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ST Morphology

23 bytes added, 23:28, 16 January 2010
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[[Image:changing_ST.png|thumb|right|300px|ST changes occur when the endocardial and epicardial actionpotentials action potentials cease to counterbalance each other]] The '''ST segment''' represents ventricular repolarisationrepolarization. Repolarisation Repolarization follows upon contraction and depolarisationdepolarization. During repolarisation repolarization the cardiomyocytes elongate and prepare for the next heartbeat. This process takes much more time than the depolarisationdepolarization. Repolarisation The elongation that takes place during repolarization is not passive elongation by stretch, ; it is an active process during which energy is consumed. On the ECG, the repolarisation repolarization phase starts at the junction, or ''j point'', and continues until the ''T wave''. The ST segment is normally at or near the baseline.
The '''T wave''' is usually concordant with the QRS complex. Thus if the QRS complex is positive in a certain lead (the area under the curve above the baseline is greater than the area under the curve below the baseline) than the T wave usually is positive too in that lead. Accordingly the T wave is normally upright or positive in leads I, II, AVL, AVF and V3-V6. The T wave is negative in V1 and AVR. The T wave flips around V2, but there is likely some genetical genetic influence in this as in Blacks the T wave usually flips around V3.
The T wave angle is the result of small differences in the duration of the repolarisation repolarization between the endocardial and epicardial layers of the left ventricle. The endocardial myocytes need a little more time to repolarise repolarize (about 22 msec). This difference causes an electrical current from the endocardium to the epicardium, which reads as a positive signal on the ECG.<cite>braunwald</cite>
==ST elevation==


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