140 lines
4.8 KiB
HTML
140 lines
4.8 KiB
HTML
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<TITLE>ECG morphology</TITLE>
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<B> Next:</B> <A NAME="tex2html46"
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HREF="node3.html">Heart rate variability</A>
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<H1><A NAME="SECTION00020000000000000000"></A>
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<A NAME="s:morphology"></A>
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<BR>
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ECG morphology
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</H1>
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Each beat of the heart can be observed as a series of deflections away from
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the baseline on the ECG. These deflections reflect the time
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evolution of electrical activity in the heart which initiates
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muscle contraction. A single sinus (normal) cycle of the ECG,
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corresponding to one
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heart beat, is traditionally labelled with the letters P,Q,R,S and T
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on each of its turning points (Fig. <A HREF="node1.html#f:garipqrst">1</A>).
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The ECG may be divided into the following sections:
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<UL>
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<LI>P-wave: a small low-voltage deflection away from the baseline
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caused by the depolarisation of the atria prior to atrial contraction as the
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activation (depolarisation) wave-front propagates
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from the SA node through the atria.
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<BR>
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</LI>
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<LI>PQ-interval:
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the time between the beginning of atrial
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depolarisation and the beginning of ventricular depolarisation.
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<BR>
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</LI>
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<LI>QRS-complex: the largest-amplitude portion of the ECG, caused by
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currents generated when the ventricles depolarise prior to their
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contraction. Although atrial repolarisation occurs before ventricular
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depolarisation, the latter waveform (i.e. the QRS-complex) is of much greater
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amplitude and atrial repolarisation is therefore not seen on the ECG.
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<BR>
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</LI>
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<LI>QT-interval: the time between the onset of ventricular
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depolarisation and the end of ventricular repolarisation.
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Clinical studies have demonstrated that the QT-interval
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increases linearly as the RR-interval increases [<A
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HREF="node8.html#davey99">4</A>].
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Prolonged QT-interval may be associated with delayed ventricular
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repolarisation which may cause ventricular tachyarrhythmias
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leading to sudden cardiac death [<A
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HREF="node8.html#schwartz78">9</A>].
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</LI>
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<LI>ST-interval: the time between the end of S-wave and the
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beginning of T-wave. Significantly elevated or depressed amplitudes away
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from the baseline are often associated with cardiac illness.
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</LI>
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<LI>T-wave: ventricular repolarisation, whereby the cardiac muscle
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is prepared for the next cycle of the ECG.
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HREF="index.shtml">A dynamical model for</A>
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2003-10-08
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