Effects of Losartan on acute atrial electrical remodeling.
BACKGROUND
Atrial electrical remodeling (AER) contributes to the maintainance of atrial fibrillation (AF). This study was to compare the effects of Losartan with those of Diltiazem on tachycardia-induced acute AER in rabbits.


METHODS
Twenty-one rabbits paced with maximal atrial capture rate for 3 hours in the right atrium (RA) were randomly divided into saline group, Diltiazem group and Losartan group. After autonomic blockage, we measured atrial effective refractory period (AERP), AERP rate adapting feature, AERP dispersion and RA conduction time at basic cycle lengths (BCLs) of 200 ms and 150 ms at baseline, 0.5 hour, 1 hour, 2 and 3 hours after rapid atrial pacing.


RESULTS
In the saline group, there was a prompt decrease in AERP as a result of rapid atrial pacing, and AERP200 and AERP150 were shortened sharply within 0.5 hour of pacing (30.2 +/- 10.5 ms and 24.1 +/- 9.1 ms, respectively). The AERP did not change dramatically in the Diltiazem and Losartan groups. In the saline group, the value of (AERP200-AERP150)/50 ms in high RA was 0.17 +/- 0.08 at baseline and became significantly smaller at 0.5 hour (0.08 +/- 0.06), 1 hour (0.09 +/- 0.06), 2 hours (0.08 +/- 0.04) and 3 hours (0.09 +/- 0.05) (all P < 0.05), suggesting a reduction of rate adaptation of AERP. The value of (AERP200-AERP150)/50 ms in high RA did not change during the 3 hours of pacing in both Diltiazem and Losartan groups. In the saline group, AERP dispersion increased significantly at 2 and 3 hours (P < 0.05). However, Diltiazem could not prevent the increase of AERP dispersion at 3 hours (P < 0.05). During Losartan infusion, the AERP dispersion was no longer increased after rapid atrial pacing. There was no significant difference in RA conduction time among the three groups.


CONCLUSIONS
Like calcium antagonist Diltiazem, Losartan could prevent AERP shortening and preserve rate adaptation of AERP after rapid atrial pacing. Losartan is more effective than Diltiazem in inhibiting the increase of AERP dispersion.
Li
Yue
Y
Department of Cardiology, First Clinical College, Harbin Medical University, Harbin 150001, China. ly99ly@public.hr.hl.cn
Li
Wei-min
WM
Xue
Jing-Yi
JY
Han
Wei
W
Yang
Shu-sen
SS
Gu
Hong-yue
HY
D000818:Animals; D001281:Atrial Fibrillation / Q000188:drug therapy* / Q000503:physiopathology; D002118:Calcium / Q000378:metabolism; D002304:Cardiac Pacing, Artificial; D004110:Diltiazem / Q000494:pharmacology; D006329:Heart Conduction System / Q000187:drug effects / Q000503:physiopathology; D019808:Losartan / Q000494:pharmacology*; D011817:Rabbits; D012032:Refractory Period, Electrophysiological / Q000187:drug effects
D004110:Diltiazem; D019808:Losartan; D002118:Calcium