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Naming the Straight Lines
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Naming the Straight Lines
The different straight lines connecting the various waves have also
been given names. Thus, we speak of the
PR interval
, the
ST segment
,
the
QT interval
, and so on.
What differentiates a segment from an interval? A segment is a
straight line connecting two waves, whereas an interval encompasses
at least one wave plus, in most instances, the connecting straight line.
Segment
Interval
Interval
The
PR interval
includes the P wave and the straight line connecting
it to the QRS complex. It therefore measures the time from the start of
atrial depolarization to the start of ventricular depolarization.
The
PR segment
is the straight line running from the end of the P
wave to the start of the QRS complex. It therefore measures the time from
the end of atrial depolarization to the start of ventricular depolarization.
You might be wondering: if the QRS complex has a Q wave,
shouldn’t the PR segment be called the PQ segment, and the PR
interval the PQ interval? Well, yes, but they’re not. These straight
lines are always called the PR segment and PR interval no matter
what the configuration of the QRS complex.
PR
interval
PR
segment
The
ST segment
is the straight line connecting the end of the QRS
complex with the beginning of the T wave. It measures the time from the
end of ventricular depolarization to the start of ventricular repolarization.