Bradyarrhythmias Flashcards
What is heart block?
An obstruction in the electrical conduction system of the heart
Results in problems transmitting impulses to some regions of the heart
Bradyarrythmias occur
Why does heart block cause slower heart rate?
Because there are problems in the conduction of impulses from one bit of the heart to others
The impulse takes longer to conduct, or doesn’t even get there
List some types of heart block?
R + L bundle branch block
First degree
Second degree
Third degree heart block
Where do the bundle branches transmit impulses from and to?
From the AV bundle (which has come from the AV node)
Down through the septum
To the apex of the heart where they split into Purkinje fibres
What is bundle branch block?
When electrical impulses from the AV node can’t be transmitted through the bundle branch due to a blockage
The impulse has to travel from the healthy bundle branch on one side across to the other via the muscle fibres
This is slower and more irregular
Ventricular depolarisation occurs at different times on each side
Reduced CO
Causes of bundle branch block?
MI
Heart pathologies
Cardiac surgery
Describe right BBB?
A blockage in the right BBB
Impulse goes from left BB across the heart to the right side
The ventricles don’t depolarise at the same time
What would the ECG of right BBB look like?
C1 lead shows a characteristic M shape
The ‘M’ is large and lopsided
What type of bundle branch block does RV hypertrophy cause?
Right BBB
What type of bundle branch block does LV hypertrophy cause?
Left BBB
Describe left BBB?
A blockage in the left BBB
Impulse goes from right BB across the heart to the left side
The ventricles don’t depolarise at the same time
What would the ECG of left BBB look like?
The peak of the C6 lead has a characteristic M shape
A tiny W or M!
What is the worst heart block to have?
First, second or third degree?
Third degree
Describe the electrical conduction problems briefly in:
- First degree
- Second degree
- Third degree?
First: delayed conduction from atria to ventricles
Secondary: intermittent blocking of conduction from atria to ventricles, not all impulses get through
Third degree: complete blocking of conduction from atria to ventricles
What is Wenckebach another name for?
Mobitz 1 heart block
What is ‘complete heart block’ another name for?
Third degree heart block
What is first degree heart block?
Delayed conduction from the atria to the ventricles
What does first degree heart block look like on an ECG?
Prolonged PR interval more than 0.2 seconds
No other changes, normal heart rate
Causes of first degree heart block?
Athletes
Myocarditis
Hypokalaemia
Drugs
Presentation of first degree heart block?
Asymptomatic
Often incidental finding
Management of first degree heart block?
None needed, monitor it
What are the two types of second degree heart block?
Mobitz 1
Mobitz 2
What is second degree heart block?
Some impulses are blocked from traveling from the atria to the ventricles, but not all of them
What does second degree heart block look like on ECG?
Cycles which result in a P wave being blocked from generating a QRS complex
So you get occasional P waves which are not followed by a QRS wave
Then the cycle resets, it repeats itself
Mobitz 1: prolongation of PR intervals until the dropped QRS occurs
Mobitz 2: no prolongation of PR interval
Causes of second degree heart block?
Athletes
Post MI
Lyme disease
Drugs
Symptoms of second degree heart block?
Mobitz 1 vs 2
Mobitz 1:
- light headedness
- dizziness
- syncope
Mobitz 2:
- chest pain
- dyspnoea
- tiring on exertion
Complications of second degree heart block?
Can progress to complete (third degree) heart block
Which can result in cardiac arrest and death
Treatment second degree heart block?
Implantable pacemaker
What is third degree heart block?
Complete heart block
The impulse generated in the SAN does not get to the ventricles
So an accessory pacemaker kicks in called an escape rhythm
This is a pacemaker found in the ventricles that activates independently of the SAN
So the ventricles still contract, just not in rhythm with the atria
What would third degree heart block look like on an ECG?
P waves are normal and regular
But the QRS waves are not being controlled by the SAN so they occur independently to the P waves
What is meant by ‘escape rhythm’?
An accessory pace maker found in the ventricles that activates independently of the SAN
It prevents the heart stopping completely in complete heart block
What are the causes of third degree heart block?
CHD Radiotherapy Infection Hypertension Drugs
Symptoms of third degree heart block?
Light headedness Dizziness Fatigue Syncope Bradycardia
Management of third degree heart block?
Implantable pacemaker
