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Heterogeneity of propagation of excitation in epicardium of pulmonary veins ostia in rabbit during cooling.

ABSTRACT

Objective: The purpose of this research was to study the propagation of the excitation wave along epicardium in the area of the pulmonary veins ostia in rabbit in normal conditions and while cooling.

Methods: The excitation wave spreading along epicardium in the area of pulmonary veins ostia in the left atrium at 36-37[degrees]C and when cooling to 32[degrees]C was studied by the method of electrocardiochronotopography in rabbit of Chinchilla species, five months age. The size of the registering surface of the electrode was 1.08 x 1.08 cm.

Results: The time of depolarization when cooling from 36[degrees]C to 32[degrees]C changes unevenly in various zones of pulmonary veins. On the epicardium of pulmonary veins area at temperature reduction from 36[degrees]C to 33, C, change in the direction of excitation and essential reduction of depolarization time, and its significant increase under further cooling to 32[degrees]C were observed. In the middle part of the left atrium at temperature reduction, change in the main direction of the excitation wave propagation, shift of the location of the areas of the latest depolarization were revealed and the front become more homogeneous.

Conclusion: In the area of the left atrium base the heterogeneity of the front of depolarization at temperature reduction was revealed.

Keywords: pulmonary veins, left atrium, atrial fibrillation, depolarization, rabbit

Introduction

Atrial fibrillation (AF) is the most common of all sustained cardiac arrhythmias. Recent clinical studies show that pulmonary veins (PVs) are an important source of ectopic beats, which could initiate paroxysmal tachyarrhythmias and AF, especially in the presence of certain cardioactive agents. The left atrium (LA) consists predominantly of myocardial cells but may occasionally contain subsidiary pacemaker cells. Using the perfusion methods with collagenase and protease, we have isolated cardiomyocytes from dog and rabbit PVs. We found that cardiomyocytes have distinct action potentials (APs) (pacemakers vs. non-pacemakers) and ionic current profiles, which may be responsible for the high arrhythmogenic activity of the PVs (1). Heterogeneity of myocardial sleeve morphology and gap junctions have been observed in various thoracic veins, including PVs. The heterogeneous structure could potentially form a substrate for abnormal electrical coupling and the consequent reentrant tachyarrhythmias. However, the spread of excitation from the pacemaker or ectopic site within PVs to the rest of myocardial sleeve and LA are not clear. At reduction of the temperature from 30[degrees]C the front becomes more homogeneous on the epicardium in the area of falling the pulmonary veins (PV) into the left atrium (LA) in rabbit (2).

The purpose of this research was to study the spreading of the excitation wave along epicardium in the area of pulmonary veins ostia in the left atrium in rabbit in normal conditions and when cooling.

Methods

The excitation wave spreading along epicardium in the area of the pulmonary veins ostia in the left atrium at 36-37[degrees]C and when cooling to 32[degrees]C was studied by the method of electrocardiochronotopography in rabbit of Chinchilla species, five months age. The rabbits were anesthetized with urethane (1.5 mg/kg). The electrocardiogram (ECG) in the second limb leads was used as a control one. Time counting out in ms was made relative to R-wave peak in the ECG II, before R-peak moment time is indicated with minus.

Before opening the thorax we conducted tracheotomy and the animals were put under artificial respiration. The frequency and depth of the breathing was selected for each animal individually. After opening the thorax and denuding the heart the multipolar electrode with 64 pick-up electrodes was placed on the atrial epicardium in the area of falling the pulmonary veins into the left atrium. The size of the registering surface of the electrode was 1.08 x 1.08 cm. The data obtained were processed with the aid of the system "Kardioinform" (3). The moment of arrival the excitation wave in each point of the lead was defined by the minimum of the first derivative of the potential on time.

Results

At description we used the following notions: upper part of the left atrium corresponds to the area of falling the pulmonary veins into the atrium, middle--middle part of the dorsal side of the left atrium, lower--the base of the left atrium.

The upper part (corresponds to the area of falling the pulmonary veins into the left atrium) is activated evenly, no availability of the additional zones of early and late depolarization is observed. At the temperature of 36[degrees]C and 35[degrees]C the excitation wave in the epicardium spreads from interatrial septum to the left atrium, depolarizing first the upper part of the dorsal side in ostia of the pulmonary veins in the left atrium (Fig. 1 a). Along myocardial sleeve, the excitation wave, bending around pulmonary veins, moves to the upper part of the dorsal side of the left atrium. At 36[degrees]C this area is depolarized within 4 ms, while at 35[degrees]C during 0.5 ms. Change in the direction of the excitation wave spreading is observed in the upper part of the left atrium at reduction the temperature of the body. At the temperature of 33[degrees]C the depolarization wave spreads directly from the area of pulmonary veins and time of activation forms 0.25 ms. Under further cooling to 32[degrees]C the activation wave comes to the upper part of the left atrium from interatrial septum, herewith the increase of depolarization time is observed which forms 5.25 ms (Fig. 1b).

