How to read ECG
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  • 1. How to read ECG
  • 2. ECG • Representation of Electrical activity of heart
  • 3. ECG Leads • 12 lead ECG • 6 limb leads: Lead I, II, III aVL, aVR, aVF • 6 Chest Leads: V1, V2,V3, V4, V5, V6
  • 4. ECG paper Speed 25mm/s • 1 large square= 5 small square [5mm] Voltage • 10mm =1mV
  • 5. Appearance of waves • Positive deflection [upward] • If electrical impulses flowing towards that lead • Negative deflection [downward] • If electrical impulses flowing away from that lead
  • 6. Origin of waves
  • 7. P wave Atrial depolarization PR interval Atrial depolarization to start of ventricular depolarization QRS complex Ventricular depolarization T wave Ventricular repolarization QT interval Ventricular depolarization & repolarization U wave ? Interventricular septal repolarization
  • 8. Systematic approach • The following 14 points should be analyzed carefully in every ECG: • Standardization • Heart rate • Rhythm • P waves • PR interval • QRS voltages • QRS interval • QT interval • Mean QRS axis • Precordial R-wave progression • Abnormal Q waves • ST segments • T waves • U waves
  • 9. Standardization
  • 10. Heart Rate • 1500/RR
  • 11. •If HR is irregular Count no. of QRS complexes in 30 large squares= 6 sec Multiply it with 10 HR [per min]
  • 12. Rate calculation • Memorize the number sequence: 300, 150, 100, 75, 60, 50
  • 13. • ECG machines: print out HR • DO NOT RELY ON IT!!!! • Always Calculate yourself. • Bradycardia: <60/min • Tachycardia: >100/min
  • 14. Rhythm • Rhythm strip: prolonged recording of Lead II • Sinus rhythm ? • Each QRS complex preceded by P wave • Regular/ irregular?
  • 15. •Regular Sinus rhythm
  • 16. Irregular
  • 17. QRS AXIS • Indicator of overall direction that wave of depolarization takes when passing through ventricles • Also called ANGLE • Measured • in degrees
  • 18. • Photo
  • 19. • Right axis deviation [RAD] • Beyond +90° • Left Axis Deviation [LAD] • Beyond -30°
  • 20. Method 1 • Most precise method • Use of vectors • Measure overall height of QRS in lead I & aVF • Plot in graph paper • Measure the ANGLE of vector
  • 21. Method 2 • Quick method • Identify limb lead in which QRS complex is isoelectric • [with equal positive & negative deflection] • Implies: electric flow is at Right angle to this lead
  • 22. Method 3 • For quick assessment • Look at QRS complexes in lead I & II
  • 23. • Predominantly positive QRS in lead I • Axis between -90 to +90 • Excludes RAD
  • 24. • Predominantly positive QRS in lead II  • Axis between -30 to +150 • Excludes LAD
  • 25. Lead I Lead II Cardiac Axis QRS Positive QRS Positive Normal Axis QRS Positive QRS Negative Left Axis Deviation QRS Negative QRS Positive Right Axis Deviation
  • 26. • LAD • WPW syndrome • LBBB • Inferior wall MI • RAD • RVH • WPW syndrome • Anterolateral MI • Dextrocardia
  • 27. P wave • Present or not? • Sinus rhythm • If completely absent •Atrial Fibrillation •Hyperkalemia • If intermittently absent •Sinus arrest
  • 28. • Inverted P waves? • Incorrect positioned electrodes • Dextrocardia • Abnormal atrial depolarization
  • 29. • Height of P waves • > 2.5 mm: tall • Indicative of Right Atrial enlargement • P Pulmonale
  • 30. P PULMONALE P MITRALE
  • 31. • Width of P waves • >2mm width: abnormal • Bifid P wave • Indicates Left Atrial enlargement • P Mitrale
  • 32. PR Interval • From start of P wave to start of R wave • Normally • Not <3 small squares • Not > 5 small squares • Consistent
  • 33. Short PR Interval • AV junctional rhythm • WPW syndrome • Lown –Ganong-Levine syndrome
