ECG interpretation for beginners - 1

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ECG interpretation for beginners - 1

• Paul Williams
• Cardiology Specialist Registrar

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How to read ECGs?

• 1) Have a system!
• 2) See lots pattern recognition

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Absolute basics
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A system

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

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The normal ECG
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Check quality of ECG

• Patient name
• Date of ECG
• ? interference
• 12 leads
• Rhythm strip (II or V1) at bottom
• Scale
• 25mm/s horizontal
• 10mm/mV vertical
• Little square0.04s big square0.2s

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A system

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

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Rate

• Computer calculated rate usually correct
• Still need to manually calculate!
• 300/RR interval in big squares
• If irregular average 5
• Rate is either
• Normal
• Bradycardia
• Tachycardia

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Rate
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Rhythm

• Different to rate!
• First thing to ask is there a clear P wave
  before each QRS? (lead II)
• Regular vs irregular (paper trick.)
• Tachyarrhythmias vs bradyarrhythmias (separate
  talk)
• Commonest rhythm is SR (ie. normal)
• Commonest arrhythmia is AF

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Axis
Coronal/frontal plane Normal axis is about 60
degrees LAD axis lt -30 degrees RAD axis gt 90
degrees
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Axis trick
Positive in I and II normal
Positive in I Negative in II LAD
Negative in I Positive in II RAD
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A system

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

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P wave

• Are there P waves.?
• Pointy P pulmonale (RA hypertrophy)
• Bifid P mitrale (LA hypertrophy)
• Not very accurate or useful.

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PR interval

• Start of P wave to start of QRS
• Normal 0.12-0.2s
• Too short can mean WPW syndrome (ie. an
  accessory pathway), or normal!
• Too long means AV block (heart block) -
  1st/2nd/3rd degree

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A system

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

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QRS complex

• Should be lt0.12s duration
• gt0.12s BBB (either LBBB or RBBB)
• Pathological Q waves can mean a previous MI (?
  territory)
• gt25 size of subsequent complex
• Q waves are allowed in V1, aVR and III

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BBB
Look at V1 and V6
W I LL ia M LBBB
M a RR o W RBBB
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QRS complex

• Is there LVH?
• Sum of the Q or S wave in V1 and the biggest R
  wave in V5 or V6 gt35mm
• (R wave in aVL gt11mm)
• Not actually very useful.

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A system

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

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ST segment

• ST depression
• Downsloping or horizontal abnormal
• Ischaemia (coronary stenosis)
• If lateral (V4-V6), consider LVH with strain or
  digoxin (reverse tick sign)
• ST elevation
• Infarction (coronary occlusion)
• Pericarditis (widespread)
• These are usually in territories eg.
  anterior/lateral/inferior etc. and will be
  present in contiguous leads

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T wave

• Peaked (hyperkalaemia or normal young man)
• Inverted/biphasic (ischaemia, previous infarct)
• Small (hypokalaemia)
• No pot, no tea!

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QT interval

• Dont worry about too much
• Start of QRS to end of T wave
• Needs to be corrected for HR
• Various formulae
• eg. Bazetts
• Computer calculated often wrong
• Long QT can be genetic (long QT sy.) or secondary
  eg. drugs (amiodarone, sotalol)
• Associated with risk of sudden death due to
  Torsades de Pointes

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Question 1

• What is the rate, rhythm and axis?
• Any other abnormalities?

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Question 2

• What is the rate, rhythm and axis?
• Any other abnormalities?

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Question 3

• What is the rate, rhythm and axis?
• Any other abnormalities?

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Question 4

• What is the rate, rhythm and axis?
• Any other abnormalities?
• How would you manage this patient?

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Question 5

• What is the rate, rhythm and axis?
• What is the main problem with the patient?

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Take home messages

• Remember your system!
• See lots (pattern recognition)

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Further reading
ECG made easy, 7th ed Hampton ECG
Interpretation made Incredibly Easy, 4th ed
Springhouse (? nurses) www.Emedu.org/ecg