Introduction to ECGs

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Introduction to ECGs

• EMS Professions
• Temple College

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Discussion Topics

• ECG Monitoring Basics
• Standardized Methods Devices
• Components Measurements of the ECG Complex
• ECG Analysis

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ECG Monitoring
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ECG Monitoring

• Recording of Electrical Activity
• Uses Bipolar or Unipolar leads

The ECG DOES NOT provide a recording or
evaluation of Mechanical Activity!!!
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ECG Monitoring

• Bipolar Leads
• 1 positive and 1 negative electrode
• RA always negative
• LL always positive
• Traditional limb leads are examples of these
• Lead I
• Lead II
• Lead III
• Provide a view from a vertical plane

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ECG Monitoring

• Unipolar Leads
• 1 positive electrode
• 1 negative reference point
• calculated by using summation of 2 negative leads
• Augmented Limb Leads
• aVR, aVF, aVL
• vertical plane
• Precordial or Chest Leads
• V1-V6
• horizontal plane

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ECG Monitoring

• Einthovens Triangle
• Each lead looks from a different perspective
• Can determine the direction of electrical
  impulses
• Upright electrical recording indicates
  electricity flowing towards the electrode
• positive deflection

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Standardized Methods Devices
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Standardized Methods Devices

• ECG Paper
• Device Paper Speed
• Device Calibration
• Electrode Placement
• Variations Do Exist!

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Standardized Methods Devices

• ECG Graph Paper
• Vertical axis- voltage
• 1 small box 1 mm 0.1 mV
• Horizontal axis - time
• 1 small box 1 mm 0.04 sec.
• Every 5 lines (boxes) are bolded
• Horizontal axis - 1 and 3 sec marks

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Standardized Methods Devices

• ECG Paper Examples
• Vertical Axis
• No. of mm in 10 small boxes?
• No. of small boxes in 2 mm?
• Horizontal Axis
• No. of seconds in 5 small boxes?
• No. of small boxes in 0.2 second?
• No. of small boxes in 1 second?

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Standardized Methods Devices

• Paper Speed Calibration
• Paper Speed - 25 mm/sec standard
• Calibration of Voltage is Automatic
• Both Speed and voltage calibration can be changed
  on most devices

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Standardized Methods Devices

• Electrode Placement
• Standardization improves accuracy of comparison
  ECGs
• 3 Lead and 12 Lead Placement are most common
• Assure good conduction gel
• Prep area with alcohol prep
• Avoid
• Bone
• Large muscles or hairy areas
• Limb vs. Chest placement

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Standardized Methods Devices

• Electrode Placement
• Poor placement or preparation
• Often results in artifact
• Stray energy from other sources can also lead to
  poor ECG tracings (noise)
• 60 cycle interference

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Components of the ECG
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Components of the ECG Complex

• Components Their Representation
• P, Q , R, S, T Waves
• PR Interval
• QRS Interval
• ST Segment

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Components of the ECG Complex

• P Wave
• first upward deflection
• represents atrial depolarization
• usually 0.10 seconds or less
• usually followed by QRS complex

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Components of the ECG Complex

• QRS Complex
• Composition of 3 Waves
• Q, R S
• represents ventricular depolarization
• much variability
• usually lt 0.12 sec

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Components of the ECG Complex

• Q Wave
• first negative deflection after P wave
• depolarization of septum
• not always seen

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Components of the ECG Complex

• R Wave
• first positive deflection following P or Q waves
• subsequent positive deflections are R, R, etc

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Components of the ECG Complex

• S Wave
• Negative deflection following R wave
• subsequent negative deflections are S, S, etc
• may be part of QS complex
• absent R wave in aberrant conduction

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Components of the ECG Complex

• PR Interval
• time impulse takes to move through atria and AV
  node
• from beginning of P wave to next deflection on
  baseline (beginning of QRS complex)
• normally 0.12 - 0.2 sec
• may be shorter with faster rates

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Components of the ECG Complex

• QRS Interval
• time impulse takes to depolarize ventricles
• from beginning of Q wave to beginning of ST
  segment
• usually lt 0.12 sec

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Components of the ECG Complex

• J Point
• point where QRS complex returns to isoelectric
  line
• beginning of ST segment
• critical in measuring ST segment elevation

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Components of the ECG Complex

• ST Segment
• early repolarization of ventricles
• measured from J point to onset of T wave
• elevation or depression may indicate abnormality

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Components of the ECG Complex

• T Wave
• repolarization of ventricles
• concurrent with end of ventricular systole

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ECG Analysis
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ECG Analysis

• Rate
• Rhythm/Regularity
• QRS Complex
• P Waves
• Relationships Measurements

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ECG Analysis

• Ventricular Rate
• Triplicate method
• 300-150-100-75-60-50
• R-R method
• divide 300 by of large squares between
  consecutive R waves
• 6 Second method
• multiply of R waves in a 6 second strip by 10
• Rate meter unreliable!!!

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ECG Analysis

• Rhythm
• Measure R-R intervals across strip
• Should find regular distance between R waves
• Classification
• Regular
• Irregular
• Regularly irregular
• Irregularly irregular

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ECG Analysis

• QRS Complex
• Narrow
• lt 0.12 seconds (3 small boxes) is normal
• indicates supraventricular origin (AV node or
  above) of pacemaker
• Wide
• gt 0.12 seconds is wide
• indicates ventricular or supraventricular
  w/aberrant conduction

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ECG Analysis

• P Waves
• Present?
• Do they all look alike?
• Regular interval
• Upright or inverted in Lead II?
• Upright atria depolarized from top to bottom
• Inverted atria depolarized from bottom to top

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ECG Analysis

• Relationships/Measurements
• PR Interval
• Constant?
• Less than 0.20 seconds (1 large bx)
• P to QRS Relationship
• P wave before, during or after QRS?
• 1 P wave for each 1 QRS?
• Regular relationship?

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ECG Analysis

• A monitoring lead can tell you
• How often the myocardium is depolarizing
• How regular the depolarization is
• How long conduction takes in various areas of the
  heart
• The origin of the impulses that are depolarizing
  the myocardium

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ECG Analysis

• A monitoring lead can not tell you
• Presence or absence of a myocardial infarction
• Axis deviation
• Chamber enlargement
• Right vs. Left bundle branch blocks
• Quality of pumping action
• Whether the heart is beating!!!

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ECG Analysis

• An ECG is a diagnostic tool, NOT a treatment
• No one was ever cured by an ECG!!

Treat the PATIENT not the Monitor!!!