Bundle Branch block Flashcards
Depolarisation waves travel through the heart’s septum via the ____ __ ___ and _____ ____ which are organised into left and right bundle branches
Bundle of His
Purkinje fibres
The 2 bundle branches depolarise the respective ventricles s______
simultaneously
Which bundle branch depolarises the septum?
Left bundle branch
Ventricular depolarisation (QRS) is normally complete with ___ ms
120
A broad QRS complex indicates…
abnormal ventricular depolarisation
The main feature of bundle branch bocks is the ______ of ____ ______
broadening of QRS complexes
What is the diagnostic criteria for Right bundle branch block?
Broad QRS complex longer than 120ms (3 small squares)
RSR’ pattern in V1-V3
Wide slurred S wave in lateral leads: I, aVL, V5-6
What is the RSR’ pattern in Right BBB?
An intitial upward deflection (R wave), a larger downward deflection (S wave), then another large upward deflection (R’ wave)
What mnemonic can be used to recognise left and right bundle branch blocks by looking at V1 and V6?
WiLLiaM
MaRRoW (V1 resembles M, V6 resembles W)
In right bundle branch block the SAN acts as initial pacemaker. Depolarisation reaches the AVN but through the bundle of His only on the ____ bundle branch
left
In right bundle branch block, is the septum depolarised?
Yes
(septum depolarised by left bundle branch)
In right bundle branch block the left ventricular wall depolarises as normal but the right ventricular walls eventually depolarised by the left bundle branch block by a ____ less e____ pathway
slower, less efficient
What is the diagnostic criteria for left bundle branch block?
Broad QRS complex (over 120ms or 3 small squares)
Dominant S wave in V1
Broad monophasic R wave in lateral leads: I, aVL, V5-V6
Absence of Q waves in lateral leads
Prolonged R wave over 60ms in leads V5-6
How is the septum depolarised in left bundle branch block?
Abnormally from right to left
The left ventricle has greater mass so LBBB can cause cardiac axis changes and the left bundle branch splits into _____ and ______ fascicles
anterior and posterior
In LBBB there is block in both….
left anterior fascicule and left posterior fascicle
If only the anterior fascicle is blocked, then there is ___ axis deviation
left
Posterior fascicle block may cause ____ axis deviation
right
However, posterior fascicle does less work than anterior fascicle so may not have obvious ECG changes
The right ventricular muscle doesn’t have enough mass to significantly d___ the c____ a___
deviate the cardiac axis
What is bifascicular block?
Both the right bundle branch and one of the fascicles of the left bundle branch is blocked
What is trifascicular block?
When a 3rd degree heart block exists alongside bifascicular block
____ bundle branch block is always pathological and indicates significant damage to the cardiac conduction system
Left
A broad complex tachycardia requires differentiation between v_____ tachycardia or s____ tachycardia with concurrent b___ b____ b____
ventricular
sinus
bundle branch block
