ekg for sts.docx

1、ekg for stsElectrocardiographyanterior 前面的baseline 基线bipolar 双极的coronary 冠状动脉deflection 偏转depolarization 去偏极electrocardiography 心电图electrode 电极horizontal direction 水平方向hyperthyroidism 甲状腺机能亢进interpretation 插值intracardiac 心脏内的ischemia 缺血isoelectric 等电位的lead 导联passband 通带precordial 心前区的RR interval R间期

2、ST segment ST段transthoracic 经胸廓的unipolar 单极的vector 矢量、向量ventricular 心室Pre-readingHave you ever had an ECG?Where do you see ECGs in the movies?What happens when an ECG give a flatline? Reading 1 ElectrocardiographyHistoryFocusThe part is entitled Histroy, thus it will provide the background to the to

3、pic. Its purpose is to introduce you to the field, so dont worry about every detail too much. Focus on the date of developments and what was happening around the same time and what is still in use today. Alexander Muirhead is reported to have attached wires to a feverish patients wrist to obtain a r

4、ecord of the patients heartbeat while studying for his Doctor of Science (in electricity) in 1872 at St Bartholomews Hospital.5 This activity was directly recorded and visualized using a Lippmann capillary electrometer by the British physiologist John Burdon Sanderson.6 The first to systematically a

5、pproach the heart from an electrical point-of-view was Augustus Waller, working in St Marys Hospital in Paddington, London.7 His electrocardiograph machine consisted of a Lippmann capillary electrometer fixed to a projector. The trace from the heartbeat was projected onto a photographic plate which

6、was itself fixed to a toy train. This allowed a heartbeat to be recorded in real time. In 1911 he still saw little clinical application for his work.Einthovens ECG deviceAn initial breakthrough came when Willem Einthoven, working in Leiden, Netherlands, used the string galvanometer that he invented

7、in 1903.8 This device was much more sensitive than both the capillary electrometer that Waller used and the string galvanometer that had been invented separately in 1897 by the French engineer Clment Ader.9 Rather than using todays self-adhesive electrodes Einthovens subjects would immerse each of t

8、heir limbs into containers of salt solutions from which the ECG was recorded.Einthoven assigned the letters P, Q, R, S and T to the various deflections, and described the electrocardiographic features of a number of cardiovascular disorders. In 1924, he was awarded the Nobel Prize in Medicine for hi

9、s discovery.10Though the basic principles of that era are still in use today, there have been many advances in electrocardiography over the years. The instrumentation, for example, has evolved from a cumbersome laboratory apparatus to compact electronic systems that often include computerized interp

10、retation of the electrocardiogram.11Before you proceed What other developments were happening around this time?What do you think is still in use today? ElectrocardiographyFocusWhere did the name Electrocardiography come from? Why would an English doctor write EKG instead of ECG? Electrocardiography

11、(ECG or EKG from the German Elektrokardiogramm) is a transthoracic (across the thorax or chest) interpretation of the electrical activity of the heart over a period of time, as detected by electrodes attached to the outer surface of the skin and recorded by a device external to the body.1 The record

12、ing produced by this noninvasive procedure is termed an electrocardiogram (also ECG or EKG).The etymology of the word is derived from the Greek electro, because it is related to electrical activity, cardio, Greek for heart, and graph, a Greek root meaning to write. In English speaking countries, med

13、ical professionals often write EKG (the abbreviation for the German word elektrokardiogramm) in order to avoid confusion with EEG in emergency situations where background noise is high.Most ECGs are performed for diagnostic or research purposes on human hearts, but may also be performed on other ani

14、mals, usually for research.Before you proceedWhere did the name Electrocardiography come from? Why would an English doctor write EKG instead of ECG? FunctionFocus How an ECG works. The ECG device detects and amplifies the tiny electrical changes on the skin that are caused when the heart muscle depo

15、larizes during each heartbeat. At rest, each heart muscle cell has a charge across its outer wall, or cell membrane. Reducing this charge towards zero is called depolarization, which activates the mechanisms in the cell that cause it to contract. During each heartbeat a healthy heart will have an or

16、derly progression of a wave of depolarisation that is triggered by the cells in the sinoatrial node, spreads out through the atrium, passes through intrinsic conduction pathways and then spreads all over the ventricles. This is detected as tiny rises and falls in the voltage between two electrodes p

