Atrial Structural Remodeling And Hemodynamics In Chronic Atrial Fibrillation

BackgroundAtrial fibrillation (AF) is a very common arrhythmia often associated with atrial mechanical dysfuncton and embolism. It is challenging and often frustrating to treat. There is a tendency for AF to become chronic and more resistant to cardioversion with increasing duration of the arrhythmia. Although the details are poorly understood, persistence of AF is thought to result from the atrial electrophysiological remodeling . Atrial electrophysiological remodeling refers to shortening of the atrial effective refracftory period (AERP) and reverses the normal physiological rate adaptation of refractoriness. While recently many animal expriments showed that other factors like structural remodeling may have an more important effect on the persistence of AF. Atrial structural remodeling refers to atrial dilation and alterations in extracellular matrix (ECM) and myocytes ultrastructure. Among them, the abnomal ECM metabolism may directly result in atrial dilation and ultrastructure changes and may play a key role in atrial structural remodeling. Beacause renin angiotensin system (RAS), matrix metalloproteases system (MMPs) and A disintegrin and metalloproteases system (ADAMs) were crucial for the metabolism of ECM, we therefore designed this study to determine the impact and mechanisms of RAS, MMPs/TIMPs and ADAMs /integrins on AF substrate development.Objective(1) To observe the alterations of extracellular matrix (ECM), myocytes tissue ultrastructure and atrial geometry in chronic atrial fibrillation; (2) To evaluate the effect of MMPs/TIMPs, ADAMs/Integrin and RAS on atrial structural remodeling in chronic atrial fibrillation and if the three systems have a cooperation effect in accelerating the process of atrial structural remodeling; (3) To assess whether theIntegrated Backscatter Score technique is feasible and sensitive in detecting and monitoring the histological characteristic of myocardium in atrial fibrillation.MethodsThirty six patients with rheumatic heart disease were included in the study. Twenty four of them were in chronic atrial fibrillation ( AF duration was 11~132, 51.41 ±31.60 months) and the left twelve were in sinus rhythm. Left and right atrial appendages tissue samples were obtained from these patients undergoing mitral/aortic valve replacement. The detection content is listed below. (1) All patients underwent transthoracic echocardiography examination including acoustic densitometry (AD) analysis on the post wall of left atrium. (2) Ultrastructural changes of both left and right atrial appendage tissue were observed by light and electron microscope . (3) The myocardium Angll were determined by radioimmunoassay detection. (4) The mRNA expression of ACE, AT1-R, AT2-R, collagen I, collagen III, ADAM 15, integrin P 1, MMP-9 and TIMP-1 were determinded by reverse transcription polymerase chain reaction (RT-PCR) . (5) The protein levels of tissue collagen , MMP-1, MMP-9 and TIMP-1 were analyzed by immunohistochemistry technique.Main Results(1) Echocardiography measurementAs compared with control group, the patients with AF were characterized by reduced mitral valve area (0.83+0.13 vs 1.03+0.19, p< 0.01) and increased LA (57.16 + 6.11 vs 45.50±7.64, P<0.001)and RA diameter(62.83+ 10.06 vs 51.66 + 17.14, P<0.05). The other index such as LVEDD, RVEDD, VST, PWT and LVMI have no significant differences between two groups.(2) AD analysisIn patients with AF, there was a marked upregulation of IBS% (61.27±1.36 vs 56.21±1.74) anddownregulationofCVIB(10.00±.48vs 11. 98±0.70) of the LA post wall myocardium compared with patients in SR.(3) Tissue Angll content measurementBoth the left and right atrial appendage Angll content in patients with AF weresignificantly elevated compared with patients in SR(19.55±8.91 vs 12.29+3.43 and 16.35 + 5.13 vs 12.54 + 3.41, P<0.05). In patients with AF, there were no significant difference of tissue Angll level between left and right atrial appendage.