医学数字信号处理心电图课件.ppt

1、资料仅供参考,不当之处，请联系改正。霍金教授的办公室（剑桥大学）“我的书每增加一个公式，读者就减少一半”霍金教授资料仅供参考,不当之处，请联系改正。BME在百年诺贝尔生理与医学奖中的份额 美国的保罗美国的保罗-劳特布尔和英国的彼得劳特布尔和英国的彼得-曼斯菲尔德共同获得了曼斯菲尔德共同获得了2003年年诺贝尔生理学或医学奖诺贝尔生理学或医学奖-核磁共振成像技术核磁共振成像技术-三维图象三维图象百年总计(1901-2000)91（届次）100%属于BME范畴1618 %与BME密切相关1314 %不采用BME方法、技术、设备与材料就不能完成的3943 %与BME无关的2325%资料仅供参考,不当

2、之处，请联系改正。教材作者：美国威斯康辛大学电气与计算机工程系教授 前IEEE生物医学工程学会主席 Willis J.Tompkins书名：Biomedical Digital Signal ProcessingISBN：7560925790页数：246资料仅供参考,不当之处，请联系改正。Lecture 2ElectrocardiologyElectrocardiogramECG 第第2讲讲心电学心电学资料仅供参考,不当之处，请联系改正。心脏机械收缩之前，先产生电激动，心房和心室的电激心脏机械收缩之前，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。心电图是利用心电图机从体表动可经人体组

3、织传到体表。心电图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曲线图形。记录心脏每一心动周期所产生电活动变化曲线图形。资料仅供参考,不当之处，请联系改正。心脏的特殊传导系统由窦房结、结间束（分为前、中、后结间束）、房间束（起自结间束，称Bachmann束）、房间交界区（房室结、希氏束）、束支（分为左、右束支，左束支又分为前分支和后分支）以及普肯耶纤维（Pukinje fiber）构成。心脏传导系统与每一心动周期顺序出现的心电变化密切相关。正常心电活动始于窦房结，兴奋心房的同时经结间束传导至房室结（激动传，然后循希氏束-左、右束支-普肯耶纤维顺序传导，最后兴奋心室。这种先后有序的电激

4、动的传播，引起一系列电位改变，形成了心电图上相应的波段。资料仅供参考,不当之处，请联系改正。 心电图机是记录心电图的专用仪器，有单道心电图机和多道心电图机，多道心电图机可以同时记录多导联的心电，最多有同时记录12导联的，而单道心电图机只能顺序记录12个导联，有手控的心电图机，也有程控的、微电脑控制或数字式的心电图机，在很多其它仪器中也常有心电记录电路模块。三道心电图机 顺序记录导联心电图后重新排列在一幅纸上运动心电图记录系统 资料仅供参考,不当之处，请联系改正。2.1Electrocardiologicbasis 2.1 心电学基础心电学基础2.1.1 three basic techniqu

5、es 2.1.1 三种基本技术三种基本技术1. Standard clinical ECG（12 leads） 1. 标准临床标准临床 ECG （12 导联导联） 2. VCG (3 orthogonal leads) 3. Monitoring ECG (1 or 2 lead(s) ) 2. 向量心电图向量心电图 (三维正交导联三维正交导联) 3. 监护监护 ECG (1或或2 导联导联) 资料仅供参考,不当之处，请联系改正。2.1.2 Electrodes 2.1.2 电极电极Figure 2.3 A silver-silver chloride ECG electrode. Many

6、modern electrodes have electrolyte layers that are made of a firm gel which has adhesive properties. The firm gel minimizes the disturbance of the charge double layer.资料仅供参考,不当之处，请联系改正。2.1.3 心电等效心电等效发生器发生器Figure 2.4 Both the electrical and mechanical conditions of the heart are involved in determini

7、ng the characteristics of the spread of electrical activity over the surface of the heartA model of this activity is called a cardiac equivalent generator2.1.3 The cardiac equivalent generator 资料仅供参考,不当之处，请联系改正。Figure 2.5 Einthoven equilateral triangle. RA and LA are the right and left arms and LL i

8、s the left leg. 资料仅供参考,不当之处，请联系改正。A current dipole is a current source and a current sink separated by a distance. Since such a dipole has magnitude and direction which change throughout a heartbeat as the cells in the heart depolarize, this leads to the vector representation. 电流偶极子是相隔一段电流偶极子是相隔一段距离

