page forward page back  Table of Contents Index
Rate Related Bundle Branch Block example two


In a setting of atrial fibrillation with very slow ventricular response, a very
interesting pattern is seen here.  The first QRS complex has a duration of
0.13 seconds.  It is followed by an R-R interval of 1.86 seconds and then a
QRS complex with a duration of 0.08 seconds, with normal shape.  Then
follows an R-R interval of 1.80 seconds, and a QRS with duration of 0.10
seconds, with a notch appearing in the upper lead.  Then an R-R of 1.78,
and a QRS of 0.12, with the notch deepening.  Last is an R-R of 1.74 seconds
and a QRS like the first: 0.13 seconds and with almost exactly the same
shape.  What is happening here?  The bundle branch system of this heart
seems to have a refractory period of about 1.86 seconds, the interval
between the first two beats.  The second beat is a typical junctional beat
with this much time to repolarize, the bundles are non-refractory.  As the
period between depolarizations decreases, the bundles are more and more
refractory, producing the progressively wider QRS complexes with changes
in shape.