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Tutorial in Basic ECG for Medical Students


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This is the lecture notes that I have been giving to the medical students (2nd, 3rd, final year) for the last two years (updated 2008).

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Tutorial in Basic ECG for Medical Students

  1. 1. Tutorial in ECG Dr. Chew Keng Sheng Emergency Medicine Universiti Sains Malaysia
  2. 2. The Basics <ul><li>Standard calibration </li></ul><ul><ul><li>25 mm/s </li></ul></ul><ul><ul><li>0.1 mV/mm </li></ul></ul><ul><li>Electrical impulse that travels towards the electrode produces an upright (“positive”) deflection relative to the isoelectric baseline </li></ul>
  3. 3. Vertical and horizontal perspective of the ECG Leads Leads Anatomical II, III, aVF Inferior surface of heart V1 to V4 Anterior surface of heart I, aVL, V5, and V6 Lateral surface of heart V1 and aVR Right atrium
  4. 4. Location of MI and Affected Coronary Arteries Location of MI Affected Artery Lateral Left circumflex Anterior LAD Septum LAD Inferior RCA Posterior RCA Right Ventricle RCA
  5. 5. Right Sided & Posterior Chest Leads
  6. 6. Sinus Rhythm <ul><li>The P wave is upright in leads I and II </li></ul><ul><li>Each P wave is usually followed by a Q </li></ul><ul><li>The heart rate is 60­99 beats/min </li></ul>
  7. 7. Normal Sinus Rhythm
  8. 8. Instant Recognition of Axis Deviation
  9. 9. Cardiac Axis Normal Axis Right Axis deviation Left Axis Deviation Lead I Positive  Negative  Positive  Lead II Positive  Positive  Negative  Lead III Positive Positive Negative
  10. 10. Calculating Cardiac Axis
  11. 11. P wave <ul><li>Always positive in lead I and II in NSR </li></ul><ul><li>Always negative in lead aVR in NSR </li></ul><ul><li>< 3 small squares in duration </li></ul><ul><li>< 2.5 small squares in amplitude </li></ul><ul><li>Commonly biphasic in lead V1 </li></ul><ul><li>Best seen in leads II </li></ul>
  12. 12. Right Atrial Enlargement <ul><li>Tall (> 2.5 mm), pointed P waves (P pulmonale </li></ul>
  13. 13. Left Atrial Enlargement <ul><li>Prominent terminal P negativity (biphasic) in lead V1 (i.e., &quot;P-terminal force&quot;) duration >0.04s, depth >1 mm </li></ul>
  14. 14. <ul><li>Notched/bifid (‘M’ shaped) P wave (P ‘mitrale’) in limb leads with the inter-peak duration > 0.04s (1 mm) </li></ul>Left Atrial Enlargement
  15. 15. P Pulmonale and P Mitrale
  16. 17. RAH and LAH Right Atrial Hypertrophy Left Atrial Hypertrophy
  17. 18. Short PR Interval <ul><li>WPW (Wolff-Parkinson-White) Syndrome </li></ul><ul><li>Accessory pathway (Bundle of Kent) allows early activation of the ventricle (delta wave and short PR interval) </li></ul>
  18. 19. QRS Complexes <ul><li>Non­pathological Q waves are often present in leads I, III, aVL, V5, and V6 </li></ul><ul><li>The R wave in lead V6 is smaller than the R wave in V5 </li></ul><ul><li>The depth of the S wave, generally, should not exceed 30 mm </li></ul><ul><li>Pathological Q wave > 2mm deep and > 1mm wide or > 25% amplitude of the subsequent R wave </li></ul>
  19. 20. QRS In Hypertrophy
  20. 21. RVH Changes <ul><li>A tall positive (R) wave </li></ul><ul><ul><li>instead of the rS complex normally seen in lead V1 </li></ul></ul><ul><ul><li>an R wave exceeding the S wave in lead V1 </li></ul></ul><ul><ul><li>in adults the normal R wave in lead V1 is generally smaller than the S wave in that lead </li></ul></ul><ul><li>Right axis deviation (RAD) </li></ul><ul><li>Right ventricular &quot;strain&quot; T wave inversions </li></ul>
  21. 22. Conditions with Tall R in V1
  22. 23. Right Atrial and Ventricular Hypertrophy
  23. 24. COPD
  24. 25. Left Ventricular Hypertrophy <ul><li>Sokolow & Lyon Criteria (Am Heart J, 1949;37:161) </li></ul><ul><ul><li>S in V1+ R in V5 or V6 > 35 mm </li></ul></ul><ul><li>An R wave of 11 to 13 mm (1.1 to 1.3 mV) or more in lead aVL is another sign of LVH </li></ul><ul><li>Others: Cornell criteria (Circulation, 1987;3: 565-72) </li></ul><ul><ul><li>SV3 + R avl > 28 mm in men </li></ul></ul><ul><ul><li>SV3 + R avl > 20 mm in women </li></ul></ul>
  25. 27. Hypertrophy Strain Pattern vs ACS
  26. 28. ST Segment <ul><li>Normal ST Segment is flat (isoelectric) </li></ul><ul><ul><li>Same level with subsequent PR segment </li></ul></ul><ul><li>Elevation or depression of ST segment by 1 mm or more, measured at J point IS ABNORMAL </li></ul><ul><li>“ J” (Junction) point is the point between QRS and ST segment </li></ul>
  27. 29. Variable Shapes Of ST Segment Elevations in AMI Goldberger AL. Goldberger: Clinical Electrocardiography: A Simplified Approach. 7th ed: Mosby Elsevier; 2006.