9、的电流源和穴距离的电流源和穴(漏漏)。当心肌细胞去极化当心肌细胞去极化 (读注：读注：实际应包含反极化和复实际应包含反极化和复极化极化)时，这样一个偶极时，这样一个偶极子的大小和方向在整个子的大小和方向在整个心搏周期都是变化的，心搏周期都是变化的，这就导致了向量表示法。这就导致了向量表示法。 P(t) = Px(t)X P(t) = Px(t)X 十十 Py(t)Y Py(t)Y 十十 Pz(t)Z (2.1)Pz(t)Z (2.1)Where P(t) is the time-varying cardiac vector, Pi(t) are the orthogonal component

10、s of the vector also called scalar leads, and X,Y,Z are unit vectors in the x, y, z directions.式中式中P(t) 是时变心脏偶极是时变心脏偶极子，子，Pi(t) 为该矢量的正交为该矢量的正交分量，也称为标量导联，分量，也称为标量导联， X,Y,Z 是是X,Y,Z方向的单位方向的单位矢量。矢量。资料仅供参考,不当之处，请联系改正。The forward solution provides the potential at any arbitrary point on the body surface f

11、or a given cardiac dipole. Expressed mathematically，对于给定的心电偶极子，对于给定的心电偶极子，心电正问题的解提供了心电正问题的解提供了体表任意点的电位，数体表任意点的电位，数学上表示为，学上表示为，v vn(t) = tnxPx(t)十十tnyPy(t)十十tnzPy(t) (2.2)This forward so1utlon shows that the potential vn(t) ( ie, ,the ECS) at any point n on the body surface is given by the linear sum

12、 of the products of a set of transfer coefficients tn i unique to that point and the Corresponding orthogonal dipole vector components Pi(t) 资料仅供参考,不当之处，请联系改正。The ECSs are time-varying as are the dipo1e components, while the transfer coefficients are only dependent on the t h o r a c i c g e o m e t

13、 r y a n d inhomogeneitiesThus for a set of k body surface potentials (i. e., 1eads)， there is a set of k equations that can be expressed i n m a t r i x f o r m V = TP (2.3) Where V is a k x l vector representing the time-varying potentials, T is a k x 3 matrix of transfer coefficients, Which are f

14、ixed for a given individual, and P is the 3 x 1 time-varying heart vector心电信号与偶极子分心电信号与偶极子分量一样是时变的，而量一样是时变的，而传递系数则只决定于传递系数则只决定于胸部的几何形状和非胸部的几何形状和非均匀性。因此，一组均匀性。因此，一组 k 体表电位体表电位(即即, 导联导联)， 就有就有 k equations个个方程的方程组，并可方程的方程组，并可表示成矩阵形式。表示成矩阵形式。 资料仅供参考,不当之处，请联系改正。Of course, the heart vector and transfer co

15、efficients are unknown for a given individualHowever if we had a way to compute this heart vectorWe could use it in the so1ution of the forward problem and obtain the ECS for any body surface locationThe approach to solving this problem is based on a physical model of the human torsoThe model provid

16、es transfer coefficients that relate the potentials at many body surface points to the heart vector. With this information，we se1ect three ECS leads that summarize the intrinsic characteristics of t h e d e s i re d a b n o r m a l E C S t o simulateThen we solve the inverse problem to find the card

17、iac dipole vector.自然，对于任一个体心自然，对于任一个体心脏向量脏向量P和传递系数和传递系数T 是未知的。然而，若我是未知的。然而，若我们有计算心脏矢量的方们有计算心脏矢量的方法，就可用之解正问题法，就可用之解正问题并获得任意体表位置的并获得任意体表位置的ECS。解此类问题的方解此类问题的方法建立在人体胸廓物理法建立在人体胸廓物理模型的基础上。该模型模型的基础上。该模型提供了众多体表点的电提供了众多体表点的电位与心脏向量的关系的位与心脏向量的关系的传递系数。用该信息，传递系数。用该信息，则只选择三个则只选择三个ECS导联导联就能概括欲模拟的所希就能概括欲模拟的所希望的异常望的

