Electrocardiography introduction slides for students
- 1. 1 Introduction to ECGs EMS Professions Temple College
- 2. 2 Discussion Topics ECG Monitoring Basics Standardized Methods & Devices Components & Measurements of the ECG Complex ECG Analysis
- 4. 4 ECG Monitoring Recording of Electrical Activity Uses Bipolar or Unipolar leads The ECG DOES NOT provide a recording or evaluation of Mechanical Activity!!!
- 5. 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. 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. 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
- 9. 9 Standardized Methods & Devices ECG Paper Device Paper Speed Device Calibration Electrode Placement Variations Do Exist!
- 10. 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. 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. 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. 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. 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
- 16. 16 Components of the ECG Complex Components & Their Representation P, Q , R, S, T Waves PR Interval QRS Interval ST Segment
- 17. 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. 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. 19 Components of the ECG Complex Q Wave first negative deflection after P wave depolarization of septum not always seen
- 20. 20 Components of the ECG Complex R Wave first positive deflection following P or Q waves subsequent positive deflections are R’, R”, etc
- 21. 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. 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. 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. 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. 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. 26 Components of the ECG Complex T Wave repolarization of ventricles concurrent with end of ventricular systole
- 27. 27 ECG Analysis
- 28. 28 ECG Analysis Rate Rhythm/Regularity QRS Complex P Waves Relationships & Measurements
- 29. 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. 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. 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. 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. 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. 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. 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. 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!!!