Conduction Blocks

Question 1

Define conduction blocks

Answer 1

A delay/blockage in the electrical signals that progresses throughout the structure of the heart, can vary in levels of severity

Question 2

Where are the 2 locations for conduction blocks?

Answer 2

• AV Block
• Bundle Branch Block

Question 3

Describe AV block

Answer 3

Delay occurs at the AV node

Question 4

Describe Bundle Branch Block

Answer 4

Slowed transmission of electrical impulses in the ventricular conducting system of the heart

Question 5

What are the different types of AV block?

Answer 5

• 1st degree
• 2nd degree
  
  • Mobitz Type 1
  • Mobitz Type 2
• 3rd degree

Question 6

Describe 1st degree AV block

Answer 6

Electrical impulse at AV node is delayed, WITHOUT disruption to ventricular conduction
PR interval > 0.2s (Normal interval: 0.12 – 0.2s)

Question 7

Describe 2nd degree AV block

Answer 7

Atrial impulse is occasionally obstructed, leading to failure of ventricles to contract (“dropped beat” pattern)

Question 8

Describe Mobitz type 1 AV block

Answer 8

PR becomes longer and longer until QRS disappears, and the cycle then resets

Question 9

Describe Mobitz type 2 AV block

Answer 9

consistently long PR segment, then QRS disappears and cycle resets

Question 10

Describe 3rd degree AV block

Answer 10

Complete electrical blockage between atria and ventricles; atria and ventricles beat at different rates; they are uncoordinated and random

Question 11

What are the causes of AV block?

Answer 11

Anything that causes damage to the heart and therefore scarring:
- Ischaemic Heart disease (AKA Coronary artery disease), MI
- Electrolyte abnormalities (e.g. hypokalaemia)
- Inflammation infections (Rheumatic fever, Endocarditis)
- Drugs (Antiarrhythmics and Digoxin)
- Infiltrative disease (Sarcoidosis)
- Idiopathic Degenerative diseases (Lenegre and Lev’s Disease)

Question 12

What are the symptoms of AV block?

Answer 12

1st Degree heart block is usually asymptomatic
As heart block progresses, however, the following signs/symptoms may present:

• Dizziness/Fainting (Syncope)
• Feeling of “missed” beat
• Chest Pain
• Shortness of breath (Dyspnoea)
• Unexplained nausea
• Easily fatigued

Question 13

What is the investigation for AV block?

Answer 13

ECG

Question 14

What are further investigations for AV block?

Answer 14

Mainly in 2nd and 3rd Degree, assess damage, disease or suitability for a pacemaker:

• Bloods (Cardiac biomarkers e.g. troponin for signs of ischaemia, or FBC for diseases)
• Electrolytes (Calcium and Magnesium)
• Medication and toxicity (e.g. Digoxin)

Question 15

What is the treatment for 1st degree AV block?

Answer 15

None Needed

Question 16

What is the treatment for 2nd degree T1 AV block?

Answer 16

• Often not necessary
• Can result in bradycardia which leads to hypotension; use atropine

Question 17

What is the treatment for 2nd degree T2 AV block?

Answer 17

• Permanent Pacemaker (after evaluation)
• T2 can deteriorate into complete heart block and does not respond to atropine

Question 18

What is the treatment for 3rd degree AV block?

Answer 18

• Permanent Pacemaker (after evaluation)
• If bradycardic, can use dopamine or epinephrine for temporary relief

Question 19

Describe bundle branch block (BBB) pathophysiology

Answer 19

• The Left or Right bundle branches become damaged due to injury to the myocardium
• This interruption causes electrical stimuli from the AV node to travel down the bundle of His and down the opposite side of the heart, causing the ventricle on that side to depolarise first, then the ventricle on the side with the block to depolarise after

Question 20

Which side is depolarised first in RBBB?

Answer 20

RBBB means Left ventricle depolarises first, then right

Question 21

What are causes of BBB?

Answer 21

Anything that changes the myocardium of the bundle branches:
- Dilated Cardiomyopathy (Main cause of LBBB; stretches Purkinje fibres)
- Ischaemia and MI
- Rarely Electrolyte disorders (Hyperkalaemia)
- Infections (Myocarditis)
- Increased intraventricular pressure (Stretches myocardium; pulmonary stenosis)
- Lenegre’s or Lev’s disease

Question 22

What are symptoms of BBB?

Answer 22

• In both BBB, patients may be asymptomatic
• If symptoms present, they involve:
  - Chest Pain
  - Dizziness and Fainting

Question 23

What is the epidemiology of BBB?

Answer 23

• RBBB: Incidence increases with age; 11.3% of people with it by age 80
• LBBB: Prevalent in 0.06% to 0.1% of the general population

Question 24

What is the investigation for BBB?

Answer 24

ECG, specifically leads V1 and V6

Question 25

What do leads V1 and V6 show on ECG?

Answer 25

• V1: Allows to see impulses going towards the right side of the heart/Down right ventricle
• V6: Allows to see impulses going towards the left side of the heart/Down left ventricle

Question 26

What is seen on ECG for LBBB?

Answer 26

• V1: Appears as a “W” shape but can appear as a “V” shape (Called a “QS wave” (No R wave) or “rS wave” (Little R wave)
• V6: Appears as a “notched M” shape

Question 27

What is seen on ECG for RBBB?

Answer 27

V1: Appears as an “M” shape with a large terminal R
V2: Appears as a “W” shape with a slurred S wave

Question 28

What is the treatment for BBB?

Answer 28

• Cardiac Resynchronization Therapy (CRT)
• Cardiac pacemaker

Question 29

What does WilLiaM MaRroW tell us?

Answer 29

Left V1 = W, Left V6 = M
Right V1 = M, Right V6 = W