This document provides a template for systematically analyzing 12-lead ECGs, beginning with type and recording details, rate/rhythm/axis, P wave, PR interval, QRS complex, ST segment, T wave, and other findings. Key areas of analysis include intervals, amplitudes, morphologies, and identifying pathological patterns indicative of conditions like myocardial infarction, arrhythmias, chamber enlargement, and lethal causes of syncope. The systematic approach aids accurate ECG interpretation and diagnosis.

1. ECG: Systematic
Analysis
Dr Nola McPherson CME SCGH 2014

2. ECG Interpretation Overview
1. ECG type &recording
2. Rate, Rhythm, Axis
3. P wave
4. PR interval + segment
5. Q Waves, R waves
6. QRS complex
7. ST segment
8. T wave
9. U wave
10. QT interval

3. ECG Interpretation Overview
11. Additional waves (D O E)
12. Chamber hypertrophy
13. Other
- T oxicology
- I schaemia
- E lectrolytes
- sudden death ECG
Q B R A D W H
- dextrocardia
- lead reversals
- artefacts
- pacing spikes

4. Putting it all together…
Diagnosis
Differential diagnoses
Life threats

5. ECG Interpretation Template
1. ECG type & recording

6. ECG TYPE & RECORDING
 12 lead vs rhythm strip
 Paper rate (N= 25mm/s)
 Calibration (5mm wide, 10mm
high = 1mV)
 Unusual leads
- right
- posterior

11. ECG Interpretation Template
1. ECG type &recording
2. Rate, Rhythm, Axis

12. Rate, Rhythm, Axis
RATE
Normal 60-100/min (tachy/bradycardia)
Method: 300/RR(large squares)
OR 1500/RR(small squares)
OR number of QRS x 6 (if 25mm/s)
RHYTHM
Pattern: regular or irregular (reg irreg or irreg irreg)
7 STEP APPROACH

13. Rate, Rhythm, Axis
AXIS
Normal (-30 to +90)
RAD
LAD
NW axis

14. NORMAL SINUS RHYTHM
12 Lead ECG

15. ECG Interpretation Template
1. ECG type &recording
2. Rate, Rhythm, Axis
3. P wave

16. P Wave
 ?present or absent
 Amplitude & duration (LAE/RAE/BAE)
<2.5mm amp limb leads, <1.5mm amp chest leads
<3mm duration
 Contour
monophasic lead II, biphasic lead V1
inverted aVR, upright I, II, V2-6

17. Left Atrial Enlargement

18. Left Atrial Enlargement

19. Right Atrial Enlargement

20. Right Atrial Enlargement

21. ECG Interpretation Template
1. ECG type &recording
2. Rate, Rhythm, Axis
3. P wave
4. PR interval +
segment

22. PR Interval
 Duration (N= 120-200ms)
Short (<120ms)
1. Preexcitation Syndrome
eg WPW, Lown - Ganong- Levine (LGL)
2. AV (nodal) junctional Rhythm
Long (>200ms)
1. 1 HB (alone or with other blocks)
Varying (blocks)

23. Short PR Interval - WPW
 Short PR interval (<120ms)
 Prolonged QRS (>110ms) + early slurred upstroke (delta wave)
 Dominant R in V1-3
 ST seg & T wave discordant changes

24. Short PR Interval - LGL

25. Short PR – AV (nodal)
Junctional Rhythm

26. Long PR Interval

27. PR Segment
 Elevation or Depression
1. pericarditis
2. atrial ischaemia
- Liu’s Criteria

28. ECG Interpretation Template
1. ECG type &recording
2. Rate, Rhythm, Axis
3. P wave
4. PR interval + segment
5. Q Waves, R waves

29. Q waves
 NORMAL
<1mm wide, <2mm deep
 PATHOLOGICAL
Criteria:
- >40ms (>1mm wide)
- > 2mm deep
- >25% depth of QRS complex
- seen in lead V1- V3
DDX:
1. Myocardial infarction
2. Cardiomyopathies
Hypertrophic
Infiltrative disease

30. Pathological Q Waves

31. R waves
 NORMAL
Transition point V3-V4
 ABNORMAL
Dominant R wave in aVR
Dominant R wave in V1
Poor R wave progression (Ht ≤ 3 mm in V3)

32. Dominant R Wave in aVR
CAUSES
1. Poisoning with Na channel blocking medications
(Criteria: R wave height > 3 mm, R/S ratio > 0.7)
2. Dextrocardia
3. Incorrect lead placement (L & R arms reversed)

33. Dominant R Wave in V1
CAUSES
1. RVH (PE, L to R shunt)
2. RBBB
3. POSTERIOR MI (+ STE in leads V7,8,9)
4. WPW TYPE A
5. Hypertrophic Cardiomyopathy
6. Dextrocardia
7. Normal in children and young adults

