ECG - advanced - chest pain - 2 
 

Inferior mycardial infarction
 

These are usually caused by blockage of the smaller right coronary artery.

Shown here you can see marked elevation of the ST segments in the inferior leads - III and aVF.    
Inferior myocardial infarction
 

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Remember where the direction that the leads of the ECG look at the heart.   
Image The ECG lead axes
 
 
Here is another inferior MI with reciprocal changes (ST depression) seen in the lateral chest leads V4-V6.   
 

Inferior MI with lateral reciprocal changes
 

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Extensive infarct
 

This time the infarct area (the area of ST elevation) spreads from the inferior part of the heart (Leads II, III and aVF) to include the lateral side (V4-V6) and there is also ST depression seen in V1, indicating posterior involvement.   
Infero-lateral-posterior MI
 

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Heart block in inferior infarction
 

Heart block and bradycardia are common in inferior infarction. This is because the right coronary artery ususally supplies the sinoatrial (SA) node and the atrioventricular (AV) node.
However because the dominant supply is still usually the left coronary artery, the outlook is usually good and pacing is not required. They often respond well to atropine, indicating the a high vagal tone.
In contrast, bradycardia and heart block, particulary Mobitz type II and third degree occurring in the context of an anterior infarction almost always need a temporary pacemaker, and often a permenant one.    
Intermittant Mobitz type II 2 to 1 block in an inferior MI
 

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This ECG illustrates more subtle changes, with mild ST elevation seen in leads III and aVF and reciprocal ST depression in lead aVL.
Note also the early T wave inversion seen in lead II.   
More subtle inferior MI
 

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This infarct is in the early stages of development, as shown by the very marked ST elevation in lead III.
Note the ST depression in V1. This is due to a posterior infarct. The trick to demonstrate this is to print out the ECG and then hold the ECG upside down, look through from the BACK of the paper (so you are looking at the heart as if from the back) - the ST segment is raised, indicating infarction.     
Infero-posterior MI
 

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This patient has an extensive inferior infarct, and also demonstrates the R on T phenomenon in the rhythm strip. This is regarded as an indicator of a patient's potential to have significant ventricular arrhytmias, as this patient subsequently demonstrated.   
R on T phenomenon in inferior MI
 

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When the R wave (depolarisation) occurs during the T wave (repolarisation) this is an indication of a seriously dysfunctional myocardium, and indicates that it is easy for a ventricular arrhythmia to start.   
R on T diagram