Basics: Difference between revisions

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]].

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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.

[[Image:conduction_system.svg|thumb|500px|The conduction system of the heart]]

[[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:limb_leads.png|thumb|right|The limb leads]]

[[Image:chest_leads.png|thumb|300px|right|The chest leads]]

[[Image:leads_789.png|thumb|Leads V7,V8 and V9 can be helpful in the diagnosis of posterior myocardial infarction]]

[[Image:Brugada_lead_placement.png|thumb|Changed lead positions of leads V3 and V5 to increase the sensitiviy to 'catch' a [[Brugada]] pattern on the ECG. ]]

[[File:E000559.jpg|thumb|A patient with atrial fibrillation with a 'Lewis Lead' poling of the leads. Compared with the normal lead configuration, the atrial signal is enlarged.]]

[[File:E000557.jpg|thumb|The same patient with a normal lead configuration]]

#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.

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

[[File:Ladder_diagram.svg|thumb|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]]