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Below you can find some common examples. ECGs can be magnified by clicking on the image....
|previouspage=Introduction
|previousname=Introduction
|nextpage=Rate
|nextname=Step 1: Heart Rate
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{{authors|
|mainauthor= [[user:Vdbilt|I.A.C. van der Bilt, MD]]
|supervisor=
|coauthor=
|moderator= [[user:Vdbilt|I.A.C. van der Bilt, MD]]
|editor= 
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==How do I begin to read an ECG?==
[[Image:nsr.png|thumb| A short ECG registration of normal heart rhythm (sinus rhythm)]]
[[Image:Normaal ecg.jpg|thumb| An example of a normal ECG. ''Click on the Image for an enlargement'']]
 
Click on the ECG to see an enlargement.
Where do you start when interpreting an ECG?
* on the top left are the patient's information, name, sex and date of birth
* at the right of that are below each other the [[Frequency]], the [[Conduction|conduction times]] (PQ,QRS,QT/QTc), and the [[heart axis]] (P-top axis, QRS axis and T-top axis)
* further to the right is the interpretation of the ECG written (this often misses in a 'fresh' ECG, but later the interpretation of the cardiologist or computer will be added)
* down left is the 'paper speed' (25 mm/s on the horizontal axis), the sensitivity (10mm/mV) and the filter's frequency (40Hz, filters noise from eg. lights)
* finally there is a calibration on the ECG, on the beginning of every lead is a vertical block that shows with what amplitude a 1 mV signal is drawn. So the height and depth of these signals are a measurement for the voltage. If this is not the set at 10 mm, there is something wrong with the machine setting.
* further we have the ECG leads themselves of course, these will be discussed below.
 
Note that the lay-out is different for every machine, but most machines will show the information above somewhere.
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==What does the ECG register?==
;The electrocardiogram:An electrocardiogram (ECG or EKG) is a registration of the heart's electric activity.
Just like skeletal muscles, the heart is electrically stimulated to contract. This stimulation is also called ''activation'' or ''excitation''. Cardiac muscles are electrically charged at rest. The inside of the cell is negatively charged relative to the outside (resting potential). If the cardiac muscle cells are electrically stimulated they depolarize (the resting potential changes from negative to positive) and contract. The electrical activity of a single cell can be registered as the [[action potential]].
As the impulse spreads through the heart, the electric field changes continually in size and direction. The ECG is a graphical visualisation of these electric signals in the heart.
 
==The ECG represents the sum of the action potentials of millions of cardiomyocytes==
[[Image:Hart_cells_en.png|thumb|right|The heart consists of approximately 300 trillion cells]]
[[Image:cells_in_rest_en.png|thumb|right|In rest the heart cells are negatively charged. Through the depolarization by surrounding cells they become positively charged and they contract.]]
[[Image:Ion_currents_en.png|thumb|During the depolarization sodium-ions stream inwards the cell. Subsequently the calcium-ions stream into the cell. These calcium-ions give the actual muscular contraction. Finally the potassium-ions stream out of the cell. During the repolarisation the ion concentration is corrected. On the ECG, an action potential wave coming towards the electrode is shown as a positive (upwards) signal. Here the ECG electrode is represented as an eye.]]
The individual [[action potential|action potentials]] of the individual cardiomyocytes are averaged. The final result which is shown on the ECG is actually the average of trillions of microscopic electronical signals.
{| class="wikitable" align="center" width=385px font-size="70%"
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|<flashow>http://nl.ecgpedia.org/images/5/50/Single_cardiomyocyte.swf|height=350px|width=400px</flashow>
|-
| This movie shows the contraction of a single (rabbit) heart cell. The glass electrode measures the electrical current in the heart cell (with the[[w:Patch_clamp|patch-clamp method]]). The electrical signal is written in blue and shows the actionpotential. ''Courtesy of Arie Verkerk and Antoni van Ginneken, AMC, Amsterdam, The Netherlands''.
|-
|}
 
