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==The electric discharge of the heart== | ==The electric discharge of the heart== | ||
[[Image:conduction_system_en.png|thumb|300px|The conduction system of the heart]] | [[Image:conduction_system_en.png|thumb|300px|The conduction system of the heart]] | ||
'''The | '''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]] depolarise and contract, after that the [[heart|ventricles]]''' | '''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 | 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. | ||
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> | <flashow>http://nl.ecgpedia.org/images/b/bc/Normal_SR_vector.swf|height=300px</flashow> | ||
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[[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]] | [[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]] | ||
[[Image:Qrs-shapes.png|thumb|300px| Example of the different QRS configurations]] | [[Image:Qrs-shapes.png|thumb|300px| 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 ( | 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 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 [[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 | The [[ST_morphology|'''T wave''']] represents the repolarization 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. | 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. | ||
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[[Image:limb_leads.png|thumb|right|The limb leads]] | [[Image:limb_leads.png|thumb|right|The limb leads]] | ||
[[Image:chest_leads.png|thumb|300px|right|The chest leads]] | [[Image:chest_leads.png|thumb|300px|right|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. | |||
The ten electrodes are: | The ten electrodes are: | ||
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** V2 - placed in the 4th intercostal space, left of the sternum | ** V2 - placed in the 4th intercostal space, left of the sternum | ||
** V3 - placed between V2 and V4 | ** V3 - placed between V2 and V4 | ||
** V4 - placed 5th intercostal space in the | ** V4 - placed 5th intercostal space in the nipple line. Official recommendations are to place V4 under the breast in women.<cite>Kligfield</cite> | ||
** V5 - placed between V4 and V6 | ** 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) | ** 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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{{clr}} | {{clr}} | ||
With the use of these 10 electrodes, 12 leads can be derived. There are 6 extremity leads and 6 precordial leads. | |||
===The Extremity Leads=== | ===The Extremity Leads=== | ||
[[File:ECGafleidingen.jpg|thumb|left|200px]] | [[File:ECGafleidingen.jpg|thumb|left|200px]] | ||
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===The Chest Leads=== | ===The Chest Leads=== | ||
The precordial, or | The precordial, or chest leads, '''(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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[[Image:leads_789.png|thumb|Leads V7,V8 and V9 can be helpful in the diagnosis of posterior myocardial 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. | ||
#Leads V7-V8-V9 can be used to diagnose a | #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. | ||
{{clr}} | {{clr}} | ||
==Technical Problems== | ==Technical Problems== | ||
Also read the chapter about [[Technical Problems]] | Also read the chapter about [[Technical Problems]]. That will help you recognize electrical disturbances and lead reversals. | ||
{{box| | {{box| | ||
==References== | ==References== | ||