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Introduction to ECGs

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

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  1. Introduction to ECGs Terry White, RN

  2. Discussion Topics • ECG Monitoring Basics • Standardized Methods & Devices • Components & Measurements of the ECG Complex • ECG Analysis

  3. ECG Monitoring

  4. ECG Monitoring • Recording of Electrical Activity • Uses Bipolar or Unipolar leads The ECG DOES NOT provide a recording or evaluation of MechanicalActivity!!!

  5. 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

  6. 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

  7. 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

  8. Standardized Methods & Devices

  9. Standardized Methods & Devices • ECG Paper • Device Paper Speed • Device Calibration • Electrode Placement • Variations Do Exist!

  10. 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

  11. 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?

  12. 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

  13. 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

  14. 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

  15. Components of the ECG

  16. Components of the ECG Complex • Components & Their Representation • P, Q , R, S, T Waves • PR Interval • QRS Interval • ST Segment

  17. Components of the ECG Complex • P Wave • first upward deflection • represents atrial depolarization • usually 0.10 seconds or less • usually followed by QRS complex

  18. Components of the ECG Complex • QRS Complex • Composition of 3 Waves • Q, R & S • represents ventricular depolarization • much variability • usually < 0.12 sec

  19. Components of the ECG Complex • Q Wave • first negative deflection after P wave • depolarization of septum • not always seen

  20. Components of the ECG Complex • R Wave • first positive deflection following P or Q waves • subsequent positive deflections are R’, R”, etc

  21. 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

  22. 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

  23. 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

  24. 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

  25. 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

  26. Components of the ECG Complex • T Wave • repolarization of ventricles • concurrent with end of ventricular systole

  27. ECG Analysis

  28. ECG Analysis • Rate • Rhythm/Regularity • QRS Complex • P Waves • Relationships & Measurements

  29. 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!!!

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

  31. 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

  32. 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

  33. 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?

  34. 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

  35. 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!!!

  36. 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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