I have covered common MRCP questions about ECG in my previous 2 posts, today, we are going to talk about heart block, there are two main type of heart block, AV ( atrio-ventricular) block and intraventricular block. We will talk about AV block today. As you might remember as a medical student, there are three subtypes of AV block, namely first, second and third degree heart block.
First degree heart block
It is easy to pick up in your ECG, normal PR interval is 0.12-0.20s, if PR interval is more than 0.2s, it is considered as first degree heart block.
Note: Always remember that shortened PR interval occurs in WPW syndrome!Second degree heart block
There are two types of second degree heart block,
a) Classical “Wenckebach” ( Mobitz type 1) where the PR interval gets longer (by shorter increments) until a nonconducted P wave occurs. The RR interval of the pause is less than the two preceding RR intervals, and the RR interval after the pause is greater than the RR interval before the pause.
b) Mobitz type 2- For this heart block, AV block the PR intervals are constant until a nonconducted P wave occurs. ( as below ECG)
Third degree heart blockEasy to remember, complete AV dissociation
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