This document outlines an approach for interpreting electrocardiograms (ECGs). It discusses justifying ECG use based on symptoms or exam findings. A structured approach is presented: check quality, rate, rhythm, axis, P wave, PR interval, QRS duration/morphology, ST segment, T wave, QT interval. Abnormal findings are defined, such as ST depression indicating ischemia. The goal is to develop skills in systematic ECG interpretation and identifying common abnormalities.

1. ECG
interpretation

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

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

5. The ECG

6. 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

7. ECG interpretationQuality of ECG?
Rate
Rhythm
Axis
P wave
PR interval
QRS duration
QRS morphology
Abnormal Q waves
ST segment
T wave
QT interval

8. 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

9. Calibration

10. Calibration

11. ECG interpretationQuality of ECG?
Rate
Rhythm
Axis
P wave
PR interval
QRS duration
QRS morphology
Abnormal Q waves
ST segment
T wave
QT interval

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

13. Rate

14. Rhythm
 Are there P waves?
 Are they regular?
 Does one precede every QRS complex?
 Regular vs. irregular

15. Axis

16. Axis

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

18. Axis

19. ECG interpretationQuality of ECG?
Rate
Rhythm
Axis
P wave
PR interval
QRS duration
QRS morphology
Abnormal Q waves
ST segment
T wave
QT interval

20. P wave
 Are there P waves present?
 Bifid = P mitrale (LA hypertrophy)
 Pointy = P pulmonale (RA hypertrophy)

21. P mitrale

22. P pulmonale

23. PR interval Start of P wave to start of QRS complex
 Normal = 0.12 - 0.2 seconds (3-5 small squares)
 Decreased = can indicate an accessory pathway
 Increased = indicates AV block (1st
/2nd
/3rd
)

24. ECG interpretationQuality of ECG?
Rate
Rhythm
Axis
P wave
PR interval
QRS duration
QRS morphology
Abnormal Q waves
ST segment
T wave
QT interval

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

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

27. 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

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

29. ECG interpretationQuality of ECG?
Rate
Rhythm
Axis
P wave
PR interval
QRS duration
QRS morphology
Abnormal Q waves
ST segment
T wave
QT interval

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

31. ST segment

32. ST segment

33. ST segment

34. T wave
 Small = hypokalaemia
 Tall = hyperkalaemia
 Inverted/biphasic = ischaemia/previous
infarct

35. T wave

36. T wave

37. T wave

38. 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

39. QT interval

40. ECG quiz

41. ECG 1

42. ECG 2

43. ECG 3

44. ECG 4

45. Any questions?

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