Page 194 - Critical Care Nursing Demystified

Chapter 4 CARE OF THE PATIENT WITH CRITICAL CARDIAC RHY THM DISTURBANCE NEEDS 179

across the horizontal axis. After determining the numerical value, you will be
comparing your results to what the normal value is for that conduction interval/
complex.
The PRI is completed by taking your left caliper point, placing it at the begin-
ning of the P wave, and stopping it at the beginning of the QRS. Do not measure
just one; try to get an average of them for each heartbeat across your strip. If these
measurements fall between .12 and .20 seconds, then this beat or rhythm comes
from the SA node and has been conducted to the AV node in a normal fashion.
The PRI in Figure 4–5 is 0.16 seconds or normal.

Step Six: Conduction—Measuring the QRS

Next, we will measure ventricular depolarization by measuring the QRS
interval. Start at the beginning of the Q wave and end where the S wave returns
to the baseline. Having a bit of trouble with this one? That is okay because
sometimes there is only a Q or an S. Or there also can be an RS and no Q.
So we have to fine-tune this measurement by defining each one of these
waves. It is important because you really want to be accurate with this tiny
measurement—if it is off, it means you miscalculated those all-important
ventricles. So use the following definitions and Figure 4–6 to help. 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.
• Q wave – first negative wave after the P wave
• R wave – the first positive wave after the Q wave
• S wave – the first negative wave after the R wave
The QRS in Figure 4–5 is 0.1 seconds or normal.

Step Seven: Conduction—Measuring the QTI
The QT interval is important when it comes to monitoring the results of drugs
the patient is receiving. The QT interval does not a rhythm make, but we want
to make certain it does not prolong beyond one-half the R-R interval. QTs are
measured from the beginning of the QRS complex to the end of the T wave.
The QTI in the strip in Figure 4–5 is 0.32 seconds or on the shorter side.

NURSING ALERT

Some medications like sotalol (Betapace) or amiodarone (Cordarone) slow the heart
rate down and prolong depolarization for so long that a nasty rhythm called tor-
sades de pointes takes over. This is a cardiac arrest rhythm, so always measure the QT
in relation to the R-R before you start these medications AND monitor it periodically
after starting these medications.