[FIGURE 1 OMITTED]

In the middle part (corresponds to middle part of the dorsal side of the left atrium) at temperature of 36[degrees]C and 35[degrees]C the presence of several zones of early and late depolarization is observed since in this area the front of excitation is divided into two waves and begins to disperse. One wave evenly spreads from the upper part of the atrium to the lower one, i.e. to the base of the left auricle. The second wave depolarizes directly the area of vessels. Time of activation of this area at 36[degrees]C forms 11 ms, while at 35[degrees]C--9 ms (Fig. 1 a). At 33[degrees]C the direction of the depolarization wave is not changed, but the time of depolarization increases to 13 ms. At 32[degrees]C the excitation wave changes its direction and spreads from interatrial septum in the direction of the left auricle and to the base of the atrium, time of activation increases to 31 ms (Fig. 1 b).

The base of the left atrium (the area located closer to the atrioventricular boundary at 36[degrees]C is depolarized during 4 ms, at 35[degrees]C--3-4 ms, the presence of two fronts is observed: one spreads from left auricle, the second along interatrial septum (Fig. 1a). There appear the areas of the delay of the spreading of the excitation wave in the middle part of left atrium closer to the base. At 33[degrees]C the depolarization wave spreads from the centre along the base of the atrium to interatrial septum and to left auricle, the time of activation forms 13 ms. At 32[degrees]C (Fig. 1 b) the time of depolarization increases and forms 25 ms, presence of the multiple zones of early and late activity is observed in this area.

Conclusion

The time of depolarization when cooling from 36[degrees]C to 32[degrees]C changes unevenly in various zones of pulmonary veins. On the epicardium of pulmonary veins area at temperature reduction from 36[degrees]C to 33[degrees]C change in the direction of excitation and essential reduction of depolarization time, and its significant increase under further cooling to 32[degrees]C are observed. In the middle part at temperature reduction, change in the main direction of the excitation wave propagation, shift of the location of the areas of the latest depolarization are revealed and the front becomes more homogeneous. In the area of the atrium base at temperature reduction the heterogeneity of the front of depolarization is revealed.

Acknowledgements

The work is supported by the Sc.i sc. 5118.2006.4, grant RFFI 050-49296, NSC-RFBR 050490586.

References

(1.) Chen YJ, Chen SA, Chen YC, Yeh HI, Chang MS, Lin CI. Electrophysiology of single cardiomyocytes isolated from rabbit pulmonary veins: implication in initiation of focal atrial fibrillation. Basic Res Cardiol 2002; 97:26-34.

(2.) Chudorodova SL, Tsilke PA, Roshchevskaya IM, Roshchevsky MP, Chen Y, Lai Y, et al. The sequence of depolarization of epicardium in the area of falling the pulmonary veins into the left atrium in norm and at cooling (Abstract). In: Abstracts of the 33rd International Congress on Electrocardiology and 47th International Symposium on Vectorcardiography; 2006 June 28-July 7; Cologne, Germany; p. 22

(3.) Roshchevsky MP, Arteeva NV, Kolomeyets NL, Antonova NA, Kambalov MY, Shmakov DN, et al. The system "CARDIOINFORM" for visualization and analysis of the heart electric field. Med. Academic J 2005; 5:74-9.

Svetlana L. Chudorodova, Irina M. Roshchevskaya, Mikhail P. Roshchevsky Yao-Chang Chen *, Yu-Jun Lai **, Chen-I Lin ***

Komi Science Centre, Ural Division, Russian Academy of Sciences, Syktyvkar, Russia,

* Department of Biomedical Engineering, ** Institute of Life Sciences & *** Physiology, National Defense Center, Taipei, Taiwan

Address for Correspondence: Svetlana L. Chudorodova PhD, Research Associate Laboratory of Comparative Cardiology Komi Science Centre, Ural Division, RAS 50, Pervomayskaya str., Syktyvkar 167982, Komi Republic, Russia Phone/Fax: 7-18212124-51-24 E-mail: sveta@physiol.komisc.ru
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Article Details
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Title Annotation:Original Investigation
Author:Chudorodova, Svetlana L.; Roshchevskaya, Irina M.; Roshchevsky, Mikhail P.; Chen, Yao-Chang; Lai, Yu
Publication:The Anatolian Journal of Cardiology (Anadolu Kardiyoloji Dergisi)
Article Type:Clinical report
Geographic Code:9TAIW
Date:Jul 1, 2007
Words:1576
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