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Electrocardiography: Basics Of Interpretation

Electrocardiography: Basics Of Interpretation. B. Sonnenberg, MD adapted from talk by Jonathan B. Choy, MD, FRCPC, FACC. May 2014. Disclosure of Commercial Support. This program has received no financial support from any source for this presentation .

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Electrocardiography: Basics Of Interpretation

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  1. Electrocardiography:Basics Of Interpretation B. Sonnenberg, MD adapted from talk by Jonathan B. Choy, MD, FRCPC, FACC May 2014

  2. Disclosure of Commercial Support • This program has received no financial support from any source for this presentation. • Potential for conflict(s) of interest: • Brian Sonnenberg has received no funding from industry for research studies, but participates as unfunded co-investigator in multi-center drugs studies (TeCos comparing Sitagliptin to placebo, Odyssey PCKS-9 inhibitor vs. placebo for LDL lowering). • No product will be discussed in this program.

  3. Learning Objectives • Standard 12-lead printout format • SYSTEMATIC interpretation of ECG: • Calibration • Rate • Rhythm • Axis • Intervals • Hypertrophy • Infarcts • ST elevation / ST depression • T wave abnormalities

  4. If you memorize and practice using this SYSTEMATIC ECG reading approach, NOTHING can stump you in reading ECG’s!

  5. Willem Einthoven (1860-1927)

  6. ECG Machine

  7. Limb Leads

  8. Correlation of Leads & Areas of Left Ventricle • Leads looks at current flow generated by ‘battery’ of heart  P-QRS-T • Limb leads are vectors (I+III = II), can add to generate 3 more • Chest leads use the electrical center of limb leads as one pole, chest wall electrode as other • Leads pick up signal mostly from LV, mostly from LV closest to chest where vector points I …lead I signal generated mostly by high lateral LV Pictures partly from Clip-Art

  9. Chest Leads s

  10. Components Of The ECG

  11. Standard 12-lead ECG format Limb leads Chest leads each 1mm width = 40ms, 25mm = 1s each 1mm height = 0.1mVolt

  12. Interpretation Sequence • Calibration • Rate • Rhythm • Axis • Intervals • Hypertrophy • Infarcts = Q-waves • ST/T wave abnormalities • (Comparison with previous ECG’s)

  13. Interpretation Sequence • Calibration • Rate • Rhythm • Axis • Intervals • Hypertrophy • Infarcts = Q-waves • ST/T wave abnormalities • (Comparison with previous ECG’s)

  14. Basic Interpretation:(1) Check Calibration • each 25 mm represents one second • each 10 mm represents 1 mV • aVR should be mostly -ve

  15. Interpretation Sequence • Calibration • Rate • Rhythm • Axis • Intervals • Hypertrophy • Infarcts = Q-waves • ST/T wave abnormalities • (Comparison with previous ECG’s)

  16. Rate Determination:Count-off Method • Count-off the number of large boxes between two consecutive beats • Memorize sequence “300-150-100-75-60-50”

  17. Analogy… • think of rate as a speedometer… 75 100 60 150 50 300

  18. Rate Determination:6-Second Method • Multiply the number of beats in 6 seconds (30 large boxes) by 10 • 8 X 10 = 80 bpm • Particularly good for irregular rhythms

  19. Example 1 6.0s

  20. Example 2 5.0s

  21. Example 3 5.0s

  22. Interpretation Sequence • Calibration • Rate • Rhythm • Axis • Intervals • Hypertrophy • Infarcts = Q-waves • ST/T wave abnormalities • (Comparison with previous ECG’s)

  23. Rhythm Determination • Normal rhythm is sinus, and is present if: • every P-wave followed by a QRS • every QRS preceded by 1 P-wave • P-wave upright in I, II, and III • (PR interval > 0.12 sec)

  24. Atrial Depolarization Sino-atrial node P wave

  25. Rhythm Determination normal P wave starts top RA  down & to left  best leads to see P-waves: Inferior (II, III, aVF) V1 (closest to RA forces)

