Bundle branch block Flashcards
How many bundle branches in the cardiac electrical system? (formed when the bundle of his separates into its 2 main branches)
2 - right and left
in BBB one of these is no longer conducting electrical impulses normally
the LEFT/ RIGHT bundle splits further
left - into anterior and posterior hemi-bundles
escape rate in BBB?
40bpm
what does the term ‘non-specific interventricular conduction delay’ refer to?
ECGs with broad QRS which doesn’t exhibit LBBB or RBBB morphology
what are the 3 phases of activation in BBB?
1) septal depolarisation occurring from left > right, occurring alone
2) depolarisation of free wall of left and right ventricles, occurring together
what are the ECG phases of activation in BBB?
increasing amplitude from V1 and 2 (RV) to V3 and 4 (IVS) and largest in V5 and 6 (LV)
what is BBB?
a delay in conduction in either of the bundle branches
how to determine which bundle is blocked?
look at V1 and V6
is the QRS complex narrow or broad?
> 0.12s
how does partial/ incomplete BBB differ on the ECG?
the pattern of LBBB or RBBB is present but the duration of the QRS does not exceed 0.12s
in RBBB, how is the right ventricle stimulated? How is this seen on ECG?
by the impulse from the left ventricle.
Best seen in V1 - M shaped QRS (and W shaped QRS in V6)
how to remember the ECG changes of left vs right BBB?
W i LL ia M - LLeft block
M a RR o W - RRight block
^ ^ ^
V1 Side V6
Describe the phases of activation in RBBB?
- the septum depolarises from left to right as normal
- the left ventricle is depolarised as normal
- finally the right ventricle is depolarised late (wide) in an anterior movement. Resulting QRS is wide due to slow conduction through myocardial cells as opposed to the rapid conducting system
ECG criteria for RBBB?
- QRS > 0.12s
- RSR complex in V1 (‘M-shaped’ QRS complex)
- delayed S wave in V4, 5 and 6 (>0.12s)
T/F: IF abnormal Q waves are present (e.g. MI) they will usually be masked by BBB pattern
false - not usually masked
This is because there’s no alteration of the initial part of the complex RS (in V1) and abnormal Q waves can usually still be seen
What are some of the causes of RBBB?
section not loading
in LBBB how is the left ventricle activated?
by the right bundle
which fasicles are damaged in LBBB?
results from injury to both LAHB and LPHB
ECG changes for LBBB?
best seen in V6
- W shaped QRS in V1
- M shaped QRS in V6
Describe the phases of activation in LBBB
- impulse passes to the left of the septum below the block at the same time as the paraseptal region
- activation of the RV follows (small magnitude)
- finally delayed activation of the LV which is slow due to conduction through normal myocardium
ECG criteria for LBBB?
- prolonged QRS complex (>0.12s)
- wide, notched QRS (M shaped) in I, aVL, V5, V6
- wide, noticed QS complexes in V1 (due to spread of activation away from the electrode through septum + LV)
- small R wave in V2,3 due to activation of paraseptal region
causes of LBBB?
- usually indicative of heart disease
- IHD
- MI
- cardiomyopathy
- HTN
The presence of LBBB makes the diagnosis of what challenging?
MI
