Bundle Branch Blocks

Question 1

Cardiac conduction system?

Answer 1

Made up of:

• conduction cells <— transmits electrical impulses rapidly
• contractile cells <— cell to cell transmission is much slower
• normally both ventriculus depolarise at the same time, in a coordinated manner.

Question 2

Bundle Branch block ?

Answer 2

1) interruption to normal transmission of depolarisation through the bundle branch

2) caused by some form of defect (infarction, structural changes, trauma , pressure)

3) This means that transmission isn’t able to pass through the bundle branch in the normal manner.

4) impulse is therefore conducted through opposite branch first

5) Contralateral ventricle will depolarise first, ipsilateral ventricles depolarise later (through slower CONTRACTILE CELLS)

Question 3

Right bundle branch block (RBBB) - Causes?

Answer 3

(Can be normal in patients with no heart disease)

• In the presence of cardiac symptoms it is ALWAYS ASSUMED to be pathological.

Pathological causes of RBBB include:

• myocardial infarction
• Myocarditis
• Cardiomyopathy
• Pulmonary Embolism (PE)

Question 4

RBBB - WiLLiaM MaRRoW?

Answer 4

M shape in V1
W shape in V6
= right bundle branch block

W shape In V1
M shape in V6
= left bundle branch block

Question 5

Broad, Monophasic R wave?

Answer 5

RSR pattern is not required for it to be considered a RBBB.

• Presence of a broad monophasic R wave in V1 is also considered

Question 6

Wide slurred S wave?

Answer 6

Wide S wave, making QRS > 0.12 , particularly in the S wave.

Question 7

Left bundle branch block (LBBB) ?

Answer 7

LBBB is always pathological.

NEW OR PRESUMED NEW LBBB WITH ACUTE MI, is diagnostic for pathway 1 (DIRECT TO PPCI)

Pathological causes include:

• Myocardial Infarction
• Cardiomyopathy
• Myo/endocarditis
• Valvular disease
• congenital defect

Question 8

Left bundle branch block?

Answer 8

Left bundle branch = blocked

This causes RIGHT VENTRICLE to DEPOLARISE first.

Then cell too cell via contractile cells, through to the left ventricle

Ventricles the fire depolarise from RIGHT TO LEFT . This is abnormal as depolarisation should occur left to right.

Question 9

How to spot Left Bundle Branch Block on an ECG?

Answer 9

• QRS duration= >0.12 seconds (3 small squares)

• Lead V1/V2 (septal leads) = Dominant S waves

• Lead V5, V6 , Lead 1 and aVL (lateral leads) display =

• Broad monophasic R wave

And/or

• Absence of Q waves

Question 10

Septal Activation in LBBB?

Answer 10

1) Conduction delay means impulses travel first via the right bundle branch

2) septum is activated from right —> left

3) overall depolarisation vector is directed towards lateral leads.

Question 11

B-road Monophasic R wave?

Answer 11

• RSR pattern is likely not to be seen, instead there will be a monophasic R wave in V6

Question 12

What is appropriate discordance?

Answer 12

This refers to the fact that:

Abnormal depolarisation should be followed by abnormal re-polarisation.

The heart will always repolarise in the same manner as it depolarised.

If DEPOLARISATION IS ABNORMAL.

Question 13

APPROPRIATE DISCORDANCE - how to spot on an ECG?

Answer 13

In patients with BBB (both left and right):

1) in leads with dominant S waves, ST elevation and positive T waves are often observed

2) in leads with tall/broad R waves, we would often see associated ST depression and T wave inversion.

Question 14

Bundle branch block ~ what happens?

Answer 14

1) interruption to the normal transmission of depolarisation through the bundle branch

2) caused by some form of defect ~ infarction, structural changes, trauma and pressure.

3) as a result, transmissions cannot pass through bundle branch in a normal manner.

4) impulse is therefore conducted through opposite branch first

5) contra lateral ventricle will therefore depolarise first, ipsilateral ventricle depolarises later. Through slower CONTRACTILE CELLS .