Experiment Study On Rapid Atrial Pacing-induced Atrial Electrophysiological Remodeling And Structure Remodeling In Rabbits

Objective:To investigated the effect of tachycardia-induced on atrial electrophysiological characteristics;and to assessed the effects of verapamil and hypercalcium on tachycardia-induced atrial electrical and structure remodeling.Methods:In twenty-four New Zealand big ear rabbits paced with maximal atrial capture rate for 24h were randomly divided into control group(n=8), verapamil group(n=8)and CaCl₂ group(n=8).The infusion of saline,CaCl₂, verapamil was respectively initiated 30 minutes before rapid pacing and continued throughout the study.The atrial effective refractory period(AERP) was measured with S₁S₂ programmed electrical stimulation at pre-tachycardia (after autonomic blockade),during tachycardia(0.75,1.5,3,6,12,24,hours) and post-tachycardia(10min,20min,30min,60min).To determined the effective refractory period adaptating to rate(ERP-RA),the AERPs were measured in the right atrial appendage at 3 pacing cycle lengths(150,200,250 ms)respectively.The right atrialcular appendage tissue specimen was fixated and examined by light microscope and electron microscope at last.Results:1.In the control group,AERP was shortened after 0.75h of rapid atrial pacing(from 120.00±11.10,128.13±12.80,132.5±12.82ms to 110.63±11.116, 113.13±11.63,115.00±10.69ms,P=0.04).The mimimum value of AERP150, AERP200,AERP250 occurred after 24 hours of rapid atrial pacing.The AERP recovered quickly with a return to 96%of baseline after 10 minutes of post-tachycardia.In the CaCl₂ group,AERP was significantly shortened after 0.75h of rapid atrial pacing,P=0.001,The AERP recovered with a return to within 50%of baseline after 10 minutes of post-tachycardia.However,there is no significant difference in AERP shortening in verapamil group.2.Electron microscopic studies of right atricular appendage tissues demonstrated that mitochondrial swelling and accumulation of glycogen were observed in rabbits of control group's paced for 24 hours.It demonstrated that mitochondrial swelling,accumulation of glycogen and myolysis were observed in rabbits in Ca group paced for 24 hours,while the change in verapamil group was slightly.Conclusion:1.Short-term rapid atrial pacing induces atrial electrical remodeling,which develops quickly after pacing and recovers quickly after the offset of rapid pacing.2.Verapamil,a drug with L -type Ca²⁺channel blocking property,prevents electrophysiological remodeling and structure remodeling by atrial tachycardia.3.Hypercalcium promotes electrophysiological remodeling and structure remodeling induced by atrial tachycardia.4.The ultrastructural changes may be observed after short-term atrial paing.