Effects Of Acute Atrial Dilation On Atrial Effective Refractory Period In Langendorff-Perfused Rabbit Heart And Intervention By Verapamil

Objectives: Acute atrial dilation can induce acute myocardial electrophysiological changes and increase the vulnerability to atrial fibrillation(AF).Mechanoelectric feedback may have a important role in it.lt is unclear whether verapamil,as a L-type calcium blocker.also have pharmacological effects on it.This study was focus on the effects of acute atrial dilation on myocardial electrophysiological parameters and the vulnerability to AF by a Langendorff-perfused rabbit heart model.Additionally.the effects of verapamil on electrophysiological changes induced by acute atrial dilation and the vulnerability to AF were also investigated.Methods: Twenty isolated Langendorff-perfused rabbit heart was randomly divided into two groups :the control group(n=10,normal Tyrode's solution) and verapamil group(n=10,Tyrode's solution with verapamil 0.5umol/L). All the hearts underwent a protocol with stepwise increase of right atrial pressure from 0 to 12 cmHbO.At each pressue level, sinus cycle length(SCL),atrial effective refractory period(AERP),atrioventricular wenckebach cycle length(AVWCL) and AV interval were measured.The methods of 8182 stimulation and Burst were used to evaluate the vulnerability to AF.Meanwhile.the inducibility and duration of AF were also recorded.Results: (l)In control group,the increase of right atrial pressure from 0 to 12 cmH2O significantly shortened AERP from 98.60 ?11.89 to 61.78 + 21.32ms(P<0.01).And right atrial pressure had a high Spearman correction with AERP(rs=-0.664,P<0.01).The elevation of right atrial pressure also shortened SCL and prolonged AVWCL and AV interal,but there were no statistically significant differences.(2)In control group, the elevation of right atrial pressure from 0 to 12 crnHbO significantly increased the inducibility of AF induced by 8182 stimulative method from 0/10 to 9/10(P<0.01),and the duration of AF also prolongedsignificantly(P<0.01).(3)In verapamil group, the myocardial parameters had no statistically significant differences between any two right pressure levels(P>0.05).(4)In verapamil group, the inducibility and duration of AF had no statistically significant differences between any two right pressure levels(P>0.05).Conclusion: (l)Acute atrial dilation shortens AERP significantly.but SCL,AVWCL and AV interval don't change significantly. (2)Acute atrial dilation increases the vulnerability to AF and prolongs the duration of AF significantly. (3)Verapamil can attenuate the shortening effect of acute atrial dilation on AERP. (4) Verapamil can attenuate the increasing effect of acute atrial dilation on the vulnerability to AF.