A. Inferior myocardial infarction – Explanation
The easiest method to recognize this is to:
1. Find the lead with smallest or equiphasic deflection. In this case it would be lead
aVR.
2. Look for the leads which are at right angles to the first lead you picked. This
would be lead III.
3. Look at the net deflection at the second lead (which in this ECG your eyes would
be looking at lead III. Since lead III has a negative net deflection (seen on yellow
circle on ECG), this is a left axis deviation. This can be confirmed by looking at
lead aVL where you would see a positive net deflection (seen on blue circle on
ECG).
To recap:
Lead with smallest deflection is aVR
Lead at right angles to aVR is lead III
Net deflection in lead III is negative
Thus AXIS is -60 which falls under left axis deviation
A common cause of left axis deviation is inferior myocardial infarction
Remember, this question is not asking if this is an inferior myocardial infarction hence
the ECG does not show the typical ST elevation in leads II, III, and aVF. This question
is asking, what abnormalities could represent a left axis deviation of which inferior
myocardial infarction is the only option.
ECG causes of axis deviation
Common causes of left axis deviation (LAD)
Left ventricular hypertrophy (LVH)
Left anterior fascicular block (or hemiblock)
Inferior myocardial infarction
Less common causes of left axis deviation (LAD)
Obesity
Wolff Parkinson White syndrome
Causes of right axis deviation
Right ventricular hypertrophy
Thin tall
Chronic lung disease
Pulmonary embolism
Left posterior hemiblock
Lateral myocardial infarction
Lateral wall of the left ventricle is supplied by left anterior descending. Infarction here
would cause an axis deviation away from site of infarction.
Causes of extreme right axis deviation (Also known as “no man’s land” or
“northwest axis”)
Congenital heart disease
Left ventricular aneurysm
Rules of Thumbs for Determining Cardiac Axis Deviation on ECG
Look at lead I and Lead III
A positive deflection means thumbsup and a negative deflection means thumbsdown
