Bundle Branch block Flashcards
What is a bundle branch block?
Bundle branch block is a condition in which there’s a delay or blockage along the pathway that electrical impulses travel to make the heart beat. It sometimes makes it harder for the heart to pump blood to the rest of the body.
The delay or blockage can occur on the pathway that sends electrical impulses either to the left or the right side of the bottom chambers (ventricles) of the heart.
What is the main clinical feature of a bundle branch block?
broadening of QRS complexes
As the problem is below the atria, the P waves and the PR intervals are normal
What are the two types of complete bundle branch block?
1) right
2) left
True or false: bundle branch block is usually asymptomatic
true
What is the most common cause of right bundle block?
congenital anomaly
What is the most common cause of left bundle block?
extensive left ventricular disease e.g. aortic stenosis, MIs, hypertension
What is the diagnostic criteria for a right bundle branch block?
Broad QRS complex: >120 ms (3 small squares)
RSR’ pattern in V1-V3: an initial small upward deflection (R wave), a larger downward deflection (S wave), then another large upward deflection (a second R wave, which is indicated as R’)
Wide, slurred S wave in lateral leads: I, aVL, V5-V6
What is the WiLLiaM MaRRoW mnemonic?
The WiLLiaM MaRRoW mnemonic can be used to quickly recognise left and right bundle branch blocks by looking at V1 and V6:
WiLLiaM refers to the ECG appearance of left bundle branch block (see next section)
MaRRoW refers to the ECG appearance of right bundle branch block
The middle letters of the names help you remember which bundle branch block each name is referring two (two Ls in WiLLiaM = left bundle branch block, two Rs in MaRRoW = right bundle branch block).
Each name’s first and last letter helps you recognise the ECG features of the associated bundle branch block
What does MaRRoW refer to?
M: complexes in V1 resemble the letter M: initial small upward deflection (r wave), a larger downward deflection (S wave), then another large upward deflection (second R wave)
W: complexes in V6 resemble a W: initial small downward deflection (Q wave), then a larger upward deflection (R wave), and then a wide downward deflection (S wave)
What is the pathophysiology in a right bundle branch block?
The sino-atrial node acts as the initial pacemaker
Depolarisation reaches the atrioventricular node
Depolarisation through the bundle of His occurs only via the left bundle branch. The left branch still depolarises the septum as normal.
The left ventricular wall depolarises as normal.
The right ventricular walls are eventually depolarised by the left bundle branch, this occurs by a slower, less efficient pathway.
What are some examples of Cause of a RBBB?
- Underlying lung pathology eg COPD, PE or cor pulmonale
- Primary heart muscle disease
- Ischaemic heart disease
What is the diagnostic criteria of a left bundle branch block?
Broad QRS complex: >120 ms (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
What does the mnemonic WiLLaM refer to ?
To recognise left bundle branch block, we use the name WiLLiaM and look at the first and last letters:
W: complexes in V1 resemble the letter W: deep downward deflection (dominant S wave), which may be notched
M: complexes in V6 resemble the letter M: broad, notched or ‘M’ shaped R wave in V6
What is the pathophysiology for a LBBB?
The sino-atrial node acts as the initial pacemaker
Depolarisation reaches the atrioventricular node
Depolarisation down the bundle of His occurs only via the right bundle branch. The septum is abnormally depolarised 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.
What is type pf cause is a LBBB?
Pathological
Left bundle branch block may be due to conduction system degeneration or myocardial pathologies such as ischaemic heart disease, cardiomyopathy and valvular heart disease.
LBBB may also occur after cardiac procedures, which damage the left bundle branch or His bundle. A STEMI presenting as chest pain with LBBB is exceedingly rare.
