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==How do I begin to read an ECG?==
==How do I begin to read an ECG?==
[[Image:nsr.png|thumb| A short ECG registration of normal heart rhythm (sinus rhythm)]]
{{multiple image
[[Image:Normaal ecg.jpg|thumb| An example of a normal ECG. ''Click on the Image for an enlargement'']]
| align    = right
| direction = horizontal
| width    = 200
 
| image1    = nsr.png
| caption1  = A short ECG registration of normal heart rhythm (sinus rhythm)
 
| image2    = Normaal ecg.jpg
| caption2  = An example of a normal ECG. ''Click on the Image for an enlargement''
}}


Click on the ECG to see an enlargement.
Click on the ECG to see an enlargement.
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==What does the ECG register?==
==What does the ECG register?==
;The electrocardiogram: An electrocardiogram (ECG or EKG) is a register of the heart's electrical activity.
;The electrocardiogram: An electrocardiogram (ECG or EKG) is a register of the heart's electrical activity.
Just like skeletal muscles, heart muscles are electrically stimulated to contract. This stimulation is also called ''activation'' or ''excitation''. Cardiac muscles are electrically charged at rest. The inside, 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]].
Just like skeletal muscles, heart muscles are 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 electrical impulse spreads through the heart, the electrical field changes continually in size and direction. The ECG is a graph of these electrical cardiac signals.
As the electrical impulse spreads through the heart, the electrical field changes continually in size and direction. The ECG is a graph of these electrical cardiac signals.


==The ECG represents the sum of the action potentials of millions of cardiomyocytes==
==The ECG represents the sum of the action potentials of millions of cardiomyocytes==
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 billions of microscopic electrical signals.
{{multiple image
During the depolarization, sodium ions stream into the cell. Subsequently, the calcium ions stream into the cell. These calcium ions cause the actual muscular contraction. Finally the potassium ions stream out of the cell. During repolarization the ion concentration returns to its precontraction state. On the ECG, an action potential wave coming toward the electrode is shown as a positive (upwards) signal. Here the ECG electrode is represented as an eye.
| align    = right
[[Image:Ion_currents_en.png|thumb|left|300px|Ion currents of the cardiomyocytes]]
| direction = horizontal
[[Image:Hart_cells_en.png|thumb|right|300px|The heart consists of approximately 300 trillion cells]]
| width    = 315
[[Image:cells_in_rest_en.png|thumb|right|300px|In rest the heart cells are negatively charged. Through the depolarization by surrounding cells they become positively charged and they contract.]]
 
| image1    = Ion_currents_en.png
| caption1  = Ion currents of the cardiomyocytes
 
| image2    = Hart_cells_en.png
| caption2  = The heart consists of approximately 300 billion cells


{| class="wikitable" align="center" width=385px font-size="70%"
| image3    = cells_in_rest_en.png
|-
| caption3  = In rest the heart cells are negatively charged. Through the depolarization by surrounding cells they become positively charged and they contract.
|<flashow>http://nl.ecgpedia.org/images/5/50/Single_cardiomyocyte.swf|height=350px|width=400px</flashow>
}}
{| class="wikitable" border="1" style="float: left"
|-
|-
| <small>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 action potential. ''Courtesy of Arie Verkerk and Antoni van Ginneken, AMC, Amsterdam, The Netherlands''.</small>
| align="center" width="800" | <flashow>http://nl.ecgpedia.org/images/5/50/Single_cardiomyocyte.swf|height=350px|width=400px</flashow>
| rowspan="2" align="center" width="800" | <youtube>j9w1qylp4TY</youtube>
|-
|-
|  width="800"  | <small>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 action potential. ''Courtesy of Arie Verkerk and Antoni van Ginneken, AMC, Amsterdam, The Netherlands''.</small>
|}
|}
<youtube>j9w1qylp4TY</youtube>


