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Almost Everything You Wanted To Know About ECGs ( But Were Afraid To Ask )

Amy Gutman MD ~ EMS Medical Director prehospitalmd@gmail.com / www.TEAEMS.com. Almost Everything You Wanted To Know About ECGs ( But Were Afraid To Ask ). Overview. Part I: Cardiac Anatomy Review Part II: The Cardiac Cycle Part III: From One Beat to Many Part IV: Rhythm Analysis.

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Almost Everything You Wanted To Know About ECGs ( But Were Afraid To Ask )

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  1. Amy Gutman MD ~ EMS Medical Director prehospitalmd@gmail.com / www.TEAEMS.com Almost Everything You Wanted To Know About ECGs(But Were Afraid To Ask)

  2. Overview • Part I: • Cardiac Anatomy Review • Part II: • The Cardiac Cycle • Part III: • From One Beat to Many • Part IV: • Rhythm Analysis

  3. What is an EKG really looking at? Part One: Cardiac Anatomy

  4. Electrocardiogram (ECG or EKG) • German “Elektrokardiogramm” • Record of the heart’s electrical depolarizations & repolarizations over time • Arrhythmias, ischemia, & conduction abnormalities • Electrolyte disturbances • Non-cardiac diseases (i.e. hypothermia, PE)

  5. 3 Lead vs 12 Lead • 3 lead “overview” image of heart • I (lateral) • II (inferior) • III (inferior) • Useful for checking arrhythmias • Not great for looking for ischemic changes

  6. What is a 12 Lead EKG?

  7. EKG = Electrical Record of Cardiac Activity

  8. EKG = Precordial + Limb Leads

  9. Limb Leads • Leads I, II & III are “limb leads” • Leads aVR, aVL, & aVF are “augmented” limb leads

  10. Precordial Lead Placement • V1 - 4th ICS to right of sternum • V2 - 4th ICS to left of sternum

  11. Precordial Lead Placement • V3 - Between V2 & V4

  12. Precordial Lead Placement • V4 - 5th ICS at MCL • V5 - Horizontally with V4 at AAL

  13. Precordial Lead Placement • V6 - Horizontally with V4 & V5 at MAL

  14. What Do the Leads Mean? I AvR V1 V3 II AvL V2 V4 III AvF V3V5 Lead II Continuous Strip

  15. Leads Correspond to Coronary Arteries I AvR V1 V4 Lateral Septal Anterior II AvL V2 V5 Inferior Lateral Septal Lateral III AvF V3 V6 Inferior Inferior Anterior Lateral

  16. Coronary Arteries • Right Coronary Artery (RCA) perfuses right ventricle / inferior heart • Inferior heart • Left Main Artery (LMA) divides into: • Left Anterior Descending Artery (LAD) perfuses anterior left ventricle • Left Circumflex Artery (LCX) perfuses lateral left ventricle

  17. Consider This… • Each coronary artery = one part of the EKG • You must see changes in >two “contiguous” leads to diagnose ischemia • Contiguous leads = heart “territories”: • Inferior, Anterior, Lateral, Septal

  18. Inferior Territory = Right Coronary Artery II, III, AvF • Right ventricle positioned downward & inferior • Innervated by vagus nerve • Same nerve as stomach • IMIs often present with N/V not “chest pain”

  19. Inferior Leads: RCA II Inferior III AvF Inferior Inferior

  20. Septal Territory = RCA & LADV1, V2 • Two vessels cover large area • V2 overlaps septal & anterior areas • Septal MI is best seen in V1 & V2

  21. Septal Leads V1 Septal V2 Septal

  22. Anterior Territory = Left Anterior Descending (V2), V3, V4 • Septum & anterior left ventricle are the “precordial” leads • V1 & V2 directly over cardiac septum • V2 (septal overlap), V3, V4 look at anterior heart

  23. Anterior Leads V4 Anterior V3 Anterior

  24. Lateral Territory: LMA & LCXI, AvL, V5, V6 • Winds around lateral heart & left ventricle • LMA “Widow Maker”: • Divides into LAD & LCX, perfuses left ventricle • LMA occlusion causes massive antero-lateral MI