  28. 30. T wave <ul><li>The normal T wave is asymmetrical, the first half having a more gradual slope than the second half </li></ul><ul><li>The T wave should generally be at least 1/8 but less than 2/3 of the amplitude of the corresponding R wave </li></ul><ul><li>T wave amplitude rarely exceeds 10 mm </li></ul><ul><li>Abnormal T waves are symmetrical, tall, peaked, biphasic or inverted. </li></ul>
  29. 31. T wave <ul><li>As a rule, the T wave follows the direction of the main QRS deflection. Thus when the main QRS deflection is positive (upright), the T wave is normally positive. </li></ul><ul><li>Other rules </li></ul><ul><ul><li>The normal T wave is always negative in lead aVr but positive in lead II. </li></ul></ul><ul><ul><li>Left-sided chest leads such as V4 to V6 normally always show a positive T wave. </li></ul></ul>
  30. 32. QT interval <ul><li>QT interval decreases when heart rate increases </li></ul><ul><li>A general guide to the upper limit of QT interval. For HR = 70 bpm, QT<0.40 sec. </li></ul><ul><ul><li>For every 10 bpm increase above 70 subtract 0.02 sec. </li></ul></ul><ul><ul><li>For every 10 bpm decrease below 70 add 0.02 sec </li></ul></ul><ul><li>As a general guide the QT interval should be 0.35­ 0.45 s, and should not be more than half of the interval between adjacent R waves (R­R interval). </li></ul>
  31. 33. QT Interval
  32. 34. Long QT Syndrome
  33. 35. QT Interval <ul><li>The QT interval increases slightly with age and tends to be longer in women than in men. </li></ul><ul><li>Bazett's correction is used to calculate the QT interval corrected for heart rate (QTc): QTc = QT/ Sq root [R­R in seconds] </li></ul>
  34. 36. U wave <ul><li>Normal U waves are small, round, symmetrical and positive in lead II, with amplitude < 2 mm (amplitude is usually < 1/3 T wave amplitude in same lead) </li></ul><ul><li>U wave direction is the same as T wave direction in that lead </li></ul><ul><li>More prominent at slow heart rates and usually best seen in the right precordial leads. </li></ul><ul><li>Origin of the U wave is thought to be related to afterdepolarizations which interrupt or follow repolarization </li></ul>
  35. 37. Calculation of Heart Rate <ul><li>Method 1: Count the number of large (0.2-second) time boxes between two successive R waves, and divide the constant 300 by this number OR divide the constant 1500 by the number of small (0.04-second) time boxes between two successive R waves. </li></ul><ul><li>Method 2: Count the number of cardiac cycles that occur every 6 seconds, and multiply this number by 10. </li></ul>
  36. 38. Calculation of Heart Rate
  37. 39. Question <ul><li>Calculate the heart rate </li></ul>
  38. 40. RBBB and LBBB <ul><li>RBBB = MaRroW </li></ul><ul><li>LBBB = WiLLiaM </li></ul>
  39. 41. Rhythm Disturbances
  40. 42. Cardiac Arrest & Peri-arrest Rhythms <ul><li>Cardiac Arrest </li></ul><ul><ul><li>Shockable </li></ul></ul><ul><ul><ul><li>VF, Pulseless VT </li></ul></ul></ul><ul><ul><li>Non Shockable </li></ul></ul><ul><ul><ul><li>Asystole, PEA </li></ul></ul></ul><ul><li>Peri arrest rhythms </li></ul><ul><ul><li>Tachyrrhythmias </li></ul></ul><ul><ul><li>Bradyarrhythmias </li></ul></ul><ul><li>Drugs to control rate </li></ul><ul><li>Drugs to revert the rhythms </li></ul>
  41. 43. Note that by this time, if 3 rd shock is required, it is the DRUG ->SHOCK-> CPR sequence. It is the same sequence thereafter The drugs to be given at this stage are vasopressors Cardiac Arrest
