Effect of heart electric stimulation on repolarization of ventricular myocardium of fish and amphibians

The distributions of repolarization durations and end of repolarization time were studied on the ventricular epicardium in pikes (Esox lucius) and frogs (Rana esculenta) and in the ventricular intramural layers in toads (Bufo bufo) at the ectopic heart excitation by using method of the synchronous multielectrode cartography (24 unipolar leads). The time of arrival of the excitation wave and the end of repolarization in each lead were determined from the minimum of time derivative of potential at the period of QRS complex and by minimum of T wave, respectively. It has been established that at the ventricle electrostimulation, alongside with deceleration and a change of sequence of myocardium activation, the redistribution occurs of the local durations of repolarization, being longer than in zones of early activation (p < 0.05). At stimulation, the apicobasal gradient of repolarization is predominantly changed due to electrophysiological processes in the apical areas. In all the studied species, at the ectopic excitation of the heart the sequence of its repolarization repeats the depolarization sequence due to a delay of activation (in fish) and redistribution of repolarization durations (in amphibians).     

Rheumatoid involvement of the aortic arch

The clinical course of rheumatoid arthritis may be complicated by cardiac involvement. Indeed, postmortem studies suggest rheumatoid involvement in up to 50% of pericardial, 5% of myocardial, and 60% of valvular specimens. Yet, in our search of the literature, we found only a single case report describing aortic valve replacement for rheumatoid valvulitis. This discrepancy may be related to the paucity of symptoms in this sedentary group of patients. A complete cardiac evaluation of patients with rheumatoid arthritis is recommended to select those with significant valvular involvement for timely surgical intervention prior to the development of irreversible left ventricular dysfunction. Two patients who benefitted from aortic valve replacement for rheumatoid valvular disease are presented.     

Erythrocyte distribution in the vascular bed at the level of the aortic arch based on morphological research data

Erythrocyte distribution in the vascular bed according to their maturation rate has been studied. A relative content of young erythrocytes was shown to be higher in cerebral arterial than in peripheral blood. Such distribution is believed to be physiologically important, as young erythrocytes are capable of more effective oxygen exchange for carbon dioxide.     

Respiration-dependent shift in the region of the aortic arch

The contents of the mediastinum take part in a different degree in its inspiratory longitudinal expansion: Heart, pulmonary root, and the bifurcation of the trachea--all of them connected with the diaphragm by pericardium or membrana bronchopericardiaca--move caudad proportional to the sinking of the diaphragm. Compared with the corona cordis the planum cardiacum moves further caudad according to its distance from the upper apertura thoracis. So the heart necessarily has to compensate for this difference by taking an upright position and by rotation to the right. The arcus aortae, however, fixed in the neck by its three main branches cannot perform such a proportional excursion. A significant distance of the left pulmonary root from the aortic arch is the result. At the same time a subaortal space, the 'spatium subaortale mediastini', unfolds into which a bulge of the pleura mediastinalis moves. This bulge is filled with tissue of the upper lobe of the left lung.     

Computational study of growth and remodelling in the aortic arch

Opening angles (OAs) are associated with growth and remodelling in arteries. One curiosity has been the relatively large OAs found in the aortic arch of some animals. Here, we use computational models to explore the reasons behind this phenomenon. The artery is assumed to contain a smooth muscle/collagen phase and an elastin phase. In the models, growth and remodelling of smooth muscle/collagen depends on wall stress and fluid shear stress. Remodelling of elastin, which normally turns over very slowly, is neglected. The results indicate that OAs generally increase with longitudinal curvature (torus model), earlier elastin production during development, and decreased wall stiffness. Correlating these results with available experimental data suggests that all of these effects may contribute to the large OAs in the aortic arch. The models also suggest that the slow turnover rate of elastin limits longitudinal growth. These results should promote increased understanding of the causes of residual stress in arteries.