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==The electric discharge of the heart==
__TOC__
[[Image:conduction_system_en.png|thumb]]
'''The sinal node (SA node) contains pacemakercells which determine the heart frequency.'''
'''First the [[heart|atria]] depolarise and contract, after that the [[heart|ventricles]]'''
The electrical signal between the atria and the ventricles goes from the sinus node, via the atria to the AV-node (atrioventricular transition) to the His bundle and subsequently to the right and left bundle branch, which end in a dense network of Purkinje fibers.
<flashow>http://nl.ecgpedia.org/images/b/bc/Normal_SR_vector.swf|height=300px</flashow>
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==The different ECG waves==
==Ischemia & Myocardial Infarction==
[[File:PQRS_origin_en.png|thumb|left|200px|The origin of the different waves on the ECG]]
<div align="left">
[[Image:Epi_endo_en.png|thumb| The QRS complex is formed by the sum of the electric avtivity of the inner (endocardial) and the outer (epicardial) cardiomyocytes]]
[[Image:coronary_anatomy.png|thumb|300px| An overview of the coronary arteries. LM = 'Left Main' = mainstem; LAD = 'Left Anterior Descending' artery; RCX = Ramus Circumflexus; RCA = 'Right Coronary Artery'.]]
[[Image:Qrs-shapes.png|thumb| Example of the different QRS configurations]]
The [[P_wave_morphology|'''P wave''']] is the result of the atrial depolarization. This depolarization starts in the SA (sino-atrial) node. The signal produces by pacemakercells in the SA node is conducted by the conduction system to the right and left atria. Normal atrial repolarisation is not visible on the ECG (but can be visible during [[atrial infarction]] and [[pericarditis]]).
 
The [[QRS_morphology|'''QRS complex''' ]] is the average of the depolarization waves of the inner (endocardial) and outer (epicardial) cardiomyocytes. As the endocardial cardiomyocytes depolarize slightly earlier than the outer layers, a typical QRS pattern occurs (figure).
 
The [[ST_morphology|'''T wave''']] represents the repolarisation of the ventricles. There is no cardiac muscle activity during the T wave.
 
One heart beat consists of an atrial depolarization --> atrial contraction --> p-wave, ventricular depolarization --> ventricular contraction --> ORS-complex and the resting phase (including the repolarization during the T-wave) between two heart beats.
 
Have a look at this excellent [[http://www-medlib.med.utah.edu/kw/pharm/hyper_heart1.html animation of the heart cycle]]
 
The origin of the '''U wave''' is unknown. This wave possibly results from "afterdepolarizations" of the ventricles.


The letters "Q", "R" and "S" are used to describe the QRS complex:
<div style="width:689px">
*Q: the first negative deflection after the p-wave. If the first deflection is not negative, the Q is absent.
Guess the culprit coronary artery that was occluded in these examples of myocardial infarctions
*R: the positive deflection
*S: the negative deflection after the R-wave