17、laced either side of the heart which is displayed as a wavy line either on a screen or on paper. This display indicates the overall rhythm of the heart and weaknesses in different parts of the heart muscle.Usually more than 2 electrodes are used and they can be combined into a number of pairs (For e

18、xample: Left arm (LA), right arm (RA) and left leg (LL) electrodes form the three pairs LA+RA, LA+LL, and RA+LL). The output from each pair is known as a lead. Each lead is said to look at the heart from a different angle. Different types of ECGs can be referred to by the number of leads that are re

19、corded, for example 3-lead, 5-lead or 12-lead ECGs (sometimes simply a 12-lead). A 12-lead ECG is one in which 12 different electrical signals are recorded at approximately the same time and will often be used as a one-off recording of an ECG, traditionally printed out as a paper copy. 3- and 5-lead

20、 ECGs tend to be monitored continuously and viewed only on the screen of an appropriate monitoring device, for example during an operation or whilst being transported in an ambulance. There may or may not be any permanent record of a 3- or 5-lead ECG, depending on the equipment used.Before you proce

21、ed What is a lead?What are the 3 basic kinds of ECG? Which on is commonly printed on paper? ECG graph paperFocusThe layout of ECG paper on how to read it. One second of ECG graph paperThe output of an ECG recorder is a graph (or sometimes several graphs, representing each of the leads) with time rep

22、resented on the x-axis and voltage represented on the y-axis. A dedicated ECG machine would usually print onto graph paper which has a background pattern of 1mm squares (often in red or green), with bold divisions every 5mm in both vertical and horizontal directions.It is possible to change the outp

23、ut of most ECG devices but it is standard to represent each mV on the y axis as 1cm and each second as 25mm on the x-axis (that is a paper speed of 25mm/s). Faster paper speeds can be used, for example, to resolve finer detail in the ECG. At a paper speed of 25mm/s, one small block of ECG paper tran

24、slates into 40ms. Five small blocks make up one large block, which translates into 200ms. Hence, there are five large blocks per second. A calibration signal may be included with a record. A standard signal of 1mV must move the stylus vertically 1cm, that is, two large squares on ECG paper.LayoutBy

25、definition, a 12-lead ECG will show a short segment of the recording of each of the 12-leads. This is often arranged in a grid of 4 columns by three rows, the first columns being the limb leads (I,II and III), the second column the augmented limb leads (aVR, aVL and aVF) and the last two columns bei

26、ng the chest leads (V1-V6). It is usually possible to change this layout so it is vital to check the labels to see which lead is represented. Each column will usually record the same moment in time for the three leads and then the recording will switch to the next column which will record the heart

27、beats after that point. It is possible for the heart rhythm to change between the columns of leads.Each of these segments is short, perhaps 1-3 heart beats only, depending on the heart rate and it can be difficult to analyse any heart rhythm that shows changes between heart beats. To help with the a

28、nalysis it is common to print one or two rhythm strips as well. This will usually be lead II (which shows the electrical signal from the atrium, the P-wave, well) and shows the rhythm for the whole time the ECG was recorded (usually 56 seconds). Some ECG machines will print a second lead II along th

29、e very bottom of the paper in addition to the output described above. This printing of Lead II is continuous from start to finish of the process.The term rhythm strip may also refer to the whole printout from a continuous monitoring system which may show only one lead and is either initiated by a cl

30、inician or in response to an alarm or event.Before you proceedHow is ECG graphpaer layed out?What can make it hard to read? Reading ComprehensionWhat is the difference between ECG and EKG?What does an ECG measure?What is a lead?What are the basic types of ECG?When are they used? What does ECG graphp

31、aper look like? Pre-readingReading 2Focus Different uses of the word lead. LeadsThe term lead in electrocardiography causes much confusion because it is used to refer to two different things. In accordance with common parlance the word lead may be used to refer to the electrical cable attaching the

32、electrodes to the ECG recorder. As such it may be acceptable to refer to the left arm lead as the electrode (and its cable) that should be attached at or near the left arm. There are usually ten of these electrodes in a standard 12-lead ECG.Alternatively (and some would say properly, in the context of electrocardiography) the word lead may refer to the tracing of the voltage difference between two of the electrodes and is what is actually produced by