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Module title = Tutorial: Bundle Branch Blocks
Lesson title = RBBB
This is lesson 5 of 8 in this module
Right bundle branch block (RBBB) is not a mirror image of LBBB. Some important differences include:
RBBB is common in normal healthy hearts (LBBB is not)
RBBB does
not
cause big changes in the ST segment or the T wave. This is because LV depolarization and repolarization are both normal because the left bundle is conducting normally.
RBBB therefore does not cause diagnostic interference with infarction, ischemia, or LVH
Let's look at what happens to depolarization and the ECG in RBBB. Remember that the LV will be depolarized first and that LV depolarization will be normal. The septum is the first to depolarize:
This will produce an early upgoing R wave in V
1
/V
2
and it might produce a small downgoing (Q wave) in V
6
:
Next, the rest of the LV depolarizes, mostly toward V
6
:
This will produce a downward deflection (S wave) in V
1
/V
2
and an upward deflection (R wave) in V
6
Finally, the RV is SLOWLY depolarized as the electric impulse is transmitted without the fast conducting fibers:
This will produce a second upward deflection in V
1
/V
2
and we call this waveform R prime (R').
In V
6
we have a wide downgoing waveform and this is called a "slurred" S wave:
We ran out of letters for upgoing waves in the QRS, so that is why we use "
R prime
" which is designated as R' ... not to be confused with Optimus Prime. Remember that similar to LBBB, one entire ventricle is depolarized slowly. Therefore, one of the diagnostic criteria is the same:
QRS duration > 120 ms.
RBBB has the
RSR' configuration in V
1/2
. You can remember RBBB: it has
RaBBBit ears
.
RBBB also has the
slurred S wave in V
5/6
(and usually also lead I since it is similar to V
6
). The slurred S wave needs to be either
wider that the R wave
or
> 40 ms
(1 little square). The slurred S wave has a rounded "bottom", as opposed to a pointy bottom, and it is wide.
You might see lower case "r" and "s" with upper case "R" and "S". These simply designate a small waveform (lower case) and a large waveform (upper case). For example, in V
1
above, we might say it is
rSR'
because the
second R wave is larger
than the first R wave.
Another point that is important when you compare LBBB vs. RBBB : remember that in RBBB in V
6
the upgoing R wave is caused by FAST depolarization of the LV. This means that we would expect this portion of the QRS to be narrow and the
V
6
intrinsicoid deflection to be normal/narrow
.
Sumary of diagnostic criteria for RBBB:
QRS > 120 ms
RSR' configuration in V
1/2
slurred (wide) S wave in V
5/6
Exceptions to the rule:
if the patient has had an
old anterior infarct with Q waves,
then the
first R wave in V
1/2
might be missing
(because the R wave is replaced by a Q wave)
Reference:
1. Surawicz B, Childers R, Deal BJ, Gettes LS. AHA/ACCF/HRS Recommendationsfor the Standardization and Interpretation of the Electrocardiogram. J Am Coll Cardiol 2009;53:976–981.
Lesson 5 of 8
That was the last lesson!
