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==test== | |||
<CSO_iFrame> src="http://docs.google.com/present/embed?id=dcwtsh74_0f8d6pvhk&interval=5&size=m" frameborder="0" width="555" height="451"</CSO_iFrame> | |||
==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)]] | [[Image:nsr.png|thumb| A short ECG registration of normal heart rhythm (sinus rhythm)]] | ||
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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]]. | 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. | 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. | ||
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==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== | ||
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** V6 - placed in the midaxillary line on the same height as V4 (horizontal line from V4, so not necessarily in the 5th intercostal space) | ** V6 - placed in the midaxillary line on the same height as V4 (horizontal line from V4, so not necessarily in the 5th intercostal space) | ||
Using these 10 electrodes, 12 leads can be derived. There are 6 extremity leads and 6 precordial leads. | |||
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==The Extremity Leads== | ==The Extremity Leads== | ||
[[Image:ECGafleidingen.jpg|thumb]] | [[Image:ECGafleidingen.jpg|thumb]] | ||
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==The Chest Leads== | |||
The precordial, or chestleads, '''(V1,V2,V3,V4,V5 and V6)''' 'observe' the depolarization wave in the frontal plane | The precordial, or chestleads, '''(V1,V2,V3,V4,V5 and V6)''' 'observe' the depolarization wave in the frontal plane | ||
''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. | ||
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==Lead reversals== | |||
[[Image:cableReversal1.png|thumb|Right and left arm lead reversal can be distinguished from the (much rarer) dextrocardia by looking at the precordial R wave progression.]] | |||
[[Image:cableReversal2.png|thumb|Right arm and left leg lead reversal. Lead II now measures the signal between the left and right leg, which is remote from the heart.]] | |||
[[Image:dextrocardia.jpg|thumb|A patient with dextrocardia (and previous inferior myocardial infarction)]] | |||
Sometimes an ECG is not made properly. Mistakes do happen and leads can be switched. Always remain careful to check this or you might come to the wrong conclusions. One of the most common mistakes is to switch the right and left arm. This will result in negative complexes in I, indicating a right axis deviation! | |||
Common mistakes are reversal of: | |||
*right leg and right arm: | |||
**Hardly any signal in lead II. | |||
*right and left arm electrodes; | |||
**reversal of leads II and III | |||
**reversal of leads aVR and aVL | |||
*left arm and left leg: | |||
**reversal of leads I and II | |||
**reversal of leads aVR and aVF | |||
**inversion of lead III | |||
*right arm and left leg: | |||
**inversion of leads I, II and III | |||
**reversal of leads aVR and aVF | |||
It is possible to distinguish lead reversal and [[w:Dextrocardia|dextrocardia]] by watching the precordial leads. Dextrocardia will not show any R wave progression in leads V1-V6, whereas lead reversal will. | |||
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==Artifacts== | |||
<gallery perRow="3"> | |||
Image:Noise_move.png|Movement artifacts | |||
Image:ECG_Parkinson.png|Increasing movement artifacts in a Parkinson patient. The patient was in sinus rhythm! (which doesn't show on this short recording) | |||
Image:BaselineDrift.png|Baseline drift. The amplifier in the ECG machine has to re-find the 'mean'. This often occurs right after lead connection and after electric cardioversion. | |||
Image:cardioversion_from_afib.jpg|Cardioversion from atrial fibrillation to sinus rhythm, with clear baseline drift. | |||
Image:electric_noise_ecg.png|Electrical interference from a nearby electrical appliance. A typical example is a 100 Hz background distortion from fluorescent lights. Not to be confused with [[Atrial_Fibrillation|atrial fibrillation]]. | |||
Image:electric_noise_ecg2.jpg|Another example of an artefact caused by an electrical appliance. The patients rhythm is regular. This strip shows 10 QRS complexes. | |||
</gallery> | |||
artifacts (disturbances) can have many causes. Common causes are: | |||
*Movement | |||
*Electrical interference | |||
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==Special Leads== | ==Special Leads== | ||
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#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. | #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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==References== | ==References== | ||