  42. 44. After the 3 rd sequence and giving adrenaline/vasopressin, consider giving antiarrhythmics like amiodarone for VF or magnesium for torsades de pointes. The sequence is still the same DRUG->SHOCK-> CPR. At any time, if rhythm becomes non-shockable, follow the non-shockable algorithm Cardiac Arrest
  43. 45. For cardiac arrest, the first thing to know is whether the rhythm is shockable or not shockable. In periarrest rhythms (bradyarrhythmias and tachyarrhythmias, the first thing to know is whether it STABLE or NOT STABLE
  44. 46. When The Arrhythmias Is Unstable <ul><li>Four main signs </li></ul><ul><li>Signs of low cardiac output – systolic hypotension < 90 mmHg, altered mental status </li></ul><ul><li>Excessive rates: <40/min or >150/min </li></ul><ul><li>Chest pain </li></ul><ul><li>Heart failure </li></ul><ul><li>If unstable, electrical therapy: cardioversion for tachyarrhythmias, pacing for bradyarrhythmias </li></ul>
  45. 47. Atropine 0.5 mg each bolus up to 3 mg. Atropine as temporizing measure only. Needs transcutaneous/transvenous pacing
  46. 48. Four Rhythms At Risk Of Developing Asystole <ul><li>Recent asystole </li></ul><ul><li>Mobitz II 2 nd degree AV Block </li></ul><ul><li>Complete Heart Block (especially with broad QRS or initial heart rate <40/min) </li></ul><ul><li>Ventricular standstill more than 3 sec </li></ul><ul><li>For these, consider also electrical therapy </li></ul><ul><ul><ul><ul><li>Only mentioned in European Resuscitation Council Guidelines 2005 </li></ul></ul></ul></ul>
  47. 49. Bradyarrhythmias <ul><li>2 nd degree Mobitz type 1 </li></ul><ul><li>the block is at AV Node </li></ul><ul><li>Often transient </li></ul><ul><li>Maybe asymptomatic </li></ul><ul><li>2 nd degree Mobitz type 2 </li></ul><ul><li>Block most often below AV node, at bundle of His or BB </li></ul><ul><li>May progress to 3 rd degree AV block </li></ul>
  48. 50. * For polymorphic VT – if patients become unstable, perform defibrillation rather than cardioversion. If ever in doubt whether to perform cardioversion or defibrillation, then perform DEFIBRILLATION Rule of thumb – if your eye cannot synchronize to each QRS complex, neither can the machine!
  49. 51. Tachyarrhythmias <ul><li>For stable tachyarrhythmias, we need to further decide whether it is NARROW QRS or WIDE QRS </li></ul><ul><li>For each type, further divide into </li></ul><ul><ul><li>Regular </li></ul></ul><ul><ul><li>Irregular </li></ul></ul>
  50. 52. Tachyarrhythmias <ul><li>Narrow QRS tachyarrhythmias </li></ul><ul><ul><li>Regular </li></ul></ul><ul><ul><ul><li>Sinus Tachycardia, PSVT, atrial flutter with regular AV conduction </li></ul></ul></ul><ul><ul><li>Irregular </li></ul></ul><ul><ul><ul><li>Atrial Fibrillation, Atrial flutter with variable AV Block </li></ul></ul></ul><ul><li>Wide (Broad) QRS tachyarrhythmias </li></ul><ul><ul><li>Regular </li></ul></ul><ul><ul><ul><li>Ventricular Tachycardia, SVT with BBB </li></ul></ul></ul><ul><ul><li>Irregular </li></ul></ul><ul><ul><ul><li>Polymorphic VT, AF with BBB </li></ul></ul></ul>
  51. 53. Narrow complexes and regular – attempt vagal maneuver and adenosine; Narrow complexes but not regular- likely AF. Don’t give adenosine. May attempt rate control using beta blocker or diltiazem
  52. 54. Amiodarone can be given for both regular and irregular broad complexes
  53. 55. Recommended Resources <ul><li>ABC of Clinical Electrocardiography </li></ul><ul><ul><li> </li></ul></ul><ul><li>Goldberger: Clinical Electrocardiography: A Simplified Approach, 6th edition. </li></ul><ul><ul><li>Access via </li></ul></ul><ul><li>ECG Learning Center </li></ul><ul><ul><li> </li></ul></ul><ul><li>ECG Library </li></ul><ul><ul><li> </li></ul></ul>
  54. 56. Thank You Contact me: Dr. K.S. Chew [email_address]