  25. Lateral Leads I Lateral AvL V5 Lateral Lateral V6 Lateral

  26. Contiguous Leads I, AvL, V5, V6 II, III, AvF V1, V2 (V2, V3) V3, V4 I AvR V1 V4 Lateral Septal Anterior LMA, LCX RCA, LAD LAD II AvL V2 V5 Inferior Lateral Septal Lateral RCA LMA, LCX RCA, LAD LMA, LCX III AvF V3 V6 Inferior Inferior Anterior Lateral RCA RCA LAD LMA, LCX

  27. The heart is nothing more than a mechanical pump running on electricity Part II: The Cardiac Cycle

  28. The Cardiac Cycle • The heart is a mechanical pump running on electrical energy • Electrical energy pathways determine how well the heart functions • Changes in electricity = changes in heart function

  29. Cardiac Anatomy Left Atrium Sinoatrial Node Atrioventricular Node Bundle of His Right Atrium Right Ventricle Left Ventricle

  30. Electrical Pathway SA Node • SA Node • AV Node • Bundle of His • Right & Left Ventricles Left Ventricle AV Node Right Ventricle His Bundle

  31. The Cardiac Cycle • One complex = one cardiac cycle • Recognizing normal means understanding abnormal

  32. One Cardiac Cycle = One Heart Beat Atrial Depolarization Ventricular Depolarization Ventricular Repolarization

  33. Cardiac “Waves” • Width = time • Height & depth = voltage • Upward deflection = positive • Downward delection = negative

  34. P Waves • SA to AV node path causes atrial contraction • Upright in II, III, & aVF • Inverted in aVR • Variable P wave shapes suggests ectopic pacemaker

  35. PR Interval • 120 - 200 ms (3 to 5 small boxes) • Long = 1st degree heart block • Short = pre-excitation syndrome (WPW) • Variable = other heart blocks • PR depression = atrial injury or pericarditis

  36. WPW • Short PR interval • <120 ms, <3 small boxes • Slurred QRS upstroke = “delta wave” • Young, healthy person with CP & palpitations • Consider with “shackalitis”

  37. WPW Looks Normal at Rest But Degenerates to VT • Atrial impulses conducted to ventricles via accessory pathway causing reentry

  38. QRS Complex • Ventricular contraction coordinated by Bundle of His & Purkinje fibers • 0.06 to 0.10 sec • Duration, height & shape diagnose arrhythmias, conduction abnormalities, hypertrophy, infarction, electrolyte derangements

  39. QRS Interval • Short: • <0.08 secs • Seen in SVT • Long: • >0.12 secs • Often related to a bundle branch block

  40. Q Waves • Normal (physiologic) or abnormal (pathologic) • Normal: • Septal depolarization • Best seen in lateral leads I, aVL, V5 & V6 • Qs > 1/3 R wave height, or >0.04 sec length abnormal • May show infarction

  41. ST Segment J Point • 0.08 - 0.12 sec • J point to beginning of T wave • Flat or depressed ST: • Ischemia • ST elevation: • Infarction

  42. T Wave • Ventricular repolarization • T wave usually upright • Inverted: ischemia, hypertrophy, CVA • Tall: hyperkalemia • Flat: ischemia, hypokalemia

  43. QT Interval • Beginning of QRS to end of T wave • Ventricular depolarization to “resetting” the conduction system • Normal ~ 0.40 secs • Interval varies based on HR & must be adjusted (Corrected QT / QTc)

  44. QT Prolongation • The heart takes too long to repolarize leaving it vulnerable to aberrant electrical impulses • Torsades de pointes, VT, VF

  45. Torsades de Pointes • Prolonged QT interval • Alcohol abuse • Hypomagnesemia, hypokalemia • May have a pulse, but are never “stable” • RX: magnesium bolus

  46. U Waves • Not always seen, typically small, follows T wave • Purkinje fiber repolarization • Hypokalemia, hypercalcemia, hypothermia, CVA, or thyroid disease • Inverted U wave: ischemia, volume overload

  47. Putting it together… Part III: From One Beat to Many

  48. Step I: Rate & EKG Paper • 1 small block = 1 mm² = 0.04 s = 40 ms • 5 small blocks = 1 large block = 0.20 s = 200 ms • 5 large blocks = 1 second

  49. Step 1: Rate • Each large black line = • 300 • 150 • 100 • 75 • 60 • 50

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