18、异常ECS的本质特的本质特征。然后，就解逆问题征。然后，就解逆问题以求出心脏偶极向量。以求出心脏偶极向量。资料仅供参考,不当之处，请联系改正。Thus, for three heart vector component, there are three linear equations of the form因此，对于因此，对于 三个心脏向三个心脏向量的分量，有如下形式的量的分量，有如下形式的三个线性方程三个线性方程 Px(t) = bx1v1(t) + b x2 v2(t) + + bxk vk(t) (2.5) P = BV (24) Where B is a 3 x k matrix o

19、f lead coefficients that is directly derived from inverting the transfer coefficients matrix T. 资料仅供参考,不当之处，请联系改正。If we select k body surface ECS leads v1(t), v2(t), ， vk(t) for which the lead coefficients，T (or B)，are known from the physical model of the human torso, we can solve the inverse proble

20、m and compute the timevarying heart vector, P, using Eq. (2.4). Once we have these dipole components, we solve the forward problem using Eq. (2.3) to compute the ECS for any point on the body surface.如果选择了如果选择了K个体表个体表E C S 导 联导 联 v1( t ) , v2(t), vk(t) ，且由且由人体胸廓的物理模型人体胸廓的物理模型得知了导联系数得知了导联系数T (或或B） ，则

21、就可由，则就可由(2.4)式求解逆问题并计算式求解逆问题并计算时变的心脏向量时变的心脏向量P 。一旦有了这些偶极分一旦有了这些偶极分量，则就可用方程量，则就可用方程(2.3)解正问题以计算任意解正问题以计算任意点的点的ECS.资料仅供参考,不当之处，请联系改正。2.1.4 Genesis of the ECS2.1.4 心电的起源心电的起源Time varying motion of the cardiac vector produces the body surface ECS for one heartbeat with its characteristic P and T waves a

22、nd QRS complex.心脏向量的时变运动心脏向量的时变运动产生体表心电，每搏产生体表心电，每搏都有其都有其 特征性的特征性的P、T 波和波和QRS复合波。复合波。Figure 2.7 Basic configuration for recording an electrocardiogram. Using electrodes attached to the body, the ECG is recorded with an instrumentation amplifier. (a) Transverse (top) view of a slice of the body showi

23、ng the heart and lungs. (b) Frontal view showing electrodes connected in an approximate lead II configuration. 资料仅供参考,不当之处，请联系改正。For the points in time that the vector points toward the electrode connected to the positive terminal of the amplifier, the output ECS will be positive-goingIf it points t

24、o the negative electrode，the ECS will be negative(The following statement is better and more detailed. “If the vector points to the electrode connected to the negative terminal of the amplifier, the ECS will be negative”) ) 在心脏矢量指向的在心脏矢量指向的电极连到放大器正电极连到放大器正端的那些时间点，端的那些时间点，输出的输出的ECS为正的。为正的。若心电向量指向的若心电

25、向量指向的电极连到放大器负电极连到放大器负端，则输出的端，则输出的ECS为负的。为负的。资料仅供参考,不当之处，请联系改正。Figure 2.8 Electrocardiogram (ECG) for one normal heartbeat showing typical amplitudes and time duration for the P, QRS, T waves. 资料仅供参考,不当之处，请联系改正。Figure 2.9 Relationship between the spread of cardiac electrical activation represent at v

26、arious time instants by a summing vector (in the upper frames) and the genesis of t h e E C S ( i n t h e l o w e r f r a m e s ) . 资料仅供参考,不当之处，请联系改正。 In Figure 2.9(a), the slow moving depolarization of the atria which begins at the sinoatrial(SA) node produces the P wave. As Figure 2.9(b) shows, th

27、e signal is delayed in the atrioventricular (AV) node resulting in an isoelectric region after the P wave, then as the Purkinje system starts delivering the stimulus to the ventricular muscle, the onset of the Q wave occurs. In Figure 2.9(c), rapid depolarization of the ventricular muscle is depicte

28、d as a large, fast-moving vector which begins producing the R wave. Figure 2.9(d) illustrates that the maximal vector represents a point in time when most of the cells are depolarized, giving rise to the peak of the R wave. In Figure 2.9(e), the final phase of ventricular depolarization occurs as th

29、e excitation spreads toward the base of the ventricles (to the top in the picture) giving rise to the S wave.资料仅供参考,不当之处，请联系改正。 In Figure 2.9(a), the slow moving depolarization of the atria which begins at the sinoatrial(SA) node produces the P wave. As Figure 2.9(b) shows, the signal is delayed in