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 billions of microscopic electrical signals.
During the depolarization, sodium ions stream into the cell. Subsequently, the calcium ions stream into the cell. These calcium ions cause the actual muscular contraction.
Finally the potassium ions stream out of the cell. During repolarization the ion concentration returns to its precontraction state. On the ECG, an action potential wave coming toward the electrode is shown as a positive (upwards) signal. Here the ECG electrode is represented as an eye.
{{clr}}
{{clr}}


==The electric discharge of the heart==
==The electric discharge of the heart==
[[Image:conduction_system.svg|thumb|500px|The conduction system of the heart]]
[[Image:conduction_system.svg|thumb|450px|left|The conduction system of the heart]]
{| class="wikitable" border="1" style="float: right"
|-
|align="center" | <flashow>http://nl.ecgpedia.org/images/b/bc/Normal_SR_vector.swf|height=300px</flashow>
|}
 
'''The sinoatrial node (SA node) contains the fastest physiological pacemaker cells of the heart; therefore, they determine the [[Rate|heart rate]].'''
'''The sinoatrial node (SA node) contains the fastest physiological pacemaker cells of the heart; therefore, they determine the [[Rate|heart rate]].'''
'''First the [[heart|atria]] depolarize and contract. After that the [[heart|ventricles]]''' depolarize and contract.
'''First the [[heart|atria]] depolarize and contract. After that the [[heart|ventricles]]''' depolarize and contract.
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 branches, which end in a dense network of Purkinje fibers.
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 branches, which end in a dense network of Purkinje fibers.
The depolarization of the heart results in an electrical force which has a direction and magnitude; an electrical vector. This vector changes every millisecond of the depolarization. In the animation vectors for atrial depolarization, ventricular depolarization and ventricular repolarization are shown.
The depolarization of the heart results in an electrical force which has a direction and magnitude; an electrical vector. This vector changes every millisecond of the depolarization. In the animation vectors for atrial depolarization, ventricular depolarization and ventricular repolarization are shown.
<flashow>http://nl.ecgpedia.org/images/b/bc/Normal_SR_vector.swf|height=300px</flashow>
{{clr}}
{{clr}}


==The different ECG waves==
==The different ECG waves==
[[File:PQRS_origin_en.png|thumb|left|300px|The origin of the different waves on the ECG]]
[[File:PQRS_origin_en.png|thumb|left|300px|The origin of the different waves on the ECG]]
[[Image:Epi_endo_en.png|thumb|300px| The QRS complex is formed by the sum of the electric avtivity of the inner (endocardial) and the outer (epicardial) cardiomyocytes]]
{{multiple image
[[Image:Qrs-shapes.png|thumb|300px| Example of the different QRS configurations]]
| align    = right
| direction = vertical
| width    = 320
 
| image1    = Epi_endo_en.png
| caption1  = The QRS complex is formed by the sum of the electric avtivity of the inner (endocardial) and the outer (epicardial) cardiomyocytes
 
| image2    = Qrs-shapes.png
| caption2  = 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 (sinoatrial) node. The signal produced by pacemaker cells in the SA node is conducted to the right and left atria. Normal atrial repolarization is not visible on the ECG (but can be visible during [[atrial infarction]] and [[pericarditis]]).  
The [[P_wave_morphology|'''P wave''']] is the result of the atrial depolarization. This depolarization starts in the SA (sinoatrial) node. The signal produced by pacemaker cells in the SA node is conducted to the right and left atria. Normal atrial repolarization is not visible on the ECG (but can be visible during [[atrial infarction]] and [[pericarditis]]).  


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==The ECG electrodes==
==The ECG electrodes==
[[Image:limb_leads.png|thumb|right|The limb leads]]
{{multiple image
[[Image:chest_leads.png|thumb|300px|right|The chest leads]]
| align    = right
| direction = vertical
| width    = 200
 
| image1    = limb_leads.png
| caption1  = The limb leads
 
| image2    = chest_leads.png
| caption2  = The chest leads
}}
 
Electrical activity going through the heart can be measured by external (skin)electrodes. The electrocardiogram (ECG) registers these activities from electrodes which have been attached onto different places on the body. In total, twelve leads are calculated using ten electrodes.
Electrical activity going through the heart can be measured by external (skin)electrodes. The electrocardiogram (ECG) registers these activities from electrodes which have been attached onto different places on the body. In total, twelve leads are calculated using ten electrodes.