  • 34. Long PR Interval • Denotes delay in conduction through AV node • First Degree Block • PR prolonged, constant
  • 35. Second degree Block • Mobitz Type I • PR progressively increase until one P wave fails to produce QRS complex
  • 36. • Mobitz Type II • PR interval normal & fixed, • But occasional P waves fail to produce QRS
  • 37. • Third Degree Block [Complete AV Block] • No relationship between P waves & QRS complex
  • 38. • 2:1 Block • Alternate P waves are not followed by QRS complex
  • 39. Q WAVE • First negative deflection in QRS complex • ? Pathological Q waves • If • >2 small squares deep • >1 small square wide • >25% of height of the following R wave in depth
  • 40. QRS complex • Appearance of QRS Complex vary from lead to lead
  • 41. • Width: Narrow/ wide • Wide QRS: • > 3 small squares • Bundle branch block • Ventricular arrhythmia
  • 42. • Size of QRS complex • Small: • Pericardial effusion • ?incorrect calibration
  • 43. • Big QRS complex • Ventricular hypertrophy: R/L • WPW syndrome
  • 44. Progression of R wave • V1: small R wave , large S wave, • Gradually R wave increases, S wave decreases • V6: small Q wave, large R wave • V3 and V4 : located midway between V1 and V6, QRS complex nearly isoelectric in one of these leads
  • 45. Progression of R wave
  • 46. Left ventricular Hypertrophy • R Wave in V5 or V6 >25mm • S Wave in V1 or V2 > 25mm • Sum of R wave in V5 Or V6 & S wave in V1 or V2 >35mm
  • 47. LVH
  • 48. Right Ventricular Hypertrophy • Right axis deviation • Deep S Waves in leads V5 & V6 • R>S in V1 • RBBB
  • 49. RBBB • Right Bundle Branch Block • Broad QRS complex • Small r wave in V1, small Q wave in V6 • S wave in V1, R wave in V6 • R‟ wave in V1, S wave in V6
  • 50. LBBB • Left Bundle Branch Block • Broad QRS • Small Q wave in V1, Small r wave in V6 • R wave in V1, S wave in V6 • S wave in V1, R‟ wave in V6
  • 51. • “WILLIAM MORROW” • William: „W‟ in V1 & „M‟ in V6: LBBB • Morrow: „M‟ in V1 & „W‟ in V6: RBBB
  • 52. • LBBB • Ischemic Heart Disease • Cardiomyopathy • LVH • Fibrosis • RBBB • Ischemic heart disease • Cardiomyopathy • ASD • Massive pulmonary embolism
  • 53. ST Segment • From end of S wave to start of T Wave • Normally: Isoelectric • ? Depressed/ elevated
  • 54. • Elevated ST segment • Acute MI • Prinzmetal’s angina • Pericarditis • LV aneurysm • High take off
  • 55. • Depressed ST segment • Myocardial ischemia • Posterior MI • Ventricular hypertrophy with ‘Strain’ • Drugs: Digoxin
  • 56. Ventricular Hypertrophy with “strain” pattern • Tall R waves • Deep S waves • ST segment depression • T wave inversion
  • 57. T Wave
  • 58. T wave • Inverted? • Normal in aVR • V1,V2, III • Size • Normal: not > ½ size of preceeding QRS complex • Too small? • Too large?
  • 59. Tall T waves • Hyperkalemia • Acute MI
  • 60. Too small T Waves • Hypokalemia • Pericardial effusion • hypothyroidism
  • 61. Inverted T waves • Normal in few leads: aVR, V1, V2, III • MI • Myocardial ischemia • Ventricular hypertrophy with “strain” • Digoxin toxicity
  • 62. QT Interval • From start of QRS complex to end of T wave • Varies with HR
  • 63. Corrected QT interval • QTC • QTC =QT/√RR • Normal: 0.35-0.43 sec
  • 64. Prolonged QTc • If ≥0.44 sec • Hypocalcemia • Acute myocarditis • Torsades de pointes
  • 65. U waves • Mostly in anterior chest leads • Difficult to identify clearly
  • 66. • Prominent U Waves • Hypoklemia • Hypercalcemia • Hyperthyroidism
  • 67. Common ECG Problems
  • 68. ACUTE MI
  • 69. Ischemia
  • 70. HYPERKALEMIA
  • 71. LVH WITH STRAIN
  • 72. PERICARDITIS