Study On Expression Of CX40 In Atrial Muscle Cell And Myocardial Fibrosis In Patients With Atrial Fibrillation

Background and objective: Atrial fibrillation is the most frequently encountered sustained cardiac arrhythmia in clinical practice at present and is a great hazard to human health, the incidence rate has gradually improved accompany with age. But its pathogenesis is not conclusive. The investigation of animal models of atrial fibrillation and human surgical specimens of atrial fibrillation has demonstrated that the incidence and maintenance of atrial fibrillation may be realated to myocardial fibrosis and gap junctions. There are five gap junction proteins had been confirmed exist in heart, these are CX31.9, CX37, CX40, CX43 and CX45. In addition, CX40, CX43 and CX45 are mainly distributed in atrial tissue, CX43 is widely distributed in atrial and ventricular muscle cells, as for CX40, it is mainly distributed in atrial and Purkinje conduction system, the content of CX45 is less contrast to other gap junction proteins and its expression in atrial is slightly higher than in ventricular. Myocardial fibrosis is mainly reflected as the increase of collagen fiber deposition in interstitial tissue of myocardium, moreover, in all the collagen fiber in interstitial tissue of myocardium, collagen type I accounts for more than 80%. We collected 25 cases of rheumatic heart disease atrial tissue samples, using transmission electron microscopy and immunohistochemical to study relationship of atrial remodeling, distribution of CX40, the content and distribution of collagen type I with atrial fibrillation and to further explore the mechanism of the incidence and maintenance of atrial fibrillation. Methods: 25 patients with rheumatic heart disease who received thoracotomy were divided into atrial fibrillation group and sinus rhythm group according to preoperative cardiac rhythm. Right atrial appendage tissue was obtained, transmission electron microscopy was used to detect the difference of atrial ultrastructure between the two groups and immunohistochemical staining was used to study the difference of content and distribution of CX40 and collagen type I.Results:1: Accord to clinical data, we found that the left atrial diameter of atrial fibrillation group was significantly increased in atrial fibrillation group compared with sinus rhythm group (P<0.05).2: Accord to the result of transmission electron microscopy, atrial muscle of patients in the two groups all has a certain degree of muscle dissolved, glycogen accumulation and interstitial fibrosis, but the degree of muscle dissolved and interstitial fibrosis was more serious in atrial fibrillation group than sinus rhythm group.3: Accord to the result of immunohistochemical, the content of CX40 was significantly lower in atrial fibrillation group than that in sinus rhythm group (P <0.05) and its distribution is uneven. Moreover, the content of Collagen type I in atrial fibrillation group was significantly higher compared with sinus rhythm group (P <0.01).The content of CX40 was negatively correlated with the content of Collagen type I(r=-0.96,P<0.01).Conclusion:1: The results of electron microscopy and immunohistochemistry all reveled that interstitial fibrosis was significantly increased in atrial fibrillation group which suggesting that atrial fibrosis may be responsible for the incidence and maintenance of atrial fibrillation. 2: The content of CX40 in atrial fibrillation group was significantly reduced than that in sinus rhythm group, furthermore, the distribution of CX40 is uneven. It is a clue that the decrease expression of CX40 may be an important known cause to the incidence and maintenance of atrial fibrillation.