Basic Electrocardiography

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Basic Electrocardiography

• Dr. Mark ONeill
• Senior Lecturer and Consultant Cardiologist
• Imperial College Healthcare NHS Trust

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• "I do not imagine that electrocardiography is
  likely to find any very extensive use in the
  hospital. It can at most be of rare and
  occasional use to afford a record of some rare
  anomaly of cardiac action.
• Augustus D. Waller
• Barker LF Electrocardiography and
  phonocardiography A collective review. Bull
  Johns Hopkins Hosp 191021358359

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Outline

• Common Problems with ECG recording
• Interpreting the 12 lead ECG
• Key Diagnosis using ECGs
• Interpreting 24 hour ECGs

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Problems with ECG recording

• Patient identity
• Lead position
• Paper speed and amplification
• Artifact
• Misinterpretation is much more common than poor
  recording technique.

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Patient Identity
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Lead Position
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Paper Speed and Amplification
1 second
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Paper Speed
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Signal Amplification
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Artifact
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Artifact
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Look at all the leads
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Interpreting the 12 lead ECG

• There are 2 critical types of information to be
  gleaned from the ECG
• The sequence of Cardiac Electrical Activation
  i.e. electrical recording reflecting electrical
  phenomena
• The anatomy/geography of the abnormality
• Localising conduction disturbance (accurate)
• Localising perfusion disturbance (less accurate,
  because it is not a perfusion recording)

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Cardiac Activation sequence
SA Node
AV Node
PR Interval
BBs
QRSd
Ventricles
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The poor mans guide
J point
PR interval
QRSd
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Interpreting the 12 Lead ECG
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Key Diagnoses using 12 lead ECG

• Conduction Disturbance
• 2nd Degree AV block
• 3rd Degree AV block
• Arrhythmias
• Atrial fibrillation
• Broad Complex vs Narrow complex tachycardia
• Acute Myocardial ischaemia

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Conduction Disturbance

• Sinoatrial node
• Failure of impulse initiation
• Sinus node arrest
• Atrioventricular node
• Intermittent failure of impulse conduction
• Ist and 2nd Degree AV block
• Complete failure of impulse conduction
• 3rd Degree AV block

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Where is the Conduction Problem?
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1st Degree AV block
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2nd Degree AV block
Mobitz I or Wenckebach type AV block
Note Progressive PR prolongation followed by
loss of AV conduction
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2nd Degree AV block
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2nd Degree AV block
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3rd Degree AV Block
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Atrial Fibrillation

• Predominantly of left atrial origin
• High rate of atrial activation (gt300bpm)
• IRREGULAR VENTRICULAR RESPONSE
• Filtering effect of the AV node
• Protects the ventricle from high atrial rates
• Explains why we rate control AF

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Atrial Fibrillation
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Atrial Fibrillation
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Atrial Flutter
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Narrow Complex Tachycardia
Uses the normal cardiac conduction pathways to
activate the ventricles Generally originates
above the AV node Highly unlikely to be life
threatening In individuals with a normal
heart Common Symptoms are from the ventricles
following the tachycardia from above
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Narrow Complex tachycardia
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Ventricular (Broad Complex) Tachycardia
Ignores the normal cardiac conduction pathways to
activate the ventricles Originates below the AV
node Can be life threatening in individuals
with a normal heart Together with VF, accounts
for the vast majority of SCD in patients with
ischaemic HD
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Broad Complex Tachycardia
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Interpreting 24 hour ECGs

• You have only 2 leads
• They are not the same as the leads recorded with
  a 12 lead machine
• Artifact is very common
• Morphology of ST segments counts for nothing
• The majority of 24h tapes are normal!

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Lead Positions
Beijing
London
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Occasionally interesting!
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What is this?
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Summary

• All information is in front of you on the
  recording
• Take a logical and structured approach to the
  recording
• If in doubt, ask a colleague its what I do

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