Location of the electrical center of ventricular depolarization in rabbits.

This is a study on the location of the ventricular depolarization center, carried out on fifteen healthy rabbits according to the method of Ritsema van Eck. It is established that the level of equivalent heart dipole coincides with the fourth or fifth intercostal space, but in some laboratory animals this level displays a lower positioning. The inference is reached that to secure correct application of Frank's lead system it is necessary to use a prompt and precision method for determination of the level in question in each individual case. Such a method has not been developed as yet. For the time being, the optimal solution of the problem could be accomplished through a lead system that is less sensitive to electrode positioning errors.

Disorders of ventricular contractility and electrogenesis in the early stage of endotoxin shocked rabbits.

This is a report on ventricular contractility and electrogenesis disorders in rabbits, following intravenous injection of E. coli endotoxin at a dose of 2 mg.kg-1. At the 30th min, the right ventricular contractility indices (dP/dtmax)/P and [(dP/dt)/P]max had lower values, whereas end diastolic pressure (EDP), right ventricular systolic pressure (RVSP) and P(dP/dtmax) showed higher values compared to the initial ones. Most of the left ventricular contractility indices tested showed significantly lower values at the 30th and 60th min of the registration. In the scalar orthogonal ECG leads, at the 5th min an increased Qz amplitude, and at the 60th min an increased Rz amplitude, a decreased Ry amplitude, and QRS complex widening and bradicardia, were registered. In the spatial magnitude curve an increased amplitude of the main vectors of ventricular depolarization was documented. The changes in electrogenesis are interpreted first and foremost by the presence of hemodynamic disorders. The inference is reached that both left and right ventricular dysfunction have been already formed during the initial stage of endotoxin shock.

A study of ventricular electrogenesis and contractility in acute pressure overload of the right heart ventricle.

A model of fat embolism induced acute pressure overload of rabbit right ventricle of heart is presented. A decrease in right ventricular contractility is registered as early as the first minutes after loading. Changes in spatial magnitude and polar coordinates of vectors of ventricular depolarization, and myocardial ischemia manifestations are recorded. The changes in electrogenesis described are attributed basically to ensuing development of hemodynamic disorders.

Decreases in left ventricular contractility during endotoxin shock in rabbits.

The participation of the heart in shock syndrome formation during endotoxin shock is a problem still awaiting solution. The task undertaken is to assess the work of the left ventricle and arterial pressure in rabbits before and after endotoxin injection at a dose of 2 mg.kg-1. Heart rate is the first to reach significantly lower values--at 30 min (p less than 0.05). At 45 min, there are significant reductions in dP/dtmax (p less than 0.01), (dp/dt)/P40 (p less than 0.001), LVP (p less than 0.05), and increase in dP/dtneg (p less than 0.02). Both the systolic and diastolic blood pressures were significantly decreased at 60 min. The data obtained warrant the assumption that impaired myocardial contractility plays a part in the formation of shock syndrome in rabbits exposed to endotoxin.

[The effect of endotoxin on the cardiovascular system]. / Vliianie éndtoksina na serdechno-sosudistuiu sistemu.

The dynamics of changes in myocardial contractility and pressure in the left ventricle of the heart and the femoral artery were studied in rabbits before and after intravenous infusion of 2 mg/kg endotoxin. The left ventricle was catheterized. The signal from the left-ventricular pressure transducer was fed into a microcomputer after analog-digital conversion for calculating the maximal rate of increase in intraventricular pressure. All the parameters studied began decreasing as early as the 5th minute after endotoxin administration. A statistically significant decrease (p less than 0.05) of the heart rate was recorded first on the 30th minute, than the left-ventricular pressure and maximal rate of intraventricular pressure increase took place on the 45th minute, and systolic and diastolic pressure in the femoral artery decreased on the 60th minute. The detected disorders of myocardial contractility provoke the appearance of hypotension the main role in the development of which is played by damage to the peripheral vascular network.

Effect of calcium blocking agent verapamil on blood pressure, ventricular contractility, parathyroid hormone, calcium and phosphorus in plasma, catecholamines, corticosterone and plasma renin activity in spontaneously hypertensive rats.

In four-month-old spontaneously hypertensive rats (SHR) the effect of a calcium blocking agent verapamil on blood pressure, ventricular contractility indices, parathyroid hormone (PTH), plasma renin activity (PRA), plasma and adrenal corticosterone content and catecholamines in hypothalamus, myocardium and adrenal gland was evaluated. Calcium and phosphorus in plasma were also determined. Verapamil treatment resulted in a significant decrease in systolic and diastolic blood pressure and a reduction in maximum left ventricular pressure. Verapamil exerted a negative inotropic effect, evaluated by a decrease in dP/dt max and dP/dt neg. PRA was elevated, calcium tended to decrease, and no changes in PTH and phosphorus were found. The hypotensive effect of verapamil in SHR was accompanied by a decrease in plasma and adrenal corticosterone content, and a fall in catecholamine concentration in adrenal glands and myocardium.

Angular velocity and acceleration of the QRS vector in the electrocardiogram of rabbits.

The curves of the spatial angular velocity (AV) and of its first derivative (AA) are described for 103 healthy rabbits. After analog-to-digital conversion, the amplified X-, Y- and Z-signals after McFee and Parungao are fed for calculation on a microcomputer. In 41 per cent of the cases the AV curve has two basic waves, in 29 per cent--three, in 21 per cent--one, and in 9 per cent--four, which coincide with the lowest points in the spatial magnitude curve. The AA curve consists of biphasic waves with approximately identical amplitudes of their positive and negative parts. The results are interpreted in connection with the chronotopography of the ventricular depolarization and reorientation of the activation front.

