Heart Block Flashcards
What is another name for atrioventricular block?
Heart block
What is heart block?
It is when there is impaired electrical conduction between the atria and ventricles
What are the three types of heart block?
1st degree
2nd degree
3rd degree
What is first degree heart block?
This is when there is delayed AV conduction through the AV node
What is a sign of first degree heart block on ECGs?
PR interval > 0.2s
How do we manage first degree heart block?
It is usually asymptomatic and doesn’t require treatment
What is second degree heart block?
This is where some of the atrial impulses don’t make it through the AV node to the ventricle
This means that there are instances where P waves don’t lead to QRS complexes
What are the two subtypes of second degree heart block?
Mobitz type I
Mobitz type II
What is another term for Mobitz type I?
Wenckebach’s phenomenon
What is Mobitz type I?
This is where the atrial impulses becomes gradually weaker until it does not pass through the AV node
After failing to stimulate a ventricular contraction the atrial impulse returns to being strong
This cycle then repeats
How does Mobitz 1 present on ECG scan?
Increasing PR interval until the P wave no longer conducts to ventricles
An absent QRS complex after a P wave
The PR interval then returns to normal but progressively becomes longer again until another QRS complex is missed
This cycle repeats itself
What is Mobitz type II?
This is is where there is intermittent failure or interruption of AV conduction
This results in missing QRS complexes
The PR interval remains constant; however, the P wave is not often followed by a QRS complex
What is a 3:1 Mobitz type II heart block?
There are three P waves to each QRS complex
What is another term for third degree heart block?
Complete heart block
What is third degree heart block?
This is where there no impulses are passed from the atria to the ventricles
This means that there is no association between the P waves and QRS complexes
Which artery is usually affected in complete heart block?
Right coronary artery
In which two heart blocks is there a risk of astolye?
Second degree Mobitz type II
Third degree heart block
What are the five clinical features of heart block?
Syncope
Bradycardia (30 – 50bpm)
Wide Pulse Pressure
JVP Cannon Waves
Variable Intensity of S1
What is the first line management option for heart block?
Atropine
What is the mechanism of action for atropine?
This is an antimuscarinic medication and works by inhibiting the parasympathetic nervous system
What dose of atropine is initially administered?
500mcg IV
What do we do if the initial dose of atropine doesn’t make any improvement?
We can repeat up to 6 doses for a total of 3mg
What is the second line management option for heart block?
Inotropes
What inotrope agent can be administered to treat heart block?
Noradrenaline
What is the third line management option for heart block?
Transcutaneous cardiac pacing
What is transcutaneous cardiac pacing?
This involves using an electrode on the end of a wire that is inserted into a vein and fed through the venous system to the right atrium or ventricle to stimulate them directly