35. Poor R Wave Progression
CAUSES
1. Prior anteroseptal infarction
2. LVH
3. Dilated cardiomyopathy
4. Transpositioin of leads V1 & V3
5. May be normal

37. ECG Interpretation Template
1. ECG type &recording
2. Rate, Rhythm, Axis
3. P wave
4. PR interval + segment
5. Q Waves, R waves
6. QRS complex

38. QRS Complex
 Duration
N = 70-100ms
narrow (Supraventricular)
wide (ventricular or SVT
with aberrant
conduction)
 Amplitude
High voltage eg LVH
Low voltage
Alternans eg
pericardial effusion
 Morphology
Notched
RBBB
LBBB
 Spot Diagnoses
Brugada Syndrome
WPW Syndrome (delta
waves)
Tricyclic poisoning (wide
QRS + dom R in aVR

40. ECG Interpretation Template
1. ECG type &recording
2. Rate, Rhythm, Axis
3. P wave
4. PR interval + segment
5. Q Waves, R waves
6. QRS complex
7. ST segment

41. ST Segment
 Displacement
Elevation
Depression
 ST Depression Morphology
Horizontal
Up sloping
Down sloping

42. ST Segment Elevation

43. ST Segment Depression

44. ECG Interpretation Template
1. ECG type &recording
2. Rate, Rhythm, Axis
3. P wave
4. PR interval + segment
5. Q Waves, R waves
6. QRS complex
7. ST segment
8. T wave

45. T Wave
Normal
= < 5mm height in limb leads
= < 15mm height in precordial leads
= < 2/3 R

46. T Wave Amplitude &
Morphology
Peaked eg hyperkalaemia
Flat eg myocardial ischaemia, hypoK
Hyperacute eg early STEM, Prinzmetal angina
Inverted eg ischaemia & infarction, increased ICP
Biphasic eg Myocardial ischaemia, hypoK, Wellens

47. T Wave Morphology

48. ECG Interpretation Template
1. ECG type &recording
2. Rate, Rhythm, Axis
3. P wave
4. PR interval + segment
5. Q Waves, R waves
6. QRS complex
7. ST segment
8. T wave
9. U wave

49. U Wave
 Normal
= 0.5 mm (max 2mm)
= 10% TW (max 25% TW)
 Prominent
 Inverted

50. U Wave
 Prominent
> 1-2mm or > 25% ht TW
CAUSES
Bradycardia
HypoK
HypoCa, HypoMg
Hypothermia
Increased ICP
LVH
Hypertrophic cardiomypy
Digoxin
 Inverted
abnormal if in leads with upright
T waves
CAUSES
Heart disease
**HIGHLY SPECIFIC FOR HEART
DISEASE**
**Predicts >75% stenosis of
LAD/LMCA and suggests LV
dysfn**

51. ECG Interpretation Template
1. ECG type &recording
2. Rate, Rhythm, Axis
3. P wave
4. PR interval + segment
5. Q Waves, R waves
6. QRS complex
7. ST segment
8. T wave
9. U wave
10. QT interval

52. QT Interval
 Normal QTc
= 390-440ms M/460 ms
F
< ½ preceding RR
inversely prop to HR
Measure in lead II or V5-6
Large U waves (>1 mm) fused
to T included in measurement
Small, separate U waves
excluded in measurement
 Long (>440/460 ms)
 Short (<350ms)

53. QT Interval

54. ECG Interpretation Template
11. Additional waves (D O E)

55. Additional Waves (D O E)
 Delta Wave
WPW
= slurred upstroke to QRS
Additional Features:
Short PR interval (<120ms)
Broad QRS (>100ms)

56. Additional Waves (D O E)
 Osborn Wave (J waves)
= positive deflection at J point
Most prominent in precordial leads
Causes
Hypothermia
Hyper Ca
Medications
Raised ICP
Normal varient

57. Additional Waves (D O E)
 Epsilon Wave
Arrythmogenic RV dysplasia (in
30% patients)
= pos deflection buried in end of
QRS
Additional Features
TWI V1-3
Prolonged S Wave upstroke V1-3

59. ECG Interpretation Template
11. Additional waves (D O E)
12. Chamber hypertrophy
13. Other
- T oxicology
- I schaemia
- E lectrolytes
- sudden death ECG
- dextrocardia
- lead reversals
- artefacts
- pacing spikes

60. Lethal Causes Syncope
Q BRAD W H
1. QT syndrome (Long/short)
2. Brugada Syndrome
3. RV infarction
4. Arrythmogenic RV Dysplasia
5. Dilated Cardiomyopathy
6. WPW
7. Hypertrophic Cardiomyopathy

61. Questions & Comments

62. References
 Life in the Fast Lane ECG Library