Bundle branch block Flashcards
the right bundle branch depolarises
the right ventricle
the left bundle branch depolarises
the left ventricle
the right and left bundle branch depolarise at the
at the same time
producing one uniform R wave
V1 veiws the heart from the
right
V6 veiws the heart from the
left
why does depolarisation from the left ventricles havee a greater impact on the ECG trace
because there is greater muscle mass on the left side of the heart compared to the right
how long should ventricular depolarisation take
0.12 seconds
what causes a broad QRS
abnormal ventricular depolarisation
pathways are disrupted or changed, meaning depolarisation takes longer
p wave is
atrial depolarisation
the PR interval is
conduction through the AV to the ventricles
the QRS is
ventricular depolarisation
the Q wave is
the first downward deflection
the T wave is
ventricular repolarisation
why are p waves and PR intervals normal in bundle branch blocks
because the problem is below the atria
diagnostic criteria for right bundle branch block
QRS > 120ms (3 small squares)
RSR pattern in V1-V3
wide, slurred S wave in lateral leads - I, aVL, V5-V6
pneumonic for right bundle branch block
MaRoW
complexes in V1 resemble the letter M and complexes in V6 resemble a W
what happens in right bundle branch block
- the sinoatrial node acts as the initial pace maker
- depolarisation reaches the atrioventricular node
- depolarisation through the bundle of His occurs only via the left bundle branch. the left branch still dpeolarises the septum as normal
- the left ventricular wall depolarises as normal
- the right ventricular walls are ventually depolarised by the left bundle branch. this occurs by a slowerm less efficient pathway
aetiology of RBBB
can be either physiologicl or the result of damage to the right bundle branch
causes of damage includee
- underlying lung pathology eg. COPD, pulmonary emboli, cor pulmonale
- primary heart muscle disease (ARVC)
- congenital heart disease eg. ASD
- ischaemia heart disease
- primary degeneration of the right bundle
what will be the ECG findings for LBBB
V1: (view from the right-hand side where net depolarisation travels away from the detector, towards the left): the first downward deflection represents the right ventricle, the second downward deflection (slightly delayed) corresponds to the depolarisation of the left ventricle
V6: (view from the left hand side where the depolarisation is travelling toward the detector): two positive peaks due to the delay in left ventricular depolarisation
how does the electrical impulse move in left bundle branch block
- the sinoatrial node acts as the initial pacemaker
- depolarisation reaches the atrioventricular node
- depolarisation down the bundle of His occurs only vie the right bundle branch. the septum is abnormally polarised from right to left
- the right ventricular wall is depolarised as normal
- the left ventricular walls are eventually depolarised by the right bundle branch, this occurs by a slower, less efficient pathway
how should the septum be depolarised
right to left
what is the diagnostic criteria for LBBB
- QRS duration >120ms (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 >60ms in leads V5-V6
pneumonic for LBBB
WiLliaM
when is LBBB pathological
always
what might cause LBBB
may be due to conduction system degeneration or a result of myocardial pathologies such is ischaemic heart disease
cardiomyopathy and valvular heart disease
may also occur after cardiac procedures which damage the left bundle branch or His bundle
fascicles of th left bundle branch
LBBB = left anterior fasicular block + Left posterior fasicular block
when the fascicles of the LBB are damaged in isolation
posterior or anterior branch
anterior fascicle block is more common
anterior fascicle block causes
left axis deviation
more common
posterior fascicle block causes
right axis deviation
the posterior fascicle does much less work than the anterior fascicle so can be blocked without any obvious ECG changes
can the right ventricular muscle deviate the cardiac axis
the right ventricular muscle does not have great enough mass to significantly deviate the cardia axis
bifascicular block
involves both right bundle branch block as well as blockade of one of the fascicles of the left bundle branch
trifascicular block
when 3rd degree heart block exists alongside bifascicular block