*small print letters (q, r, s) are used to describe deflections of small amplitude. For example: qRS = small q, tall R, deep S.  
{{ImageC |image=ami0001.jpg |link=MI 1|text=[[MI 1]]}}
*R`: is used to describe a second R-wave (as in a [[right bundlebranch block]])
{{ImageC |image=ami0002.jpg |link=MI 2|text=[[MI 2]]}}
See figure for some examples of this.
{{ImageC |image=ami0003.jpg |link=MI 3|text=[[MI 3]]}}
{{ImageC |image=ami0004.jpg |link=MI 4|text=[[MI 4]]}}
{{ImageC |image=ami0005.jpg |link=MI 5|text=[[MI 5]]}}
{{ImageC |image=ami0006.jpg |link=MI 6|text=[[MI 6]]}}
{{ImageC |image=ami0007.jpg |link=MI 7|text=[[MI 7]]}}
{{ImageC |image=ami0008.jpg |link=MI 8|text=[[MI 8]]}}
{{ImageC |image=ami0009.jpg |link=MI 9|text=[[MI 9]]}}
{{ImageC |image=ami0010.jpg |link=MI 10|text=[[MI 10]]}}
{{ImageC |image=ami0011.jpg |link=MI 11|text=[[MI 11]]}}
{{ImageC |image=ami0012.jpg |link=MI 12|text=[[MI 12]]}}
{{ImageC |image=ami0013.jpg |link=MI 13|text=[[MI 13]]}}
{{ImageC |image=Casus2_2.jpg |link=MI 14|text=[[MI 14]]}}
{{ImageC |image=AMI_anterior_LAD.jpg |link=MI 15|text=[[MI 15]]}}
{{ImageC |image=KJcasus5.jpg |link=MI 16|text=[[MI 16]]}}
{{ImageC |image=KJcasus6.jpg |link=MI 17|text=[[MI 17]]}}
{{ImageC |image=KJcasus7.jpg |link=MI 18|text=[[MI 18]]}}
{{ImageC |image=KJcasus8.jpg |link=MI 19|text=[[MI 19]]}}
{{ImageC |image=KJcasus10.jpg |link=MI 20|text=[[MI 20]]}}
{{ImageC |image=KJcasus12.jpg |link=MI 21|text=[[MI 21]]}}
{{ImageC |image=KJcasus13.jpg |link=MI 22|text=[[MI 22]]}}
{{ImageC |image=KJcasus16.jpg |link=MI 23|text=[[MI 23]]}}
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</div>
==The history of the ECG==
</div>
A [[A_Concise_History_of_the_ECG| concise history of the ECG]] is presented in a different chapter.
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==Arrhythmias==
==The ECG electrodes==
{{ImageC |image=Casus2_2.jpg |link=Case 1|text=[[Case 1]]}}
[[Image:limb_leads.png|thumb|The limb leads]]
{{ImageC |image=KJcasus3.jpg |link=Case 2|text=[[Case 2]]}}
[[Image:chest_leads.png|thumb|The chest leads]]
{{ImageC |image=KJcasus9.jpg |link=Case 3|text=[[Case 3]]}}
Electric activity going through the heart, can be measured by external (skin)electrodes. The electrocardiogram (ECG) registers these activities from these electrodes which have been attached on different places on the body. In total, twelve leads are calculated using ten electrodes.
{{ImageC |image=Triblock.png |link=Case 4|text=[[Case 4]]}}
 
{{ImageC |image=JJ00004.jpg |link=Case 5|text=[[Case 5]]}}
The ten electrodes are:
* '''the extremity electrodes:'''
** LA - left arm
** RA - right arm
** N - neutral, on the right leg (= electrical earth or point zero to which the electrical current is measured)
** F - foot, on the left leg
It makes no difference whether the electrodes are attached proximal or distal on the extremities. ''However'', it is best to be uniform in this. (eg. do not attach an electrode on the left shoulder and one on the right wrist).
 
* '''the chest electrodes:'''
** V1 - placed in the 4th intercostal space, right of the sternum
** V2 - placed in the 4th intercostal space, left of the sternum
** V3 - placed between V2 and V4
** V4 - placed 5th intercostal space in the nippleline. Official recommendations are to place V4 under the breast in women.<cite>Kligfield</cite>
** V5 - placed between V4 and V6
** V6 - placed in the midaxillary line on the same height as V4 (horizontal line from V4, so not necessarily in the 5th intercostal space)
 
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==Electrolyte Disorders==
Using these 10 electrodes, 12 leads can be derived. There are 6 extremity leads and 6 precordial leads.
{{ImageC |image=KJcasu17-1.jpg |link=Case 100|text=[[Case 100]]}}
===The Extremity Leads===
{{ImageC |image=KJcasu18-3.jpg |link=Case 101|text=[[Case 101]]}}
[[File:ECGafleidingen.jpg|thumb|left|200px]]
The extremity leads are:
 
