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The Normal 12-Lead EKG
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The QRS Interval
A normal QRS interval, representing the duration of the QRS
complex, is 0.06 to 0.1 seconds in duration.
QRS
interval
The ST Segment
The ST segment is usually horizontal or gently upsloping in all leads.
It represents the time from the end of ventricular depolarization to
the start of ventricular repolarization.
The T Wave
The T wave represents ventricular
repolarization
.
Unlike depolarization, which is largely passive, repolarization
requires the expenditure of a great deal of cellular energy (remember
the membrane pump). The T wave is therefore highly susceptible to
all kinds of influences, both cardiac and noncardiac (
e.g
., hormonal,
neurologic), and is therefore variable in its appearance.