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Results of experiments carried out in animals and of measurements made on electrophysical and analogue models are presented. It has been found that with routinely employed manipulations in the electric impulse therapy of arrhythmias the denstiy of the current in the chest and directly underneath the defibrillator's electrodes is distributed in a non-uniform fashion. This results in high defibrillation thresholds, possible damages of the heart and body teguments. The causes responsible for this non-uniformity are analyzed, the non-uniformity itself is assessed and ways of its elimination are indicated.

The paper describes a technique and some results of experimental measurements of electrical potentials generated by an isolated dog heart in homogeneous conductor, drawing equipotential maps of the field, and calculating the characteristics of the dipole equivalent generator of the heart. The form of potential distribution on a spherical surface around the heart and its ideal orthogonal vectorcardiograms are discussed.

An experimental study in an electrophysiological model of the human body showed defibrillator discharge current, used for closed electrodestruction of His' bundle in cases of drug-resistant supraventricular tachycardias, to cause a spark discharge and high-energy shock wave around the intracardiac electrode resulting in contusion of the heart. To stop the sparking, it is suggested that impulse voltage should be reduced while its duration should be prolonged in order to maintain local destruction potential. The relationship between the damaging effect of the impulse, and its force and duration was examined so that optimum action parameters could be established.

A possibility was studied of applying the deep and infrequent respiration test with an object of increasing the informativeness of the statistical parameters of the ECG sequence interval as applicable to the quantitative evaluation of the functional state of man. Examination of patients with wound infection shown that the deep respiration test makes in possible to assess quantitatively the status of test subjects on the basis of two statistical parameters (the mean value of RR interval of ECG and root-mean-square deviation).

A statistical analysis of prolonged ECG records has been carried out in patients with various heart rhythm and conductivity disorders. The distribution of absolute R-R duration values and relationships between adjacent intervals have been examined. A two-step algorithm has been constructed that excludes anomalous and "suspicious" intervals from a sample of consecutively recorded R-R intervals, until only the intervals between contractions of veritably sinus origin remain in the sample. The algorithm has been developed into a programme for microcomputer Electronica NC-80. It operates reliably even in cases of complex combined rhythm and conductivity disorders.

A biophysical model heart--body designed for experimental electrocardiographic investigations is described. The model consists of an isolated perfused dog heart immersed in a liquid volumetrical conductor filling the vessel in the form of a human torso with implanted electrodes for various ECG leads. The volumetrical conductor presents a hypotonic NaCl solution. In order to prevent heart damage by the solution, use is made of an artificial pericardium manufactured from current conductive rubber film.

A new method of ECG diagnosis, based on a mathematical model of electrical heart generator as a mobile dipole, was clinically verified in 10 healthy subjects and 2 patients with combined cardiopathy and pronounced bilateral ventricular hypertrophy. Electrocardiograms were recorded in 80 unipolar leads from the body surface; recordings were processed by a computer. The output information were the pathways of the heart electrical centre (dipole) during the heart cycle. The trajectories in patients with combined ventricular hypertrophy markedly differed--even in the absence of ECG changes in standard leads--from trajectories in healthy subjects. The new method of ECG diagnosis consequently offers information which cannot be obtained when using conventional and corrected orthogonal ECG leads.

A simple decisive rule for classifying RR-intervals of electrocardiograms by two types, sinusoidal and anomalous, is deduced using the theory of pattern recognition. Parameters of the decisive rule according to the minimum of the Buyess probability of the classification error are selected. The algorithm may be realized with microprocessors and used in cardiac rhythm monitors.

Statistical analysis of prolonged continuous recordings of the ECG RR intervals was carried out in 64 patients with purulent surgical infection. The following indices were considered: the mean value of the RR intervals, the mean quadratic deviation (delta), the variation amplitude, the 1st and the 3rd correlation coefficients, the excess, asymmetry, the RR/delta ratio. Besides, the size and the shape of the autoregression could was analyzed. Statistically significant differences of the RR/delta ratio, of the mean quadratic deviation, and of the variation amplitude were revealed in 3 groups of patients differing by the severity of condition. These differences were reflected in the size and shape of the autoregression cloud. The results obtained suggest that statistical characteristics of prolonged recordings of the cardiac rhythm could be used for objective assessment of the severity of the patient's condition and of the therapeutic effect in the patients with a purulent surgical infection.

The electric field of the isolated dog heart immersed into a liquid volumetric conductor was subjected to a thorough investigation. Measurements and subsequent calculations showed that in precordial leads the quantitative description of the cardiac generator by a multipole equivalent generator of the 1st order (dipole) is rough approximation. Addition of a multipole component of the 2nd order (quadripole) to the equivalent generator increases but relatively little the accuracy of description. It is suggested that in this problem the multipole expansion proves to be a slowly convergent series. For this reason, application of multipole equivalent cardiac generator fixed in the electrical center of the heart in the clinical electrocardiography is to be considered as having no prospect.

The study is concerned with quantitative mapping of electrocardiographic potentials on the human body surface at various applications of equivalent multipole heart generators. The accuracy or reproduction of the electrical heart field with the application of mobile and immobile dipole and quadrupole generators is compared. The immobile equivalent generator (EG) is fixed in the geometrical centre of the trunk, whereas the mobile EG follows the path of the electrical heart centre during the heart cycle. Four healthy subjects and two patients with permanent postmyocardial ECG changes were examined. On transition from the immobile to the mobile model, in both groups of probands the relative contribution of the quadrupole component to the total potential of the body surface steeply diminished, with consequent substantial increase in accuracy of the dipole heart description. The dipole following the path of the electric heart centre during the heart cycle represents one of the most promising models, and deserves attentive clinical testing.