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''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.
''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.
==ECG variants==
Besides the standard 12 lead ECG a couple of variants are in use:
*The '''3 channel ECG''' uses 3 or 4 ECG electrodes. Red is on the right, yellow on the left arm, green on the left leg ('sun shines on the grass') and black on the right leg. These basic leads yield enough information for rhythm-monitoring. For determination of ST elevation, these basic leads are inadequate as there is no lead that gives (ST) information about the anterior wall. ST changes registered during 3-4 channel ECG monitoring should prompt acquisition of a 12 lead ECG.
*The '''5 channel ECG''' uses 4 extremitiy leads and 1 precordial lead. This improves ST segment accuracy, but is still inferior to a 12 lead ECG.  <cite>drew</cite><cite>Klootwijk</cite>
*In '''vector electrocardiography''' the movement of electrical acitivity of the P, QRS and T wave is described. Additional X,Y and Z leads are recorded. Vector electrocardiography is rarely used nowadays, but is sometimes useful in a research setting.
*In '''body surface mapping''' several arrays are used to accurately map the cardiac electrical wavefront as it moves over de body surface. With this information the electrical acitivity of the heart can be calculated. This is sometimes used in a research setting.
==Color coding of the ECG leads==
Two systems for ECG lead color coding are used: the AHA (''American Heart Association'') system and the IEC (''International Electrotechnical Commission'') system:
{| class="wikitable" cellpadding="7"
||
| colspan="2" | AHA (''American Heart Association'')
| colspan="2" | IEC (''International Electrotechnical Commission'')
|-
!| Location
!| Inscription
!| Colour
!| Inscription
!| Colour
|-
|-
| | Right Arm
!| RA
| | White
!|R
| | Red
|-
| | Left Arm
!|LA
| | Black
!|L
| | Yellow
|-
| | Right Leg
!|RL
| | Green
!|N
| | Black
|-
| | Left Leg
!|LL
| | Red
!|F
| | Green
|-
| | Chest
!|V1
| | Brown/Red
!|C1
| | White/Red
|-
| | Chest
!|V2
| | Brown/Yellow
!|C2
| | White/Yellow
|-
| | Chest
!|V3
| | Brown/Green
!|C3
| | White/Green
|-
| | Chest
!|V4
| | Brown/Blue
!|C4
| | White/Brown
|-
| | Chest
!|V5
| | Brown/Orange
!|C5
| | White/Black
|-
| | Chest
!|V6
| | Brown/Purple
!|C6
| | White/Violet
|}


