The Effect Mechanism of 48h Rapid Pacing on Atrial Pathological Remodeling in Elder Canine
Objective To investigate the effect of 48 h rapid pacing on atrial pathological remodeling in the ageing canines.Methods 20 purebred canines were randomized into four groups according to whether receiving the endocardial atrial pacing or the age exactly as the adult sinus rhythm group,the elder sinus rhythm group,the adult pacing group,the elder pacing group.The electrophysiological properties,the cardiac ultrasound,the heart rate variability and the transmission electron microscope were tested after the establishments of atrial fibrillation(AF)models to figure out the atrial pathological remodeling mediated by rapid pacing.Results The PR intervals were enlarged in the elder pacing group,the bilateral atrial and four pulmonary venous effective refractory period significantly shortened,as well as the elevated AF inducibility(P＜0.05).Such instable electrophysiological parameters were accompanied by the expansive left atrial diameter,the increased left ventricular systolic diameter and the decreased ejection fraction(P＜0.05).From the results of heart rate variability analysis,we found that rapid pacing can enhance the systemic sympathetic tone and decrease the parasympathetic tone compared to the ageing groups(P＜0.05).Transmission electron microscope showed that the myotomes of atrial myocytes are elongated,and the morphology of mitochondrial membranes and ridges are significantly changed with the increase of age.In addition,aging combined with rapid pacing could aggravate the cytoskeletal destruction and mitochondrial cleavage.Conclusion Rapid ectopic activities could significantly facilitate the"AF begets AF"vicious cycle by potentially inducing the electrical and structural remodeling in the ageing canines,increasing the sympathetic tone and accelerating atrial myotome destruction and mitochondrial damage.
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