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Introduction to ECGs. Terry White, RN. Discussion Topics. ECG Monitoring Basics Standardized Methods & Devices Components & Measurements of the ECG Complex ECG Analysis. ECG Monitoring. ECG Monitoring. Recording of Electrical Activity Uses Bipolar or Unipolar leads.

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introduction to ecgs

Introduction to ECGs

Terry White, RN

discussion topics
Discussion Topics
  • ECG Monitoring Basics
  • Standardized Methods & Devices
  • Components & Measurements of the ECG Complex
  • ECG Analysis
ecg monitoring1
ECG Monitoring
  • Recording of Electrical Activity
  • Uses Bipolar or Unipolar leads

The ECG DOES NOT provide a recording or evaluation of MechanicalActivity!!!

ecg monitoring2
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
ecg monitoring3
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
ecg monitoring4
ECG Monitoring
  • Einthoven’s 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
standardized methods devices1
Standardized Methods & Devices
  • ECG Paper
  • Device Paper Speed
  • Device Calibration
  • Electrode Placement
  • Variations Do Exist!
standardized methods devices2
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
standardized methods devices3
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?
standardized methods devices4
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
standardized methods devices5
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
standardized methods devices6
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
components of the ecg complex
Components of the ECG Complex
  • Components & Their Representation
    • P, Q , R, S, T Waves
    • PR Interval
    • QRS Interval
    • ST Segment
components of the ecg complex1
Components of the ECG Complex
  • P Wave
    • first upward deflection
    • represents atrial depolarization
    • usually 0.10 seconds or less
    • usually followed by QRS complex
components of the ecg complex2
Components of the ECG Complex
  • QRS Complex
    • Composition of 3 Waves
      • Q, R & S
      • represents ventricular depolarization
      • much variability
    • usually < 0.12 sec
components of the ecg complex3
Components of the ECG Complex
  • Q Wave
    • first negative deflection after P wave
    • depolarization of septum
    • not always seen
components of the ecg complex4
Components of the ECG Complex
  • R Wave
    • first positive deflection following P or Q waves
    • subsequent positive deflections are R’, R”, etc
components of the ecg complex5
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
components of the ecg complex6
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
components of the ecg complex7
Components of the ECG Complex
  • QRS Interval
    • time impulse takes to depolarize ventricles
    • from beginning of Q wave to beginning of ST segment
    • usually < 0.12 sec
components of the ecg complex8
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
components of the ecg complex9
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
components of the ecg complex10
Components of the ECG Complex
  • T Wave
    • repolarization of ventricles
    • concurrent with end of ventricular systole
ecg analysis1
ECG Analysis
  • Rate
  • Rhythm/Regularity
  • QRS Complex
  • P Waves
  • Relationships & Measurements
ecg analysis2
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!!!
ecg analysis3
ECG Analysis
  • Rhythm
    • Measure R-R intervals across strip
    • Should find regular distance between R waves
    • Classification
      • Regular
      • Irregular
        • Regularly irregular
        • Irregularly irregular
ecg analysis4
ECG Analysis
  • QRS Complex
    • Narrow
      • < 0.12 seconds (3 small boxes) is normal
      • indicates supraventricular origin (AV node or above) of pacemaker
    • Wide
      • > 0.12 seconds is wide
      • indicates ventricular or supraventricular w/aberrant conduction
ecg analysis5
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
ecg analysis6
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?
ecg analysis7
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
ecg analysis8
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!!!
ecg analysis9
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!!!

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