30、the atrioventri-cular (AV) node resulting in an isoelectric region after the P wave, then as the Purkinje system starts delivering the stimulus to the ventricular muscle, the onset of the Q wave occurs. In Figure 2.9(c),rapid depolarization of the ventricular muscle is depicted as a large, fast-movi

31、ng vector which begins producing the R wave. Figure 2.9(d) illustrates that the maximal vector represents a point in time when most of the cells are depolarized, giving rise to the peak of the R wave. In Figure 2.9(e), the final phase of ventricular depolarization occurs as the excitation spreads to

32、ward the base of the ventricles (to the top in the picture) giving rise to the S wave. 图图2.9(a)中，始于窦房中，始于窦房结的、慢运动的心房结的、慢运动的心房去极化，产生去极化，产生P波。波。正如图正如图2.9(b)所示，所示，信号通过房室结时被信号通过房室结时被延迟，产生延迟，产生P波后的波后的等电区。然后，当等电区。然后，当Purkinje系统开始发系统开始发送刺激到心室肌时，送刺激到心室肌时，Q波开始发生波开始发生。在图。在图2.9(c)中，心室肌的中，心室肌的快速去极化表现为大快速去极化表现为大

33、而快速运动的矢量，而快速运动的矢量，开始产生开始产生R波。图波。图2.9(d)说明，最大矢说明，最大矢量代表了大多数细胞量代表了大多数细胞去极化的时间点，产去极化的时间点，产生生R波的峰。图波的峰。图2.9(e)是激动向心室的基底是激动向心室的基底部部(向图的顶部向图的顶部)传播传播时的心室去极化的终时的心室去极化的终末时相，产生末时相，产生S波。波。资料仅供参考,不当之处，请联系改正。2.1.5 The standard limb leads 2.1.5 标准肢体导联标准肢体导联I + III II = 0 (2.6) Figure 2.10 Leads I, II and III are

34、the potentials difference between the limbs as indicated. RA and LA are the right and left arms and LL is the left leg.From Kirchhoff s voltages law, the sum of the voltages around a loop equals zero. Thus 资料仅供参考,不当之处，请联系改正。2.1.6 The augmented limb leads 2.1.6 加压肢体导联加压肢体导联 Figure 2.11 The augmented

35、limb lead aVL is measured as shown. From the bottom left loop iR+iR-II=0 (2.8)or iR=II/2 (2.9) From the bottom right loop i iR+III+aVL=0 (2.10)R+III+aVL=0 (2.10)Or aVL=iOr aVL=iRIII (2.11)RIII (2.11)Combining Eqs. (2.9) and (2.11) givesaVL=II/2III=(II-2aVL=II/2III=(II-2III)/2 (2.12)III)/2 (2.12) Fro

36、m the top center loop II = III + I (2.13)II = III + I (2.13) Substituting gives Substituting gives aVL=(IIII-2aVL=(IIII-2III)/2=(IIII)/2 (2.14)III)/2=(IIII)/2 (2.14)资料仅供参考,不当之处，请联系改正。2.2 ECS lead systems 2.2 心电导联系统心电导联系统 心电学中有三种常用的心电学中有三种常用的基本导联系统。最通用基本导联系统。最通用的是的是12导联方法，该法导联方法，该法定义了定义了12种电位差的集种电位差的

37、集合，构成标准临床合，构成标准临床ECG。第二种导联系统规定了第二种导联系统规定了记录记录VCG的电极位置。的电极位置。典型的监护系统只分析典型的监护系统只分析1或或2个导联。个导联。 There are three basic lead systems used in cardiology. The most popular is the 12-lead approach, which defines the set of 12 potential differences that make up the standard clinical ECG. A second lead system

38、 designates the location of electrodes for recording VCG. Monitoring systems typically analyze one or two leads. 资料仅供参考,不当之处，请联系改正。2.2.1 12 lead ECS 2.2.1 12 导联心电导联心电 资料仅供参考,不当之处，请联系改正。Figure 2.16 Standard 12-lead clinical electrocardiogram. (a) Lead I. (b) Lead II. (c) Lead III. Note the amplifier

39、polarity for each of these limb leads. (d) aVR. (e) VL.(f) aVF. These aug-mented leads require resistor networks which average two limb potentials while recording the third. (g) The six V leads are recorded referenced to Wilsons central terminal which is the average of all three limb potentials. Eac

