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Basics: Difference between revisions
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* At the right of that are below each other the [[Frequency]], the [[Conduction|conduction times]] (PQ,QRS,QT/QTc), and the [[heart axis]] (P-top axis, QRS axis and T-top axis) | * At the right of that are below each other the [[Frequency]], the [[Conduction|conduction times]] (PQ,QRS,QT/QTc), and the [[heart axis]] (P-top axis, QRS axis and T-top axis) | ||
* Farther to the right is the interpretation of the ECG written (this may be missing in a 'fresh' ECG, but later the interpretation of the cardiologist or computer will be added) | * Farther to the right is the interpretation of the ECG written (this may be missing in a 'fresh' ECG, but later the interpretation of the cardiologist or computer will be added) | ||
* | * Down left is the 'paper speed' (25 mm/s on the horizontal axis), the sensitivity (10mm/mV) and the filter's frequency (40Hz, filters noise from eg. lights). | ||
* There is a calibration. At the beginning of every lead is a vertical block that shows with what amplitude a 1 mV signal is drawn. So the height and depth of these signals are a measurement for the voltage. If this is not | * There is a calibration. At the beginning of every lead is a vertical block that shows with what amplitude a 1 mV signal is drawn. So the height and depth of these signals are a measurement for the voltage. If this is not set at 10 mm, there is something wrong with the machine setting. | ||
* | * Finally we have the ECG leads themselves.These will be discussed below. | ||
Note that the layout is different for every machine, but most machines will show the information above somewhere. | Note that the layout is different for every machine, but most machines will show the information above somewhere. | ||
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==What does the ECG register?== | ==What does the ECG register?== | ||
;The electrocardiogram:An electrocardiogram (ECG or EKG) is a | ;The electrocardiogram: An electrocardiogram (ECG or EKG) is a register of the heart's electrical activity. | ||
Just like skeletal muscles, | 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 impulse spreads through the heart, the | 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 signals in the heart. | ||
==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 | 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 | 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 the repolarization the ion concentration returns to its precontraction state. On the ECG, an action potential wave coming towards the electrode is shown as a positive (upwards) signal. Here the ECG electrode is represented as an eye. | ||
[[Image:Ion_currents_en.png|thumb|left|300px|Ion currents of the cardiomyocytes]] | [[Image:Ion_currents_en.png|thumb|left|300px|Ion currents of the cardiomyocytes]] | ||
[[Image:Hart_cells_en.png|thumb|right|300px|The heart consists of approximately 300 trillion cells]] | [[Image:Hart_cells_en.png|thumb|right|300px|The heart consists of approximately 300 trillion cells]] | ||