page forward page back  Table of Contents Index
Second Degree Block two-to-one type



This is second degree A-V block, with conduction of every other atrial impulse.
Note the prolonged QRS complexes.   The atrial rhythm is regular, with a
normal P-R interval in the conducted beats (0.16 seconds).  This rhythm is
commonly called two-to-one block.  Is this a Wenckebach mechanism, or an
intermittent increase in degree of a bundle branch block?   It's not possible
to know.  Consider: the non-conducted atrial impulses could be arriving at a
completely refractory A-V node.  This would be the Wenckebach mechanism.
Alternatively, a bundle branch block is visible, and it is quite plausible that
the bundle branch that is functioning in these beats may have a refractory
period greater than the P-P interval, causing complete block on alternate
beats.  Either mechanism could produce this pattern.