Conduction Blocks Flashcards
Define conduction blocks
A delay/blockage in the electrical signals that progresses throughout the structure of the heart, can vary in levels of severity
Where are the 2 locations for conduction blocks?
- AV Block
- Bundle Branch Block
Describe AV block
Delay occurs at the AV node
Describe Bundle Branch Block
Slowed transmission of electrical impulses in the ventricular conducting system of the heart
What are the different types of AV block?
- 1st degree
- 2nd degree
- Mobitz Type 1
- Mobitz Type 2
- 3rd degree
Describe 1st degree AV block
Electrical impulse at AV node is delayed, WITHOUT disruption to ventricular conduction
PR interval > 0.2s (Normal interval: 0.12 – 0.2s)
Describe 2nd degree AV block
Atrial impulse is occasionally obstructed, leading to failure of ventricles to contract (“dropped beat” pattern)
Describe Mobitz type 1 AV block
PR becomes longer and longer until QRS disappears, and the cycle then resets
Describe Mobitz type 2 AV block
consistently long PR segment, then QRS disappears and cycle resets
Describe 3rd degree AV block
Complete electrical blockage between atria and ventricles; atria and ventricles beat at different rates; they are uncoordinated and random
What are the causes of AV block?
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)
What are the symptoms of AV block?
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
What is the investigation for AV block?
ECG
What are further investigations for AV block?
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)
What is the treatment for 1st degree AV block?
None Needed
What is the treatment for 2nd degree T1 AV block?
- Often not necessary
- Can result in bradycardia which leads to hypotension; use atropine
What is the treatment for 2nd degree T2 AV block?
- Permanent Pacemaker (after evaluation)
- T2 can deteriorate into complete heart block and does not respond to atropine
What is the treatment for 3rd degree AV block?
- Permanent Pacemaker (after evaluation)
- If bradycardic, can use dopamine or epinephrine for temporary relief
Describe bundle branch block (BBB) pathophysiology
- 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
Which side is depolarised first in RBBB?
RBBB means Left ventricle depolarises first, then right
What are causes of BBB?
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
What are symptoms of BBB?
- In both BBB, patients may be asymptomatic
- If symptoms present, they involve:
- Chest Pain
- Dizziness and Fainting
What is the epidemiology of BBB?
- 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
What is the investigation for BBB?
ECG, specifically leads V1 and V6
What do leads V1 and V6 show on ECG?
- 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
What is seen on ECG for LBBB?
- 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
What is seen on ECG for RBBB?
V1: Appears as an “M” shape with a large terminal R
V2: Appears as a “W” shape with a slurred S wave
What is the treatment for BBB?
- Cardiac Resynchronization Therapy (CRT)
- Cardiac pacemaker
What does WilLiaM MaRroW tell us?
Left V1 = W, Left V6 = M
Right V1 = M, Right V6 = W
