Med Equipment & Diagnosis
Page 21
TMS
Pericarditis Cont.
The time in between these waves is represented by the S-T segment
which indicates the time the ventricles are isoelectric. Remembering
back from your basic electronics course or Physics I, you see that
isoelectric carries the same concept, even in biology. Isoelectric in heart
tissue is the point at which the membrane carries no net charge across it.
Range of times for the P-R segment and S-T segment are 50 to 120 ms
and 80 to 120 ms respectively. The figure shows one example of an exaggerated P-R depression and S-T segment elevation as seen on an
ECG. Another way to look at the S-T segment is, ―It is the time between
Ventricular depolarization and repolarization‖ when the net charge is neutral, leading to the baseline of ―0‖ on the waveform. In other leads, such
as aVR, the P-R segment will be elevated, while the S-T segment will be
depressed. Eit \