Effect Of Zhiganeao Decoction On Atrial Electrical And Structural Remodeling Reduced By Rapid Atrial Pacing In Rabbits

[Objective]Though studying the effects of Zhigancao Decoction on atrial myocytes effective refractory period (AERP), AERP rate adaptability, inducibility and duration of induced atrial myocytes fibrillation (AFIc and AFDr) and atrial myocytes structural changs. This study is to investigate the effects of Zhigancao Decction (ZD) on atrial electrical remodeling (AER) and structural remodeling (SR) induced by rapid atrial pacing(RAP) in rabbits and to explore the prevention and therapy mechanism of ZD on atrial fibrillation (AF)[Methods]Eighteen rabbits were randomly divided into control group (n=6), pacing group (n=6) and drug group (n=6). ZD21ml (equivalent to47.25g crude drug) was given to rabbits by intragastric adminis-tration5days before starting rapid right atrial pacing in drug group, and equal volume saline was administered in control group and pacing group. After medial thoracotomy was performed, stimulating electrode was sutured to right atrial appendage of rabbits, the recording electrode was sutured to left atrium, rabbits were paced at600beats per minute for8hours in pacing group and drug group, whereas they were not paced in control group. After pacing8hours, the monophasic action potential (MAP)recording and heart program electric stimulation techniques (S1S2)were used to measure atrial effective refractory period (AERP) under different basic pacing cycle length(200ms and150ms), rate adaptability of AERP, inducib-ility and duration of induced AF. At last, the rabbits were killed and left atrial myocytes tissue specimen was fixated and examined by electron microscope in order to observe the ultrastructure in three groups.[Results](1) The AERP was significantly shortened, and the rate adap-tability of AERP was markly decreased in pacing group (P<0.05) Moreover, the inducibility and duration of induced AF were increased (P<0.05) in pacing group, and the difference between drug group and control group had no statistical signif icance(P>0.05).(2) Electronic microscopy findings of left atrial myocytes:in control group,a well arranged sarcomeric structure with rows of uniformly sized mitochondria.Cristae of mitochondria lined up in order. obviously, atrial muscle fiber disorder, swelling mitochon-dria, irregular shape,cell vacuole, and crista disorder,and even fusion or disappeared were seen in pacing group. The ultrastructure change was seen in drug group were simi lar to that observed in pacing group:parts of atrial muscle fiber disorder,swelling mitochon-dria, irregular shape, cell vacuole, and crista unclear, disorder, and even fusion or disappeared.[Concludes](1)Atrial electrical remodeling and ultrastructure changes were induced by rapid right atrial pacing8h persistently in rabbits, Which including:①The AERP was significantly shortened, and the rate adaptabil-ity of AERP was markly decreased in pacing group(P<0.05). Moreover, the inducibility and duration of induced AF were increased (P<0.05) in pacing group, and the difference between drug group and control group had no statistical significance (P>0.05).②Ultrastructural observation:in control group, a well arrang-ed sarcomeric structure with rows of uniformly sized mitochondr-ia. Cristae of mitochondria lined up in order. obviously, atrial muscle fiber disorder, swelling mitochondria, irregular shape,cell vacuole,and crista disorder, and even fusion or disappeared were seen in pacing group. The ultrastructure change was seen in drug group were similar to that observed in pacing group:parts of atrial muscle fiber disorder, swelling mitochondria, irregular shape, cell vacuole,and crista unclear, disorder,and even fusion or disappeared.(2) ZD can inhibit atrial electrical remodeling,but can not reverse atrial structural remodeling induced by rapid right atrial pacing, which may be prevention and therapy mechanism of ZD on AF.