Figure 2-9. Calculation of heartbeat rate.
(2) The heartbeat rate for irregular heartbeat rhythm is based on the 6-
second strip method. The minimum amount of time needed to determine cardiac
rhythm is 6 seconds. The method described here is the quickest and easiest method
although it is not as accurate as the "box" method. The vertical notches in the upper
margin of the paper are 3 seconds apart.
(a) Count the number of QRS complexes in a 6-second strip.
(b) Multiply by 10 to get the heart rate for one minute.
c. P Waves. P waves are small positive deflections that occur on the
oscilloscope. These waves represent atrial depolarization. Normally, the P waves are
rounded, uniform, and upright and come before the QRS complex. These waves are
either regular or irregular. Measured distances between all P waves should be
constant. Determine whether there is a P wave for every QRS complex. Determine
whether the P wave is in front of the QRS complex and see if there are more P waves
than QRS complexes. Check to see if all the P waves look alike. See if there are
irregular P waves associated with ectopic or irregular beats.
d. P-R Intervals. All P-R intervals should be constant. Measure the P-R
intervals to determine if the intervals are normal or abnormal. A normal P-R interval is
from 0.12 to 0.20 seconds. If the P-R interval varies, notice if there is a pattern to the