ИСТИНА

Much attention is paid to the pulmonary veins (PVs) myocardium as a region responsible for atrial fibrillation (AF) triggering. It has been recognized re-entrant circuits and anisotropic conduction in the human PVs myocardial sleeves, that probably responsible for the onset of AF. However, the electrophysiologic properties of the PVs including conduction of excitation in laboratory animals have not been well characterized. The aim of the present study is to investigate excitation wave conduction in rabbit and rat PVs myocardium with use of optical mapping technique. Rabbits (male, 2.6-3.2 kg) and rats (male, 250-300 g) were anaesthetized with an urethane (1.5 g/kg i.v. and 2 g/kg i.p, respectively), preparations consisting of left atrium (LA) and PVs of left lung lobe were dissected. All procedures were conducted according to current Russian guidelines for the use of experimental animals. Tyrode superfused isolated preparations were treated with potential sensitive dye di-4-ANEPPS (5 µM) in presence of 2,3-butanedione monoxime (1 g/l) for excitation mapping. Optical signals were captured with use of high speed CCD camera (WuTech Instruments). For conduction velocity, action potentials duration (APDs) estimation and isochronic maps reconstruction Cardioplex software (RedShirtImaging) was applied. Rabbit PVs characterized by a very short zone (2-3 mm), which conduct excitation and by an abrupt transition to unexcitable nonmyocardial regions. Maximal conduction velocity (θ) in the conducting zone of rabbit PVs does not demonstrate significant difference with LA (65±7 and 69±6 cm/s, respectively, n=8, P>0.1). Also, no differences were seen for wavelength (55±6 and 58±6 mm, n=8) estimated using APDs. No conduction slowing, disturbances or blocks were observed in rabbit PVs at various patterns of stimulation or acetylcholine (ACh) application (5 µM). Conduction of excitation was observed in distal and even intrapulmonary regions of rats PVs. Rat LA and PV myocardium also demonstrated weak differences in the conduction velocity. Maximal θ in LA - 84 ± 14 cm/s, the same parameter in PVs was 71 ± 11 cm/s (n=12, P>0.1). Wavelength for rat LA - 37 ± 5, and for PVs 43 ± 7 mm (n=12, P>0.05). Regions characterized by conduction slowing and blocks, were shown in rat PVs, but not in LA myocardium. Marked decreasing of conduction velocity and inexcitability were demonstrated in the rat PVs after periods (5 min) of quiescence (absence of stimulation). Application of ACh (5 µM, n=6) restore excitability and conduction velocity to the normal level. These data suggest functional similarity LA and PVs myocardium and PVs nonsusceptibility to conduction abnormalities in rabbits in contrast to rats. Significant distinction of conduction in PVs may be critical to experimental data interpretation in AF investigation.