gms | German Medical Science

Introduction: According to large randomized trials, angiotensin II ( Ang II ) receptor blocker ( ARB ) prevented the new onset of atrial fibrillation ( Af ), but its mechanism has been unclear. Then we noted a direct suppressive action of Ang II on impulse conduction possibly related to the occurrence of Af that is the subject in this study.

Method: Left atrial preparations were isolated from the heart of 11 young adult( 15-20 weeks of age ) and 11 old ( 35-40 weeks of age ) SHRIzm. A thick muscle trabeculae traversing from mitral orifice to appendage catched from which trandsmembrane action potential( AP ) was recorded through glass microelectrode at 2Hz of baseline interval. Resting membrane potential ( RMP ), action potential duration ( APD ), dV/dtmax and functional refractory period ( FRP ) were measured. The preparations were stimulated at rapid rate of 12.5Hz for 60sec under normal Tyrode, and plus Ang II ( 10-7M ), and Ang II ( 10-7M ) plus ARB( candesartan;10-6M). The frequency of conduction block in these conditions were counted, then compared it between both groups.

Results: FRP of old SHR ( 51.7msec ) was significantly prolonged as compared to young one ( 33.2 msec ). Although there were not significant difference in RMP and Dv/dtmax in both groups, activation times in old SHR were significantly prolonged to 39.5% as compared to young one ( 29.7% ) during rapid stimulation. When Ang II ( 10-7M ) was superfused, the frequency of conduction block was increased significantly ( 37.5% ) in old SHR but it did not in young SHR ( 13.6% ). While the frequency of conduction block was decreased under perfusion of ARB plus Ang II.

Conclusion: Ang II accelerated left atrial conduction delay during rapid stimulation in old SHR. If this delay is occurred in heterogeneous order due to aging and also remodeling, reentrant tachyarrhythmias may be persist, while ARB will inhibits it .