电针对家兔缺血心肌单相动作电位的影响

<正> 电针能够纠正急性心肌缺血后心脏血液动力学的紊乱,增加心肌张力,调整收缩性能,促使心脏泵血功能好转;还能增加冠脉血流量,改善心肌氧供,恢复心肌的正常代谢,从而缩小缺血性损伤的范围。这些结果提示,电针在改善缺血心肌电稳定性,促使可逆性损伤心肌电活动向正常转化方面有一定的作用。本实验拟采用心肌单相动作电位(Monophasic Ac-tion Potential,简称MAP)为指标,观察电针“内关”对心肌缺血早期电稳定性及可逆性缺血性损伤心肌电活动的影响。

EFFECT OF ELECTRO-ACUPUNCTURE ON MONOPHASIC ACTION POTENTIALS OF THE ISCHEMIC MYOCARDIUM IN RABBITS

It has been reported that the recovary of acute ischemic myocardial injury and ischemic ECG could be promoted by electro-acupuncture(EA) at acupoint "Naiguan", these suggested that EA was favorable to the impro- vement of cardial electric stability in the early stage of ischemia. The present investigation was carried out to study the effect of EA on the ischemic myocardial electric activity, the monophasic action potential (MAP) was used as the index. 30 mongrel rabbits of either sex, weighing 2.3-2.8 kg. were rendomly divided into ischemic, electro-acupuncture and control group. All the ani- mals anesthetized with sodium pentobarbital and incubated with an endo- trachacheal tube. Following artificial positive-pressure ventilation and immobilized with flaxedil, a left thoractomy was performed through the surface of the 4th costa. The heart was exposed and suspend in a pericar- dial cradle. The model of myocardial ischemia in this study was produced by twice ligation of the ventricular branch of the left coronary artery(LVB).LVB was occluded for 8 min first and reperfused for 50 min, then occluded again for 60 min The animals of control group didn't undergo the liga- tion of LVB. The procedure of EA group was the same as the above except perfor- ming EA at "Neiguan" from 1 min after the first ligation to the immediate time after release, and from 1 min to 10 min after the second ligation. MAP was recorded by epicardial contact electrode(ECE).The recording electrode was placed perpendicularly, with the pressure of 150-200g, on the apex of the heart during the first ligation and raperfusion, and in the regions of center and border zone respectively for the second ligation; the referential electrode was placed in the hypoderm of neck. In this study, MAP and standard lead Ⅱ of ECG at different period prior to and after the first ligation and reperfusion, and MAPs at the different period prior to and after the second ligation of LVB were recor- ded. MAP Amplitude(MAPA), MAP Duration of 50% and 90% repolariza- tion(MAPD_(50) and MAPD_(90))were used to evaluate the electric activity condition of myoeardium, ST segment of ECG lead Ⅱ(ST_(Ⅱ))was used to reflex the myocardial isohemic condition in the early stage of LVB occlu- sion. The heart was excised immediately after the experiment was finished, and superperfused with 37℃ normal saline via aorta. The maximal transve- rse and longitudinal diameters of ischemic region were measured roughly. After the first ligation of LVB, the MAPA in the ischemic group was reduced rapidly and decreased by about 50% at 8 min, comparing it with its own value before the ligation(P<0.01).Meanwhile, MAPD_(50) and MAPD_(90) shortened obviously(P<0.01). In EA group, MAPA was decreased only by 27% at 8 min, slight cha- nges of MAPD_(50) were also observed; MAPD_(90) in this group remained essentially unchanged during the occlusion of LVB, comparing three indices with those of ischemic group, the differences were significant(P<0.01). Following the reperfusion in the earlystage of myocardial ischemia, MAPA in ischemic group went up to the maximum in 1-3 min, then, fell down continuously, accompaning with the further shortening of MAPD_(90); on the contrary, the MAPD_(50) in this group had the tendency to recover, although it was still shorter than the pre-ligation value at 50 min(P<0.05). These couldn't be considered as the recovery of the membrane mechanism. However, in EA group, MAPA was almost unchanged after reaching the maximum and similar to that of the control group(P>0.05).MAPD_(50) was also recovered immediately after reperfusion, and returned to the pre-liga- tion value(P>0.05)within 5 min. Moreover, MAPD_(90) was always remai- ned at the level of pre-ligation value(P>0.05)during the whole period of reperfusion. It was suggested that EA could normalize the ischemic myo- cardium which was damaged reversibly. The early changes of MAP both in border zone and center zone of isc- hemic group after the second ljgation of LVB were similar to those after the first ligation, but the degree of MAP alterations in border zone was smaller. As time of occlusion went on, MAPA in center zone declined con- tineously while the changes of MAPD_(50) among the individuals of the isc- hemic group tended to dispersion, these were different from those in bor- der zone which the decrease of MAPA didn't company with the disper- sion of MAPD_(50). The changes of MAP in center zone of EA group were almost same as those of ischemie group, no significant differences were found between two groups. This indicated that EA could hardly act on the ischemic center zo- ne. However, the the declination of MAPA in border zone was slowed do- wn obviously by the EA and MAPD_(50) returned to normal gradually, too. In addition, concomitant with the normalization of electrophysiological condition of border zone, the maximal transverse diameters of ischemic region in all animals of EA group were also reduced remarkedly(P<0.01). All results mentioned above implicated that EA could save the jeopardiz- ed myocardium, reduce the size of infarction, correct the disorder of cardial electric activity and increase the electric stability, these effects will help to reduce the mortality of coronary heart disease resulted from se- rious arrhythmia.