==Special Leads==
==Special Leads==
{{multiple image
| align    = left
| direction = horizontal
| width    = 200
| image1    = leads_789.png
| caption1  = Leads V7,V8 and V9 can be helpful in the diagnosis of posterior myocardial infarction
| image2    = Brugada_lead_placement.png
| caption2  = Changed lead positions of leads V3 and V5 to increase the sensitiviy to 'catch' a [[Brugada]] pattern on the ECG.
}}
{{multiple image
| align    = right
| direction = vertical
| width    = 200
| image1    = E000559.jpg
| caption1  = A patient with atrial fibrillation with a 'Lewis Lead' positioning of the leads. Compared with the normal lead configuration, the atrial signal is enlarged. Although some parts have a 'sawtooth' appearance consistent with atrial flutter, the rhythm is atrial fibrillation as there is a changing pattern in the atrial activity.
| image2    = E000557.jpg
| caption2  = The same patient with a normal lead configuration. The rhythm is atrial fibrillation. The atrial activity in lead V1 is organized probably due to a organisation of electrical activity after it enters the right atrial appendage, close to lead V1.
}}
Throughout history extra lead positions have been tried. Most are rarely used in practice, but they can deliver very valuable diagnostic clues in specific cases.
Throughout history extra lead positions have been tried. Most are rarely used in practice, but they can deliver very valuable diagnostic clues in specific cases.
===Leads to improve diagnosis in right ventricular en posterior infarction===
*Leads to improve diagnosis in '''right ventricular en posterior infarction''':
[[Image:leads_789.png|thumb|Leads V7,V8 and V9 can be helpful in the diagnosis of posterior myocardial infarction]]
In case of an inferior wall infarct, extra leads may be used:
In case of an inferior wall infarct, extra leads may be used:
#On a right-sided 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. The ECG should be marked as a ''Right-sided ECG''. V4R (V4 but right sided) is a sensitive lead for diagnosing right ventricular infarctions.
:::: 1. On a right-sided 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. The ECG should be marked as a ''Right-sided ECG''. V4R (V4 but right sided) is a sensitive lead for diagnosing right ventricular infarctions.
#Leads V7-V8-V9 can be used to diagnose a posterior infarct. After V6, leads are placed towards the back. See the chapter[[Ischemia]] for other ways of diagnosing posterior infarction.
 
===Leads to improve detection of atrial rhyhtm===
:::: 2. Leads V7-V8-V9 can be used to diagnose a posterior infarct. After V6, leads are placed towards the back. See the chapter [[Ischemia]] for other ways of diagnosing posterior infarction.
In wide complex tachycardia, good detection of atrial rhythm and atrio-ventricular dissociation can be very helpful in the diagnosis process. An esophagal ECG electrode placed close to the atria can be helpful. Another, less invasive, method is the '''Lewis Lead'''. This is recorded by changing the limb electrodes, placing the right arm electrode in the second intercostal space and the left arm electrode in the fourth intercostal space, both to the right of the sternum. Furthermore gain is increased to 20mm/mV and paper speed to 50mm/sec.<cite>Lewis1</cite><cite>Lewis2</cite>
 
===Lead positioning to enhance detection of Brugada syndrome===
 
[[Image:Brugada_lead_placement.png|thumb|300px|Changed lead positions of leads V3 and V5 to increase the sensitiviy to 'catch' a [[Brugada]] pattern on the ECG. ]]
*Leads to improve detection of '''atrial rhyhtm''':
::In wide complex tachycardia, good detection of atrial rhythm and atrio-ventricular dissociation can be very helpful in the diagnosis process. An esophagal ECG electrode placed close to the atria can be helpful. Another, less invasive, method is the '''Lewis Lead'''. This is recorded by changing the limb electrodes, placing the right arm electrode in the second intercostal space and the left arm electrode in the fourth intercostal space, both to the right of the sternum. Furthermore gain is increased to 20mm/mV and paper speed to 50mm/sec.<cite>Lewis1</cite>ß
 
*Lead positioning to enhance detection of [[Brugada]] syndrome
{{clr}}
{{clr}}
==Ladder diagram==
[[File:Ladder_diagram.svg|thumb|right|A ladder diagram is a diagram that shows the presumed origin of impulse formation and conduction in the heart. A = atrial, AV = AV node, V = ventricles]]
A ladder diagram is a diagram to explain arrhythmias. The figure shows a simple ladder diagram for normal sinus rhythm, followed by av-nodal extrasystole. The origin of impulse formation (sinus node for the first two beats and AV junction for the third beat) and the conduction in the heart are shown.
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==Technical Problems==
==Technical Problems==
Also read the chapter about [[Technical Problems]]. That will help you recognize electrical disturbances and lead reversals.
Also read the chapter about [[Technical Problems]]. That will help you recognize electrical disturbances and lead reversals.
{{box|
{{box|
==References==
==References==
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#Hurst pmid=9799216
#Hurst pmid=9799216
#Kligfield pmid=17322457
#Kligfield pmid=17322457
#Lewis1 pmid=20022196
</biblio>
</biblio>
}}
}}
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