Step 1 HEART RATE
Heart rate can be calculated simply with the following method:
Work out the number of large squares in one R-R interval
Then divide 300 by this number and you have your answer
Example : if there are 3 squares in an R-R interval 300/3=100
So the heart rate is 100.
Step 2 HEART RYTHM
Heart rhythm can be either REGULAR or IRREGULAR.
This can be determined by looking again at the R-R wave interval.
If the R-R interval is inconsistent then the rhythm would be classed as irregular.
Step 3 CARDIAC AXIS
Cardiac axis describes the overall direction of electrical spread within the heart.
In a healthy individual the axis should spread from 11 o clock to 5 o clock.
To figure out the cardiac axis you need to look at leads I,II & III.
Normal cardiac axis
In normal cardiac axis Lead II has the most positive deflection compared to Leads I & III
Right axis deviation
In right axis deviation Lead III has the most positive deflection & Lead I should be negative
This is commonly seen in individuals with Right Ventricular Hypertrophy
Left axis deviation
In left axis deviation Lead I has the most positive deflection & Leads II & III are negative
Left axis deviation is seen in individuals with heart conduction defects
Step 4 P WAVES
-Are P-waves present?
-Do they occur regularly?
-Is there sinus rhythm (does a P-wave precede each QRS complex?)
-Do the P-waves look normal? (smooth, rounded & upright)
If P waves are absent and there is an irregular rhythm it may suggest atrial fibrillation
Step 5 P-R Interval
The P-R interval should be between 0.12-0.2 seconds(3-5 small squares)
Are the P-R intervals consistent or do they change throughout the ECG?
If P-R intervals are prolonged it may suggest presence of heart block.
Step 6 QRS complex
Check the width of the QRS complexes.
The QRS complex should be 0.04-0.12 seconds(3 small squares).
If longer than 0.12 seconds it suggests the complex originated in the ventricles.
If shorter than 0.12 seconds it suggests the complex is supra-ventricular in origin.
Task: Describe this ECG based on the 6 steps above. Try it. Practice make perfect.
The answer will be announce tomorrow.
Reference:
1. Professor Ilya Grigorevic Pocinka, Head of Department for Myocardial Infarction in Nizhny Novgorod
2. geekymedics.com/2011/02/28/how-to-read-an-ecg
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