范本片段

第一节Section I 心电学基础知识（心电产生原理）Basic knowledge of electrocardiology (ECG generating principle)

心脏机械收缩之前，先产生电激动，心房和心室的电激动可经人体组织传到体表。Before the heart carries out the mechanical contraction, it will produce the electric activation and those atrial and ventricular electric activation can be transmitted to the body surface via human tissues. 心电图( electrocardiogram，ECG)是利用心电图机从体表记录心脏每一心动周期所产生电活动变化的曲线图形。Electrocardiogram (ECG) is a curvilinear figure of electrical activities by using ECG device to record the each cardiac cycle on the body surface.

心肌细胞在静息状态时，膜外排列阳离子带正电荷，膜内排列同等比例的阴离子带负电荷，保持平衡的极化状态，不产生电位变化。When the myocardial cells are in a quiescent condition, outer membrance permutation of positive ions are with positive charge while the same percentage of intramembrance permutation of negative ions are with negative charge, which will keep a balanced polarized state without producing the potential changes. 当细胞一端的细胞膜受到刺激（阈刺激），其通透性发生改变，使细胞内外正、负离子的分布发生逆转，受刺激部位的细胞膜出现除极化，使该处细胞膜外正电荷消失而其前面尚未除极的细胞膜外仍带正电荷，从而形成一对电偶( dipole)。When cell membrance is received the stimulation at one end (threshold stimulus) and its permeability will change that makes the distribution of internal and external positive and negative ions reversed and the stimulated membrance appears depolarization, then the positive charge at this position will be disappeared while its front membrance has not yet depolarized still with the positive charge thereby forming a pair of dipole. 电源（正电荷）在前，电穴（负电荷）在后，电流自电源流入电穴，并沿着一定的方向迅速扩展，直到整个心肌细胞除极完毕。Power source (positive charge) is in the front while the electric cave is behind (negative charge). The current flows into the electric cave from the power source and spreads rapidly along with the certain direction until the depolarization of whole myocardial cells is finished. 此时心肌细胞膜内带正电荷，膜外带负电荷，称为除极( depolarization)状态。At this moment, the myocardial cell membrance is with the positive charge while the outer membrance is with the negative charge, or namely called depolarization state. 嗣后，由于细胞的代谢作用，使细胞膜又逐渐复原到极化状态，这种恢复过程称为复极( repolarization)过程，复极与除极先后程序一致，但复极化的电偶是电穴在前，电源在后，并较缓慢向前推进，直至整个细胞全部复极为止。Afterwards, because of the cellular metabolism, the membrance will be gradually recovered to the polarized state, which is called repolarization. The successive process of repolarization and depolarization is consistent. But the dipole of repolarization is that the electric cave is front and the power supply behind, slowly being pushed forward until the depolarization of whole myocardial cells is finished. 就单个细胞而言，在除极时，检测电极对向电源（即面对除极方向）产生向上的波形，背向电源（即背离除极方向）产生向下的波形，在细胞中部则记录出双向波形。With regard to a single cell, the detecting electrodes subtend the power supply (i.e. face to the direction of depolarization) and generates the upward waves while back to the power supply (i.e. deviate from the direction of depolarization) and generates downward waves in depolarization. The bi-directional waves are recorded in the middle part of cells. 复极过程与除极过程方向相同，但因复极化过程的电偶是电穴在前，电源在后，因此记录的复极波方向与除极波相反。The direction of repolarization and depolarization is the same, but because the dipole of repolarization is with the electric cave front and the power supply behind, so the direction recorded between the repolarization waves depolarization waves is opposite. 需要注意，在正常人的心电图中，记录到的复极波方向常与除极波主波方向一致，与单个心肌细胞不同。In the normal people’s ECG, need to notice that the recorded direction of repolarization waves is usually in accordance with the direction of depolarization, which is different from the single myocardial cell. 这是因为正常人心室的除极从心内膜向心外膜，而复极则从心外膜开始，向心内膜方向推进，其确切机制仍未完全清楚。This is because the normal people’s ventricular depolarization is started in the endocardium towards the epicardium while the repolarization is started in the epicardium towards the endocardium. The exact mechanism has remained unknown. 由体表所采集到的心脏电位强度与下列因素有关：①与心肌细胞数量（心肌厚度）呈正比关系；②与探查电极位置和心肌细胞之间的距离呈反比关系；③与探查电极的方位和心肌除极的方向所构成的角度有关，夹角愈大，心电位在导联上的投影愈小，电位愈弱。The strength of cardiac potential collected from the body surface is related to the following factors: ① It is direct in proportion with the quantity (myocardial thickness) of myocardial cells. ② It is in inverse proportion with the position of probing pole and distance among myocardial cells. ③ It is associated with the angles formed by the direction of probing electrodes and orientation of myocardial depolarization. The bigger the included angle, the smaller the projection and weaker the potential will be in the leads of cardio-electric potential. 这种既具有强度，又具有方向性的电位幅度称为心电“向量”(vector)，通常用箭头表示其方向，而其长度表示其电位强度。This potential amplitude either with strength or directivity is called the ECG “vector” and its direction is often expressed by arrows and the length for potential strength. 心脏的电激动过程中产生许多心电向量。Heart generates many heart ECG vectors during electric activation. 由于心脏的解剖结构及其电活动相当错综复杂，致使诸心电向量间的关系亦较复杂，然而一般均按下列原理合成为“心电综合向量”(resultant vector)：同一轴的两个心电向量的方向相同者，其幅度相加；方向相反者则相减。Due to the complicated cardiac anatomical structure and electrical activities, the relations between ECG vectors are also complex. However, the “ECG resultant vector” is generally compounded according to the following principles: if the directions of two ECG resultant vectors are the same in a same axis, its amplitude is added up while the direction is opposite, its amplitude is subtracted. 两个心电向量的方向构成一定角度者，则可应用“合力”原理将二者按其角度及幅度构成一个平行四边形，而取其对角线为综合向量。When the directions of two ECG resultant vectors form to angles, those two can be made up a piece of parallelogram upon the angles and amplitude by using the principle of “resultant forces” thereby taking the diagonal as a resultant vector. 可以认为，由体表所采集到的心电变化，乃是全部参与电活动心肌细胞的电位变化按上述原理所综合的结果。It may be concluded that ECG changes from the body surface are resulting from all potential changes of myocardial cells taking part in the electrical activities according to the above-mentioned principles.