page forward page back  Table of Contents Index
Sinus Rhythm with First Degree Block



Notice the prolonged P-R interval.   The average here is about 0.24 seconds, with the normal range
being 0.14 to 0.20 seconds.  Although every atrial impulse is conducted, there is an abnormal delay
in conduction between the atria and the ventricles.  This is first degree block.
A note about degrees of block that may make them easier to remember: in first degree block, all atrial
impulses are conducted, but with an prolonged delay.  In second degree block, some but not all atrial
impulses are conducted.  In third degree block, no atrial impulses are conducted.