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

changing measurements.

MD0571

2-13

Integrated Publishing, Inc. |