*'''I''' from the right to the left arm
*'''II''' from the right arm to the left leg
*'''III''' from the left arm to the left leg
An easy rule to remember: lead '''I''' + lead '''III''' = lead '''II'''
This is done with the use of the height or depth, independent of the wave (QRS, P of T).
Example: if in lead I, the QrS complex is 3 mm in height and in lead III 9mm, the height of the QRS-complex in lead II is 12mm.
 
Other extremity leads are:
 
*'''AVL''' points to the left arm
*'''AVR''' points to the right arm
*'''AVF''' points to the feet
 
The capital A stands for "augmented" and V for "voltage".
 
(aVR + aVL + aVF = 0)
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==Miscellaneous==
Click on the text below the ECG for the '''answers'''. Click on the ECG for '''enlargement of the ECG''' itself...


===The Chest Leads===
<gallery>
The precordial, or chestleads, '''(V1,V2,V3,V4,V5 and V6)''' 'observe' the depolarization wave in the frontal plane
Image:RVDB1.jpg|[[Example 23]]
Image:DVA0011.jpg|[[Example 24]]
Image:DVA0229.jpg|[[Example 25]]
</gallery>


''Example'': V1 is close to the right ventricle and the right atrium. Signals in these areas of the heart have the largest signal in this lead. V6 is the closest to the lateral wall of the left ventricle.
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==Advanced cases==
==Special Leads==
For more advanced cases see:
[[Image:leads_789.png|thumb|Leads V7,V8 and V9 can be helpful in the diagnosis of posterior myocardial infarction]]
*[[Rhythm Puzzles]] by Prof. A.A.M. Wilde, MD, PhD
In case of an inferior wall infarct, extra leads may be used:
*[[Case reports by W.G. De Voogt%2C MD%2C PhD]]
#In a right side ECG, V1 and V2 remain on the same place.V3 to V6 are placed on the same place but mirrored on the chest. So V4 is in the middle of the right clavicle. On the ECG it should be marked that it is a ''Right sided ECG''. V4R (V4 but right sided) is a sensitive lead to diagnose right ventricular infarction.
*The ''[[De Voogt ECG Archive]]'' contains > 2000 categorized ECGs
#Leads V7-V8-V9 can be used to diagnose a posteriorinfarct. It is means that after V6, leads are placed towards the back. See the chapter[[Ischemia]] for other ways of diagnosing posterior infarction.
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{{:Technical Problems}}
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==References==
<biblio>
#Dubois Du Bois-Reymond, E. ''Untersuchungen über thierische Elektricität''. Reimer, Berlin: 1848.
#Hoffa Hoffa M, Ludwig C. 1850. ''Einige neue versuche uber herzbewegung''. Zeitschrift Rationelle Medizin, 9: 107-144
#Waller Waller AD. ''A demonstration on man of electromotive changes accompanying the heart's beat.'' J Physiol (London) 1887;8:229-234
#Einthoven Einthoven W. ''Le telecardiogramme''. Arch Int de Physiol 1906;4:132-164
#Einthoven2 Einthoven W. ''Über die Form des menschlichen Electrocardiogramms''. Pfügers Archiv maart 1895, pagina 101-123
#Marey Marey EJ. ''Des variations electriques des muscles et du couer en particulier etudies au moyen de l'electrometre de M Lippman.'' Compres Rendus Hebdomadaires des Seances de l'Acadamie des sciences 1876;82:975-977 
#Marquez pmid=12177632
#Hurst pmid=9799216
#Kligfield pmid=17322457
</biblio>
}}
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==External links==
*[http://www.ecglibrary.com/ecghist.html An extensive history of the ECG]
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[[Category:Cases and Examples]]
[[Category:ECG Course]]
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