Page 189 - Critical Care Nursing Demystified

174 CRITICAL CARE NURSING DeMYSTIFIED

TABLE 4–4 The Waveforms of the Heartbeat
Waveform What It Means How It Is Measured Its Normal Value
P wave Two things From the beginning of Upright rounded
happen here: the first upstroke of the and symmetrical
SA node firing heartbeat to the end of Usually smaller
AND atrial that upstroke than T wave
depolarization Usually not measured, There are two
but we look at the atria but one little
configuration of the hump! They
wave depolarize
together
PR interval Three things Beginning of the P wave From three to five
(PRI) happen here: SA including the isoelectric little boxes hori-
node firing, atrial or flat line after it and zontally OR from
depolarization, ending where the .12 seconds to
AND the message baseline goes up or .20 seconds
getting down to down (QRS complex)
the AV node Do not include any of
the QRS in this one or
you will be including ven-
tricles!
QRS This is ventricular Can include three From 1.5 to 2.5 Downloaded by [ Faculty of Nursing, Chiangmai University 5.62.158.117] at [07/18/16]. Copyright © McGraw-Hill Global Education Holdings, LLC. Not to be redistributed or modified in any way without permission.
complex depolarization: different waveforms little boxes OR
a bit tougher as The Q wave is the first .06 to .10 sec-
this complex negative deflection after onds
might have three the PRI Amazing, even
waves! though the ven-
The R wave is the first
positive deflection after tricles are bigger,
the PRI they take less
The S wave is the first time to depolar-
ize!
negative deflection after
the R wave
When the R wave comes
back to the isoelectric
line, then the QRS
stops
ST Time between Distance in between Usually isoelectric
segment ventricular where the S wave stops but abnormal in
depolarization and and at the point the 12-lead ECG in
repolarization T wave starts upward consistent leads
Not usually measured may indicate an
for rhythm detection, impending MI
but important in Bad if more than
determining one box up or one
ischemia box down!