Figure 2-11. QRS complexes.
For instructional purposes, the lines on the figures showing heartbeats are
sometimes heavier than normal.
a. Normal Sinus Rhythm (NSR).
(1) Normal sinus rhythm originates in the SA node (pacemaker) and travels
through the normal conduction pathways. It is not an arrhythmia (abnormality in the
normal cardiac rhythm) or dysrhythmia (a disturbance in cardiac rhythm) because it is a
Normal sinus rhythm is analyzed in this manner:
(a) When the R-R intervals and the P-P intervals are constant, the
rhythm is considered regular.
(b) The atrial and ventricular rates equal 60 to 100 heartbeats per
minute with no added or lost P, QRS, or T waves.
The P wave has a uniform configuration with one P wave in front of
(d) The P-R interval is constant between 0.12 and 0.20 seconds.
(e) The QRS complex measures less than 0.12 seconds.
There is no treatment for normal sinus rhythm.