  26. Rhythm Determination • Normal HR 60-100 bpm • < 60 bpm: sinus bradycardia • > 100 bpm: sinus tachycardia

  27. Example 1 Sinus Rhythm

  28. Example 2 Ectopic Atrial Rhythm

  29. Example 3 False p-waves, actually fibrillatory = f-waves 8.0s Atrial Fibrillation—no organized P-waves

  30. Interpretation Sequence • Calibration • Rate • Rhythm • Axis • Intervals • Hypertrophy • Infarcts = Q-waves • ST/T wave abnormalities • (Comparison with previous ECG’s)

  31. QRS Axis Determination Normal … if leads I + II are +ve, normal axis!

  32. One Method • Axis = average QRS vector in limb leads • ECG is a summation of vector forces • Look at leads I and aVF • Count number of net squares in each lead (either positive or negative) • Plot on an X,Y graph • Estimate angle visually

  33. Example 1 Net 3 mm positive Net 5 mm positive - 90o ± 180o + 0o I +ve + 60o + 90o aVF +ve

  34. Example 2 Net 8 mm positive Net 4 mm negative -90o -20o ± 180o + 0o I +ve + 90o aVF +ve

  35. ( - 90º ) ( - 90º ) ( - 30º ) ( - 30º ) ( - 150º ) ( - 150º ) -ve aVL aVL aVR aVR -ve +ve  180º  180º ( 0º ) ( 0º ) I I +ve I I I I I I I I I I aVF aVF ( +60º ) ( +60º ) ( +120º ) ( +120º ) ( +90º ) ( +90º ) 2nd Method • put QRS axis into 90º sector easily • 1st check I & aVF  locate QRS quadrant check if QRS is +ve in lead I check if QRS is +ve in lead aVF

  36. 2nd Method • once locate quadrant, check other leads to see if +ve or -ve • Iso-electric QRS  ~90º to lead direction • with other leads, can locate 30º sector ( - 90º ) ( - 90º ) ( - 30º ) ( - 150º ) I -ve aVF-ve I +ve aVF-ve aVL aVR  180º  180º ( 0º ) ( 0º ) I I I -ve aVF+ve I +ve aVF+ve I I I I I aVF aVF ( +60º ) ( +120º ) ( +90º ) ( +90º )

  37. Example 1 Net positive (more) net positive ( - 90º ) I -ve aVF-ve I +ve aVF-ve  180º ( 0º ) I I -ve aVF+ve I +ve aVF+ve aVF ( +90º )

  38. Example 2 (more) net positive net negative ( - 90º ) I -ve aVF-ve I +ve aVF-ve  180º ( 0º ) I I -ve aVF+ve I +ve aVF+ve aVF ( +90º )

  39. Interpretation Sequence • Calibration • Rate • Rhythm • Axis • Intervals • Hypertrophy • Infarcts = Q-waves • ST/T wave abnormalities • (Comparison with previous ECG’s)

  40. Normal Intervals • PR 0.12 - 0.20 sec • QRS ≤ 0.12 sec • Corrected QT* ≤ 0.46 sec

  41. PR interval

  42. Example 1 • PR interval = 4 mm boxes (4mm = 4 x 40ms) • 4 X 0.04 = 0.16 sec = 160ms = normal

  43. Example 2 • PR interval = 7 small boxes • 7 X 0.04 = 0.28 sec • 280ms = delay in AV node = mild ‘AV block’

  44. QRS interval

  45. QRS width • QRS interval = 2 small boxes • 2 X 0.04 = 0.08 sec = normal

  46. Schematic Diagram OfCardiac Conduction Pathways

  47. Causes of long QRS • Right bundle branch block • Left bundle branch block • Accessory = bypass tracts • Non-specific QRS widening

  48. Right Bundle Branch Block

  49. RBBB • ‘bunny ears’ on right = right bundle branch • late RV firing = late forces coming toward V1  R’ • also  fat, wide S wave on left leads I, aVL, V6 V1: Rs R’ V6: R S

  50. Right Bundle Branch Block • V1: Late M-shaped QRS (RSR'); sometimes wide notched R or qR • I + V6: wide S wave • late depolarization of RV • slow, via ‘back alley’ cell conduction •  late +ve right forces •  R’ in V1, V2 • & wide, fat S waves in I, aVL, V5, V6

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