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HUF-16 Origin of ECG (why 12 ECG leads are used (Unipolar: measure…
HUF-16 Origin of ECG
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electrical activity that leads to P wave, QRS complex and T wave
P waves: depolarisation of atria, Ta waves: repolarisation of atria but covered by QRS complex
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QRS complex: depolarisation of the ventricles, Q wave: septal depolarisation, R wave: apex, S wave: lateral wall
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Why various segments (TP, PR, ST) would correspond
to the isoelectric line of the ECG
J point/ST segment: the end of QRS complex, isoelectric due to the plateau phase of ventricular myocyte
TP: baseline of ECG recording, thus isoelectric
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the origin of the ECG.
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Measures the overall electrical activities of the heart, which could be viewed as a dipole with p.d. thus can be measured by ECG
why ECG recorded using different leads give positive or
negative deflections of different amplitudes.
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Amplitude depends on a) myocardial mass, b) projection, c) distance and d) thickness and conductance of intervening tissue
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