The question: 'Tell me about this ECG.'
The answer: 'This is an ECG of Mrs. Bloggs taken 2 days ago.' This information might not be on the ECG but it is very important that the patient's name is there. While doing this, take an overall look at the ECG. Is there anything obvious? Does it have any answers at the top of the page?! Do you know the patient? OK, so this might not help you in your exams, but hey.
Now work systematically through the ECG:
'The rate is...' To work out the rate take 300 and divide by the distance between two QRS complexes. Normal is 60 - 100 beats per minute in the average Mr Bloggs.
6 squares = 300/6 = 50bpm (bradycardia)
5 squares = 300/5 = 60bpm
4 squares = 300/4 = 75bpm
3 squares = 300/3 = 100bpm
2 squares = 300/2 = 150bpm (tachycardia)
(Counting squares to calculate the rate assumes a normal paper speed of 25mm/second).
'The rhythm is...' Is the rhythm regular? This can be worked out by marking the QRS distances on a piece of paper and shifting it along to see if the pattern always fits. If it is irregular, is it irregularly irregular? If there are P waves before each QRS and it is regular, the rhythm is 'sinus'.
'The axis is...' The axis of the heart is the average direction of impulse flow. To assess this, look at leads I, II and III. For axis, look at the overall deflection of the QRS. Is it up (positive) or down (negative)? The normal axis of the heart is from +90 to -30 , measured from 3 o'clock as 0°.
I find the easiest way to think of this is as vectors. In the normal ECG all three leads are positive.
If lead I is negative, there is right axis deviation.
If leads II and III are negative, there is left axis deviation.
'The P wave...' The P wave should be normal in shape and size (<2.5mm tall). It reflects the atrial depolarization. Abnormalities reflect changes in the atria and valves.
'The PR interval...' Reflects the transmission from atria to ventricles, it should be 3-5 small squares. Abnormalities can be extra pathways or block.
'The QRS complex...' Q waves can be normal in some leads but bigger than 1mm might signify previous MI. QRS should be less than 3 small squares wide. Wider complexes imply abnormal depolarization. Very tall R waves can reflect left ventricular hypertrophy.
'The ST segment is...' The gap between the S and T waves should be around the baseline, it can be elevated (MI) or depressed.
'The T wave is...' Normal is <10mm tall. Abnormal T waves can be peaked or inverted.
'U waves...' Are rarely seen in normal people or hypocalcemia.
'Overall I think that ……… or…….. this is normal……..or…….. I don't know!'