1. ECG interpretation Dr Ally Duncan May 2012
SpR In Anaesthesia & Clinical Fellow in Undergraduate Medical Education
Manchester Royal Infirmary
May 2012

2. Objectives Justify the reasons for performing an ECG
Develop a structured approach to interpreting an ECG
Practice interpreting ECGs

3. The ECG
“The ECG (electrocardiogram) is a transthoracic interpretation of the electrical activity of the heart.”

4. The ECG
Cardiac conducting system

5. Why perform an ECG? It’s part of the admission bundle
Indicated by the patient’s symptoms
- symptoms of IHD/MI
- symptoms associated with dysrhythmias
Indicated by the patient’s examination findings
- cardiac murmur

6. ECG interpretation Quality of ECG? Rate Rhythm Axis P wave PR interval
QRS duration
QRS morphology
Abnormal Q waves
ST segment
T wave
QT interval
It’s vital to have a system in place to interpret the ECG.

7. Quality of the ECG Patient name Date of the ECG
Is there any interference?
Is there electrical activity from all 12 leads?
Calibration:
- speed = 25mm/second
- height = 1cm/mV
Small square 0.04s; Large square 0.2s

8. Calibration

9. Calibration

10. ECG interpretation Quality of ECG? Rate Rhythm Axis P wave PR interval
QRS duration
QRS morphology
Abnormal Q waves
ST segment
T wave
QT interval
It’s vital to have a system in place to interpret the ECG.

11. Rate 300/number of big squares between R waves Rate is either:
- normal
- bradycardic
- tachycardic

12. Rate

13. Rhythm Are there P waves? Are they regular?
Does one precede every QRS complex?
Regular vs. irregular
Can use lead II

14. Axis
The normal axis is around 60 degrees.

15. Axis

16. Axis Positive in I and II = NORMAL
Positive in I and negative in II = LAD
Negative in I and positive in II = RAD

17. Axis
The normal axis is around 60 degrees.

18. ECG interpretation Quality of ECG? Rate Rhythm Axis P wave PR interval
QRS duration
QRS morphology
Abnormal Q waves
ST segment
T wave
QT interval
It’s vital to have a system in place to interpret the ECG.

19. P wave Are there P waves present? Bifid = P mitrale (LA hypertrophy)
Pointy = P pulmonale (RA hypertrophy)
Not very useful signs.

20. P mitrale

21. P pulmonale

22. PR interval Start of P wave to start of QRS complex
Normal = seconds (3-5 small squares)
Decreased = can indicate an accessory pathway
Increased = indicates AV block (1st/2nd/3rd)
Short PR interval can be accessory pathway or can be normal

23. ECG interpretation Quality of ECG? Rate Rhythm Axis P wave PR interval
QRS duration
QRS morphology
Abnormal Q waves
ST segment
T wave
QT interval
It’s vital to have a system in place to interpret the ECG.

24. QRS complex Normal = <0.12 seconds
>0.12 seconds = Bundle Branch Block

25. QRS complex
W I LL ia m = LBBB
M a RR o w = RBBB

26. QRS complex Is there LVH?
Sum of the Q or S wave in V1 and the tallest R wave in V5 or V6
>35mm is suggestive of LVH

27. Q waves Q waves are allowed in V1, aVR & III
Pathological Q waves can indicate previous MI

28. ECG interpretation Quality of ECG? Rate Rhythm Axis P wave PR interval
QRS duration
QRS morphology
Abnormal Q waves
ST segment
T wave
QT interval
It’s vital to have a system in place to interpret the ECG.

29. ST segment ST depression - downsloping or horizontal = ABNORMAL
ST elevation
- infarction
- pericarditis (widespread)

30. ST segment

31. ST segment

32. ST segment
ST segment changes are usually in “territories”

33. T wave Small = hypokalaemia Tall = hyperkalaemia
Inverted/biphasic = ischaemia/previous infarct
Tall = can be normal young man

34. T wave

35. T wave

36. T wave

37. QT interval Start of QRS to end of T wave Needs to be corrected for HR
Normal QTc = < 400ms
Long QT can be genetic or iatrogenic
Long QT syndrome. Amiodarone, sotalol.

38. QT interval
Long QT syndrome is associated with Torsades de pointes

39. ECG quiz

40. ECG 1 AF

41. ECG 2
INFERIOR MI

42. ECG 3
LBBB with lateral MI

43. ECG 4

44. Any questions?

45. Summary Discussed the indications for performing an ECG
Introduced an approach to interpreting ECGs
Discussed common ECG abnormalities