40、h of the six leads labeled V1-V6 are recorded from a different anatomical site on the chest.资料仅供参考,不当之处，请联系改正。资料仅供参考,不当之处，请联系改正。中心电端C相连。所有单极导联皆参考此点电压。所有输入端皆采 用高输入阻抗电路。资料仅供参考,不当之处，请联系改正。12个标准心电图导联双极肢体导联：I、II、III单极加压肢体导联：aVL、aVR、aVF胸导联：V1、V2、V3、V4、V5、V6电极安放的位置：肢体导联监护导联资料仅供参考,不当之处，请联系改正。Figure 2.17 The

41、 12-lead ECG of a normal patient. Calibration pulses on the left side designate 1 mV. The recording speed is 25 mm/s. Each minor division is I mm, so the major division are 5 mm. Thus in lead I, the R-wave amplitude is about 1.1 mV and the time between beats is almost 1 S (i. e., heart rate is about

42、 60 bpm). The notes are ID 0042804, S=26, L=2, C=1, I, II, III, aVR, aVL, aVF, V1, V2, V3, V4, V5, V6, Patient NO: 4307400 respectively. 资料仅供参考,不当之处，请联系改正。2.2.2 VCS lead system2.2.2 向量心电导联系统向量心电导联系统Figure 2.18 The electrode placement for the Frank vector ECS system.Figure 2.19 The resistor network f

43、or combining body surface potentials to produce the three time-varying scalar leads of the Frank VCS lead system. 资料仅供参考,不当之处，请联系改正。Figure 2.20 The vectorcardiogram of a normal male patient. The three time-varying scalar leads for one heartbeat are shown on the left and are the x, y and z leads from

44、 top to bottom. In the top center is the frontal view of the tip of the vector as it moves throughout one computed heartbeat. In bottom center is a transverse view of the vector loop looking down from above the patient. On the far right is a left sagittal view looking toward the left side of the pat

45、ient. 资料仅供参考,不当之处，请联系改正。2.2.3 Monitoring ECS lead system2.2.3 监护心电导联系统监护心电导联系统Monitoring application do not use standard electrode positions but typically use two leads. Since the principal goal of these systems is to reliably recognize each heartbeat and perform rhythm analysis, electrodes are plac

46、ed so that the primary ECS has a large R-wave amplitude. This ensures a high signal-to-noise ratio for beat detection. Since Lead II has a large peak amplitude for many patients, this lead is frequently recommended as the first choice of a primary lead by many manufacturers. A secondary lead with di

47、fferent electrode placements serves as a backup in case the primary lead develops problems such as loss of electrode contact. 监护应用不采用标准电极位置，典型使用两个导联。因该系统的主要目标是可靠识别每一心搏，完成节律分析，所以电极的放置以能获得最大R波幅度为准，这样就能保证检测心搏时有高的信噪比。因II导联对很多病人都有大的峰值，故该导联常被很多厂家推荐为首选导联。第二种导联有各种电极方法，作为主要导联发生问题(如电极接触不良)时的备用导联。资料仅供参考,不当之处，请

48、联系改正。2.3 ECS characteristics2.3 心电信号特征心电信号特征Figure 2.21 Bandwidth used in electrocardiography. The standard clinical bandwidth for the 12-lead clinical ECG is 0.005-250Hz. Monitoring systems typically use a bandwidth of 0.5-50Hz. Cardiotachometers for heart rate determination of subjects with predom

49、inantly normal beats use a simple bandpass filter centered at 17Hz and with a Q(Q-factor: quality factor) of about 3 or 4.资料仅供参考,不当之处，请联系改正。心电图机原理心电图机原理体表心电经电极、导联线送至心电图机，心电图机主体从原理上可分为输入回路、导联选择、放大电路、描笔驱动和走纸部分，现代心电图机通常还有程控部分。资料仅供参考,不当之处，请联系改正。资料仅供参考,不当之处，请联系改正。资料仅供参考,不当之处，请联系改正。导联线导联线是连接电极和心电图机的多股电缆线，各股电缆线应绞合在一起以减小磁场干扰，并屏蔽以减少电场干扰。 导联线导联线可记录的导联可记录的导联3芯线I or II or III5芯线aVR, aVL, aVF, V12芯线I, II, III, aVR, aVL, aVF, V1-V6资料仅供参考,不当之处，请联系改正。谢谢！谢谢！