| Objective: To study the possible mechanism of atrioventricular nodal reentrant tachycardia by observing and detecting the morphology characteristic and Cx43 expression in coronary sinus and posterior extension .Method: 20 New Zealand rabbits were divided into two groups by electro-physiological examination: dual-pathway group and non-dual-pathway group. In the former group, jump phenomenon or atrium / ventricle double reaction or atrioventricular nodal reentrant tachycardia was found out during electro-physiological stimulus, nor the later group. Then the preparation Includes coronary sinus and Koch's triangle was cut out and devided into two parts since 1mm from the coronary sinus ostium(CSO). Coronal sections apply to Koch's triangle in order to observe the morphology of PNE . The rest preparation was sliced by Sagittal plane. To observe Cx43 by H-E and immunohistochemistry of posterior extension and coronary sinus.Ipp6.0 was used to analysis quantitatively Cx43 expression ,then statistical analysis data by SPSS11.0 software .Results:1 .Electro-physiological stimulus:Atrioventricular nodal reentrant tachycardial was induced in 5 rabbits during electro-physiological stimulus. There are 1 rabbit with jump phenomenon and 1 rabbit with ventricle double reaction were found out in 2 rabbits; There is no correlation between the size of Koch's triangle and the AV interval and the cycle of tachcardia in dual-pathway group.2.Morphology:(1) Coronary sinus was surrounded by myocardial coat, which become thin from CSO toward distal, even was covered only by epicardical fat or fibers. Compact node was consisted of two layers cell bundle. PNE was found by serial sections from compact node that is deep layer cells of AVN to CSO in all specimens. Three specimens have left posterior extension. Right posterior extension can be seen in all specimens. Cells in PNE were sparser compared with compact node.3. Immunohistochemistry:Cx43 express negative in deep atrioventricular node cells, weakly positive in superficial and intermediate cells. Cx43 express negative in posterior extention in both groups. coronary sinus myocardial coat Cx43 Positive expression in membrane. In dual-pathway group, coronary sinus expression of Cx43 are higher than left atrium. Non-dual-pathway group had no significant differenceConclusion:1. conduction of slow pathway has special structure rather than base on size of Koch's triangle.2. Coronary sinus connect left atrium and right atrium by myocardial coat,which involve in reentrant cycle.3. Compact node and posterior extension have characteristic of slow pathway. Dual A-V nodal pathways display when conduction of velocity or refractory changed. Due to there are more than one fast pathway, impulse propagation not only from deep layer of transitional cells to left atrial septum ,then reach to right atrium via of coronary sinus,but also from superficial layer of transitional cells to the top of Koch's triangle. 4. Cx43 negative express in deep atrioventricular node cells, weakly positive express in superficial and intermediate cells can explain longitudinal dissociation. Sinus impulse propagation from atrium to Superficial layer and middle layer cell bud dle ,then reach to His bundle. Premature systole block in the fastway because of refractory .The activation conduct from inferior margin of CSO to PNE, which have charateristics of nodal cells and express Cx43 negatively. After successful ablation of right posterior extension, the charateristics of slow conduction display in left posterior extension. Difference in morphology of coronary sinus and difference in expression of Cx43 maybe the pathology mechanism of AVNRT. We consider the block of reverse transmission is limiting factor of atrioventricular nodal reentranttachycardia.Multiple phenomenon of electrophysiology seems easy to understand according to this view. The study on the possible mechanism of AVNRT can provide theoretical evidence for radiofrequency catheter ablation on different focal. |
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