ECG Basics An introduction to the 12 lead ECG

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ECG BasicsAn introduction to the 12 lead ECG
Lisa G. Smith, R.N., MSN/ED NUR 2242
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What is an EKG anyway??

• Wave forms depicting depolarization and
  repolarization of myocardial cells
• All cell membranes are charged (,-)
• Cells at rest polarized (-)
• Inside of cell more negative than the outside
• Cells electrically stimulated depolarize and
  contractdepolarization
• Cells return to restingrepolarization
• Reference page 862

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EKG

• Measures electrical potential
• Does not measure muscle contraction

Na
Na
K
Na
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ECG

• Measurement of the flow of electrical current as
  it moves across the conduction pathway of the
  heart.
• Recorded over time
• Represents different phases of the cardiac cycle

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What do patients think.

• Non-invasive and painless diagnostic procedure.
• Provides information about the function and
  structure of the heart structure
• The ECG is not an accurate predictor of future
  cardiac events.
• Comparison with previous ECGs is essential when
  interpreting the ECG.

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ECG Measurement of Electrical Activity

• Can occur through a variety of ways
• 12-lead ECG machine
• 15-lead readings are also now available
• Single Lead Monitoring System

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Evolution of the 12 Lead ECG

• Single channel
• Multi-channel

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12-Lead EKG

• Representation of the hearts electrical activity
  from different angles recorded from electrodes on
  the bodys surface.
• 12 lead EKG provides spatial information about
  the hearts electrical activity in 3 basic
  directions
• Each lead represents an orientation in space

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Single Lead monitoring

• AKA Rhythm monitoring
• Provides continuous information
• Chest lead picks up activity and places it on a
  cardiac monitor
• Electrodes, conductive gel disks or tabs,
  replaced before drying out

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Types of Single lead monitoring

• Hardwire 3 or 5 wire system
• Telemetry also 3 or 5 wire
• Holter monitoring

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12 Lead placement
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5 lead placement
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Review of conduction system
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Unique properties of myocardial cells

• Automaticity
• Synchronicity
• Conductivity

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Cardiac Cycle

• The heart maintains a constant pathway of
  conduction normally
• Two types of electrical processes
• 1. Depolarization Systole
• 2. Repolarization -- Diastole

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Electrical Conduction
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Basic ECG Interpretation
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Isoelectric line
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Measure the waveforms

• PRI .12 - .20
• QRS .04 - .12
• QT .34 - .43
• These are normal ranges

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Rate How can you count it?
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Triplets and counting!
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2 More Methods to Count Rate

• When the rhythm is regular, the heart rate is 300
  divided by the number of large squares between
  the QRS complexes.
• For example, if there are 4 large squares between
  regular QRS complexes, the heart rate is 75
  (300/475).
• The second method can be used with an irregular
  rhythm to estimate the rate. Count the number of
  R waves in a 6 second strip and multiply by 10.
• For example, if there are 7 R waves in a 6 second
  strip, the heart rate is 70 (7x1070).

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Sequential approach(One method)

• 1. Is there a P wave before every QRS, Is there a
  QRS after every P
• 2. Rhythm Regular or irregular
• 3. Rate
• 4. Is the rhythm atrial or ventricular?
• 5. Is there any ectopy/aberancy (abnormal beat)
• 6. Measure basic waveforms (PRI, QRS, QT)
• Questions
• What is the dominant rhythm or arrhythmia?
• What is the clinical significance of the
  arrhythmia?
• What is the treatment for the arrhythmia?

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Step 1 P waves - Are they present?
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Are there P waves?
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Are there P waves?
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Are there P waves ?
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Step 2 Is the Rhythm Regular?R to R
interval should be Regular
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Irregular R to R intervals
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Ask why is the rhythm Irregular?

• Early (premature beats)
• Pauses
• Abnormal beats
• Is it slightly irregular?
• This is called Sinus Arrhythmia
• Normal in children and young adults
• Usually result of increased vagal tone

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Irregular Rhythm
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Irregular
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What makes this irregular??
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Step 3 - What is the rate?

• We have looked for p waves
• We have looked for QRS to follow every p
• We have determined if rhythm is regular or
  irregular
• Now we count the rate

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Step 4

• At this point you should now know if your rhythm
  is atrial or ventricular
• Atrial presence of P waves
• Ventricular Absence of P waves

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Step 5 Is there ectopy?

• Remember abnormal beats

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Premature Atrial Contraction
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Premature Atrial Contraction
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Premature Beat
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PVCs
Possible Causes Clinical Significance
Stimulants Usually benign
Electrolyte Imbalances May ? CO
Hypoxia Ventricle contracts before filling completely with blood
Exercise May affect pulse because contraction is not sufficient enough to generate a pulse
Stress Determine if the PVCs are perfusing
MI
MVP
Heart Failure
CAD
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Multifocal PVCs
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Bigeminy
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Couplets
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Trigeminy
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Step 6 Measure the waveforms

• PRI .12 - .20
• QRS .04 - .12
• QT .34 - .43
• These are normal ranges
• Abnormal findings may indicate disease or a
  compromised state

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Rhythm Interpretation
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Sinus rhythm
P before every QRS a QRS after every P
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Recognizing Normal Sinus Rhythm

• Rate is 60-100
• P waves are normal and size and length
• There is a P wave before every QRS and a QRS
  following every P wave
• QRS is normal in width

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Normal Sinus Rhythm
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Atrial Arrhythmias

• Tachycardia
• Bradycardia
• Conduction problems

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Atrial Tachycardia
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Sinus Bradycardia
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Atrial Flutter
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Atrial Fibrillation
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Heart Blocks

• First Degree
• Second Degree
• Mobitz I/Type I
• Mobitz II/Type II
• Third Degree (Complete Heart Block)

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Conduction BlocksFirst degree heart block
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Conduction Blocks Second-Degree, Type I

• Also called Mobitz I
• Also called Wenckebach

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Conduction blocksSecond Degree Heart Block

• Also called Mobitz II
• Also called 2nd degree type II

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Complete Heart Block

• Also called 3rd degree Heart Block

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Atrial versus Ventricular Ectopy Review
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Atrial vs Ventricular
Atrial
Ventricular
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Arial or Ventricular?
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Atrial or Ventricular Rhythm?
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Ventricular Tachycardia
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Ventricular Fibrillation
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QRS configuration
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Asystole

• V-Tach to V-Fib
• can lead to.
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  Asystole Asystole

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Pacer rhythms
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Examples of paced EKG recordings
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Electrolyte Imbalances

• Calcium
• Magnesium
• Potassium

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Hypokalemia
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Hyperkalemia
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• P Wave size, shape, direction, location
• Rhythm regular or irregular
• Rate atrial and ventricular
• Conduction Where is the rhythm coming from
  atrial or ventricular
• Is there Ectopy?
• 6. Measure QRS complexes size, shape,
  direction, location PRI, ST segment