beat-to-beat, from continual body surface ECG records in 9 healthy men resting supine, during head-up tilting and sitting. Spontaneous variability of the BSPMs parameters, both at rest and during postural reactions, was characterized by significant respiratory and low frequency oscillations, more pronounced when related to repolarization. Head-up tilting and sitting-up evoked significant decrease in the QRST-BSPM amplitudes, widening of the angle alpha and reduction of nondipolarity indexes, compared to the respective supine values. All these changes were gradual, characterized by transition phenomena and prolonged after-effects. Tilting back to horizontal restored the resting supine values. The postural effects on depolarization were individually more variable and in the average showed a minimal QRS-BSPM amplitude increase. Beat-to-beat analysis of a train of ECG BSPMs provided the first evidence of spontaneous, non-random, respiratory and low frequency oscillations of the ventricular repolarization pattern, and the first insight into the dynamics of body posture associated changes in ventricular recovery.

Analysis of the effect of apex-base wall curvature on the vectorial representation of ventricular depolarization: a model study.

A computer model of propagated activation study is presented to investigate the possible effect of the ventricular wall curvature on the vectorial representation of its activation. The shape of the ventricle is changed by gradually decreasing the value of the input parameter determining the relative apex-base curvature of the ventricular wall (rvc) from 1.0 to 0.5. Two series of simulation experiments were accomplished. In the first series all input parameters of the model were held constant, except for rvc. In the second series, the height of the ventricles was altered simultaneously with the value of rvc in order to hold the volumes of the ventricular walls and cavities constant. In both series, the gradual increase of the apex-base curvature of the ventricular walls led to a slight decrease of initial heart vectors and an increase of laterally oriented vectors accompanied with their downward deviation. In addition, this increase caused a decrease in the terminal heart vectors along with their rotation to the left. The degree of this changes was proportional to the difference in the relative apex-base curvature of the two ventricles compared. The apex-base curvature of ventricular walls was found to be an effective factor influencing the cardiac electric field and consequently its representative quantitative parameters.

An interactive computer model of propagated activation with analytically defined geometry of ventricles.

A computer model of propagated activation in cardiac ventricles was developed for simulation experiments in an interactive regime on personal computers. In the model, the geometry of ventricles is defined by parts of "compound quasi-ellipsoids". The parameters specifying these ellipsoids as well as their spatial positions are derived from input data characterizing the heart geometry. Because the ventricles are defined analytically, the model renders a wide range of possibilities to vary their shape and gross dimensions. The activation is propagated from predetermined starting elements in agreement with Huygen's principle. Different propagation velocities for the myocardium and the subendocardial mesh of Purkinje fibers also may be simulated. The results of computer simulations may be evaluated both qualitatively, by isochrones of the activation propagation, and quantitatively, by the resulting cardiac vector computer in any moment of activation process.

Etalon (standard) for surface potential distribution produced by electric activity of the heart.

The authors submit etalon (standard) equipotential maps as an aid in the evaluation of maps of surface potential distributions in living subjects. They were obtained by measuring potentials on the surface of an electrolytic tank shaped like the thorax. The individual etalon maps were determined in such a way that the parameters of the physical dipole forming the source of the electric field in the tank corresponded to the mean vectorcardiographic parameters measured in a healthy population sample. The technique also allows a quantitative estimate of the degree of non-dipolarity of the heart as the source of the electric field.

Physically corrected orthogonal electrocardiographic lead systems in macaques and baboons.

The adequacy of various physically corrected electrocardiographic lead systems for lower primates was compared with the aid of physical models of the cardiac electrical field. Electrolytic tanks fashioned from plaster casts of the thorax of young adult male and female macaques and baboons were used. A dipole source situated at different points in the heart region simulated the electrical activity of the heart. Statistical evaluation and reciprocal comparison of the resultant parameters showed that the proposed modification of the McFee-Parungao lead system for macaques and baboons was most satisfactory, followed by the human variant of the same lead system and then by the variant for dogs. The greatest variability was displayed by parameters determined from measurements made with Frank's lead system, which was ranked last in the evaluation.

Role of left ventricular geometry in the alteration of initial QRS vectors due to concentric ventricular hypertrophy.

The relation between serial magnitudes of instantaneous spatial vectors, obtained throughout ventricular depolarization, and echocardiographically estimated left ventricular (LV) mass was investigated in 64 patients with congenital aortic stenosis and in 16 patients with coarctation of the aorta. While the correlation was positive between LV mass and vector magnitudes at 50 and 60 ms after QRS onset (r = .530 and .557, P < .01), it was found to be negative with regard to the magnitude of the initial 10 and 20 ms vectors (r = -.285 and -.355, P < .01). Computer simulation of activation propagation in different models of LV enlargement has shown that the decrease of the spatial magnitude of initial vectors, as well as a marked decrease of the area of the anterior portion of the horizontal plane QRS loop and of the Q amplitude of the orthogonal z lead, are characteristic of concentric LV hypertrophy with decreased diastolic volume and were not observed with unchanged or dilated chamber size. Repeated assessment of the magnitude of initial QRS vectors may indicate changes of LV remodeling in patients with LV pressure overload.