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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 | 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. | ||
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| align = right | | align = right | ||
| direction = horizontal | | direction = horizontal | ||
| width = | | width = 315 | ||
| image1 = Ion_currents_en.png | | image1 = Ion_currents_en.png | ||
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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. | 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. | |||
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. | |||
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| | |align="center" | <flashow>http://nl.ecgpedia.org/images/b/bc/Normal_SR_vector.swf|height=300px</flashow> | ||
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==Special Leads== | ==Special Leads== | ||
{{multiple image | {{multiple image | ||
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| image1 = E000559.jpg | | image1 = E000559.jpg | ||
| caption1 = A patient with atrial fibrillation with a 'Lewis Lead' | | 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 | | image2 = E000557.jpg | ||
| caption2 = The same patient with a normal lead configuration | | 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. | ||
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:::: 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. | :::: 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. | ||
:::: 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. | :::: 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. | ||
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==Ladder diagram== | ==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]] | |||
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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. | 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== | ||