Experimental Evaluation of Myocardial Fibrosis in a Rapid Atrial Pacing Model in New Zealand Rabbits using Quantitative Analysis of Ultrasonic Backscatter

BACKGROUND The aim of this study was the establishment of a rapid atrial pacing (RAP)-induced atrial fibrillation (AF) model with electrophotoluminescence and the application of ultrasonic backscatter quantitative analysis of the degree of myocardial fibrosis in New Zealand white rabbits. MATERIAL AND METHODS Sixteen New Zealand white rabbits were randomly divided into 2 groups: 1) a sham operation group (n=8) with implanted electrodes and no rapid pacing and 2) a pacing group (n=8) with an AF model induced by short-term rapid right atrial pacing for 12 h. Establishment of an AF model, atrial myocardium of myocardial fibrosis was tested by Masson staining and expression of collagen I and collagen III protein was detected with pathologic immunohistochemistry integrated back-scatter (IBS). Back scattering integral cycle variation (CVIB) were detected in atrial septal and posterior wall of the right atrium. RESULTS Rapid atrial pacing successfully induced the atrial fibrillation model in rabbits. Masson staining showed myocardial fibrosis significantly increased in the pacing group. Expression of collagen I and collagen III protein was strongly positive in the pacing group, and expression of collagen I and collagen III protein were weakly positive in the sham operation group. Compared with the sham operation group, AII was increased (8.24±0.85 vs. 15.56±1.30, P<0.05) and (7.58±0.56 vs. 16.60±2.45, P<0.05). CVIB was significantly decreased (2.78±0.86 vs. 1.08±0.13, P<0.05) and (3.12±0.65 vs. 1.56±0.15, P<0.05) in septal and posterior wall of the right atrium of the pacing group. CONCLUSIONS Ultrasonic backscatter measurement technique can be used to evaluate degree of myocardial fibrosis in a right atrial pacing-induced atrial arrhythmia model.