Effect of captopril on some ventricular contractility indices in spontaneously hypertensive rats (SHR).

Two groups of SHR were treated with captopril (Squibb): the first group (1 month old)--30 mg/kg i.p. twice daily for 77 days, and the second group (8 months old)--20 mg/kg p.o. twice a day for 23 days. The recording of electrocardiogram (ECG), systolic blood pressure (SBP), diastolic blood pressure (DBP), and some isometric indices of the left-ventricular contractility indicate that in all treated animals the values of most of the parameters are considerably lowered compared to the controls. The ratio between velocity of pressure increase and intraventricular pressure/equal to 50 mmHg--(dP/dt)/ICP50/does not change significantly. It can be concluded that in SHR, captopril practically does not influence the inotropic condition of the myocardium.

Spectral analysis of the normal electrocardiogram of rabbits.

A spectral analysis of the QRS complex of the rabbit's electrocardiogram was made. The amplified ECG signals were filtered through low-pass filters with cut-off frequency 500 Hz and steepness 12 dB/oct, and fed to a multichannel oscilloscope monitor. The images obtained were photographed. They were subjected to analog-to-digital conversion. The values were fed for processing to an EC 1035 computer. A standard discrete Fourier transformation was used. The spectral curve exhibited a considerable amplitude of the higher harmonics. Point -20 dB was at 164 Hz and point -30 dB was at 314 Hz. It was concluded that for accurate reproduction of the rabbit's ECG the recording electrocardiograph would have a bandwidth up to 225 Hz. An amplitude error not exceeding 10 per cent would be guaranteed.

Spatial magnitude of the normal QRS-complex in the electrocardiogram of rabbits. Velocity and acceleration of the spatial magnitude.

The article describes the curves of the spatial magnitude (SM) of the normal QRS-complex in 52 rabbits, as well as of the velocity and acceleration of SM as a function of time. The X-, Y- and Z-recordings after McFee and Parungao are subjected to analogue-to-digital conversion and computer-calculation. The SM-curve consists of two and less frequently of three peaks, the third peak having the greatest amplitude and the first peak--the smallest. The three peaks are discovered at 16, 41 and 64 per cent, respectively, of the duration of the QRS-complex. The results are discussed in relation to data about other mammals and humans. The characteristic points in the curves of the recorded parameters are compared.

Comparative study of three vectorcardiographic lead systems.

A homogeneous model of rabbit torso and physical dipole are used. A comparison is made between the corrected orthogonal vectorcardiographic lead systems after Frank, McFee-Parungao and Zao. The components X, Y, Z of the lead vectors are measured for 15 points which can be inserted in the cardiac volume under normal conditions. The modules of the lead vectors and the angles between them are calculated. The three vectorcardiographic systems are compared with respect to the ratio between the modules (X:Y:Z) and the deviations of the angles from the real value. Best orthogonality are found with the system after Frank, if the thoracic electrodes are placed precisely at the level of the so-called electrical cardiac centre. No essential differences are found between the systems after Frank and after McFee-Parungao with respect to correctedness and orthogonality.

Investigation of Frank's vectorcardiographic lead system on homogeneous rabbit torso model.

The applicability of Frank's lead system in experiments on rabbits is studied by using a homogeneous rabbit torso model. The influence of dipole localization on the modules of the lead vectors at the level of 4th, 5th and 6th intercostal spaces is studied. The lead vector modules along the axes X, Y and Z for the level of the dipole are calculated to be equal to 1:0.99:0.92. The maximum angular errors in the planes XY, XZ and YZ are calculated, being for the same level theta yz = -6 degrees 50', theta xy = theta xz = 0 degrees 00'. The authors have reached the conclusion that Frank's system produces good levelling of the lead vector modules and has satisfactory orthogonality on rabbit torso model.

[Changes in electrolyte homeostasis in acute loading of the right heart]. / Promeni v elektrolitnata khomeostaza pri ostro obreminiavane na diasnoto surtse.

The authors carried out experimental studies on electrolyte homeostatis of healty cats and of cats with experimental stenosis of the lung artery after venous infusion of the dextran plasma substitute Reoisodex. There was a statistically significant reduction only of the level of ionized calcium under the influence of the infusion. The authors established an increase of the level of inorganic phosphorus and of the serum bicarbonates in animals with experimental stenosis of the lung artery.

[Electrocardiographic and histomorphological changes in the myocardium of rats with Selye's experimental hypertension]. / Elektrokardiografski i khisto-morfologichni promeni v miokarda na plukhove pri eksperimentalna khipertoniia po Selie.

The authors described electrocardiographic and histomorphological changes in white rats with coarctation hypertention, induced by the method of Selye. The electrocardiographic changes were manifested as prologation of preauricular-ventricular conduction time, dislocation of the intermediate part ST to the isoelectrical line, low, negative or biphasic T-wave at the initial stages of the experiment, but after the thirthieth day there was a pathologic Q-wave, a reduced voltage of the steap curves and manifested left type of ECG in the majority of the experimental animals. Histomorphological and histochemical study on thmyocardium revealed in the beginning of the experiment mainly lesion changes, but sign of myocardial hypertrophy and manifested difuse and/or focal myocardial fibrosis on the 30th to the 90th day of the experiment.