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Internal Med 2023 > Bundle branch block > Flashcards

Bundle branch block Flashcards

1
Q

the right bundle branch depolarises

A

the right ventricle

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2
Q

the left bundle branch depolarises

A

the left ventricle

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3
Q

the right and left bundle branch depolarise at the

A

at the same time
producing one uniform R wave

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4
Q

V1 veiws the heart from the

A

right

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5
Q

V6 veiws the heart from the

A

left

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6
Q

why does depolarisation from the left ventricles havee a greater impact on the ECG trace

A

because there is greater muscle mass on the left side of the heart compared to the right

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7
Q

how long should ventricular depolarisation take

A

0.12 seconds

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8
Q

what causes a broad QRS

A

abnormal ventricular depolarisation
pathways are disrupted or changed, meaning depolarisation takes longer

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9
Q

p wave is

A

atrial depolarisation

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10
Q

the PR interval is

A

conduction through the AV to the ventricles

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11
Q

the QRS is

A

ventricular depolarisation

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12
Q

the Q wave is

A

the first downward deflection

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13
Q

the T wave is

A

ventricular repolarisation

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14
Q

why are p waves and PR intervals normal in bundle branch blocks

A

because the problem is below the atria

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15
Q

diagnostic criteria for right bundle branch block

A

QRS > 120ms (3 small squares)
RSR pattern in V1-V3
wide, slurred S wave in lateral leads - I, aVL, V5-V6

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16
Q

pneumonic for right bundle branch block

A

MaRoW
complexes in V1 resemble the letter M and complexes in V6 resemble a W

17
Q

what happens in right bundle branch block

A
  1. the sinoatrial node acts as the initial pace maker
  2. depolarisation reaches the atrioventricular node
  3. depolarisation through the bundle of His occurs only via the left bundle branch. the left branch still dpeolarises the septum as normal
  4. the left ventricular wall depolarises as normal
  5. the right ventricular walls are ventually depolarised by the left bundle branch. this occurs by a slowerm less efficient pathway
18
Q

aetiology of RBBB

A

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

19
Q

what will be the ECG findings for LBBB

A

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

20
Q

how does the electrical impulse move in left bundle branch block

A
  1. the sinoatrial node acts as the initial pacemaker
  2. depolarisation reaches the atrioventricular node
  3. depolarisation down the bundle of His occurs only vie the right bundle branch. the septum is abnormally polarised from right to left
  4. the right ventricular wall is depolarised as normal
  5. the left ventricular walls are eventually depolarised by the right bundle branch, this occurs by a slower, less efficient pathway
21
Q

how should the septum be depolarised

A

right to left

22
Q

what is the diagnostic criteria for LBBB

A
  • 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
23
Q

pneumonic for LBBB

A

WiLliaM

24
Q

when is LBBB pathological

A

always

25
Q

what might cause LBBB

A

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

26
Q

fascicles of th left bundle branch

A

LBBB = left anterior fasicular block + Left posterior fasicular block

27
Q

when the fascicles of the LBB are damaged in isolation

A

posterior or anterior branch
anterior fascicle block is more common

28
Q

anterior fascicle block causes

A

left axis deviation
more common

29
Q

posterior fascicle block causes

A

right axis deviation
the posterior fascicle does much less work than the anterior fascicle so can be blocked without any obvious ECG changes

30
Q

can the right ventricular muscle deviate the cardiac axis

A

the right ventricular muscle does not have great enough mass to significantly deviate the cardia axis

31
Q

bifascicular block

A

involves both right bundle branch block as well as blockade of one of the fascicles of the left bundle branch

32
Q

trifascicular block

A

when 3rd degree heart block exists alongside bifascicular block

Internal Med 2023 (52 decks)

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