page forward page back  Table of Contents Index
Sinus Rhythm Variants



None of the above three strips are normal, but they are all examples of sinus rhythm nonetheless.  In each strip, there is a P-wave before every QRS, and a QRS after every P-wave.  In each strip the rate is between 60 and 100 per minute, and these qualities define sinus rhythm.   Are all of the P-R intervals normal?   No, in the top two strips the interval is prolonged beyond 0.20 seconds.  Are all of the QRS durations normal, and are the QRS complexes normally shaped?  No, they are all prolonged beyond 0.11 seconds, and they are all oddly shaped.  What is the cause of these abnormal intervals and shapes?   In each case, it is the improper functioning of the specialized conduction system that is being revealed to us.  The prolonged P-R intervals are caused by abnormal delays at the A-V node, and the shape and duration of the QRS complexes are caused by malfunctions - blocks - in the intraventricular conduction system, the bundle branches.