(4) Ultrastructure observationCompared to patients in SR, the atrial myocytes from patients with AF showed remarkable changes in ultrastructure , the following characteristic changes were observed: (1) Contractile material was depleted (myolysis). The disappearance of sarcomeres was often limited to the vicinity of the nucleus but also frequently involved the entire cytosol.As a result of the myocysis , remnants of sarcomeres, especially clumped Z-band material, are often seen. Mitochondria filled the myolytic space. (2) Huge amounts of glycogen filled the myolytic space in almost all cells that underwent myolysis. (3) A network of disorganized membranes, probably altered profiles of sarcoplasic reticulum were present in myolytic areas. (4) Mitochondria increased and clustered, typical changes in size and shape of mitochondria were seen in areas depleted of sarcomeres : many mitochodria had become elongated and samall and were in differents size. (5) Nuclei was heterotypical, the heterochromatin was nubbly gathered throughout the nucleoplasm. (6)Intercalated disc was asynechia and distorted seriously.(5) Immunohistochemistry detectionCompared to patients in SR, the protein levels of MMP-1 and MMP-9 in patients with AF increased while the protein level of TIMP-1 decreased significantly in both appendages. In AF patients, the MMP-9 protein level in LAA atrial tissue was higher and TIMP-1 protein level was lower than that of RAA atrial tissue. The MMP-1 protein level have no significant difference between two appendages.(6) Quantification of gene expressionIn patients with AF, the mRNA levels in left atrial appendage of collagen I, collagen III, ATiR, AT2R, ADAM15 and MMP-9 were significantly elevated (P <0.05~0.01) compared to those patients in SR, while the TIMP-1 gene expression significantly decreased (P <0.001). There were no significant changes of ACE andIntegrin P 1 gene expression in two groups (P >0.05).As to right atrial appendage in patients with AF, the mRNA levels of collagen III, ADAM 15, Integrin P 1 and MMP-9 were significantly elevated (P <0.05~0.01)while the mean amounts of TIMP-1 mRNA significantly decreased (P <0.032)compared to that in SR patients. There were no significant difference of ACE , collagen I, ATiR and AT2R gene expression between two groups (P >0.05).In AF group, the gene expression of ATiR, AT2R and MMP-9 in LAA tissue was increased while Integrin P 1 was decreased greatly compared to that of RAA.(7) Relationship between hemodynamic indices and changes of molecular biologyIn the left atrial appendage, collagen I, ATiR, ADAM15, MMP-9 and TIMP-1 gene expression correlated significantly with left atrial diameter (r=0.410,0.478,0.461,0.613 and -0.542, P<0.01~0.001) . The collagen I, ATjR , AT2R, and MMP-9 mRNA levels showed a positive correlation with AF duration (r=0.455,0.527 , 0.588, and 0.466, P<0.05~0.01), in contrast the TIMP-1 mRNA level negatively correlated with AF duration (r=-0.525, P<0.01). Genes like collagenl, collagen III, ATiR, AT2R and MMP-9 mRNA expression significantly correlated with Angll (r=0.400,0.373, 0.448, 0.437 and 0.447 , P<0.05~0.01). Genes like collagen I, ATiR, ADAM 15 and MMP-9 negatively coreelated with mitral valve area (r=-0.434,-0.382,-0.368 and -0.412, P<0.05).In the right atrial appendage, collagen I, AT2R, ADAM 15, MMP-9 and TIMP-1 gene expression correlated significantly with right atrial diameter (r=0.415, 0.366, 0.426, 0.544 and -0.462, P<0.05~0.01) . Collagen III, AT2-R, Integrin P 1 and MMP-9 gene expression showed a positive correlation and TIMP-1 showed a negative correlation with AF duration (r=0.448, 0.390, 0.636, 0.526 and -0.463, P<0.05~0.001) , Genes like collagen I, collagen III, AT2R, Integrin P 1 and MMP-9 mRNA expression positively correlated with Angll (r= 0.401, 0.455, 0.385, 0.599 and 0.428, P<0.05~0.001). Collagen I, ATjR AT2R and MMP-9 gene expression showed a positive correlation and TIMP-1 showed a negative correlation with AF duration (r=0.557, 0.492,0.491,0.494and -0.386, P<0.05~0.001).